Carolina Moraes-Cabe

Magali Rancez

Bénédicte Charmeteau-De-Muylder

Suzanne Figueiredo-Morgado

Magali Mas

Rémi Cheynier

Angelina Mimoun

Suzanne Figueiredo

Anne Couëdel-Courteille

Mucosal IL-7 response in the gut during HIV/SIV acute infection

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Introduction

Interleukin-7 (IL-7) is an essential cytokine for the development and homeostasis of T lymphocytes. This cytokine has long been described as constitutively produced by stromal cells of lymphoid and non-lymphoid organs. Homeostatic production of IL-7 is independent of extrinsic stimuli, plasma IL-7 levels being regulated by its consumption by T-cells (Fry andMackall 2005, Mazzucchelli andDurum 2007). However, IL-7 production by stromal cells can be regulated by the microbiota as well as by bacterial and viral infections (Shalapour et al., 2010).

We recently demonstrated that IL-7 production is transiently increased in the gut of acutely SIV-infected rhesus macaques (Ponte et al., 2017), suggesting a regulation by inflammatory cytokines. This increase leads to local expression of several chemokines and immune cell homing into the gut, with a possible consequence on both the initiation of the antiviral immune response and the establishment of viral reservoirs (Ponte et al., 2017).

Aims

This work aims at deciphering the implication of intestinal mucosal cells on IL-7 production and IL-7-dependent chemokine expressions observed in the gut of acutely SIV-infected macaques.

Methodology

Primary epithelial cells and fibroblasts purified from healthy tissue and endothelial cells differentiated from blood progenitors were cultured in the presence of HIV/SIV-infected PBMCs supernatants or inflammatory cytokines (TNFa, IFNa, IFNb or IFNg. IL-7, IL-7Ra and chemokine expressions were quantified by RT-qPCR.

IL-7 potentiates the effect of inflammatory cytokines for the expression of some chemokines in human fibroblasts

IL-7 potentiates the effect of inflammatory cytokines for the expression of some chemokines in human endothelial cells

Conclusions

• The supernatant of HIV-infected PBLs triggers IL-7

production by epithelial cells and fibroblasts, contrarily to the supernatant of non-infected PBLs.

• Endothelial cells and fibroblasts are able to overexpress CD127 expression upon inflammatory stimulation.

• In combination with TNFa, IL-7 triggers increased mRNA expression of CCL2, CCL4 and CCL5 in human endothelial cells. IL-7 also increases the mRNA expression of CCL2, CCL3, CCL4, CXCL8 in primary fibroblasts in combination with type I and type II interferons (!-IFN, "-IFN and #-IFN).

• During the acute phase of SIV-infection, as a result of the inflammatory environment and IL-7 production, epithelial cells, endothelial cells and fibroblasts are likely to participate to the increase of chemokine production that leads to immune cell recruitment into infected tissues.

IL-7Ra (CD127) phosphorylation upon IL-7 stimulation

Fig 4 .

 4 Fig 4. Chemokines transcription is up-regulated in stimulated fibroblasts mRNAs coding for CCL2), CCL3, CCL4, CCL5, CXCL8 and CXCL10 in nonstimulated and overnight stimulated fibroblasts were quantified by RT-qPCR.

Fig 5 .

 5 Fig 5. Chemokines transcription is up-regulated in stimulated endothelial cells mRNAs coding for CCL2, CCL4, CCL5, CCL20, CXCL8 and CXCL10 in nonstimulated and 4H stimulated human EC were quantified by RT-qPCR.

Fig 1 .

 1 Fig 1. Mucosal cells overexpress IL-7 when stimulated with the supernatant of HIV-infected PBL. IL-7 mRNAs expressed by simian primary intestinal epithelial cells (A) and human primary fibroblasts (B) were quantified by RT-qPCR and normalized to HPRT mRNA. At each culture condition, each symbol represents one sample/donor. Results are presented as fold changes over non-stimulated cells values. Medians are shown as horizontal bars. NS: non-stimulated; NI PBL: supernatant of non-infected PBL; INF PBL: supernatant of HIV/SIV-infected PBL IL-7Ra (CD127) is expressed on endothelial cells and fibroblasts and up-regulated upon stimulation

Fig 3 .

 3 Fig 3. IL-7 stimulation phosphorylates IL-7Ra on mucosal cells. Phosphorylation of CD127 was verified by Western Blot in IL-7-stimulated fibroblasts (top) and epithelial cells (bottom). Specific p-CD127 antibody was used to detect phosphorylated CD127. Actin was used as internal control. Blots are representative of 2 independent experiments.

Acknowledgment

This work was supported by the ANRS, SIDACTION, INSERM, CNRS and Université Paris Descartes. Thank you to IDMIT animal caretakers and veterinaries, to core facilities (Cybio and Genom'IC platforms at Cochin Institute) and other collaborators for additional support.


M Rancez

S Logerot

S Figueiredo

B Charmeteau-De-Muylder

I Bourgault-Villada

A Couëdel-Courteille

R Cheynier

IL-7 AS AN ADJUVANT FOR MUCOSAL VACCINE DEVELOPMENT

We here evidenced that 10µg of sIL-7, administered by spray on rhesus macaques vaginal mucosa, stimulates local transcription of CCL2, CCL5, CCL7, CCL17, CCL19, CCL20, CCL21, CCL22, CXCL10, CXCL12, CXCL13, and CX 3 CL1 by 48 H after administration. Local expression of these chemokines leads to massive mDC, macrophages, NK, CD4 + T-, CD8 + T-, and B-cells infiltration into the vaginal mucosa.

Healthy rhesus macaques immunized with a cocktail of antigens (Diphtheria Toxoid + the HIV-1 gp41-P1 peptide) directly applied on the vaginal mucosa two days after vaginal sIL-7 (10µg) administration developed an earlier and stronger mucosal antigen-specific immune response as compared to animals receiving the antigenic cocktail alone. Indeed, during the immunization protocol, sIL-7 pre-treatment promoted then sustained a robust production of antigen-specific IgAs and IgGs in vaginal secretions, as detected by ELISA.

By attracting immune cells, local sIL-7 administration prepares the mucosal immune system, gathering conditions that result in enhanced antigen-specific vaginal immune responses. Moreover, throughout the immunization protocol, CXCL12, CXCL13, CCL19 and CCL21 known to contribute to tertiary lymphoid organ formation and organization (Nat Immunol 2006, 7: 344-53), which could support the induction of immune responses, in particular by sustaining productive immunoglobulin class switching in germinal centers, were increased only in the vaginal mucosa of sIL-7 treated macaques, and sIL-7 pretreatment favored the formation of tertiary lymphoid organs genesis in the vaginal mucosa. Besides, high levels of IgAs in the vaginal secretions are produced by mucosally localized plasma cells as evidenced by reverse IHF. CXCL12 is known as mucosal chemoattractant molecule for IgA-and IgG-secreting plasma cells (J Exp Med 2002, 196(1):65-75), suggesting its role in mucosal infiltration of DT-and P1-specific plasma cells. Finally, we evidenced an Increased frequency of B-cell response in peripheral blood.

