Search

[Display omitted]

The aim of this work was to obtain an in-depth understanding of the U(VI) adsorption mechanism over amino-functionalized mesoporous silica SBA-15 and highlights its high efficiency in aqueous media for U(VI) removal and preconcentration. The samples were synthesized and functionalized by both grafting and co-condensation methods, using different alkyl-substituted amine groups and were characterized using X-ray diffraction, N2physisorption, Fourier transform infrared spectroscopy, and elemental C–H–N–S analyses. The properties for U(VI) adsorption were evaluated under discontinuous conditions, with the determination of the effect of several parameters (initial pH, contact time, initial U(VI) concentration, functionalization method, and organic moiety composition). U(VI) adsorption over grafted materials reached equilibrium at around 30 min, with a maximum adsorption capacity of 573 mgU·gads–1for the most efficient material at its optimal adsorption pH (equal to 6) at 20 °C. Functionalized materials by grafting exhibit better adsorption capacities than co-condensed samples because of higher function surface density and function availability. U(VI) adsorption mechanisms were also studied by measuring the electrophoretic mobilities of the particles, aqueous U(VI) speciation, in situ attenuated total reflection infrared and Raman spectroscopies, and transmission electron microscopy analysis. U(VI) adsorption occurred through the formation of an inner sphere complex. The localization of adsorbed U(VI) has also been determined inside of the mesopores, with the formation of several particles on the nanometer scale, in the size of U-hydroxy phases. Besides, the study of the reusability of amino-functionalized SBA-15 by applying adsorption–desorption cycles was also conducted. The adsorption capacity of the material remains stable for at least four adsorption–desorption cycles without any noticeable capacity decrease.

A bimetallic cobalt molybdenum sulfide (Co0.5Mo0.5Sx) material was studied as candidate electrocatalyst to replace platinum-based cathode for HER reaction in alkaline media. The Co0.5Mo0.5Sxwas obtained from a hydrothermal synthesis methodology employing sodium diethyldithiocarbamate as sulfurizing agent, a non-conventional compound. The recovered sulfide material was physicochemically characterized by XRD, Raman spectroscopy, TEM and XPS measurements. Analogous monometallic sulfides were also synthesized to compare their HER activities to that of Co0.5Mo0.5Sx. Such electrochemical characterization was performed by the application of polarization and EIS analyzes in 1 M KOH. An evident synergistic effect emerged in the bimetallic sulfide and it was associated with the design of a catalyst less susceptible to air-oxidation added to the roles performed by cobalt- and molybdenum-based species in the HER mechanism. Finally, a physical mixture of Co0.5Mo0.5Sxand Carbon Vulcan was prepared aiming to enhance the electronic conductivity of the electrode. As result, an overpotential of 131 mV was requested to achieve −10 mA cm−2. In addition, to achieve −200 mA cm−2, this electrode only needed an overpotential 66 mV higher than the one necessary for the benchmarking 40% Pt/C electrocatalyst.

Mesoporous Co3O4mixed CoO onto reduced graphene oxide (rGO) nanocomposites were obtained by an easy surfactant-free synthesis using urea as hydrolyzing agent. This route enabled nanomaterials presenting tuned morphology, surface composition and oxide-rGO interactions as revealed by the different characterization techniques. Indeed, nanostructures varied from broom-like, chrysanthemum-like to micro-sized sheet-like morphologies. The amount of Co3O4phase was shown to be gradually rising as the urea amount increases being always higher at the surface than in the bulk. Different oxide-rGO interactions have also been demonstrated, suggesting that high amounts of urea cause a decrease in the size of the nanoparticles and limit their superposition. The catalysts prepared at high urea concentrations showed more exposed electroactive surface and enhanced activity as bifunctional oxygen electrocatalysts. Furthermore, the most active nanocomposite exhibited remarkable stability, making it a very promising candidate for the elaboration of a stable and truly reversible air electrode in alkaline media.