Removal of Cr in water by superoxide anion-mediated redox reaction assisted by lignin-rich kiwifruit twig biochar: Application of DFT calculation.

This research aims to investigate the role of reactive oxygen species (ROS) in the adsorption and reduction of Cr on lignin-rich biochar under dark conditions and under various oxygen treatment conditions. The research found that under aerobic conditions, the reduction content of Cr (0.38 mg) and the production content of ·O (20.36 × 10 mg·L) are the highest, followed by untreated conditions (0.32 mg, 15.03 × 10 mg·L), and the lowest under anaerobic conditions (0.21 mg, 5.14 × 10 mg·L). Compared with anaerobic conditions, the reduction content of Cr increased by 1.52 times under untreated conditions. Meanwhile, under anaerobic conditions, ·O disappeared, indicating that ·O had played an important role in the reduction of Cr. Kinetic results showed that the role of ·O in the reduction of Cr mainly occurred in liquid solution. DFT calculations confirmed that C-OH was the main electron supplier in the reduction process of Cr, and there was a positive correlation between the production content of ·O and the content of C-OH in liquid solution. The present research is expected to provide a scientific basis for the transformation of Cr on lignin-rich biochar in liquid solution.