Emily S Darling
email: edarling@wcs.org

Tim R Mcclanahan

Joseph Maina

Georgina G Gurney

J Graham

Fraser Januchowski-Hartley

Joshua E Cinner

Camilo Mora

Christina C Hicks

Eva Maire

Nicholas A J Graham

Marji Puotinen

William J Skirving

Mehdi Adjeroud

Gabby Ahmadia

Rohan Arthur

Andrew G Bauman

Maria Beger

Michael Berumen

Lionel Bigot

Jessica Bouwmeester

Ambroise Brenier

Tom Bridge

Eric Brown

Stuart J Campbell

Sara Cannon

Bruce Cauvin

Chaolun Allen Chen

Joachim Claudet

Vianney Denis

Simon Donner

E Estradivari

Nur Fadli

David A Feary

Douglas Fenner
email: douglasfennertassi@gmail.com

Helen Fox

Erik C Franklin

Alan Friedlander

James Gilmour

Claire Goiran

James Guest

Jean-Paul A Hobbs

Andrew S Hoey

Peter Houk

Steven Johnson

Stacy Jupiter

Mohsen Kayal

Chao-Yang Kuo

Joleah Lamb

Michelle A C Lee

Jeffrey Low

Nyawira Muthiga

Efin Muttaqin

Yashika Nand

Kirsty L Nash

Osamu Nedlic

John M Pandolfi

Shinta Pardede

Lucie Penin

Lauriane Ribas-Deulofeu

Zoe Richards

T Edward Roberts

S Ku'ulei

Rodgers

Che Din

Mohd Safuan

Enric Sala

George Shedrawi

Min Tsai

Sin

Patrick Smallhorn-West

Jennifer E Smith

Brigitte Sommer

Peter D Steinberg

Makamas Sutthacheep

Chun Hong

James Tan

Gareth J Williams

Shaun Wilson

Thamasak Yeemin

John F Bruno

Marie-Josée Fortin

Martin Krkosek

David Mouillot

Strategic conservation and management of coral reefs in the Anthropocene

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Abstract: Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF]. Strategic conservation and management will require identifying the environmental conditions and socioeconomic characteristics associated with scleractinian coral assemblages -the foundation species of coral reef ecosystems. Here, we compiled coral abundance from 2,584 Indo-Pacific sites to evaluate the influence of 21 climate, social, and environmental drivers on reef coral assemblages. Higher abundances of frameworkbuilding corals were typically associated with: weaker past thermal disturbances and longer recovery intervals from past bleaching events; slower human population growth; reduced access to human settlements and markets; and less agricultural use. Given the variability in climate exposure faced by coral reefs [START_REF] Beyer | Risk-sensitive planning for conserving coral reefs under rapid climate change[END_REF], we used this information to propose a framework of three management strategies (protect -recover -transform) by considering if reefs were, (i) above or below a proposed threshold of >10% cover of coral taxa important for structural complexity and carbonate accretion, and (ii) their exposure to severe thermal stress during the 2014-2017 global coral bleaching events. Based on our dataset, we identify a subset of reefs (n = 449, or 17.4%) that meet the criteria for protecting potential ecological refuges, amidst other locations that may ultimately be priorities for recovery actions (n = 1405, or 54.4%) or transformation away from reef-dependent livelihoods (n = 728, 28.2%). Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.

Main text:

With the increasing intensity of human impacts from globalization and climate change, tropical coral reefs have entered a new era of the Anthropocene [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Hughes | Coral reefs in the Anthropocene[END_REF] and face unprecedented losses of up to 90% by mid-century [START_REF] Frieler | Limiting global warming to 2 °C is unlikely to save most coral reefs[END_REF]. Against a backdrop of globalized anthropogenic stressors, the impacts of climate change can transform coral communities [START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF] and reduce coral growth rates that are crucial to maintain structure and track rising sea levels [START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF].

Under expectations of continued reef degradation and reassembly in the Anthropocene (4), time is growing short. Given such concerns about the long-term functional erosion of coral communities, one conservation strategy is to prioritize protecting reefs that currently maintain key ecological functions, i.e., reefs with abundant fast-growing and structurally-complex corals that can maintain net carbonate accretion and vertical reef growth [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF]. However, efforts to identify these potentially functioning reefs across large spatial scales are often hindered by a focus on total coral cover, an aggregate metric that can overlook taxa-specific differences in structural complexity and carbonate accretion [START_REF] Denis | A functional approach to the structural complexity of coral assemblages based on colony morphological features[END_REF][START_REF] González-Barrios | A framework for measuring coral speciesspecific contribution to reef functioning in the Caribbean[END_REF]. To date, global empirical studies of scleractinian coral communities -and their environmental and socioeconomic drivers -are rare, in part due to the absence of large-scale assemblage datasets -a key challenge that must be overcome in modern ecology. Here, we apply a method developed from trait-based approaches to evaluate regional patterns and drivers of Indo-Pacific coral assemblages.

We assembled the largest dataset of tropical scleractinian corals from 2,584 Indo-Pacific reefs within 44 nations and territories and spanning 61° of latitude and 219° of longitude (see Methods). Surveys were conducted between 2010 and 2016, during continuous and repeated mass bleaching events, notably following the 1998 El Niño. A 'reef' was defined as a unique sampling location where coral genera and species-level community composition were evaluated on underwater transects using standard monitoring methods. Compared to coral reef locations selected at random, our dataset is representative of most conditions: 78 out of 83 Indo-Pacific marine ecoregions with coral reef habitat are represented with <5% disparity, although there are exceptions of undersampled (Palawan/North Borneo and Torres Strait Northern Great Barrier Reef) and oversampled (Hawaii, Rapa-Pitcairn and Fiji Islands) ecoregions (Table S1).

On each reef, we evaluated total coral cover and the abundance of different coral life history types previously developed from a trait-based approach with species characteristics of colony morphology, growth, calcification, and reproduction (9) (www.coraltraits.org, Table S2).

The abundance of different coral taxa can affect key ecological processes for future reef persistence, including the provision of reef structural complexity, carbonate accretion (the process by which corals and some other organisms lay down carbonate on the reef), and ultimately reef growth (the vertical growth of the reef system resulting from the processes of carbonate accretion and erosion) [START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF][START_REF] Denis | A functional approach to the structural complexity of coral assemblages based on colony morphological features[END_REF][START_REF] González-Barrios | A framework for measuring coral speciesspecific contribution to reef functioning in the Caribbean[END_REF][START_REF] Perry | Changing geo-ecological functions of coral reefs in the Anthropocene[END_REF]. Fast-growing, branching, plating and densely calcifying massive coral taxa that can maintain these processes are expected to be functionally important, not only by maintaining critical geo-ecological functions that coral reefs provide, but might also help reefs recover from climate disturbances, track sea level rise [START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF], and continue to provide critical habitat for reef fisheries [START_REF] Robinson | Productive instability of coral reef fisheries after climatedriven regime shifts[END_REF].

Here, we build on a previous classification of four coral life history types to evaluate Indo-Pacific patterns of total coral abundance and trait-based groups of corals, and their key socio-environmental drivers. Specifically, we consider four coral life histories (9) (Table S2): the 'competitive' life history describes fast-growing branching and plating corals that can accrete structurally-complex carbonate reef architectures but are disproportionately vulnerable to multiple stressors; the 'stress-tolerant' life history describes large, slow-growing and long-lived massive and encrusting corals that can build complex high-carbonate reef structures to maintain coral-dominated, healthy and productive reefs, and often persist on chronically disturbed reefs; by contrast, 'generalist' plating or laminar corals may represent a subdominant group of deeper water taxa, while smaller brooding 'weedy' corals typically have more fragile, lower-profile colonies that provide less structural complexity and contribute marginally to carbonate production and vertical growth [START_REF] Perry | Changing geo-ecological functions of coral reefs in the Anthropocene[END_REF][START_REF] Alvarez-Filip | Shifts in coral-assemblage composition do not ensure persistence of reef functionality[END_REF][START_REF] Darling | Relationships between structural complexity, coral traits, and reef fish assemblages[END_REF]. We therefore consider competitive and stresstolerant life histories as key framework-building species given their ability to build large and structurally complex coral colonies. We hypothesize that the abundance of different life histories within a coral assemblage provides a signal of past disturbance histories or environmental conditions (14-17) that may affect resilience and persistence to future climate impacts [START_REF] Kayal | Predicting coral community recovery using multi-species population dynamics models[END_REF]. Across the 2,584 reefs, total hard coral cover varied from <1% to 100% (median +/-SD, 23.7 +/-17.0%). Competitive and stress-tolerant corals were the dominant life history on 85.7% of reefs (competitive: 42.4%, n = 1,095 reefs; stress-tolerant: 43.3%, n = 1,118 reefs); generalist and weedy taxa dominated only 8.8% and 5.6% of reefs respectively (Fig. 1a,b; Fig. S1). It is striking that the majority of reefs were able to achieve dominance by structurally-important corals even following the 1998 mass bleaching event, despite different histories of ongoing bleaching impacts and recovery [START_REF] Gilmour | Recovery of an isolated coral reef system following severe disturbance[END_REF][START_REF] Graham | Predicting climatedriven regime shifts versus rebound potential in coral reefs[END_REF]. Notably, these findings are in contrast to contemporary Caribbean reefs where very few reefs are dominated by key reef-building species and instead comprised of weedy taxa with limited functional significance [START_REF] González-Barrios | A framework for measuring coral speciesspecific contribution to reef functioning in the Caribbean[END_REF][START_REF] Green | Increasing relative abundance of Porites astreoides on Caribbean reefs mediated by an overall decline in coral cover[END_REF]. However, Indo-Pacific reefs varied in their absolute abundance of the four types (Fig. 1c), also suggesting the potential for dramatic structural and functional shifts away from expected historical baselines of highly abundant competitive branching and plating corals [START_REF] Montaggioni | History of Indo-Pacific coral reef systems since the last glaciation: Development patterns and controlling factors[END_REF], a warning sign given recent community shifts in the Caribbean [START_REF] Jackson | Status and trends of Caribbean coral reefs: 1970-2012[END_REF].

