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

Dan Zhang,Junhua Li

doi:10.1007/s11434-012-5594-0

Abstract

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.

Highlights

Surface NH2-functionalized SBA-15 mesoporous silica was synthesized using toluene diisocyanate (TDI) as a bridge molecule
We proposed a novel method to synthesize aminofunctionalized SBA-15 (Figure 1)
Toluene diisocyanate (TDI) was employed as a “bridge” molecule whose one bridgehead group -NCO was used to link with an silanol group on the SBA-15 surface and the other was left to link with an amino group of ethylenediamine (EDA)

Summary

Preparation of surface NH2-functionalized SBA-15 mesoporous silica

The preparation of amino-functionalized SBA-15 involved three steps. Pure siliceous SBA-15 was prepared according to the reported literature [23,24]. 1.0 g of assynthesized SBA-15 powder without templates was added into a mixed solution of 8.3 mL TDI and 16.7 mL of toluene. After stirring at 60°C for 5 h, the powder (denoted as T-SBA-15) was filtered and Soxhlet-extracted with CH2Cl2 for 48 h. 1.0 g of dried T-SBA-15 powders was added into a mixed solution of 20.0 mL of ethylenediamine (EDA) and 20.0 mL of ether. The mixture was stirred at 20°C for 24 h, and the final powder (denoted as NH2SBA-15) was filtered, Soxhlet-extracted and dried

Adsorption experiments

Characterization of materials

Results and discussion

Conclusion