Yongsheng Fu

Catalytic hydrogenation of nitrophenols and nitrotoluenes over a palladium/graphene nanocomposite

We report a stable palladium/graphene (Pd/G) nanocomposite with differing Pd content for use in the catalytic hydrogenation of nitrophenols and nitrotoluenes. Various microscopic and spectroscopic techniques were employed to characterize the as-prepared catalysts. Catalytic hydrogenation reactions of nitrophenols were conducted in aqueous solution by adding NaBH4, while the nitrotoluene hydrogenation was carried out in methanol in the presence of H2 because of the poor solubility in water. The Pd/G hybrids exhibited much higher activity and higher stability than the commercial Pd/C. Due to the presence of a large excess of NaBH4 compared to p-nitrophenol, the kinetic data can be explained by the assumption of a pseudo-first-order reaction with regard to p-nitrophenol. The resulting high catalytic activity can be attributed to the graphene sheets’ strong dispersion effect for Pd nanoparticles and good adsorption ability for nitrobenzene derivatives via π–π stacking interactions. A plausible mechanism is proposed. Considering inductive and conjugation effects that may affect the reactions, the reactivity of nitrophenols in this study is expected to follow the order m-NP > o-NP > p-NP > 2,4-DNP > 2,4,6-TNP, which is in good agreement with the experimental results.

Magnetic Bi25FeO40-graphene catalyst and its high visible-light photocatalytic performance

Magnetic Bi25FeO40-graphene visible-light photocatalysts were prepared by a one-step alkaline hydrothermal method and were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET) surface area analysis, Raman spectroscopy, X-ray photoelectron spectra (XPS) and magnetic hysteresis loop measurements. XRD characterization indicated that under identical hydrothermal conditions, perovskite type bismuth ferrite (BiFeO3) was obtained without graphene addition, while the presence of graphene led to the formation of sillenite type bismuth ferrite (Bi25FeO40). In contrast to BiFeO3, the Bi25FeO40-graphene composite was superparamagnetic, and could be readily recovered in an external magnetic field. Additionally, Bi25FeO40-graphene photocatalyst exhibited higher catalytic activity for the degradation of methylene blue (MB) under visible-light irradiation than BiFeO3 and Bi25FeO40. This is due to enhanced MB adsorption and effective suppression of electron-hole recombination via preferential electron transfer from Bi25FeO40 to graphene. Moreover, increasing graphene content enhanced the catalytic activity of the composite catalyst. Accordingly, the photocatalytic MB degradation over Bi25FeO40-(20) graphene followed the Langmuir–Hinshelwood model, indicative of an adsorption controlled reaction mechanism.

Fabrication of an exfoliated graphitic carbon nitride as a highly active visible light photocatalyst

Graphitic carbon nitride (g-C3N4) nanosheets were synthesized by exfoliating bulk g-C3N4 with a thermal treatment under H2 for the first time. The g-C3N4 nanosheets exhibited a 2D structure with a thickness of 2 nm, a high surface area and a low recombination rate of photogenerated electron–hole pairs, enhancing the visible light photocatalytic activity.

A magnetically separable P25/CoFe2O4/graphene catalyst with enhanced adsorption capacity and visible-light-driven photocatalytic activity

A straightforward strategy is designed for the fabrication of a magnetically separable P25/CoFe2O4/graphene photocatalyst with differing P25 contents via a facile one step hydrothermal approach. TEM observations show that graphene sheets are exfoliated and decorated with well-dispersed TiO2 and CoFe2O4 nanoparticles. The adsorption capacity and visible-light-driven photocatalytic activity are evaluated in terms of the efficiencies of adsorption and photodegradation of various dyes, including methylene blue (MB), methyl orange (MO) and neutral dark yellow (DY). The evaluation results demonstrate that the P25/CoFe2O4/graphene photocatalyst exhibits the best performance among P25/CoFe2O4/graphene (PCG), CoFe2O4/graphene (CG), P25/CoFe2O4 (PC) and P25/graphene (PG) photocatalysts, not only in the adsorption progress, but also in the photocatalytic degradation. The significant enhancement after combination can be attributed to the synergistic effect among individual components. Furthermore, CoFe2O4 nanoparticles themselves have excellent magnetic properties, which are largely maintained in the composite, and therefore, it is no longer necessary to introduce additional magnetic supports for magnetic separation in a suspension system.

Yolk–shell-structured MnO2 microspheres with oxygen vacancies for high-performance supercapacitors

Yolk–shell-structured MnO2 microspheres with oxygen vacancies (ov-MnO2@MnO2) were successfully constructed by a facile three-step method. Morphological observations showed that the as-obtained ov-MnO2@MnO2 microspheres possessed distinctive yolk@void@shell configurations with an average diameter of 1.13 μm. Both the shell and yolk were assembled by a large amount of homogeneous MnO2 nanoparticles with an average diameter of 12 nm. The yolk–shell-structured ov-MnO2@MnO2 microsphere electrode exhibited a large specific surface area (259.83 m2 g−1) and good conductivity, thus it achieved high specific capacitance (452.4 F g−1 at 1 A g−1 and 316.1 F g−1 at 50 A g−1), excellent cycling stability (10 000 cycles) and superior rate capability (∼79.2% and 69.9% of the initial capacity at 20 A g−1 and 50 A g−1, respectively). It is noted that the asymmetric supercapacitor (ASC) composed of yolk–shell-structured ov-MnO2@MnO2 microspheres (as the positive electrode) and commercial activated carbon (as the negative electrode) can deliver a high energy density of 40.2 W h kg−1 and a maximum power density of 22.28 kW kg−1. The superior electrochemical performance of ov-MnO2@MnO2 is mainly ascribed to the unique yolk@void@shell nanostructure, the presence of oxygen vacancies in the crystal lattice and the synergistic effect of the individual components of the hybrid.

Three-dimensional low-defect carbon nanotube/nitrogen-doped graphene hybrid aerogel-supported Pt nanoparticles as efficient electrocatalysts toward the methanol oxidation reaction

Although direct methanol fuel cells present a huge potential for application in modern society, the lack of high-efficiency anode catalysts with acceptable cost has largely hindered their large-scale commercialization. Here, we demonstrate a bottom-up approach for the fabrication of ultrafine Pt nanoparticles dispersed on 3D low-defect carbon nanotube/nitrogen-doped graphene hybrid aerogels (Pt/LDCNT–NG) via a convenient and cost-effective self-assembly process. Both experiments and theoretical calculations reveal that the rationally assembled 3D Pt/LDCNT–NG architectures possess a low defect density, optimized electronic structure, and enhanced Pt stability, thus showing high electrocatalytic activity as well as a long lifespan toward the methanol oxidation reaction, which are far superior to those of conventional Pt/carbon black, Pt/acid-treated CNT, Pt/graphene, and Pt/nitrogen-doped graphene catalysts. It is anticipated that the synthetic strategy presented here can be further extended to the construction of various 3D heteroatom-doped low-defect carbonaceous nanomaterials that contain metals or metal oxides, which are conducive to the development of high-performance energy storage and conversion devices.