Preparation Of Graphene Oxide/Chitosan Composite Film And Exploration Of Its Antibacterial Properties And Controlled Wettability

Since graphene was isolated from graphite in 2004 by means of mechanical exfoliation, it has been served as star materials of which the preparation, characterization and synthesis of derivatives and composite materials have been widely explored. As one of the most important derivatives of graphene, graphene oxide (GO) with the existence of reactive oxygen groups, is more inclined to be dispersed, functionalized and compounded with other substances. In recent years, the researches about graphene and graphene oxide based composites have been more and more active because of their excellent performance and they have been widely applied in many fields such as solar cells, biosensors, tumor detection and therapy and so on. Chitosan (CS) as a kind of natural amino polysaccharide, due to the existence of active groups such as amino and hydroxy, also has excellent ability to be functionalized and compounded with other materials. In this paper, GO and CS were successfully combined together by a one-step vacuum filtration method resulting in fabricating laminar composite films. Then a series of experiments were designed to explore the bacteriostatic effect of the composite films. Moreover, different composite films were fabricated using GO and CS mixed solutions with different pH, and the relationships of the wettability of different films and pH were also explored.First GO suspension was fabricated using modified Staudenmaiers methods combined with the assist of ultrasonication and then its morphology and size were observed with transmission electron microscope (TEM). GO and CS mixed solutions with different proportion of CS were prepared and vacuum-filtrated to obtain different graphene oxide/chitosan (GO/CS) composite films. According to the stability of different films the proportion of CS was optimized, and through the scanning electron microscope (SEM), tensile testing machine and other characterizations, both surface and cross-section morphologies of the film and its mechanical properties were obtained. Then the antibacterial effect of the GO/CS composite films was explored--first of all, the airborne bacteria test based on previous literature was conducted to explore whether it has bacteriostatic effect as reported; then the composite film was set under different liquid and solid environment to verify its interaction with bacteria. The pH of mixed solutions were also adjusted to obtain different GO/CS films and the relationship of pH and the wettability containing water contact angles in the air, oil contact angles under water and adhesion force of oil under water of the films were further explored.Through the experiment, finely dispersed GO suspension was successfully prepared. TEM images showed that the GO has single layer, but the flakes have many wrinkles to stand stable rather than keep absolute flat. By the means of vacuum filtration, GO/CS composite films with different ratios of CS were fabricated. After soaked and ultrasounded in water for a certain time, it was proved that only when the content of CS is 40%, the composite film is intact and stable. The SEM images showed that the film has a laminar structure. Through the airborne bacteria test according to the literature it is preliminarily concluded that the antibacterial effect of the composite film is not obvious. After the films were set into liquid medium for a certain time, a large amount of bacteria with complete cellular structure were observed to adhere on the films which further verified that the films were not bacteriostatic. We envisaged that the electrostatic interaction between GO and CS impaired the antibacterial effect of both GO and CS. Although GO/CS composite film was not bacteriostatic, it can isolate bacteria from nutrients which provides the possibility to apply in packing materials. By adjusting the pH of GO and CS solution, films with different wettability containing water contact angles in the air, oil contact angles under water and adhesion force of oil under water were obtained. Therefore it is possible to achieve wettability-controlled surfaces by adjusting pH of the mixing solutions.