Tengfei Jiang

Carrier concentration-dependent electron transfer in Cu2O/ZnO nanorod arrays and their photocatalytic performance

In this paper, we have engineered the interface electronic structure in Cu2O/ZnO nanorod arrays, via adjusting the carrier concentration of Cu2O, and applied them to photocatalysis. The photoinduced charge transfer kinetics at the interface between Cu2O and ZnO were systematically investigated. The Cu2O (pH 11.0)/ZnO nanorod arrays have the largest magnitude of interfacial electric field, and photoinduced charge carriers can be separated rapidly and efficiently, which generates the highest photocatalytic efficiency for the reduction of methylviologen. Heterojunction construction is an exciting direction to pursue for highly active photocatalysts, and also offers opportunities to investigate the relationship between the electronic structure and the photocatalytic performance.

Synthesis of highly efficient C-doped TiO(2) photocatalyst and its photo-generated charge-transfer properties.

Carbon-doped anatase TiO(2) was prepared by a facile hydrothermal process without adding additional carbon source. The as-prepared sample shows highly efficient photocatalytic activity, which only requires 4min and is about 11 times higher than that of Degussa P25 TiO(2) in degradation of methyl orange (MO) dye under UV light irradiation. Moreover, a highly visible-light activity is also observed. UV-vis diffuse reflectance spectra and X-ray photoelectron spectroscopy confirm that the carbon atoms are incorporated into the interstitial positions of TiO(2) lattice and form a strong interaction with titanium atoms and extend photoresponding range to 700nm. Surface photovoltage spectra (SPS) and transient photovoltage (TPV) suggest that the presence of interstitial carbons induce several localized occupied states in the gap, enhance the separation extent and restrain the recombination of the photo-induced electron and hole carriers in TiO(2).

Surface treatment with Al3+on a Ti-doped α-Fe2O3 nanorod array photoanode for efficient photoelectrochemical water splitting

In this paper, we present the fabrication of Ti-doped α-Fe2O3 and surface treatment with Al3+ for application as a photoanode in photoelectrochemical water splitting. The Ti-doped α-Fe2O3 with Al3+ treatment shows a 100 mV cathodic shift of the onset potential and a notable improvement of the photocurrent density. The samples were characterized by SEM, TEM, HRTEM, XRD, Raman, UV-vis and XPS to obtain the information after surface treatment. Based on electrochemistry and photoelectrochemistry techniques, it appears that surface treatment with Al3+ passivates the surface states and decreases the accumulation of charge at the surface of Ti–Fe2O3. The results show that Ti-doped Fe2O3 with Al3+ surface treatment can be used as an efficient photoanode for photoelectrochemical water splitting.

Study on formaldehyde gas-sensing of In2O3-sensitized ZnO nanoflowers under visible light irradiation at room temperature

In2O3-sensitized flowerlike ZnO with visible light photoelectric response properties were synthesized by a facile two-step process, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), EDAX, HRTEM and UV-vis diffuse reflectance spectroscopy. The results revealed that In2O3 nanoparticles have grown and eventually coalesced on the surface of the flowerlike ZnO successfully, and the samples exhibited significant response to visible light. The photoelectric gas-sensing of the In2O3-sensitized ZnO was also studied to formaldehyde (HCHO) under 460 nm light irradiation at room temperature with the help of surface photocurrent technique. It was found that ZnO sensitized with In2O3 could enhance the gas response to HCHO under the visible light illumination. This may be due to the fact that the composite structure of In2O3–ZnO extends the photo absorbing range to visible light area, inhibits the recombination of photo-generated electrons and holes, and thus increases the utilization of photo-generated carriers in photoelectric gas detection, resulting in the higher sensing response in some extent. The gas response to 5 ppm and 100 ppm formaldehyde can reach to 19% and 419% under visible light irradiation at room temperature, respectively. These results should be valuable for designing a new type of visible-light assisted gas sensor at room temperature.