Altogether, these data demonstrate the capacity of sIL-7 to be used as a mucosal adjuvant leading to enhanced mucosal antibody response, a very promising strategy to confer protection to numerous sexually transmitted infections. CONCLUSION  LOCAL IMPACT OF sIL-7 ADMINISTRATION BY SPRAY ON VAGINAL MUCOSA  Administration by vaginal spray of sIL-7 (10µg) induces the highest local chemokine transcription  sIL-7 administration in vaginal mucosa stimulates T-cells, B-cells, and antigen-presenting cells (macrophages and myeloid dendritic cells) migration into the chorion

RESULTS

Development of mucosal immune responses, while certainly essential to allow protection against numerous sexually transmitted infections, is still hard to induce in most models. Despite some progresses in the development of adjuvants possibly helping for the setting of this kind of immunity, results in terms of protection as for induction of the local antibody production and specific T-cells remain largely disappointing.

We have showed that systemic injection of IL-7 stimulates chemokine-induced recruitment of circulating T-cells into the mucosa (Blood 2009, 114(4):816-25), and evidenced local IL-7 expression in acutely infected mucosae (Front Immunol 2017, 19;8:588).

In this study, we aimed at using recombinant glycosylated simian IL-7 (sIL-7) as an immunostimulating molecule for vaginal immune responses in vaccine protocols. We administrated sIL-7 by spray directly on rhesus macaque's vaginal mucosa surface and quantified local transcription of 19 chemokines by qRT-PCR and cell infiltration by immunochemistry plus image analysis to define the optimal dose of sIL-7 to be sprayed on mucosal surface. Then, six macaques were immunized with antigens (Diphtheria Toxoid (DT) and the HIV-1 gp41-P1 peptide) applied directly on the vaginal mucosa, two days after either IL-7 or PBS administration. The immunizations were repeated thrice, four months apart, and the macaques were euthanized 2 weeks after the last immunization. Antigen-specific IgA and IgG productions were quantified in vaginal secretions by ELISA. Antigen-specific plasma cells were detected by reverse immunohistochemistry and by B-cell ELISPOT.

INTRODUCTION and OBJECTIVES

Fig 1 :

 1 Fig 1: Impact of vaginal sIL-7 administration on chemokine transcription (A) mRNAs coding for CXCL12 and CCL7, were quantified and normalized to HPRT mRNAs in each vaginal biopsies sampled one month before (PRE) and 48 H after the administration of 1µg (n=2), 5µg (n=2), 10µg (n=3) or 15µg (n=2) of sIL-7 (POST), by vaginal spray. Each point represents the median of a triplicate quantification in a given biopsy. (B) mRNAs coding for 19 chemokines, were quantified in triplicate and normalized to HPRT mRNAs in each vaginal biopsies sampled one month before (PRE) and 48 H after the administration of 10µg (n=3) and 15µg (n=2) of sIL-7 (POST), by vaginal spray. Each point represents the mean of all the quantifications performed per animal PRE and POST administration of the sIL-7. Four biopsies per animal PRE and POST administration. *: p<0.05 by the Wilcoxon Signed-Rank Test.

Fig 2 :Figure 3 :

 23 Fig 2: Immune cell recruitment into vaginal chorion of sIL-7 treated macaques (A) Sections of monkey vaginal mucosa biopsies sampled one month before (Ctrl), or 48 H after (IL-7) the administration of 10µg of sIL-7 by vaginal spray were labeled for CD3, CD11c, PM-2K and CD20 (Alexa-Fluor ® 546) in combinaison with CD4 or CD8, DC-SIGN, CD20 and MHC-II MamuLa-DR (Alexa-Fluor ® 488), respectively. Nuclei were stained with DAPI. EP= Pluristratified Epithelium. (B, C) Cell quantifications by image analysis of IHF staining (expressed as number of cells per 500,000 µm2 of chorion ± SEM) were realized from 20 to 32 vaginal mucosa biopsies (8 macaques, except for PM-2K+ cells quantification: 5 macaques) sampled one month before (Ctrl -white bars) and 48 H after (IL-7 48 H -black bars) the administration of 10µg of sIL-7. (Mann-Whitney U test).

Figure 4 :Fig 5 :

 45 Figure 4: DT specific IgGs plasma cells are more abundant in vaginal draining lymph nodes while DT specific IgAs plasma cells are more abundant in the vaginal mucosa of sIL-7 treated macaques at necropsy IgG and IgA anti-DT-specific ASC were quantified by B-cells ELISPOT assay on isolated cells from iliac LN from 3 macaques per group (A) and on isolated cells from vaginal chorion from 1 animal per group (C), sampled at necropsy (group IL-7+Ags, black bars; or PBS+Ags, white bars). Results are expressed as IgG or IgA anti-DT-specific ASC per 10 6 cells. Bars and error bars represent means ± SEM. LN: Lymph nodes; Ags: Antigens; ASC: antibody secreting cells. (Mann-Whitney U test). Sections of monkey iliac LN (B) and vaginal fornix (D), sampled at necropsy, were labeled after incubation with DT, thanks to an anti-DT antibody. Representative examples of the draining LN of sIL-7-treated (IL-7+Ags) or ctrl (PBS+Ags) macaques co-labeled with DT (green) and anti-IgG (red, B) or anti-IgA (red, D) are shown. Nuclei were stained with DAPI. (B, D) Arrowheads indicate single-stained cells. (D) Arrows identify IgA anti-DT-specific ASC.

  vaginal and rectal washes sampled (every week and before each spray)

The authors thank the staffs of the Institut Pasteur (Paris, France) and Infectious Disease Models and Innovative Therapies (IDMIT, Fontenay-aux-Roses, France) Primate Centers. The authors greatly acknowledge Maryline Favier, Franck Letourneur and Pierre Bourdoncle, respectively heads of HistIM, GENOM'IC and IMAG'IC core facilities of the Institut Cochin. The authors thank Thomas Guilbert from IMAG'IC platform at the Institut Cochin for writing the routine for ImageJ image analysis software. The authors acknowledge Cytheris S.A. (now Revimmune Inc.), for R-sIL-7gly (sIL-7). This work was supported by ANRS, INSERM and Université Paris Descartes.

