Xin-Xin Guan

Facile synthesis of 3D nitrogen-doped graphene aerogel nanomeshes with hierarchical porous structures for applications in high-performance supercapacitors

3D nitrogen-doped graphene aerogel nanomeshes (N-GANMs) with hierarchical porous structures were facilely synthesized from graphene oxide and urea using iron nitrate as the etching agent. The resulting materials were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and N2 adsorption–desorption. The supercapacitor performance was characterized by cyclic voltammetry, galvanostatic charge discharge, and electrochemical impedance spectroscopy, respectively. Compared with the bare graphene aerogel (GA), N-GANMs showed higher specific surface area, more abundant meso-macroporous pores, and much better electrochemical properties. The specific capacitance of N-GANMs was as high as 345.8 F g−1, which was much higher than that of GA and most of the reported carbon-based materials, and the value remains at about 321.0 F g−1 over 2000 cycles at 1.0 A g−1 in 2.0 M KOH. In addition, the N-GANMs demonstrated a high energy density of 20.82 W h kg−1 at a power density of 449.97 W kg−1 and their cycle performance remained approximately 100% after 10 000 cycles at 5.0 A g−1 in 1.0 M Na2SO4. The excellent behaviors might have originated from their hierarchical porous structures and the incorporation of nitrogen.

Esterification of levulinic acid into hexyl levulinate over dodecatungstophosphoric acid anchored to Al-MCM-41

ABSTRACT Aluminum-substituted MCM-41 (Al-MCM-41) were hydrothermally synthesised and used as supports to fabricate the mesostructured H3PW12O40 (HPW) solid acid catalysts via an impregnation method. The influences of various HPW loadings on the structures of the catalysts were verified by X-ray diffraction (XRD), nitrogen physisorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), ultraviolet–visible (UV–Vis) spectroscopy and Fourier-transform infrared spectroscopy (FT-IR) measurements and their acidities were evaluated by infrared of pyridine adsorption (Py-IR) and temperature-programmed desorption of ammonia (NH3-TPD) measurements. The optimisation of the reaction conditions for levulinic acid esterification with n-hexanol such as the reaction temperature and time, the reactant molar ratio, and the catalyst dosages was performed to maximise the conversion of levulinic acid. The effects of various HPW loadings on the conversion of levulinic acid were investigated under the optimised and harsh reaction conditions. The reusability of the catalysts was also investigated. The results showed that these catalysts retained the hexagonal mesoporous structure of Al-MCM-41 and the Keggin characteristic of HPW, although their textural parameters decreased with increasing loading of HPW. In particular, the catalysts were found to be efficient in the esterification of levulinic acid with n-hexanol, resulting in hexyl levulinate which could replace the petroleum-derived chemical feedstocks.