Effect of the modification sequence on the reactivity, electron selectivity, and mobility of sulfidated and CMC-stabilized nanoscale zerovalent iron

Abstract

Dual modification in which carboxymethyl cellulose (CMC) stabilization and sulfidation are coupled is an effective strategy to solve the insufficient electron selectivity, reactivity, and mobility of nanoscale zerovalent iron (nZVI). We compared the sulfur content, suspension composition, viscosity, zeta potential, and sedimentation of dual-modified nZVI suspensions synthesized in different modification sequences to analyze the interaction among CMC, the sulfidation reagent, and nZVI. The results show that the dissolved CMC does not take up S2−, and the CMC coating on the surface does not block S2− during sulfidation. However, CMC can peel off the FeS shell, resulting in a low sulfur content in nZVI. The Na+ of the sulfidation reagent and the Fe2+ dissolved from the FeS precipitates reduce the CMC viscosity, causing accelerated sedimentation and reduced mobility of nZVI. The peeled off FeS shell increases the free Fe2+ concentration, thereby enhancing nitrobenzene reduction. Additionally, CMC promotes nitrobenzene reduction and hydrogen evolution reactions due to the increased nZVI dispersibility. These findings explain why postsulfidated and one-pot nZVI has higher reactivity and electron selectivity, while presulfidated nZVI has higher mobility. This study highlights the importance of the modification sequence for the dual-modified nZVI properties and provides support for the synthesis method.