Highly selective adsorption of Pt2+ and Pd2+ using thiol-functionalized mesoporous silica

A noble metal ion (Pt2+ and Pd2+) adsorbent with uniform mesopore channels was prepared by grafting a thiol functional group, (3-mercaptopropyl)trimethoxysilane (MPTMS), onto ordered mesoporous silica, SBA-15. Results show that the ordered mesostructure of SBA-15 was retained after modification and the thiol functional group was immobilized mainly inside the mesopore channel, as evidenced by Brunauer-Emmett-Teller surface area, small-angle X-ray scattering, Fourier transform infrared, and elemental analyses. The thiolated mesoporous silica exhibited a highly selectively adsorptive capability for noble metal ions such as Pd2+ and Pt2+, while the binding capability for other metal ions (Ni2+, Cu2+, and Cd2+) both in the presence of equimolarity and at 10 times excess conditions was greatly decreased. These selective adsorptions of thiolated mesoporous adsorbent for noble metal ions (Pt2+ and Pd2+) were explained by thermodynamic calculation assuming that the selective adsorption occurred by a chemical adsorption on the surface of a confined pore channel. In addition, the adsorption characteristics of the thiolated mesoporous material were examined.