Mg–Zn@HA–AC nanocomposites: Sunlight-induced kinetic degradation of methylene blue and methyl orange with larvicidal activity against Aedes larvae

Synthetic dye contamination and mosquito-borne diseases remain critical challenges in tropical and subtropical regions. In this study, a multifunctional Mg–Zn@HA-AC (magnesium–zinc doped hydroxyapatite–activated carbon) nanocomposite was synthesized via a green co-precipitation method. Structural and spectroscopic analyses confirmed successful incorporation of Mg and Zn into the hydroxyapatite - carbon matrix. UV–Vis and Tauc plot analysis revealed a band gap energy of 3.8 eV, while photoluminescence studies indicated defect-mediated emission behavior and improved charge separation within the composite structure. Under natural sunlight, the nanocomposite achieved 76.47% degradation of methylene blue and 73.76% degradation of methyl orange within 180 min, following pseudo-first-order kinetics (R2 ≥ 0.97). In addition, the nanocomposite exhibited strong larvicidal activity against Aedes aegypti larvae with an LC50 value of 76.9 μg/mL. The enhanced photocatalytic and biological performance is attributed to synergistic interactions, increased active sites, and efficient electron–hole separation within the composite matrix. These findings demonstrate the potential of Mg–Zn@HA-AC as an eco-friendly and solar-driven material for wastewater remediation and vector control applications.