Optimal synthesis of amino-functionalized mesoporous silicas for the adsorption of heavy metal ions

Amino-functionalized mesoporous silicas (AFMS) were synthesized by a neutralization route using the anionic surfactant dodecanoic acid (DAA) as structure-directing agent (SDA), aminopropyltrimethoxysilane (APTMS) as co-structure-directing agent (CSDA), and tetraethoxysilane (TEOS) as silicon source. The synthesis parameters, which affect the structural properties and the amino loadings of the resultant AFMS, were optimized. Various techniques, such as FT-IR, XRD, N2 adsorption-desorption, and TEM, were used to characterize the synthesized AFMS. The selective removal of Cu2+, Pb2+, Cd2+, and Zn2+ from aqueous solutions in single-, binary-, ternary-, and quaternary-component systems by the synthesized AFMS was thoroughly investigated. The measured single-component adsorption isotherms of Cu2+, Pb2+, Cd2+, and Zn2+ on the AFMS optimally synthesized can be well described by the Sips model, in which the extracted adsorption capacities are 2.34, 2.86, 1.71, and 1.36 mmol/g (0.149, 0.593, 0.192, and 0.089 g/g) for Cu2+, Pb2+, Cd2+, and Zn2+, respectively, higher than those on other adsorbents reported in the literature. Furthermore, Pb2+ and Cu2+ can be more selectively removed by the synthesized adsorbent, compared to Cd2+ and Zn2+, confirmed by the results on the multi-component adsorption.