Mussel-inspired preparation of layered double hydroxides based polymer composites for removal of copper ions

A novel ternary composite consisting of Mg/Al layered double hydroxides (LDH), polydopamine (PDA) and poly(methyl vinyl ether-alt-maleic anhydride) (PMVE-MA) was fabricated by a facile combination of mussel-inspired chemistry and a ring-opening reaction. Dopamine can serve as a "minimalist mimic" of mussel adhesive protein to form a layer of polydopamine (PDA) on the LDH surface under rather mild conditions (including air atmosphere, aqueous solution, and catalyst free). Subsequently, the PMVE-MA brushes were immobilized onto the PDA modified LDH via a ring-opening reaction. The morphology and chemical compositions of the as-prepared samples were characterized by SEM, TEM, FT-IR, TGA, and XPS. To evaluate the adsorption performance of the PMVE-MA modified LDH (LDH@PDA@PMVE-MA) composites, the obtained samples were used as adsorbents for the removal of copper ions (Cu²⁺) from an aqueous solution. The results demonstrated that the LDH@PDA@PMVE-MA composites showed a significant improvement in the adsorption efficiency towards Cu²⁺, and the adsorption capacity of the LDH@PDA@PMVE-MA composites was found to be 2 times higher than that of pristine LDH. Adsorption kinetics showed that the experimental data were fitted well by the pseudo-second-order kinetic model. Equilibrium data could be best described by the Langmuir isotherm model, with the maximum monolayer adsorption capacity of 193.78 mg/g. Thermodynamic studies indicated that the adsorption of Cu²⁺ onto the LDH@PDA@PMVE-MA composites is an endothermic and spontaneous process. Importantly, it can be easily regenerated by low-cost reagents, and exhibited high removal efficiencies after four cycles of adsorption-desorption. These results suggest that the LDH@PDA@PMVE-MA nanocomposites are good candidate for Cu²⁺ removal from aqueous solutions.