Attachment to the land. From Modern violence to eco-sensitive bonds: toward an agriculture of relations

Introduction

As all inquiries, this one starts with an enigma, emerging from an encounter with a spontaneous and yet strange wording: the fact that many farmers -people that I have directly met on my field inquiries or that I have indirectly met by reading and watching sociological and historical materials about French agriculture -when asked about the relations between them and the land they work with, spontaneously talk about an attachment. This is the problem from which this inquiry starts: what does it means, for a farmer, to say that he feels attached to his land? What this instinctive wording of attachment seems to imply, is that the relation to the land cannot be fully understood through the Modern prism describing the relations to non-human entities in agriculture, that means with concepts such as property or exploitation. My hypothesis is that there is something else behind this use of the word attachment, something complex and quite undefined, something undescribable with our Moderns categories; an attachment to a land and its history, to a landscape and the texture of a soil, to a flora and a fauna, in a word an attachment to an entangled web of ecological, sensitive and co-constitutive bonds.

Mapping the attachments: a political problem

First, to define a theoretical framework for this inquiry on the problem of attachments in modern agriculture, we need to focus on this spontaneous wording of an attachment to the land as a mapping problem, or, to be more specific, as a way of questioning the old modern political map. In a 2000's paper, "Factures/Fractures", Bruno Latour proposed to rethink the modern dichotomy between emancipation and attachment as a false problem. For Latour, because "we have never been really moderns", the problem was never to truly free ourselves from any kind of attachments, but always to choose between positive and negative attachments. More recently, in his Inquiry into modes of existence, he proposes the following definition for the concept of attachment, which I'll use as a conceptual structure for this talk: The term "attachment", like "association", draws our attention to the other beings necessary for existence (…) and therefore enables us to get away from the idea of emancipation and autonomy by taking attachments in the positive sense and by re-qualifying emancipation as a sliding from one attachment to another (not as the absence of attachments).

Following Latour's proposal, in order to go beyond this old map -which have been, as French philosopher Serge Audier recently pointed out, a strong and structuring divide between Left progressists and ecologists during the last century -we need to fracture this single axis diagram by arguing that we are always-already entangled-beings, part of complex, co-constitutive, and interdependent assemblages, and that it is illusory to think of emancipation as a liberation from any kind of attachments.

But that being said, how can we approach our particularly fantasized form of attachment -the attachment between a farmer and his/the/our land -without being trapped in the old binary axis? The old map would oppose on one hand a reactionary perspective, barresian and petainist, inheritance of nationalist's use of the concept of land, and, on the other hand, a strictly modern perspective of emancipation through progress, based on a narrow definition of materiality, leading to an ideology of "leaving the ancient ties behind".

So how can we get out of this modern trap? Or, to be more specific, how can we criticize the dominant agricultural model, which, as we will see, clearly connects the very possibility of emancipation to a liberation process from any so-called natural attachments, without falling into the usual reactionary counterpart of modernization which considers that the only alternative is to go back to the good old days?

In other words, how can we make sure that the new perspectives opened by agroecological approaches will lead to a real ecologization of agriculture, and not to a new step of modernization or to a nostalgic reaction? In a recent interview in SOLDES journal, Latour proposes an inspiring but yet unsolved program for doing so and "resetting modernity". Drawing on Emilie Hache's book, What we care for, he says:

Agriculture modernization: violence and emancipation

I would like to now focus on how agricultural modernization have dealt with those attachments to the land as an impediment to progress. This will allow us to understand the preliminary conditions for this new way of noticing and taking care of our attachments.

The question here is: why modernization needs to get rid of attachments -or at least to make To achieve this goal, agroformation needs, among other things, to proceed to a systematic disqualification of all the remaining forms of attachments, in order to ensure both scalability and substitutability without the interferences of the complex tempos of an entangled assemblage. And where do those attachments still lurk? Both in farmer's knowledges and narratives. Two processes are needed to get rid of those existing attachments, and to replace them with a modernized web of new attachments. The first one is the systematic disqualification of situated agronomic knowledges as empirical approximations or even worse as superstitions.

This undertaking mostly relies on an authoritarian agronomic epistemology, which started to

Conclusion -Ecologizing agriculture: the bonds of agroecologies

Now that we have briefly seen how agricultural modernization has made every attachment invisible and unspeakable, we need to go back to our initial problem. The persistence of the spontaneous wording from which we started our inquiry tells us something: modernization didn't manage to really get rid of the old attachments. It has only managed to make them blurry, undefined, indescribable. This is why the sentence "I'm attached to my land" can be seen as a fuzzy way to speak of an entanglement of care and bounds, because modernization deprived us from a richer lexicon to describe the complexity in the middle of which we stand. But many farmers I've met during my field inquiries reclaim, in a militant political way or within the daily fabric of their practices, the right to speak afresh about the complexity of their attachments, both in epistemological, practical and sensitive terms. The matter is, as Bruno Latour once said, to reclaim "the right not to be deprive of the bonds that make one exist". From what I have witnessed, this reclaim can take many forms: a new awareness of the soil as a complex ecosystem that allows a deep change of agronomic practises and an empowerment regarding scientific knowledge; an explicit use of attachment as a point to defend a territory or a specific being -a particular tree a neighbour wants to cut off for example; a more local-toglobal perspective in which an attachment to a situated and threatened land leads to a political involvement to defend agricultural lands in general against artificialization. But in all those different situations, an "art of noticing", as Tsing puts it, seems to come out of those renewed attachments, echoing what Baptiste Morizot calls an "eco-sensitivity", that means "a sensitivity to the vibrant tracery of the living world, to its streaked cosmos of meanings and interactions".

And I think this underlying link between caring and reclaiming, points out very accurately the apparent eco-political paradox which is at the very heart of the agricultural ecologization issue:

how, being aware that we are co-constitute by our relations with an entanglement of other beings, we can acknowledge that those attachments can bound us, while freeing us at the same time?

  believe that it allows farmers to get rid of attachments? The key concepts to start unravelling this problem are scalability and substitutability, which are two necessary conditions for agricultural modernization. Here, by agricultural modernization, I mean more specifically an objective alliance between industrial constraints and an agronomic science structured around a Aurélien Gabriel Cohen -Attachment to the land 8 th Annual Conference on the New Materialisms June 7-9, 2017, Paris Environmental Humanities and New Materialisms: The Ethics of Decolonizing Nature and Culture 4 nomological and prescriptive epistemology. The concept of scalability is very well defined by Anna Tsing in her recent book The Mushroom at the end of the world. Her idea is that scalability,that means the ability to scale up without changing the framework of a project, has been "the formula [that] shaped the dreams we have come to call progress and modernity". To illustrate this idea, she takes an example which can be interesting for our perspective: the Portuguese sugarcane plantations in colonial Brazil at the end of the sixteenth century. The characteristics of those kind of plantations are first the interchangeability of planting stock, and second the interchangeability of workers. This is the point where substitutability and scalability become the necessary conditions of a big scale pre-industrial project -and later of every industrial one. To ensure those features, the Portuguese used deterritorialization technics as a way of making both plants and workers deprive from any kind of attachments and, as Tsing says, "oblivious to encounter". For plants, this was done by a strangely heralding technic of bringing cultigen fromEurope and then cloning them by vegetative reproduction. By doing so, plants had few interspecies relations, and were "scale up ready" without the necessity for any local, ecological or agronomical inquiry. And for workers, slavery was the answer. Following the same pattern, enslaved Africans were used as attachment-free workers, with neither social relations nor ecological or territorial bonds.Above and beyond its particular and yet forerunner context, this example of sugarcane plantations shows the strong link between scalability and subsituability as attachment-depriving tools. Applied to extractist agricultural modernization, it becomes an epistemological problem of metrology for agronomic sciences, with strong ecological, social and political consequences.The metrological pattern follows this logic: if you want to compare, exchange and rationalize the use of the land, you need to establish standards. And to establish standards, you need to cut off parts of the material world that exceed any possibility of standardization -and modellingbecause of their inherent complexity. This is what I call, for the specific problem of agroindustrial modernization, the process of agroformation. The concept of agroformation is a direct reference to the idea of terraformation, invented by science-fiction writer Jack Williamson to name the transformation of a planet to make it habitable by Earth-like life. Sharing with terraformation a geo-constructivist inclination, agroformation can be define as an extensive transformation of the land to make it cultivable under the techno-scientific principles of dominant agronomy.Aurélien Gabriel Cohen -Attachment to the land 8 th Annual Conference on the New Materialisms June 7-9, 2017, Paris Environmental Humanities and New Materialisms: The Ethics of Decolonizing Nature and Culture 5

  structure itself in France and Germany at the end of the nineteenth century around agricultural chemistry. This historical form of agronomy tends to use the normative power of positive science to hop from local explanation to nomological prescription. The second part of this process is the critic of any kind of sensitive and caring relation to the land as part of an obscure agrarian sentimentalism. This process has been well explored by ecofeminist's critics of the Green Revolution, and characterized as a colonial and patriarchal takeover. Once you've achieved both processes, once the perception of the land has been freed from what Anna Tsing calls a "rush of stories", you can easily replace those old, situated, entangled stories by a new unified narrative of emancipation and progress -which is only, in real terms, a replacement of the ancient attachments by a new reliance to the technical and industrial infrastructure. And the price for this large-scale rationalization of attachments is an immense violence done to what and whom farmers used to care for.

