Chromate adsorption on bifunctional, magnetic zeolite composites

Zeolite composites with magnetic iron oxide in the form of maghemite (γ-Fe2O3) were synthesized from Y zeolites using a Fe2+–Fe3+ ion mixture and were subsequently functionalized with 3-aminopropyltriethoxysilane (APTES) to form bifunctional zeolite composites. The amine functionalized iron oxide/zeolite composites were characterized by powder X-ray diffraction to verify crystallinity, thermal gravimetric analysis to quantify the functionalization and zeta potential measurements to monitor surface charge. The iron oxide phase was assigned to maghemite based on X-ray photoelectron spectroscopy and Mössbauer spectroscopy. The APTES functionalization increased the zeta potential and this lead to increased chromate adsorption relative to unfunctionalized iron oxide/zeolite composites. Chromate adsorption on the composite materials was attributed to external surface adsorption through an electrostatic interaction between the positively charged amine groups and the negatively charged chromate anions. Recovery of the iron oxide/zeolite composite can be accomplished using the magnetic properties of the material and the chromate can be desorbed by increasing the pH.