Hydrothermal synthesis of nitrogen- and sulfur-co-doped carbon quantum dots from rice straw for fluorescent detection of Hg ²⁺ in aqueous media

and surface O-, N-, and S-containing functional groups, with a minor contribution from dynamic quenching. Furthermore, application to real water samples demonstrated reliable recoveries and good reproducibility. This work provides a sustainable strategy for valorizing agricultural residues into high-performance fluorescent nanomaterials and offers a promising platform for environmental mercury monitoring.