Immobilization of nanoscale zerovalent iron in hierarchically channelled polyacrylonitrile for Cr(VI) remediation in wastewater

Abstract

Nanoscale zerovalent iron (NZVI) was immobilized within porous millimeter-sized polyacrylonitrile (PAN) beads by chemical coagulation followed by a heat treatment in air for stabilization of the polymer structure. SEM-EDS and porosimetry analysis showed that the nanoparticles were uniformly distributed in micron-scale agglomerates within the hierarchically channeled inner structure of the PAN spheres. XRD measurements demonstrated that α-Fe phase was the main crystalline component until 230 °C preserving, in the latest case, around 50 % of the original NZVI mass, according to Mössbauer spectroscopy. Comparative studies undertaken in this work showed that both, free NZVI in suspension and PAN-immobilized NZVI, presented a removal capacity of 52–56 mg Cr(VI)/g Fe(0). The effect of NZVI loading, initial pH and heat treatment temperature of the beads in the composition, structure and reactivity of the nanocomposites, was studied. Complete Cr(VI) removal was achieved with the beads pre-treated at 230 °C containing 17 % (m/m) of NZVI at pH 3. After parametric optimization of the synthesis process, a versatile and simple procedure for production of PAN-immobilized NZVI was achieved, with no significant decrease in reactivity and potential application in fixed-bed large scale remediation processes.