Inherent Minerals Facilitated Bisphenol A Sorption by Biochar: A Key Force by Complexation

Abstract

Biochar is a multiphase carbonaceous structure with inherent minerals. The role of minerals in organic sorption is essential for biochar application in environmental remediation. In this work, combined with X-ray diffraction (XRD) and 13C nuclear magnetic resonance (NMR) techniques, the composition of minerals and the sorption behavior of bisphenol A (BPA) were investigated. A demineralization treatment was applied to remove surface minerals containing silicon (Si), aluminum (Al), and calcium (Ca) elements, resulting in the exposure of micropores in aromatic carbon. These minerals could serve as vital sites to facilitate BPA sorption due to the complexation mechanism. The role of mineral elements in enhanced sorption could be in the sequence of Al mineral > Ca mineral > no mineral. Density functional theory (DFT) calculation confirmed the occurrence of complexation between minerals and BPA as evidenced by sorption energy. After demineralization, declined release ratio (RR) values implied that adsorbed BPA on demineralized biochars was more difficult to desorb than on original biochars owing to the restriction of micropores. The enhanced energy gap also verified that BPA molecules were more stable on demineralized biochars. This research casts new light on recognizing biochar minerals in relation to their underlying sorption mechanism for phenolic compounds.