Tiannan Zhou

A simple and efficient method to prepare graphene by reduction of graphite oxide with sodium hydrosulfite.

Inspired by an ancient reducing method used in textile production, sodium hydrosulfite was used to reduce graphite oxide as an efficient reducing agent in our work. The reduced materials were characterized by x-ray photoelectron spectroscopy, thermogravimetric analysis, wide-angle x-ray scattering, Raman spectroscopy, solid state (13)C NMR spectroscopy and electrical conductivity measurements, respectively. The results showed that graphite oxide can be reduced with sodium hydrosulfite in a few minutes, with a degree of reduction comparable to those achieved with hydrazine. It provides an efficient method to reduce graphite oxide and could be used as a method to prepare novel composites.

Wet-grinding assisted ultrasonic dispersion of pristine multi-walled carbon nanotubes (MWCNTs) in chitosan solution

Ultrasonication is often used to disperse nano-particles in aqueous solution. However, a good dispersion of nano-particles in aqueous solution is not always achieved, due to the fact that incoming ultrasonicwaves in liquid are usually reflected and damped at the gas/liquid interface. In this work, we report a so-called wet-grinding assisted ultrasonication (GU) method, in which wet-grinding of multi-walled carbon nanotubes (MWCNTs) in chitosan solution is carried out before ultrasonication. The dispersions of MWCNTs were characterized by visual comparison, UV/vis spectroscopy, and scanning electron microscopy (SEM). The results demonstrate that the dispersion quality of chitosan/MWCNT suspension prepared by wet-grinding assisted ultrasonication is much better than that by ultrasonication or wet-grinding alone. It was found that wet-grinding could improve the water wettability of MWCNTs and eliminate the barrier of air layer around MWCNTs to ultrasonicwaves. Meanwhile, the composite from the chitosan/MWCNTs suspension prepared by GU method has an obvious improvement in mechanical property compared to pure chitosan. This simple method for integrating MWCNTs and biocompatible chitosan into a homogeneous dispersion may have great potential application in biotechnology, such as preparing composite materials for medicine, bio-fiber, biosensor, antibacterial coating, and cell cultivation.

An environmentally friendly and fast approach to prepare reduced graphite oxide with water and organic solvents solubility

In this paper, reduced graphite oxide (RGO) was prepared using thiourea dioxide as reductant and polyvinylpyrrolidone (PVP) as stabilizer. Thiourea dioxide, a cheap and nontoxic industrialized material, was demonstrated to be an efficient reducing agent for graphite oxide (GO) in this paper. Ultraviolet and visible (UV-vis) spectroscopy results revealed that the reduction of GO could be readily achieved in 10 min, a reaction time which is much shorter than those required in common reduction reactions. The procedures of reduction including the by-products are all nontoxic, thus it is absolutely environmentally friendly. To the best of our knowledge, this is the first time that thiourea dioxide was successfully used to prepare RGO. Moreover, the stabilizer, PVP, which could be easily absorbed onto the surface of RGO, provided RGO with good water and organic solvents solubility, with low conductivity though. However, by controlling the content of PVP, RGO with balanced solubility and conductivity can be obtained. The resultant RGO could be used as nanofillers to prepare conductive materials and biomaterials with potential applications as electrical devices or biosensors.

Size Distribution and Anisotropy of the Minor Phase Droplets in Polypropylene/Ethylene-Octene Copolymer Blends： Effects of Shear and Component Miscibility

In this work, polypropylene (PP)/octene-ethylene copolymer (POE) blends were injection-molded using the socalled dynamic packing injection technique, which imposed oscillatory shear on the gradually cooling melt during the packing solidification stage. In this way, the effect of shear on the size distribution and anisotropy of the minor phase droplets could be investigated. Besides, by using two kinds of POE with different octene contents, the effect of component miscibility was also studied. The results show that the droplet size is mainly determined by composition and miscibility, and droplet anisotropy is mainly determined by droplet size and shear. Most importantly, under the same processing condition, droplet anisotropy increases with droplet size, and there seems a linear fit between them, disregarding the miscibility factor. These results may provide guidance for preparing polymer blends with desired properties by tailoring their phase morphologies.

Enhanced crystallization behaviors of poly(ethylene terephthalate) via adding expanded graphite and poly(ethylene glycol)

A compound additive system consisting of expanded graphite (EG) and poly(ethylene glycol) (PEG) was designed to enhance the crystallization of poly(ethylene terephthalate) (PET). In this additive system, EG acted as a heterogeneous nucleating agent to reduce energy barrier for nucleation, while PEG played as plasticizer to improve mobility of PET chains. Simultaneously adding EG and PEG resulted in faster crystallization kinetics than the cases of solely adding EG or PEG in both of non-isothermal and isothermal crystallization processes, indicating a synergistic effect of EG and PEG on enhancing PET crystallization. However, for non-isothermal crystallization process, in which crystallization occurred from a cooling melt, EG played a dominant role. As to isothermal crystallization process where crystallization took place in a super-cooling state, PEG seemed to be more important. Moreover, the chain conformation change among the semi-crystalline PET specimens was ascertained by Fourier transform infrared spectroscopy.

The different effect of reduced graphene oxide and graphene oxide on the performance of chitosan by using homogenous fillers

How reduced graphene oxide (rGO) and graphene oxide (GO) affect the performance of chitosan (CS) nanocomposites is discussed in this paper. A special two-step reduction method was used to prepare the CS–rGO nanocomposite films, firstly, the CS–GO nanocomposite films were prepared by the solution casting method, and secondly, the prepared CS–GO films were immersed into a reducing agent aqueous solution in which the reducing agents could diffuse onto the surface of the GO sheets and then reduce them. So this method could avoid the phenomena of aggregation, morphology change and rearrangement of the GO sheets, which would happen if they are directly reduced in the CS–GO solution with or without a surfactant. The results show that the loading of the two kinds of fillers can enhance the tensile strength of the nanocomposites, but the mechanism is different, one reason is due to the strong interfacial interaction between GO and CS, and another one may be due to the high mechanical strength of rGO and the recrystallization of the CS matrix during the reduction process. This work provides a new way to analyze the interfacial interaction between the filler and CS matrix, and also could be used in other polymer systems to find the essential mechanism of how the filler could affect on the mechanical properties of nanocomposites.