Cristina Adán

Photoelectrocatalytic study and scaling up of titanium dioxide electrodes for wastewater treatment

Different TiO2 photoelectrodes have been characterized and tested for the photoelectrocatalytic oxidation of methanol. Particulate electrodes (TiO2/Ti and TiO2/ITO) have been shown to notably favour charge-carrier transfer at the electrolyte interface while a thermal electrode (Ti) has been shown to favour charge-carrier separation when applying an electric potential bias according to cyclic voltammetry technique, as a consequence of differences in TiO2 surface between particulate and thermal electrodes. Particulate electrodes lead to a higher photoelectrocatalytic activity for methanol oxidation compared to that of the thermal electrode, probably due to the pure-rutile TiO2 phase composition of the latter and its lower surface area. TiO2/Ti electrode has been shown to be the most effective photoelectrode tested for methanol oxidation since its activity was improved by the combination of the particulate TiO2 layer and the high electrical conductivity of the support. Generally, photocurrent density measured in the photoelectrochemical cell seems to correlate with activity, whereas this correlation is not observed when using a larger photoelectrocatalytic reactor. In contrast, the activity obtained for the scaled-up electrode is found to be similar in terms of surface kinetic constant to that obtained at laboratory scale.

Determination of Photochemical, Electrochemical and Photoelectrochemical Efficiencies in a Photoelectrocatalytic Reactor

Abstract The relation between the amount of incident photons, absorbed photons, oxidant species, reaction products and electrons in the external circuit should be analyzed individually to determine the step limiting the efficiency of the global photoelectrocatalytic processes. This work discusses the evaluation of three different titania electrodes for the oxidation of methanol in a photoelectrocatalytic reactor. The electrode prepared with three titania coating cycles shows a high efficiency in terms of photochemical (photons to product molecules), electrochemical (product molecules to electrons) and photoelectrochemical (photons to electrons) what explain its high activity for the photoelectrocatalytic oxidation of methanol.

Photocatalytic Activity of Suspended and Immobilized Niobium Oxide for Methanol Oxidation and Escherichia coli Inactivation

Abstract Materials based on niobium oxide (Nb2O5) have been shown to be alternative catalytic materials in heterogeneous photocatalytic processes for water treatment. Physicochemical characterization of a commercial Nb2O5 material was carried out to understand the impact on its photocatalytic activity, evaluated both in the photocatalytic oxidation of methanol and the inactivation of Escherichia coli bacteria under UVA. The Nb2O5 raw material showed an amorphous structure without X-ray diffraction signals. Thermal treatment of the material at temperatures above 550 °C leads to the formation of the orthorhombic phase of Nb2O5. However, annealing produce a significant aggregation of particles that reduced dramatically the surface area and the photocatalytic activity. The raw Nb2O5 material showed higher activity both for methanol oxidation and bacterial inactivation tests, being the latter very sensitive to the chemical composition of water. Immobilization of the photocatalyst in the walls of the photocatalytic reactor avoided the necessity of removal of the Nb2O5 particles after the treatment but decreases significantly the activity. In contrast, immobilization of the photocatalyst on a Raschig rings fixed-bed leads to a moderate decrease in activity (negligible in the presence of H2O2) that is counteracted by the improvement in the long term stability of the material.

Synthesis, Characterization, and Photonic Efficiency of Novel Photocatalytic Niobium Oxide Materials

Abstract The application of niobium oxides as photocatalytic materials for the removal of contaminants is scarcely reported in the literature. This work reports the methodology to synthesize four different mesoporous niobium oxide materials and the correlation between the physicochemical properties and the photocatalytic activity. X‐ray diffraction, UV–vis diffuse reflectance spectra (DRS), transmission electron microscopy, and nitrogen adsorption techniques are used to characterize the structure and composition of the obtained materials. The photocatalytic oxidation of methanol is used as reaction test to assess the photocatalytic activities and photonic efficiencies of the materials as a function of the catalyst concentration. Nb2O5 materials display lower reaction rates, which can be attributed to the relatively high average particle size. By contrast, NaNbO3 materials show higher activity, especially for high catalyst loading. No significant differences in absorption and scattering of light are observed among the materials, indicating that the higher photonic efficiency of NaNbO3 should be the result of a lower charge recombination derived from its microstructure, sodium composition, low particle size, and high specific surface area of these materials.