  The problem is clearly posed: we need to take root, to criticize the modern illusory program of systematic emancipation from any kind of attachments, but at the same time, we also need to avoid the reactionary trap of a toxic and nationalist way of being attached to a land. And as I

	rootedness requires to take into consideration a bunch of things that we don't
	really know how to deal with, especially left-wing thinkers: attachment to places,
	to traditions, to loyalties, all kind of attachments that are assumed to be
	reactionary -and that often are, but not necessarily. [I translate]

Aurélien Gabriel Cohen -Attachment to the land 8 th Annual Conference on the New Materialisms June 7-9, 2017, Paris Environmental Humanities and New Materialisms: The Ethics of Decolonizing Nature and Culture 3 What is the territory on which we are settled? What are the agencies, the potencies with which we are ready to work with? It is this replanting, this rerootedness which define current politics. Except that this process of resaid, this problem is particularly sharp in agriculture, because it has this long history of being a shelter for reactionary values. But we can guess that there is another land to care for, something that is neither a resource-land, in which one plot is substitutable to another all pedological, agronomical and biochemical characteristics being equal, and nor a land-of-the-ancestors, a form of a blood-and-land attachment on which romantic nationalism once -and stillflourish. This awareness leads us to look for a path beyond the old divide between freedom and ties, by introducing, as Baptiste Morizot proposes in his book Les Diplomates, relations with non-humans into politics and other living's territories into geopolitics, as a new way to diplomatically deal with entanglements and attachments.


Laroussi Chaabane

Emmanuel Beyou
email: beyou@univ-lyon1.fr.

Amel El Ghali

Mohammed Hassen

V Baouab

Comparative studies on the adsorption of metal ions from aqueous solutions using various functionalized graphene oxide sheets as supported adsorbents

Keywords: Graphene oxide sheets, Functionalization, Adsorption of heavy metal ions, Removal of metal ions

Graphene oxide (GO) was chemically modified by bis(2-pyridylmethyl)amino groups (BPED) through a multistep procedure. For comparison, and to justify the grafting of BPED groups onto the GO sheets, the GO-based material obtained after each step was used as a solid phase adsorbent for removing Cu(II), Ni(II) and Co(II) metal ions from aqueous solutions.

The influence of metal ion concentrations, pH, contact time and temperature on their adsorption onto the GO-based adsorbents was investigated and the GO-EDA-CAC-BPED adsorbent showed the highest ability to adsorb Cu(II), Ni(II) and Co(II) with a concentration of 250 mg.L -1 at pH=7. Additionally, it was demonstrated that the equilibrium adsorption capacities of these metal ions followed the order of Cu(II)>Ni(II)>Co(II) whatever the GObased adsorbent. Moreover, to examine the underlying mechanism of the adsorption process, pseudo-first order, pseudo-second order, Elovich or Roginsky-Zeldovich and intraparticle diffusion models were fitted to experimental kinetic data. It was shown that the pseudosecond-order model was the most appropriate one to describe the adsorption of heavy metal ions by the GO-based materials. Finally, it was demonstrated that their desorption/regeneration capacities were higher than 10 cycles, opening the path to the removal of metal ions from wastewater solutions.

Introduction

Nowadays, human activities and industrial development increasingly contributes to the pollution of air, soil and water [START_REF] Tan | High-Performance Coral Reef-like Carbon Nitrides: Synthesis and Application in Photocatalysis and Heavy Metal Ion Adsorption[END_REF]. Among these, water contaminants especially heavy metals ions, have become worldwide issues due to their extreme toxicity, non-biodegradability and bioaccumulation in the living environments [START_REF] Madadrang | Adsorption Behavior of EDTA-Graphene Oxide for Pb (II) Removal[END_REF]. In particular, several heavy metal ions such as Cu(II), Ni(II) and Co(II) are used in the electroplating, battery manufacturing and light industries and accordingly the aqueous effluents often contains high metal ion concentrations [START_REF] Uoginte | Study of Cu (II), Co (II), Ni (II) and Pb (II) removal from aqueous solutions using magnetic Prussian blue nano-sorbent[END_REF]. The discharges of effluents containing these heavy metal ions have serious risk to both Earth's ecological cycle and human beings [START_REF] Ahrouch | Lead removal from aqueous solution by means of integral natural clays honeycomb monoliths[END_REF]. For exemple, some health effects associated to human exposure to copper ions are known for causing cramps, hypoglycemia, nervous system damage and Wilson disease [START_REF] Chaabane | Synthesis and characterization of Ni (II), Cu (II), Fe (II) and Fe3O4 nanoparticle complexes with tetraaza macrocyclic Schiff base ligand for antimicrobial activity and cytotoxic activity against cancer and normal cells[END_REF]. Today, the removal of metal ions from contaminated environment is still one of the biggest challenges. In the last several years, various methods such as chemical precipitation, reverse osmosis, photo-catalytic reduction, membrane separation and adsorption have been used to remove heavy metals from wastewater [START_REF] Fu | Removal of heavy metal ions from wastewaters: a review[END_REF][START_REF] Mehdaoui | Sono-heterogeneous Fenton system for degradation of AB74 dye over a new tetraaza macrocyclic Schiff base cellulose ligand-loaded Fe3O4 nanoparticles[END_REF][START_REF] Barakat | New trends in removing heavy metals from industrial wastewater[END_REF].

However, most of these methods have some disadvantages and limitations, such as low efficiency and sludge production [START_REF] Jiang | Adsorption behavior of copper ions from aqueous solution onto graphene oxide-CdS composite[END_REF]. Adsorption is a more versatile and widely used method for the treatment of wastewater in industry due to its simplicity, high efficiency and easy scale up [START_REF] Duru | Graphene oxides for removal of heavy and precious metals from wastewater[END_REF][START_REF] Xiang | 3D hierarchical flower-like nickel ferrite/manganese dioxide toward lead (II) removal from aqueous water[END_REF][START_REF] Yuan | Purification of phenol-contaminated water by adsorption with quaternized poly(dimethylaminopropyl methacrylamide)-grafted PVBC microspheres[END_REF]. Over the years, a large number of adsorbents have been designed and used for removing heavy metal ions including active carbon, polymer resins and biomass materials [START_REF] Chen | A novel polyvinyltetrazole-grafted resin with high capacity for adsorption of Pb(II), Cu(II) and Cr(III) ions from aqueous solutions[END_REF][START_REF] Zhao | Polymer-based nanocomposites for heavy metal ions removal from aqueous solution: a review[END_REF]. It is clear that polymeric materials and activated carbon are the most widely considered substrates due to their commercial availability [START_REF] Tang | Comparison of the removal and adsorption mechanisms of cadmium and lead from aqueous solution by activated carbons prepared from Typha angustifolia and Salix matsudana[END_REF]. Historically, thousands of research focused on the use of low-cost adsorbents such as cow bone [START_REF] Moreno | Removal of Mn, Fe, Ni and Cu Ions from Wastewater Using Cow Bone Charcoal[END_REF], wood bark [START_REF] Xiao | Competitive Adsorption of Aqueous Metal Ions on an Oxidized Nanoporous Activated Carbon[END_REF], bentonite clay [START_REF] Olu-Owolabi | Calcined biomass-modified bentonite clay for removal of aqueous metal ions[END_REF] and so on. Despite the low-cost of these materials, they exhibit low adsorption capacity and it takes a long time to achieve equilibrium in heavy metal ions adsorption on their surfaces [START_REF] Al-Khaldi | Effect of acid modification on adsorption of hexavalent chromium (Cr(VI)) from aqueous solution by activated carbon and carbon nanotubes[END_REF]. Recently, various new adsorbents based on modified magnetic iron oxide [START_REF] Sigdel | Arsenic removal from aqueous solutions by adsorption onto hydrous iron oxide-impregnated alginate beads[END_REF], carbon nanotubes [START_REF] Anitha | Removal of Heavy Metal Ions Using a Functionalized Single-Walled Carbon Nanotube: A Molecular Dynamics Study[END_REF] and graphene sheets [START_REF] Kommu | Removal of Pb(II) Ion Using PAMAM Dendrimer Grafted Graphene and Graphene Oxide Surfaces: A Molecular Dynamics Study[END_REF][START_REF] Huang | Adsorption of Eu(III) and Th(IV) on three-dimensional graphene-basedmacrostructure studied by spectroscopic investigation[END_REF] have been developped. For example, Chen et al., [START_REF] Chen | Adsorption of Ni(II) from Aqueous Solution Using Oxidized Multiwall Carbon Nanotubes[END_REF] used oxidized carbon nanotubes as adsorbent for the adsorption of Ni(II) and they obtained a removal efficiency of 80%.

