Mingxi Chen

Three-dimensional graphene-based aerogels prepared by a self-assembly process and its excellent catalytic and absorbing performance

A simple one-step method for fabricating graphene-based hydrogels (GHs) with interconnected 3D networks using Cu nanoparticles was developed. During this process, graphene oxide (GO) was reduced by Cu nanoparticles to form reduced GO (rGO) which then self-assembled to form GHs. Meanwhile, the Cu nanoparticles were oxidized to form copper(I) oxide which deposited onto the rGO sheets and became imbedded in the GHs. The GHs were transformed to graphene-based aerogels (GAs) by a green freeze-drying method. The composition of the GAs can be easily adjusted by simply changing the initial amount of Cu nanoparticles or the concentration of the GO suspension. The GAs not only possess good catalytic performance for the catalytic reduction of 4-nitrophenol and the photocatalytic degradation of methyl orange but also have excellent capacities for removing various oils and dyes from water.

A one-step method for reduction and self-assembling of graphene oxide into reduced graphene oxide aerogels

Reduced graphene oxide (rGO) aerogels were fabricated under mild conditions from an aqueous solution of graphene oxide (GO) using a one-step method which included the reduction of GO by mercaptoacetic acid and the self-assembling of rGO. The reduction of GO was confirmed with Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis and X-ray diffraction analysis. The elemental compositions of the GO and rGO aerogels were determined with X-ray photoelectron spectroscopy. The effect of different mercapto compounds on the assembly of rGO was investigated and the results showed that rGO can also accomplish self-assembling in water when mercaptoacetic acid and mercaptoethanol were used. The porous structure of the rGO aerogels was observed with scanning electron microscopy and their porosities were in the range of 90–96% when mercaptoacetic acid was used as the reductant. The high porosity gives the rGO aerogels excellent absorption abilities for metal ions.

Sn powder as reducing agents and SnO2 precursors for the synthesis of SnO2-reduced graphene oxide hybrid nanoparticles.

A facile approach to prepare SnO2/rGO (reduced graphene oxide) hybrid nanoparticles by a direct redox reaction between graphene oxide (GO) and tin powder was developed. Since no acid was used, it is an environmentally friendly green method. The SnO2/rGO hybrid nanoparticles were characterized by ultraviolet-visible spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The microstructure of the SnO2/rGO was observed with scanning electron microscopy and transmission electron microscopy. The tin powder efficiently reduced GO to rGO, and the Sn was transformed to SnO2 nanoparticles (∼45 nm) that were evenly distributed on the rGO sheets. The SnO2/rGO hybrid nanoparticles were then coated on an interdigital electrode to fabricate a humidity sensor, which have an especially good linear impedance response from 11% to 85% relative humidity.

Fast synthesis of Ag–Pd@reduced graphene oxide bimetallic nanoparticles and their applications as carbon–carbon coupling catalysts

Ultrafine Ag–Pd bimetallic nanoparticles homogeneously distributed on reduced graphene oxide (rGO) were prepared by redox reactions between Pd2+, Ag+ and GO. This method is simple, and the use of rGO as a support facilitated the separation and reuse of the Ag–Pd@rGO catalyst. The Ag–Pd@rGO bimetallic nanoparticles were characterized by ultraviolet-visible spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction analysis, and X-ray photoelectron spectroscopy. The microstructure of the Ag–Pd@rGO was investigated with scanning electron microscopy and transmission electron microscopy. The Ag–Pd@rGO catalyst exhibited high catalytic activities in the Suzuki-Miyaura carbon coupling reaction and the Sonogashira carbon coupling (SCC) reaction. These reactions used mild, efficient, ligand-free and heterogeneous conditions. Interestingly, the presence or absence of oxygen in the SCC catalytic system resulted in two different products, in which oxygen can be used as “switch” to control different products.

Graphene oxide reduced and modified by environmentally friendly glycylglycine and its excellent catalytic performance

An environmentally friendly new approach to prepare reduced graphene oxide (RGO) was developed by using glycylglycine (glygly) as both a reducing and stabilizing agent. Graphene oxide (GO) was transformed to RGO with the appropriate pH, temperature and reducing agent/GO ratio. The RGO was characterized by ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, xray diffraction, xray photoelectron spectroscopy (XPS), and transmission electron microscopy. The RGO aqueous suspension showed extraordinary stability in the absence of any external stabilizing reagents. The XPS analysis showed that this excellent stability is due to modifications of the RGO nanosheets by the glygly molecules. The modified RGO complex with copper shows good catalytic performance for reduction of 4-nitrophenol to 4-aminophenol.

Fabrication of 3D photonic crystals from chitosan that are responsive to organic solvents.

Inspired by photonic nanostructures in nature, such as the hair-like chaetae on the body of sea mice, inverse opal photonic crystals films were fabricated with chitosan, a kind of biomacromolecule found in nature. First, monodispersed polystyrene (PS) colloidal crystal templates with different particle sizes were prepared. The inverse opal films (IOFs) were fabricated through in situ cross-linking of the PS templates. The IOFs contain periodically ordered interconnecting pores that endow the films with photonic stop bands and structural colors, which are visible to the naked eye. The IOFs exhibit rapid reversible changes in their structural colors and reflectance peaks in response to alcohols and phenols. Possible mechanisms for the shifts in the IOFs reflectance peaks are proposed. The changes in the IOFs in response to alcohols and phenols provide a potential way to visually detect these organic solvents.