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

Abstract

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 °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.