In the quest for efficient photoelectrolysis devices for solar-driven water splitting, designing a high-performance photoanode compatible with the electrolyte buffer of the photocathode for tandem photoelectrochemical (PEC) cells remains a challenge. One promising solution is the development of an efficient and durable photoanode under acidic conditions. Despite the potential benefits, the limiting factors affecting performance under such conditions are not well understood yet. Two main strategies to enhance photocurrent density and durability are generally considered: applying a surface co-catalyst, or passivating using ultrathin titanium oxide layers as a barrier. In this study, we present a scalable alternative method that combines sol-gel chemistry and dip-coating, to create thinner TiO2 layers on Mo doped-BiVO4 photoanodes for surface passivation. We developed Mo-doped-BiVO4/Co-Pi photoanodes with cobalt-phosphate (Co-Pi) as co-catalyst, which resulted in a major breakthrough by achieving a photocurrent density of 1.9 mA cm-2 at 1.23VRHE (pH 6) under standardized illumination conditions, along with a significant improvement in photoanode durability. Additionally, our investigation explores the evolution of the photoanode chemistry within the material after doping, and at the surface after Co-Pi deposition at different stages of the PEC process.

Acceptability and relevance of nanoparticles in the society is greatly improved using a safer-by-design strategy. However, this is difficult to implement when too late in the development process or when nanoparticles are already on the market (e.g., TiO2). We employ this strategy for emerging nanoparticles of lanthanide oxysulfide of formula (Gd,Ce)2O2S, relevant for photocatalysis as well as for multimodal imaging, as the bandgap of the nanoparticles, related to their Ce content, impacts their ability to absorb visible light. As a first step, we investigated the production of reactive oxygen species (ROS) as a function of cerium content, in abiotic conditions and in vitro using murine macrophage RAW 264.7 cell line. We demonstrate that, at sub-lethal doses, Ce-containing oxysulfide nanoparticles are responsible for a higher ROS intracellular formation than cerium-free Gd2O2S nanoparticles, although no significant inflammatory response or oxidative stress was measured. Moreover, there was no significant loss of cerium as free cation from the nanoparticles, as evidenced by X-ray fluorescence mapping. Based on these results, we propose a risk analysis for lanthanide oxysulfide nanoparticles, leading to a technology assessment that fulfills the safer-by-design strategy.

Anatase TiO2 structure has been widely studied as an electrode for Li-ion battery and as electrocatalyst for water splitting. Inserting guest species into TiO2 has been demonstrated as an effective approach to tune the electronic structure and consequently improves the hydrogen evolution reaction (HER) catalytic activity. In this work, by using mesoporous TiO2 electrodes, we have demonstrated the interplays between HER and Li-ion insertion in Water-in-Salt Electrolyte (WISE). Low C-rates favor the electro-catalytic reaction (HER), but the latter does also depend on the amount of Li in the electrode. Finally, this study guides the experimental conditions for an optimum functioning either in battery environment or in electro-catalysis.

The development of original nanoparticle size and shape requires a detailed knowledge and rationalization of the formation mechanism. A consolidated mechanism of gamma-AlOOH boehmite nanorod formation in aqueous hydrothermal conditions is proposed based on an advanced characterization of the final product, kinetic studies, and surface energy calculations. Boehmite nanorods with a width of about 10 nm and more than 100 nm in length are obtained in slightly acidic conditions from Al(III) molecular precursors at temperature higher than 150 degrees C. The identification of protoboehmite as an intermediate in the kinetic study combined with the low solubility of aluminum in reacting conditions and the presence of stacking defects in the rods is indicative of an aggregation mechanism. Electron diffraction studies show that the crystallites are oriented in the nanorods with a [001] preferential growth direction. Using DFT calculations, we demonstrated that the nanorod morphology is not the expected thermodynamically stable one in these experimental conditions. An explanation of the oriented aggregation of primary particles is proposed based on an eased depletion of the solvation water molecules of the (001) surface compared to the other surfaces.