Drawing on theoretical and empirical studies of socio-economic and environmental drivers on coral reefs [START_REF] Duffy | Biodiversity enhances reef fish biomass and resistance to climate change[END_REF][START_REF] Kittinger | Human dimensions of coral reef social-ecological systems[END_REF][START_REF] Cinner | Bright spots among the world's coral reefs[END_REF], we tested the influence of 21 social, climate, and environmental covariates on coral abundance, while controlling for sampling methodologies and biogeography (Table S3). These include: (i) social drivers (human population growth, management, agricultural use, national development statistics, the 'gravity' of nearby markets, and human populations that measure the size and accessibility of the nearest major market and human settlement, respectively), (ii) climate drivers (the intensity and time since past extreme thermal stress, informed by Degree Heating Weeks, DHWs), (iii) environmental characteristics (depth, habitat type, primary productivity, cyclone wave exposure, and reef connectivity), and (iv) sampling effects and biogeography (survey method, sampling intensity, latitude, and coral faunal province). We fit hierarchical mixed-effects regression models using the 21 covariates to predict the percent cover of total coral cover and the four coral life history types individually. Models were fit in a Bayesian multilevel modelling framework and explain ~25-48% of the observed variation across total cover and the four life histories (Table S4). We also fit these models to four common coral genera (Acropora, Porites, Montipora, Pocillopora) as a complementary taxonomic analysis (Fig. S2).

Climate variables describing the frequency and intensity of past thermal stress events strongly affected coral assemblages (Fig. 2). Total hard coral cover and the abundance of all four life histories increased with time since the strongest past thermal disturbance, providing empirical support for the importance of recovery windows for corals [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF]. These results also highlight the consequences of shrinking recovery windows for coral community structure, and its potential associations with ecosystem function as the abundance of live coral declines [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF].

Reefs with more extreme past climate disturbances (assessed by maximum DHWs) had fewer competitive and generalist corals (Fig. 2), consistent with expectations that branching and plating corals are extremely vulnerable to temperature anomalies and bleaching [START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF][START_REF] Darling | Life histories predict coral community disassembly under multiple stressors[END_REF][START_REF] Kayal | Predicting coral community recovery using multi-species population dynamics models[END_REF]. Stresstolerant and weedy corals were less affected by the magnitude of past thermal stress, as suggested by long-term studies in Kenya [START_REF] Darling | Life histories predict coral community disassembly under multiple stressors[END_REF] and Indonesia [START_REF] Denis | A functional approach to the structural complexity of coral assemblages based on colony morphological features[END_REF] that have shown these corals can persist through acute disturbances. There was no effect of the magnitude of past thermal stress on patterns of total coral cover, likely because this composite metric overlooks differences in species and trait responses.

Our results also reveal the important role of socioeconomic drivers on some life histories: reefs adjacent to human populations and agricultural use were associated with a lower abundance of stress-tolerant and generalist corals (Fig. 2). The mechanisms underpinning these relationships could include the overexploitation of grazing herbivorous fishes that control macroalgae, declining water quality from agriculture and urban centers that can increase turbidity and nutrients to smother corals and fuel algal overgrowth or disease, or increases in coral disease or mortality from destructive fishing practices, tourism or industrial activities [START_REF] Pollock | Sediment and turbidity associated with offshore dredging increase coral disease prevalence on nearby reefs[END_REF][START_REF] Mcmanus | Effects of some destructive fishing methods on coral cover and potential rates of recovery[END_REF]. We also observed two positive associations of coral abundance with human use: generalist corals with nearby agricultural land use, and weedy corals with market gravity. In some cases, these relationships may be complex and require further investigation; for example, the abundance of generalists (e.g., deeper-water plating corals) was negatively associated with the expansion of nearby croplands between 2002-2012, but positively associated with a more croplands by 2012 (Fig. 2). Overall, we identify human gravity and agricultural use as key social drivers that can reduce the abundance of structurally-complex corals and increase the abundance of 'weedier' corals; drivers that could therefore be locally mitigated to promote structurally complex and calcifying reefs that can sustain important ecological functions.

Local management actions in the form of no-take reserves or restricted management (e.g., gear restrictions) were associated with higher total coral cover, and greater abundance of stresstolerant and weedy corals, but not competitive or generalist corals (Fig. 2). The finding that management did not increase the abundance of all coral life histories may be surprising, because protection from local stressors is often expected to support coral resilience by increasing herbivory and suppressing macroalgae, reducing coral disease, and providing chemical cues that facilitate coral recruitment [START_REF] Lamb | Reserves as tools for alleviating impacts of marine disease[END_REF][START_REF] Dixson | Chemically mediated behavior of recruiting corals and fishes: A tipping point that may limit reef recovery[END_REF]. However, our analyses did not account for reserve age, size, design, or compliance, which could influence these outcomes; for example, older marine protected areas (MPAs) have been shown to reduce the loss of total coral cover [START_REF] Selig | A global analysis of the effectiveness of marine protected areas in preventing coral loss[END_REF].

Nevertheless, these results are also consistent with our findings that competitive and generalist corals are vulnerable to thermal stress, and with the argument that MPA effects can be swamped by the effect of climate change and bleaching mortality [START_REF] Bruno | Climate change, coral loss, and the curious case of the parrotfish paradigm: why don't marine protected areas improve reef resilience?[END_REF], especially for taxa that can be extremely sensitive to bleaching losses [START_REF] Alvarez-Filip | Shifts in coral-assemblage composition do not ensure persistence of reef functionality[END_REF][START_REF] Darling | Life histories predict coral community disassembly under multiple stressors[END_REF]. Our results also suggest that partial protection is associated with increases in coral abundance similar to fully no-take areas. For corals, any type of management that reduces destructive fishing practices (e.g., dynamite bombing, trawling, or anchoring) can have benefits for coral survival and growth [START_REF] Mcmanus | Effects of some destructive fishing methods on coral cover and potential rates of recovery[END_REF][START_REF] Mangi | Quantifying the environmental impacts of artisanal fishing gear on Kenya's coral reef ecosystems[END_REF], compared to global studies of reef fish that highlight the importance of compliant, no-take fisheries management [START_REF] Cinner | Bright spots among the world's coral reefs[END_REF][START_REF] Edgar | Global conservation outcomes depend on marine protected areas with five key features[END_REF].

Environmental factors such as latitude, reef zonation (depth and habitat), primary productivity, wave exposure and cyclone intensity were also strongly associated with coral abundance (Fig. 2). Competitive corals were more abundant on reef crests, shallower reefs and on reefs with higher wave exposure, compared to stress-tolerant corals that were more abundant on deeper reefs and reefs with lower wave exposure. Stress-tolerant, weedy and generalist corals were typically associated with higher latitudes, smaller reef areas, and deeper depths. Primary productivity and cyclone exposure were associated with a decrease in the abundance of competitive, stress-tolerant and weedy corals, likely associated with unfavourable conditions for coral growth in areas of eutrophication and high productivity [START_REF] Costa | Nutrification impacts on coral reefs from northern Bahia, Brazil. Island, Ocean and Deep-Sea Biology[END_REF], or hydrodynamic breakage or dislodgement of coral colonies [START_REF] Madin | Ecological consequences of major hydrodynamic disturbances on coral reefs[END_REF]. These findings suggest that environmental conditions are important in predicting conservation baselines and guiding management investments, such as restoring or maintaining grazer functions when environmental conditions can support corals and other calcifying organisms [START_REF] Robinson | Environmental conditions and herbivore biomass determine coral reef benthic community composition: implications for quantitative baselines[END_REF]. After controlling for method and sampling effort in the models (Fig. 2), our results suggest that future comparative studies would benefit from standardized methods and replication to allow for faster comparative approaches for field-based monitoring, especially given the urgency of tracking changes to coral assemblages worldwide [START_REF] Edmunds | Why more comparative approaches are required in time-series analyses of coral reef ecosystems[END_REF].

The livelihoods of millions of people in the tropics depend on healthy and productive coral reefs [START_REF] Cinner | Building adaptive capacity to climate change in tropical coastal communities[END_REF], yet coral reefs worldwide are imperilled by climate change [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Frieler | Limiting global warming to 2 °C is unlikely to save most coral reefs[END_REF][START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF][START_REF] Bruno | Climate change, coral loss, and the curious case of the parrotfish paradigm: why don't marine protected areas improve reef resilience?[END_REF].

Previous studies have identified 10% hard coral cover as a minimum threshold for carbonate accretion on Caribbean [START_REF] Perry | Caribbean-wide decline in carbonate production threatens coral reef growth[END_REF] and Indo-Pacific [START_REF] Januchowski-Hartley | Drivers and predictions of coral reef carbonate budget trajectories[END_REF][START_REF] Perry | Remote coral reefs can sustain high growth potential and may match future sea-level trends[END_REF] reefs, where reefs around this threshold (or 'boundary point') are more likely to have a neutral carbonate budget and may succumb to reef submergence with rising sea levels [START_REF] Perry | Loss of coral reef growth capacity to track future increases in sea level[END_REF]. Here, we adapt this threshold as the live cover of competitive and stress-tolerant corals (hereafter, 'framework' corals) as these are two life histories that can build large, structurally-complex colonies to maintain carbonate production and vertical reef growth [START_REF] Perry | Changing geo-ecological functions of coral reefs in the Anthropocene[END_REF][START_REF] Januchowski-Hartley | Drivers and predictions of coral reef carbonate budget trajectories[END_REF]. Prior to the third global bleaching event between 2014 and 2017, 71.8% of reefs (1,856 out of 2,584) maintained a cover of framework corals above 10% (Fig. 3a), suggesting the majority of reefs could sustain potential function. We then assessed the exposure to potential bleaching-level thermal stress for the 2,584 reefs in our dataset during the third global bleaching event. Between 2014 and 2017, reefs were exposed to variable maximum thermal stress, ranging between 0 to 30.5 DHWs annually (Fig 3a; Methods); nearly threequarters of the surveyed reefs (74.9%, n = 1935 reefs) were exposed to >4 DHWs, a common threshold for potential bleaching and mortality [START_REF] Heron | Warming trends and bleaching stress of the world's coral reefs 1985-2012[END_REF] (see also Fig. S3). Coral abundance, as related to potential thresholds of function (10%; but see sensitivity analysis in Table S5), was independent of the thermal stress experienced in the 2014-2017 bleaching event. This creates the potential for three strategic types of management: 1) protect functioning reefs exposed to less intense and frequent climate disturbances, 2) recover reefs exposed to potential bleaching-level stress but above a potential functioning threshold before bleaching, and 3) on degraded reefs exposed to potential bleaching-level thermal stress, assist societies to transform away from reefdependent livelihoods (Fig. 3a).

