A low-cost hydrothermal method was used to synthesize high-purity bipyramidal single-crystals of TiO₂ enclosed with high percentage of (101) facets. The oriented attachment behavior can be controlled by fine tuning the reaction temperature. This played an important role in determining the crystal growth along [001] direction resulting in the self-assembly of the bipyramid crystals into connected ones to form single-crystal nanrods without the loss of surface area. In addition, the relationship between oriented attachment and the photovoltaic performance of such anatase TiO₂ nanocrystals in photoanodes of DSCs was investigated. The highly oriented sample reached a maximum overall energy conversion efficiency of 8.63 %. These results further illustrated that the highly oriented samples have superior charge transport ability derived from the enhanced long-range atomic arrangement with reduced grain boundaries and comparable uptake of dye molecules.

The process of using solar energy to split water to produce hydrogen assisted by an inorganic semiconductor is crucial for solving our energy crisis and environmental problems in the future. However, most semiconductor photocatalysts would not exhibit excellent photocatalytic activity without loading suitable co-catalysts. Generally, the noble metals have been widely applied as co-catalysts, but always agglomerate during the loading process or photocatalytic reaction. Therefore, the utilization efficiency of the noble co-catalysts is still very low on a per metal atom basis if no obvious size effect exists, because heterogeneous catalytic reactions occur on the surface active atoms. Here, for the first time, we have synthesized isolated metal atoms (Pt, Pd, Rh, or Ru) stably by anchoring on TiO₂, a model photocatalystic system, by a facile one-step method. The isolated metal atom based photocatalysts show excellent stability for H₂ evolution and can lead to a 6–13-fold increase in photocatalytic activity over the metal clusters loaded on TiO₂ by the traditional method. Furthermore, the configurations of isolated atoms as well as the originality of their unusual stability were analyzed by a collaborative work from both experiments and theoretical calculations.

Invited for the cover of this issue is the group of Hua Gui Yang at the East China University of Science and Technology. The image depicts the stable single Pt atoms on TiO₂ as active sites for photocatalytic hydrogen production. Read the full text of the article at 10.1002/chem.201303366.

The successful design of photocatalytic hydrogen generation from water relies on a thorough understanding of the role of cocatalyst. The photoreactivity was studied as a function of the cluster size of the oxidized platinum cocatalyst. The maximum turnover frequency is found on the smallest-sized cocatalyst. This effect can be attributed to the size-dependent proton adsorption.

Fluorine-doped hierarchical porous single-crystal rutile TiO₂ nanorods have been synthesized through a silica template method, in which F⁻ ions acts as both n-type dopants and capping agents to make the isotropic growth of the nanorods. The combination of high crystallinity, abundant surface reactive sites, large porosity, and improved electronic conductivity leads to an excellent photoelectrochemical activity. The photoanode made of F-doped porous single crystals displays a remarkably enhanced solar-to-hydrogen conversion efficiency (≈0.35 % at −0.33 V vs. Ag/AgCl) under 100 mW cm⁻² of AM=1.5 solar simulator illumination that is ten times of the pristine solid TiO₂ single crystals.

Anatase TiO₂ as a promising photocatalyst has been widely employed in the decontamination treatment of polluted water, air purification and water splitting. Coupling TiO₂ with other semiconductor materials could further enhance the photocatalytic activity. Here, we successfully synthesized the SnO₂/TiO₂ catalyst by depositing SnO₂ particles on the anatase TiO₂ {105} facets through a gas phase oxidation process. The SnO₂/TiO₂ catalyst shows higher photocatalytic activity for decomposition of MB than that of the pure TiO₂ catalyst. The enhanced photocatalytic activity can be attributed to the efficient charge separation since TiO₂ and SnO₂ catalyst have staggered energy level.

In this paper, band-structure matching strategy of a TiO₂-based heterojunction within which electrons can be collected from TiO₂ nanoparticles and transported rapidly in the bulk structure is reported. On the basis of the band-structure analysis of different TiO₂-based heterostructures, focus was directed to the SnO₂ nanosheet because of its appropriate band position and high electrical conductivity. Through a systematic investigation of the incorporation of ultrathin SnO₂ nanosheet scaffolds for TiO₂-based photoanodes in dye-sensitized solar cells (DSCs), we propose an anisotropy “constrained random walk” model to describe the controlled electron transit process. In this system, electrons are transferred orientedly overall, as well as randomly locally, leading to a significant reduction in the charge diffusion route compared to the conventional isotropic “random walk” model. In brief, the 2D ultrathin nanosheets provide rapid transit pathways and improved light-scattering centers, which can ensure a sufficient amount of dye loading and slow recombination. An overall light-to-electricity conversion efficiency as high as 8.25 % is achieved by embedding the appropriate amount of SnO₂ scaffold in a TiO₂-based photoanode.

Multicomponent CuCu₂OTiO₂ nanojunction systems were successfully synthesized by a mild chemical process, and their structure and composition were thoroughly analyzed by X-ray diffraction, transmission electron microscopy, field-emission scanning electron microscopy, and X-ray photoelectron spectroscopy. The as-prepared CuCu₂OTiO₂ (3 and 9 h) nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of the degradation of organic compounds than those of the CuCu₂O, CuTiO₂, and Cu₂OTiO₂ starting materials. Moreover, time-resolved photoluminescence spectra demonstrated that the quenching times of electrons and holes in CuCu₂OTiO₂ (3 h) is higher than that of CuCu₂OTiO₂ (9 h); this leads to a better photocatalytic performance of CuCu₂OTiO₂ (3 h). The improvement in photodegradation activity and electron–hole separation of CuCu₂OTiO₂ (3 h) can be ascribed to the rational coupling of components and dimensional control. Meanwhile, an unusual electron–hole transmission pathway for photocatalytic reactions over CuCu₂OTiO₂ nanojunctions was also identified.

Magnetic-luminescent nanocomposites have obtained a great deal of attention due to their potential applications in magnetic separation of cells, magnetic resonance imaging and luminescence imaging, and so on. Herein, a new and facile two-step synthetic strategy was developed to prepare magnetic Fe₃O₄ modified single crystalline up-conversion luminescent NaYF₄: Yb³⁺, Er³⁺ nanocrystals using Fe₃O₄ nanoparticles as the seeds. Acting as the "nuclei" in the reaction, the presence of Fe₃O₄ nanoparticles facilitates the formation of up-conversion NaYF₄: Yb³⁺, Er³⁺ nanocrystals on their surfaces through heterogeneous nucleation process. The structure and properties of these multifunctional nanocrystals were characterized by transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), photo luminescence (PL) and X-ray diffraction (XRD). The results revealed that the as-prepared multifunctional nanocrystals show dual distinct properties of up-conversion fluorescent and superparamagnetism, which were cubic in shape and very uniform in size with an average size ranging 30–40 nm. These unique functionalities could be very attractive for biological systems, and some biological applications such as cell-labelling were also demonstrated.

Photocatalytic water splitting using semiconductor photocatalysts has been considered as a “green” process for converting solar energy into hydrogen. The pioneering work on electrochemical photolysis of water at TiO₂ electrode, reported by Fujishima and Honda in 1972, ushered in the area of solar fuel. As the real ultimate solution for solar fuel-generation, overall water splitting has attracted interest from researchers for some time, and a variety of inorganic photocatalysts have been developed to meet the challenge of this dream reaction. To date, high-efficiency hydrogen production from pure water without the assistance of sacrificial reagents remains an open challenge. In this Focus Review, we aim to provide a whole picture of overall water splitting and give an outlook for future research.