Coffee grounds modified zero-valent iron for efficient heavy metal removal

Abstract

Surface modification is one of the most important approach for improving the reactivity of zero-valent iron. In this study, waste coffee grounds (CG) were chosen to modify zero-valent iron through a mechanochemical method. The synthesized CG-ZVI exhibited a 166 times faster Cr(VI) removal rate. Structural characterization and ATR-FTIR analysis indicated that CG modification endowed ZVI with abundant carboxylic acid groups, and accelerated the adsorption of Cr(VI) via the complexation effect of CG-COOH···HCrO4−. Moreover, the polyphenolic substances from CG-ZVI, as an electron shuttle, accelerated the electron transfer from the iron core to generated surfaced bound Fe2+, resulting in high efficiency of Cr(VI) removal. In addition, CG-ZVI selectively removed Cr(VI) in the presence of anions (Cl−, NO3−, SO42−) and acted as a permeable reactive barrier material for in situ treatment of heavy metal-contaminated water. This work demonstrates that CG modification can function as an excellent candidate for perfecting the reactivity of ZVI. More importantly, it opens up a new way for the utilization of discarded CG.