Yongfan Zhang

Multivalency Iodine Doped TiO2: Preparation, Characterization, Theoretical Studies, and Visible-Light Photocatalysis

Multivalency iodine (I(7)+/I(-)) doped TiO(2) were prepared via a combination of deposition-precipitation process and hydrothermal treatment. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area, UV-vis diffuse reflectance spectra, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and electric-field-induced surface photovoltage spectroscopy. The electronic structure calculations based on the density functional theory revealed that upon doping, new states that originated from the I atom of the IO(4) group are observed near the conduction-band bottom region of TiO(2), and the excitation from the valence band of TiO(2) to the surface IO(4-) is responsible for the visible-light response of the I-doped TiO(2). The as-prepared I-doped TiO(2) showed high efficiency for the photocatalytic decomposition of gaseous acetone under visible light irradiation (lambda > 420 nm). A possible mechanism for the photocatalysis on this multivalency iodine (I(7)+/I(-)) doped TiO(2) under visible light was also proposed.

Synthesis and photocatalytic hydrogen production of a novel photocatalyst LaCO3OH

A novel orthorhombic LaCO3OH photocatalyst is synthesized by a facile hydrothermal method. The prepared LaCO3OH sample exhibits high photocatalytic activity for hydrogen evolution from aqueous methanol solutions under UV light irradiation, which is about 3 times higher than that of anatase TiO2. The Mott–Schottky plot shows the VCB of the prepared LaCO3OH of −0.87 V vs. RHE at pH 7. Theoretical calculations of the electronic structures for LaCO3OH reveal that the top of the valence band (VB) and the bottom of the conduction band (CB) are mainly composed of O 2p and La 4f states, respectively. The superior photocatalytic performance of LaCO3OH could be ascribed predominantly to the high reduction potential of photoinduced electrons. A possible mechanism for the hydrogen evolution over LaCO3OH is proposed. This work highlights the potential application of lanthanum-based materials in the field of energy conversion.

Morphology-controlled synthesis and efficient photocatalytic performances of a new promising photocatalyst Sr0.25H1.5Ta2O6·H2O

A new photocatalyst Sr0.25H1.5Ta2O6·H2O (HST) with high surface area was successfully prepared by a facile and mild hydrothermal reaction using Ta2O5·nH2O as a precursor. TEM images revealed that their different morphologies, from nanoplate to nanopolyhedron, were formed under different pH values of the reactive solutions. The formation mechanism of HST was also studied and proposed. Growth of HST nanocrystallites followed a reaction-crystallization model. By analyzing the results of XRD, DRS, XPS, electrochemistry and theoretical calculation, the crystal and electronic structural characterizations of HST was established. Compared with isostructural Sr0.4H1.2Nb2O6·H2O (HSN), the Ta 5d orbitals were the main contribution to the bottom of the conduction band of HST, inducing the energy level more negative while the top of valence band, which was dominated by O 2p states, remained almost unchanged. Due to the more suitable electronic band structure and various morphologies, the photocatalyst showed superior photocatalytic activities for water splitting to generate H2 and for degrading benzene as compared with HSN. The rate of H2 evolution and the conversion ratio of benzene were 81 times and 4 times higher than that of TiO2 (Degussa P25), respectively. The proposed mechanisms for photocatalytic reactions based on the experimental results were discussed.

First-principles studies of the TE properties of [110]-Ge/Si core/shell nanowires with different surface structures

Based on first-principle electronic structure calculations and Boltzmann transport theory, we investigate the composition-dependent thermoelectric properties of germanium/silicon core/shell [110]-oriented nanowires, as well as the surface passivation effects. The results demonstrate that the ZT values depend on the surface structure and the Ge/Si ratio. Significantly, for n-type [110]-Ge/Si core/shell NWs (about 2.6 nm in diameter) ZT = 0.65 at 300 K can be obtained, that is 65 times that of bulk Si, and 1.8 times that of SiNW without the core/shell structure at the same temperature.