Mingxin Ye

One step hydrothermal synthesis of TiO2-reduced graphene oxide sheets

We demonstrated an environmentally friendly and efficient route for the preparation of titanium oxide (TiO2) nanoparticles-reduced graphene oxide composite with a one-step hydrothermal method using glucose as the reducing agent. The reducing process was accompanied by generation of TiO2 nanoparticles. The structure and composition of the nanocomposite has been characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray diffraction, thermal gravimetric analysis and atomic force microscopy. The TiO2-coated RGO nanocomposite was shown to improve the photocatalytic property of TiO2, which would be promising for practical applications in future nanotechnology.

Synthesis of Amphiphilic Graphene Nanoplatelets

Graphene, a flat monolayer of carbon atoms tightly packed into a two-dimensional honeycomb lattice, has attracted a great deal of attention in recent years for potential applications in many technological fields, such as nanoelectronics, nanocomposites, and hydrogen supercapacitors. One possible route to harnessing these properties would be to incorporate graphene sheets into composite materials. The manufacturing of such composites requires not only that the graphene sheets are produced on a sufficient scale, but also that they are incorporated, and homogeneously distributed, into various matrices. Graphite, which consists of a stack of flat graphene sheets, is available in large quantities from natural sources. It is likely the most readily available and least expensive source for the production of bulk graphene sheets. Graphite oxide (GO) is a layered material produced by the oxidation of graphite. In contrast to pristine graphite, the graphene-derived sheets in GO are heavily oxygenated and bear hydroxyl and epoxide functional groups on their basal planes, in addition to carbonyl and carboxyl groups located at the sheet edges. Unfortunately, owing to their hydrophilic nature, graphene oxide sheets can only be dispersed in aqueous media that are incompatible with most organic solvents and polymers. In addition, GO is electrically insulating, which limits its usefulness for the synthesis of composites. However, it has been demonstrated that the electrical conductivity of GO can be significantly increased and very thin graphene-like sheets can be obtained through the chemical reduction of exfoliated GO. Just like carbon nanotubes, a key challenge in the synthesis and processing of bulk-quantity graphene sheets is aggregation. Graphene sheets, due to their high specific surface area, tend to form irreversible agglomerates or even restack to form graphite through van der Waals interactions. As with carbon nanotubes, full utilization of graphene sheets in polymer nanocomposite applications will inevitably depend on their ability to achieve complete dispersion in the polymer matrix of choice.

Liquid Phase Exfoliation of Two-Dimensional Materials by Directly Probing and Matching Surface Tension Components

Exfoliation of two-dimensional (2D) materials into mono- or few layers is of significance for both fundamental studies and potential applications. In this report, for the first time surface tension components were directly probed and matched to predict solvents with effective liquid phase exfoliation (LPE) capability for 2D materials such as graphene, h-BN, WS2, MoS2, MoSe2, Bi2Se3, TaS2, and SnS2. Exfoliation efficiency is enhanced when the ratios of the surface tension components of the applied solvent is close to that of the 2D material in question. We enlarged the library of low-toxic and common solvents for LPE. Our study provides distinctive insight into LPE and has pioneered a rational strategy for LPE of 2D materials with high yield.

Mechanical, thermal and swelling properties of poly(acrylic acid)–graphene oxide composite hydrogels

Graphene oxide (GO) is added into poly(acrylic acid) (PAA) hydrogels to modify their mechanical and thermal properties. The original PAA hydrogels, which are commonly crosslinked by N,N-methylenebisacrylamide (BIS), generally exhibit pronounced weakness and brittleness. When GO was added into the BIS-gel, the GO–BIS-gels become very tough and exhibited fairly good strength. The mechanical and thermal properties of GO–BIS-gels vary greatly by changing GO or BIS content. As for the swelling behaviors of the hydrogels, they are found to be still sensitive to pH. However, the BIS-gels have a higher equilibrium swelling ratio and swell faster than that of corresponding GO–BIS-gels. In addition, the deswelling ratio decreases with the increase of GO content. The cross-linking of GO with PAA is the main factor for these phenomenon. Thus, the content of GO and BIS can be adjusted for preparing hydrogels with different properties for a wide range of applications.

Covalent attaching protein to graphene oxide via diimide-activated amidation.

In this paper, graphene oxide nanosheets (GOS) are functionalized by bovine serum albumin (BSA) via diimide-activated amidation under ambient conditions. The obtained GOS-BSA conjugate is highly water-soluble. Results of atomic force microscopy (AFM), Raman spectra and Fourier transform infrared spectroscopy analysis confirm that GOS-BSA conjugate contains both GOS and BSA protein. AFM image shows that GOS are fully exfoliated. Results of cyclic volatammograms show that the protein in the GOS-BSA conjugate retains its bioactivity. The present method may also provide a way to synthesize graphene-based composites with other biomolecules.

