Enhanced removal of aqueous Cr(VI) by a green synthesized nanoscale zero-valent iron supported on oak wood biochar

Green nanoscale zero iron (nZVI) on an oak wood biochar support was prepared from tea polyphenol (TP–nZVI–OB), and applied to the removal of hexavalent chromium (Cr(VI)) from aqueous solution. The effects of experimental parameters on the Cr(VI) removal were evaluated by varying the Fe/C mass ratio, contact time, initial pH, and initial Cr(VI) concentration. The Cr(VI) removal performance of the TP–nZVI–OB was optimized at an Fe/C mass ratio of 2:1. The initial pH significantly affected the Cr(VI) removal, and 99.9% of the Cr(VI) was eliminated at pH 2.0. The kinetic data were well fitted to a pseudo-second order model, indicating that Cr(VI) removal was dominated by chemisorption. The successful TP–nZVI–OB synthesis and effective Cr(VI) removal mechanisms were confirmed by multiple techniques. The reaction between Cr(VI) and TP–nZVI–OB (2:1) involved multiple processes (sorption, reduction and co-precipitation), clarifying that TP–nZVI–OB is a potentially superior composite for Cr(VI) treatment of contaminated aqueous solution.