Jianping Gao

Preparation of aligned porous gelatin scaffolds by unidirectional freeze-drying method

Porous gelatin scaffolds with microtubule orientation structure were manufactured by unidirectional freeze-drying technology, and their porous structure was characterized by scanning electron microscopy. Scaffolds with tunable pore size and high porosity up to 98% were obtained by adjusting the concentration of the gelatin solution and crosslinking agent during the preparation process. All the porous gelatin scaffolds exhibited oriented microtubule pores, with width and length from 50 to 100 microm and 100 to 500 microm, respectively. Meanwhile, the properties of the scaffolds, such as porosity, water adsorption ability and compressive strength, were studied. In vitro enzymatic degradation results showed that the absolute weight loss of the gelatin scaffolds exhibited an increasing trend from low to high gelatin concentration used to prepare gelatin scaffolds; in vitro cell culture results indicated that the porous gelatin scaffolds were non-toxic to cartilage cells, since the cells spread and grew well.

High strength graphene oxide/polyvinyl alcohol composite hydrogels

Polyvinyl alcohol (PVA) hydrogels have been proposed for use as promising biomaterials in biomedical and tissue engineering but their poor mechanical and water-retention properties have hindered their development. Graphene oxide (GO), an excellent nanofiller, was added to PVA to make GO/PVA composite hydrogels by a freeze/thaw method. The mechanical properties of the GO/PVA hydrogels were significantly improved. Compared to pure PVA hydrogels, a 132% increase in tensile strength and a 36% improvement of compressive strength were achieved with the addition of 0.8 wt% of GO, which suggests an excellent load transfer between the GO and the PVA matrix. The incorporation of certain amount of GO into composite hydrogels does not affect the toxicity of PVA to osteoblast cells.

Cost-Effective Reduced Graphene Oxide-Coated Polyurethane Sponge As a Highly Efficient and Reusable Oil-Absorbent

Reduced graphene oxide coated polyurethane (rGPU) sponges were fabricated by a facile method. The structure and properties of these rGPU sponges were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray diffraction, and scanning electron microscopy. The rGPU sponges are hydrophobic and oleophilic and show extremely high absorption for organic liquids. For all the organic liquids tested, the absorption capacities were higher than 80 g g(-1) and 160 g g(-1) (the highest value) was achieved for chloroform. In addition, the absorption capacity of the rGPU sponge did not deteriorate after it was reused 50 times, so the rGPU sponge has excellent recyclability.

Factors that Affect Pickering Emulsions Stabilized by Graphene Oxide

Stable Pickering emulsions were prepared using only graphene oxide (GO) as a stabilizer, and the effects of the type of oil, the sonication time, the GO concentration, the oil/water ratio, and the pH value on the stability, type, and morphology of these emulsions were investigated. In addition, the effects of salt and the extent of GO reduction on emulsion formation and stability were studied and discussed. The average droplet size decreased with sonication time and with GO concentration, and the emulsions tended to achieve good stability at intermediate oil/water ratios and at low pH values. In all solvents, the emulsions were of the oil-in-water type, but interestingly, some water-in-oil-in-water (w/o/w) multiple emulsion droplets were also observed with low GO concentrations, low pH values, high oil/water ratios, high salt concentrations, or moderately reduced GO in the benzyl chloride-water system. A Pickering emulsion stabilized by Ag/GO was also prepared, and its catalytic performance for the reduction of 4-nitrophenol was investigated. This research paves the way for the fabrication of graphene-based functional materials with novel nanostructures and microstructures.

Fabrication of gold nanoparticle/graphene oxide nanocomposites and their excellent catalytic performance

A simple method was used to fabricate gold nanoparticle/graphene oxide nanocomposites that exhibited unexpected catalytic activity for the Suzuki–Miyaura coupling reaction of chlorobenzene and phenylboronic acid.

An environmentally friendly method for the fabrication of reduced graphene oxide foam with a super oil absorption capacity

Three kinds of graphene oxide (GO) foams were fabricated using different freezing methods (unidirectional freezing drying (UDF), non-directional freezing drying, and air freezing drying), and the corresponding reduced graphene oxide (RGO) foams were prepared by their thermal reduction of those GO foams. These RGO foams were characterized by Fourier transform infrared spectroscopy, thermal gravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The absorption process and the factors that influence the absorption capacity were investigated. The RGO foams are hydrophobic and showed extremely high absorbing abilities for organic liquids. The absorption capacity of the RGO foams made by UDF was higher than 100 g g(-1) for all the oils tested (gasoline, diesel oil, pump oil, lubricating oil and olive oil) and had the highest value of about 122 g g(-1) for olive oil. The oil absorption capacity of the GO foams was lower than that of the RGO foams, but for olive oil, the absorption capacity was still high than 70 g g(-1), which is higher than that of most oil absorbents.

Actuator materials based on graphene oxide/polyacrylamide composite hydrogels prepared by in situ polymerization

Actuator materials based on graphene oxide/polyacrylamide (GO/PAM) hydrogels were prepared by in situ polymerization. Their structure and properties were characterized by scanning electron microscopy, X-ray photoelectron spectrometry, thermogravimetric analysis, Fourier transform infrared spectroscopy and mechanical testing. The results indicate that some PAM macromolecules were grafted onto the GO nanosheets, and this led to good dispersion of the GO nanosheets in the composite hydrogels and consequently a significant improvement of their mechanical properties. The compressive strength of the GO/PAM hydrogel loaded with 1 wt% GO increased 6-fold in comparison to that of pure PAM hydrogel. The GO/PAM based hydrogels were responsive to external stimuli such as pH and electric fields.

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.

Oxidation of SO2 to SO3 catalyzed by graphene oxide foams

Porous graphene oxide foams were prepared by unidirectional freeze-drying technology and used to investigate the reaction between graphene oxide (GO) and SO2. The structure and composition changes of the graphene oxide were monitored by X-ray photoelectron spectrometry (XPS), Raman, X-ray diffraction (XRD), Thermogravimetric analysis (TGA), and ultraviolet-visible spectroscopy (UV-vis), and the product of the reaction was analyzed by an EDTA titration. The results show that SO2 was oxidized to SO3 and the GO was reduced. GO not only acts as the oxidant in the reaction, but also as the catalyst to catalyze the reaction of SO2 and O2 to form SO3. This catalytic action is more active in the aqueous GO suspensions than in the foams. The GO foams can adsorb SO2 and convert it to SO3 which then changes to SO42− on contact with water. This offers a new effective method of converting noisome SO2 gas to SO3 at room temperature.

Porous graphene oxide/carboxymethyl cellulose monoliths, with high metal ion adsorption.

Orderly porous graphene oxide/carboxymethyl cellulose (GO/CMC) monoliths were prepared by a unidirectional freeze-drying method. The porous monoliths were characterized by Fourier transform infrared spectra, X-ray diffraction and scanning electron microscopy. Their properties including compressive strength and moisture adsorption were measured. The incorporation of GO changed the porous structure of the GO/CMC monoliths and significantly increased their compressive strength. The porous GO/CMC monoliths exhibited a strong ability to adsorb metal ions, and the Ni(2+) ions adsorbed on GO/CMC monolith were reduced by NaBH4 to obtain Ni GO/CMC monolith which could be used as catalyst in the reduction of 4-nitrophenol to 4-aminophenol. Since CMC is biodegradable and non-toxic, the porous GO/CMC monoliths are potential environmental adsorbents.