ACKNOWLEDGMENT

W4 W20 W35

Presented at the 22nd International AIDS Conference -Amsterdam, the Netherlands #AIDS2018 | @AIDS_conference | www.aids2018.org


Isabelle Trenque

‡ Greta

Camilla Magnano

Jan Bárta

Frédéric Chaput

Marie Alexandrine Bolzinger

Isabelle Pitault

Stéphanie Briançon

Karine Masenelli-Varlot

Matthieu Bugnet

Christophe Dujardin

Václav Čuba

David Amans
email: david.amans@univ-lyon1.fr

Synthesis routes of CeO 2 nanoparticles dedicated to organophosphorus degradation: a benchmark †

Exposure to organophosphorus compounds, in military conflicts or terrorist acts, requires an emergency procedure including the availability of efficient decontamination system. Systems based on nanosized cerium (IV) oxide (CeO 2 ) are suitable candidates. CeO 2 is a heterogeneous catalyst for the degradation of the organophosphorus compounds such as VX agent or sarin. While the synthesis method influences the physicochemical characteristics of the nanoparticles surface and thus their degradation activity, we have compared the degradation activity of nanosized CeO 2 powders commercially available, or developed using different synthesis process, namely hydrothermal process, photochemistry, and laser ablation in liquids. The degradation activity was evaluated in vitro by measuring the degradation kinetics of paraoxon organophosphate. A quenching of the degradation activity is observed on the as-produced particles with a surface pollution, especially when organic molecules with carboxylate ion R-COO -are involved in the synthesis process. In contrast, lasergenerated nanoparticles in ultra-pure water show the best activity, while the sample presents the lowest specific surface area. After annealing, almost all samples present a clean surface and the degradation activity is mainly driven by the specific surface area. We then sought to define a figure of merit including the particles activity for the degradation of Paraoxon, the production costs and the production time. Indeed the two last parameters are essential to assess the relevance of each method in view of marketing.

Introduction

Exposure to Organophosphorus compounds (OPs) during terrorist attacks and military conflicts requires an emergency procedure including the availability of efficient decontamination system 1 . OPs compounds, highly represented among the Chemical Warfare Agents (CWA) group, mainly enter the body via skin penetration as well as inhalation and ingestion, causing severe injuries and possible death 2,3 . After exposure to organophosphorus toxic agents, the conventional procedure calls for the application of absorbent powders or water rinsing, which makes the skin decontamination possible, but not the OPs degradation. Some solutions combining a rinsing effect and a toxic degradation are also available (such as RSDL lotion, M258 ou M280 kits). They are impregnated sponges or wipes to be applied on small skin surfaces 2,3 . However, they have specific actions, often high pH and are limited to small surfaces. It would be highly beneficial to develop cheap, efficient and easy to handle reactive sorbents 4 . In recent decades, several nanocrystalline metal oxides have been studied for the degradation of chemicals warfare agents (CWA) and their simulants, including CeO 2 [4][5][6][7] , MnO 2 8 , MgO 9,10 , CaO 11 , Al 2 O 3 12,13 , TiO 2 14 , ZnO 15 . These nanomaterials in the form of dry powders are particularly promising systems. They have the advantage of being able to strongly adsorb toxic molecules and rapidly decompose them into less toxic and/or non-toxic compounds. They thus ensure a concomitant displacement and degradation action of the toxic agent. They are called "destructive/reactive sorbents" to distinguish them from conventional adsorbents, such as active carbon, that simply retain chemical compounds, do not alter their structure and therefore do not annihilate their toxicity 6 . The high specific surface area of the particles increases their sorption capacity allowing the adsorption of the toxic substance 16 . CeO 2 is well known for its catalytic activity and its UV absorbing ability 17,18 . Cerium dioxide nanoparticles have shown exciting potential for fast degradation of Chemical Warfare Agents (CWA), including organophosphorous compounds 5 and organochloride compounds 19 . However, the physicochemical parameters of the CeO 2 powders favouring the CeO 2 -catalysed hydrolysis of the organophosphorus compounds remain to be defined. The nature of the reactive sites, as well as the effect of the surface oxidation states of cerium (Ce + 3 /Ce + 4 ratio) remain open issues 7 . In our previous work 7 , we addressed the activity of different crystallographic planes (facets), which offer different reactive sites. Paraoxon (POX) was chosen as a model OP compound, and the kinetics of degradation was evaluated in vitro in aqueous suspension. CeO 2 NPs of different shape such as nano-octahedra, nanocubes, nanorods, and truncated nano-octahedra were selectively obtained using a hydrothermal method. The rate constant of the degradation kinetics normalized by the specific surface area (k/S BET ) clearly showed that the surface sites of the {111} facets lead to a higher activity as compared to the ones on the {100} facets. The relative activity between crystal faces was ascribed to (i) the adsorption probability of the toxic substance, assuming the coordination between the phosphoryl oxygen and cerium atoms, and (ii) the surface density of the Ce doublets with a short Ce-Ce distance (0.383 nm), favouring the phosphatase mimetic activity of CeO 2 . However, the surface contamination, the surface defects and the specific surface area also have a strong influence on the degradation kinetics and are mainly set by the synthesis route. In our previous study, the morphologies which have shown better activities are the nano-octahedra (k = 1.08 × 10 -2 min -1 ) and the nanorods (k = 8.00 × 10 -3 min -1 ). The nano-octahedra only had {111} facets; this was not the case of the nanorods, which in turn were characterized by the largest amount of defects as well as the largest specific surface area (S BET ). However, for each synthesis method, a controlled tuning of the physico-chemical parameters is not always an easy task, or simply not always a possible task. Reaction temperature, concentration of reactants, presence of surfactants etc. can affect those parameters.

