Facile synthesis and characterization of ZnO:Al/ZnS/NiO heterojunction thin films with enhanced photocatalytic activities

Abstract

This study covers a physical investigation of ZnO:Al/ZnS/NiO heterojunction thin films and their photocatalytic activities. The obtained samples were analyzed using XRD, FTIR, SEM/EDS, AFM, and UV–vis spectroscopy. The XRD and FTIR results confirmed that the nanocrystalline ZnO, ZnS, and NiO phases were successfully prepared. SEM morphological analysis of the multilayer film indicated that depositing different nanocrystalline layers above one another could deteriorate the adherence of the upper layer. In addition, AFM shows acceptable surface roughness for application as a photocatalyst. Optical analysis revealed that the ZnO:Al/ZnS/NiO multilayer film exhibited an average transmittance of 65%. The Eg value of the ZnO:Al monolayer of 3.26 eV is decreased to 3.15 eV after Al–ZnO/ZnS coupling, whereas ZnO:Al/ZnS/NiO exhibits an additional absorption value of 3.52 eV due to the NiO layer. The photocatalytic activity of ZnO:Al/ZnS/NiO under visible light exhibited an approximately 96% photodegradation efficiency against methylene blue after only 50 min. However, under sunlight, the degradation rates reached 90, 85, and 65% for methylene blue, crystal violet, and Congo red, respectively, in 90 min. This study shows that a synthesized ZnO:Al/ZnS/NiO heterojunction multilayer photocatalyst can efficiently degrade organic pollutants.