Selective adsorption of toxic heavy metal ions using guanine-functionalized mesoporous silica [SBA-16-g] from aqueous solution

The removal of toxic metal ions e.g. Pb2+, Hg2+ and Cd2+ from aqueous solution were explored using guanine functionalized SBA-16 [SBA-16-G). Nitrogen sorption isotherm, HRXRD, FESEM, HRTEM, EDA-X analysis were performed to investigate the changes in the surface morphology and chemical characteristics of [SBA-16-G) before and after the adsorption of toxic metal ions. Owing to the presence of large number of active functional groups of -NH, -C=O on the surface, this adsorbent demonstrated proficient toxic metal ions removal capacities (maximum adsorption capacity, q(max): 289.9 mg g(-1) for Pb2+ at 303 K, 259.9 mg g(-1) for Hg2+ at 308 K and 228.8 mg g(-1) for Cd2+ at 313 K, respectively) from aqueous medium. The isotherm study dictated that the adsorption data better comply to Langmuir isotherms with R-L value < 1 showing the favourable condition of adsorption. A careful analysis of data revealed that adsorption of these toxic metal ions followed pseudo-second order kinetics. The plot of intra-particle diffusion model depicted two-stage process of adsorption i.e. mass transfer of metal ions to the boundary layer through dispersion followed by sorption into the pores due to intra-particle diffusion. The desorption study indicated that used adsorbent can easily be regenerated using acidic/basic solution and reused several times without causing any significant loss in their adsorption efficiency.