Hefang Wang

H3PW12O40/mpg-C3N4 as an efficient and reusable bifunctional catalyst in one-pot oxidation–Knoevenagel condensation tandem reaction

A single-site bifunctional catalyst for the oxidation–Knoevenagel condensation tandem reaction was prepared by the immobilization of phosphotungstic acid (HPW) on mesoporous graphitic carbon nitride (mpg-C3N4) via electrostatic interaction (HPW/mpg-C3N4). The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), solid-state 31P nuclear magnetic resonance (solid-state 31P NMR), zeta potentials, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) demonstrated that HPW was successfully immobilized on the protonated mpg-C3N4 by electrostatic interaction. The acid amounts of the catalysts were determined by NH3 temperature programmed desorption (NH3-TPD). The textural properties and morphology of HPW/mpg-C3N4 were characterized by N2 adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). 30% HPW/mpg-C3N4 shows the best catalytic performance in the tandem reaction with 98.4% benzyl alcohol conversion and 96.2% selectivity to benzylidene malononitrile. The excellent catalytic performance of 30% HPW/mpg-C3N4 in the tandem reaction is due to the good catalytic performance of HPW in the oxidation and Knoevenagel condensation, respectively. Furthermore, protonated mpg-C3N4 not only acts as a support to facilitate good dispersion of HPW but also promotes the Knoevenagel condensation reaction effectively. Moreover, the HPW/mpg-C3N4 catalyst could be recycled easily without significant loss of catalytic activity.

A novel bifunctional Pd–ZIF-8/rGO catalyst with spatially separated active sites for the tandem Knoevenagel condensation–reduction reaction

A novel bifunctional catalyst with spatially separated active sites was prepared by the immobilization of Pd nanoparticles (NPs) via covalent interaction and coordination of a zeolitic imidazolate framework (ZIF-8) on the surface of graphene oxide (GO), respectively, which was used as an efficient catalyst for the Knoevenagel condensation–reduction tandem reaction. The results of Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Raman spectroscopy, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA) demonstrated that Pd and ZIF-8 were successfully immobilized on the surface of GO, and the GO was reduced to reduced graphene oxide (rGO) using NaBH4 as the reductant in the preparation of Pd–ZIF-8/rGO. The textural properties and morphology of Pd–ZIF-8/rGO were characterized by N2 adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Pd–ZIF-8/rGO shows excellent catalytic performance in the tandem reaction with 100% benzaldehyde conversion and 98.3% selectivity to benzylmalononitrile. The excellent catalytic performance of Pd–ZIF-8/rGO in the tandem reaction is due to the high catalytic activities of spatially separated Pd NPs and ZIF-8 active sites and concentrated reactants on the surface of Pd–ZIF-8/rGO due to the π–π interaction between rGO and the reactants. The anchoring and stabilization effects of oxygenated groups of GO inhibit the aggregation and leakage of active sites, leading to good catalytic recyclability with almost unchanged catalytic activity for more than eight cycles in the tandem reaction.

H5PMo10V2O40 immobilized on functionalized chloromethylated polystyrene by electrostatic interactions: a highly efficient and recyclable heterogeneous catalyst for hydroxylation of benzene

H5PMo10V2O40 (PMoV2) was immobilized on N,N-dimethylhexadecylamine functionalized chloromethylated polystyrene (DMA16-CMPS) by electrostatic interaction and used as a catalyst for the direct hydroxylation of benzene to phenol with H2O2. The results of FT-IR, XRD and TGA indicated that PMoV2 was immobilized and finely dispersed on DMA16-CMPS, and the structure was well preserved. UV-vis DRS, EPR and XPS confirmed the presence of V4+ in the catalyst due to electronic interactions between PMoV2 and DMA16-CMPS. The textural and morphological properties of the catalyst were characterized by N2 adsorption–desorption, SEM and TEM. The hydrophobicity of the catalyst was also characterized by contact angle measurement. PMoV2/DMA16-CMPS exhibited excellent catalytic performance with 22.1% conversion of benzene and a phenol yield of 21.9% at 65 °C. The high catalytic performance of PMoV2/DMA16-CMPS is attributed to high dispersion of PMoV2 on mesoporous and macroporous DMA16-CMPS, good benzene adsorption and phenol desorption ability, and V5+/V4+ redox pairs in the catalyst. Meanwhile, PMoV2/DMA16-CMPS has the advantages of facile recovery and recycling.

Graphene oxide edge grafting of polyaniline nanocomposite: an efficient adsorbent for methylene blue and methyl orange

Polyaniline (PANI) chains were grafted at the edge of graphene oxide (GO) sheets by in-situ chemical oxidation polymerization. The obtained GO-PANI composite was used for the adsorption of cationic methylene blue (MB) and anionic methyl orange (MO) dyes from aqueous solutions. The structure of the GO-PANI composite was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electronic micrograph (SEM), X-ray photoelectron spectroscopy (XPS) and zeta potentials. GO-PANI exhibited a high adsorption capacity for MB (962 mg/g) and MO (885 mg/g) compared with other reported absorbents, which was due to adsorption through strong π-π stacking and anion-cation interactions. The nanocomposite could be recycled five times without significant loss in removal abilities for MB (87.8%) and MO (75.0%), respectively. GO-PANI composite is a promising adsorbent for the adsorption of anionic and cationic dyes from aqueous solutions.

One-pot conversion of cyclohexanol to ɛ-caprolactam using a multifunctional Na2WO4-acidic ionic liquid catalytic system

Na 2 WO 4 -acidic ionic liquid was used as a simple, ecofriendly, recyclable and efficient catalytic sys-tem for the one-pot conversion of cyclohexanol to e-caprolactam. The effect of the structure of the ionic liquid on the catalytic activity of this system was investigated, and the results revealed that sulfonic acid-functionalized ionic liquids with HSO 4 - as an anion gave the best results. The highly efficient performance of this catalyst system was attributed to the phase-transfer behavior of the cation of the ionic liquid, the improved coordination of the substrate to bisperoxotungstate during the oxidation reaction, and the stabilization of the intermediate formed during the Beckmann rear-rangement.