By now, graphene has received particular interest due to its exceptional electrochemical, thermal and mechanical properties and its very high specific surface area (2600 m 2 /g) [START_REF] Srinivasan | Oxygen-Promoted Chemical Vapor Deposition of Graphene on Copper: A Combined Modeling and Experimental Study[END_REF][START_REF] Sitko | Suspended Aminosilanized Graphene Oxide Nanosheets for Selective Preconcentration of Lead Ions and Ultrasensitive Determination by Electrothermal Atomic Absorption Spectrometry[END_REF]. However, graphene is hydrophobic which may not favor the adsorption of metal ions from aqueous solutions [START_REF] Pytlakowska | Graphene oxide covalently modified with 2,2′-iminodiacetic acid for preconcentration of Cr(III), Cu(II), Zn(II) and Pb(II) from water samples prior to their determination by energy dispersive X-ray fluorescence spectrometry Spectrochim[END_REF]. Nevertheless, one famous route to make graphene hydrophilic is based on its oxidation [START_REF] Guimont | Pentadecane functionalized graphite oxide sheets as a tool for the preparation of electrical conductive polyethylene/graphite oxide composites[END_REF]. For this purpose, graphene oxide (GO) is usually obtained from natural graphite by using the Hummer's method [START_REF] Pazat | In situ emulsion cationic polymerization of isoprene onto the surface of graphite oxide sheets[END_REF]. GO sheets display a highly oxygenated surface with carboxyl, epoxy and hydroxyl groups [START_REF] Guimont | Grafting of polyethylene onto graphite oxide sheets: a comparison of two routes[END_REF]. These functional containing oxygenous groups are expected to increase the adsorption capacity of metal-based clusters [START_REF] Sitko | Suspended Aminosilanized Graphene Oxide Nanosheets for Selective Preconcentration of Lead Ions and Ultrasensitive Determination by Electrothermal Atomic Absorption Spectrometry[END_REF][START_REF] Pytlakowska | Graphene oxide covalently modified with 2,2′-iminodiacetic acid for preconcentration of Cr(III), Cu(II), Zn(II) and Pb(II) from water samples prior to their determination by energy dispersive X-ray fluorescence spectrometry Spectrochim[END_REF][START_REF] Guimont | Pentadecane functionalized graphite oxide sheets as a tool for the preparation of electrical conductive polyethylene/graphite oxide composites[END_REF][START_REF] Pazat | In situ emulsion cationic polymerization of isoprene onto the surface of graphite oxide sheets[END_REF]. Yang et al., [START_REF] Yang | Folding/aggregation of graphene oxide and its application in Cu 2+ removal[END_REF] showed that the maximum adsorption capacity of GO was 0.733mmol.g -1 for Cu(II) which was higher than the active carbon one. Indeed, it is well known that oxygen atoms of carboxyl acid groups are efficient ligand groups while the adsorption properties of an adsorbent depend on the nature of its functional groups and their affinity for pollutants [START_REF] Cui | EDTA functionalized magnetic graphene oxide for removal of Pb(II), Hg(II) and Cu(II) in water treatment: Adsorption mechanism and separation property[END_REF]. Moreover, the functionalization of GO may enhance its properties and in particular its maximum adsorption capacity. It has been established that adsorbent containing nitrogen chelating ligands such as amino, imidazole and amidoxime groups could be effective in adsorption of heavy metal ions [START_REF] Gul | Functionalization of magnetic chitosan with graphene oxide for removal of cationic and anionic dyes from aqueous solution[END_REF][START_REF] Lia | Efficient removal of uranium from aqueous solution by zero-valentiron nanoparticle and its graphene composite[END_REF][START_REF] Huang | Simultaneous elimination of cationic uranium(vi) and anionic rhenium(vii) by graphene oxide-poly(ethyleneimine) macrostructures: a batch, XPS, EXAFS, and DFT combined study[END_REF]. For instance, Chen et al., [START_REF] Chen | Functionalization of 4-aminothiophenol and 3-aminopropyltriethoxysilane with graphene oxide for potential dye and copper removal[END_REF] modified GO sheets with 3-aminopropyltriethoxysilane (APTS) and 4-aminothiophenol (ATP) respectively, for removing Cu(II) ions. The maximum adsorption capacities were 1.625mmol.g -1 and 1.560mmol.g -1 for APTS and ATP respectively, which was 10 times higher than GO. Moreover, Fang et al., [START_REF] Fang | Removal of cobalt ions from aqueous solution by an amination graphene oxide nanocomposite[END_REF] prepared GO-supported aromatic diazonium salt and then they studied the adsorption of Co(II) ions from aqueous solution and they obtained a maximum adsorption capacity of 1.974mmol.g -1 . The detection and analysis of such heavy metal ions in water is still considered as a challenge. Many modern methods such as anodic stripping voltammetry, neutron activation analysis, flame atomic adsorption spectrometry and inductively coupled plasma-mass spectromertry have been developed for the rapid analysis and detection of heavy metal ions from aqueous solutions [START_REF] Zhu | Spectrophotometeric determination of Cu(II), Co(II) and Ni(II) ions in Mono and Multi component systems[END_REF][START_REF] Huang | Interaction mechanism of uranium(VI) with three-dimensional graphene oxide-chitosan composite: Insights from batch experiments, IR, XPS, and EXAFS spectroscopy[END_REF]. Regrettably, most of these methods are not appropriate for the determination of metal ions concentrations, because of the use of expensive equipment, high cost of maintenance and use of complicated experimental procedures [START_REF] Abbasi-Tarighat | Simultaneous Spectrophotometric Determination of Cu(II), Co(II) and Ni(II) using Ratio Spectra-Continuous Wavelet Transformation in some Food and Environmental Samples[END_REF]. Spectrophotometry and UV-Vis absorption spectrometry are known as the most appropriate techniques for the development of low-cost, rapid and simple analytical methods [START_REF] Devi | Spectrophotometric Determination of Iron(II) and Cobalt(II) by Direct, Derivative, and Simultaneous Methods Using 2-Hydroxy-1-Naphthaldehyde-p-Hydroxybenzoichydrazone[END_REF]. Unfortunately, the absence of chromophore groups on metal ions makes their corresponding solutions weak colored or colorless so that it is necessary to add a color reagent [START_REF] Ghali | Preparation, characterization and application of a [copper (II)/ethylenediamine-cotton] complex for the removal of AB25 from aqueous solution in a laboratory scale column[END_REF]. For instance, Moghadam et al., [START_REF] Moghadam | Simultaneous spectrophotometric determination of copper, cobalt, nickel and iron in foodstuffs and vegetables with a new bis thiosemicarbazone ligand using chemometric approaches[END_REF] used bis-thiosemicarbazone as a color reagent for the spectrophotometric determination of Co(II), Ni(II) and Cu(II) ion concentrations in aqueous solution.

The present work aims to design a novel multi-functional GO-based adsorbent for high efficiency removal of Cu(II), Ni(II) and Co(II) ions from aqueous solutions. First, GO was modified by ethylenediamaine (GO-EDA) followed by the grafting of chloroacetychloride (GO-EDA-CAC). Then, the grafting of bis(2-pyridylmethyl)amino groups (BPED) onto GO-EDA-CAC was realized and producing the adsorbent (GO-EDA-CAC-BPED). All GO-based materials were characterized with the help of FTIR, TGA, XPS, SEM and UV-Vis. Then, the effect of the functionalization of GO sheets on their metal ion adsorption capacities was studied by using GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED as adsorbents to remove Cu(II), Ni(II) and Co(II) metal ions from aqueous solutions. To understand the adsorption behavior of these materials towards heavy metal ions, the influence of pH, initial metal ion concentrations and contact time onto their adsorption onto the GO-based surfaces were studied and discussed, thoroughly. Additionally, the experimental data were fitted to the pseudo-first order, pseudo-second order, Rorginsky-Zeldovich (or Elovich) and intraparticle diffusion kinetic models. Furthermore, adsorption data were analyzed by the Freundlich, Langmuir and Jossens approaches and the thermodynamic parameters were also systematically calculated. Finally, the regeneration experiments of adsorbed metal ions in presence of EDTA as a base were explored to evaluate the reusability of these GO-based adsorbents.

Experimental details

2.1.Reagents

Natural graphite powder (4 µm in size, 99.99% purity) provided by TIMCAL Graphite and Carbon, France. Graphite Oxide (GO) was prepared from natural graphite powder using a modified Hummers' method as described in our previous work [START_REF] Dhahri | Synthesis and characterization of Au-immobilized nanoparticles onto cellulose-ethylenediamine-grafted reduced graphite oxide sheets[END_REF]. Di-tert-butyl dicarbonate (DTBT), ethylenediamine (EDA), 2-chloromethylpyridine hydrochloride (CPH), 2-(7-aza-1H-benzotriazole1yl)-1,1,3,3-tetramethyluronium hexafluoro phosphate (HATU), chloroacetyl chloride, sodium carbonate, sodium hydroxide, hydrochloric acid, sodium sulfate. Copper (II) chloride dihydrate (CuCl2.2H2O ; 99.99 %), Nickel (II) chloride hexahydrate (NiCl2.6H2O ; ≥98 %), Cobalt (II) chloride hexahydrate (CoCl2.6H2O ; ≥98 %), sodium chloride, potassium hydrogen phthalate, dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dichloromethane (DCM), tetrahydrofuran (THF), toluene, ethyl acetate, methanol, diethyl ether, hexane and ethanol were purchased commercially and used without any further purification. All reagents and solvents were provided by sigma-Aldrich-France and used as received. All standard aqueous solutions were diluted with ultra-pure water from Milli-Q plus system (Millipore, Molsheim, France-Lyon).

Instruments

1 H (600 MHz) and 13 C (150 MHz) spectra were recorded at 25 °C in CDCl3 using at Bruker instrument (FEI, USA). The Fourier transform-infrared spectroscopy (FTIR) spectra of the dried samples were recorded on a Nicolet 460 spectrometer (Thermo Nicolet Corporation, USA) in the wavenumber range of 4000-400 cm -1 with a resolution of 1.5 cm -1 at room temperature. Thermogravimetric analysis (TGA) analysis was conducted under nitrogen atmosphere with a heating rate of 5°C.min -1 by using a Perkin Elmer thermal analyzer instrument (Nicolet, TA SDT Q600, USA). The X-ray photoetlectron spectroscopy (XPS) analysis were performed using a PHI physical electronic spectrometer (Quantra SXM instrument, USA) with a monochromated Al Kα radiation and 180° hemispherical electron energy analyzer assuring an energy resolution of 0.3 eV and 4mA. The binding energy in the range -2 to 1400 eV and the core level characteristic peaks for C1s and N1s were measured.

The surface morphologies powder samples were visualized using a FEI Quanta-250 FEG scanning electron microscope (FEI Company, The Netherlands), at a typical accelerating voltage of 10 Kv. The concentration of Cu(II), Ni(II) and Co(II) ions in the aqueous solutions were analyzed using UV-Visible spectrophotometer (Perkin Elmer, USA) through the formation of metal (II)/hydrogen phthalate complex. All digital images were recorded by a CANON Power shot SX210 IS 14.1 MP 14 x Wide zoom.

Grafting of chloroacetyl chloride onto GO-EDA: (GO-EDA-CAC)

GO-EDA sheets were prepared according to our previous work [START_REF] Dhahri | Synthesis and characterization of Au-immobilized nanoparticles onto cellulose-ethylenediamine-grafted reduced graphite oxide sheets[END_REF]. 1 g of GO-EDA was sonicated in 100 mL of anhydrous DMF and Et3N (3 mL) was added. Afterwards, 20 mL of chloroacetyl chloride was placed in around bottom flask and heated at 70 °C for 72 h. At the end of the reaction, the product was collected by centrifugation and washed with diethyl ether (Et2O) several times and finally during under vacuum at 70 °C overnight.

