Visible-light- driven photocatalytic degradation of dyes in wastewater using L-lysine-based carbon Dot/TiO2 nanocomposites

• L-Lysine-derived CQDs@TiO₂ enable efficient visible-light dye degradation • Optimal NCs achieved >99% MB and RhB removal with pseudo-first-order kinetics • CQDs narrowed TiO₂ bandgap (∼3.0 eV), boosting light absorption and charge transfer • Nanocomposites showed recyclability, stability, and ROS-driven degradation pathways • Biocompatibility confirmed with >60% cell viability and ROS-scavenging capacity Efficient removal of dye pollutants from wastewater remains a critical environmental challenge. In this work, we introduce the rational design of L-lysine derived carbon dots (LCQDs) integrated with TiO₂ to develop visible-light-responsive LCQDs@TiO₂ nanocomposites (NCs). Five composite materials with systematically varied LCQD loadings were synthesized and comprehensively characterized to elucidate structural, optical, and interfacial properties governing photocatalytic behavior. Incorporation of LCQDs effectively narrowed the TiO 2 bandgap (3.0 eV) and significantly enhanced charge separation, resulting in markedly improved photocatalytic degradation efficiencies of methylene blue (94.6%) and rhodamine B (99.5%) under visible light irradiation. The optimized nanocomposites exhibited substantially higher rate constants than bare TiO 2 , following pseudo-first-order kinetics and demonstrated good stability over at least two consecutive photocatalytic cycles. In vitro cytocompatibility studies in HaCaT keratinocytes revealed acceptable cell viability and minimal perturbation to cell-cycle distribution at relevant exposure concentrations (50 μg/mL), suggesting limited acute biological stress. Overall, this work highlights LCQDs@TiO 2 as an efficient and biologically tolerant photocatalyst platform, offering a promising strategy for sustainable dye remediation under visible-light irradiation .