Chromate adsorption on amine-functionalized nanocrystalline silicalite-1

Nanocrystalline silicalite-32 nm, which has a large external surface area (∼100 m2/g), was functionalized with aminopropyltriethoxysilane (APTES). The functionalized nanocrystalline silicalite was characterized by powder X-ray diffraction to verify crystallinity, solid state 29Si MAS NMR and thermal gravimetric analysis to quantify the functionalization, and zeta potential measurements of surface charge. As the amount of APTES functionalization increased, the zeta potential increased and this lead to increased chromate (Cr2O72-) adsorption. Chromate adsorption on the APTES functionalized silicalite-32 nm was attributed to external surface adsorption by an electrostatic interaction between the positively charged amine groups and the negatively charged chromate anions.