In the present work, the issue of the degradation activity is addressed in a systematic and pragmatic approach. While the synthesis process influences the raw degradation activity, i.e. the decay parameter k, which is the relevant parameter for the development of an efficient decontamination system, we have compared different synthesis process of CeO 2 . We then sought to define a figure of merit including the particles activity for the degradation of Paraoxon, the production costs and the production time. Indeed the two last parameters are essential to assess the relevance of each method in view of industrial application. In literature, many techniques have been used to obtain CeO 2 , including chemical routes such as precipitation 20 , microemulsion synthesis 21 , sol-gel methods 22 , polyvinyl pyrrolidone (PVP) solution route 23 , solvothermal processes 7,24,25 , photochemistry 26,27 or sonochemical and microwave assisted chemistry 28 ; and physical routes such as pulsed laser ablation in liquids 29 , mechanical synthesis 30 , plasma synthesis 31 . In this study, CeO 2 nanoparticles were elab-orated by hydrothermal method (nano-octahedra and nanorods, which have shown the best phosphatase mimetic activity in our previous work), by photochemistry (truncated nano-octahedra), by pulsed laser ablation in liquids (truncated nano-octahedra), and compared to commercial particles (nanopolyedra). The role of the nanoparticles synthesis method on the degradation kinetics of POX was studied in-vitro in an aqueous suspension. Since the 1990s 32 , laser ablation in liquids has proven its reliability and its versatility to synthesize nanomaterials in pure water [33][34][35][36][37][38][39][40][41] , including doped nanoparticles and alloys. The nanoparticles are formed during the fast cooling of the laser-generated plasma in the early microseconds following each laser pulse 42 . PLAL provides biocompatible and ligand-free colloids. PLAL can be operated continuously with production rates of several grams per hour 43,44 . Thanks to these advantages, laser-generated nanoparticles are marketed for almost a decade [START_REF]USA) and the i-Colloid in-house branch of IMRA America, Inc. (USA)[END_REF] .

Experimental details

Nanotruncated octahedra (Φ-NTO) were realized by pulsed laser ablation of a cerium oxide target in ultrapure water (18 MΩ•cm). Targets of pure CeO 2 were sintered pellets made from a commercial micrometer-sized powder of cerium (IV) oxide from Alfa Aesar (Ref. 11327) with a purity of 99.99%. The powder was pressed (0.22 GPa, 3 times for 20 s, 15 s and then 10 s) and then annealed in an oven at 1350 • C for 24 h. A circulation system (see figure 1A) was used in order to keep the solvent clear and limit the absorption of the laser beam by the generated nanoparticles. In a typical procedure, the target was placed into a flow cell, whose upper part consists of a glass window, allowing the ablation of the target through it (see figure 1). The flow cell was also connected to ultrapure water source (18 MΩ•cm) with a flow velocity of 5 ml/min. Then, the surface of the tar-get was irradiated for several hours at room temperature by a Nd:YAG laser (λ = 1064 nm) with a repetition rate of 1 KHz and a pulse duration of 500 ps. The laser source is composed of a passively Q-switched kilohertz Nd:YAG laser amplified with a laser gain module from FiberCryst Company (Taranis module [START_REF] Martial | [END_REF] ). The energy per pulse was set to 1.8 mJ per pulse. The Gaussian TEM00 beam (beam quality M 2 < 1.3) was expanded to reach a 1/e 2 diameter 2W of 6.5 mm, and was then focused at the surface of the target using a F-Theta lens with 160 mm focal length. The expected beam waist 2W 0 on the target was then 44 µm. It leads to a surface power density of 2.4 × 10 11 W/cm 2 . A fast steering mirror system was used to move the laser spot on the surface. The scanning parameters were 5 pulses per spot, 10 µm distance between two spots. After each scan, the laser beam is blocked until the ablation chamber is filled with fresh solution to avoid re-ablation of the particles. It leads to a dead time of 0.9% of the total synthesis duration.

20.4 L of colloidal CeO 2 solution was produced in 68 hours by irradiating successive targets. The measured pH of the colloidal solution was 6.5. This suspension was concentrated with a rotary evaporator (60 • C, 120 mbar) to reach a few mL. Finally, the resulting suspension was dried in a drying oven at 60 • C for one night in ambient air. 2 g of dried powder was obtained. UV irradiation of aqueous solutions containing various metal ions (Ag, Rh, Cu, Pb, Ba, Zn, Al . . . ) and sensitizers, for instance formate HCOO -, is a reliable and efficient method to produce nanoparticles of metal oxides [47][48][49][50] , including doped particles 51,52 and cerium (IV) oxide 26,27 . A photochemical pilot plant with a reactor of an effective volume of 80 liters has been designed at Czech Technical University to perform large-scale photochemical preparation. The pilot plant is equipped with 28 amalgam low-pressure mercury lamps (44 W, T5Q408-4P-44W from UV Technics) protected by fused silica tubes and immersed into a double-walled photochemical reactor. The reactor was continually cooled by water circulating in the outer layer of the reactor and a coolant unit set to 20 • C (hysteresis 1 • C).

Photochemical ( χ hν) method

The synthesis was adapted from Pavelková et al. 27 . Assuming an inner effective volume of 80 liters, the salts were weighted to reach the required concentrations of 5 × 10 -3 mol.dm -3 cerium nitrate Ce(NO 3 ) 3 •6 H 2 O (173.68 g of cerium nitrate hexahydrate) and 10 -1 mol.dm -3 ammonium formate HCOONH 4 (504.48 g). The theoretical yield of CeO 2 from this solution should be 68.8 g. Both salts were weighted separately to prevent precipitation of poorly-soluble cerium formate, and a filling procedure of the reactor has been established. The photochemical reactor was partly filled by deionized water (above 30 liters). Cerium nitrate dissolved in deionized water was then introduced into the reactor by a peristaltic pump. The liquid was stirred for several minutes and diluted by some more deionized water (above 10 liters), after which ammonium formate was added. Just after the introduction of the ammonium formate, no precipitate was observed in the photo-reactor. It was then filled to the top to reach 80 liters and the solution was mixed by stirring and circulation through the sedimentation tank for 30 minutes.

The liquid was then irradiated by the low-pressure mercury lamps for 26 hours. During the process, the solution was vigorously stirred in the inner layer of the photo-reactor. Thanks to the hydrostatic pressure, the irradiated liquid passed into a sedimentation vessel and was then pumped back into the photoreactor by a peristaltic pump (flow≈2 litres per minute). Over the course of irradiation, samples of the solution (10 ml each) were collected and analyzed for the presence of Ce 3+ ions. For each sample, 5 min centrifugation at RCF 1467 g was performed to separate the synthesized particles from the supernatant containing the remaining Ce 3+ ions. The analysis consisted in contacting 8 ml of the supernatant with 0.832 ml of a solution containing 0.144 mol.dm -3 potassium oxalate (i.e. up to 4 × 10 -5 Ce 3+ + 1.2 × 10 -4 ox 2-), yielding cerium(III) oxalate precipitate. The cerium oxalate hydrate was then weighed (see Figure S1 in supplementary Information). It appears that the cerium concentration decreased very slowly and the conversion yield to CeO 2 after 26 hours is 38%. The main cause of this effect may be an efficient absorption of UV light by the formed colloidal particles, which did not sediment fully in the sedimentation vessel and were recirculated back to the reactor.