A protect strategy was identified for 449 reefs (out of 2,584, or 17.4%), which were exposed to minimal bleaching-level stress (<4 DHWs during 2014-2017) and had >10% cover of framework corals (Fig. 3a; Table S5). These reefs were located throughout the Indo-Pacific (Fig. 3b, Fig. S4, Table S6) suggesting that it is currently possible to safeguard a regional network of functioning coral reefs (3). The conservation goal for protect reefs is to maintain reefs above functioning thresholds ideally through future potential bleaching events, i.e., through policies that can dampen the market and population impacts of nearby populations, or through management that can include restrictions on fishing, development, tourism, pollution and run-off [START_REF] Hughes | Coral reefs in the Anthropocene[END_REF][START_REF] Pollock | Sediment and turbidity associated with offshore dredging increase coral disease prevalence on nearby reefs[END_REF][START_REF] Maina | Global gradients of coral exposure to environmental stresses and implications for local management[END_REF][START_REF] Guest | A framework for identifying and characterising coral reef "oases" against a backdrop of degradation[END_REF]. The recover strategy comprised the majority of surveyed reefs: 1407 reefs (out of 2584, or 54.4%) exceeded 10% cover of framework corals, but were likely exposed to severe bleaching-level heat stress during 2014-2017 El Niño (i.e., >4 DHWs). As these reefs had recently maintained 10% cover, mitigating local stressors as described above alongside targeted investments in coral reef rehabilitation and restoration could help to accelerate natural coral recovery. For the transform strategy, we identified 728 reefs (or 28.2%) below 10% cover that were likely on a trajectory of net erosion prior to the 2014-2017 bleaching event. Here, societies may ultimately need to transform away from dependence on coral reef livelihoods, which could be assisted with long-term social investments in livelihoods, education, and adaptive capacity; investments which can also accompany the protect and recover strategies [START_REF] Cinner | Building adaptive capacity to climate change in tropical coastal communities[END_REF][START_REF] Sen | The ends and means of sustainability[END_REF].

We also investigated how combinations of key drivers could affect the predicted cover of framework corals (Fig. 3c). While certain driver combinations were predicted to reduce cover below a 10% threshold (e.g., low recovery time from climate disturbances with high population or market gravity, or with high cyclone exposure; at levels of high gravity and high primary productivity; Fig. 3c), the majority of parameter space predicted coral cover above 10%. This is hopeful in that even as the frequency of bleaching events is expected to increase, reducing the impact of local stressors may provide conditions that can sustain coral reefs [START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF]. Our results show that while addressing global climate change is paramount, other factors such as recovery time from bleaching events, low to medium levels of net primary productivity (e.g., through improving water quality) or dampening the effects of nearby populations and markets should help to maintain the cover of framework corals above 10% (Fig. 3c) at a minimum, and ideally sustain reefs at higher levels of coral cover.

Our dataset describes contemporary coral assemblages within a period of escalating thermal stress, notably following the 1998 bleaching event. However, patterns of coral bleaching vary spatially (1), and we can make no predictions about which reefs might escape future bleaching events or mortality. The long-term persistence of corals within potential climate refuges (i.e., the protect strategy) requires a better understanding of future climate conditions and tracking the long-term ecological responses of different reefs [START_REF] Edmunds | Why more comparative approaches are required in time-series analyses of coral reef ecosystems[END_REF][START_REF] Maina | Global gradients of coral exposure to environmental stresses and implications for local management[END_REF]. Predicting and managing coral reefs through a functional lens is challenging but necessary [START_REF] Perry | Changing geo-ecological functions of coral reefs in the Anthropocene[END_REF][START_REF] Guest | A framework for identifying and characterising coral reef "oases" against a backdrop of degradation[END_REF]. Here, we adapt previous estimates of 10% coral cover as a threshold of net-positive carbonate production.

However, this threshold is based on methods that estimate the three-dimensional structure of a reef [START_REF] Perry | Caribbean-wide decline in carbonate production threatens coral reef growth[END_REF], while our dataset consists of primarily planar two-dimensional methods that do not account for the vertical or three-dimensional components of complex colonies [START_REF] Bellwood | The meaning of the term 'function' in ecology: a coral reef perspective[END_REF]. Thus, the 10% threshold based on planar methods should be considered an uncertain, but potentially precautionary, threshold of net carbonate accretion. A sensitivity analysis considering this threshold at 8% or 12% cover finds similar distributions of reefs across the three strategies (Table S5), suggesting a three-strategy framework is robust to uncertainty around thresholds of functionality. Future work can help refine these thresholds by considering species-specific contributions to complexity and carbonate production, as has been recently developed for Caribbean corals [START_REF] González-Barrios | A framework for measuring coral speciesspecific contribution to reef functioning in the Caribbean[END_REF].

Facing an Anthropocene future of intensifying climate change and globalized anthropogenic impacts, coral reef conservation can be more strategic by explicitly incorporating climate impacts and ecological functioning into priority actions [START_REF] Hughes | Coral reefs in the Anthropocene[END_REF]. Given expectations that coral assemblages will shift towards smaller and simpler morphologies and slower growth rates to jeopardize reef function [START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF][START_REF] Denis | A functional approach to the structural complexity of coral assemblages based on colony morphological features[END_REF][START_REF] Darling | Life histories predict coral community disassembly under multiple stressors[END_REF], our findings highlight the importance of urgently protecting and managing reefs that support diverse assemblages of large, complex branching, plating and massive taxa [START_REF] Perry | Changing geo-ecological functions of coral reefs in the Anthropocene[END_REF]. Our findings reveal key drivers of coral assemblages, and identify some locations where societies can immediately enact strategic actions of protect, recover, or transform. Our framework also provides a way to classify reefs for management based on two simple thresholds of their potential ecological function and recent exposure to thermal stress; thresholds that have the potential to be incorporated into measurable indicators of global action under the Convention on Biological Diversity's post-2020 Strategic Plan that will include a revised target for coral reefs. Local management alone, no matter how strategic, does not alleviate the urgent need for global efforts to control carbon emissions; the widespread persistence of functioning coral assemblages requires urgent and effective action to limit warming to 1.5-2˚C [START_REF] Hughes | Spatial and temporal patterns of mass bleaching of corals in the Anthropocene[END_REF][START_REF] Frieler | Limiting global warming to 2 °C is unlikely to save most coral reefs[END_REF][START_REF] Hughes | Global warming transforms coral reef assemblages[END_REF]. Our findings suggest there is still time for the strategic conservation and management of the world's last functioning coral reefs, providing some hope for global coral reef ecosystems and the millions of people who depend on them. [START_REF] Goatley | The roles of dimensionality, canopies and complexity in ecosystem monitoring[END_REF]. A random subsampling method was used to evaluate the representation of our dataset across Indo-Pacific coral reefs, whereby we compared locations of empirical surveys to the global distribution of coral reefs by generating 2600 randomly selected Indo-Pacific coral reef sites using the 'dismo' package [START_REF] Keith | Faunal breaks and species composition of Indo-Pacific corals: the role of plate tectonics, environment and habitat distribution[END_REF] from a 500 m resolution tropical coral reef grid [START_REF] Hijmans | dismo: Species Distribution Modeling. R package version 1[END_REF].

Methods

Comparing our empirical surveys (n = 2,584 reefs) to the randomly generated reefs allowed us to estimate ecoregions with relative undersampling or oversampling (Table S1).

Climate, social and environmental covariates were organized at three spatial scales, following the methods of ( 26):

(i) Reef (n = 2,584). Coral community surveys were conducted at the scale of "reefs", defined as a sampling location (with a unique latitude, longitude and depth) and comprised of replicate transects. Surveys occurred across a range of depths (1-40 m; mean ± standard deviation, 8.9 ± 5.6 m), though the majority of surveys (98.8%) occurred at depths shallower than 20 m. Surveys were conducted across a range of reef habitat zones, classified to three major categories: reef flat (including back reefs and lagoons), reef crest, and reef slope (including offshore banks and reef channels).

(ii) Site (n = 967). Reefs within 4 km of each other were clustered into "sites". The choice of 4 was informed by the spatial movement patterns of artisanal coral reef fishing activities as used in a global analysis of global reef fish biomass [START_REF] Cinner | Bright spots among the world's coral reefs[END_REF]. We generated a complete-linkage hierarchical cluster dendrogram based on great-circle distances between each point of latitude and longitude. This provided a median of 2.0 reefs (+/-2.83) per site.

We then used the centroid of each cluster to estimate site-level social, climate and environmental covariates (Table S3).

(iii) Country (n = 36). Reefs and sites were identified within geopolitical countries to evaluate national-level covariates (GDP per capita, voice and accountability in governance, and Human Development Index). Overseas territories within the jurisdiction of the United States, United Kingdom and France were informed by their respective country.

Coral communities and life histories. At each reef, underwater surveys were conducted using one of three standard transect methods: point-intercept transects (n = 1,628 reefs), line-intercept transects (n = 399 reefs) and photo quadrats (n = 557 reefs). We estimated sampling effort as the total number of sampled points during each reef survey. Line-intercept transects were estimated as having sampling points every 5 cm, since most studies only estimate the length of corals Analysis of drivers. We first assessed multicollinearity among the different covariates by evaluating variance inflation factors (Table S7) and Pearson correlation coefficients between each pairwise combination of covariates (Fig. S5). This led to the exclusion of four covariates: (i) local population size, (ii) national GDP per capita, (iii) national voice and accountability, and (iv) years since maximum annual extreme cyclone days. A final set of 16 covariates was included in statistical models, whereby all pairwise correlations were less than 0.7 and all variance inflation factors were less than 2.5 indicating that multicollinearity was not a serious concern (Table S7, Fig. S5).

To quantify the multi-scale social, human and environmental factors on hard coral assemblages, we modelled total percent cover of hard corals and the percent cover of each life history as separate responses. We fit mixed-effects Bayesian models of coral cover that represent spatial organization as hierarchical random effects, where reef was nested within site, and site nested within country; we also included a random effect of coral faunal province to account for regional biogeographic patterns [START_REF] Goatley | The roles of dimensionality, canopies and complexity in ecosystem monitoring[END_REF]. For each response variable, we converted percent coral cover into a proportion response and fit linear models using a Beta regression, which is useful for continuous response data between 0 and 1 [START_REF] Madin | The Coral Trait Database, a curated database of trait information for coral species from the global oceans[END_REF]. We incorporated weakly informative priors: Normal (mean 0, standard deviation 10) on the global intercept, Normal (mean 0, standard deviation 2) on slope parameters, and Student t (degrees of freedom 3, mean of 0, scale of 25) on the beta dispersion parameter. We fit our models with 5,000 iterations across four chains, and discarded the first 1,000 iterations of each chain as a warm-up; in total, the posterior sample was 16,000 for each model. We ensured chain convergence by visual inspection (Fig. S6), and ensuring that Rhat (the potential scale reduction factor) was less than 1.05 and the minimum effective sample size (neff) was > 1000 for all parameters [START_REF] Ferrari | Beta regression for modelling rates and proportions[END_REF]. We also conducted posterior predictive checks and estimated Bayesian R 2 values for each model as an indication of the proportion of variance explained [START_REF] Gelman | Bayesian Data Analysis[END_REF]. We fit models with Stan (55), brms (56) and R 3.5.2 [START_REF] Bürkner | brms: An R Package for Bayesian Multilevel Models Using Stan[END_REF].

