Junxia Wang

A novel solid acid catalyst synthesized from ZnAl2O4 spinel and its application in the esterification of acetic acid and n-butyl alcohol

A new spinel-style S2O82−/ZnAl2O4 solid acid catalyst was prepared by sol–gel method. The catalytic performance was evaluated by the esterification of n-butyl acetate. The structure, morphology and acidity of the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Field emission scanning electron microscopy (FE-SEM), N2 physisorption, X-ray photoelectron spectroscopy (XPS) and NH3 temperature programmed desorption (NH3-TPD). The results showed that the catalytic performances were significantly affected by the calcination temperature. S2O82−/ZnAl2O4-600 exhibited the highest catalytic activity of 91.7% under the optimum reaction conditions. The characterization showed that the mesoporous structure S2O82−/ZnAl2O4-600 maintained the well crystallinity of spinel as well as the spinel-style carrier in the sulfidation and recycling.

Effects of citric acid and urea on the structural and morphological characteristics of BiVO4 synthesized by the sol–gel combustion method

Micro-sized spherical BiVO4 photocatalysts composed of nanoparticles were synthesized by the sol–gel combustion method. The effects of citric acid and urea on the structural and morphological characteristics of samples were studied by X-ray diffraction, field emission scanning electron microscopy, N2 adsorption and desorption and UV–Vis spectroscopy. The photocatalytic activity was evaluated by the photocatalytic degradation of rhodamine B under visible light. The results showed the sphere-shaped BiVO4 sample to have excellent photocatalytic performance compared with the bulk sample prepared by solid-state reaction. This enhancement could be attributed to the special spherical morphology, which enhanced the absorption ability, increased the separation efficiency of photon-generated carriers and improved surface reaction sites for consumption of photon-generated carriers.Graphical AbstractUniform micro-sized spherical BiVO4 samples composed of nanoparticles were successfully synthesized by the sol–gel combustion method. The relationships between the morphologies and citric acid with urea contents were studied by using the field emission scanning electron microscopy (FE-SEM) technology.FE-SEM images of the samples (A) the samples synthesized with different citric acid contents and (B) the samples synthesized with different urea contents

Enhanced visible light photocatalytic performances of self-assembled hierarchically structured BiVO4/Bi2WO6 heterojunction composites with different morphologies

Novel self-assembled hierarchical BiVO4/Bi2WO6 heterostructured composites with different morphologies were controllably synthesized via a facile and template-free solvothermal method. The effects of the molar ratio of V to W on the structure, morphology, photocatalytic activity and photoelectrochemical properties of the BiVO4/Bi2WO6 composite photocatalysts were investigated in detail. The results showed that all the BiVO4/Bi2WO6 composites exhibited much better photocatalytic activities for methylene blue (MB) degradation and photoelectrochemical performances than pure BiVO4 and Bi2WO6. Among the composites, the BiVO4/Bi2WO6 microsphere with the molar ratio of V to W of 2 : 1 exhibited the best photocatalytic performance. The mechanism of enhanced activity was systematically investigated by UV-vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy, and photo-electrochemical methods including transient photocurrent responses, electrochemical impedance spectroscopy (EIS) and Mott–Schottky plots. The enhanced photocatalytic activity could be ascribed to the tetragonal–monoclinic heterophase structure, high surface oxygen vacancy concentration, narrow band gap energy and mainly the formed heterojunction structure which could effectively promote the separation of photogenerated electron–hole pairs. In addition, a possible photocatalytic mechanism for the enhanced photocatalytic activity was proposed on the basis of the calculated energy band positions of BiVO4 and Bi2WO6.

Synthesis, characterization and properties of Ce-modified S2O82−/ZnAl2O4 solid acid catalysts

A new spinel solid acid catalyst of S2O82−/ZnAl2O4-x wt% Ce was simply prepared by modifying S2O82−/ZnAl2O4 with Ce for acid catalysis of acetic acid and n-butanol. The prepared catalysts were characterized by means of XRD, IR, TG, XPS, NH3-TPD, SEM and N2-physisorption. The experimental results showed S2O82−/ZnAl2O4-x wt% Ce solid acid catalysts belonged to the spinel-type ZnAl2O4 structure. The addition of Ce played a key role in stabilizing the surface sulfur species and consequently increasing the acid strength of S2O82−/ZnAl2O4-x wt% Ce. The appropriate modification of Ce was 4 wt% and S2O82−/ZnAl2O4-4 wt% Ce catalyst had 95.9% esterification efficiency under the optimum reaction conditions. Compared with unmodified S2O82−/ZnAl2O4 catalyst, S2O82−/ZnAl2O4-4 wt% Ce solid acid catalyst showed much better reusability, which could remain above 80% esterification even after being used for six times. The loss of sulfur species on the surface of S2O82−/ZnAl2O4-4 wt% Ce solid acid was one of the essential reasons for its deactivation during the acid catalyzed reaction.

Synthesis of SO42−/TiO2–ZnAl2O4 composite solid acids as the esterification catalysts

A series of novel sulfated ZnAl2O4–TiO2 (SO42−/ZnAl2O4–TiO2) composite solid acids were synthesized for the esterification of biomass derived acids. The properties were characterized by XRD, FT-IR, XPS, NH3-TPD, acid–base titration, TG and FE-SEM. The experimental results showed that the introduction of ZnAl2O4 spinel oxide played a key role in stabilizing the structure of the composite catalysts as well as the surface sulfate groups. The composition of SO42−/TiO2–ZnAl2O4 catalysts significantly influenced their catalytic properties and performance in esterification reactions. The optimal SO42−/ZnAl2O4–TiO2 (6:4) catalyst with the largest number of acid sites showed superior conversion of 95.8% in oleic acid esterification and 98.5% conversion in acetic acid esterification. Moreover, the SO42−/ZnAl2O4–TiO2 (6:4) catalyst showed excellent reusability in these reactions, which was ascribed to its stable structure and good resistance of the surface sulfate groups. The efficient and reusable SO42−/ZnAl2O4–TiO2 composite solid acid coupled with spinel modification is expected to bring new opportunities in the design of favorable acid catalysts.