Synthesis and characterization of a new starch/SnO₂ nanocomposite for efficient adsorption of toxic Hg²⁺ metal ion

In this study, starch based nanocomposite (starch/SnO₂) was synthesized and used as an effective adsorbent for the removal of Hg²⁺ from aqueous medium. The as-prepared starch/SnO₂ nanocomposite was characterized by means of the XPS, XRD, BET, FTIR, SEM and TEM analyses. The effects of contact time, pH, initial Hg²⁺ concentration and temperature on the adsorption performance of starch/SnO₂ nanocomposite were investigated thoroughly. The experimental results showed that starch/SnO₂ nanocomposite had high ability to remove Hg²⁺ ion from aqueous medium. The adsorption of Hg²⁺ was maximum at the pH 6 and equilibrium was achieved within 60 min. The pseudo-second-order equation represented the adsorption kinetics with high correlation coefficient (>0.998) and the Freundlich isotherm model fitted the adsorption data better than the Langmuir. The maximum adsorption capacity was found to be 192 mg g^-1 at 25 °C which was increased with the temperature, indicated the endothermic adsorption. The feasibility of Hg²⁺ adsorption onto starch/SnO₂ nanocomposite was also studied thermodynamically and the results showed that the adsorption was spontaneous and chemical in nature. The adsorption capacity of the regenerated adsorbents could still be maintained at 94% by the fourth adsorption-desorption cycle.