Grafting of BPED onto GO-EDA-CAC: (GO-EDA-CAC-BPED)

First, the synthetic route for the preparation of N,N-bis(2-pyridylmethyl)ethylenediamine (BPED) is presented in Scheme 1 ( Section 1, Supporting information †) and the corresponding experimental procedure is also described in supporting information (section 1).

Then, BPED was grafted onto the GO-EDA-CAC according to the experimental conditions described in the literature [START_REF] Chauhan | Design, Synthesis, bioactivity, and computational studies of some morpholine-clubbed coumarinyl acetamide and cinnamide derivaties[END_REF] and in a typical experiment, 1.00 g of GO-EDA-CAC was dispersed in 30 mL anhydrous DMF by ultrasonication for 30 min followed by the addition of Et3N (4 mL). Then, BPED (3.63 g, 15mmol) was added in the mixture and stirred under reflux at 80°C for 24h. After the reaction, the solution was cooled to room temperature, centrifugated, and washed with ethanol to remove the excess of BPED. This purification step was monitored by UV-Visible analysis until there is no remaining free BPED in the mixture (Fig. S7 †). Finally, GO-EDA-CAC was dried under vacuum at 50 °C overnight.

Removal of metal ions from aqueous solutions

The adsorption behavior of the four adsorbents (GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED) towards the different metal ions (Cu(II), Ni(II) and Co(II)) were studied in details. Indeed, the effect of pH (3.0-8.0), contact time (0-24h)), initial metal ion concentration (50-500 mg.L -1 )) on metal ion adsorption were invertigated. The zero point charge is shown in section 2 (Supporting information †). The effect of pH on the different metal ion (Cu(II), Ni(II) and Co(II)) adsorption was studied in the range 3-8 and adjusted with a Clark-Lub's buffer solutions [START_REF] Ghali | Aminated cotton fibers loaded with copper(II) ions for enhanced pesticide removal performance from water in a laboratory scale batch[END_REF]. In a typical experiment, 100 mg of adsorbent and 100 mL of a metal ion concentration of 250 mg.L -1 in water were stirred at room temperature for 24 h to achieve adsorption equilibrium. Then, the concentration of metal ions in the solution before and after adsorption by the GO-based adsorbents was measured by UV-Vis spectrometry using calibration curve (Section 1, Supporting information †). In case of the presence of impurities (formation of metal hydroxides solid particles at pH>7) in the aqueous suspension, the surnageant was filtered through a 0.45 µm membrane filter.

Morover, the adsorption kinetics were carried out using different adsorption time intervals: GO (From 0 to 9 h at pH=5), GO-EDA (From 0 to 8 h at pH=6), GO-EDA-CAC (From 0 to 6 h at pH=6) and GO-EDA-CAC-BPED (From 0 to 4 h at pH=7).

Additionally, the isothermal adsorption experiments of GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED were investigated by changing the concentration of the metal ion solution within the range of 50-500 mg.L -1 . In addition, all the isotherm experiments were performed in the temperature range 293 K-353 K and the adsorption thermodynamic parameters were calculated.

The equilibrium adsorption capacity (Qe; mmol.g -1 ) was calculated with the following equation (Eq.1):

Q e = 𝑉(𝐶 0 -𝐶 𝑒 ) 𝑚 (1)
Where C0 and Ce are the initial and equilibrium concentrations (mmol.L -1 ) of the metal ions of each remaining solutions, respectively. V is the volume (mL) of the heavy metal ion solution and m (mg) is the mass of adsorbent.

Regeneration and recycling studies of adsorbents

After the adsorption study, the adsorbent loaded with heavy metal ions was collected and slightly washed with deionized water several times and finally dried under vacuum at 60 °C overnight. Then, 0.1g of each adsorbent loaded with metal ions (Cu(II), Ni(II) and Co(II)) was stirred at 25 °C for 10 h with EDTA at different concentrations (0.005, 0.01 and 0.02 M).

After filtration, the remaining metal ion concentration in the filtrates was determined by UV-Vis spectrometry using calibration curve (Section 1, Supporting information †) and the adsorbents (GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED) were subjected to the next ten adsorption-desorption cycles using the same procedure.

Results and discussion

The synthesis of the new adsorbent material requires a multistep procedure and is based on the introduction of nitrogen and oxygen chelating groups within chemically functionalized graphite oxide sheets (GO). First, the graphite oxide sheets (GO) were produced by the oxidation of a natural graphite powder using a modified Hummers' method, as described in our previous work [START_REF] Guimont | Grafting of polyethylene onto graphite oxide sheets: a comparison of two routes[END_REF]. Then, the covalent functionalization of GO sheets was performed in three steps (Scheme 1). First, GO was modified with ethylenediamine to introduce some amino and amide groups onto the GO surface by converting epoxy and carboxylic groups, respectively. Then, the treatment of the amino groups with chloroacetyl chloride lead to the formation of the GO-EDA-CAC adsorbent. Finally, the GO-EDA-CAC adsorbent reacted with N,N-bis(2-pyridylmethyl)ethylenediamine (BPED) to yield the GO-EDA-CAC-BPED adsorbent. Nevertheless, as discussed before, the main interest in functionalizing GO sheets was highlighted by studying the heavy metal ion adsorption capacities of Cu(II), Ni(II) and Co(II) after each functionalization step.

Scheme 1. Functionalization of GO sheets with BPED in three steps.

3.1.Characterization of GO-based materials

As described in a previous article [START_REF] Dhahri | Synthesis and characterization of Au-immobilized nanoparticles onto cellulose-ethylenediamine-grafted reduced graphite oxide sheets[END_REF], we synthesized GO-EDA by the direct grafting of ethylenediamine onto GO in DMF. The introduction of the chloromethyl groups onto the GO-EDA surface through an amination reaction was qualitatively evidenced by FT-IR analysis (Fig. 1c). It can be observed, that the FTIR spectrum of the GO-EDA-CAC (Fig. 1c) displays nearly the same absorption peaks as the GO-EDA ones (Fig. 1b) while the peak in the range 600-650 cm -1 may be attributed to both the stretching vibration of amide groups and the stretching vibrations of the C-Cl groups. In addition, by comparing the spectra of GO-EDA-CAC (Fig. 1c) and GO-EDA-CAC-BPED (Fig. 1d), it can be observed that the stretching vibration bands of the C-Cl groups in GO-EDA-CAC disappear while a new absorption peak located at 767 cm -1 appears that can be attributed to the out-of-plane bending vibration of the pyridine groups. The presence of both CAC and BPED groups onto the GO-EDA surface was confirmed by using the X-ray photoelectron spectroscopy (XPS). The XPS spectra of C 1s sand N 1s of the GO-EDA-CAC and GO-EDA-CAC-BPED samples are presented in Fig. 2 and Fig. 3, respectively. Based on the XPS results, the peak area ratios of carbon and nitrogen containing groups were calculated (Table 1 andTable 2). The high resolution C 1s spectra of GO-EDA-CAC (Fig. 2a) can be deconvoluted into four peaks corresponding to C=C/C-C at 284.55 eV, C-N at 285.92 eV, O-C-O at 287.18 eV and C=O at 288.82 eV. After grafting BPED, C-N species ratio content increase from 17.0% to 31.4% for GO-EDA-CAC and GO-EDA-CAC-BPED, respectively, as expected (Table 1). Furthermore, the high resolution N 1s spectra of GO-EDA-CAC (Fig. 3a) show three types of nitrogen atoms with three peaks located at 399.01 eV (C=N), 400.16 eV (C-NR2) and 401.76 eV (N-C=O). Moreover, it can be observed that the amount of O=C-N (11.2%) and C=N-(10.2%) significantly increase when compared Studying the stability of GO-based suspensions in a solvent is also usual after a grafting step, so GO-EDA (a), GO-EDA-CAC (b) and GO-EDA-CAC-PBED (c) were dispersed at a concentration of 0.2 mg.mL -1 in various organic solvents and water. Fig. 4a shows that highly stable suspensions were obtained in water and some organic solvents such as DMF and DMSO for GO-EDA, as reported earlier literature [START_REF] Dhahri | Synthesis and characterization of Au-immobilized nanoparticles onto cellulose-ethylenediamine-grafted reduced graphite oxide sheets[END_REF]. After the grafting of chlororacetyl groups onto the GO-EDA surface (Fig. 4b), the resulting material precipitates in water and DMF which may be attributed to an increase of its hydrophobicity. Finally, after the chemical modification of GO-EDA-CAC with BPED, the corresponding GO-EDA-CAC-BPED sheets (Fig. 4c) display a better dispersibility in polar protic solvents (water and ethanol) and DMSO. This behavior may be explained by the stronger hydrogen bond interactions in presence of amino and pyridine groups. Then, all the GO-based materials were analyzed by thermogravimetric analysis (TGA).

