Synthesis of CdS/GO modified ZnO heterostructure for visible light dye degradation applications

ZnO nanorods (NRs), ZnO/CdS binary and ZnO/CdS/GO ternary heterostrcutures were prepared by thermal-decomposition and aqueous-solution methods, for applications in visible-light photocatalysis. The morphological, optical, chemical-bonding and luminescence characteristics of the heterostructure photocatalysts were studied. The photocatalytic behaviour of the heterostructures was investigated by methyl orange (MO) dye-degradation under visible-light illumination. CdS with a narrow band gap was used as the principal light absorbing material. However, ternary ZnO/CdS/GO heterostructures were found more effective than the ZnO/CdS binary heterostructures and ZnO nanorods. The ZnO/CdS/GO ternary nanostructure photocatalyst demonstrated a dye-degradation rate constant of ∼1.6 × 10−2 min−1 which is ∼3.64 times higher compared to that of pristine ZnO. Incorporation of CdS and GO onto the ZnO nanorods contributed remarkably to the visible-light photocatalytic performance by: (a) increased photo-absorption over a wider span towards lower energy, (b) improved separation of photogenerated electron-hole pairs via (i) formation of a cascade band layer between ZnO and CdS, further by (ii) utilizing the high electrical conductivity and charging capacity of GO sheets, and also by the (c) significantly increased specific surface area of the photocatalyst (∼148.21 m2 g−1), enabling abundant adsorption of dye on the active sites for photodegradation; thereby, increasing the overall photodegradation yield.