Shaoqing Jin

Effects of Zn2+ and Pb2+ dopants on the activity of Ga2O3-based photocatalysts for water splitting

Zn-doped and Pb-doped β-Ga2O3-based photocatalysts were prepared by an impregnation method. The photocatalyst based on the Zn-doped β-Ga2O3 shows a greatly enhanced activity in water splitting while the Pb-doped β-Ga2O3 one shows a dramatic decrease in activity. The effects of Zn(2+) and Pb(2+) dopants on the activity of Ga2O3-based photocatalysts for water splitting were investigated by HRTEM, XPS and time-resolved IR spectroscopy. A ZnGa2O4-β-Ga2O3 heterojunction is formed in the surface region of the Zn-doped β-Ga2O3 and a slower decay of photogenerated electrons is observed. The ZnGa2O4-β-Ga2O3 heterojunction exhibits type-II band alignment and facilitates charge separation, thus leading to an enhanced photocatalytic activity for water splitting. Unlike Zn(2+) ions, Pb(2+) ions are coordinated by oxygen atoms to form polyhedra as dopants, resulting in distorted surface structure and fast decay of photogenerated electrons of β-Ga2O3. These results suggest that the Pb dopants act as charge recombination centers expediting the recombination of photogenerated electrons and holes, thus decreasing the photocatalytic activity.

Nitrogen-doped layered oxide Sr5Ta4O15−xNx for water reduction and oxidation under visible light irradiation

Development of a photocatalyst with wide visible light absorption is of vital importance in solar-chemical energy conversion. In this work, we introduce a new nitrogen-doped layered oxide, Sr5Ta4O15−xNx, which exhibits a significantly extended absorption edge compared with the undoped oxide Sr5Ta4O15. The extension of the visible light absorption has been ascribed to the substitution of nitrogen for oxygen atoms as well as the formation of Ta–N bonds, which was confirmed by X-ray diffraction (XRD) patterns, X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Judged by the first principle calculation, the N 2p states mixed with pre-existing O 2p states shift the valence band maximum upward and result in wide visible light absorption. Band structure analysis combined with UV-Vis diffuse reflectance spectrum (DRS) and Mott–Schottky (M–S) measurement shows that the conduction and valence bands of Sr5Ta4O15−xNx are sufficient for water reduction and oxidation, respectively. The photocatalytic water splitting performances of Sr5Ta4O15−xNx are strongly related to the deposited cocatalyst. With an optimized cocatalyst, the Sr5Ta4O15−xNx shows both H2 and O2 evolution activities under visible light irradiation using CH3OH and AgNO3 as scavengers respectively. Following the optimized cocatalyst deposition of the Sr5Ta4O15−xNx, the cocatalyst-modified nitrogen-doped tantalum-based layered oxides Sr2Ta2O7−xNx and Ba5Ta4O15−xNx also exhibit activities for both the water splitting half reactions. This work demonstrates that the nitrogen-doped tantalum-based layered oxides may be a new type of potential photocatalyst with wide visible light absorption for solar water splitting.

Photo-induced H2 production from a CH3OH-H2O solution at insulator surface

In a conventional photocatalytic or photochemical process, either a photocatalyst or a molecule is excited by irradiation light that has energy greater than the forbidden band (i.e., the band gap) of the semiconductor or the transition energy of an excited state of the molecule, respectively, for a reaction to occur. However, in this work, we found that a considerable amount of H2 can be generated from a CH3OH-H2O solution at a quartz surface using light with energy far outside the electronic absorbance range of the CH3OH-H2O solution; this process should not occur in principle via either conventional photocatalysis or a photochemical process. The H2 production was further confirmed using 266 nm and 355 nm lasers as light sources. Our work demonstrates that photo-induced H2 production can occur on insulator surfaces (e.g., quartz), which were commonly believed to be inert, and will shed light on the surface nature of insulators.

UV Raman Spectroscopic Characterization of Catalysts and Catalytic Active Sites

UV Raman spectroscopy has been demonstrated to be a powerful technique in catalysis because it can avoid the fluorescence interference occurring in visible Raman spectroscopy and concurrently enhance the Raman scattering intensity owing to the short wavelength of the excitation laser and resonance Raman effect. This article briefly reviews the recent advances in the study on heterogeneous catalysis by UV Raman spectroscopy, including the identification of isolated transition metal ions in molecular sieves, in situ study of zeolite assembly mechanisms and catalytic reaction mechanisms, and the monitoring of the surface phase transformation of metal oxide photocatalysts. UV (resonance) Raman spectroscopy, with the power of resonance enhancement for Raman signal and the advantage of high sensitivity for surface structure, coupling with in situ methodology, can provide the information about the active sites/phase and their assembling mechanisms, which are helpful for the understanding of heterogeneous catalysis and the rational design of highly active and selective catalysts.Graphical Abstract

Note: Deep ultraviolet Raman spectrograph with the laser excitation line down to 177.3 nm and its application

Deep UV Raman spectrograph with the laser excitation line down to 177.3 nm was developed in this laboratory. An ellipsoidal mirror and a dispersed-subtractive triple monochromator were used to collect and disperse Raman light, respectively. The triple monochromator was arranged in a triangular configuration with only six mirrors used. 177.3 nm laser excited Raman spectrum with cut-off wavenumber down to 200 cm(-1) and spectral resolution of 8.0 cm(-1) can be obtained under the condition of high purity N2 purging. With the C-C σ bond in Teflon selectively excited by the 177.3 nm laser, resonance Raman spectrum of Teflon with good quality was recorded on the home-built instrument and the σ-σ(*) transition of C-C bond was studied. The result demonstrates that deep UV Raman spectrograph is powerful for studying the systems with electronic transition located in the deep UV region.

Effect of Pt cocatalyst in Pt/TiO2 studied by in situ FTIR of CO adsorption

In situ transmission infrared spectroscopy was used to study the role of pt cocatalyst in pt/tio2 using co as a probe molecule. an 11 cm(-1) redshift of co adsorbed on pt/tio2 was observed under irradiation in the absence of changes in the co coverage or sample temperature. in contrast, no co shift was detected on pt/al2o3. this indicates that the redshift of the co adsorption peak is due to the photogenerated electron transfer from tio2 to pt, and this accounts for the increased photocatalytic activity by the loaded pt cocatalyst. (c) 2014, dalian institute of chemical physics, chinese academy of sciences. published by elsevier b.v. all rights reserved.