A good photocatalyst maximizes the absorption of excitation light while reducing the recombination of photogenerated carriers. Among visible light responsive materials, CdS has good carrier transport capacity; however, its photostability is poor and limits its use. Here, the synthesis of a new hydrothermal CdS is reported, and post-synthesis annealing determines crystal properties and spectroscopic characteristics. The introduction of sulfur vacancies as intra band gap states is the key factor for the enhancement of photocatalytic activity. In fact, by spectroscopic and photo-electrochemical experiments, we demonstrate that sulfur vacancies act as an electron sink, favoring the charge transfer process to methyl orange. In addition, the studied hydrothermal CdS is characterized by very high stability, thus enabling a visible-light active photocatalyst that is overall recyclable, stable and more efficient than the commercial benchmark.
Keywords: azo bond; hydrogenation; hydrothermal CdS; photocatalysis; photostability; sulfur vacancies; visible light.