No abstract

No abstract

2 Graphical abstract Highlights: ZrO2-TiO2 heterojunction with high photocatalytic activity were obtained by solgel. Energy states at heterojunction interface altered the semiconducting properties. 5 mol% ZrO2 in ZrO2-TiO2 heterojunction propitiated a better electron-hole separation. Photocatalytic activity is improved by favoring the charge transfer process. Direct and indirect charge transfer process involved in phototocatalytic process. Abstract.In this paper, ZrO2-TiO2 composites were synthesized by sol-gel method with different ZrO2:TiO2 molar ratios (01:99, 05:95 and 10:90). The results identified two trends; at a low ZrO2 content, the incorporation of Zr 4+ into the TiO2 lattice was possible provoking generation of oxygen vacancies (1 mol % of ZrO2); while at higher ZrO2 contents, ZrO2-TiO2 heterojunctions were created (5 and 10 mol % of ZrO2). The photocatalytic activity was evaluated by measuring photodegradation of phenoxyacetic acid, 2,4-dichlorophenoxyacetic acid or 4-chlorophenol solutions. The ZT-5 composite shows the best performance attributed to surface states at the interface of ZrO2-TiO2 heterojunctions.These surface states act as traps for charge carriers favoring the spatial separation of electron-hole pairs until reaching a maximum in the composite with 5 mol% of ZrO2. The ZT-5 composite showed the most negative flat band potential and the highest donor density indicating that these surface states are in optimal concentration. At higher ZrO2 contents, charge carrier separation is less effective, which decreases the photocatalytic activity.Nevertheless, the molecule structure has an impact on the direct or indirect charge transfer process as was evidenced by EIS measurements.

BACKGROUND The technology for generating hydrogen using a photocatalyst has attracted considerable attention. Coupling TiO2 with other semiconductor oxides provided excellent results in decreasing recombination by transferring one of the charge carriers to another oxide. These photogenerated charge carriers play key roles in the reduction and oxidation process in photocatalytic hydrogen production. Nevertheless, even if the (e−‐h+) are separated, the reaction cannot happen without proper active sites. So, co‐catalysts are needed to improve the reduction and oxidation process on the surface of photocatalyst. RESULTS The hydrogen production of SnO2@TiO2 structure with CuO and CoO co‐catalysts (1 wt% of co‐catalyst: 1Co‐ST, 1Cu‐ST and 1Co‐1Cu‐ST) was studied under UV light, and characterized by XRD, N2 adsorption, UV‐vis reflectance diffuse, XPS and photoelectrochemical test. The dispersion of co‐catalyst on the surface of ST material during impregnation generates a decrease in the surface area and defect states in the optical properties. Maximum hydrogen production rate 1486.4 µmol g−1 h−1 is observed on 1Co‐1Cu‐ST photocatalyst. This improvement in photocatalytic reaction is related to the role played by each co‐catalyst. CONCLUSIONS The photocatalytic activity for H2 evolution shows the role of co‐catalyst in the redox reactions process. In the case of CuO co‐catalyst, it helps charge transfer, specifically electrons, to be carried out more efficiently by reducing water to produce H2. On the other hand, the role of CoO co‐catalyst is to catalyze the oxidation process, improving charge carriers separation and providing electrons to the SnO2@TiO2. © 2017 Society of Chemical Industry

Reaction rate for 4-nitrophenol photoreduction over ZrO2–TiO2 increases 19 times due to the synergistic interaction between methanol and sulfite ions.