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International audience; Sub-stoichiometric titanium oxide (TiOx) reactive electrochemical membrane (REM) were integrated for the first time as anode in the electro-Fenton (EF) process. Hydroxyl radicals (•OH) were produced both in the retentate from Fenton's reaction and at the REM from anodic oxidation (AO). Optimal mass transport conditions were implemented because of convection-enhanced mass transport of (i) organic pollutants towards the REM surface during filtration and (ii) dissolved 02 towards cathode active sites owing to the use of a 3D carbon felt cathode in flow-through configuration for H202 generation. The efficiency of the REM/EF process was much higher than EF or REM used as standalone processes. For instance, taking paracetamol as target pollutant, (67 ± 2)% removal of 55 mg L - i of initial TOC was achieved with a high mineralization current efficiency (MCE) of ( 43 ± 1)%. By comparison, standalone REM and EF processes achieved only 47% (MCE = 30%) and 31 % (MCE = 20%) of TOC removal, respectively. By monitoring TOC removal both in retentate and permeate, the effect of homogeneous oxidation in the bulk retentate and heterogeneous oxidation at the REM could be observed separately. It was thus highlighted that the efficiency of AO might be affected by the presence of • OH and Fe2 + in the bulk. It was also emphasized a synergistic effect related to the formation of carboxylic acids in the bulk retentate that are more easily mineralized at the REM where both • OH-mediated oxidation and direct electron transfer occur.

International audience; Photocatalytic water splitting into hydrogen is considered as one of the key solutions to the current demand for eco-responsible energy. To improve the efficiency and sustainability of this process, the development of a TiO2-based photoanode by adding bio-sourced surfactants to the sol–gel preparation method has been considered. Three different polymeric biosurfactants (GB, GC, and BIO) have been tested, giving rise to three different materials being structurally and morphologically characterized by XRD, Rietveld refinement, BET, SEM, AFM, and XPS, which was completed by light absorption, photocatalytic (Pilkington test), electronic (EIS and C-AFM), and photoelectrochemical (cyclic voltammetry) measurements. Correlations between the structure/morphology of materials and their functional properties have been established. One specific surfactant has been proven as the most suitable to lead to materials with optimized photoelectrochemical performance in direct relation with their photocatalytic properties essentially controlled by their specific surface area.

This study evaluated the feasibility of the electrooxidation process using a sub-stoichiometric titanium oxides (TiOX) reactive electrochemical membrane (REM) as anode for the treatment of a secondary effluent from a wastewater treatment plant. The main objectives were to analyze (i) the degradation of a pharmaceutical pollutant, carbamazepine, added at a concentration of 100 µg L−1, (ii) the mineralization of the residual total organic carbon (TOC = 7 mg L−1), (iii) the formation of toxic by-products and (iv) the energy consumption of the REM process. Two main operating parameters were tested: the current density applied to the REM (74, 149 and 290 A m−2) and the flux of TOC passing through the membrane. The results revealed that the efficiency of the process was maintained above 70% of mineralization and >98% of degradation of carbamazepine until a limiting value of TOC flux was reached. The higher the current density, the higher the limiting value of the TOC flux above which the efficiency decreased. This trend was ascribed to the limitation from the amount of reactive species produced on the REM surface (current limitation instead of mass transport limitation at lower TOC flux). As the energy efficiency strongly increased when applying a higher TOC flux, it is therefore crucial to apply the process around this threshold value. This study also showed that it is possible to control the formation of toxic chlorine-containing by-products (ClO3−, ClO4−, AOCl) by decreasing the current density. This issue is particularly important for such effluents containing a significant amount of Cl− ions. By taking into consideration both advantages and drawbacks, optimal results were obtained with the lowest current density of 73 A m−2 and a TOC flux through the membrane of 4.41 g h−1 m−2 corresponding to 1.34 m3 h−1 m−2. These conditions allowed for >98% degradation of carbamazepine and 70% of mineralization with an energy consumption of 0.15 kWh g−1 of TOC removed (i.e. 0.74 kWh m−3 of treated wastewater).

