Pyrogallic acid modified nanoscale zero-valent iron efficiently removed Cr(VI) by improving adsorption and electron selectivity

Pyrogallic acid (pyGA) was firstly introduced into nanoscale zero-valent iron (nZVI) synthesis process by sodium borohydride to obtain a new catalyst pyGA-nZVI. The characterization of the material indicated successful coating of pyGA on nZVI surface. pyGA-nZVI could completely remove 50 mg·L−1 Cr(VI) within 4 min, while only 41.4% of Cr(VI) was removed by nZVI within 30 min. The material presented high Cr(VI) removal in a wide pH range of 3–12. Ortho-phenol hydroxyl groups played a crucial role in synthesizing highly effective nZVI. Fe(II) and Fe0 were mainly responsible for Cr(VI) removal in the pyGA-nZVI and nZVI systems, respectively. pyGA modification reduced the charge transfer resistance and enhanced electron transfer of nZVI. Density functional theory calculation indicated enhanced Cr(VI) adsorption on pyGA-nZVI. The reactivity of pyGA-nZVI toward H2O was hindered, increasing the electron selectivity for Cr(VI) removal. This article provides a new strategy for synthesizing highly reactive nZVI using polyphenols to remove Cr(VI).