The irradiated solution, along with the brownish particles, was poured out of the pilot plant into two 50-liter barrels, where the formed CeO 2 settled overnight. The gelatinous precipitate composed of the solid product dispersed in liquid was collected and then centrifuged following a recursive protocol. A part of the gelatinous material was centrifuged at RCF 4075 g for 5 min, the supernatant was poured out and another part of the solution was added. In such way, approximately 80 ml of the gelatinous product were separated, containing 26.2 g of CeO 2 . The gelatinous product was then dried in a drying oven at 70 • C for 24 hours in ambient air.

Chemical ( χ ) method

Cerium oxide nanoparticles were also obtained by a chemical ( χ ) way. Nanorods ( χ -NR), and nano-octahedra ( χ -NO) were elaborated by hydrothermal process. The details of the preparation were described previously 7 . All chemicals were purchased and used without further purification. Cerium nitrate hexahydrate Ce(NO 3 ) 3 •6 H 2 O (Alfa Aesar, 99.5%) was used as the cerium source. To obtain CeO 2 nanorods, 0.03 mol of Ce(NO 3 ) 3 •6 H 2 O dissolved in 100 mL of distilled water was added to 3.6 mol of sodium hydroxide NaOH (Carlo Erba, ACS grade) dissolved in 500 mL of distilled water. After stirring for 20 minutes at room temperature, the solution was transferred into a Teflon-lined stainless steel autoclave and heated at 100 • C (1 bar) for 6 hours. To obtain CeO 2 nano-octaedra, 0.0255 mol of Ce(NO 3 ) 3 •6 H 2 O was dissolved in 20 mL of distilled water. This solution was added to a 130 mL solution containing 0.102 mol of ammonium hydroxide NH 4 OH (Carlo Erba, ACS grade) at room temperature under strong stirring. After stirring for 20 min, the solution was transferred into a Teflon-lined stainless steel autoclave and heated at 180 • C (10.5 bars) for 24 hours. Following the hydrothermal treatment, nanorods and nano-octahedra were cooled at room temperature. Then, fresh precipitates were separated by centrifugation, washed four times with distilled water, and dried in a drying oven at 60 • C for one night in ambient air. 5.1 g of nanorods powder were obtained for 13 g of cerium nitrate hexahydrate (one batch, about 100% yield), and 4.4 g of nano-octahedra powder were obtained for 11.1 g of cerium nitrate hexahydrate (one batch, about 100% yield).

Commercial sample

A commercial suspension (pH 10.2) of nanoparticles with irregular shapes (nanopolyedra, Φ-NPO) was obtained from Baikowski (CTX product). The mass fraction of CeO 2 in the water suspension was 40.4%. The suspension was dried in a drying oven at 60 • C for one night in ambient air.

Annealing post-treatment

A fraction of each synthesized sample was annealed in air at 500 • C for two hours. The annealed powders are designated by an asterisk referring to the annealing post-treatment. Thus, Φ-NPO , Φ-NTO , χ hν-NTO , χ -NR and χ -NO refer to Φ-NPO, Φ-NTO, χ hν-NTO, χ -NR and χ -NO annealed powder respectively.

Characterization methods

Particle sizes and shapes were observed via transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) on a JEOL 2100 HT apparatus with an accelerating voltage of 200 kV. The TEM samples were prepared by drop-casting onto TEM grids (01844 from Ted Pella, pure carbon film on 400 mesh copper) a droplet of the dispersed powders in water using ultrasonic dispersion. For Φ-NPO sample, characterized by a large polydispersity, the particle size distribution was measured with a Mastersizer 3000 from Malvern based on the technique of laser diffraction. A droplet of the pristine solution was injected in the flow system and the Mie scattering model was used.

Specific surface area was measured by BET method from the N 2 adsorption/desorption isotherms at 77 K using a Belsorp-max instrument.

X-ray diffraction (XRD) patterns were recorded on a Bruker D8 Advance diffractometer equipped with a sealed Cu X-ray tube (40 kV, 40 mA) and a linear Lynxeye XE detector. Data were collected over the range 5-90 • with 0.0205 • steps. The lattice parameters and the crystallite sizes were extracted from XRD patterns by profile matching (LeBail fit) using the elementary pseudo-Voigt function with the FullProf program packages.

Raman spectra were measured in the range 200-1200 cm -1 using a LabRAM Aramis (HORIBA) confocal automated microRaman system with a He-Ne external laser excitation source working at 633 nm and a 50× UV objective. The typical data acquisition time was 5 s. The obtained Raman spectra were normalized relative to the maximum intensity of the F2g mode of the fluorite CeO 2 phase (≈460 cm -1 ) to allow comparison of the different samples.

The nature of the species adsorbed at the surface of the nanoparticles was studied by infrared spectroscopy on a Perkin-Elmer spectrophotometer (Spectrum 100 FT-IR with universal ATR sampling accessory). The infrared spectra were recorded in the range 550-4000 cm -1 . The spectral resolution was 4 cm -1 .

Degradation tests

The protocol for in vitro degradation efficacy of CeO 2 NPs after an exposure to paraoxon (POX) was derived from the protocol described by Salerno et al. 4 with some improvement and was already used in our previous study 7 dealing with the activity of different crystal facets. A solution of 200 µmol/L of POX (0.055 g/L) was prepared in deionized water. For each degradation experiment, 200 mg of CeO 2 was dispersed in 2 mL of the POX solution. A solution of 200 µmol/L of POX, without nanoparticles, was used as a blank.

The samples were taken in glass vials and stirred at 32 • C in a water bath under magnetic stirring at 450 rpm for 5 h in order to facilitate interactions between CeO 2 NPs and POX. The degradation of POX was monitored by periodic quantification of POX concentration using High Pressure Liquid Chromatography (HPLC).

Every 30 min, the solution containing nanoparticles was centrifuged at RCF 2292 g for 2 min. 100 µL of supernatant was collected, diluted to 1:10 in deionized water, and filtered through a nylon membrane disc filter (reference Econofltr Nyln 13m, 0.45 µm pore-size) before HPLC analysis. The same procedure has been applied for the blank sample. Table 1 {hkl} Crystal facets, sizes estimated from TEM images, specific surface area S BET of the nanoparticles elaborated by physical and chemical methods before annealing, and S BET after annealing. The size evolution from as-produced particles to annealed particles is displayed only when significant.

Sample

Crystal facets Sizes from TEM (nm) before → after annealing S BET → S BET (m 2 .g calibration curve of POX was linear in the concentration range of 0-50 µmol.L -1 (according to the dilution, a maximum of 20 µmol.L -1 is expected). Data collection and analysis were performed using the Empower Pro software. Under these conditions, the limit of detection of POX was 420 pg. This value corresponds to a minimum concentration of 4.2 × 10 -5 g.L -1 in the 10 µL injected, i.e. to the residual concentration after removal of 99.2% of POX. The coefficients of variation of repeatability were 0.5% at a concentration level 10 mg.L -1 (36 µmol.L -1 ).