The objective of this study was to implement electrochemical advanced oxidation processes (EAOPs) for mineralization and biodegradability enhancement of nanofiltration (NF) concentrate from landfill leachate initially pre-treated in a membrane bioreactor (MBR). Raw carbon felt (CF) or Fe II Fe III layered double hydroxides-modified CF were used for comparing the efficiency of homogeneous and heterogeneous electro-Fenton (EF), respectively. The highest mineralization rate was obtained by heterogeneous EF: 96% removal of dissolved organic carbon (DOC) was achieved after 8 h of electrolysis at circumneutral initial pH (pH 0 = 7.9) and at 8.3 mA cm −2 . However, the most efficient treatment strategy appeared to be heterogeneous EF at 4.2 mA cm −2 combined with anodic oxidation using Ti 4 O 7 anode (energy consumption = 0.11 kWh g −1 of DOC removed). Respirometric analyses under similar conditions than in the real MBR emphasized the possibility to recirculate the NF retentate towards the MBR after partial mineralization by EAOPs in order to remove the residual biodegradable by-products and improve the global cost effectiveness of the process. Further analyses were also performed in order to better understand the fate of organic and inorganic species during the treatment, including acute toxicity tests (Microtox ® ), characterization of dissolved organic matter by three-dimensional fluorescence spectroscopy, evolution of inorganic ions (ClO 3 − , NH 4 + and NO 3 − ) and identification/quantification of degradation by-products such as carboxylic acids. The obtained results emphasized the interdependence between the MBR process and EAOPs in a combined treatment strategy. Improving the retention in the MBR of colloidal proteins would improve the effectiveness of EAOPs because such compounds were identified as the most refractory. Enhanced nitrification would be also required in the MBR because of the release of NH 4 + from mineralization of refractory organic nitrogen during EAOPs.

M-doped TiO2 and mixed oxides MxOy–TiO2 (M = V, Bi, W) were synthesized by the reactive mineralization of ash-free filter paper under anhydrous conditions. Mixtures of metal chlorides (TiCl4 with VOCl3, WCl6, or BiCl3) were reacted directly with cellulose, and three different Ti/M atomic ratios were used (99, 19, and 9). The resulting materials consist of original nanoflower assemblies of needle-shaped primary particles. Their physicochemical characteristics were investigated by various techniques (X-ray diffraction, diffuse-reflectance UV/Vis spectroscopy, electron microscopy, and elemental analysis). The incorporation of the doping metal or the formation of mixture of oxides with TiO2 (WO3, Bi2O3) depends on the metal and the proportions used. The photocatalytic activities of the materials were tested for the degradation of phenol. The vanadium-doped materials exhibit true solid-solution formation and their band gaps shift into the visible range.

International audience; A cathodic electro-Fenton (EF) process consisting of thermally treated carbon felt and anodic photoelectrochemical (PEC) oxidation process consisting of bismuth vanadate – bismuth oxyiodide electrodeposited on fluorine doped tin oxide glass (FTO-BiVO4/BiOI) were coupled into a single electrochemical advanced oxidation system for the mineralisation of paracetamol. EF degradation of paracetamol yielded 71 % total organic carbon (TOC) removal after 4 h with a current density of 20 mA cm−2. With the coupled EF/PEC system, the complete removal of paracetamol was achieved within 2 h and a higher mineralisation of 92 % TOC removal after 4 h was recorded with a 10 mA cm−2 current density. The specific energy consumption of the EF/PEC process was about 64 % lower than the energy consumption of EF process alone. The treated aqueous solution exhibited reduced toxicity in comparison with the untreated solution with about 1% inhibition of Vibrio fisheri. This EF/PEC system showed a synergic improvement in performance over EF and PEC.

International audience; Reactive Electrochemical Membrane (REM) prepared from carbothermal reduction of TiO2 is used for the mineralization of biorefractory pollutants during filtration operation. The mixture of Ti4O7 and Ti5O9 Magnéli phases ensures the high reactivity of the membrane for organic compound oxidation through •OH mediated oxidation and direct electron transfer. In cross-flow filtration mode, convection-enhanced mass transport of pollutants can be achieved from the high membrane permeability (3300 LMH bar-1). Mineralization efficiency of oxalic acid, paracetamol and phenol was assessed as regards to current density, transmembrane pressure and feed concentration. Unprecedented high removal rates of total organic carbon and mineralization current efficiency were achieved after a single passage through the REM, e.g. 47 g m-2 h-1 - 72% and 6.7 g m-2 h-1 - 47% for oxalic acid and paracetamol, respectively, at 15 mA cm-2. However, two mechanisms have to be considered for optimization of the process. When the TOC flux is too high with respect to the current density, aromatic compounds polymerize in the REM layer where only direct electron transfer occurs. This phenomenon decreases the oxidation efficiency and/or increases REM fouling. Besides, O2 bubbles sweeping at high permeate flux promotes O2 gas generation, with adverse effect on oxidation efficiency.

