Carboxymethyl cellulose stabilized and sulfidated nanoscale zero-valent iron: Characterization and trichloroethene dechlorination

摘要

Polymer stabilization can enhance subsurface transport of nanoscale zero-valent iron (nZVI) while sulfidation can reduce its hydrogen evolution reaction (HER) and enhance electron utilization efficiency (epsilon(e)). However, the combined impacts of stabilization and sulfidation on particle characteristics, reactivity and efficiency, and therefore longevity for contaminant remediation/capacity, has not been adequately investigated. Carboxymethyl cellulose stabilized and sulfidated nZVI (CMC-S-nZVI) was synthesized by both one-pot and two-step approaches and characterized with SEM, TEM-SAED, XRD, XPS and FTIR techniques. Dithionite was used as the sulfur source for the one-pot particles and sulfide was used for the two-step particles. We found that CMC stabilization did not affect the degree of sulfidation. Both stabilization of S-nZVI and sulfidation of CMC-nZVI enhanced particle reactivity by one order of magnitude. The two-step CMC-S-nZVI generally exhibited much higher reactivity than the one-pot counterparts, mainly because dithionite consumes Fe-0. CMC stabilization significantly decreased epsilon(e), an effect not quantified before, while sulfidation compensated for the decrease. Almost full s e compensation against stabilization was obtained at S/Fe 0.5, where the epsilon(e) was similar to 14% and 13%, for the non-stabilized and the two-step CMC-S-nZVI, respectively. Sulfidation at S/Fe > 0.2 completely eliminated the HER in the two-step CMC-S-nZVI after 2d with > 73% of Fe-0 preserved, and had a perfect epsilon(e) of 100% after 8d of ageing (i.e., the longevity of CMC-nZVI). Our results suggest that through stabilization and sulfidation, a balance between particle stability and longevity/capacity of nZVI could be achieved.