Synthesis and characterization of reduced graphene oxide-loaded cotton as phase-boundary catalyst in the oxidation of styrene by aqueous hydrogen peroxide

Abstract

The research described in this thesis is a comprehensive account of the synthesis and characterisation of reduced graphene oxide-loaded textile as a phase-boundary catalyst in the oxidation of styrene with aqueous hydrogen peroxide. A new model of phase-boundary catalyst (PBC) is designed from octadecyltrichlorosilane /polypyrrole/reduced graphene oxide/cotton (OTS/PPy/RGO/CT) for the oxidation of styrene by aqueous hydrogen peroxide. Cotton cellulose textile acts as a layered platform where the reduced graphene oxide (RGO) and polypyrrole (PPy) embedded on it. It has been reported that graphene arose as a candidate as a catalyst for oxidation reaction. Cotton textile is chosen owing to the relatively high network surface area, the abundance of hydroxyl functional group and ability to immobilize graphene oxide (GO) on its surface. Polypyrrole is one of conducting polymers capable to increase the conductivity and induced magnetic field. The effect of magnetic field on the selectivity and activity of the PBC has been studied by applying an electric current on the conductive layered catalyst. A well-attached graphene oxide to cotton (GO/CT) composite has been prepared by dipping pristine cotton in GO ink, and followed by the reduction of GO to reduced graphene oxide (RGO) in order to produce RGO/CT. The composite surface was further modified with polypyrrole (PPy) via chemical polymerization to obtain PPy/RGO/CT composite. Finally, the PPy/RGO/CT was functionalized with octadecyltrichlorosilane (OTS) in order to get floated layered catalyst (OTS/PPY/RGO/CT) in the immiscible liquid-liquid system. The catalysts were characterised by X–ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible (UV–Vis) spectroscopy, Field-emission scanning electron microscopy (FESEM), thermal analysis and chemical analysis, followed by X–ray photoelectron (XPS) spectroscopy, while the influence of improving electric current of textile by PPy and RGO was also examined using four-point probe technique. The results from FTIR and XPS spectral analyses proved that the polypyrrole and RGO were successfully attached to the textile. The four-point probe technique proved that the presence of PPy and RGO increased the electrical conductivity of cotton textile. PPy plays an important role in increasing the electrical conductivity compared to RGO since PPy is conducting material and its amount is larger than RGO. Meanwhile, apply electric current did not give significant effect on the catalyst‘s activity in static condition. The catalytic activity of OTS/PPy/RGO/CT in stirring condition shows that the reduced graphene oxide act as the catalytic active site in the oxidation of styrene with aqueous hydrogen peroxide, as indicated by the 21% increase in the conversion of styrene when the RGO amount was increased (12 times) in OTS/RGO/CT. Meanwhile, main products of the conversion of styrene using reduced graphene oxide–loaded cotton catalyst were styrene oxide and benzaldehyde, with a higher selectivity toward styrene oxide. However, individual graphene materials and PPy before grafting to cellulose fibers were more selective toward benzaldehyde. Lastly, it can be concluded that, based on its properties, reduced graphene oxide-loaded cotton textile is a promising phase-boundary catalyst for the oxidation reaction, specifically for the oxidation of styrene with aqueous hydrogen peroxide.