Photocatalytic treatment of tannery wastewater using reduced graphene oxide and CdS/ZnO to produce hydrogen with simultaneous sulfide abatement

Abstract

This paper addresses the photocatalytic treatment of sulfide-rich liming bath wastewater from tanneries in an oxygen-free atmosphere. The photoactivity assessment of composites obtained from cadmium sulfide (CdS) and zinc oxide (ZnO) hybridization as well the influence of reduced graphene oxide (RGO) on the photocatalytic activity to generate hydrogen and mitigate sulfide was performed under visible-light irradiation. The results of the X-ray diffraction analysis allowed us to identify the crystalline phases in each synthesized sample. The photocatalysts RGO/(CdS)1.0/(ZnO)0.4 and RGO/(CdS)1.0/(ZnO)0.73/(ZnS)0.57 showed the best performances for hydrogen production of 1.6 mmol g −1cat h−1 and 1.4 mmol g −1cat h−1, respectively, with mitigation of 80–90% of the sulfide content in the tannery wastewater. Long-term reaction tests indicated that the photocatalysts are active for a period of 24 h, and they retain the photoactivity after three photocatalytic cycles. The materials have demonstrated great potential for application in energy recovery from tannery wastewater with simultaneous sulfide abatement, especially the photocatalyst RGO/(CdS)1.0/(ZnO)0.73/(ZnS)0.57, which is more eco-friendly because of its lower cadmium content and minimal leaching of this toxic metal ion during photocatalytic treatment.