Zixing Shi

Facile Synthesis of Soluble Graphene via a Green Reduction of Graphene Oxide in Tea Solution and Its Biocomposites

The chemical reduction of graphene oxide (GO) typically involves highly toxic reducing agents that are harmful to human health and environment, and complicated surface modification is often needed to avoid aggregation of the reduced GO during reduction process. In this paper, a green and facile strategy is reported for the fabrication of soluble reduced GO. The proposed method is based on the reduction of exfoliated GO in green tea solution by making use of the reducing capability and the aromatic rings of tea polyphenol (TP) that contained in tea solution. The measurements of the resultant graphene confirm the efficient removal of the oxygen-containing groups in GO. The strong interactions between the reduced graphene and the aromatic TPs guarantee the good dispersion of the reduced graphene in both aqueous and a variety of organic solvents. These features endow this green approach with great potential in constructing of various graphene-based materials, especially for high-performance biorelated materials as demonstrated in this study of chitosan/graphene composites.

Mechanically strong graphene oxide/sodium alginate/polyacrylamide nanocomposite hydrogel with improved dye adsorption capacity

In this paper, a novel graphene oxide (GO)/sodium alginate (SA)/polyacrylamide (PAM) ternary nanocomposite hydrogel with excellent mechanical performance has been fabricated through free-radical polymerization of acrylamide (AAm) and SA in the presence of GO in an aqueous system followed with ionically crosslinking of calcium ions. As-prepared GO/SA/PAM (weight ratio SA : AAm = 1 : 2) ternary nanocomposite hydrogel with 5 wt% of GO displays a compressive stress as high as 1.543 MPa at the compressive deformation of 70%. The tensile strength and modulus of the hydrogel achieved ∼201.7 and ∼30.8 kPa, respectively. In the meantime, the ternary nanocomposite hydrogels can recover a large proportion of elongation at breakage and exhibits good elasticity. Additionally, the GO/SA/PAM ternary nanocomposite hydrogel exhibited good adsorption properties for water-soluble dyes. After introducing GO, the dye adsorption capacities of the hydrogel were significantly improved.

Boron nitride nanosheets: large-scale exfoliation in methanesulfonic acid and their composites with polybenzimidazole

Boron nitride nanosheets (BNNSs) are two dimensional crystals composed of boron and nitrogen atoms covalently bonded in a hexagonal manner with exceptional physiochemical properties. However, the researches on BNNS are rather limited due to the lack of an efficient method to prepare BNNS. In this study, we report a facile and efficient method for the fabrication of BNNS through liquid-phase exfoliation of hexagonal boron nitride particles (h-BNs) in methanesulfonic acid. The resultant BNNS can be readily disperse in a number of organic solvents, such as N-methyl-2-pyrrolidone. Transmission electron microscopy and atomic force microscopy confirms that the obtained BNNSs are mainly single or few-layered with a thickness less than 3 nm. X-Ray photoelectron and infrared spectroscopy reveal that almost no compositional change occurred in BNNS during the superacid-assistant exfoliation process. The BNNS holds great promise in a number of important applications as demonstrated in this study of poly [2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI)/BNNS composites. The OPBI/BNNS composites showed superior mechanical and thermal properties as compared to neat OPBI and h-BN reinforced ones.

Self-assembly of graphene into three-dimensional structures promoted by natural phenolic acids

Three-dimensional (3D) structures of graphene have attracted extensive interest for their practical applications, such as supercapacitors and catalyst supports. Self-assembly is a typical technique to fabricate macroscopic graphene materials integrated with various superior properties. However, an efficient and environmentally-friendly strategy is still needed. In this paper, we report a green and mild method for the synthesis of 3D architectures of graphene. This proposed method is based on the chemical reduction of graphene oxide (GO) with the aid of a range of natural phenolic acids and in situ self-assembly of graphene sheets via π–π interactions. The obtained monolithic graphene exhibits low density, super hydrophobicity, high porosity, excellent mechanical strength and electrical conductivity. These multifunctional products can be used as adsorbents for removal of oils, organic solvents and dyes from contaminated water, as well as electrode materials for supercapacitors.

Direct exfoliation of graphene in methanesulfonic acid and facile synthesis of graphene/polybenzimidazole nanocomposites

The emerging field of graphene(GP)-based polymer nanocomposites has continued to be the focus of considerable interest in recent years because of the unparalleled improvement shown in mechanical, thermal, and electrical properties compared to the neat polymer. However, these improvements largely depend on the synthesis of well-exfoliated and high-quality GP. In this paper, we report a facile method for the production of GP sheets through the liquid-phase exfoliation of graphite in methanesulfonic acid (MSA). Raman, X-ray photoelectron and infrared spectroscopies reveal that the obtained GP has a low-defect density with a low degree of oxidation. Transmission electron microscopy and atomic force microscopy further confirm that the resulting GP is in the well-exfoliated state. Using this GP/MSA solution as a reaction solvent medium, polymer nanocomposites are prepared by in situpolymerization of poly [2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI). Compared to pure OPBI, the resulting OPBI/GP nanocomposites show simultaneously improved Youngs modulus, tensile stress, toughness, storage modulus and thermal stability with the addition of extremely small amounts of GP. The high levels of reinforcement are attributed to the good dispersion and effective stress transfer between polymer and GP as evidenced by SEM images of the fracture surfaces, and the excellent intrinsic properties of the high-quality GP. All these features make this simple procedure a potential route for the fabrication of low-cost and high-performance polymer nanocomposites.