International audience; Metal hollow fibre membranes offer excellent chemical and mechanical stability and are promising platforms for the removal of harsh contaminants from solutions. Stainless steel (SS) membranes are however prone to oxidation and advanced decoration routes are required to passivate the surface of such materials. Here, SS membranes were modified with nanoscale coatings of graphene to promote electrochemical reactions and prevent premature corrosion of the bare metal reinforcement upon electro-Fenton (EF) reaction. Samples decorated with graphene oxide or reduced graphene oxide were compared to bare SS membranes to assess the impact of graphitization on the electrochemical performance of the membranes. Membranes properties were characterized using both cyclic and linear scanning voltammetry. The results evidenced that electron transfer kinetics were significantly enhanced on the reduced graphene oxide, compared to raw material. In addition, the removal efficiency of a pharmaceutical pollutant, paracetamol, was evaluated in electro-Fenton batch experiments, on the three membrane electrodes. The best mineralization current efficiency at 37% was found when using reduced graphene oxide membrane cathode at optimal applied potential of -0.5 V vs. SCE (Saturated Calomel Electrode). Finally, the coupling of electro-Fenton and filtration processes was carried out on a pilot-scale unit. Various electrochemical and hydrodynamic parameters that affect mineralization efficiency were studied. By coupling filtration and electrochemical processes, the mineralization current efficiency value was increased remarkably by 165% and remained stable for three consecutive cycles. This strategy opens up opportunities to generate low cost catalytic membrane reactors with high flux and selectivity from the materials reactivity as opposed to sieving, with potential for harsh chemicals mineralization.

In this study, the role of mixing hydrodynamics during the sol–gel synthesis of titania nanoparticles and the consequences on their photocatalytic properties were investigated. For the first time three different T-mixer geometries were tested. Alcoholic solutions of titanium tetra-isopropoxide and water were mixed in three different T-mixers with turbulence promoters and thus different mixing characteristics. The changes of nanoparticle sizes during the induction time of the sol–gel process were followed by dynamic light scattering and velocity and turbulence fields were simulated by Computational Fluid Dynamics (CFD) for the three T-mixer geometries. The results indicated that macro-mixing is crucial during the first step as it determines the nucleation rate and then the primary particle size. The micro-mixing has an influence on particle properties, especially on particle stability. Titanium dioxide nanoparticles synthesized by the sol–gel process were deposited on alumina supports. A homogeneous film of about 200 nm was deposited in all cases. Degradation of Acid Orange 7 (AO7) was used to evaluate the photocatalytic activity of TiO2 coatings. No difference was observed between the photoactivity of synthesized TiO2. Total mineralization of the dye occurred after 24 h irradiation.

This work evidences the interest of coupling advanced oxidation process (Electro-Fenton reaction) to dynamic filtration technology, using a tubular electrochemically reactive carbon graphite membrane, acting as cathode. This original coupling would be ideally adapted to confine organic pollution while achieving the complete degradation of refractory molecules from wastewater (domestic or industrial). The investigation was carried out using Acid Orange 7 (AO7) as a model pollutant. The electrochemical behavior of the membrane was firstly characterized in batch reactor in term of cathodic reactivity, for H2O2 selective production (in situ production from air supply followed by catalyzed ●OH generation). The influence of various parameters was studied to mark out the experimental domain to be investigated in a dynamic cross-flow reactor for AO7 degradation. In the latter case, a 23 full factorial design of experiments was used to screen the effect of operating conditions on two target responses: AO7 degradation efficiency (%) and kinetic constant value. Results showed that interactions effects between pH, current density and catalyst concentration influenced the AO7 degradation efficiency significantly. Moreover, better kinetic performances were obtained under dynamic filtration conditions, compared to a batch reactor. HPLC–MS analyses enabled elucidating at least six by-products formed throughout the process.

The bactericidal activity of an Al 2 O 3 -TiO 2 -Ag granular material against an Escherichia coli strain was confirmed by a culture-based method. In particular, 100% of microorganisms were permanently inactivated in 30 to 45 min. The present work aimed to investigate the mechanisms of the bactericidal action of this material and their dynamics on Escherichia coli using different techniques. Observations by transmission electron microscopy (TEM) at different times of disinfection revealed morphological changes in the bacteria as soon as they were put in contact with the material. Notably highlighted were cell membrane damage; cytoplasm detachment; formation of vacuoles, possibly due to DNA condensation, in association with regions exhibiting different levels of electron density; and membrane lysis. PCR and flow cytometry analyses were used to confirm and quantify the observations of cell integrity. The direct exposure of cells to silver, combined with the oxidative stress induced by the reactive oxygen species (ROS) generated, was identified to be responsible for these morphological alterations. From the first 5 min of treatment with the Al 2 O 3 -TiO 2 -Ag material, 98% of E. coli isolates were lysed. From 30 min, cell viability decreased to reach total inactivation, although approximately 1% of permeable E. coli cells and 1% of intact cells (10 5 genomic units · ml −1 ) were evidenced. This study demonstrates that the bactericidal effect of the material results from a synergic action of desorbed and supported silver. Supported silver was shown to generate the ROS evidenced.

