Competitive adsorption mechanisms of Cd(), Cu() and Pb() on bioinspired mesoporous silica revealed by complementary adsorption/isothermal titration calorimetry studies

This study presents the adsorption properties of a bioinspired grafted mesoporous silica material and the competitive effects between Cd( ii ) or Cu( ii ) and Pb( ii ) during the adsorption process. Glutathione, a natural antioxidant known for its metal binding properties, has been successfully grafted to SBA-15 mesoporous silica and the optimum adsorption parameters were determined. This original and multidisciplinary approach combines classical adsorption studies with thermodynamic investigations to understand the adsorption behavior of Cd( ii ), Cu( ii ) and Pb( ii ) on this material. To this end, isothermal titration calorimetry (ITC) has been used to elucidate the mechanisms of single-metal and two-metal adsorption. The results showed affinity in the order Pb( ii ) > Cu( ii ) > Cd( ii ) in single metal systems. Cd( ii ) adsorption relied mainly on physical contributions while Cu( ii ) and Pb( ii ) adsorption was shown to be chemically driven. Two-metal systems highlighted that Cd( ii ) and Pb( ii ) are adsorbed on the same coordination sites, whereas Cu( ii ) and Pb( ii ) are adsorbed on different sites. The material showed good selectivity and encouraging results were obtained on real effluents. This work presents an original adsorption/isothermal titration calorimetry (ITC) study that allowed highlighting the competitive adsorption mechanisms of Cd( ii ), Cu( ii ) and Pb( ii ) on bioinspired mesoporous silica.