Application of carbon nitride nanosheets for adsorption of various humic substances from aqueous solutions

Abstract

Humic substances (HSs) cause serious problems such as membrane fouling and disinfection by-products. Particularly, HSs as the main UV-quenching substances in landfill leachate pose great challenges. In this study, we evaluated the application of carbon nitride nanosheets (CN-Ns) for adsorption of various HSs, as well as leachate nanofiltration concentrates (LNCs). The characterization revealed that as increasing thermal oxidation temperature, the properties of CN-Ns were affected, such as morphology, porosity, and crystallinity. The surface area of CN-N at 575 °C (CN-N-575) was 145.3 m2·g−1, resulting in an enhanced adsorption performance. The adsorption capacity of CN-N-575 for lignite humic acid (LHA) and soil fulvic acid (SFA) was considerably greater than that of bulk CN; the maximum adsorption amounts of LHA and SFA were 143.11 and 63.27 mg C·g−1, respectively. Upon adsorption, the removal rate of LHA and Elliott soil humic acid was about 90 %. Among HSs and LNCs, the humic-like components showed superior affinity; in some cases, the removal rate reached 100 %. The adsorption preference of aromatic compounds in HSs and LNCs was ascribed to π-electron interactions. The adsorption of LHA was more pH-dependent than that of SFA, attributed to the interactions (electrostatic, hydrogen bonding, and complexation) along with a specific conformation effect. The findings proved the great potential of CN-Ns in HSs adsorption, especially in the treatment of landfill leachate.