We present a concept of the sol–gel reactor with injection of stock solutions through a T mixer, environmental gas control, thermal control of the reactive medium and in–situ particle size measurement using a monomode optical fibre probe. The rapid injection of the whole amount of reagents leads to short time of nucleation, and the micro-mixer eliminates gradients of concentrations, which results in higher local nucleation and aggregation rates. The reactor is used for production of mono-disperse nanometric titanium oxide sols. With this reactor, induction kinetics are reproducible and agree with a model describing the mean particle size increase by a slow aggregation process. As well as the in–situ size measurement technique, the reactor is a kinetic tool for determination of the sol aggregation rate. As the rules for scale-up of its equipment are already established, it is of interest for the operation and the design of industrial-scale sol–gel reactors.

We report on observations of the temperature dependence ( T = 5–40 °C) of the titanium oxide sols precipitation kinetics in the sol–gel process using Ti(OPr i ) 4 as a metal organic precursor. The nanometric sol particles are produced in the sol–gel reactor with rapid reagent mixing and temperature and atmosphere control. Precipitation kinetics was followed in situ by the light scattering method using an optical fibre probe. From these measurements the activation energy E a = 0.33 ± 0.02 eV has been obtained and assigned to the secondary hydrolysis–condensation reactions between surface Ti–OPr i groups. Careful analysis of experimental data allows concluding about a decrease of the fractal dimension D f of the precipitate with an increase of the temperature, which provides D f = 1 at 35 °C.

The behavior of TiO 2 /Al 2 O 3 composite membranes under different pH conditions was investigated. Filtration and photodegradation were coupled by using these TiO 2 /Al 2 O 3 membranes in a photocatalytic membrane reactor under UV light. Membrane performances were first evaluated by measuring water flux and then by measuring permeate flux and degradation rate during filtration of a model molecule Acid Orange 7 (AO7). Experimental results clearly showed that water permeability of alumina and TiO 2 /Al 2 O 3 composite membranes is influenced by pH conditions. Nonetheless, flux variation with pH is less pronounced for TiO 2 /Al 2 O 3 composite membranes. In addition, UV light enables a stabilization of flux because of hydrophilic properties of TiO 2 . For both membranes, higher permeate flux were obtained at the isoelectric point. It appeared that surface of composite membrane is photoreactive and permits to mitigate membrane fouling with an efficiency which depends on pH of the solution. Initial degradation rate of AO7 also depends on pH as it influences not only the surface properties of TiO 2 but also the dissociation of AO7 and the formation of hydroxyl radicals. Higher initial degradation rate was observed under acidic conditions (pH = 4).

TiO2/Al2O3 composite membranes were prepared using a sol–gel technique. After membrane characterization, six layers as optimal number of coatings was chosen (0.2 μm homogenous thin film). Filtration and photodegradation were coupled by using TiO2/Al2O3 membranes in a photocatalytic membrane reactor under UV light. Experimental results clearly showed that TiO2 thin film under UV irradiation enhanced the wettability of the ceramic membrane, were higher and more stable water flux were reached rapidly. Acid Orange 7 (AO7) were used as model pollutant. Dye was not completely degraded, 25% of degradation was obtained for only one pass corresponding to a contact time of several milliseconds. Photonic efficiency equal to 0.29 was reached. Evolution of the kinetic degradation versus the initial concentration of AO7 were consistent with the Langmuir Hinselwood model. The photodegradation allows to increase significantly composite membrane flux and to strongly prevent flux decrease when AO7 solutions were filtrated. Membrane cleaning was performed without chemicals by irradiating membrane surface under static conditions.

A new kind of metal affinity membrane based on a ceramic support was prepared. It was elaborated in four steps: (i) deposition of a chitosan layer in order to functionalize the ceramic support, (ii) cross-linking with epichlorohydrin to stabilise the polymer layer and to enable the grafting, (iii) iminodiacetic acid grafting, (iv) Cu2+ adsorption. Due to the ceramic support, this membrane is highly resistant and the chitosan layer brings its biocompatibility properties. Each step of the membrane elaboration was studied and the membrane structure was characterized. Both thin coating of the polymer on the alumina grains of the support and the chemical modification of the membrane were proved. Then, bovine serum albumin (BSA) was used as a model protein to test protein retention of the affinity membrane. The protein/membrane interactions were investigated showing that some non-specific ones are involved. Finally, the effect of buffer concentration was checked and it appears that, in the studied range, an increase of the buffer concentration entailed a limitation of the non-specific interactions inducing a better BSA recovering and a higher selectivity.

International audience