Investigation on electron donors for Cr(VI) reduction on surface of modified biomass adsorbent

In this work, modified corn stalk (CS-AE) was used as model adsorbent to study the electron donor groups involved in Cr(VI) reduction to Cr(III) during adsorption process in aqueous solution. Batch adsorption experiments showed the formation of Cr(III) both in liquid solution and solid adsorbent. Approximately 10%−35% adsorbed Cr(VI) was reduced to Cr(III), and most (> 65%) of formed Cr(III) was bound to CS-AE. X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance ( 13 C-NMR) and Fourier transform-infrared spectroscopy (FT-IR) were employed to characterize surface element composition and functional groups of CS-AE. XPS characterization showed that N content in CS-AE surface decreased after reaction with Cr(VI) as well as the relative content of quaternary ammonium groups, indicating quaternary ammonium group was oxidized by Cr(VI) as electron donors. 13 C-NMR and FT-IR also found that the decrease of quaternary ammonium groups and a little increase of carboxylic groups. Determination results of total organic carbon (TOC), total nitrogen (TN) and nitrate (NO 3 − -N) in adsorption solution suggested that TN, NO 3 − -N, TOC content increased with initial Cr(VI) concentration and exhibited positive correlations with the production of Cr(III) (P