Huihu Wang

Photochemical preparation of the ternary composite CdS/Au/g-C3N4 with enhanced visible light photocatalytic performance and its microstructure

A ternary composite photocatalyst CdS/Au/g-C3N4 was synthesized by a facile two-step photoreduction method. In this hybrid structure, CdS nanoparticles and CdS@Au core–shell nanoparticles are homogeneously deposited on the surface of g-C3N4 to produce two different structures CdS–g-C3N4 and CdS@Au–g-C3N4. The microstructure analysis results of the composition, chemical states, and optical properties of as-prepared ternary hybrid reveal that a strong interaction exists between CdS nanoparticles, CdS@Au nanoparticles and the g-C3N4 bulk. The ternary composite CdS/Au/g-C3N4 exhibits significantly enhanced photocatalytic activity for RhB degradation under visible light irradiation compared with the binary composites CdS/g-C3N4, Au/g-C3N4 and pure g-C3N4. Meanwhile, CdS/Au/g-C3N4 also demonstrates good photostability in the recycling test of RhB degradation. The active species in the photocatalytic reaction over CdS/Au/g-C3N4 are detected as O2˙− and h+. The superior photocatalytic performance of CdS/Au/g-C3N4 should be attributed to the enhanced separation efficiency of photogenerated electrons–holes induced by the formed heterojunctions CdS–g-C3N4 and Z-scheme structure CdS@Au–g-C3N4 where Au nanoparticles serve as electrons mediator.

Theoretical calculation and analysis of ZrO 2 spherical nanometer powders

ZrO2 spherical nanometer powders containing 3.5 mol% Y2O3 have been prepared via the coupling route of water/oil (W/O) emulsion with dimethyl oxalate homogenous precipitation. ZrO2 powders and their precursor powders have been characterized by XRD, TEM and SEM. According to the XRD result, phase volume fractions of powders were calculated by comparing the peaks’ intensities of spectrum. Furthermore, phase crystal lattice constants were obtained using crystal interplanar spacing formula and Bragg equation. With these results, the theoretical density of powders was analyzed. Finally, powders’ spherical degree was revealed via the method of comparison between theoretical density and actual density.

Mechanism of enhancing visible-light photocatalytic activity of BiVO4 via hybridization of graphene based on a first-principles study

The interface properties of the hybrid graphene/BiVO4(001) heterojunction were investigated by first-principle calculations incorporating semiempirical dispersion-correction schemes to correctly describe van der Waals interactions. The results indicate that graphene and BiVO4 are in contact and form a stable heterojunction. After equilibration of the graphene/BiVO4 interface, their energy levels are adjusted with the shift of their Fermi levels based on calculated work functions. In addition, electrons in the upper valence band of BiVO4 can be excited to the conduction band under irradiation, and then arrive at the C pz orbital of graphene, in which the electrons cannot migrate back to BiVO4 and thus are trapped in graphene. Thus, substantial holes are accumulated in the BiVO4(001) surface, facilitating the separation of photogenerated e−/h+ pairs. The calculated charge density difference unravels that the charge redistribution drives the interlayer charge transfer from graphene to the BiVO4(001) surface. It is identified that the hybridization between the two components induces an increase of optical absorption of BiVO4 in the visible-light region. A deep understanding of the microcosmic mechanisms of interface interaction and charge transfer in this system would be helpful for fabricating BiVO4-based heterojunction photocatalysts.

Effects of low melting point metals (Ga, In, Sn) on hydrolysis properties of aluminum alloys

Abstract Low melting point metals (Ga, In, Sn) as alloy elements were used to prepare Al–In–Sn and Al–Ga–In–Sn alloys through mechanical ball milling method. The effects of mass ratio of In to Sn and Ga content on the hydrolysis properties of aluminum alloys were investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy disperse spectroscopy (EDS) were used to analyze the compositions and morphologies of the obtained Al alloys. The results show that the phase compositions of Al–In–Sn ternary alloys are Al and two intermetallic compounds, In 3 Sn and InSn 4 . All Al–In–Sn ternary alloys exhibit poor hydrolysis activity at room temperature. Al–In–Sn alloy with the mass ratio of In to Sn equaling 1:4 has the highest hydrogen yield. After Ga is introduced to the ternary alloys, the hydrolysis activity of aluminum alloys at room temperature is greatly improved. It is speculated that the addition of Ga element promotes the formation of defects inside the Al alloys and Ga–In 3 Sn–InSn 4 eutectic alloys on the alloys surface. Al atoms can be dissolved in this eutectic phase and become the active spots during the hydrolysis process. The small size and uniform distribution of this eutectic phase may be responsible for the enhancement of hydrolysis activity.