We applied the same modelling approach to the percent cover of four dominant coral genera: Acropora, Porites, Montipora, and Pocillopora, in order to provide a comparison between life history and taxonomic responses (Fig. S2). For ecological condition, we assessed whether each reef had the potential for a net positive carbonate budget prior to the 2014-2017 bleaching event based on 10% cover of competitive and stress tolerant corals. We assumed that this threshold represents a potential tipping point (i.e. unstable equilibrium, or boundary point) for reef growth and carbonate accretion, whereby 10% hard coral cover is a key threshold above which reefs are more likely to maintain a positive carbonate budget and therefore net reef growth [START_REF] Perry | Caribbean-wide decline in carbonate production threatens coral reef growth[END_REF][START_REF] Januchowski-Hartley | Drivers and predictions of coral reef carbonate budget trajectories[END_REF][START_REF] Perry | Remote coral reefs can sustain high growth potential and may match future sea-level trends[END_REF]. Additionally, 10% coral cover is suggested to be a threshold for reef fish communities and standing stocks of biomass [START_REF] Core | R: A language and environment for statistical computing[END_REF][START_REF] Lamy | Three decades of recurrent declines and recoveries in corals belie ongoing change in fish assemblages[END_REF][START_REF] Beldade | More coral, more fish? Contrasting snapshots from a remote Pacific atoll[END_REF], and also associated with some thresholds to undesirable algal-dominated states at low levels of herbivore grazing and coral recruitment [START_REF] Harborne | Modelling and mapping regional-scale patterns of fishing impact and fish stocks to support coral-reef management in Micronesia[END_REF]. As a sensitivity analysis for the 10% coral cover threshold, we also considered how 8% and 12% coral cover thresholds would affect the distribution of conservation strategies across the 2,584 reefs (Table S5). This sensitivity analysis helps account for the uncertainty in how two-dimensional planar estimates of percent cover recorded during monitoring may affect three-dimensional processes on coral reefs, like carbonate production [START_REF] Bellwood | The meaning of the term 'function' in ecology: a coral reef perspective[END_REF]. Ultimately, applying thresholds of recent potential bleaching-level stress and reef condition (percent cover of competitive and stress tolerant corals) led to the proposed framework of three management strategies: protect, recover and transform, which we mapped across the Indo-Pacific based on the surveys in our dataset (Fig. 3, Fig. S4). HDI indicates the national statistic Human Development Index. For the effects of population gravity on stress-tolerant and weedy corals which can appear to intersect zero, there was a 96.0% (15,362 out of 16,000 posterior samples) and 98.0% (15,670 out of 16,000) probability, respectively, of a negative effect; for market gravity and competitive corals, there was a 90.2% (14,424 out of 16,000 posteriors) probability of a negative effect. Models of dominant coral genera are shown in Fig. S2.

Strategic

• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Total coral

  We conducted coral community surveys along 8,209 unique transects from 2,584 reefs throughout the Indian and Pacific Oceans, covering ~277 km of surveyed coral reef. Our dataset provides a contemporary Indo-Pacific snapshot of coral communities between 2010 and 2016; surveys occurred during repeated mass bleaching events (e.g., 1998, 2005, 2010), but were not influenced by widespread mortality during the 2014-2017 global coral bleaching event. Surveys spanned 61 degrees of latitude (32.7°S to 28.5°N) and 219.4 degrees of longitude (35.3°E to 105.4°W) and represented each of the 12 coral faunal provinces described for Indo-Pacific corals

  portfolios. We developed three conservation strategies (protect, recover and transform) based on the potential thermal stress during the 2014-2017 bleaching event, and each reef's previous observed ecological condition. To evaluate the potential thermal stress experienced by the 2,584 reefs during the Third Global Bleaching Event, we estimated the maximum annual Degree Heating Weeks (DHWs) between 2014 and 2017 from two global satellite products: NOAA's CoralTemp dataset (Coral Reef Watch version 3; see Drivers section) and NOAA's Coral Reef Watch version 2 (https://coralreefwatch.noaa.gov). There was generally strong agreement in maximum annual DHWs experienced by each reef between the two datasets (Pearson correlation, r = 0.68). Here, we use DHWs derived from the CoralTemp version 3 product, which provides more accurate SSTs although the climatologies to interpret bleachinglevel stress DHW thresholds remain in development (W. Skirving, pers. comm). Potential bleaching-level thermal stress can occur at different thresholds, likely between 2 and 4 DHWs, and this range of thresholds also represents the lowest quintile of DHW exposure for the 2,584 reefs during the 2014-2017 El Niño (0-20th quintile: 0 -3.2 DHW). Considerations of different thresholds were highly correlated and identified similar 'no-regrets' locations of limited thermal stress exposure between 2014 and 2017 (Fig. S3).

Fig. 1 .

 1 Fig. 1. Indo-Pacific patterns of reef coral assemblages. (A) Percent cover of four coral life histories from 2,584 reef surveys in 44 nations and territories; colour indicates life history and 695 circle size indicates percent cover. Circles are semi-transparent; locations with many surveyed reefs are darker than locations with fewer surveyed reefs. (B) Example of life histories, from left to right: fast-growing competitive; slow-growing and long-lived massive stress-tolerant; subdominant generalists; fast-growing brooding weedy taxa. (C) Distribution of abundance (percent cover) for each life history; dotted line identifies 10% cover, a potential threshold for net-700 positive carbonate production. Maps are shown separately for each life history in Fig. S1.

Fig. 2 .

 2 Fig. 2. Relationship between climate, social, environment and methodology variables with total coral cover and life history type. Standardized effect sizes are Bayesian posterior median values with 95% Bayesian credible intervals (CI; thin black lines) and 80% credible intervals (coloured thicker lines); filled points indicate the 80% CI does not overlap with zero and open circles indicate an overlap with zero and a less credible trend. DHW indicates Degree Heating Weeks;

  Photo quadratsLine intercept transects

Fig. 3 .

 3 Fig. 3. Strategic management approaches of protect -recover -transform across Indo-Pacific coral reefs. (A) The 2,584 reefs varied in their exposure to maximum annual DHWs during the 2014-2017 Third Global Coral Bleaching Event. Reefs previously above a 10% threshold of framework corals (combined cover of stress tolerant and competitive corals, associated with net positive carbonate budgets), and with limited exposure to potential bleaching-level thermal stress (<4 DHWs, see Fig. S4) may be potential refuges of ecological function to protect (blue dots, n = 449, or 17.4%). Recovery could be a priority for reefs that have recently maintained cover above 10% but were then exposed to severe potential bleaching stress in 2014-2017 (>4 DHWs, orange dots; n = 1407, or 54.5%). Societies may ultimately need to transform away from reef-dependent livelihoods as coral cover falls below potential accretion thresholds (<10% hard coral cover, dark red dots; n = 728, or 28.2%). (B) The three management strategies are distributed throughout the Indo-Pacific (Fig. S4, TableS6), suggesting there remain opportunities to sustain a network of functioning reefs while supporting coral recovery or social transformations for the majority of reefs. (C) Combinations of key drivers that differentiate between reefs below (red) and above 10% cover of framework corals (yellow to blue gradient), based on model predictions (see Methods). Coral cover refers to the combined cover of competitive and stress-tolerant corals; gravity estimates are reported as log(values).

We also investigated how combinations of key drivers differentiated between reefs below or above 10% cover of competitive and stress-tolerant corals (Fig. 3C). Using the Bayesian hierarchical models for competitive and stress-tolerant corals, we predicted coral cover across a range of observed values for five key covariates: population and market gravity, years since maximum DHW, primary productivity and cyclone exposure. For each covariate combination, we kept all other parameters at their median values for continuous predictors, or their reference value for categorical predictors (management: fished; habitat: reef slope; method: PIT); we then added the median predicted cover of competitive and stress-tolerant corals from 10,000 posterior samples for an estimate of combined cover.

Acknowledgements All data contributors would like to thank their monitoring partners and funders; see additional supplementary acknowledgements. We thank A. Baird, E. Buthung, P. Chabanet, Y. Chancerelle, D. Harvell, A. Heyward, P. Jokiel, R. Komeno, R. Lawton, S. Maxin, M. Pratchett, B. Randriamanantsoa, C. Rodney, E. Rudi, C. Russo, S. Tasidjawa, B. Vargas-Angel, I. Williams, B. Willis, J. Zavatra for data collection. We thank S. Anderson, K. Fisher and H. Beyer for assistance with analysis and data extraction. Major funding for this work was provided by a David H. Smith Conservation Research Fellowship from the Cedar Tree Foundation, a Banting Postdoctoral Fellowship from the Natural Sciences and Engineering Research Council of Canada, and the John D. and Catherine T. MacArthur Foundation through grants to the Wildlife Conservation Society.

Data availability Data available on request from the authors.

greater than 3 or 5 cm (T. McClanahan, A. Baird pers. comm). On average, the number of sampling points was 300.0 ± 750.0 (median ± SD), although effort ranged from 30 to 5,138 sampling points. Method and sampling effort were included as fixed effects in the models to control for their effects.

The absolute percent cover of hard corals was evaluated to the taxonomic level of genus or species for each transect. Surveys that identified corals only to broader morphological or life form groups (e.g., branching, massive corals) did not meet the criteria for this study. The majority of surveys recorded coral taxa to genus (1506 reefs out of 2584, or 58.2%), and the remainder recorded some or all taxa to species level; a small proportion of corals that remained unidentified from species or genus surveys (0.30% of all surveyed coral cover) were excluded from further analyses. We estimated the total hard coral cover on each transect, and classified each coral taxa to a life history type following the classification presented in [START_REF] Darling | Evaluating lifehistory strategies of reef corals from species traits[END_REF]; some species of Pocillopora, Cyphastrea and Leptastrea were reclassified by expert coral taxonomists and ecologists following the methods of [START_REF] Zinke | Gradients of disturbance and environmental conditions shape coral community structure for south-eastern Indian Ocean reefs[END_REF]. A representative list of species and their life history types are provided in Table S2, and original trait information is available from the Coral Traits Database (https://coraltraits.org/) [START_REF] Burke | Reefs at Risk Revisited[END_REF]. For genera-level monitoring that included species across more than one life history classification (Hydnophora, Montipora, Pocillopora, Porites), we distributed coral cover of each genus proportional to the number of species within each life history, which was estimated separately for each faunal province based on available species lists.

