Semi-liquid-state flux assisted synthesis of CdS for boosting photocatalytic hydrogen evolution

So far, the study of efficient and durable photocatalysts for hydrogen production from water splitting has remained a paramount avenue for mitigating the ongoing energy crisis and environmental pollution. Nevertheless, CdS nanoparticles, which are one of the most popular photocatalysts for research, still have problems such as easy agglomeration and low separation efficiency of photogenerated carriers. Herein, a low-temperature heat treatment strategy assisted by NaCl-KCl mixed molten salts was employed to synthesize a superior CdS photocatalyst for hydrogen production. During the heating process under only 500 °C, the complex molten salts existed in a "semi-liquid solution" state due to their Tammann temperature, which helped to not only improve the crystallinity and inhibit the oxidation of CdS, but also introduce Cl dopants and S vacancies into CdS. It has been experimentally and theoretically evidenced that the defects in CdS facilitated the phase transition of CdS from a cubic to a more stable hexagonal structure, and also provided increased carrier density as well as more active sites for CdS. As a result, the modified CdS exhibited a 40 times boosted photocatalytic hydrogen evolution rate up to 4.33 mmol h −1 g −1 with an apparent quantum efficiency of 5.8% at 420 nm without a co-catalyst. This work highlighted the critical role of complex chloride molten salts in obtaining high-quality semiconductor photocatalysts during the calcination process. Highly crystalline CdS with an S defect and a Cl dopant was synthesized through low-temperature calcination within semi-liquid-state complex chloride molten salts.