Ordered SBA-15 mesoporous silica with high amino-functionalization for adsorption of heavy metal ions

Surface NH₂-functionalized SBA-15 mesoporous silica was synthesized using toluene diisocyanate (TDI) as a bridge molecule. First, the surface Si-OH groups of SBA-15 were reacted with the -NCO groups of TDI. Then, the remaining unreacted -NCO groups of TDI were reacted with the -NH₂ groups of ethylenediamine (EDA). Finally, the NH₂-groups were successfully grafted onto the mesoporous SBA-15 surface by the above two-step method. XRD, N₂ adsorption-desorption analysis, FT-IR, and ²⁹Si MAS NMR were used to identify the well-ordered structure and the successful incorporation of the -NH₂ groups onto the surface of the synthesized materials. Characterizations revealed that such -NH₂ grafting is an effective method to obtain a high loading of -NH₂ groups onto the SBA-15. When subjected to toxic heavy metal ions in aqueous solution, the obtained NH₂-functionalized SBA-15 showed very high adsorption rates 99.9%, 99.7%, 99.8%, 99.5% and 99.9% for Pb²⁺, Cr³⁺, Cd²⁺, Ag⁺ and the Cu²⁺, respectively, which is attributed to the strong complexation reactions between the metal ions and the grafted -NH₂ groups.