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Mo6+ doping increases the photoelectrochemical performance of BiVO4 photoanodes in water oxidation. Herein, the underlying mechanisms is elucidated through a systematic structural, morphological, and photoelectrochemical investigation on photoelectrodes of pure and Mo6+ doped BiVO4 prepared by a novel multistep spin‐coating deposition approach, leading to multilayer flat films with high optical transparency. Transient absorption spectroscopy in the nano‐ to microsecond time scale reveals a longer lifetime of photogenerated holes in the doped films. Besides confirming that Mo6+ ions improve the electron transport in the material bulk, impedance spectroscopy also reveals the crucial role of the dopant on the surface properties of BiVO4 photoanodes. The presence of intra‐bandgap states, acting as traps of photogenerated charge carriers in pure BiVO4, is detected through the build‐up of the interfacial surface state capacitance. The limited activity of pure BiVO4 in water oxidation is largely improved upon 3 at% Mo6+ incorporation, ensuring a more efficient charge carrier transport with respect to pure BiVO4, together with the beneficial passivation of its trap surface states. [ABSTRACT FROM AUTHOR]

Researchers from Italy investigated the effects of humic acid on U(VI) reduction in aqueous solutions using laser induced fluorescence.

Synchronous and time-resolved fluorescence techniques proved useful in the investigation of low concentration metal ion-humic acid (HA) interactions. Comparable values of intrinsic binding constants for Tl(III) and Cr(III), regardless of pH, metal:ligand ratio and fluorescence method used, were obtained with the use of an electrostatic discrete site approach. Tl(III) and Cr(III) complexation results also revealed that other species may also bind to humic acids beside the aquo ion and the first hydroxo complex.

The ability of humic acid to function as a sensitizer during photoinduced reduction of Cr(VI) to Cr(III) in suspensions containing ZnO particles was investigated using equilibrium sorption studies. The results showed that Cr(VI) adsorption on ZnO was very low while Cr(III) was completely adsorbed on ZnO. Cr(VI) photoreduction was induced by solar irradiation and it led to a substantial increase in the volume of Cr adsorbed on the mineral oxide.

The performance of ZnFe2O4 photoanodes largely depends on their nanostructure, crystallinity and n-type doping, though decoupling their impact on photoactivity remains a challenge. Herein, the combined effects of the synthesis temperature and reductive annealing post-treatment on the photoelectrochemical performance of planar ZnFe2O4 photoanodes are investigated in relation to a comprehensive range of film thicknesses, enabled by an optimized sol–gel synthetic approach. By eliminating the effects of the nanostructure, a synergistic effect is revealed between the material crystallinity, controlled by the synthesis temperature, and the n-type doping triggered by the H2-treatment, which is maximum for the thickest photoactive layers. Intensity modulated photocurrent spectroscopy measurements performed in operando evidence the crucial impact of the synthesis temperature and the reductive treatment on inducing effective surface charge injection and improved bulk charge transport, respectively, to enhance the photoelectrochemical performance of planar ZnFe2O4 films. [ABSTRACT FROM AUTHOR]

The fast, single‐step and easily scalable production by plasma electrolytic oxidation (PEO) of large area TiO2 electrodes with excellent photoactivity in water splitting under simulated solar light is systematically investigated here. In particular, the effects that the cell voltage (100–180 V) and the processing time (0.5–15 min) have on the electrode properties are studied. The PEO‐produced oxide layers are porous, the predominant crystalline structure shifting from anatase, to an anatase‐rutile mixture, and finally to rutile by rising the cell voltage. The electrodes show a double‐layered structure, with a more compact layer at the interface with the titanium substrate and a thick porous layer on the external surface. The photocurrent density versus wavelength reflects the phase composition, with a maximum incident photon‐to‐current efficiency of 90% at 320 nm. The highest H2 production rate is attained with the mixed anatase‐rutile electrode prepared by 300 s‐long PEO at 150 V. [ABSTRACT FROM AUTHOR]