Photoelectrochemical degradation of orange II dye in wastewater at a silver-zinc oxide/reduced graphene oxide nanocomposite photoanode

In the search for novel and efficient electrochemical materials as electrodes for photoelectrochemical degradation and mineralisation of organic pollutants in water treatment, a photoanode consisting of a composite of silver (Ag), zinc oxide (ZnO) and reduced graphene oxide (rGO) was synthesized, characterised and photoelectrochemically applied in the degradation and possible mineralisation of organic pollutants in a water treatment process. The ZnO and Ag-ZnO nanoparticles were synthesised by a facile one-step co-precipitation method followed by calcination at 400 degrees C. The nanoparticles were further used to dope reduced graphene oxide by dispersion in methanol, sonicated and dried. The prepared materials were characterised using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), UV-visible spectroscopy (UV-vis), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The obtained Ag-ZnO-rGO nanocomposite was compressed and fabricated into an electrode. The photoelectrochemical applicability of Ag-ZnO-rGO as a photoanode material was tested by the photoelectrochemical degradation of orange II dye as target organic pollutant in 0.1 M Na2SO4 solution at a current density of 15 mA cm(-2). The results revealed that the photoelectrochemical process was pH and current density dependent and that the Ag-ZnO-rGO electrode has a higher photoelectrochemical performance (93% removal efficiency) compared to the ZnO-rGO electrode (87% removal efficiency) and rGO (73% removal efficiency). The degree of mineralisation of the dye was determined using total organic carbon (TOC) measurement which gave better removal efficiency for the Ag-ZnO-rGO electrode (67.9%) in relation to ZnO-rGO (58.7%) and rGO (45.3%) electrodes.