Gelatin-assisted fabrication of water-dispersible graphene and its inorganic analogues

Two dimensional nanomaterials are of great significance in a wide range of applications due to their high surface area and novel properties. Here we offer a simple and large-scale method to prepare graphene and its inorganic analogues (MoS2, WS2 and boron nitride) by the sonication of their bulk materials in an aqueous solution of gelatin. The concentrations of the obtained stable dispersions were up to 0.6, 0.8, 0.9 and 1.4 mg mL−1 for graphene, MoS2, WS2 and boron nitride, respectively. Transmission electron microscopy strongly suggests that the materials have been exfoliated into few- or mono-layer thin sheets. Specifically, graphene and MoS2 dispersion have been directly employed to fabricate gelatin–graphene composites. Scanning electron microscope images show that graphene flakes were homogeneously dispersed in the composites. The tensile test results show that the mechanical properties of gelatin films have been remarkably improved by graphene rather than MoS2.

Gum arabic assisted exfoliation and fabrication of Ag–graphene-based hybrids

Gum arabic (GA), a natural polymer, is extensively used in food, drug, confectionery and soft drinks processing. In this paper, we present a green and facile approach for preparing graphene–Ag nanohybrids assisted by GA. In brief, GA functionalized graphene sheets (GA-G) were prepared by directly exfoliating graphite flakes in gum arabic (GA) aqueous solution with sonication. The yield of graphene exfoliation was systemically studied by varying the initial graphite concentration, GA concentration and sonication time. Furthermore, the GA functionalized graphene sheets–Ag nanoparticle hybrids (Ag/GA-G) were fabricated by adding AgNO3 aqueous solution into the GA-G water dispersion. The silver ions were directly reduced and immobilized on the surface of the GA-G nanosheets by GA. The Ag/GA-G hybrid materials can be used as suitable substrates of SERS for the detection of 4-aminothiophenol (4-ATP) at a detectable level of a concentration of 10−6 M in aqueous environments.

Unzipped multiwalled carbon nanotube oxide/multiwalled carbon nanotube hybrids for polymer reinforcement.

Multiwalled carbon nanotubes (MWNTs) have been widely used as nanofillers for polymer reinforcement. However, it has been restricted by the limited available interface area of MWNTs in the polymer matrices. Oxidation unzipping of MWNTs is an effective way to solve this problem. The unzipped multiwalled carbon nanotube oxides (UMCNOs) exhibit excellent enhancement effect with low weight fractions, but agglomeration of UMCNOs at a relatively higher loading still hampered the mechanical reinforcement of polymer composites. In this paper, we interestingly found that the dispersion of UMCNOs in polymer matrices can be significantly improved with the combination of pristine MWNTs. The hybrids of MWNTs and UMCNOs (U/Ms) can be easily obtained by adding the pristine MWNTs into the UMCNOs aqueous dispersion, followed by sonication. With a π-stacking interaction, the UMCNOs were attached onto the outwalls of MWNTs. The morphologies and structure of the U/Ms were characterized by several measurements. The mechanical testing of the resultant poly(vinyl alcohol) (PVA)-based composites demonstrated that the U/Ms can be used as ideal reinforcing fillers. Compared to PVA, the yield strength and Youngs modulus of U/M-PVA composites with a loading of 0.7 wt % of the U/Ms approached ∼145.8 MPa and 6.9 GPa, respectively, which are increases of ∼107.4% and ∼122.5%, respectively. The results of tensile tests demonstrated that the reinforcement effect of U/Ms is superior to the individual UMCNOs and MWNTs, because of the synergistic interaction of UMCNOs and MWNTs.

Graphene–aramid nanofiber nanocomposite paper with high mechanical and electrical performance

A novel mechanically strong, electrically conductive nanocomposite paper based on reduced graphene oxide nanosheets and aramid nanofibers was prepared by vacuum-assisted filtration followed by reduction.

Functionalization of unzipped carbon nanotube via in situ polymerization for mechanical reinforcement of polymer

Multiwalled carbon nanotubes (MWNTs) have been widely used as mechanical reinforcement agents during the past decades. However, the complete achievement of mechanical enhancement has been greatly impeded by their limited available interfacial area (AIA) and weak adhesion force with the polymer matrix. In this paper, we use unzipped MWNTs (uCNTs) as a precursor to fabricate poly(methyl methacrylate) (PMMA) functionalized uCNTs (uCNTs-P) via in situ free radical polymerization. Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), X-ray photoelectron spectra (XPS), Raman, and thermogravimetric analysis (TGA) are applied to characterize the structure of resultant uCNTs-P. The mechanical testing of composite films indicated that uCNTs-P were more effective than uCNTs and functionalized MWNTs in improving the tensile strength and Youngs modulus. This excellent reinforcement is attributed to uCNTs-Ps highly available interfacial area and the strong interlocking force with the polymer matrix. This study will guide the design of functionalized uCNTs and the preparation of high-performance polymer composites.