Magnetic photocatalysts were synthesized by coating titanium dioxide particles onto colloidal magnetite and nano-magnetite particles. The photoactivity of the prepared coated particles was lower than that of singlephase TiO 2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavorable heterojunction between the titanium dioxide and the iron oxide core, leading to an increase in electron-hole recombination. Interactions between the iron oxide core and the titanium dioxide matrix upon heat treatment were also seen as a possible cause of the observed low activities of these samples. Other issues considered include the physical and chemical characteristics of the samples, such as surface area and the presence of surface hydroxyl groups. Depending on the calcination conditions, these photocatalysts were found to suffer from varying degrees of photodissolution. Photodissolution tests revealed the greater the extent of the heat treatment, the lower the incidence of photodissolution. This was explained in terms of the stability of the iron oxide phases present, as well as the photoactivity of the titanium dioxide matrix. Our studies revealed that the observed photodissolution was in fact to be induced photodissolution. That is, the photogenerated electrons elevated to the conduction band of the titanium dioxide nanocrystals were being injected into the lower lying conduction band of the iron oxide core, leading to its reduction.

No abstract

The development of bifunctional water‐splitting electrocatalysts that are efficient and stable over a wide range of pH is of great significance but challenging. Here, an atomically dispersed Ru/Co dual‐sites catalyst is reported anchored on N‐doped carbon (Ru/Co–N–C) for outstanding oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in both acidic and alkaline electrolytes. The Ru/Co–N–C catalyst requires the overpotential of only 13 and 23 mV for HER, 232 and 247 mV for OER to deliver a current density of 10 mA cmgeo−2 in 0.5 m H2SO4 and 1 m KOH, respectively, outperforming benchmark catalysts Pt/C and RuO2. Theoretical calculations reveal that the introduction of Co–N4 sites into Ru/Co–N–C efficiently modify the electronic structure of Ru by enlarging Ru–O covalency and increasing Ru electron density, which in turn optimize the bonding strength between oxygen/hydrogen intermediate species with Ru sites, thereby enhancing OER and HER performance. Furthermore, the incorporation of Co–N4 sites induces electron redistribution around Ru–N4, thus enhancing corrosion–resistance of Ru/Co–N–C during acid and alkaline electrolysis. The Ru/Co–N–C has been applied in a proton exchange membrane water electrolyzer and steady operation is demonstrated at a high current density of 450 mA cmgeo−2 for 330 h.

No abstract

The kinetics of UV/TiO 2 photocatalytic reduction of Se(VI) in the presence of formic acid was investigated. Competitive adsorption models for the Se(VI) and HCOOions onto the same active sites on TiO 2 surface were derived, based on the adsorption of one Se(VI) ion onto two adsorptive sites. The use of the above adsorption models allows for the modeling of the Se(VI) photoreduction rates on the basis of the Langmuir-Hinshelwood (LH) reaction mechanism. The new model was able to represent the experimental data reasonably well, and it supported the experimental observation that the optimum Se(VI) photoreduction rate occurred at the molar adsorption ratio of formate-to-Se(VI) ions of approximately 3:1. A composite rate expression incorporating the effect of catalyst loading was also presented.