Indeed, it is well known that TGA permit to determine of the grafting density of the organic moieties. The TGA curve of GO (Fig. 5a) displays two main weight loss in the temperature range 50-120°C and 150-300°C, respectively. The loss of mass below 100 °C corresponds to physically adsorbed moisture while the major mass loss at about 200°C may be attributed to the pyrolysis of oxygen containing groups [START_REF] Ghali | Aminated cotton fibers loaded with copper(II) ions for enhanced pesticide removal performance from water in a laboratory scale batch[END_REF][START_REF] Samadaei | A structural study on ethylenediamine-and poly(amidoamine)-functionalized graphene oxide: simultaneous reduction, functionalization, and formation of 3D structure[END_REF][START_REF] Akhtar | Functionalized Graphene Oxide Bridging between Enzyme and Au-Sputtered Screen-Printed Interface for Glucose Detection[END_REF]. After EDA grafting, a new weight loss is observed in the temperature range 230-550 °C which corresponds to an EDA grafting density of 19mmol.g -1 . The grafting of chloroacetyl groups onto the GO-EDA surface was suggested by an increase of the weight loss (~5 wt%) on the TGA curve (Fig. 5c) in comparison with the one of GO-EDA (Fig. 5b). Finally, it can be observed that the TGA curve of the GO-EDA-CAC-BPED (Fig. 5d) does not display the same thermal decomposition behavior with the appearance of a weight loss at a higher temperature which may be attributed to the presence of BPED groups. Moreover, the higher residual weight content at 700 °C in comparison with the TGA curves of the other GO-based materials suggests that the BPED groups participated to the formation of char during burning. The effect of the chemical modification of GO sheets onto the morphology of the resulting materials was studied by scanning electron microscopy (SEM). As shown in Fig. 6a, the GO sheets are stacked together and they exhibit wrinkled areas due to oxidation process while their edges seem crooked. After reaction with ethylenediamine (Fig. 6b), the GO-EDA surface shows the presence of randomly crumpled thin large flakes [START_REF] De Leon | Simultaneous Reduction and Functionalization of Graphene Oxide via Ritter Reaction[END_REF]. Moreover, all the functionalized GO-based sheets display a higher surface roughness (Fig. 6b-6d) than the GO one (Fig. 6a). The UV-Vis absorption spectra of aqueous suspensions of GO, GO-EDA and GO-EDA-CAC-BPED were also studied (Fig. 7). The GO sample exhibits a broad absorption band at 260 nm which is related to the (π→π*) transitions of aromatic ring (C=C) (Fig. 7a) while this main absorbance band is shifted to 243 nm, after EDA grafting (Fig. 7b) [START_REF] Dhahri | Synthesis and characterization of Au-immobilized nanoparticles onto cellulose-ethylenediamine-grafted reduced graphite oxide sheets[END_REF]. After BPED grafting, Fig. 7c shows the appearance of a new absorption band at 340nm which is related to (n→π*) transitions of the C=N bonds, suggesting a successful functionalization of GO-EDA-CAC with BPED.

Influence of pH, contact time and initial metal ion concentration on heavy metal ion adsorption

Effect of pH on the adsorption capacities

The pH of metal ion aqueous solutions may play an important role in their adsorption by adsorbents. Indeed, adsorption of metal ions relates mostly on the deprotonation and protonation of binding sites of the chelating molecules located onto the surface of an adsorbent and on the metal species present in solution [START_REF] Wang | Preparation of dithiocarbamate polymer brush grafted nanocomposites for rapid and enhanced capture of heavy metal ions[END_REF]. For comparison, the adsorption capacities of the GO-based materials to Cu(II), Ni(II) and Co(II) were investigated and the results are depicted in Fig. 8. As it can be seen, the adsorption capacities of these materials towards different metal ions increase with increasing pH in the range 4-6. This behavior may be attributed to the protonation of the active sites of the adsorbents in a too much acidic media that alter the metal ion adsorption. Indeed, the concentration of H + ions is high at very low pH which leads to the development of positive charge on the active metal ion binding sites and thereby a competition between the adsorption of metal ions and H + ions. Therefore, a less competition is expected by increasing the pH. To understand the underlying phenomena, the pH point zero charge (pHPZC) of the various adsorbents were measured (plots of ΔpH vs pHi) (Fig. S8 †) and we obtained 3.9, 5.6, 5.7, and 6.8 for GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED, respectively. It is well known that the adsorbent surface is positively charged at pH<pHPZC and it is negatively charged at pH>pHPZC [START_REF] Wang | Preparation of dithiocarbamate polymer brush grafted nanocomposites for rapid and enhanced capture of heavy metal ions[END_REF] so the active metal ion binding sites located onto the GO-based adsorbent will be protonated at pH<pHPZC which should compete successfully with the adsorption of metal ions, as discussed above. Therefore, for the GO-EDA-CAC-BPED adsorbent exhibiting a pHPZC of 6.8, it is expected that its adsorption capacity will be favored at pH higher than 6.8, confirming the obtained experimental values (Fig. 8.).

We consider that the higher maximum adsorptions (qpH) is observed at pH=7 for the GO-EDA-CAC-BPED adsorbent with QCu(II)=3.464±0.112mmol.g -1 , QNi(II)=3.254±0.095mmol.g -1

and QCo(II)=3.054±0.091mmol.g -1 because the removal of metal ions is facilitated at pH˃7 due to the precipitation of metal hydroxides in the aqueous solution which leads to increased removal efficiencies, as discussed by Samantary et al., [START_REF] Samantary | Water Remediation Aided by a Graphene-Oxide-Anchored Metal Organic Framework through Pore-and Charge-Based Sieving of Ions[END_REF].

Effect of the initial metal ion concentration on their adsorption

The effect of the metal ion concentration (50 to 500 mg.L -1 ) on their adsorption by the GO-based adsorbents (GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED) at 293K, keeping all the other parameters constant, is shown in Fig. 9. It is clear that the equilibrium adsorption capacities of the various adsorbents increase with increasing the metal ion concentrations. As discussed by Zhang et al. [START_REF] Zhang | Design and Preparation of Biomass-Derived Carbon Materials for Supercapacitors: A Review[END_REF], the increase in metal ion removal efficiency may be explained by the higher interaction between metal ions and the active sites located onto the surface of the adsorbents. Besides, when the initial concentration of metal ions increases from 50 to 250 mg.L -1 , the maximum adsorption capacities become nearly constant for a metal ion concentration higher than 250 mg.L -1 . This latter value is probably related to the saturation of the available binding active sites of the adsorbent.

Effect of contact time on the adsorption capacities of GO-based adsorbents

To understand the adsorption behaviors of GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED towards heavy metal ions, the equilibrium adsorptions capacities of Cu(II), Ni(II)

and Co(II) at different contact time were investigated (Fig. 10). The measurements were performed using a metal ion concentration of 250 mg.L -1 at pH=5 for GO, pH=6 for GO-EDA and GO-EDA-CAC and pH=7 for GO-EDA-CAC-BPED. At the first stage of the adsorption of heavy metal ions, a huge increase in the adsorption capacity is observed whatever the metal ion nature and then it reaches a plateau for content time higher than 4 hours (Fig. 10). The time required to reach equilibrium depends on the adsorbent so that it is 9 h for GO, 8 h for GO-EDA, 6 h for GO-EDA-CAC and 4 h for GO-EDA-CAC-BPED. Thus, GO-EDA-CAC-BPED can achieve an equilibrium adsorption faster than GO-EDA-CAC, GO-EDA and GO.

By comparing these adsorption kinetics, it can be concluded that GO-EDA-CAC-BPED displays the highest ability to adsorb of Cu(II), Ni(III) and Co(II) with equilibrium adsorption capacities of 3.464±0.100mmol.g -1 , 3.254±0.098mmol.g -1 and 3.054±0.093mmol.g -1 ,

respectively. These results indicate that the presence of various oxygenated and nitrogenated groups onto the surface of GO favor the adsorption of heavy metal ions. =250 mg.L -1 , T = 293 K, [adsorbent] = 0.100 g/100 mL and using optimal pH conditions : pH=5 for GO, pH=6 for GO-EDA, pH=6 for GO-EDA-CAC and pH=7 for GO-EDA-CAC-BPED).

Additionally, the equilibrium adsorption capacities of the various metal ions onto all the adsorbents followed the order: Cu(II)>Ni(II)>Co(II). As discussed by Su et al., [START_REF] Su | High-performance iron oxide-graphene oxide nanocomposite adsorbents for arsenic removal Colloids Surf[END_REF], the behavior of the adsorption of heavy metal ions is explained by their intrinsic properties such as atomic number, atomic weight, electronegativity and density. Therefore, we have compared the metal ion characteristics of Cu(II), Ni(II) and Co(II) (Table 3).

Table 3. Metals ordered according to ionic properties and adsorbent

The higher equilibrium adsorption capacity of Cu 2+ onto all adsorbents may mainly relies on its higher electronegativity and density (Table 3).

Adsorption kinetics of the metal ions

The kinetic data were analyzed with four used kinetic models, including the pseudo first order model [START_REF] Lee | Pseudo First-Order Adsorption Kinetics of N719 Dye on TiO2 Surface[END_REF], the second order model [START_REF] Xiao | Erroneous Application of Pseudo-Second-Order Adsorption Kinetics Model: Ignored Assumptions and Spurious Correlations[END_REF], the Elovich or Roginsky-Zeldovich model [START_REF] Juang | Application of the Elovich Equation to the Kinetics of Metal Sorption with Solvent-Impregnated Resins[END_REF] and the Weber and Morris model [START_REF] Weber | Kinetics of adsorption on carbon, from solutions[END_REF], more recently called intra-particle diffusion model [START_REF] Abdeen | Adsorption of Mn (II) ion on polyvinyl alcohol/chitosan dry blending from aqueous solution[END_REF].

The pseudo-first-order equation can be expressed in the linear form as follows:

𝐿𝑛(𝑄 𝑒 -𝑄 𝑡 ) = 𝐿𝑛𝑄 𝑒 -𝐾 1 × 𝑡 (2)
Where Qe and Qt (mmol.g -1 ) are the adsorption capacity at equilibrium and at test time t (min), respectively; K1 (min -1 ) is the rate constant of pseudo-first-order adsorption.

The slope and intercept of plots of log (Qe-Qt) versus t were used to determine the rate constant k1 and Qe.

Metal characteristics Metal order according to its property Atomic number

Cu (II) [START_REF] Pazat | In situ emulsion cationic polymerization of isoprene onto the surface of graphite oxide sheets[END_REF] The linear form of pseudo-second-order equation could be expressed as follows :

𝑡 𝑄 𝑡 = 1 𝐾 2 ×𝑄 𝑒 2 + 𝑡 𝑄 𝑒 (3)
Where K2 (g.mmmol -1 .min -1 ) is the rate constant of pseudo-second-order adsorption. The values of k2 and Qe can be calculated from the slopes (1/Qe) and intercepts (1/k2Qe 2 ) of the plots of t/Qt versus t, respectively.

