Photocatalytic degradation of methylene blue by CdS quantum dots biosynthesized by cysteine synthetase TtCsa1 from Tetrahymena thermophila.

H2S is a crucial endogenous gaseous signaling molecule involved in various metabolic pathways and is associated with the biological response to heavy metal stress. The biomineralization of CdS serves as a critical mechanism for responding to cadmium stress and removing Cd2+ in different organisms. CdS is also a widely utilized semiconductor material for the photocatalytic degradation of dyes. In this study, we found that cysteine synthetase 1 (TtCsa1) is involved in CdS formation under cadmium stress in Tetrahymena thermophila. TtCsa1 also catalyzed CdS formation in vitro, and the synthesized CdS material exhibited controllable particle size and photoluminescence. Concurrently, cysteine and glutathione functioned as capping agents to regulate CdS particle size. The biosynthetically produced CdS degraded 90 % of methylene blue under UV light. Furthermore, CdS-ZnS nanocomposites were synthesized by adding Zn2+ into the CdS biosynthetic system, which decreased the size of CdS particles and increased the degradation rate of methylene blue. The results indicate that the CdS biosynthesized by TtCsa1 from Tetrahymena thermophila is effective in the photocatalytic degradation of organic dyes.