Photo-electrochemical application of novel carbon - metal oxides nanocomposites for the degradation of selected organic pollutants in water : experimental and computational studies

Ph.D. (Chemistry)Abstract: In the search for novel photo-electrode material, the photocatalytic properties of selected materials were studied before their applications for photoelectrochemical degradation of organic pollutants. In this research work, carbon materials such as reduced graphene oxide (RGO) and exfoliated/expanded graphite (EG) were used to form carbon-metal oxides nanocomposite materials. The materials were characterised using UV-Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), energy dispersive X-ray spectrometry (EDX), Fourier transformed infrared spectroscopy (FTIR) and Raman spectroscopy, cyclic voltammetry, linear sweep voltammetry and chronoamperometry response. Furthermore, the materials were employed for photocatalytic, electrocatalytic and photo-electrocatalytic degradation of organic pollutants in water. In this regard, a nanocomposite consisting of silver, silver oxide (Ag2O), zinc oxide (ZnO) and graphene oxide (GO) was synthesised, characterised and photocatalytically applied in the degradation of organic pollutants in water treatment process. The Ag-Ag2O-ZnO nanostructure was synthesised and calcined at 400 ºC. It was functionalised using 3- aminopropyl triethoxysilane and anchored on carboxylated graphene oxide via the formation of an amide bond to give the Ag-Ag2O-ZnO/GO nanocomposite. The as- prepared Ag-Ag2O-ZnO/GO nanocomposite was investigated as a photocatalyst for the photocatalytic degradation of acid blue 74 dye under visible light irradiation in synthetic wastewater containing the dye. The results showed that Ag-Ag2O-ZnO/GO nanocomposite has a higher photocatalytic activity (90% removal with a kinetic rate constant of 10.69 × 10-3 min-1) than Ag-Ag2O-ZnO (85% removal) and ZnO (75% removal) respectively. Due to the high photocatalytic activity of the Ag-Ag2O-ZnO/GO nanocomposite, a photoanode consisting of a composite of silver (Ag), zinc oxide oxide (ZnO) and reduced graphene oxide (rGO) was photoelectrochemically applied in the degradation and possible mineralisation of organic pollutants in water treatment process. The ZnO and Ag-ZnO nanoparticles were synthesised. The nanoparticles were used to dope reduced graphene oxide by dispersion in methanol, sonicated and dried. The obtained Ag-ZnO-rGO nanocomposite was compressed and fabricated into an electrode. The Ag-ZnO-rGO as a photoanode material was used for the photoelectrochemical degradation of orange II dye as target organic pollutant in 0.1 M Na2SO4 solution at a current density of 15 mAcm-2. The ..