Synergistic effects of aluminum doping and amino functionalization to enhance adsorption capacity of ultrathin-nanosheet-assembled calcium silicate hydrate architectures for effective removal of Pb2+ and Cu2+ from aqueous solution

This study demonstrates for the first time the potential of the novel combination of aluminum (Al) doping and amino functionalization to drastically enhance the adsorption capacity of nanosheet-assembled hierarchical calcium silicate hydrate (CSH) architectures for heavy metal Pb2+ and Cu2+ ions in aqueous solution. The designed and prepared amino-functionalized Al-doped CSH (CASH-NH2) exhibits excellent adsorption capability to adsorb Pb2+ and Cu2+ ions. The maximum adsorption capacity of Pb2+ and Cu2+ ions is 911 and 509 mg g-1, respectively, which is much higher than that of pure CSH and other relative CSH-based adsorbents. The experimental measurements of cation exchange capacity (CEC) and surface composition discover that the adsorption of Pb2+ and Cu2+ ions on CASH-NH2 is preponderantly achieved by the cation exchange and surface complexation, in which Al doping substantially enhances the exchange capacity between Ca2+ of CSH and Pb2+ or Cu2+, and the functional amino groups chelate Pb2+ or Cu2+ to realize surface complexation of CASH architectures. Thereby the excellent adsorption performance of CASH-NH2 is attributed to the significant enhancement in the CEC between Ca2+ of CASH and Pb2+ or Cu2+, and the amino functionalization-induced surface complexation of the CASH, which are achieved by the synergistic effect of Al doping and amino functionalization. This work opens a new way for simultaneously exploiting metal doping and amino functionalization to boost the adsorption performance of other adsorbents to achieve highly efficient removal of toxic cationic species from polluted water.