Tunable surface charge and hydrophilicity of sodium polyacrylate intercalated layered double hydroxide for efficient removal of dyes and heavy metal ions

Sodium polyacrylate (PAAS) intercalated layered double hydroxide (LDH) composites were fabricated and applied for removal of methylene blue (MB), Pb2+ and Hg2+ ions in aqueous solution. The properties of PAAS/LDH, such as surface area, surface charge and hydrophilicity, were investigated. The effects of contact time, adsorbent dosage, pH of solution, temperature and interfering ions on adsorption process were examined. The fast kinetics and high adsorption capacity (210.9 mg/g for MB, 345.4 mg/g for Pb2+ and 142.7 mg/g for Hg2+) showed that PAAS/LDH was an efficient adsorbent. Moreover, PAAS/LDH could rapidly lower the concentrations of MB, Pb2+ and Hg2+ from ppm levels to 3−4 ppb. The adsorption kinetic followed the pseudo-second order model. And the adsorption isotherms were well described by Langmuir model. The negative value of ΔGo and the positive value of ΔHo indicated spontaneous and endothermic nature of these adsorption processes. Abundant carboxyl groups, negative charge and super-hydrophilicity of laminate were the basis of adsorption. In addition, adsorption of Pb2+ and Hg2+ might be attributed to the formation of complexes between carboxyl groups and heavy metal ions. The above results confirmed that PAAS/LDH was a promising adsorbent to efficiently remove heavy metal ions and cationic dye from aqueous solution.