Immobilization of g-C3N4 nanosheets on diatomite via electrostatic adsorption and their photocatalytic activity

Graphitic carbon nitride (g-C3N4) nanosheets have been successfully immobilized on diatomite to form a g-C3N4/diatomite hybrid through a facile electrostatic adsorption method and subsequent calcination process. Electron microscopy studies confirm that the surface of the diatomite is tightly covered with g-C3N4 nanosheets. In addition, the characterization results of Fourier transform infrared spectra (FTIR) and X-ray photoelectron spectra (XPS) verify that there is a strong interaction between the g-C3N4 and diatomite components inside the hybrids. The visible light absorption edge of the hybrids exhibits a significant redshift compared with the bare g-C3N4 nanosheets and diatomite, which leads to the improvement of visible light absorption and utilization. The photocatalytic results demonstrated that the photocatalytic performance for methyl orange and phenol degradation using the hybrids as photocatalysts has been obviously improved compared to that of g-C3N4 nanosheets, which may be ascribed to its adsorption/photocatalysis synergistic effect.

Effect of post-heat treatment on the photocatalytic activity of titanium dioxide nanowire membranes deposited on a Ti substrate

Titanium dioxide nanowire membranes have been synthesized by a hydrothermal growth on the surfaces of Ti substrates in a 12 M NaOH aqueous solution at 160 °C for 24 h, followed by ion-exchange with 0.5 M HCl aqueous solution and subsequent heat treatment such as calcination or a second hydrothermal treatment. The as-prepared TiO2 nanowires as well as their precursor were characterized by field emission scanning electron microscopy (FE-SEM), thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), the Brunauer–Emmett–Teller (BET) method, ultraviolet-visible (UV-Vis) spectrophotometry, transmission electron microscopy (TEM) and energy dispersive X-ray (EDX) spectrometry. FE-SEM observations indicated that the TiO2 nanowires were 50–250 nm in diameter and up to several dozens of microns in length. TG-DTA and XRD results demonstrated that the crystalline phases of the nanowires obtained from calcinations of their precursor at different temperatures above 350 °C consisted mostly of anatase. BET, UV-Vis, TEM and EDX results showed that the nanowires obtained upon calcination of their precursor at 550 °C had the greatest degradation efficiency for Rhodamine-B, and that, at the same temperature of 250 °C, the hydrothermal treatment process of TiO2-precursor nanowires had a more significant effect on the photocatalytic activity of the resulting TiO2 nanowires than the calcination.

Preparation of an ultrathin 2D/2D rGO/g-C3N4 nanocomposite with enhanced visible-light-driven photocatalytic performance

A simple solvent method was developed to construct an ultrathin 2D/2D rGO/g-C3N4 nanocomposite using a suspension of thermally exfoliated g-C3N4 nanosheets and graphene oxide (GO) followed by a NaHSO3 reducing process. Different from the g-C3N4 bulk, the results revealed that the g-C3N4 nanosheets and rGO components in the as-prepared ultrathin nanocomposite have a strong interfacial interaction and abundant coupling interfaces. Moreover, improved visible light absorption properties and fast charge carrier separation efficiency were observed in the ultrathin 2D/2D rGO/g-C3N4 nanocomposite, as compared to the pure g-C3N4 nanosheets, which ensures its enhanced photocatalytic activity for methyl orange (MO) degradation and CO2 photoreduction. It was confirmed that the thermally exfoliated g-C3N4 nanosheet is a good 2D material for the construction of 2D/2D heterostructures.

Effect of thickness of inner carbon fibre reinforced polymer tubes on axial compressive behaviour of steel-concrete-carbon fibre reinforced polymer-concrete columns

Abstract Steel-concrete-carbon fibre reinforced polymer-concrete columns (SCCC columns) have been introduced as a new form of hybrid columns by first author. An SCCC column consists of an outer steel tube, an inner carbon fibre reinforced polymer tube, an annular concrete between two concentric tubes and a core concrete encased in carbon fibre reinforced polymer tube. This paper presents the results of a test study that was conducted to investigate the effect of thickness of inner carbon fibre reinforced polymer tube on the axial compressive behaviour of SCCC columns. Four SCCC columns with carbon fibre reinforced polymer tubes of two different thicknesses of 0·167 mm and 0·334 mm in addition to two reference columns without carbon fibre reinforced polymer tube were prepared. All the six short columns, each 260 mm in diameter, 780 mm in height, were manufactured and tested to failure under pure axial compression. Test results demonstrate that the circular hybrid SCCC columns are of excellent axial compression behaviour, and that increasing the thickness of inner carbon fibre reinforced polymer tube can increase the ultimate axial load capacity and ultimate axial strain of SCCC columns remarkably.

Failure analysis of TiB2–TiC composite-coated electrodes for spot-welding galvanised steel plates

Abstract In order to improve the lifespan of electrodes used for spot-welding galvanised steel plates, electrodes coated with TiB2–TiC composite were studied. Scanning electron microscope and X-ray diffraction were employed to analyse the failure process of TiB2–TiC composite-coated electrodes when they were used for spot-welding galvanised steel plates. The analysis results show that the influence of mechanical force and welding heat, along with other factors, could lead to the generation of cracks in the originally complete TiB2–TiC composite coating. The developed cracks weave into a mesh, which enhances the extent of alloying between the TiB2–TiC composite-coated electrode and the zinc coating of the galvanised steel plate. Because of the influence of local alloying, the coatings tend to peel off in pieces, resulting in a higher level of alloying and the final failure of TiB2–TiC composite-coated electrodes. Failure of TiB2–TiC composite-coated electrodes is the result of both alloying and plastic deformation.