Deciphering the adsorption heterogeneity of ultraviolet quenching substances on carbon nitride using experiment and theoretical calculations

Ultraviolet quenching substances (UVQSs) in landfill leachate are associated with membrane concentrate and disinfection byproducts, and adsorption and photocatalysis are regarded as promising treatment methods. However, the adsorption heterogeneity of UVQSs, induced by their versatile structures and properties, has not been fully ascertained, posing challenges to the treatment of UVQSs. Herein, the adsorption heterogeneity of various UVQSs, including leachate concentrates (LCs) and humic acids (HAs), on graphitic carbon nitride (g-CN) was thoroughly elucidated based on experiments and density functional theory (DFT) calculations. First, the structural properties of UVQSs, i.e., various LCs and HAs, were characterized, including chemical compositions, functional groups, aromaticity, molecular weight, and other spectral characteristics. The great heterogeneity of various UVQSs in structures and properties was confirmed. Then, two typical forms of g-CN, including bulk g-CN (BCN) and porous g-CN heterojunction (CNH), were fabricated and characterized. Most textural properties of both BCN and CNH showed high similarity, but CNH possessed more porous structures compared to BCN. Finally, the bulk adsorption behaviors, feature-dependent adsorption heterogeneity, and adsorption interaction mechanisms were investigated. The adsorption heterogeneity, where highly aromatic compounds in UVQSs showed preferential adsorption, was found to be driven by π-π interactions according to DFT calculations and experiments. These findings provide insights into the adsorption of UVQSs and offer far-reaching prospects for facilitating effective treatment of landfill leachate.