NOx photocatalytic degradation over ZnO–CdS heterostructure composite under visible light irradiation

Abstract

ZnO–CdS composites with different loadings of CdS were prepared by a simple wet chemical synthesis method for NOx degradation under visible light. The influence of CdS presence on the morphological and structural features of the synthesized composites was investigated through SEM, nitrogen adsorption–desorption isotherms, DRS, XRD, and FTIR analyses. XRD results and SEM images revealed the growth of ZnO nanoparticles along the “c” axis due to the presence of CdS leading to the formation of composites with needle/flower-like structures depending on the CdS content. The increased surface area and the enhanced visible light harvesting (e.g., ~ 2.4 eV) were observed for the photocatalyst containing CdS, as BET and DRS results show. The photocatalytic activity measurements evidenced that the NOx degradation using ZnO–CdS composites (60%) is higher comparatively with pristine ZnO (20%). This can be ascribed to the enlargement of surface area, the formation of flower-shaped structure, and the extended visible light response of the composites. Results indicate that there is on optimum value for CdS loading and the ZnO-15% CdS shows the best photoactivity for NO decomposition (60%). The proposed mechanism shows that the creation of heterojunction structure between CdS and ZnO and the subsequent charge separation can be responsible for the high photocatalytic performance of the as-prepared composites. Based on the results, this work represents a way forward in development of ZnO application in NOx abatement in urban environments.