Reduced Graphene Oxide Film:Controllable Preparation And Its Biocompatibility

As a two-dimensional crystal of sp~2 skeleton carbon atoms, the discovery of graphene has attracted a series of research attentions and is considered to be the mother of all graphitic families. Compared with the traditional nano materials such as carbon nanotubes, graphene has a larger surface area(2630 m2/g), high electric charge carrier mobility(1.5×104 cm2V-1s-1), and excellent mechanical properties(tensile strength 130 GPa), which makes graphene a promising candidate in many fields of application. Recently, biological properties of graphene have focused more and more scientific interest for potential applications in thermotherapy, drug delivery, biosensors, and tissue engineering. In addition, such kind of novel material exhibits superior antibacterial activity for antibacterial medical applications and green environmental aspects such as in water treatment and energy conversion.Similar to other nanocarbon materials, graphene also suffers from the bottleneck of hard handling treatment and complicated process for its commercial advances. Thus, it is essential to prepare a macroscopic three-dimentional(3D) structure while maintaining the unique properties of individual graphene sheets. At present, various graphene-based 3D architectures have been constructed including graphene oxide(GO)/reduced graphene oxide(rGO) film, hydrogel, foams et al employing graphene materials(pristine graphene, single-/few-layer graphene, GO flakes) as building blocks. These materials can be used in the field of composites, batteries, supercapacitors, electronics, sensors, water treatment and tissue engineering et al due to their excellent mechanical, thermal, electrical properties and biological properties.rGOF, also known as reduced graphene oxide paper(with thickness over 1 μm) is a paper-like film with layered structure composed of functionalized graphene sheets. There are two ways for preparation of rGOP, i.e. thermal/flash/chemical reduction of GOF and flow-directed filtration of individual reduced graphene oxide sheets, electrophoresis deposition, layer-by-layer self-assembly and liquid-air interface evaporation process. The most common methods above all are thermal reduction and reducing agent reduction of GO. For the letter, such toxic or costly reducer as hydrazine, metal hydride, active metal, reducing acid or phenol is mainly used that may meanwhile affect the flexibility of the product; for the former, during annealing treatment at high temperature, oxygen-containing functional groups(epoxy, carboxyl, and carbonyl) will be removed as small molecules(CO2, CO, and H2O) to approach the pristine structure and recover physicochemical properties. However, the GOF, especially for the free-standing one, it has been demonstrated that the heating process will easily cause delamination problem and the film-like morphology is hard to maintain. Even at relatively lower temperature(e.g. 200℃), macroscopic crumples also occurred and lustrous appearance disappeared most probably due to the release of vigorous gas.In this work, we proposed a step-by-step heating method for preparation of high quality rGOF. This method has been proved to be an advantage of high yield, simple to operate, low temperature, no additional reducing agent and the protection of gas, high safety and no pollution to the environment. Firstly, the modified Hummers method was used to prepare graphite oxide colloids, coating the GO colloids on different substrate such as glass substrate, polystyrene board and polypropylene tube; heating up to 60、120、180℃, respectively for 12 h. The prepared rGOF demonstrates metallic luster on both sides with flat surface and macroscopic continuous structure. To investigate surface topography, chemical state and mechanical properties of the rGOF, we prepared rGOF by optimizing heating process, GO colloid concentration and volume on different substrates.rGOF prepared on polypropylene tube was chosen to characterize cell biocompatibility(Cal72) and antibacterial activity(E.Coli and S.aureus). Both the front and back of the rGOF have been measured. The experiment was divided into two with and without serum and the experimental time were 2 h and 48 h, with the control group setting up to test the cell adhesion of the rGOF. The results indicated that both sides of the r GOF have good cell biocompatibility and antibacterial activity to E.Coli.