Interfacial engineering enhances the reactivity of zero-valent iron by oxalic acid etching and xanthan gum dispersion for efficient Cr(VI) reduction

A dual-modified ZVI is developed via oxalic acid etching and XG stabilization. • Ox and XG synergistically tune interfacial hydrogen bond to accelerate H + transfer. • XG/Ox-ZVI achieves ∼22.3–fold higher Cr(VI) removal capacity compared with ZVI BM . Rapid surface passivation and particle aggregation severely limit the interfacial reactivity of zero-valent iron (ZVI) during aqueous redox processes, yet overcoming both simultaneously remains challenging. Herein, a surface engineering strategy integrating oxalic acid (Ox) etching with xanthan gum (XG) stabilization was developed to regulate the interfacial chemistry and suspension stability of ZVI. Ox etching reconstructed the dense passive layer into a loose, porous ferrous oxalate shell, facilitating proton transport and exposing reactive sites, whereas XG suppressed particle aggregation through steric stabilization and viscosity. Their interaction shifts the interfacial hydrogen-bond network toward highly mobile 2−HB-H 2 O (from 43.3% to 50.9%), providing efficient proton-transfer channels. The synergy reduces charge-transfer resistance, enhances corrosion activity, and modulates the passivation layer, lowering Fe 0 consumption from 54.4% (Ox-ZVI) to 37.3% and increasing electron selectivity for Cr(VI) reduction by ∼1.8-fold. Consequently, XG/Ox-ZVI delivers ∼22.3-fold higher Cr(VI) removal capacity than ZVI BM , with joint enhancement reaching 49.09 mg g −1 , exceeding the summed individual enhancements (41.06 mg g −1 ). XG/Ox-ZVI also exhibited porous-media transportability (92.2% vs. 59.4% for Ox-ZVI at 120 m/day) and adaptability in natural waters. This study provides a surface engineering strategy to concurrently suppress passivation and aggregation in developing highly reactive ZVI remediation materials. Download: Download high-res image (131KB) Download: Download full-size image