Yangen Zhou

Monolayered Bi2WO6 nanosheets mimicking heterojunction interface with open surfaces for photocatalysis.

Two-dimensional-layered heterojunctions have attracted extensive interest recently due to their exciting behaviours in electronic/optoelectronic devices as well as solar energy conversion systems. However, layered heterojunction materials, especially those made by stacking different monolayers together by strong chemical bonds rather than by weak van der Waal interactions, are still challenging to fabricate. Here the monolayer Bi2WO6 with a sandwich substructure of [BiO]+–[WO4]2−–[BiO]+ is reported. This material may be characterized as a layered heterojunction with different monolayer oxides held together by chemical bonds. Coordinatively unsaturated Bi atoms are present as active sites on the surface. On irradiation, holes are generated directly on the active surface layer and electrons in the middle layer, which leads to the outstanding performances of the monolayer material in solar energy conversion. Our work provides a general bottom-up route for designing and preparing novel monolayer materials with ultrafast charge separation and active surface.

Gold-plasmon enhanced solar-to-hydrogen conversion on the {001} facets of anatase TiO2 nanosheets

A 64-fold improved efficiency of solar-to-hydrogen conversion (SHC) was achieved via exposing Au nanoparticles (NPs) on the {001} facets of anatase TiO2 nanosheets. The SHC follows a surface plasmon resonance-mediated electron injection mechanism, where Au NPs can not only harvest visible light and convert them to free energetic electrons, but promote the SHC by increasing the electron–hole pair formation rate driven by the electromagnetic field formed nearby the semiconductor.

Bi2MoO6 Nanobelts for Crystal Facet‐Enhanced Photocatalysis

γ-Bi2MoO6 single-crystal nanobelts with dominant {010} facets exhibit facet-enhanced photocatalytic property for the photodegradation of dye pollutants under visible light irradiation. The charge carriers are more efficiently separated on the low-index facets due to the exposure of more photoactive sites to the reacting substrates.

Probing the Electronic Structure and Photoactivation Process of Nitrogen‐Doped TiO2 Using DRS, PL, and EPR

The electronic structure and photoactivation process in N-doped TiO(2) is investigated. Diffuse reflectance spectroscopy (DRS), photoluminescence (PL), and electron paramagnetic resonance (EPR) are employed to monitor the change of optical absorption ability and the formation of N species and defects in the heat- and photoinduced N-doped TiO(2) catalyst. Under thermal treatment below 573 K in vacuum, no nitrogen dopant is removed from the doped samples but oxygen vacancies and Ti(3+) states are formed to enhance the optical absorption in the visible-light region, especially at wavelengths above 500 nm with increasing temperature. In the photoactivation processes of N-doped TiO(2), the DRS absorption and PL emission in the visible spectral region of 450-700 nm increase with prolonged irradiation time. The EPR results reveal that paramagnetic nitrogen species (N(s)·, oxygen vacancies with one electron (V(o)·), and Ti(3+) ions are produced with light irradiation and the intensity of N(s)· species is dependent on the excitation light wavelength and power. The combined characterization results confirm that the energy level of doped N species is localized above the valence band of TiO(2) corresponding to the main absorption band at 410 nm of N-doped TiO(2), but oxygen vacancies and Ti(3+) states as defects contribute to the visible-light absorption above 500 nm in the overall absorption of the doped samples. Thus, a detailed picture of the electronic structure of N-doped TiO(2) is proposed and discussed. On the other hand, the transfer of charge carriers between nitrogen species and defects is reversible on the catalyst surface. The presence of oxygen-vacancy-related defects leads to quenching of paramagnetic N(s)· species but they stabilize the active nitrogen species N(s)(-).

Self-assembly synthesis of LaPO4 hierarchical hollow spheres with enhanced photocatalytic CO2-reduction performance

Urchin-like LaPO4 hollow spheres were successfully synthesized by a facile solution route using citric acid (CA) as a structure-directing agent. The size of the three-dimensional (3D) hollow spheres was tuned by changing the concentration of CA. The formation mechanism of the 3D LaPO4 hollow spheres was revealed by studying the time-dependent morphology evolution process. Importantly, compared with monodispersed one-dimensional (1D) LaPO4 nanorods, the 3D LaPO4 hollow spheres self-assembled from nanorods showed a 6.8-fold enhancement in photocatalytic activity for CO2 reduction, which is attributed to the synergistic effect of their hierarchical hollow structure, higher light-harvesting capacity, and faster electron transfer. Our findings provide not only a simple, facile method for the synthesis of hierarchical hollow micro/nanoarchitectures but also an efficient route for enhancing the photocatalytic performance.