In total, we were able to classify 97.2% of surveyed coral cover to a life history, and then summed coral cover for each of the four life histories on each reef.

Climate, social and environmental drivers.

To evaluate the relative influence of climate, social and environmental drivers on total hard coral cover and coral assemblages, we identified a suite of covariates at reef, site and country scales (Table S3). These covariates included: the frequency and intensity of thermal stress since 1982 as indicators of ocean warming and bleaching, local human population growth, market and settlement gravity (a function of human population size and accessibility to reefs), management, nearby agricultural use, national Human Development Index, primary productivity, depth, reef habitat, wave exposure, cyclone history, and habitat connectivity. A full description of covariates, data sources and rationale can be found in the Supplementary Information.

Author contributions E.S.D. envisioned and led the project, performed all analyses, secured funding, and wrote the manuscript. T.M., J.M., G.G., N.A.J.G., F. J.-H., J.E.C., C.M., C.H., M.-J. F., and M.K. contributed to the conceptual ideas, design, analysis, design and writing. All other authors contributed data, edited and approved the manuscript.

Competing interests

The authors declare no competing interests.


Chadlia Mchiri
email: chadliamchiri@gmail.com

Abdelkader Ouakouak

Soumaya Nasri

Abdesslem Jedidi

Ilona Turowska-Tyrk

Samir Acherar

Céline Frochot

Thierry Roisnel

Habib Nasri

DABCO Cadmium(II) Tetrakis(4-metoxyphenyl)porphyrin Complex -Structure, Photophysical properties, and Adsorpion removal of methylene blue dye

Keywords: Cadmium porphyrin complex, DABCO ligand, Photophysical properties, Kinetic adsorption, Adsorption isotherms

may come     DABCO cadmium(II) tetrakis(4-metoxyphenyl)porphyrin complex -Structure, photophysical properties, and adsorpion removal of methylene blue dye

Introduction

For more than a half century, porphyrins and metalloporphyrins have attracted high interest from researchers due to their structural diversity and wide applications such as the organic catalysis [START_REF] Yu | One-pot catalytic transformation of olefins into cyclic carbonates over an imidazolium bromide-functionalized Mn(III)-porphyrin metal-organic framework[END_REF], and the chemical sensing [START_REF] Yang | Porphyrin-GO Nanocomposites Based NIR Fluorescent Sensor Array for Heparin Sensing and Quality Control[END_REF], in photodynamic therapy of cancers [START_REF] Satrialdi | Correction: The optimization of cancer photodynamic therapy by utilization of a pi-extended porphyrin-type photosensitizer in combination with MITO-Porter[END_REF] and in solar photovoltaic cells [START_REF] Zeng | Molecular engineering strategies for fabricating efficient porphyrin-based dye-sensitized solar cells[END_REF]. Among the metalloporphyrins systems, the cadmium (II) porphyrins have been of general interest. Indeed, Cd (II) ion is too big to fit co-planarly into the cavity of porphyrin, it is located out of the ligand plane and distorts it. Therefore, the structure deformation of cadmium(II) metalloporphyrins results in kinetic lability making them good transmetalation precursors for metalexchange reactions as well as peculiar photophysical and photochemical behavior [START_REF] Valicsek | Formation, photophysics, and photochemistry of cadmium(II) complexes with 5,10,15,20tetrakis(4sulfonatophenyl)porphyrin and its octabromo derivative: the effects of bromination and the axial hydroxo ligand[END_REF][START_REF] Valicsek | Application of the electronic spectra of porphyrins for analytical purposes: The effects of metal ions and structural distortions[END_REF]. Cd(II)porphyrins are also of particular interest for some biological applications such as inhibition of DNA cleavage by HaeIII enzyme at high concentration (from 10 -5 to 10 -6 M), [START_REF] Nyarko | Interactions of Tetracationic Mercury (II), Cadmium (II) and Lead (II) Porphyrins with DNA and their Effects on DNA Cleavage[END_REF] induction of DNA conformational change [START_REF] Tabata | Enhanced Conformational Changes in DNA in the Presence of Mercury(II), Cadmium(II) and Lead(II) Porphyrins[END_REF] and anti-parasite activity on Trypanosoma brucei brucei. [START_REF] Nyarko | Toxic Effects of Mercury(II), Cadmium(II) and Lead(II) Porphyrins on Trypanosoma Brucei Brucei Growth[END_REF]. On the other hand, the environmental contamination caused by several organic dyes in many industries including textile, leather, paper, food, cosmetics, printing and plastics [START_REF] Ucun | Equilibrium, thermodynamic and kinetics of reactive black 5 biosorption on loquat (Eriobotrya japonica) seed[END_REF] has generate serious pollution with increasing industrialization and population. The remediation of dyeing industry wastewater can be accomplished by various physical and chemical methods such as photodegradation and adsorption processes. [START_REF] Makhado | Sequestration of methylene blue dye using sodium alginate poly(acrylic acid)@ZnO hydrogel nanocomposite: Kinetic, Isotherm, and Thermodynamic Investigations[END_REF][START_REF] Pandey | Fast and highly efficient removal of dye from aqueous solution using natural locust bean gum based hydrogels as adsorbent[END_REF][START_REF] Elfeky | Fouda Multifunctional cellulose nanocrystal /metal oxide hybrid, photodegradation, antibacterial and larvicidal activities[END_REF][START_REF] Pandey | Photocatalysts in Advanced Oxidation Processes for Wastewater Treatment in book: Photocatalysts in Advanced Oxidation Processes for Wastewater Treatment[END_REF]. Among organic dyes, the methylene blue (MB) is one of the most used. This organic species is also named, methylthioninium chloride (Scheme 1), is a member of the thiazine class of dyes with many applications [START_REF] Mahapatra | Production of activated carbon from sludge of food processing industry under controlled pyrolysis and its application for methylene blue removal[END_REF][START_REF] Ma | Rapid voltammetric determination of maltol in some foods and beverages using a poly(methylene blue)/graphene-modified glassy carbon electrode[END_REF] which was first prepared by Heinrich Caro in 1876 [START_REF] Yan | Transformation and dehydration kinetics of methylene blue hydrates detected by terahertz time-domain spectroscopy[END_REF].

Methylene blue is considered one of the most commonly used dyes that cause many health problems including vomiting, diarrhea, skin irritation, nausea and eye burns in human body, in addition to environmental pollution [START_REF] Cengiz | Removal of methylene blue by invasive marine seaweed: Caulerparacemosa var. cylindracea[END_REF][START_REF] Alzaydien | Adsorption of methylene blue from aqueous solution onto a low cost natural Jrdanian Tripoli[END_REF]. In recent years, the development of new materials has intensified in wastewater treatment due to their ability to remove various contaminants in water as well as efficient recovery of adsorbents after adsorption processes. Thus far, adsorption techniques have been widely used for the removal of dyes from aqueous solutions due to low-cost, regenerable, effective process and ease of operation [START_REF] Faria | Adsorption of anionic and ˜ cationic dyes on activated carbons with different surface chemistries[END_REF]. Many types of adsorbent have been used of adsorption removal of dyes, such as hydrogels, clay minerals and carbon-based materials [START_REF] Zhang | Adsorption of Pb(II) from Aqueous Solution by Chitosan-g-poly(acrylic acid)/ Attapulgite/Sodium Humate Composite Hydrogels[END_REF][START_REF] Zhu | Synthesis of Sodium Alginate Graft Poly (Acrylic Acid-Co-2-Acrylamido-2-Methyl-1-Propane Sulfonic Acid)/Attapulgite Hydrogel Composite and the Study of its Adsorption[END_REF].

It is worth noting that the use of porphyrins, metalloporpyrins and their derivatives in the removal of organic dyes by the absorption method has been the subject of a large number of publications in recent years [START_REF] Aly | A facile synthetic route and dual function of network luminescent porous polyester and copolyester containing porphyrin moiety for metal ions sensor and dyes adsorption[END_REF][START_REF] Hou | Porphyrin-Alkaline Earth MOFs with the Highest Adsorption Capacity for Methylene Blue[END_REF]. During the last few years, our research group has published a number of works concerning the use of metalloporphyrins in adsorption removal of some organic dyes [START_REF] Soury | Nasri Tetrakis(ethyl-4(4-butyryl)oxyphenyl)porphyrinato zinc complexes with 4,40bpyridin: synthesis, characterization, and its catalytic degradation of Calmagite[END_REF][START_REF] Guergueb | Zinc(II) triazole meso-aryl substituted porphyrins for UV-visible chloride and bromide detection. Adsorption and catalytic degradation of malachite green dye[END_REF][START_REF] Guergueb | Effect of the coordination of p-acceptor 4cyanopyridine ligand on the structural and electronic properties of meso-tetra(para-methoxy) and meso-tetra(para-chlorophenyl) porphyrin cobalt(II) coordination compounds. Application in the catalytic degradation of methylene blue dye[END_REF].

Materials and Methods

Synthesis of [Cd(TMPP)(DABCO)]1.5CHCl 3 1.5C 6 H 12 N 2 (I)

In the present work, the meso-tetrakis(4-tert-methoxyphenyl)porphyrin (H 2 TMPP) and the starting material complex [Cd(TMPP)] were synthesized, following literature methods [START_REF] Adler | A Simplified Synthesis for Meso-Tetraphenylporphine[END_REF][START_REF] Rodesiler | Molecular Distortions and Solid-state 113Cd NMR: Crystal and Molecular Structure of the Piperidine Adduct of (5,10,15,20-Tetraphenylporphyrinato)cadmium(II), 113 Cd NMR Solution and Solid-state Spectra, and Potential Energy Calculations[END_REF]. The synthesis of [Cd(TMPP)(DABCO)] (I) was performed by dissolving [Cd(TMPP)] (25 mg, 0.03 mmol) in chloroform (2 mL). A saturated DABCO-chloroform solution (3 mL) was added. The mixture obtained was stirred for 12 hours then, 10 mL of n-hexane was added to the [Cd (TMPP)]-DABCO mixture. The resulting solution was left to infuse and crystallize for a minimum of 3 days, resulting in dark-purple crystals (yield 80%). The synthetic route to complex (I) is shown in Scheme (nm) in CH 2 Cl 2 , (ε x 10 -3 , mol -1 L cm - 1 )]: 440(307), 573 [START_REF] Yan | Transformation and dehydration kinetics of methylene blue hydrates detected by terahertz time-domain spectroscopy[END_REF],617 [START_REF] Makhado | Sequestration of methylene blue dye using sodium alginate poly(acrylic acid)@ZnO hydrogel nanocomposite: Kinetic, Isotherm, and Thermodynamic Investigations[END_REF]. IR (cm

Reagents

All reagents and solvents were commercially available, reagent grade, and used without further purification.