Tin oxide nanoparticles (SnO2 NPs) as electrocatalyst for the production of formate from CO2 reduction reaction (CO2RR). We synthesize, characterize and evaluate high surface area SnO2 NPs (2.4 nm and 299 m(2) g(-1) in diameter size and surface area, respectively), for the continuous production of formate at high current density within a flow electrolyzer. SnO2 NPs under Ar and CO2 reduction conditions were studied by cyclic voltammetry. SnO2-based gas diffusion electrodes (SnO2-GDEs) were manufactured to perform continuous CO2RR. A maximum formate con-centration value of 27 g L-1 was achieved with a Faradaic efficiency (FE) of 44.9 % at 300 mA cm(-2), which was significantly stable and reproducible when operated up to 10 h. Nevertheless, ohmic drop contribution due to the semiconducting properties of SnO2 was not negligible. The low total FE (< 60 %) of products pointed out a leakage of formate by crossover migration through the membrane from the catholyte towards the anolyte.

The reduction degree of graphene oxide substrate governs the activity and stability of Co3O4/rGO nanocomposites toward oxygen reduction reaction and oxygen evolution reaction. In this work, Co3O4 nanoparticles with narrow size distribution were uniformly deposited onto graphene oxide materials with different reduction degrees, by using a microwave-assisted hydrothermal method. The physicochemical characterization of these nanocomposites indicates that oxygenated groups grafted onto a reduced graphene oxide surface allow creating strong interactions between the carbon-based substrate and Co3O4 nanocrystals. The obtained results denote that the electrocatalytic activity and stability of these nanocomposites toward the ORR and OER depend on the entanglement between the strength of the carbon/oxide interaction and the electronic conductivity of the substrate. (C) 2019 The Electrochemical Society.

In view of the practical deployment of Al-ion batteries for stationary energy storage, novel and cost-efficient cathodes consisting of earth-abundant chemical elements are imperative. Titanium dioxide TiO2 is an appealing candidate as a cathode material due to high natural reserves of the constituent elements as well as its nontoxicity and high chemical robustness. In this work, we assessed the potential of anatase TiO2 nanorods as a cathode material for Al-ion storage. This material delivers high capacities of 112-165 mAh g(-1) at a current density of 50 mA g(-1) in AlCl3/1-Ethyl-3-methylimidazolium chloride ionic liquid electrolyte of various acidity. The mechanism of aluminum intercalation into anatase TiO2 nanorods and the related crystal structure changes were assessed by density functional theory, ex situ X-ray photoelectron and energy-dispersive X-ray spectroscopies.

The influence of the support on the nucleation of ZSM-5 nanoparticles has been studied for three supports: gamma-alumina, zirconia and carbon nanotubes (CNT). While zeolite nucleation was suppressed in presence of alumina and strongly delayed in presence of zirconia, it occurred without delay in presence of CNT. These differences are explained by the partial dissolution of the support (for alumina and zirconia supports) that modify the composition of the zeolite nucleation solution. For the CNT/zeolite sample, the obtained composite contains about 60 wt% of zeolite and develops a surface area of 776 m(2) g(-1).

Thanks to aqueous sol–gel chemistry, it is now possible to prepare several phase pure TiO 2 brookite colloidal systems that significantly differ on nanoparticles size and shape. This TiO 2 polymorph is more difficult to be obtained as phase pure material than anatase or rutile. Here we have prepared a set of four different sol–gel brookite syntheses with particles size ranging from 10 to 500 nm and significantly different morphologies as demonstrated by X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. We have studied their photocatalytic activities in aqueous solution on phenol and formic acid. The brookite sample with higher specific surface displays better activity for both pollutants abatement than anatase and rutile reference samples and very close to the TiO 2 P25 commercial reference. Additional experimental characterization of photogenerated charge carriers and their lifetime is performed using time-resolved microwave conductivity. We could then explain why another efficient brookite material is able to compensate a significantly lower specific surface with a higher photon conversion rate. This study involving a broad set of pure phase brookite samples brings back that phase into the TiO 2 polymorphs race for light-enhanced applications. It confirms that size/shape–activity correlation already observed for the anatase polymorph is also valid for the brookite phase.

