Xiaochao Zhang

Nitrogen-doped carbon quantum dots/Ag3PO4 complex photocatalysts with enhanced visible light driven photocatalytic activity and stability

Novel nitrogen-doped carbon quantum dots/Ag3PO4 (NCQDs/Ag3PO4) complex photocatalysts were synthesized by a facile precipitation method at room temperature. The physical and chemical properties of Ag3PO4 and NCQDs/Ag3PO4 photocatalysts were detected through X-ray powder diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and electron spin resonance techniques. The as-prepared 3-NCQDs/Ag3PO4 composite exhibited much higher activity than the pure Ag3PO4 for eliminating methyl orange and bisphenol A solution under visible light (λ>420nm). Moreover, in the cyclic experiments, the 3-NCQDs/Ag3PO4 exhibited an excellent stability for the decolorization of methyl orange at some level. This suggested that NCQDs played an important role in the process of degradation. The function of NCQDs was discussed and a new mechanism was put forward for the degradation of methyl orange. The high activities and stability were attributed to the transfer of photogenerated charges through the vector of Ag3PO4→NCQDs→Ag in the photocatalytic process, leading to effective charge separation of Ag3PO4.

Citric acid-assisted synthesis of nano-Ag/BiOBr with enhanced photocatalytic activity

In this study, silver nano-particles have been anchored in the surface of BiOBr photocatalysts by a citric acid-assisted photoreduction method. The citric acid was served as a chelating and reductive agent for the preparation of Ag-decorated BiOBr photocatalysts (named as Ag/BiOBr-2). The as-synthesized samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV-Vis diffuse reflection spectroscopy (DRS). The Ag/BiOBr-2 photocatalyst exhibited excellent and stable photocatalytic activities on MO and phenol degradation under simulated sunlight irradiation. The enhanced photocatalytic activity could be ascribed to the smaller size, rough surface, and the surface plasma resonance (SPR) effect of Ag. Also, the Schottky junction, between the surface of the BiOBr and silver nanoparticles, accelerated the efficient transfer and separation of photoinduced electron-hole pairs and promoted the photocatalytic performance. The active species tests indicated that the superoxide radical (·O2−) was responsible for the enhanced photocatalytic performance of Ag/BiOBr-2. Finally, a possible photocatalytic mechanism was proposed.

An in vitro study on the cytotoxicity of bismuth oxychloride nanosheets in human HaCaT keratinocytes

As an emerging nanomaterial, bismuth oxychloride (BiOCl) has attracted explosive interests in diverse areas. However, how it interfaces with biological systems, particularly its interaction with human cells and the resulting effects are completely unknown. In this paper, the cytotoxicity of BiOCl nanosheets (NSs) was investigated toward a human skin derived cell line (HaCaT). It was found that BiOCl-NSs had no cytotoxicity at low concentrations (<0.5 µg/mL), whereas higher concentrations (5-100 µg/mL) of BiOCl-NSs could trigger toxic effects on HaCaT cells, with changes in cell morphology and impairment of intracellular structures (mitochondria and cytoskeleton). BiOCl-NSs also led to cell apoptosis and cells cycle arrest in G0/G1 phase. Flow cytometric data showed that BiOCl-NSs were effectively incorporated into HaCaT cells. Transmission electron microscope (TEM) images further revealed that BiOCl-NSs sequestered in the lysosomes, mitochondria, nuclei, and vesicles. Results of DCFH-DA assay and nutritional antioxidant N-acetylcysteine (NAC) experiments suggested that an oxidative stress mechanism was involved in the cytotoxic effects of BiOCl-NSs. Taken together, this work represents the first study on the behavior of BiOCl-NSs on human cells, and constitutes the first and essential step for the risk assessment of BiOCl nanomaterials.

Theoretical Study on Free Fatty Acid Elimination Mechanism for Waste Cooking Oils to Biodiesel over Acid Catalyst

A theoretical investigation on the esterification mechanism of free fatty acid (FFA) in waste cooking oils (WCOs) has been carried out using DMol(3) module based on the density functional theory (DFT). Three potential pathways of FFA esterification reaction are designed to achieve the formation of fatty acid methyl ester (FAME), and calculated results show that the energy barrier can be efficiently reduced from 88.597kcal/mol to 15.318kcal/mol by acid catalyst. The molar enthalpy changes (ΔrHm°) of designed pathways are negative, indicating that FFA esterification reaction is an exothermic process. The obtained favorable energy pathway is: H(+) firstly activates FFA, then the intermediate combines with methanol to form a tetrahedral structure, and finally, producing FAME after removing a water molecule. The rate-determining step is the combination of the activated FFA with methanol, and the activation energy is about 11.513kcal/mol at 298.15K. Our results should provide basic and reliable theoretical data for further understanding the elimination mechanism of FFA over acid catalyst in the conversion of WCOs to biodiesel products.

Synthesis and evaluation of activated carbon spheres with copper modification for gaseous elemental mercury removal

Millimeter resin-based activated carbon spheres were introduced for the removal of elemental mercury, and some metallic oxides were doped to activated carbon spheres to enhance the Hg0 removal ability. The experimental results indicated that prepared activated carbon spheres (PAC) and PAC-Cu presented almost identical with a smooth surface without cracks and show well-developed pore structure with high surface area. The Hg0 removal performance of PAC was higher than that of commercial activated carbon spheres (SAC) due to the more active groups, and PAC-Cu showed the highest Hg0 removal ability among doped metallic oxides. Besides, the doped Cu can enhance the redox ability of PAC and be beneficial to activate the active component of PAC, which can promote observably the Hg0 removal performance. Meanwhile, PAC-Cu has an ability of sulfur resistance. Furthermore, the mercury combination property and XPS analysis results of the fresh and used PAC-Cu indicates that the possible removal mechanism of PAC-Cu is the synergism of Hg0 oxidation by active species of C=O or C–O and the doped Cu catalysis activation.

HCl post-processing BiOBr photocatalyst: structure, morphology, and composition and their impacts to activity

This work reports a systematic investigation on the structure, morphology, and composition, and their impacts on photocatalytic performance, for a HCl post-processing BiOBr photocatalyst. We dispersed BiOBr powders into different concentration HCl aqueous solutions to synthesize a series of samples at room temperature. With the HCl concentration increasing, SEM images revealed that as-prepared flower-like BiOBr microspheres transformed gradually into the interweaved nanosheets, and ultimately, obtaining the stacked nanosheet structures. The XRD, EDX, BET, UV-vis DRS and photocurrent data demonstrated that HCl post-processing had in-deep effects on the element composition, specific surface area, optical property and photoelectrochemical properties of samples. Moreover, the detailed formation mechanism and good correlations among their structure, composition, morphology, and enhanced activity have been established by degrading methyl orange (MO) dye molecules under simulated solar light. The HCl post-processing BiOBr samples exhibited better photocatalytic activity and stability than the pure BiOBr sample. Results indicate that there is particular emphasis placed on the roles of H+ and Cl− ions in the micro- and macro-performance improvements of BiOBr photocatalysts. Our findings should provide important knowledge for further understanding the roles of H+ and Cl− ions in such ‘like-BiOX’ layered-structure systems.