Hefeng Cheng

One-Step Synthesis of the Nanostructured AgI/BiOI Composites with Highly Enhanced Visible-Light Photocatalytic Performances

The nanostructured AgI/BiOI composites were prepared by a facile, one-step, and low temperature chemical bath method with Bi(NO(3))(3), AgNO(3), and KI. Several characterization tools, such as X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), the Brunauer-Emmett-Teller (BET) surface area, photoluminescence (PL) spectra, and UV-vis diffuse reflectance spectroscopy, were employed to study the phase structures, morphologies, and optical properties of the samples. The PL intensity of AgI was greatly decreased when combined with BiOI, indicating the corresponding decreased recombination of the carriers. The photocatalytic properties of the as-prepared products were measured with the degradation of methyl orange and phenol at room temperature under visible light irradiation. The AgI/BiOI composites showed much higher photocatalytic performances over BiOI as well as AgI. It was also found that the AgI amount in the AgI/BiOI composites played an important role in the corresponding photocatalytic properties and the optimized ratio was obtained at 20%. The dramatic enhancement in the visible light photocatalytic performance of the AgI/BiOI composites could be attributed to the effective electron-hole separations at the interfaces of the two semiconductors, which facilitate the transfer of the photoinduced carriers. By the detection of hydroxyl radicals through a fluorescence technique, the photoinduced holes (h(VB)(+)) were considered to be the dominant active species in the photodegradation process, which was also deduced from the theoretical speculations. The photocatalytic performances of the AgI/BiOI composites were maintained for the cycling experiments. In addition, based on the XRD and XPS patterns of the AgI/BiOI composites before and after reaction, AgI was stable in the composites under visible irradiation, indicating that AgI/BiOI composites could be used as stable and efficient visible-light-induced photocatalysts.

In situ ion exchange synthesis of the novel Ag/AgBr/BiOBr hybrid with highly efficient decontamination of pollutants

A novel Ag/AgBr/BiOBr hybrid was prepared by a rational in situ ion exchange reaction between BiOBr hierarchical microspheres and AgNO(3) in ethylene glycol followed by light reduction, which displayed superior visible light driven photocatalytic activities in sterilization of pathogenic organism and degradation of organic dye compared to N-doped P25.

An anion exchange approach to Bi2WO6 hollow microspheres with efficient visible light photocatalytic reduction of CO2 to methanol

An anion exchange strategy is explored to synthesize Bi(2)WO(6) hollow microspheres based on the microscale Kirkendall effect. The as-prepared Bi(2)WO(6) hollow microspheres display high CO(2) adsorption capacity and visible light photocatalytic conversion efficiency of CO(2) into methanol without the aid of any co-catalyst.

Facile Template-Free Synthesis of Bi2O2CO3 Hierarchical Microflowers and Their Associated Photocatalytic Activity

Hierarchical Bi(2)O(2)CO(3) flowerlike microstructures have been synthesized for the first time using a facile, template-free, and low-temperature solution method. With an average diameter of about 3 microm, the as-prepared Bi(2)O(2)CO(3) microflowers are composed of numerous two-dimensional nanosheets with oriented terminal engagement. On the basis of electron microscopy observations, a plausible growth mechanism is proposed as a spatial self-assembly process accompanied by Ostwald ripening. The molar ratio of the initial reagents plays an important role in determining the morphologies of the Bi(2)O(2)CO(3) microstructures. UV/Vis spectroscopy is employed to analyze the band gaps of the products. Both mesopores and macropores are revealed in the Bi(2)O(2)CO(3) microflowers by means of nitrogen sorption and pore-size distribution. Moreover, evaluated by the degradation of methyl orange under UV illumination, the photocatalytic performance of the Bi(2)O(2)CO(3) hierarchical microflowers is almost six times higher than that of commercial Bi(2)O(2)CO(3). The higher specific surface area, the meso/macropores, and the intra-electric field formed between the (Bi(2)O(2))(2+) layer and the slabs comprising CO(3) (2-) in the Bi(2)O(2)CO(3) crystal structure, are believed to facilitate the separation of the photoinduced electrons and holes and thus improve the corresponding photocatalytic activity.

Crystal facets controlled synthesis of graphene@TiO2 nanocomposites by a one-pot hydrothermal process

We report a facile and simple way to synthesize graphene@TiO2 nanocomposites with controlled crystal facets by a one-pot hydrothermal process. By controlling the concentrations of the starting materials and reaction times, graphene@TiO2 nanocomposites with various exposed crystal facets can be obtained. The surface states and the growth process of graphene@TiO2 nanocomposites have been studied. Owing to the exposed high-reactive crystal facets and high dispersities of TiO2 nanocrystals on graphene surfaces, the as-prepared sample exhibited enhanced photocatalytic activities over graphene@P25 nanocomposites.