Spectroscopic and photophysical measurements

1 H NMR spectra were recorded on a Bruker AVANCE spectrometer (400 MHz). UV-Visible spectra were measured with a UV-3600 Shimadzu spectrophotometer. FT-IR spectra were recorded in the region of 400-4000 cm -1 on a Nicolet Impact 410 spectrophotometer. Fluorescence spectra were recorded on a Fluorolog-3 spectrofluorometer FL3-222 with a thermostated cell compartment (25 °C) using a 450 W Xenon lamp. Fluorescence quantum yield (φ f ) were determined using tetraphenyl porphyrin (H 2 TPP) solution in toluene as fluorescence standard (φ f = 0.11) [START_REF] Seybold | Fluorescence Spectra and Quantum Yields[END_REF].

Crystal structure determination

A suitable crystal of [Cd(TMPP)(DABCO)] complex (I) were chosen and their X-ray analysis were done using the unit-cell parameters were calculated and refined from the full data and the data collection was performed with a Bruker D8 VENTURE diffractometer at 150 K. Data were corrected for absorption effects by the Multi-Scan method [START_REF] Becker | Extinction within the limit of validity of the Darwin transfer equations. I. General formalism for primary and secondary extinction and their applications to spherical crystals[END_REF]. The structure was solved by direct method by using SIR-2004 program [START_REF] Burla | SIR2004: an improved tool for crystal structure determination and refinement[END_REF] and refined by full-matrix least-squares techniques on F 2 by using the SHELXL-97 program [START_REF] Sheldrick | Crystal structure refinement with SHELXL[END_REF]. The structure was refined as an inversion twin with a final BASF parameter of 0.430 [START_REF] Yang | Porphyrin-GO Nanocomposites Based NIR Fluorescent Sensor Array for Heparin Sensing and Quality Control[END_REF]. One chloroform and one n-hexane solvent molecules located in a very close positions were refined with a 50%/50% occupation ratio. The anisotropic displacement ellipsoids (ADPs) of the chloroform solvent molecule and the free DABCO molecules are very elongated; therefore, there is static disorder in the molecular structure of (I). For fragments involving these atoms, the DFIX, DANG, and SIMU constraint commands in the SHELXL-97 software were used [START_REF] Byrom | PARSET and PARSYM -production of files for neutron powder structure refinement program MORGUE and solution/refinement program PARAM[END_REF]. The ADPs of the atoms of the DABCO axial ligand (C59-C62-C64) exhibits also high ADPs values for which the ISOR and SIMU constraint commands were applied. The drawings were made with Mercury [START_REF] Macrae | Mercury CSD 2.0 -New Features for the Visualization and Investigation of Crystal Structures[END_REF]. Crystal data and details of the structure determination are summarized in Table S1 (Supplementary Materials). Selected bond lengths and angles of complexes are listed in Table 1.

Crystallographic data have been deposited as supplementary publication number CCDC No 2012300.

Adsorption experiments and data analysis

Tests of methylene blue dye adsorption onto [Cd(TMPP)(DABCO)] were carried out in a batch manner. Briefly, 6 mg of adsorbent was dispersed in Erlenmeyer flasks containing 20 mL of MB dye solution at known concentration. Then, the mixture was stirred (at 200 rpm) during the desired time.

After filtering the solution through a 0.45 µm membrane filter, the residual MB content was determined by UV-visible spectrophotometer. The characteristic peak for methylene blue was (~ 664 nm) has been employed to monitor the adsorption. All tests of MB dye adsorption were performed at pH = 7.0 ± 0.1. The removed quantity of MB dye from solution at any time t (q t , mg/g) and at equilibrium (q e , mg/g) were calculated by the following equations (1-2):

(1)

0 ( ) * / t t q C C V m   (2) 0 ( ) * / e e q C C V m  
where C 0 , C t and C e (mg/L) are the MB dye concentration at beginning, at time t, and at equilibrium, respectively. V (L) is the volume of MB dye solution whereas m (g) represents the mass of adsorbent used.

In order to investigate the MB dye adsorption mechanisms onto [Cd(TMPP)(DABCO)], three common models of kinetics and isotherms were selected for modelling the experimental data. The non-linear forms of the pseudo-first-order (PFO) [START_REF] Lagergren | about the theory of so-called adsorption of soluble substances[END_REF], the pseudo-second-order (PSO) [START_REF] Blanchard | Removal of heavy metals from waters by means of natural zeolites[END_REF] and the Elovich [START_REF] Lintock | The Elovich equation in chemisorption kinetics[END_REF] kinetic models are given by equations (3-5), respectively.

(

)   1 1 k t t e q q e    3
2 1 e t e q k t q q k t   (5) 1 ln( 1)

t q t    
where q t , q e , and C e are defined above in Equations (1)-(2), k 1 (L/min) is the rate constant of PFO equation; k 2 (g/mg × min) is the PSO rate constant; α (mg/g × min) is the initial adsorption rate of Elovich model; and β (mg/g) is the desorption constant during any one experiment.

To describe the adsorption isotherm, the non-linear forms of Langmuir [START_REF] Langmuir | The adsorption of gases on plane surfaces of glass, mica, and platinum[END_REF], Freundlich [START_REF] Freundlich | Adsorption in solution[END_REF] and Redlich-Peterson [START_REF] Redlich | A useful adsorption isotherm[END_REF] models are given by Equations (6-8), respectively:

(6) e L e L o e C K C K Q q   1 max (7) n e F e C K q  (8) g e e RP e aC C K q   1
where Q o max (mg/g) is the maximum monolayer capacity of Langmuir; K L (L/mg) is the Langmuir affinity constant; K F (mg/g)(L/mg) n represents the Freundlich constant; n (dimensionless; 0< n <1) is the intensity parameter of Freundlich; K RP (L/g) and a RP (mg/L) -g refer to the Redlich-Peterson constants and g (dimensionless) is an exponent which must be between 0 and 1.

In this study, the Origin software was used to calculate the relevant parameters of all models by applying the non-linear technique.

The difference between the experimental and calculated values of the adsorbed quantity (q e and q t in mg/g) was evaluated using the coefficient of determination (R 2 ) and the chi-square test (χ 2 ) [START_REF] Tran | Chao Mistakesand inconsistencies regarding adsorption of contaminants fromaqueous solutions: a critical review[END_REF].

(9) (10) 2 ,exp , 2 , (
)

e e cal e cal q q q    
where q e,mean (mg/g) is the mean of q e experimental (q e,exp ) values and q e,cal (mg/g) is the adsorbed quantity determined from the selective model.

Computational details

All the calculations were performed using the Gaussian09 suites [START_REF] Frisch | Gaussian 09; revision A.02[END_REF] and monitored by Gaussview Software [START_REF] Dennington | [END_REF]. The density functional theory (DFT) method has been applied with the B3LYP functional [45] in connection with a valence double-zeta (6-31G) basis set, adds to the 6-31G basis set five d-type Cartesian-Gaussian polarization functions on each of the atoms C, N, O, S, Cl and H [START_REF] Moran | Popular theoretical methods predict benzene and arenes to be nonplanar[END_REF], and the SDD basis set for Cd metal [START_REF] Dolg | Energy-adjusted ab initio pseudopotentials for the rare earth elements[END_REF]. No symmetry constraints were used in the geometry optimizations, and the final geometries were confirmed to be minimum potential energy structures through frequency calculations. Weak interactions have been included in the energy evaluation using 'Empirical Dispersion' option with Grimme D3 corrections. The effect of solvent (water) on the relative stabilities was calculated using the Tomasi's polarized continuum (PCM) model [48]. The calculation of NMR spectrum of the different structures was performed using the GIAO (Gauge-Including Atomic Orbitals) method [START_REF] Wolinski | Efficient Implementation of the Gauge-Independent Atomic Orbital Method for NMR Chemical Shift Calculations[END_REF].

2 ,exp , 2 2 ,exp , ( ) 1 (
)

e
e cal e e mean q q R q q      

Results and discussion

3.1. Crystal Structures of [Cd(TMPP)(DABCO)]1.5CHCl 3 1.5C 6 H 12 N 2 (I)

Single crystal X-ray diffraction analysis reveals that complex (I) crystallizes in the triclinic P-1 space group with Z=2. Crystallographic data and structure refinement are reported in Table S1. The asymmetric unit contains one molecule of [Cd(TMPP)(DABCO)], one half chloroform and one half DABCO molecules. The ORTEP drawings of the molecular structure of complex [Cd(TMPP)(DABCO)] is shown in Figure 1 and the main geometrical parameters are listed in Table 1. The central cadmium is linked by four N-donor nitrogen atoms of the tetradentate deprotonated porphyrin ligand (TMPP 2-), and axially by the nitrogen atom of the DABCO axial ligand leading to a pentacoordinate Cd(II) porphyrin complex. Table 1 lists the selected bond lengths and angles. The average equatorial distance between the Cd 2+ central ion and the four nitrogen atoms of the pyrrole rings (Cd-N p ) is in the normal range of pentacoordinate Cd(II) metalloporphyrins with a value of 2.192( 5) Å (Table 2). The Cd-N (DABCO) bond length [2.320( 5) Å] is considerably close to those of the reported related five-coordinate Cd(II) porphyrin complexes (Table 2).

The geometry of any penta-coordinated metal center may conveniently be measured by the Addison parameter (τ) [START_REF] Addison | Synthesis, structure, and spectroscopic properties of copper(II) compounds containing nitrogen-sulphur donor ligands; the crystal and molecular structure of aqua[1,7-bis(N-methylbenzimidazol-2′-yl)-2,6dithiaheptane]copper(II) perchlorate[END_REF]. The value of τ is defined as the difference between the two largest Ligand-Metal-Ligand angles divided by 60, [τ = (ϴ-Ф)/60, where ϴ and Ф are the two largest of the coordination sphere], τ is 0 for the ideal square pyramid and 1 for the trigonal bipyramid. In the present complex, the τ values of Cd center was calculated to be 0.52 indicating a distorted square-pyramidal geometry.