We successfully prepared bifunctional catalysts with the distance between metallic and acid sites tuned at the nanometer scale. Sols of beta-zeolite nanoparticles were synthesized and mixed in optimized conditions with a gamma-AlOOH boehmite suspension to yield alumina/zeolite aggregates with a nanometer scale intimacy. The composition of the aggregate could be tuned from pure alumina to pure zeolite. Then, by carefully choosing the Pt precursor and the pH conditions, we were able to selectively deposit platinum, either on alumina or in zeolite domains. A subsequent, soft thermoreduction step was applied that produced well-dispersed Pt nanoparticles either on alumina or in the zeolite nanodomains as confirmed by 3D tomography microscopy experiments. The catalytic properties of the obtained nanostructured catalysts were studied through n-heptane conversion. Comparison of these original bifunctional catalysts with monofunctional or conventional bifunctional catalysts showed the impact of the location of the metallic particles on the selectivity.

The preparation of photocatalytic heterostructures of platinum on Bi2WO6 nanoparticles by a wet reduction method is described in this report and compared with other preparation methods. The as-obtained photocatalysts were characterized by XPS and TEM, the results of which confirmed the presence of solely zero-valent metal nanoparticles on the surface of Bi2WO6. The photocatalytic activity of these heterostructures was evaluated by the degradation of Rhodamine B under blue light (λmax = 445 nm). The deposited noble metal nanoparticles were shown to significantly improve the photocatalytic performance of the bismuth-based material under visible light. Both the preparation mode and the metal loading may impact on the efficiency. The observed photocatalytic enhancement has been attributed to an electron transfer from the semiconductor to the metal, which prevents fast electron/hole recombination. The electrons trapped in the metals may then participate in the multi-electron reduction of O2.

Anatase nanoparticles with shape controlled bipyramidal morphology (TiO2-A-bipy) exhibited mainly {101} facets were synthesized through the sol-gel method and then used for the photodegradation of three model pollutants - Rhodamine B, phenol and formic acid - under UV-A radiation exposure. These titania samples exhibit better photocatalytic efficiency than the commercial TiO2-P25 reference for the dye degradation while this one demonstrates a higher activity for both phenol and formic acid. Moreover, supplementary washings of the particles significantly enhanced their photocatalytic efficiency in any case. To better understand these differences in term of photoactivity and the role of the TiO2 surface according to the nature of the targeted organic pollutant, various characterization techniques such as XRD, TEM and N-2-sorption were used. Their surface properties were studied by FT-IR, TRMC and EPR. The presence of more acidic sites on TiO2-A-bipy surface could explain the faster degradation of the dye molecule through surface-mediated reactions. On the other side, a better generation and separation dynamic of photogenerated charges for TiO2-P25 could account for its higher photocatalytic efficiency for both formic acid and phenol degradation. This study shows that even if a quick test of dye degradation is mostly used in literature to confirm the efficiency of a photocatalyst, further investigation is often needed. (C) 2016 Elsevier B.V. All rights reserved.

We discuss here for the first time how to combine iron and titanium metal ions to achieve a high photoelectrochemical activity for TiO2-based photoanodes in water splitting devices. To do so, a wide range of photo electrode materials with tailored Ti/Fe ratio and element vicinity were synthesized by using the versatility of aqueous sol gel chemistry in combination with a microwave-assisted crystallization process. At low ferric concentrations, single phase TiO2 anatase doped with various Fe amounts were prepared. Strikingly, at higher ferric concentrations, we observed the concomitant crystallization of two polymorphs of Fe2TiO5. The as-synthesized compounds were tested as photoelectrodes and compared with pure nanoparticles of TiO2, Fe2TiO5, and alpha- or gamma-Fe2O3 and with corresponding nanocomposites. When TiO2 is slightly doped by Fe, the performance of this photoelectrode improves particularly in the low-bias region (<1.0 V vs reversible hydrogen electrode.) The photoanode exhibits a higher photocurrent than nanocomposite with TiO2/Fe2O3 and FeTi2O5 and more cathodic onset potential. The former can be partly explained by a lower bandgap and a hole with a longer lifetime. For the latter, we propose that the nature of the heterojunction impacts charge carrier recombination. The results presented herein not only answer whether iron and titanium should be combined in the same structure or into heterostructured systems but also on the importance of the arrangement of ions in the structure to improve the performances of the photoanode.

