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 theanionic surfactant dodecanoic acid (DAA) as structure-directing agent (SDA), aminopropyltrimethoxysilane(APTMS) as co-structure-directing agent (CSDA), and tetraethoxysilane (TEOS) assilicon source. The synthesis parameters, which affect the structural properties and the amino loadings ofthe 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 Cu2þ, Pb2þ, Cd2þ, andZn2þ from aqueous solutions in single-, binary-, ternary-, and quaternary-component systems by thesynthesized AFMS was thoroughly investigated. The measured single-component adsorption isothermsof Cu2þ, Pb2þ, Cd2þ, and Zn2þ on the AFMS optimally synthesized can be well described by the Sipsmodel, 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 Cu2þ, Pb2þ, Cd2þ, and Zn2þ, respectively, higher than those on other adsorbentsreported in the literature. Furthermore, Pb2þ and Cu2þ can be more selectively removed by the synthesizedadsorbent, compared to Cd2þ and Zn2þ, confirmed by the results on the multi-componentadsorption.