Construction of Shallow Surface States through Light Ni Doping for High-Efficiency Photocatalytic Hydrogen Production of CdS Nanocrystals

Ni-doped CdS nanowires were synthesized by a simple one-step method. X-ray diffraction, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy confirmed that light Ni doping can form shallow surface states due to the presence of substitutional Ni ions, and heavy Ni doping can form deep surface states due to the presence of interstitial Ni ions. Surface photovoltage spectroscopy and transient photovoltage measurements revealed that the shallow surface states can prolong the lifetime of the photogenerated charge carriers, whereas the deep surface states lead to recombination of the photogenerated charge carriers. The relationship between different surface states and the photocatalytic performance of CdS nanocrystals are discussed. The enhanced density of shallow surface states due to light Ni doping significantly promotes photocatalytic H2 production.

pH-dependent assembly of tungsten oxide three-dimensional architectures and their application in photocatalysis.

In this work, tungsten oxide (WO3) with three-dimensional flower-like and wheel-like architectures, based on the spontaneous aggregation of one-dimensional nanorods, were successfully fabricated by adjusting the pH of the precursor solution. The influence of pH on the morphologies of WO3 was systematically studied, and the different WO3 architectures were used to photocatalytically degrade rhodamine B. The kinetic features of photoinduced charges of as-prepared WO3 have been investigated by surface photovoltage spectroscopy and transient photovoltage techniques in detail. WO3 with wheel-like and flower-like structures possess the higher charge separation efficiency and the lower recombination rate of photoinduced charges, resulting in higher photocatalytic activity for the degradation of RhB.

Surface charge transfer properties of high-performance Ag-decorated ZnO photocatalysts

Silver-decorated ZnO (Ag/ZnO) chain-like nanoparticle aggregates were prepared by a facile nonaqueous sol–gel method. The influence of Ag decoration on the surface photo-induced charge transfer behaviour of ZnO was investigated by means of surface photovoltage spectroscopy, electric field-induced surface photovoltage spectroscopy and transient photovoltage techniques. The photovoltage spectra revealed that an electronic interaction between Ag and ZnO formed. Ag acted as electron acceptors and effectively inhibited the charge recombination in ZnO with UV light illumination, while under the illumination of visible light a redshift was observed due to the appearance of a plasmon-induced band resulting from the formation of Ag nanoparticle clusters. These were responsible for the significant enhancement in the photocatalytic activity of the Ag/ZnO sample. The results also suggested that the high-performance visible light photocatalytic activity could be manipulated by external biases.

Photoinduced charge transfer process in p-Cu2O/n-Cu2O homojunction film and its photoelectric gas-sensing properties

In this study, the p-Cu2O/n-Cu2O homojunction film was prepared by a simple two-step electrodeposition method. The photoinduced charge transfer process in p-Cu2O/n-Cu2O homojunction film was studied using surface photovoltage technique. Then, the p-Cu2O/n-Cu2O homojunction film was assembled into a photoelectric gas sensor for sensing acetaldehyde both under 405 nm and 532 nm light irradiation at room temperature. For 532 nm light irradiation, excess photoinduced electrons migrate to the irradiated n-Cu2O side affected by the interfacial built-in electric field and promote desorption of acetaldehyde, which results in a higher sensitivity than that under 405 nm light. Our results demonstrated that constructing junction structure in photoelectric gas-sensing materials is an effective approach to achieve high sensitivity at room temperature.

Surface photovoltage phase spectroscopy study of the photo-induced charge carrier properties of TiO 2 nanotube arrays

By using the surface photovoltage (SPV) technique based on a lock-in amplifier, surface states located 3.1 eV below the conduction band of TiO2 have been detected in TiO2 nanotube arrays prepared by anodization of titanium foil in fluoride-based ethylene glycol solution. The photo-induced charge transportation behavior of TiO2 nanotube arrays was also studied by qualitatively analyzing their SPV phase spectra measured under different external bias. When a negative bias was applied, carriers excited from surface states have the same transportation properties as those excited from the valence band; in contrast, when a positive bias was applied, these two kinds of photo-excited carriers exhibit different transportation behavior.