The Addison parameter τ of (I) is close to those of reported Cd(II)-porphyrin complexes with Ndonor of axial ligands (such as pyridine and 2-NH 2 -pyridine). Furthermore, the planarity of porphyrin core has been analyzed and as shown in Figure 2. The Cd(II) cation of (I) has a large atomic radius which implies that central ion is too large to fit into the central hole of the porphyrin with a distance between the cadmium atom and the mean plane made by the 24atom core of the porphyrin (Cd __ P C ) of 0.746 Å, in agreement with DFT calculations showing a distance of 0.770 Å. This high value induces a significant porphyrinato core doming which is similar to those of the related five-coordinated cadmium metalloporphyrin with N-donor axial ligand (Table 2). involved in other intermolecular C-H … O interactions with the oxygen of the methoxy group of TMPP. These three different types of interactions lead to a pseudo-2D superstructure (Figure 3).

Details of the geometric features of C-H … X (X = N, O) interactions in crystal lattice of (I) are given in Table 3. Table 3. Geometric features (distances in Å and angles in °) of the intramolecular interactions for (I).

Molecular modeling of the complexes

The Cd-TMPP complex has been modeled in order to study the formation of [Cd-TMPP-DABCO] complex (). Geometry optimization and vibrational frequencies have been performed at B3LYP/6-31G(d)/SDD level of theory. The structural analysis (bond lengths and angles) is shown in Table S2 and the IR spectra is presented in Figure 4. 4).

Electronic and emission spectra of complex (I)

The porphyrins and metalloporphyrins have a π strongly conjugated electron system. These molecules absorb in the visible range and have characteristic absorption spectra induced by π → π* transitions.

The first one involves the transition from the ground state (S 0 ) to the second excited state (S 2 ). corresponding to the B band (known as the Soret band). The range of the S 0  S 2 absorption band s between 380-500 nm depending on whether the porphyrin is β-or meso-substituted. The second region consists of a weak π → π* transition corresponding to the S 0 →S 1 transition from the ground state to the first excited state in the range between 500-750 nm (the Q bands).

The electronic spectra, recorded in dichloromethane of the free base porphyrin H 2 TMPP, the [Cd(TMPP)] starting material and complex (I) are depicted by Figure 5. The absorption data of these species and several other related Cd(II) meso-arylporphyrins are summarized in Table S3. The λ max values of the Soret and Q bands of the free base H 2 TMPP are 422nm and 518, 555, 594, 650, respectively. After metallation of the porphyrin by the cadmium ion, the color changes from purple to green and the number of the Q bands decreases from four to two due to the symmetry change from D 2h to D 4h . The color change is due to the important redshift of the Soret band from 422 nm for the H 2 TMPP to 437 nm for the [Cd(TMPP)] starting material. The Q bands of this complex are also redshifted (573, 617 nm) compared to those of the free base porphyrin (518, 555, 594 and 650 nm) (Figure 5). The coordination of the DABCO to the Cd(II) ion of the tetracoordinated starting material leads a slightly redshift of both the Soret and the Q bands (Figure 4, Table S3). Notably, the important bathochromic shift of the absorption bands is related to the deformation of the porphyrin core [START_REF] Reddy | Bis(aryloxo) derivatives of tin(IV) porphyrins: synthesis, spectroscopy and redox activity[END_REF]. The fluorescence emission spectra of the free base porphyrin H 2 TMPP, and its cadmium complexes at room temperature were recorded in dichloromethane (c~ 10 -6 M) upon photoexcitation at the wavelength 437 nm leads to forming two emission bands S 1  S o allocated as the Q(0,0) and Q(0,1) transitions. The fluorescence parameters, i.e. the  max fluorescence wavelength values of the Q (0,0) and Q (0,1) bands, and the fluorescence quantum yields (Φ f ), as well as the fluorescence lifetimes (τ f ) of H 2 TMPP, [Cd(TMPP)] and complex (I) are listed in Table S4.

As shown by Figure 5b the heavy diamagnetic ion Cd(II) leads to weak fluorescence, the cadmium insertion resides in a very important hypsochromic shifts of ~ 50 nm for the strongest emission band Q(0,0), and ~ 60 nm for the second band Q(0,1 accompanied by a highly important reduction in the fluorescence intensity. This quenching of the fluorescence is explained by the "heavy-atom effect" of the cadmium heavy metal and the distortion of the porphyrin core, which promotes the loss of the "motion energy" by other non-radiative energy dissipation processes than light emission [START_REF] Kumar | New molecular arrays based on a Tin (IV) porphyrin scaffold[END_REF][START_REF] Gentemann | Unusual picosecond 1 (π, π *) deactivation of ruffled nonplanar porphyrins[END_REF].

Adsorption removal of methylene blue (MB) dye

Adsorption

The adsorption of the MB dye on our synthetic cadmium(II)-DABO derivative was carried out at room temperature in aqueous solutions and the adsorption spectra of MB dye as a function of time in presence of (I) are shown in Figure S1 (supplementary information). As shown in this figure, the main absorption band ( max = 664 nm) of the BM dye decreases after adding complex (I) as function of time and almost disappears after 120 min of stirring time.

It has been reported that in the case of the porphyrin-based porous organic polymer (PPOPs-OH) [START_REF] Ti | Facile One-pot Synthesis of A Porphyrin-based Hydrophilic Porous Organic Polymer and Application as Recyclable Absorbent for Selective Separation of Methylene Blue[END_REF], the π-π interactions (of the porphyrin macrocycle) is one of the driving force of the adsorption phenomenon. In our case, the adsorption phenomenon is most probably due to the fact that complex (I) is coordinated to a very aromatic ligand which is the meso-tetrakis(4-tertmethoxyphenyl)porphyrin and to the cyclic N-donor ligand DABCO. Therefore, the adsorption of the dye on (I) involves - interactions and probably weak H bonds and van der Waals interactions involving the MB due molecule and our cadmium-DABCO-TMPP porphyrin coordination compound.

Kinetic Adsorption

As mentioned in the experimental section, three kinetic models have been used study the MB dye adsorption on complex (I) which are the non-linear forms of the pseudo-first-order (PFO) [START_REF] Lagergren | about the theory of so-called adsorption of soluble substances[END_REF], the pseudo-second-order (PSO) [START_REF] Blanchard | Removal of heavy metals from waters by means of natural zeolites[END_REF] and the Elovich [START_REF] Lintock | The Elovich equation in chemisorption kinetics[END_REF]. The adsorption capacity curves as function of time for our Cd(II)-DABCO derivative (I) are given in Figure 6 which shows that the adsorption rate of MB dye increases with increasing stirring time and the equilibrium (or saturation) is reaches after about 60 min of the contact of MB dye with (I). It can be seen from the curves given in Figure 6 that the adsorption mechanism is speedy, with around 80.7% of total MB dye in the solution being adsorbed within 15 min of stirring time. The results obtained using the three models which were evaluated based on the regression coefficient R 2

and chi-square (χ 2 ) values, given in Table 5, indicate that the experimental results are better fitted using the Elovich and the PSO models with R 2 / χ 2 values of 0.994/0.577 and 0.993/0.766 respectively. This finding is also well confirmed by the fitting lines presented in Figure 6.

Table 5. Kinetic data for the adsorption of MB dye using complex (I) (Co = 10 mg L -1 , pH = 7.0, m = 6 mg) -0.577 -

Model

Adsorption isotherm

In this study, Langmuir, Freundlich and Redlich-Peterson models are used to analyze the equilibrium data of MB adsorption. The fitting curves of the studied models are displayed in Figure 7. In addition, Table 6 summarizes the relevant parameters for the previously mentioned models. In the light of R 2 and χ 2 values, Langmuir gives the best fit of the experimental data of adsorption isotherm at 298 K because it exhibits the highest R 2 and the lowest χ 2 values, in comparison with Freundlich and Redlich-Peterson models (Table 6).This finding suggests a monolayer adsorption of MB molecules onto homogeneous surface of [Cd(TMPP)(DABCO)] adsorbent. Furthermore, the maximum adsorption capacity was found to be 69.24 mg.g -1 according to the Langmuir equation.

Comparison of our adsorption results with other reported investigations

Many investigations concerning the MB dye adsorption have previously been reported in the literature (Table 7). As depicted in this table, the removal yield and the capacity of adsorption (Q max ) using our Cd(II) porphyrin derivative [Cd(TMPP)(DABCO)] (I) with values: Q max = 69.24 mg.g-1 and 80.7% yield, are slightly better than those of the two first examples reported in Table 7 of non-porphyrinic systems used to remove the MB dye. By the other hand, the adsorption removal systems, reported in the same Table 7, using a poloxometallate and porphyrin base compounds exhibits higher adsorption capacities and yields that our synthetic complex (I). Nevertheless, in our case we used a low concentration of the MB dye ringing from 2 to 10 mg.L -1 which is not the case of the other adsorbents reported in Table 7. Indeed, in the case of the related porphyrinic absorbents such as the "Porphyrincalcium {[Ca(HDCPP) 2 (DMF) 2 ] n polymer" [START_REF] Hou | Porphyrin-Alkaline Earth MOFs with the Highest Adsorption Capacity for Methylene Blue[END_REF] and the "Porphyrin-based porous organic polymer (PPOPs-OH) " [START_REF] Ti | Facile One-pot Synthesis of A Porphyrin-based Hydrophilic Porous Organic Polymer and Application as Recyclable Absorbent for Selective Separation of Methylene Blue[END_REF] , the dye concentrations are 15 and 50 mg.L -1 , respectively. Therefore, the results obtained by using complex (I) indicate the prominent potential of our Cd(II) porphyrinic system for dye treatments.

Molecular modeling of the adsorption of MB dye on (Cd-TMPP-DABCO] complex (I)

The interaction of MB dye with both [Cd-TMPP] and [Cd-TMPP-DABCO] complexes has been performed in order to calculate the adsorption energy for each case (Table 8). We calculated first the interaction between the DABCO ligand and the [Cd-TMPP] complex (Figure x). Then, we performed the adsorption of MB dye on an isolated [Cd-TMPP] complex and also in presence of DABCO (complex I). The former adsorption was made for the sake of comparison of the interaction strength.

The adsorption energy of DABCO on the [Cd-TMPP] (complex I) is found -18.3 kcal/mol, that is lower than the adsorption of MB dye on the same complex (complex II) by 5.6 kcal/mol (E ads = -12.3 kcal/mol). The adsorption energy of the MB dye in presence of DABCO is higher than the sum of the interactions between MB and DABCO with [Cd-TMPP] complex, respectively. The difference may be due to the repulsion generated between te MB dye and DABCO ligand.

Table 8. Adsorption energy (kcal/mol) of the three considered complexes (-) () Cd-TMPP-DABCO, () Cd-TMPP-MB, and () Cd-TMPP-DABCO-MB complex.

