Environmentally benign carbon dots with MII/MIII-LDHs for high-efficiency zinc ion removal: adsorption performance, isotherm and kinetic modelling

Abstract

Heavy metal contamination in aquatic bodies presents a critical challenge to both environmental sustainability and public health, particularly due to the toxic, non-biodegradable and persistent nature of metals such as zinc. This study presents a sustainable approach for the effective removal of zinc ions (Zn²⁺) from aqueous solutions using a newly developed adsorbent material. In this approach, layered double hydroxides (LDHs) were synthesized using a co-precipitation method and were further characterized using PXRD, SEM, EDX, and BET analyses and FTIR, fluorescence, photoluminescence, and time-resolved photoluminescence spectroscopies. Comprehensive batch adsorption experiments were performed for Zn²⁺ removal, and its residual concentrations were determined by atomic absorption spectroscopy (AAS). The adsorption data were systematically analyzed using adsorption isotherm models as well as kinetics parameters. The maximum adsorption capacity (q_max) was found to be 39.62 mg g⁻¹ for NiAl LDH, 313.40 mg g⁻¹ for NiAl LDH@CD, 303.52 mg g⁻¹ for MgAl LDH and 314.23 mg/g for MgAl LDH@CD. The removal efficiencies were found to be 87% for NiAl LDH, 93% for NiAl LDH@CD, 86.51% for MgAl LDH and 90.83% for MgAl LDH@CD, with reusability up to seven cycles. These results highlight the potential of LDH-based adsorbents, particularly CD-modified LDH adsorbents, as eco-friendly and cost-effective solutions for heavy metal remediation in wastewater treatment.