Preparation and characterization of Ti/SnO2-Cu-ZnS electrode for wastewater treatment by the direct anodic oxidation process

Abstract

The optimal elimination of organic pollutants in tannery wastewater remains a constant challenge. The objective of this work is to prepare a copper-doped Tin oxide-supported zinc sulfide (Ti/SnO 2 -Cu-ZnS) anode for its application in the treatment of tannery effluent by the direct anodic oxidation process. Sol-gel technique was employed to prepare the SnO 2 -Cu-ZnS sol, and dip-coating was used to coat the pretreated titanium substrate to obtain an anode-type Ti/SnO 2 -Cu-ZnS anode. Finally, the developed Ti/SnO 2 -Cu-ZnS anode was characterized from the differential thermal and thermogravimetric analyses, Fourier Transform infra-red (FTIR) and visible spectroscopies, X-ray diffraction, and linear cyclic voltammetry analyses. The results obtained showed that the Ti/SnO 2 -Cu-ZnS anode is polycrystalline with a tetragonal structure of tin oxide (SnO 2 ), which presents a more intense peak relative to the (110) orientation. The prepared SnO 2 -Cu-ZnS precursor exhibited good thermal stability. Fourier transform infra-red (FTIR) results demonstrated the presence of the main functional groups (Zn-S, Zn-O, Zn-OH, Cu-O, O-H), proving the success of the synthesis of nanostructure materials. The as-prepared electrode showed an oxygen evolution overpotential of 2.6 V vs Ag/AgCl, with a low charge transfer resistance in acidic medium. The application of the electrode materials for the removal of chemical oxygen demand from the tannery effluent reached an efficiency of 91%, with an intensity of 300 mA, a pH= 3, and an inter-electrode distance of 1 cm. The performance of the Ti/SnO 2 -Cu-ZnS anode was attributed to the high oxygen overvoltage, low charge transfer resistance, and high crystallinity, which provide more active sites by facilitating the charge transfer for the production of hydroxyl radicals. • The use of doping elements with low ionic radius promotes the increase in doping. • The incorporation of ZnS into the SnO 2 -Cu network promotes the increase in the transmittance of the Ti/SnO 2 -Cu-ZnS anode. • The incorporation of ZnS into the SnO 2 -Cu network promotes the increase of the optical gap of the Ti/SnO 2 -Cu-ZnS anode. • Doping SnO 2 with Cu and ZnS increases the oxygen release potential of the developed anode (Ti/SnO 2 -Cu-ZnS).