FT-IR Characterization

The " species are shifted compared to those of [Cd(TMPP)(DABCO)] and the MB dye before adsorption (Table 9). These finding confirm the adsorption of the dye by our Cd(II) adsorbent (I).

The Theoretical data of the absorption bands are in in agreement with the experimental data.

Conclusion

In summary, we have presented here the synthesis, the crystal structure and the photophysical properties of the (DABCO)(meso-tetrakis(4-tert-methoxyphenyl)porphyrinato)cadmium(II) These promising results obtained using our Cd(II)-TMPP-DABCO system pave the way for us to test other cadmium porphyrin complexes but using other meso-arylporphyrins as well as other types of axial ligands in order to improve the adsorption treatments of organic dyes on wastewater..

  Scheme 1. Structure of the methylene blue dye (MB).

Scheme 2 :

 2 Scheme 2: Synthetic route to [Cd(TMPP)(DABCO)] complex (I).

Figure 1 .

 1 Figure 1. ORTEP diagram and numbering scheme of [Cd(TMPP)(DABCO)]. The hydrogen atoms are not represented for clarity. 30% probability surfaces.

a:

  Estimated standard deviations are given in parentheses, b : Cd-N p is the average equatorial Cd-pyrrole nitrogen bond length, c: : Cd•••P Ct is the displacement of the Cd metal atom out of the porphyrinato mean plane, d : Cd-N ax is the Cd-axial ligand bond length. e : 2-MeHIm: 2-methylimidazole, f : py: pyridine, g : DMF: N,N-diméthylformamide, h : pip: piperidine, i : 2-NH 2 -py: 2-aminopyridine.

Figure 2 .

 2 Figure 2. Formal diagrams of the porphyrinato core showing the Doming distortion in [Cd(TMPP)DABCO] complex (I)

Figure 3 .

 3 Figure 3. Schematic representation of the pseudo-2D supramolecular architecture of complex (I) via C-H … N and C-H … O interactions. Only relevant atoms have been shown.

  is the donor atom, b : A is the acceptor atom.

Figure 4 .

 4 Figure 4. Theoretical IR spectra of the complex (I).

Figure 5 .

 5 Figure 5. (a) UV-Visible spectra of H 2 TMPP, [Cd(TMPP)] and complex (I) in CH 2 Cl 2 (c~ 10 -5 M), (b) fluorescence emission spectra of the same three porphyrinic species in CH 2 Cl 2 (c~ 10 -6 M), excitation λ exc =437 nm.

Figure 6 .

 6 Figure 6. MB dye (C o =10 mg.L -1 ) as a function of time for complex (I) (m = 6 mg, pH = 7.0). Dots represents the experimental data and the curves where plotted using the pseudo-first-order, the pseudosecond-order and the Elovich models.

Figure 7 .

 7 Figure 7. Adsorption isotherms of MB dye onto [Cd(TMPP)(DABCO)] (I) and fitting curves of the selective models.

  FT-IR spectra of [Cd(TMPP)(DABCO)], MB, and MB-[Cd(TMPP)(DABCO)] species are depicted in Figures 8 and S3 and the characteristic absorption bands are listed in Table 9. Inspection of Figures 9 and S3 shows that the characteristic absorption bands of the "MB [Cd(TMPP)(DABCO)]

Figure 8 .

 8 Figure 8. FT-IR spectra of [ Cd(TMPP)(DABCO)], MB, and MB-[Cd(TMPP)(DABCO)].

  Complex (I)). The supramolecular assembly of this complex is made by weak non-conventional hydrogen bonds type C __ H … N and C __ H … O. Absorption spectra reveal that the insertion of Cd(II) metal ion into the TMPP porphyrinate and the addition of the DABCO axial ligand are accompanied by a redshift of the Soret and Q bands. While the Q bands of fluorescence emission spectra are blue shifted with a decrease of the fluorescence intensity, quantum yield (φ f ) and lifetime (τ f ). This quenching of the fluorescence is explained by the "heavy-atom effect" of the cadmium heavy metal. Cationic MB dye adsorption removal from aqueous solution using our synthetic cadmium(II)-DABO porphyrin derivative yield an adsorption capacity of 69.24 mg.g -1 . DFT simulations on the interaction of MB and DABCO on complex (I) was lower than the interaction of DABCO alone (exothermic behavior), this is in agreement with experimental finding. FT-IR characterization was used to confirm the adsorption of the MB dye molecule in [Cd(TMPP)(DABCO)].

2 .

 2 Elemental analysis (%) calcd for C 57.5 H 54.5 CdN 7 O 4 Cl 1.5 (1073.15 g/mol) C, 64.35; H, 5.11; N, 9.13%.

	Found: C, 64.68; H, 5.17; N, 9.19%. UV-Vis (CH 2 Cl 2 ): [ max

Table 1

 1

. Selected bond lengths (Å) and angles (deg) of [Cd(TMPP)(DABCO)]1.5CHCL 3 1.5C 6 H 12 N 2 (I)

Table 2 .

 2 Experimental and theoretical study of the structural parameters: bond lengths (Å) a and angles () of

	[Cd(TMPP)(DABCO)]1/2CHCl 3 1/2C 6 H 12 N 2 (I) and several related five-coordinate cadmium porphyrin
	complexes

Table 4 .

 4 IR assignments of the [Cd-TMPP] and [Cd-TMPP-DABCO] complexes

	Measured (theoretical)*
	[

Cd-TMPP] [Cd-TMPP-DABCO] [Cd-TMPP-DABCO-MB] Assignment

	1247 (1289)	1247 (1289)	1247 (1290)	(O-CH 3 )
	-(1262)	-(1261)	-(1263)	(C-C)
	1511 (1532)	1511 (1534)	1511 (1530)	(C=C)
	-(3033)	-(3033)	-(3033)	(C-H) methyl
		-(3062)	-(3066)	(C-H) DABCO
			-(3270)	(C-H) MB
	-(3196-3200)	2837-2987 (3196-3234)	2837-2987 (3198-3236)	(C-H) proph
	-(3283)	-(3279)	-(3282)	(C-H) pyrrol
	-(1284)	-(1285)	-(1285)	(C=N) asym
	-(1305)	-(1307)	-(1305)	(C=N) sym
	-(1014)	-(1008)	-(1009)	(Cd-N p )**
	(*) From the DFT vibrational frequency calculations

**Cd-Np is the average equatorial Cd-pyrrole nitrogen bond length

Table 6 .

 6 Parameters of adsorption isotherms of MB dye on [Cd (TMPP) (DABCO)] (I) adsorbent.

	Model	Unit	Value	Standard Error
	Langmuir
	Q o max	mg/g	69.24	10.23
	K L	L/mg	0.070	0.018
	R 2	-	0.968	-
	χ 2	-	5.71	-
	Freundlich
	K F	(mg/g)/(mg/L) n	6.60	1.34
	n	-	0.616	0.080
	R 2	-	0.938	-
	χ 2	-	10.97	-
	Redlich-Peterson
	K RP	L/g	4.86	2.284
	a RP	(mg/L) -g	0.070	0.194
	g	-	0.988	0.683
	R 2	-	0.963	-
	χ 2	-	6.27	-

Table 7 .

 7 Comparison of the adsorption removal of MB dye

	_________________________________________________________________________________
	Absorption system	Experiment conditions	Yield, Q max , reaction time	Ref.
	_________________________________________________________________________________
	Corncobs from Pakistan	[MB] 0 = 30-300 mg L-1.	Q max = 45.86 mg.g -1	[62]
	particle sizes (105-400 μm)	303 K, m = 0.05 g, pH = 6.8	91.7%, 200 min
	Raw bentonite (Algeria)	[MB] 0 = 10 mg L -1 .	Q max = 65.36 mg.g -1	[63]
			293 K, m = 0.015 g, pH > 7	60 min
	Keggin-type		[MB] 0 = 25 mg L -1 .	95% yield, 50 min	[64]
	Polyoxometalate,	298 K, m = 45 mg
	[Cu{(HOCH 2 CH 2 ) 2 (NCS) 2 } 2 ] 3
	[PW 12 O 40 ]
	Porphyrin-calcium,	[MB] 0 = 15 mg L -1 .	Q max = 952 mg.g -1	[61]
	Polymer	298 K, m =5 mg	180 min
	{[Ca(HDCPP) 2 (DMF) 2 ] n a
	Porphyrin-based porous	[MB] 0 = 50 mg L -1 .	Q max = 980.4 mg.g-1	[60]
	organic polymer (PPOPs-OH) 298 K, m =5 mg	100 min.
	[Cd(TMPP)(DABCO)]	[MB] 0 = 10 mg.L -1 .	Q max = 69.24 mg.g -1	this work
	1.5CHCL 3 1.5C 6 H 12 N 2	298 K, m = 6 mg, pH = 7	Yield = 80.7%, 20 min
	____________________________________________________________________________________________________________

a : H 2 DCPP = 5,15-di(4-carboxyphenyl) porphyrin.

Table 9 .

 9 Important FT-IR data (cm-1) of [ Cd(TMPP)(DABCO)], MB, and MB-[Cd(TMPP)(DABCO)].

	System	Total Energy+D3 (H)	E ads (kcal/mol)
	Cd-TMPP	-2538.570
	DABCO	-345.351
	MB	-1643.244
	Complex ()	-2883.950	-18.3
	Complex ()	-4181.835	-12.7
	Complex ()	-4527.203	-23.6

Acknowledgements

The authors gratefully acknowledge financial support from the Ministry of Higher Education and Scientific Research of Tunisia.The authors extend their appreciation to the deanship of Scientific Research at Majmaah University, Saudi Arabia. A.J. is grateful to the High-Performance Computing Center (Aziz Supercomputer) at King Abdulaziz University (KAU) for the resources and the support.

Supporting information

CCDC 2012300 contain the supplementary crystallographic data of complex (I). These data can be obtained free of charge from the Cambridge Crystallographic Data Centre viawww.ccdc.cam.ac.uk/data_request/cif. Conflict of interest All Authors declares that thereis no conflict of interest.

Highlights

 Synthesis of the DABCO-tetrakis[4(methoxy)phenylporphyrin] cadmium complex.

 Molecular structure was determined by single crystal X-Ray diffraction technique.

 Density Functional Theory (DFT) have been used for calculations on the structure, 1 H NMR spectroscopy and IR spectra analysis.

 UV-visible and Fluorescence investigations were made.

 Adsorption removal of methylene blue using our Cd-DABCO-porphyrin compound.