Results

Morphological studies

The morphology of nanoparticles synthesized by both physical and chemical processes was carried out by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). Figure 3 shows images of the as-produced nanoparticles, before the annealing treatment. All the interplanar distances and angles between crystallographic planes fit those reported in the ICDD file 00-034-0394 corresponding to cubic cerium dioxide (space group 225, Fm3m).

The process used by Baikowski led to the formation of Φ-NPO cerium oxide particles with a very large particle size distribution, from a few nm to a few hundred nm, and irregular shapes (Figure 3A). Because of these irregularities, it was not possible to determine crystal faces for Φ-NPO. the broad size distribution. By using pulsed laser ablation in ultrapure water, two types of particles were obtained for Φ-NTO: a majority of nanotruncated octahedra of approximatively 4 nm, and some spherical nanoparticles between 10 nm and 50 nm (Figure 3B,C). The nanotruncated octahedra present {111} and {100} crystal facets. By using photochemistry synthesis, only nanotruncated octahedra of approximatively 4 nm were obtained, with {111} and {100} crystal facets at their surface (Figure 3D). By using the hydrothermal process, nanorods and nano-octahedra were obtained (Figure 3E-F). The morphologic details of these samples are described in our previous study 7 . Briefly, the χ -NR (Figure 3E) consist of rods about 7-9 nm in diameter and 50-200 nm long, which grew along the < 110 > direction. They are porous, polycrystalline and don't present well defined facets. The χ -NO (Figure 3F) have sizes ranging between 6 nm and 35 nm. They are in an octahedron shape with truncation at the apexes and their surface is dominated by {111} crystal facets. All the morphologic characteristics of the nanoparticles are reported in Table 1 along with their specific surface areas.

The morphology of the annealed nanoparticles was also studied. HTEM images, TEM images and the report of morphological characteristics of the annealed nanoparticles are presented in supplementary information (see Figure S3). No significant modification of the morphology was observed with the annealing treatment except for nanotruncated octahedra prepared by photochemical synthesis and for nanorods. In the case of nanotruncated octahedra prepared by photochemical synthesis, the annealing treatment induces the sintering of the nanoparticles and an increase in size from 4-5 nm to 6-11 nm. This leads to a decrease of the specific area (145 m 2 .g -1 for χ hν-NTO, 45 m 2 .g -1 for χ hν-NTO ). In the case of nanorods, the annealing treatment did not affect the size or the shape, but a decrease of the specific surface area was noticed after the annealing (132.5 m 2 .g -1 for χ -NR, 90 m 2 .g -1 for χ -NR ). An explanation could be a decrease of the porosity of the objects with the annealing treatment.

Phase determination and structural refinements

The crystal structure of the nanoparticles was characterized by XRD analysis. The XRD patterns of the as-prepared nanoparticles are presented in Figure 4A. All the diffraction patterns present only reflections characteristic of the cubic fluorite structure of cerium dioxide (ICDD 00-034-0394, space group 225, Fm3m). The nature of the crystalline phase was not affected by the annealing treatment (Figure 4B). The lattice parameters and the crystallite size of the different samples, before and after annealing, determined from profile matching refinements, are reported in Table 2. Except for χ hν-NTO and χ -NR, the lattice parameter of the as-prepared nanoparticles is slightly higher than -, although quite close to -the value of the lattice parameter of bulk CeO 2 (5.411 Å), consistently with the Madelung constant in an ionic crystal of CeO 2 53,54 . For χ -NR and χ hν-NTO, a higher value of the lattice parameter is observed, about 5.43 Å. The distortion of the crystal lattice of the nanorods χ -NR has been previously attributed to the strain induced by twist boundaries, as well as by the presence of Frenkel-type oxygen defects 7 . After the annealing, the lattice parameter of the nanorods χ -NR as well as of the nanotruncated octahedra χ hν-NTO is moving toward the bulk value, showing that the strain is considerably reduced by the annealing step. This is consistent with the increase of the crystallite size.

Raman spectroscopy

The Raman spectra of the CeO 2 nanoparticles before and after the annealing treatment in the 350-700 cm -1 range are shown in Figure 5. The full spectra are available in supplementary information, figure S4. For all samples, the Raman spectrum is dominated by a strong peak at ≈460 cm -1 , with weak bands at ≈600 cm -1 . The peak at ≈460 cm -1 (labelled F 2g ) is typical for the CeO 2 fluorite phase, and corresponds to a symmetric breathing mode of the oxygen atoms around cerium ions. This mode is affected by any disorder in the sublattice, and is size dependent 55,56 . Thus, it is not surprising that the presence of twist boundary or of other structural defects in χ -NR or in χ hν-NTO involve a redshift, and a broadening of the F 2g peak compared to other morphologies (Figure 5). The peak around 600 cm -1 (labelled D) is assigned to oxygen defects, and most probably due to the presence of Frenkel-type oxygen defects where an oxygen atom is displaced from its lattice position to an interstitial site 57,58 .

The relative intensity ratio I D /I F2g gives information about the quantity of intrinsic defect sites in the structure. The I D /I F2g ratio of the different samples is reported in Table 2. Before the annealing, the I D /I F2g ratio of χ hν-NTO and χ -NR is more than six times higher than the values of the other samples (Figure 5A,B and Table 2), indicating that χ hν-NTO and χ -NR have the largest quantity of Frenkel-type oxygen defects. The I D /I F2g ratio is not significantly affected by the annealing treatment, except for the nanotruncated octahedra elaborated by photochemistry and for the nanorods (Figure 5C,D and Table 2). The I D /I F2g of χ hν-NTO and χ -NR is reduced by a factor four with respect to the values of the as-produced samples. This result is consistent with an annealing in presence of oxygen (in air) which is expected to induce a decrease of oxygen defects. The results from Raman and XRD are then consistent. A large amount of Frenkel-type oxygen defects leads to an increase of the lattice parameter, and both are reduced by the annealing treatment.

Nature of the adsorbed species

The nature of the adsorbed species at the surface of the CeO 2 nanoparticles was characterized by infrared spectroscopy. Figure 6 shows IR spectra of the different samples before and after the annealing step. The assignment of the peaks is detailed in the supplementary information (Table S1). In the following, we focus on the main information provided by the IR spectroscopy.

