Reversal of Zeta Potential of Proton-Type Zeolite Y after Surface Modifications in Sodium Ion Aqueous Solutions

Simple methods for reversing the zeta potential of high Al/Si ratio proton-type zeolite Y (HY) to be positive in sodium ion solutions have been developed. The characterizations by using inductively coupled plasma-mass spectrometer (ICP-MS), electron spectroscopy for chemical analysis (ESCA), X-ray diffraction (XRD), and 27Al magic-angle spinning solid-state nuclear magnetic resonance (27Al MAS solid-state NMR) have been carried out. The results reveal that a partial reorganization among various aluminum species occurs in HY in sodium ion solutions, thus inducing a considerable enrichment of distorted framework Al and extra-framework Al (EFAL) species on the exterior surface. These Al species in synergy with adsorbed sodium render the zeta potential of HY to shift positively. The resulting zeolite samples can be applied for the adsorption of heavy-metal oxyanions with negative charges. The superiority for removing Cr(VI) oxyanions from aqueous solutions with pH close to neutral has been demonstrated.