Efficient removal of Cd(II) and Pb(II) on NiFeAl-LDH@Polystyrene nanocomposite in single and binary systems: Optimization, kinetic and isotherm studies

Abstract

Toxic heavy metals have undesirable consequences for the health of all living things, and their presence in the aquatic environment is a significant concern. In this study, a core-shell nanocomposite (NiFeAl-LDH@Polystyrene(PS)) was synthesized by recycling styrofoam waste with PS:LDH ratios of 2:1 and characterized using (TEM, SEM/EDS, XRD, FTIR, and BET). Then investigate its ability to adsorb Cd⁺² and pb⁺² ions in single and binary systems. Results showed a hexagonal platelet morphology of NiFeAl-LDH uniformly covered by a shell of PS nanosphers with an average pore diameter of 28.63 nm and a successful adsorption of Cd⁺² and pb⁺² ions on NiFeAl-LDH@PS. The optimization and influence of adsorption parameters (pH, dosage, agitation speed, initial concentration, and contact time) on the adsorption process were investigated using RSM analysis, yielding a good fit between experimental data and predicted responses with a correlation coefficient (R²) of 0.9956 and 0.9521 for Cd⁺² and pb⁺², respectively. Adsorption experiments showed that the removal efficiency of Cd⁺² and pb⁺² in single-component system was 94.42 % and 99.65 %, respectively. While in the binary system, the removal efficiencies of Cd⁺² and pb⁺² were reduced, indicating that Cd⁺² and Pb⁺² adsorption was affected by the presence of other metal ion. The Langmuir isotherm model with a maximum capacity of 57.4713 and 177.305 mg/g, for Cd⁺² and pb^+2, respectively, and the competitive Langmuir model best described the adsorption data in a single-and binary-component system. In a single-component system, it was found that the PSO models accurately described the adsorption, indicating a chemosorption process. Additionally, the modified PSO was used to describe the binary adsorption data on NiFeAl-LDH@PS. Electrostatic force interaction, oxygen-containing functional groups, and complexation reactions controlled the adsorption process. NiAlFe-LDH@PS showed significant reusability as the efficiency was 38.56 % and 42.37 % for Cd⁺² and Pb⁺², respectively, after six regeneration cycles. In conclusion, NiAlFe-LDH@PS nanocomposite can be considered as an effective adsorbent in the removal of heavy metals from aqueous solutions.