Enhanced Removal of Cr(VI) Using Nitrogen-Doped Soy Sauce Residue Biochar: A Comprehensive Study on Preparation, Mechanisms, and Applications

This study is dedicated to investigating the potential of self-nitrogen enriched biochar derived from soy sauce residue (N-SRB) for the efficient removal of Cr(VI) from wastewater. N-SRB, synthesized from readily available and low-cost soy sauce residue, exhibited a high removal efficiency of Cr(VI). The maximum Cr(VI) removal rate achieved was 99.93% at pH of 2.0. The removal process, under optimized conditions, was most accurately represented by the intra-particle diffusion model and the pseudo-second-order kinetic model. Multiple techniques were employed to verify the role of pyrrole-N, pyridine-N, graphite-N, -COOH, -OH and C=O serving as electron contributors for the reduction of Cr(VI). The primary mechanisms driving the elimination of Cr(VI) using N-SRB were identified as electrostatic attraction, redox reactions, and complexation. Nitrogen-rich bio-carbon eliminates the requirement for supplementary nitrogen sources and ensures the absence of secondary pollution during the pollutant removal process, making it environmentally benign. The development of this low-cost material has significant theoretical and practical implications for the efficient removal of Cr(VI) from contaminated water.