Before heat treatment the infrared spectra have different absorption bands according to the approach used for the synthesis. Thus, for the powders resulting from syntheses in autoclave ( χ -NR and χ -NO), the following bands are observed: 3400, 1630, 1540, 1330, 1050, 850, 710 cm -1 . The first two bands are due to adsorbed water molecules and OH surface groups. The rest of the bands are assigned to carbonates interacting with basic surface lattice oxygen. The carbonates thus bonded exhibit different modes of interaction: Monodentate, Bidentate and Polydentate. The last two are the most likely, in view of the position of the bands 59,60 . For these two ceria nanopowders, the shape of the spectra was slightly affected by the post-annealing treatment.

For Φ-NPO and χ hν-NTO nanoparticles, bands are very slightly visible around 2900 cm -1 , which are characteristics of C-H stretching. For the χ hν-NTO sample, this band and the two strong COO bands (above 1550 cm -1 and 1350 cm -1 ) are a manifestation of the formate ions HCOO -used as sensitizers in the photochemical synthesis. For Φ-NPO sample, the same bands are probably a signature of ligands used to stabilize the colloidal CeO 2 suspension. In both case, molecules used in the synthesis protocols lead to an important pollution of the nanoparticles surface, but the annealing step leads to their degradation: for χ hν-NTO nanoparticles, the C-H peak (above 2900 cm -1 ) and the COO bands (1600-1200 cm -1 range) disappear with the annealing step; while they are reduced for Φ-NPO .

For PLAL-synthesized nanoparticles, the peaks at 1100 cm -1 (ν(CO)) and 1262 cm -1 (δ (COH)) observed on the FTIR spectrum of the as-produced sample are characteristic of the presence of hydrogen carbonate at the surface of the particles 60 , probably originating from dissolved CO 2 . The pH value of the colloidal solution is 6.5 and is thus consistent with the presence of hydrogen carbonate (pKa 1 =6.4 for H 2 CO 3 / HCO - 3 and pKa 2 =10.3 for HCO - 3 / CO 2- 3 ). Both hydrogen carbonate signature are not observed on Φ-NTO .

Finally, for all cerium oxide nanopowders, the strong band below ≈600 cm -1 corresponds to O-Ce-O vibration of cerium oxide.

Degradation activity

The degradation of paraoxon using the as-produced particles as well as after their annealing is shown in Figure 7. The in vitro method used for the test gives information about the degradation efficiency of the particles in aqueous phase at 32 • C. The as-produced particles (Figure 7A) can be classified in two groups based on the kinetic of degradation. The first group causes the degradation of approximatively 40% of the ini-tial POX in 1 hour and of almost all initial POX in 5 hours. The second group allows the degradation of less than 10% of initial POX in 1 hour and around 30% of initial POX in 5 hours. The first group is constituted of Φ-NTO, χ -NO and χ -NR, and the second group is constituted of χ hν-NTO and Φ-NPO. After the annealing treatment (Figure 7B), some important modifications were observed : 1) an increase of the degradation efficiency for the nanorods prepared by hydrothermal process, for the nanotruncated octahedral particles synthesized by photochemistry and for the nanopolyhedra produced by wet grinding, 2) a decrease of the degradation efficiency for the nanotruncated octahedra elaborated by PLAL. The kinetics of the nano-octahedra prepared by hydrothermal process did not seem to be affected by the annealing treatment. The evolution of paraoxon degradation with time specific surface area, 145 m 2 .g -1 (see table 1). In contrast, lasergenerated nanoparticles in ultra-pure water Φ-NTO show the best activity, while this sample presents the worst specific surface area, 13 m 2 .g -1 (see table 1). After the annealing, the degradation activity is mainly driven by the specific surface area: the larger is the specific surface area, the higher is the rate constant k. All samples present different facets, at least {111} and {100}, including the so called nano-octahedra χ -NO and χ -NO which appear slightly truncated. Then, despite the higher activity of the {111} facets with respect to the {100} facets 7 , the shape of particles appears as a second order effects with respect to the specific surface area for the annealed samples, keeping in mind that all samples present a large amount of {111} facets. The values of the ratio k/S BET for the annealed samples are similar, 1.6 ± 0.8 × 10 -4 g.m -2 .min -1 .

Benchmarking of degradation activity, costs and productivity

To compare the different synthesis methods, we have sought to assess the pros and cons of each of them through the definition of relevant quantities, i.e. the productivity (g/day), the hourly production rate (mg/h), the costs (e/g) and the rate constant k (min -1 ). The values are displayed in table 4 for the samples with the highest rate constant k for each synthesis method, i.e. the as-produced sample or the annealed sample. The commercial sample is excluded since the information on costs, the productivity and the hourly production rate are confidential.

The costs include labor costs (26.14 eper working hour for an operator including taxes, 1607 working hours per years), the depreciation of the investment (equipment) assuming a depreciation time of five years (1760 hours of useful machine time per year), the rental cost of the facilities (109 eper working day for an experimental room of 30 m 2 , including a fume hood, the processing of the chemical waste, fluids consumption, air conditioning, cleaning, building maintenance and security), the energy costs (0.12 e/kWh VAT excluded), the chemicals (VAT excluded) and the lab consumables (VAT excluded). Research and development costs, as well as the quality control are not included, but would be similar for all synthesis methods. The detail of the calculation is available in supplementary information (Excel file).

The productivity (g/day) for each method, assuming a continuous process and a parallelization of the production steps, is driven by the step in the production process with the longest operating times. The productivity is thus driven by the immobilization of critical equipment, including its cleaning and/or cooling times. It corresponds to the laser setup for the PLAL method, the autoclave for the hydrothermal process, and the photochemical reactor for the photochemical method. The hourly production rate corresponds to the weight of dried powder produced in one batch divided by the overall time to release one batch (mg/h). The productivity (g/day) and the hourly production rate (mg/h) are complementary information. The facilities costs mainly relied on the productivity, while the labor and the depreciation mainly relied on the hourly production rate.

It appears from table 4 and figure 8 that the hydrothermal process is slightly less expensive than the photochemical method, and both of them are substantially less expensive than laser ablation in liquids. Moreover, the hydrothermal process leads to the powders with the best degradation activity, namely the nanorods. PLAL is penalized by the low productivity which results mechanically in a rise of the costs, including labor costs, the depreciation of the investment and the facilities costs. However, a drastic rise of the productivity, from 21 mg/hour (overall process) to a few g/hour is possible with available laser sources 43,44 . For productivity larger than a few g/hour, laser ablation in liquids would compete with the chemical routes 61 , keeping in mind that as-produced sample from PLAL exhibits one of the best degradation activity. The Photochemical method is penalized by the conversion yield obtained, only 38%, limiting the amount of particles produced in one batch, which results mechanically in a rise of the costs. In contrast the conversion yield reported for the hydrothermal process is 100%. An increase of the conversion yield by means of an optimization of the photochemical method (in-line filtering, forced sedimentation etc.) would leads to reduced costs which may reach 8.26 e/g for an ideal conversion yield of 100%, i.e. in the range of the hydrothermal method costs.

