Synthesis and characterization of an activated carbon-supported silver-silica nanocomposite for adsorption of heavy metal ions from water

We report synthesis and characterization of an activated carbon-supported silver-silica nanocomposite (AC-Ag-SiO2) for removal of Cu2+, Pb2+, Cd2+ and Zn2+ ions from single and multi-metal aqueous solutions. Characterization experiments included Atomic force microscopy (AFM), Ultraviolet–visible spectrophotometry (UV–Vis), Fourier transform Infrared spectrophotometry (FT-IR) and X-ray diffraction (XRD) analysis. Adsorption of heavy metals onto the composite strongly depended on contact time (280 min maximal), adsorbent dosage (0.1–0.4 g), solution pH (5.5 ± 0.5 maximal), temperature (298–328 K) and initial metal concentration. Equilibrium data were fitted to the Langmuir, Freundlich and Temkin isotherm models. Kinetic data were fitted to pseudo-first-order and pseudo-second-order kinetic models with the Freundlich isotherm model (R2 ˃ 0.99) and pseudo-second-order kinetic mode (R2 ˃ 0.999) providing a better fit to the experimental data. The maximum adsorption capacity was found to be 84.75 ± 0.24, 81.30 ± 0.2, 87.72 ± 0.96 and 81.97 ± 0.39 mg/g for Cu2+, Pb2+, Cd2+ and Zn2+ ions, respectively. The obtained values of thermodynamic parameters such as ΔG° (−13.72 ± 0.20 to −5.45 ± 0.35 kJ/mol), ΔH° (95.10 ± 14.33 to 162.4 ± 27.17 J/K.mol), and ΔS° (22.81 ± 4.50 to 39.12 ± 8.70 kJ/mol) showed that the adsorption process of Cu2+, Pb2+, Cd2+ and Zn2+ ions onto AC-Ag-SiO2 composite was spontaneous, feasible, endothermic and physical in nature. Regeneration studies suggested that AC-Ag-SiO2 composite could be reused effectively with no statistical significance among the cycles (p > 0.9 for all the four metal ions).