Bismuth vanadate has attractive photocatalytic properties under visible light. The influence of structure and morphology of BiVO4 nanomaterials on its photocatalytic properties in the UV and the visible domain was investigated. The selection of different sets of synthetic parameters in aqueous solutionpH or the use of organic additivesallowed the formation of tetragonal zircon, tetragonal scheelite, and monoclinic scheelite structure and different morphologies of that last phase. First, the tetragonal zircon was found to be the only inactive structure. Then, the best material for photocatalytic degradation of rhodamine B in solution and stearic acid deposited directly on the photocatalyst is the coreshell tetragonal zircon-monoclinic scheelite system prepared in the presence of sodium dodecyl sulfate. The enhanced properties are explained by the presence of strong surface acidic sites corresponding to the presence of surface sulfate residues rather than to the specific morphology of the material. Additionally, an EPR study on the ability of BiVO4 to generate active surface radical showed that hydroxyl radicals are not generated and that superoxide ion concentration under irradiation is close to the detection threshold. Depending on the selected irradiation wavelength, bismuth vanadate may present a better photocatalytic activity than titanium oxide. It is shown to be equivalent to bismuth tungstate under blue light.

The ecotoxicity of nanoparticles (NPs) is a growing area of research with many challenges ahead. To be relevant, laboratory experiments must be performed with well-controlled and environmentally realistic (i.e., low) exposure doses. Moreover, when focusing on the intensively manufactured titanium dioxide (TiO2) NPs, sample preparations and chemical analysis are critical steps to meaningfully assay NP's bioaccumulation. To deal with these imperatives, we synthesized for the first time TiO2 NPs labeled with the stable isotope (47)Ti. Thanks to the (47)Ti labeling, we could detect the bioaccumulation of NPs in zebra mussels (Dreissena polymorpha) exposed for 1 h at environmental concentrations via water (7-120 μg/L of (47)TiO2 NPs) and via their food (4-830 μg/L of (47)TiO2 NPs mixed with 1 × 10(6) cells/mL of cyanobacteria) despite the high natural Ti background, which varied in individual mussels. The assimilation efficiency (AE) of TiO2 NPs by mussels from their diet was very low (AE = 3.0 ± 2.7%) suggesting that NPs are mainly captured in mussel gut, with little penetration in their internal organs. Thus, our methodology is particularly relevant in predicting NP's bioaccumulation and investigating the factors influencing their toxicokinetics in conditions mimicking real environments.

The richness of titanium dioxide sol-gel syntheses described in literature provided a set of four different morphologies of pure anatase nanoparticles to study the impact of the exposed surfaces on the photocatalytic efficiency of the corresponding material. The selection of the experimental parameters such as the temperature, the heating method or organic additives allowed the synthesis of pure anatase materials with significantly different shapes. A thorough microscopic study of these particles gave the exposed crystallographic faces. The photocatalytic activity of the different materials was estimated following the degradation of the rhodamine B dye under UV-light and significantly different behaviors were observed. In the applied photodegradation conditions, two samples were shown to be more efficient than the reference photocatalyst P25. The rationalization of these results was done through the study of the oxide surface properties, using FT-IR spectroscopy with pyridine as a surface probe and the EPR analysis of photogenerated radicals under UV light. The most efficient photocatalyst for rhodamine B degradation was found to be the morphology presenting the stronger acidic surface sites. (C) 2015 Elsevier B.V. All rights reserved.

We introduce a magic-angle spinning NMR experiment to estimate specific distances in a solid material between a given site occupied by a quadrupolar nucleus and the nearby spin-1/2 nuclei. The new sequence, called DANTE-S-REDOR, consists of a frequency-selective dephasing experiment where heteronuclear dipolar couplings are reintroduced by applying a symmetry-based sequence (S-REDOR). The selectivity is achieved by applying a pulse train, such as Delays Alternating with Nutations for Tailored Excitation (DANTE), to the quadrupolar nucleus. This new method allows quantitative analysis of proximities in the 3-4 angstrom range of protons in OH ligands and one of the V-51 sites in a complex decavanadate cluster, namely Cs-4[H(2)V(10)O(28]center dot)4H(2)O. The high selectivity of the DANTE-S-REDOR sequence offers the possibility to investigate a wide range of materials with different quadrupolar nuclei, including polyoxometalates, oxides, zeolites, and aluminophosphates.