A novel Zn2GeO4 superstructure for effective photocatalytic hydrogen generation

Crystal orientation-ordered hexagonal Zn2GeO4 nanorod-bundles have been obtained via a synergistic self-assembly route. Each nanorod unit of the bundles maintains its individual hexagonal rod-shaped structure and is dominated by (110) and (0) facets, and all of them are aligned parallel to the growth direction in a high density. An ordered self-assembly of anisotropic nanorods was suggested to elucidate the formation of the unique bundle structures. The novel structure of Zn2GeO4 bundles assembled from hexagonal nanorods leads to a surprisingly high UV-light-driven activity for the photocatalytic decomposition of water–methanol solution to hydrogen. The correlation of structure and photocatalytic activity of the ordered nanorod-bundles was discussed, indicating a new strategy of bundling Zn2GeO4 nanorods with reactive facets to effectively enhance photocatalytic activities of 1-D nanostructures.

Photoinduced Reactions between Pb3O4 and Organic Dyes in Aqueous Solution under Visible Light

Pb(3)O(4) could react with organic dyes in aqueous solution under visible light irradiation, in which Pb(3)O(4) was transformed into Pb(3)(CO(3))(2)(OH)(2) along with oxidation of the organic dyes. Cu(2+) has considerable effect on the reaction. In the presence of Cu(2+), MO (20 ppm) and RhB (10(-5) mol L(-1)) were completely degraded under visible light within 6 and 20 min, respectively, while both Pb(3)O(4) and Cu(2+) keep almost stable during photodegradation. The mechanisms of the reactions with and without Cu(2+) ions were studied. The photochemical system of Pb(3)O(4) cooperating with Cu(2+) ions is probably used for the treatment of organic pollutants in water under visible light.

Enhanced photocatalytic CO2 conversion over LaPO4 by introduction of CoCl2 as a hole mediator

The photocatalytic CO2 reduction over LaPO4 was significantly enhanced by simply introducing CoCl2 into the aqueous medium. The introduced CoCl2 functioned as a co-catalyst accelerating photogenerated hole transfer, by the reversible redox couple CoIII–Cl/CoII–Cl, effectively suppressing the recombination of photogenerated charges.

Influence of Surface States on the Evaluation of the Flat Band Potential of TiO2

Flat band potential (Vfb) is one of the most important physical parameters to study and understand semiconductor materials. However, the influence of surface states on the evaluating Vfb of titanium oxide (TiO2) and other semiconductor materials through a Mott-Schottky plot is ignored. Our study indicated that the influence of surface states should be introduced into the corresponding equivalent circuit even when the kinetic process did not occur. Ignoring the influence of surface states would lead to an underestimation of the space charge capacitance. Our paper would be beneficial for accurate determination of Vfb of semiconductor materials. We anticipate that this preliminary study will open new perspectives in understanding the semiconductor-electrolyte interface.

One-step synthesis of mesoporous Pt–Nb2O5 nanocomposites with enhanced photocatalytic hydrogen production activity

Mesoporous Pt–Nb2O5 photocatalysts with high photocatalytic hydrogen production activity were synthesized by a one-step method. The mesoporous structure of the as-made samples was characterized by X-ray diffraction, N2 adsorption–desorption isotherms and transmission electron microscopy. Pt–Nb2O5 exhibited higher hydrogen production activity than pure Nb2O5 and 0.8-Pt–D–M–Nb exhibited the best photocatalytic activity. In addition, Pt–Nb2O5 synthesized by a one-step method exhibited higher photocatalytic hydrogen production activity than that prepared by an incipient wetness impregnation method; 0.8-Pt–D–M–Nb exhibits a H2 evolution rate of 9.79 mmol h−1 g−1, while 0.8-Pt–I–M–Nb2O5 exhibits a H2 evolution rate of 7.73 mmol h−1 g−1. The enhanced photocatalytic activity of Pt–Nb2O5 was predominantly attributed to the efficient separation of photoinduced electrons and holes.