One-pot hydrothermal synthesis of Ag-reduced graphene oxide composite with ionic liquid

A one-pot hydrothermal reaction was used to prepare a reduced graphene oxide sheets (RGO)-silver (Ag) nanoparticles composite using graphite oxide and silver nitrate as starting materials. It was found that graphene oxide could be well reduced under the hydrothermal conditions with ascorbic acid as the reductant, while the Ag nanoparticles were grown on the RGO surface simultaneously. The reduction of graphene oxide and synthesizing of Ag-RGO were confirmed by Fourier-transform infrared spectroscopy, Raman spectroscopy, thermogravimetric analysis, X-ray diffraction and X-ray photoelectron spectroscopy. Microscopy techniques (scanning electron microscopy, atomic force microscopy and transmission electron microscopy) have been employed to probe the morphological characteristics as well as to investigate the exfoliation of RGO sheets. The intensities of the Raman signals of RGO in the composite are greatly increased by the attached Ag nanoparticles, showing surface-enhanced Raman scattering activity. Besides, it was found that the antibacterial activity of free Ag nanoparticles is retained in the composite, suggesting that it can be used as RGO-based biomaterials.

Covalent synthesis of organophilic chemically functionalized graphene sheets.

In this study, we report a scalable, fast, and easy method for preparation of organophilic chemically functionalized graphene (OCFG) sheets. The basic strategy involved the preparation of graphite oxide (GO) and the complete exfoliation of GO into graphene oxide sheets, followed by reacting with 1-bromobutane to obtain OCFG sheets. Thermogravimetric analysis, Raman spectroscopy, and Fourier transform infrared spectroscopy indicated the functionalization of GO. Transmission electron microscopy and atomic force microscopy were used to demonstrate the structure of produced graphene oxide and OCFG sheets. Ultraviolet-visible spectroscopy confirmed that OCFG sheets disperse well in organic solvents and the solutions obey Beers law. The resulting organic dispersions are homogeneous, exhibit long-term stability, and are made up of graphene sheets a few hundred nanometers large. The ability to prepare graphene dispersions in organic media facilitates their combination with polymers to yield homogeneous composites.

Preparation and characterization of pH- and temperature-responsive hydrogels with surface-functionalized graphene oxide as the crosslinker

A methodology is described for the preparation of pH- and temperature-responsive semi-interpenetrating hydrogels with surface-functionalized graphene oxide (GO) as the crosslinker, N-isopropylacrylamide (NIPAM) as the monomer and sodium alginate (SA) as an additive. GO sheets were first prepared via an oxidation reaction in aqueous solution and then modified with 3-(trimethoxysilyl)propylmethacrylate (TMSPMA) via a silanization reaction. Free-radical polymerization of NIPAM and SA was then carried out with the presence of TMSPMA-modified GO sheets at 20 °C in a water bath, leading to the formation of pH- and temperature-responsive PNIPAM/SA/GO hydrogels crosslinked with TMSPMA-modified GO sheets. The effects of TMSPMA-modified GO sheets content on various physical properties were investigated. Results show that PNIPAM/SA/GO hydrogels undergo a large volumetric change in response to temperature. It also exhibits significantly larger water uptake compared to conventional PNIPAM/SA hydrogels. Moreover, the PNIPAM/SA/GO hydrogels have a much better mechanical properties than the conventional PNIPAM/SA hydrogels.

Synthesis of hydrophilic and organophilic chemically modified graphene oxide sheets.

In this work, hydrophilic and organophilic chemically modified graphene oxide (CMGO) sheets were prepared through a two-step diimide-activated amidation. The hydrophilic and organophilic products were characterized by atomic force microscopy, transmission electron microscopy and ultraviolet-visible spectroscopy. The resulted dispersions are homogeneous and exhibit long-term stability, which will facilitate the combination of CMGO sheets with polymers to yield homogeneous composites.

Synthesis of graphene oxide-based biocomposites through diimide-activated amidation

In this work, a novel and facile method for covalent attachment of biomaterials to graphene oxide sheets (GOS) was developed. Four conjugates were obtained via the diimide-activated amidation reaction under ambient conditions. Final products were characterized by FT-IR spectroscopy, atomic force microscopy and transmission electron microscopy. Electrochemical characterization of the composite showed that the covalently bonded biomaterial retained its bioactivity. This method may provide a way for further preparation of graphene-based biodevices.