Binary ZnO/Cs_0.33WO₃ heterojunction: A highly effective visible light photocatalyst for the degradation of rhodamine B and methylene blue dyes

Binary nanocomposites of (ZnO)_(100-x)%/(Cs_0.33WO₃)_x% heterojunctions with different weight ratios were prepared. Structural, morphological, and spectral analyses proved that the desired heterojunction nanocomposites are successfully formed. The band gap energy decreased as the concentration of Cs_0.33WO₃ component increased. The photocatalytic experiments revealed that the heterojunction nanocomposite with an optimal ratio of x = 20 % displays superior photodegradation activity in comparison to pristine ZnO and Cs_0.33WO₃ nanostructures. Furthermore, the findings specify that the radicals •OH and ·O₂^–, and photogenerated h⁺ (with following order of •OH > ·O₂^– > h⁺) are the effective species and have the chief function in controlling the photocatalysis process toward the degradation of organic dyes (methylene blue and rhodamine B). It is demonstrated that the creation of ZnO/Cs_0.33WO₃ heterojunction nanocomposite is crucial to boost the separation efficiency of photoexcited charges, and hence hinder the recombination speed of photoexcited charge carriers. Such a finding was further endorsed via the analyses of photoluminescence emissions. It is also established that ZnO/Cs_0.33WO₃ heterojunction nanophotocatalysts obey the Z-scheme heterojunction mechanism. Making ZnO/Cs_0.33WO₃ heterojunction allows a longer lifetime for the photogenerated e^– on the conduction band of ZnO, which was found to be effective in significantly improving their photodegradation capacity. The photocatalytic degradation of rhodamine B catalyzed using (ZnO)_(100-x)%/(Cs_0.33WO₃)_x% nanocomposite with x = 20 % obeyed first-order kinetic model and the kinetic constant rate was almost two times faster than that of pristine ZnO nanoparticles and almost sixteen times greater than that of pristine Cs_0.33WO₃ nanostructures.