High quality brookite TiO 2 nanorods have been obtained by the thermal hydrolysis of commercially available aqueous solutions of titanium bis(ammonium lactate) dihydroxide in the presence of high concentrations of urea (g6.0 M) as an in situ OHsource. Biphasial anatase/brookite mixtures are obtained at lower urea concentrations. The ratios between anatase and brookite can readily be tailored by the control of the urea concentration. The obtained powders have been characterized by X-ray diffraction, Raman spectroscopy, field emission-scanning electron microscopy, high-resolution transmission electron microscopy, UV-vis diffuse reflectance spectra, and nitrogen adsorption. The photocatalytic activity of pure anatase nanoparticles, of anatase/brookite mixtures, and of pure brookite nanorods has been assessed by hydrogen evolution from aqueous methanol solution as well as by the degradation of dichloroacetic acid (DCA) in aqueous solution. The results indicate that the photocatalytic hydrogen evolution activity of anatase/brookite mixtures and of pure brookite is higher than that of pure anatase nanoparticles despite of the lower surface area of the former. This behavior is explained by the fact that the conduction band edge of brookite phase TiO 2 is shifted more cathodically than that of anatase as experimentally evidenced under dark and UV-vis illumination conditions. On the contrary, in case of the photocatalytic degradation of DCA, anatase/brookite mixtures and pure brookite exhibit lower photocatalytic activity than pure anatase nanoparticles. This behavior correlates well with the surface area of the investigated powders.

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The surface modification of semiconductor photoelectrodes with passivation overlayers has recently attracted great attention as an effective strategy to improve the charge-separation and charge-transfer processes across semiconductor-liquid interfaces. It is usually carried out by employing the sophisticated atomic layer deposition technique, which relies on reactive and expensive metalorganic compounds and vacuum processing, both of which are significant obstacles toward large-scale applications. In this paper, a facile water-based solution method has been developed for the modification of nanostructured hematite photoanode with TiO2 overlayers using a water-soluble titanium complex (i.e., titanium bis(ammonium lactate) dihydroxide, TALH). The thus-fabricated nanostructured hematite photoanodes have been characterized by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Photoelectrochemical measurements indicated that a nanostructured hematite photoanodes modified with a TiO2 overlayer exhibited a photocurrent response ca. 4.5 times higher (i.e., 1.2 mA cm(-2) vs RHE) than that obtained on the bare hematite photoanode (i.e., 0.27 mA cm(-2) vs RHE) measured under standard illumination conditions. Moreover, a cathodic shift of ca. 190 mV in the water oxidation onset potential was achieved. These results are discussed and explored on the basis of steady-state polarization, transient photocurrent response, open-circuit potential, intensity-modulated photocurrent spectroscopy, and impedance spectroscopy measurements. It is concluded that the TiO2 overlayer passivates the surface states and suppresses the surface electron-hole recombination, thus increasing the generated photovoltage and the band bending. The present method for the hematite electrode modification with a TiO2 overlayer is effective and simple and might find broad applications in the development of stable and high-performance photoelectrodes.

The synthesis of Bi2WO6 inverse opal photonic crystals is performed via a facile and economical method. Bi2WO6 inverse opals exhibit much higher photocatalytic activities for the degradation of methylene blue and salicylicic acid under visible light illumination as compared with a reference nanofilm. The photon‐to‐hydrogen conversion efficiencies of photoelectrochemical water splitting exhibit an almost threefold increase due to the inverse‐opal structure.

a Titanium dioxide nanoparticles consisting of pure anatase, anatase-rich, brookite-rich, and pure brookite modifications were synthesized and characterized by X-ray diffraction, field emission-scanning electron microscopy and nitrogen adsorption. The phase transformations among the three modifications of TiO 2 (anatase, brookite, and rutile) and the photocatalytic activities of these nanoparticles were investigated by heat treatment over the temperature range from 400 to 800°C and by the photooxidation of methanol, respectively. Direct transformation of anatase and brookite to rutile was observed, while in the case of the anatase-brookite mixture, anatase transforms firstly to brookite and then to rutile. The photocatalytic activity measurements indicate that brookite nanoparticles exhibit higher photocatalytic activities than anatase, and a comparable activity to that of the anatase-rich nanoparticles. The phase transformations and photocatalytic results are discussed regarding their dependence on crystallite size, surface area, and phase composition.

Long-term investigations of the photocatalytic hydrogen production on platinized TiO 2 photocatalysts have been carried out employing different solutions of (deuterated) water and (deuterated) methanol. The results indicate that methanol acts as a sacrificial reagent, i.e., as an "electron donor" and that the amount of evolved molecular hydrogen is equivalent to the amount of H 2 expected from the complete reforming of methanol or even less depending on the used photocatalyst. No evidence for photocatalytic water splitting is observed even in the presence of very low methanol concentrations, i.e., no molecular oxygen has been detected. Based upon the isotopic labelling studies it was confirmed that H 2 is mainly produced by the reduction of protons originating from water. Broader contextRecently, growing environmental concern and an increasing energy demand are driving the search for new, sustainable sources of energy. In particular, solar molecular hydrogen (H 2 ) has attracted much attention because it can be regarded as a renewable and clean-burning energy source. Among the proposed technologies for its production, the photocatalytic conversion of biomass derived compounds is currently being discussed. For example, methanol is a biomass derivative from biological substrates and can be considered as a suitable hydrogen source since it contains a rather high hydrogen to carbon ratio (4 : 1). Even though its consumption during photocatalytic hydrogen production is accompanied by carbon dioxide formation, the thus produced carbon dioxide can again be converted into biomass through the plant photosynthesis. Hence, it has been stated that employing sacricial reagents, in particular biomass derived compounds, for hydrogen gas generation could be a useful intermediate step between the current fossil fuel consumption and the dream of an efficient direct photocatalytic water splitting utilizing solar energy. However, basic investigations aiming at understanding this system are still required for the realization of practical applications in the future.

Semiartificial photosynthesis integrates photosynthetic enzymes with artificial electronics, which is an emerging approach to reroute the natural photoelectrogenetic pathways for sustainable fuel and chemical synthesis. However, the reduced catalytic activity of enzymes in bioelectrodes limits the overall performance and further applications in fuel production. Here, we show new insights into factors that affect the photoelectrogenesis in a model system consisting of photosystem II and three-dimensional indium tin oxide and graphene electrodes. Confocal fluorescence microscopy and in situ surface-sensitive infrared spectroscopy are employed to probe the enzyme distribution and penetration within electrode scaffolds of different structures, which is further correlated with protein film-photoelectrochemistry to establish relationships between the electrode architecture and enzyme activity. We find that the hierarchical structure of electrodes mainly influences the protein loading but not the enzyme activity. Photoactivity is more limited by light intensity and electronic communication at the biointerface. This study provides guidelines for maximizing the performance of semiartificial photosynthesis and also presents a set of methodologies to probe the photoactive biofilms in three-dimensional electrodes.

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