The linear form of the Elovich or Roginsky-Zeldovich equation is given as:

𝑄 𝑡 = 1 𝛽 𝑙𝑛(𝛼 × 𝛽) + 1 𝛽 𝑙𝑛(𝑡) (4)
Where 𝛼 (mmol.g -1 .min -1 ) is the Elovich initial adsorption rate. 𝛽(g.mmol -1 ) is the desorption constant. The constants α and β can be obtained from the slope and the intercept of the plot of Qt versus ln (t).

The mechanism of adsorption can be explained by Weber and Morris [START_REF] Weber | Kinetics of adsorption on carbon, from solutions[END_REF] model or by the intraparticle diffusion model, which can be written as follows:

𝑄 𝑡 = 𝐾 𝑖 × 𝑡 1/2 + 𝐶 (5)
Where ki (mmol.g -1 .min -1/2 ) is the rate constant of intra-particle diffusion and C (mmol.g -1 .min -1/2 ) is a constant correlated to the thickness of the binding layer.

If the plot of Qt versus t 1/2 is intercepted at zero, the rate of adsorption will be divided in many stages in the adsorption process while if the slope of the first part is not zero, it will suggest that the binding diffusion layer controls the adsorption rate at the beginning of adsorption.

The values of the kinetic parameters calculated from both pseudo-first-order and pseudosecond-order models are summarized in table 4. According to R 2 values, the pseudo-second-order model fits better with the kinetic data than the pseudo-first-order model. Moreover, the calculated values (Qe,cal) obtained from the pseudo-second-order kinetic model are greatly closer to the experimental data (Qe,exp) than those obtained from the pseudo-first-order model (Table 4). In addition, the Qe values followed the order: GO-EDA-CAC-BPED>GO-EDA-CAC>GO-EDA>GO for removing all the studied metal ions. As discussed by Nayak et al., [START_REF] Nayak | Comprehensive Understanding of the Kinetics and Mechanism of Fluoride Removal over a Potent Nanocrystalline Hydroxyapatite Surface[END_REF] the adsorption process is probably explained by a physical adsorption which involves valence force through an exchange of electrons between adsorbent and adsorbate.

Table.4. Kinetic parameters

The Elovich equation is widely used to describe the second-order kinetic and considers that the solid surface of adsorbent is heterogeneous. The values of kinetic constants of the Elovich model for all heavy metal ions are listed in table 5. EDA>GO for removing Cu(II), Ni(II) and Co(II) and it is clear that these variations are dependent on the nature of the functional groups located onto the surface of the adsorbents.

Table.5. Kinetic parameters of

In order to understand the adsorption mechanism of Cu(II), Ni(II) and Co(II) onto the t(different adsorbents, the experiment data were fitted with the intra-particle diffusion model.

The first order rate constants and the corresponding correlation coefficients were calculated by using Eq.5 (Table 6) and plotted in Figure 11. and Co(II) ions onto the GO-based adsorbents. For GO, GO-EDA and GO-EDA-CAC, the first stage corresponds to the metal ions diffusion through the solution to the binding layer of the adsorbents or external surface of the adsorbents. The second stage may be attributed to the gradual adsorption of metal ions onto adsorbents (Fig. 11a, 11b and11c). It is clear that ki1 (first stage) is higher than ki2 (second stage) indicating that the second stage corresponds to a slower adsorption process. In addition, the intra-particle diffusion of the GO-EDA-CAC-BPED adsorbent displays three curves (Fig. 11d). The first stage is quick and it may be related to the diffusion of Cu(II), Ni(II) and Co(II) ions through the solution to the boundary layer of GO-EDA-CAC-BPED. The intra-particle diffusion in the second stage exhibit a lower diffusion rate due to further diffusion of metal ions passing through the surface to the internal layer of GO-EDA-CAC-BPED. Finally, the third stage corresponds to a well-known slowdown of the diffusion rate when the binding sites are saturated. As a result, the order of constants Ki for the adsorbent GO-EDA-CAC-BPED is: ki1 (first stage) > ki2 (second stage) > ki3 (third stage). As discussed by Vu et al., [START_REF] Vu | A new paradigm of ultrathin 2D nanomaterial adsorbents in aqueous media: graphene and GO, MoS2, MXenes, and 2D MOFs[END_REF], the rate of adsorption is possibly explained by the concentration of the adsorbate, the metal ions properties and its affinity with the adsorbents.

Adsorption isotherms of the metal ions

The study of the adsorption isotherms gives a good understanding of the adsorption mechanisms of metal ions onto adsorbents. Herein, Langmuir [START_REF] Zhang | Prediction of Adsorption Isotherms of Multicomponent Gas Mixtures in Tight Porous Media by the Oil-Gas-Adsorption Three-Phase Vacancy Solution Model[END_REF], Freundlich [START_REF] Ma | Adsorption of Low-Concentration Uranyl Ion by Amidoxime Polyacrylonitrile Fibers[END_REF] and Jossens [START_REF] Ma | Adsorption of Low-Concentration Uranyl Ion by Amidoxime Polyacrylonitrile Fibers[END_REF] models were applied to simulate and to fit the adsorption isotherms of Cu(II), Ni(II) and Co(II) onto the GO-based adsorbents. Langmuir model is commonly used to describe the adsorption on a homogeneous surface assuming the uniformity of the adsorption sites and no interaction between the adsorbate and the surface of the adsorbent.

The linear form of the Langmuir isotherm model can be expressed as:

𝐶 𝑒 𝑄 𝑒 = 𝐶 𝑒 𝑄 + 1 𝑄×𝑏 (6)
Where, Ce (mmol.L -1 ) is the equilibrium concentration of metal ions, Qe (mmol.g -1 ) is the equilibrium adsorption capacity, Q (mmol.g -1 ) is the Langmuir monolayer saturation capacity and b (L.mmol -1 ) is a constant related to the adsorption energy.

The Langmuir isotherm model can be also expressed in terms of a dimensionless constant called separation factor (RL), giving information about the feasibility of the adsorption process. It can be expressed as:

𝑅 𝐿 = 1 1+𝑏×𝐶 𝑅𝑒𝑓 (7)
Where, CRef (mmol.L -1 ) is the metal ions concentration and b (L.mmol -1 ) is the Langmuir constant related to the energy of adsorption.

The value of RL indicates the adsorption behavior: RL>1 : unfavorable ; RL =1 : linear ; 0 <RL<1 : favorable ; RL =0 : irreversible

The Freundlich isotherm model is more suitable for describing the enthalpy of adsorption on a heterogeneous surface and it can be derived, assuming a binding affinity that decreases with the increase in adsorption degree. The linear form of the Freundlich equation is given as:

𝑙𝑛Q e = 𝑙𝑛(𝐾 𝐹 ) + 1 𝑛 𝑙𝑛(𝐶 𝑒 ) (8)
Where, KF and n are the Freundlich constants representing the adsorption capacity and adsorption intensity, respectively.

The Jossens model represents a combination between the two previous models and describes a simple equation based on the energy distribution of adsorbate/adsorbent interactions at adsorption sites.

This isotherm can be written as follows:

𝑄 𝑒 = 𝑖×𝐶 𝑒 1+𝑗×(𝐶 𝑒 ) 𝑚 (9)
Where, i (L.g -1 ), j (L.mmol -1 ) and m are Jossens isotherm constants which can be obtained from adsorption data by an iterative procedure.

The Langmuir and Freundlich isotherm models were used to examine the relationship between the metal ions adsorption onto different adsorbents at different temperatures [START_REF] Song | Modeling the transport of sodium dodecyl benzene sulfonate in riverine sediment in the presence of multi-walled carbon nanotubes[END_REF]. A parameters comparison between the two models is shown in Tables S1a mmol.g -1 and QCo(II)= 3.401±0.008 mmol.g -1 ) may be also explained by its higher binding energies values. In addition, the Q values of GO and GO-EDA-CAC (Tables S1a-S1c †) increase as the solution temperature increases confirming that the adsorption of metal ions onto the adsorbents are favorable at higher temperatures, while the Q values of GO-EDA and GO-EDA-CAC-BPED decrease with an increase of temperature suggesting that a better adsorption performance can be obtained at low temperature (Table S1b and Table S1d †).

These results show that the different functional groups onto adsorbents exhibit different behaviors that are temperature dependent when combining with metal ions. Furthermore, the RL values are in the range 0-1 whatever the GO-based adsorbent (Tables S1a-S1d)

confirming that the metal ion adsorption is favorable.

Moreover, the highest values of adsorption capacity Freundlich (KF) are observed at 293 K for GO-EDA and GO-EDA-CAC-BPED adsorbents (Tables S2b andS2d †) and at 353 K for GO and GO-EDA-CAC adsorbents (Tables S2a andS2c †). In addition, the n values of the Freundlich isotherm model at all studied temperature are greater than 1 for all adsorbents, indicating that the adsorption of metal ions onto different adsorbents is favorable under our experimental conditions. In addition, the Jossens model represents a combination between Langmuir and Freundlich isotherms and it can be applied to both homogenous and heterogeneous systems. The calculated parameter values as well as the correlation coefficients at different temperatures ranging from 293 to 353 K are presented in Tables S3a andS3d †. It can be observed that the Jossens isotherm model shows better correlation coefficients (R 2 )

than both Freundlich and Langmuir models. The i and j values for GO and GO-EDA-CAC adsorbents increase with increasing temperature demonstrating that a better adsorption performance can be obtained at high temperatures (Tables S3a andS3c †). In contrary, for GO-EDA and GO-EDA-CAC-BPED adsorbents, the i and j values of decrease as the solution temperature increases suggesting that the adsorption of metal ions onto these adsorbents are favorable at low temperatures (Tables S3b andS3d †). The latter results also confirm that the Jossens model is the most suitable one in simulating the adsorption of Cu(II), Ni(II) and Co(II) onto the GO-based adsorbents.

