Effect of different sulfur precursors on efficient chromium(VI) removal by ZSM-5 zeolite supporting sulfide nano zero-valent iron

Abstract

The Cr(VI) adsorption performance of Zeolite Socony Mobil #5 (ZSM-5) supporting sulfide nano zero-valent iron (S-nZVI@ZSM-5) was affected by different sulfur precursors (S2−, S2O32−, SO42− and SO32−), which resulted the diverse physic-chemical properties and corrosion degrees of Fe0. Different physic-chemical properties of S-nZVI@ZSM-5 were characterized by BET surface areas, HRTEM, SEM-EDS, ICP-MS, XRD and XPS with respect to morphology, element content, crystalline structure and sulfur species, which correlated with corrosion degrees of Fe0. The extraordinary reactivity for Cr(VI) adsorption was observed at adsorbent that SO32− as sulfur precursor resulting from multiple factors, such as largest Fe0 content and particle size, exposed the (110) type plane of Fe0, supreme lattice constant and crystallinity, dominated sulfur specie (FeS2), etc. Additionally, sulfur precursors controlled the sulfur speciation in materials, where iron disulfide was dominant sulfur species made from SO32−, as indicated by XPS analysis. More importantly, new regenerant was introduced in regenerative experiment to successfully improve the regeneration performance for Cr(VI) adsorption, approximately 80% of removal percentage was achieved in ninth cycle. These findings are expected to open up a new avenue for selecting sulfur precursors and regenerating adsorbents, which beneficial for resolving apparent discrepancies in the reported reactivity of iron-based materials with different sulfur precursors.