The rapid reductive immobilization of Cr(VI) from the aqueous solution was achieved by reduction to Cr(III) using tannic acid (TA), and subsequent pH-triggering precipitation of the organo-Cr(III) complexes formed in the redox reaction. The effects of TA concentration, temperature, and solution pH on the reduction of Cr(VI) were examined by batch experiments, and the rapid redox reduction followed a second-order kinetics with respect to Cr(VI) concentration in the pH range of 2.0–3.0. UV–visible spectra, FTIR, and XPS confirmed the complete detoxification of Cr(VI) concomitant with carboxylation of partial phenolic hydroxyls in TA. Synchronously, the reduced Cr(III) coordinated with carboxyl groups in oxidized TA (OTA) to form complexes, which exhibited remarkable pH-dependent size distribution characteristics as illustrated by SEM images and sequential filtration/ultrafiltration. The resulted Cr(III) complexes could aggregate into colloids with larger size and precipitate out at pH range of 6.0–8.0 via cross-linking, thereby leading to 93% Cr and 89% TOC immobilization. An eco-friendly and cost-effective method for Cr(VI) elimination and immobilization is provided because polyphenols are natural polymers derived from plants.
Hexavalent chromium (Cr(VI)) and dyes are of particular environmental concern and need to be removed from water urgently due to their high toxicity. Herein, we explored the possibility of electron transferring from dye Orange II (OII) to Cr(VI) under UV and simulated solar light irradiation, expecting to simultaneously decolorize dyes and reduce Cr(VI). Experimental results show that light irradiation can partially decolorize OII but has no ability to reduce Cr(VI) in solution only with OII or Cr(VI). However, both dyes and Cr(VI) can effectively and simultaneously be decolorized and reduced in the solution containing both OII and Cr(VI) under light irradiation, and a low pH level and high OII/Cr(VI) concentration ratio significantly favor the co-removal. Additionally, insoluble organo–Cr(III) complexes identified by FTIR and XPS characterization were generated during the reaction. These complexes are beneficial to the removal of chromium and total organic carbon from water. The possible degradation pathway of OII is further proposed based on the detection of degraded products by GC-MS analysis. The results of this work offer an approach for simultaneously removing multiple contaminants.
危险品化学品经营许可证（带存储）