Thermodynamic adsorption parameters

The determination of the thermodynamic adsorption parameters may favor the understanding of the nature and feasibility of the adsorption process at different temperatures.

The study of the thermodynamic adsorption of metal ions (Cu(II), Ni(II) and Co(II)) onto the GO-based adsorbents was investigated in the temperature range 293K-313K (Table S4a-S4d †). The thermodynamic parameters such as enthalpy (ΔH°; kJ mol -1 ), entropy (ΔS°; kJ mol -1 K -1 ) and Gibb's free energy (ΔG°; kJmol -1 ) were calculated using the following equations (Eqs. [START_REF] Duru | Graphene oxides for removal of heavy and precious metals from wastewater[END_REF][START_REF] Xiang | 3D hierarchical flower-like nickel ferrite/manganese dioxide toward lead (II) removal from aqueous water[END_REF][START_REF] Yuan | Purification of phenol-contaminated water by adsorption with quaternized poly(dimethylaminopropyl methacrylamide)-grafted PVBC microspheres[END_REF]:

ln(K T ) = ΔS°R + ΔH°R T ( 10
) ΔG°= ΔH°-TΔS°= -R × T × ln(K T ) (11)
K T = K L = Q × b (12)
Where, T (K) is the absolute temperature in Kelvin, R (8.314 J.mol -1 .K -1 ) is the universal gas constant and KT is thermodynamic constant correlated to Langmuir constant KL.

The values of ΔS° and ΔH° can be geometrically calculated from the slope and intercept of the Van't Hoff plot of ln KT against 1/T.

As it can be observed in Tables S4a-S4d †, the negative values of the Gibb's free energy (ΔG°) suggest that the adsorption of Cu(II), Ni(II) and Co(II) ions onto the GO-based adsorbents is thermodynamically spontaneous and feasible. In addition, the higher negative values of ΔG° of GO and GO-EDA-CAC (Table S4a and S4c †) as the temperature increases confirm that metal ions adsorption is favorable at high temperature which could be caused by the lower electrostatic repulsions between the adsorbate and adsorbent surface and increasing mobility of metal ions to active sites. On the other hand, the negative values of ΔG° of GO-EDA and GO-EDA-CAC-BPED (Table S4b and S4d †) decrease by increasing temperature which also support that the elevated temperature would reduce the adsorption capacity of metal ions. According to these results, an increase temperature may lead to lower binding interactions between metal ions and adsorbents. In addition, the ΔG° values reflects the nature of adsorption process. As discussed by Rodrigues et al., [START_REF] Rodrigues | Phenol removal from aqueous solution by activated carbon produced from avocado kernel seeds[END_REF] the adsorption nature can be classified as chemisorption and physisorption process when the values of ΔG° are in the ranges -80 to -400 KJ.mol -1 and 0 to -20 kJ.mol -1 , respectively. Thus, the adsorption of the metal ions onto the GO-based adsorbents is a physical adsorption process. The positive values of ΔH° for GO and GO-EDA-CAC adsorbents (Table S4a and S4c †) indicate the endothermic nature of the adsorption process. To explain this behavior, we suppose that the adsorption efficiencies of metal ions onto GO and GO-EDA-CAC adsorbents are favorable at high temperature because all metal ions are dehydrated and their solubility in the aqueous solution increases with increasing temperature, as discussed by Peer et al. [START_REF] Peer | Removal of Cd (II), Pb (II) and Cu (II) ions from aqueous solution by polyamidoamine dendrimer grafted magnetic graphene oxide nanosheets[END_REF]. Morever, the positive values of ΔS° reflect the affinity of GO and GO-EDA-CAC adsorbents toward metal ions in aqueous solutions and an increase of the disorderliness at the solid/solution interface during the adsorption process. In contrary, the negative values of ΔH° obtained for GO-EDA and GO-EDA-CAC-BPED adsorbents (Table S4b and S4d †) indicate the exothermic process. Indeed, the decrease in adsorption capacity of metal ions with increasing temperature may be due to a desorption process caused by an increase in the available thermal energy, as discussed by Mekonnen et al., [START_REF] Mekonnen | Kinetic and Thermodynamic Studies of the Adsorption of Cr(VI) onto Some Selected Local Adsorbents[END_REF]. Besides, a higher temperature induces an increase in mobility of the adsorbate causing desorption and the negative values of ΔS° reveal that the order degree increases at the solid/solution interface during the adsorption process and some structure changes in the adsorbents.

3.6.Desorption and re-adsorption of metal ions

Desorption and re-adsorption studies of the GO-based adsorbents are two key parameters when assessing for commercial applications. The desorption studies of metal ions from the adsorbents show that the metal ions desorbed with a recovery above ~99.5% in presence of EDTA (Fig. S9 †). The desorption-readsorption was reiterated for ten cycles (Fig. 12) and the higher amount of metal ion adsorption after this procedure was obtained for the GO-EDA-CAC-BPED adsorbent with a decrease of the adsorption capacity from 3.464±0.100 mmol.g -1 , 3.254±0.098 mmol.g -1 and 3.054±0.093mmol.g -1 to 3.245±0.062 mmol.g -1 , 3.0521±0.054 mmol.g -1 and 2.858±0.082 mmol.g -1 , for Cu(II), Ni(II) and Co(II) ions, respectively. Nevertheless, all these results suggest that the GO-based adsorbent exhibit a high enough chemical stability and could be used as adsorbent for wasterwater treatment.

3.7.Comparison of the adsorption capacities of different adsorbents toward Cu(II),

Ni(II) and Co(II) ions

A comparison between the maximum adsorption capacities of GO, GO-EDA GO-EDA-CAC and GO-EDA-CAC-BPED adsorbents and various adsorbents previously used for the adsorption of Cu(II), Ni(II) and Co(II) ions is listed in Table 7.

Table. For example, Zhang et al., [START_REF] Zhang | Biomass based hydrogel as an adsorbent for the fast removal of heavy metal ions from aqueous solutions[END_REF] prepared a biomass soybean dregs-poly(acrylic acid) (SESD-PAA) adsorbent for removing Cu(II) ions and they obtained a maximum adsorption capacity of 1.186 mmol.g -1 , which is slightly higher than that of poly(vinyl alcohol) grafted GO sheets (GO-PVA) [START_REF] Tan | Adsorption of Cu 2+ Cd 2+ and Ni 2+ from aqueous single metal solutions on graphene oxide membranes[END_REF] but lower than that of chemically modified cellulose with hydroxyethyl methacrylate and acrylic acid (Cell-g-HEMA-Co-ACC) [START_REF] Kumar | Sorption of Ni(II), Pb(II) and Cu(II) ions from aqueous solutions by cellulose grafted with poly(HEMA-co-AAc): Kinetic, isotherm and thermodynamic study[END_REF]. Table 7 highlights that our GO-based adsorbents exhibit the highest adsorption capacities. In particular, the adsorption capacities of GO-EDA-CAC-BPED for removing Cu(II), Ni(II) and Co(II) ions are 23 times higher than the GO-Cellulose adsorbent one [START_REF] Sitko | Graphene oxide/cellulose membranes in adsorption of divalent metal ions[END_REF]. Furthermore, our GO-based adsorbents can be regenerated several times, more than 10 cycles, confirming that they are excellent candidates for commercial applications involving the effective removal of Cu(II), Ni(II) and Co(II) ions from aqueous solutions.

Conclusion

Notes

There are no conflicts to declare.

Figure 1 .

 1 Figure 1. FT-IR spectra of (a) GO, (b) GO-EDA, (c) GO-EDA-CAC

Figure 2 .

 2 Figure 2. X-ray photoelectron spectroscopy binding energies of the C1s in the (a) GO-EAD-CAC and (b) GO-EDA-CAC-BPED.

Figure 3 .

 3 Figure 3. X-ray photoelectron spectroscopy binding energies of the N 1s in the (a) GO-EAD-CAC and (b) GO-EDA-CAC-BPED

Figure 4 .

 4 Figure 4. Digital images of (a) GO-EDA, (b) GO-EDA-CAC and (c) GO-EDA-CAC-BPED dispersions in water and various organic solvents at a concentration of 0.20 mg.mL -1 and 24 h after the ultrasonication treatment : (1) Water, (2) Ethanol, (3) Hexane, (4) Toluene, (5) DMF, (6) DMSO, (7) THF, and (8)Diethyl ether.

Figure 5 .

 5 Figure 5. TGA curves of (a) GO, (b) GO-EDA, (c) GO-EDA-CAC, (d) GO-EDA-CAC-BPED.

Figure 6 .

 6 Figure 6. SEM images of (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED.

Figure 7 .

 7 Figure 7. UV-Vis spectra of an aqueous (a) GO, (b) GO-EDA and (c) GO-EDA-CAC-BPED.

Figure 8 .

 8 Figure 8. Effect of the pH of the aqueous metal ion solution onto the adsorption capacities of GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED toward (a) Cu(II), (b) Ni(II) and (c) Co(II) ions ([metal ions] = 250 mg.L -1 , T = 293 K, [Adsorbent] = 0.100 g/100 mL, t =24 h).

Figure 9 .

 9 Figure 9. Effect of the initial concentration of Cu(II), Ni(II) and Co(II) ions on their removal from aqueous solutions by the different adsorbents (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED. ([Adsorbent] = 0.100 g/100 mL, T = 293 K, t=24h and using optimal pH conditions: pH=5 for GO, pH=6 for GO-EDA, pH=6 for GO-EDA-CAC and pH=7 for GO-EDA-CAC-BPED).

Figure 10 .

