The Sun generates enough energy to power the Earth. However, solar energy should be stored into chemical energy to be conveniently used due to its low energy density and discontinuous radiation. In the last several years, photocatalysis and photoelectrochemistry for solar fuels have reattracted more and more governments’ and people’s interest from all over the world and become a very hot topic. If we utilize the abundant solar energy to convert CO2 into hydrocarbon fuels especially, it would address the problems of global climate change and solar energy storage at the same time. Recently, different new materials and ideas have been proposed and steady scientific progress has been done. However, it is still a key challenge to explore visible-light responsive materials with high photocatalytic activities. The special issue contains eight papers, where 6 papers are related to visible-light activity and 2 papers are related to UV activity.
In a paper entitled “Development of thin film amorphous silicon tandem junction based photocathodes providing high open-circuit voltages for hydrogen production” by F. Urbain et al., they prepare the a-Si:H/a-Si:H based photocathodes, which exhibit a high photocurrent onset potential of 1.76 V versus the reversible hydrogen electrode (RHE) and a photocurrent of 5.3 mA/cm2 at 0 V versus RHE. They provide an efficient and low-cost route to solar hydrogen production.
In a paper entitled “Bottom-up enhancement of g-C3N4 photocatalytic H2 evolution utilising disordering intermolecular interactions of precursor” by X. L. Wang et al., they develop a bottom-up strategy to synthesize g-C3N4 photocatalysts with improved optical property and chemical structure through using disordered dicyandiamide (D-DCDA) as reaction precursor. The carbon nitride sample condensed by D-DCDA indicates higher photocatalytic activity for hydrogen evolution due to looser structure and more effective light harvesting and charge separation efficiency.
In a paper entitled “Structure, optical properties, and photocatalytic activities towards H2 generation and CO2 reduction of GaN nanowires via vapor-liquid-solid process” by H. Pang et al., they synthesize high quality single crystalline GaN nanowires with large aspect ratio on n-type Si (111) substrate via the Au-catalyzed vapor-liquid-solid process. Photocatalytic H2 evolution and CO2 reduction over the as-prepared GaN nanowires are also investigated. Their results suggest that the GaN nanowires greatly enhanced capability compared to the GaN powders.
In a paper entitled “Band-gap engineering of NaNbO3 for photocatalytic H2 evolution with visible light” by P. Li et al., they shift the photoabsorption edge of NaNbO3 to the visible-light region by La and Co codoping. Moreover, H2 is successfully generated over the doped NaNbO3 samples under visible-light irradiation. Density-functional theory calculations show that Co-induced impurity states are formed in the band gap of NaNbO3, which is considered to be the origin of visible-light absorption upon the doped NaNbO3 sample.
In a paper entitled “Sensitization of perovskite strontium stannate SrSnO3 towards visible-light absorption by doping” by H. Chen and N. Umezawa, they calculate electronic structures of SrSnO3 after Cr3+, Fe3+, and Rh3+ and anions N3−, N2−, and S2− doping. Among all considered cation dopants, Rh3+ gives rise to the deep in gap states. The transition from Rh3+ to SrSnO3 conduction band is 0.89 eV lower than the band gap.
In a paper entitled “Surfactant-free synthesis of single crystalline SnS2 and effect of surface atomic structure on the photocatalytic property” by M. Li et al., they prepare sheet like tin disulfide SnS2 single crystal exposed with well-defined facets and flowerlike SnS2 mainly exposed with facets through a surfactant-free solvothermal process. The sheet like SnS2 showed a much higher photocatalytic activity in degradation of methyl orange than flowerlike SnS2. Theoretical and experimental results reveal that the band structure derived from the surface atomic structure played a more important role than the surface energy in the photocatalytic property.
In a paper entitled “Preparation of cerium modified titanium dioxide nanoparticles and investigation of their visible light photocatalytic performance” by J. Liu et al., they prepare CeOx/TiO2 by the hydrothermal-calcination method. The Ce ions have the two valence states, Ce3+ and Ce4+, which can act as the electron acceptor to improve the separation efficiency of the photogenerated electron-hole pairs.
In a paper entitled “Visible-light degradation of dyes and phenols over mesoporous titania prepared by using anthocyanin from red radish as template” by Z. Yan et al., they prepare highly crystalline mesoporous titania by using a natural pigment from red radish as template. The prepared mesoporous titania photocatalyst exhibited significant activity under visible-light irradiation for the degradation of dyes and phenols due to its red shift of band-gap-absorption onset and visible-light response as a result of the incorporation of surface carbon species.
Acknowledgment
We would like to thank all of the authors and the reviewers for their contributions to this special issue.
Zhigang Zou
Jinhua Ye
Michael R. Hoffmann
Wenjun Luo