Conclusions

The degradation activity of CeO 2 nanopowders was evaluated in vitro by measuring the degradation kinetics of paraoxon organophosphate. The degradation activity of the as-produced nanopowders is strongly influence by the synthesis route. A quenching of the degradation activity is observed on the asproduced particles with a surface pollution, especially when organic molecules with carboxylate ion R-COO -are involved in the synthesis process. In contrast, laser-generated nanoparticles in ultra-pure water show the best activity, while the sample presents the lowest specific surface area. After annealing, almost all samples present a clean surface and the degradation activity is mainly driven by the specific surface area. The benchmarking of costs and productivity shows that the costs are mainly driven by the productivity, disadvantaging the laser ablation in liquids with respect to the chemical and the photochemical routes. However, such a drawback is solved by cutting edge device allowing an ablation rate of a least one gram per hour. For now, chemical routes remain the least expensive while leading to the nanoparticles with the best degradation activity of the paraoxon, namely the nanorods.

Fig. 1

 1 Fig.1Schematic representation of the pulsed laser ablation in liquids (PLAL) setup, including the circulation system. A fast steering mirrors system was used to scan the target surface. The ablated surface was 9 mm×12 mm.

Fig. 2

 2 Fig. 2 Photochemical reactor setup (Pilot plant).

  HPLC consisted of the quaternary pump (Waters 600 Controller), auto sampler (model 717 plus Auto sampler), column heater (Waters temperature control module), and Photodiode Array Detector (Waters 2996). Operated at 40 • C, the column used was a Xterra MS C18 Cartridge column (5 µm, 4.6 mm×250 mm). The composition of the mobile phase was 65% of methanol (HPLC-grade, Fisher Scientific) and 35% of deionized water with 0.5% (v/v) of acetic acid (glacial acetic acid, and ultrapure analytical grade type 1 water, resistivity > 17 MΩ•cm). The flow rate used was 0.7 mL.min -1 . The total run time was 10 min and the injection volume was 10 µL. The compound POX was specified by a peak height mode at retention time 7.5 min with UV absorption at λ max 269 nm. The

Fig. 3

 3 Fig. 3 TEM and HRTEM images of the CeO 2 nanoparticles obtained by both physical and chemical methods. (A) Commercial nanopolyedra Φ-NPO. (B,C) nanotruncated octahedra synthesized by PLAL Φ-NTO. (D) nanotruncated octahedra elaborated by photochemistry χ hν-NTO. (E) nanorods χ -NR and (F) nano-octahedra χ -NO elaborated by hydrothermal process.

  -1 ) Φ-NTO / Φ-NTO {111} + {100} 4 nm for the truncated octahedra and 10 -50 nm for the spheres 13 → 16 χ -NO / χ -NO {111} 6 -35 nm 67 → 60 χ -NR / χ -NR not selective 7 -9 nm in diameter × 50 -200 nm long 133 → 90 χ hν-NTO / χ hν-NTO {111} + {100} 4 -5 nm → 6 -11 nm 145 → 45 Φ-NPO / Φ-NPO not selective few nm to few hundred nm 20 → 20

  Figure S2 in supplementary Information shows the volume-weighted size distribution delivered by the Mastersizer 3000 particle size analyzer, confirming

Fig. 4 Table 2

 42 Fig. 4 XRD patterns of the CeO 2 nanoparticles elaborated by physical and chemical methods: (A) as-prepared samples, (B) samples after annealing treatment.

Fig. 5

 5 Fig. 5 Raman spectra of the cerium oxide nanoparticles before (A,B) and after (C,D) the annealing treatment. (A,C) Raman spectra in the 350-700 cm -1 range and (B,D) enlarging in the 500-700 cm -1 range (λ exc = 633 nm). All spectra are normalized relative to the maximum intensity of the F 2g mode of the CeO 2 fluorite phase.

Fig. 7

 7 Fig. 7 Degradation kinetic of Paraoxon with the CeO 2 nanoparticles: (A) as-prepared samples, (B) samples after annealing treatment.

Fig. 8 (

 8 Fig. 8 (A) Comparison of the degradation activity, costs and productivity. (B) Cost breakdown including labor, depreciation of the investments (equipment), the rental cost of the facilities, and the energy costs, the chemicals and the consumables.

Table 4

 4 Rate constant k of paraoxon degradation, productivity, costs and hourly production rate. The table presents the samples with the best rate constant k for each synthesis method, i.e. the as-produced sample or the annealed sample. The commercial sample is excluded since the information on costs, the productivity and the hourly production rate are confidential.

	Sample	k × 10 -3	Productivity	costs	hourly production
		(min -1 )	(g/Day)	(e/g)	rate (mg/h)
	Φ-NTO	13.0	0.25	986.21	21
	χ -NO	10.8	34.33	6.61	1925
	χ -NR	22.0	15.50	14.62	873
	χ hν-NTO	3.85	13.10	21.73	481

1-13 J o u r n a l N a me , [ y e a r ] , [ v o l . ] ,

[1][2][3][4][5][6][7][8][9][10][11][12][13]

Acknowledgements

The authors are thankful to Ruben Vera for carrying out the XRD measurements. This work received financial support from the Direction Générale de l'Armement (PhD grant), and from the DGA ASTRID program (project NanoDeTox -Grant no. ANR-16-ASTR-0008). The collaboration between the Lyon University and the Institute of Physics of the Czech Academy of Sciences is funded through the European project ASCIMAT, in the framework of the European program H2020-TWINN-2015. The pilot plant experiments were supported by the Ministry of Industry and Trade of the Czech Republic project FV30139. We wish to thank Fibercryst company for the custom-development of the MOPA-based laser source, as well as for their technical support. The ablation setup was funded by the French innovation agency OSEO ALL-Mat project. We wish to thank BAIKOWSKI for providing us ceria suspension (CTX product).

after contact with CeO 2 samples was fitted with a pseudo-first order decay model (exponential decay ∝ exp(-kt), with a rate constant k (min -1 ). The detailed values of the rate constant k and the rate constant normalized by the specific surface area k/S BET are reported in Table 3.

Discussion

The degradation activity of the samples before the annealing step is driven by the surface pollution. The two samples with a poor degradation activity, namely χ hν-NTO and Φ-NPO are characterized by synthesis processes which lead to a pollution of the surface of the nanoparticles, formate ions for χ hν-NTO and ligands for Φ-NPO respectively, while χ hν-NTO presents the largest

Conflicts of interest

There are no conflicts to declare.