Controlled synthesis of Ag2O microcrystals with facet-dependent photocatalytic activities

Ag2O microcrystals with different morphologies have been successfully synthesized by using various complexing agents. To achieve kinetic control of the growth of the Ag2O microcrystals, [Ag(NH3)2]+ complexing ions are required to restrict the release rate of silver ions before adding NaOH solution. The complexing anions play an important role in the growth process of the Ag2O microcrystals. This kinetic control leads to five morphologies of Ag2O microcrystals (cubic, octahedral, rhombic dodecahedra, polyhedra with 18 faces and rhombicuboctahedral), which exhibit facet-dependent photocatalytic activity for the degradation of methyl orange (MO) under visible light irradiation. The cubic Ag@Ag2O photocatalyst with exposed {100} facets showed the greatest activity of all the other morphologies of the photocatalysts. The mechanism of dramatic enhancement of the photocatalytic activity of Ag@Ag2O with exposed {100} facets was discussed in detail from three aspects, including the highest surface energy of the {100} facet, the larger difference value between the weighted average of the effective mass of holes and electrons along the [100] direction, and the suitable redox potentials of the (100) surface.

Tailoring AgI nanoparticles for the assembly of AgI/BiOI hierarchical hybrids with size-dependent photocatalytic activities

A facile ion exchange route between BiOI hierarchical microspheres and AgNO3 solution is explored to synthesize AgI/BiOI hierarchical hybrids that consist of AgI nanoparticles (NPs) uniformly anchored on the surface of BiOI nanosheets. With the addition of poly(vinylpyrrolidone) (PVP) surfactant molecules, the size of the AgI NPs can be tailored in the range of 55–16 nm. Evaluated by the photodecomposition of 2,4-dichlorophenol (2,4-DCP) solution under visible light irradiation, the AgI NPs/BiOI hybrids displayed highly efficient photocatalytic activities. What is more, as the size of the AgI NPs decreases, the AgI/BiOI hybrids exhibit enhanced photocatalytic performance, which is believed to be related to the larger number of surface active sites and faster spatial charge transfer.

Synthesis of Bi2O2CO3/Bi2S3 hierarchical microspheres with heterojunctions and their enhanced visible light-driven photocatalytic degradation of dye pollutants.

Bismuth subcarbonate (Bi2O2CO3) microspheres were synthesized by a simple hydrothermal method using bismuth citrate and sodium hydrogen carbonate as precursors. Furthermore, through a facile ion exchange method between the Bi2O2CO3 microspheres and thioacetamide (TAA), bismuth subcarbonate/bismuth sulfide (Bi2O2CO3/Bi2S3) heterojunctions were fabricated. The structures and morphologies of the Bi2O2CO3 and Bi2O2CO3/Bi2S3 products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The photocatalytic activities of the products were evaluated by decomposing rhodamine B (RhB) under visible light irradiation. In contrast with Bi2O2CO3, the Bi2O2CO3/Bi2S3 heterojunctions showed enhanced visible light photocatalytic properties. In addition, the effect of ion exchange reaction time on the photodegradation quality was studied, and the mechanism of the enhanced photocatalytic properties was proposed.

Facile synthesis of Zn-rich (GaN)1−x(ZnO)x solid solutions using layered double hydroxides as precursors

(GaN)1−x(ZnO)x solid solutions are potential photocatalysts for water splitting and environmental decontamination under visible light. Solid solutions prepared by the traditional method are not effective because of their low Zn content (x < 0.5). Here, we show that Zn-rich solid solutions (∼0.5 < x < ∼0.8) are readily prepared by the nitridation of layered double hydroxides (LDHs) containing Zn2+ and Ga3+ ions, and that the Zn content is easily adjusted by changing the Zn/Ga ratio of the LDH precursors. The band gap of (GaN)1−x(ZnO)x decreases gradually from 2.60 eV at x = 0.46 to 2.37 eV at x = 0.81. The Zn-rich solid solutions absorb strongly above 500 nm, and these solutions loaded with 1 wt% Pt are found to be efficient for photoreducing Cr6+ ions under visible light.

One-step synthesis of AgBr microcrystals with different morphologies by ILs-assisted hydrothermal method

AgBr microcrystals with different morphologies were synthesized by an ionic liquids (ILs)-assisted hydrothermal method. A plausible growth mechanism, and influence of ionic liquids on the morphology of AgBr, were proposed and studied systematically. The samples were characterized by scanning electronic microscopy and X-ray diffraction. The relationship of morphology and photocatalytic activity of samples was studied.