Xiaoning Guo

Copper nanoparticles on graphene support: an efficient photocatalyst for coupling of nitroaromatics in visible light.

Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm(-2) ) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the NO bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene.

High photoelectrocatalytic performance of a MoS2–SiC hybrid structure for hydrogen evolution reaction

A flower-like MoS2–SiC hybrid structure assembled from folded MoS2–SiC nanosheets can activate hydrogen evolution at a very low overpotential (0.04 V) and produce a large cathodic current, which compares favorably with that produced by a commercial 20 wt% Pt/C catalyst.

Visible light-induced selective photocatalytic aerobic oxidation of amines into imines on Cu/graphene

Graphene can stabilize metallic copper nanoparticles and enable them to exhibit excellent photocatalytic activity for aerobic oxidation of various primary and secondary amines into the corresponding imines. The copper nanoparticles stabilized on graphene absorb the energy of visible light via localized surface plasmon resonance, and produce energetic hot electrons that activate the reactants adsorbed on the surface of copper nanoparticles. The formation of imines involves selective oxygenation of amines to aldehydes and subsequent condensation with amines to form imines.

Avoiding Loss of Catalytic Activity of Pd Nanoparticles Partially Embedded in Nanoditches in SiC Nanowires

Nanoditches from selective etching of periodically twinned SiC nanowires were employed to hinder the migration and coalescence of Pd nanoparticles supported on the nanowires, and thus to improve their catalytic stability for total combustion of methane. The results show that the etched Pd/SiC catalyst can keep the methane conversion of almost 100% while the unetched one has an obvious decline in the catalytic activity from 100 to 82% after ten repeated reaction cycles. The excellent catalytic stability originates from the limitation of the nanoditches to the migration and growth of Pd nanoparticles.

Graphene-supported Cu2O nanoparticles: an efficient heterogeneous catalyst for C–O cross-coupling of aryl iodides with phenols

Cu2O/graphene as a heterogeneous catalyst can effectively ignite and catalyze the Ullmann C–O cross-coupling of aryl iodides with phenols under mild conditions. The yield of diphenyl ether from the cross-coupling of phenol and iodobenzene can reach up to 96% at 150 °C in 3 h, and the turnover frequency can be as high as 1282 h−1. Meanwhile, the catalyst exhibits activity for varieties of C–O cross-coupling of aryl iodides, bromides and chlorides with phenol derivatives to form the corresponding aryl ethers.

The enhanced catalytic performance of Pd/SiC for the hydrogenation of furan derivatives at ambient temperature under visible light irradiation

By using semiconductive SiC as the support, palladium exhibits a tremendous promotion of its intrinsic catalytic activity for the hydrogenation of furan derivatives at ambient temperature under visible light irradiation. The promotion in the catalytic activity results from the fact that the Mott–Schottky contact between SiC and Pd enhances the quick transfer of the photo-generated electrons from SiC to Pd nanoparticles.

Visible-light-driven Photocatalytic N-arylation of Imidazole Derivatives and Arylboronic Acids on Cu/graphene catalyst

N-aryl imidazoles play an important role as structural and functional units in many natural products and biologically active compounds. Herein, we report a photocatalytic route for the C-N cross-coupling reactions over a Cu/graphene catalyst, which can effectively catalyze N-arylation of imidazole and phenylboronic acid, and achieve a turnover frequency of 25.4 h−1 at 25 oC and the irradiation of visible light. The enhanced catalytic activity of the Cu/graphene under the light irradiation results from the localized surface plasmon resonance of copper nanoparticles. The Cu/graphene photocatalyst has a general applicability for photocatalytic C-N, C-O and C-S cross-coupling of arylboronic acids with imidazoles, phenols and thiophenols. This study provides a green photocatalytic route for the production of N-aryl imidazoles.

Carbonylative Suzuki coupling reactions of aryl iodides with arylboronic acids over Pd/SiC

Abstract High surface area SiC has been used to prepare a Pd/SiC catalyst using the liquid reduction method, and the resulting catalyst was used for the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids. The catalyst was also characterized by X-ray diffraction, inductively coupled plasma-mass spectroscopy and high-resolution transmission electron microscopy. The results of these analyses showed that homogeneous Pd nanoparticles with a mean diameter of 2.8 nm were uniformly dispersed on the SiC surface. Optimization of the reaction conditions for the carbonylative Suzuki coupling reaction, including the solvent, base, pressure, temperature and reaction time, revealed that the model reaction of iodobenzene (1.0 mmol) with phenylboronic acid (1.5 mmol) could reach 90% conversion with a selectivity of 99% towards the diphenyl ketone using 3 wt% Pd/SiC under 1.0 MPa of CO pressure at 100 °C for 8 h with K2CO3 (3.0 mmol) as the base and anisole as the solvent. The Pd/SiC catalyst exhibited broad substrate scope towards the carbonylative Suzuki coupling reaction of aryl iodides with arylboronic acids bearing a variety of different substituents. Furthermore, the Pd/SiC catalyst exhibited good recyclability properties and could be recovered and reused up to five times with the conversion of iodobenzene decreasing only slightly from 90% to 76%. The decrease in the catalytic activity after five rounds was attributed to the loss of active Pd during the organic reaction.

Large scale production of highly-qualified graphene by ultrasonic exfoliation of expanded graphite under the promotion of (NH4)2CO3 decomposition.

Highly-qualified graphene was prepared by the ultrasonic exfoliation of commercial expanded graphite (EG) under the promotion of (NH4)2CO3 decomposition. The yield of graphene from the first exfoliation is 7 wt%, and it can be increased to more than 65 wt% by repeated exfoliations. Atomic force microscopy, x-ray photoelectron spectroscopy and Raman analysis show that the as-prepared graphene only has a few defects or oxides, and more than 95% of the graphene flakes have a thickness of ~1 nm. The electrochemical performance of the as-prepared graphene is comparable to reduced graphene oxide in the determination of dopamine (DA) from the mixed solution of ascorbic acid, uric acid and DA. These results show that the decomposition of (NH4)2CO3 molecules in the EG layers under ultrasonication promotes the exfoliation of graphite and provides a low-priced route for large scale production of highly-quality graphene.

Pyrite nanoparticles: an Earth-abundant mineral catalyst for activation of molecular hydrogen and hydrogenation of nitroaromatics

Pyrite (FeS2) nanoparticles, a kind of Earth-abundant mineral, can efficiently activate molecular hydrogen under mild conditions. At ambient pressure, H2 can be dissociatively adsorbed by FeS2 nanoparticles, react with nitrobenzene, and selectively produce aniline. The catalytic activity for hydrogenation of nitrobenzene is comparable to most non-precious metal catalysts.