 10 Figure 10. Effect of contact time on the adsorption capacities of (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED for Cu(II), Ni(II) and Co(II) ions ([metal ions]

  calculated from both pseudo-first-order and pseudosecond-order equations for adsorption of Cu(II), Ni(II) and Co(II) onto adsorbents (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED.

  Elovich equation for the adsorption of Cu(II), Ni(II) and Co(II) onto adsorbents (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED.

Figure 11 .

 11 Figure 11. Adsorption capacities versus t 1/2 calculated with the intraparticle diffusion kinetic model for the adsorption of Cu(II), Ni(II) and Co(II) ions by the adsorbents : (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED.

  -S1d † and Tables S2a-S2d †. As it can be seen, Langmuir isotherm model shows better correlation values (R 2 ) and better fit with the experimental data than the Freundlich isotherm model, indicating that the adsorptions of metal ions onto the different GO-based adsorbents are based on a monolayer and chemisorptions onto homogenous surfaces. Moreover, the Langmuir monolayer saturation capacity (Q) for Cu(II), Ni(II) and Co(II) follows the order GO-EDA-CAC-BPED>GO-EDA-CAC>GO-EDA>GO. The higher Q values at 293 K obtained for the GO-EDA-CAC-BPED adsorbent (QCu(II)=3.891±0.009 mmol.g -1 , QNi(II)= 3.508±0.009

Figure 12 .

 12 Figure 12. Adsorption capacities of (a) GO,(b) GO-EDA,(c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED for Cu(II), Ni(II) and Co(II) after desorption-readsorption cycles.(desorption condition: [EDTA]=0.02 mg.L -1 ), (adsorption conditions: [metal ions] = 250 mg.L -1 , T = 293 K, [Adsorbent] = 0.100 g/100 mL and using optimal pH and contact time conditions : pH=5 and t=8h for GO, pH=6 and t=8h for GO-EDA, pH=6 and t=6h for GO-EDA-CAC and pH=7 and t=4h for GO-EDA-CAC-BPED).

7 .

 7 Comparison of the adsorption capacities of various adsorbents for the removal of Cu(II), Ni(II) and Co(II) ions from aqueous solutions. SESD-PAA: soybean dregs-poly(acrylic acid), GO-PSF:Graphene oxide-polysulfone, WTRs: water treatment residuals, Cell-g-HEMA-Co-ACC: Cellulose (Cell) grafted by vinyl monomers hydroxyethyl methacrylate (HEMA) and acrylic acid (AAc), Cell-g-NIPAM-Co-GMA: Cellulose grafted by N-isopropylacrylamide (NIPAM) and glycidyl methacrylate (GMA) and GO-PVA:Graphene oxide grafted by poly(vinyl alcohol).

For

  the removal of Cu(II), Ni(II) and Co(II) ions from aqueous solutions, we have synthesized new graphite oxide (GO) based adsorbents through the chemical modification of GO. A multistep procedure was used to graft bis(2-pyridylmethyl)amino (BPED) groups onto the GO surface. Nevertheless, the adsorption capacities of Cu(II), Ni(II) and Co(II) of the GO-based materials were studied after each step and it was shown that the pH of the metal ion containing aqueous solution, the contact time and the initial metal ion concentration significantly affect their adsorption capacities. It was shown that the GO-EDA-CAC-BPED adsorbent exhibit the highest ability to adsorb of Cu(II), Ni(II) and Co(II) ions for a metal ion concentration of 250 mg.L -1 at pH=7 and their equilibrium adsorption capacities were as high as 3.464±0.100 mmol.g -1 , 3.254±0.098 mmol.g -1 and 3.054±0.093 mmol.g -1 , respectively.Then, considering the adsorption kinetics, the pseudo-second-order model was the most appropriate one to describe the adsorption of these metal ions by the GO-based adsorbents.Furthermore, for the adsorption isotherm it was shown that the Jossens model has been the best one in simulating the adsorption of Cu(II), Ni(II) and Co(II) onto GO, GO-EDA, GO-EDA-CAC and GO-EDA-CAC-BPED. The thermodynamic adsorption parameters were also calculated and the obtained positive values for both enthalpy change (ΔH°) and entropy change (ΔS°) demonstrated the endothermic features of the adsorption process for GO and GO-EDA-CAC adsorbents. In contrary, the adsorption process was exothermic for the GO-EDA and GO-EDA-CAC-BPED adsorbents. Finally, it was shown that all the GO-based adsorbents exhibit good recyclability and reusability for Cu(II), Ni(II) and Co(II) ions. One limitation of the GO-EDA-CAC-BPED adsorbent is the multistep synthetic procedure to graft BPED groups onto the surface of GO sheets so future work will consist in simplifying the synthetic scheme.

Table 1 .

 1 (

	Material	AC-C/AT (%) AC-N/AT (%) AO-C-O/AT (%)	AC=O/AT (%)
	GO-EDA-CAC	38.6	17.0	7.7	15.7
	GO-EDA-CAC-BPED	52.0	31.4	4.4	13.5

AC) ratios of carbon-containing bonds to total area (AT) according to the XPS results.

Table 2 .

 2 (AN) ratios of nitrogen-containing bonds to total area (AT) according to the XPS results.

Adsorbents Metal ions Elovich model α×10(mmol.g -1 .min -1 ) β (g.mmol -1 ) R²

		Ni(II)	4.916±0.2155	1.739±0.0448	0.926
		Co(II)	5.290±0.1783	1.904±0.0378	0.939
	Adsorbents	Parameters	Cu(II)	Metal ions Ni(II)	Co(II)
		R 2	0.992	0.997	0.993
		Ki1 (mmol.g -1 .min -1/2 )	0.124±0.0043	0.114±0.0025	0.100±0.0032
	a	C1 (mmol.g -1 .min -1/2 ) R 2	0.019±0.0240 0.969	-0.010±0.0137 0.958	-0.025±0.0176 0.933
		Ki2 (mmol.g -1 .min -1/2 )	0.037±0.0033	0.039±0.0042	0.031±0.0041
		C2 (mmol.g -1 .min -1/2 )	1.029±0.0604	0.928±0.0755	0.841±0.075
		R 2	0.991	0.989	0.976
		Ki1 (mmol.g -1 .min -1/2 )	0.123±0.0058	0.114±0.0042	0.095±0.0052
	b	C1 (mmol.g -1 .min -1/2 ) R 2	0.142±0.0477 0.969	0.039±0.0341 0.994	0.124±0.0426 0.976
		Ki2 (mmol.g -1 .min -1/2 )	0.019±0.0024	0.025±0.0013	0.014±0.0015
		C2 (mmol.g -1 .min -1/2 )	1.650±0.0483	1.313±0.0268	1.297±0.0314
		R 2	0.998	0.987	0.972
		Ki1 (mmol.g -1 .min -1/2 )	0.176±0.0027	0.170±0.0077	0.129±0.0089
	c	C1 (mmol.g -1 .min -1/2 ) R 2	-0.049±0.0148 0.945	-0.040±0.0427 0.960	-0.089±0.0489 0.971
		Ki2 (mmol.g -1 .min -1/2 )	0.059±0.0101	0.027±0.0038	0.037±0.0044
		C2 (mmol.g -1 .min -1/2 )	1.421±0.1661	1.541±0.0637	1.008±0.0734
		R 2	0.953	0.955	0.964
		Ki1 (mmol.g -1 .min -1/2 )	0.489±0.0762	0.410±0.0623	0.356±0.0487
	d	C1 (mmol.g -1 .min -1/2 ) R 2	-0.863±0.4081 0.934	-0.332±0.3345 0.947	-0.064±0.2613 0.
		Cu(II)	0.179±0.0770	3.143±0.0160	0.968
	a	Ni(II)	0.142±0.0911	3.134±0.0189	0.956
		Co(II)	0.120±0.0763	3.676±0.0159	0.957
		Cu(II)	0.261±0.0852	2.870±0.0174	0.967
	b	Ni(II)	0.170±0.0880	3.001±0.0183	0.959
		Co(II)	0.218±0.0621	3.745±0.0129	0.970
	Cu(II) According to the correlation coefficient values, it can be concluded that the Elovich 2.133±0.1417 2.145±0.0295 0.950
	c	Ni(II)	2.247±0.0977	2.710±0.0203	0.962
		Co(II)	1.312±0.1108	3.105±0.0230	0.937
	d	Cu(II)	3.631±0.2334	1.536±0.0486	0.932

Table.6. The intraparticle diffusion kinetic for adsorption of Cu(II), Ni(II) and Co

(II) ions by adsorbents (a) GO, (b) GO-EDA, (c) GO-EDA-CAC and (d) GO-EDA-CAC-BPED model is will adapted to describe the adsorption of Cu(II), Ni(II) and Co(II) ions onto the GObased adsorbents in comparison with the pseudo-first-order kinetic model. In addition, the initial adsorption rates are in the order: GO-EDA-CAC-BPED>GO-EDA-CAC>GO-

872 Ki2 (mmol.g -1 .min -1/2 )

	0.100±0.0264	1.545±0.0345	0.217±0.0831
	C2

(mmol.g -1 .min -1/2 )

		-0.018±0.0373	-0.0246±0.0489	-0.059±0.1175
	R 2	0.995	0.947	0.

963 Ki3 (mmol.g -1 .min -1/2 )

		0.083±0.0039	0.045±0.0107	0.026±0.0518
	C3 (mmol.g -1 .min -1/2 )	2.175±0.0524	2.563±0.1445	2.638±0.0694

Acknowledgements

The authors gratefully acknowledge the financial support from IDEXLYON-2019 (Mobilité International Des Doctorants, France) and all the staff of the Technological Centre of Microstructures of the University of Lyon 1 for their technical help.


Youssef Guedira

Hursula Mengue-Topio

Sophie Lepreux

Laurie Letalle

Marion Duthoit

Philippe Pudlo

Yannick Courbois

Christophe Kolski

User Centered Design of Digital Mobility Assistance Systems for People with Intellectual Disabilities

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