Cellulose-based materials in the treatment of wastewater containing heavy metal pollution: Recent advances in quantitative adsorption mechanisms

For the treatment of heavy metal (HM)-polluted wastewater, an increasing number of novel and practical adsorbents have been developed and applied, especially cellulose-based materials, which have received increasing attention from researchers in recent years. This research has mainly focused on the influencing factors, thermodynamics, and kinetics of HM ion removal, and the associated mechanisms have been investigated theoretically. Density functional theory (DFT) is typically combined with experimental research to develop new materials and investigate their applications, and considerable progress has been achieved. Parameters calculated by DFT, such as the adsorption or interaction energy (Eads), frontier molecular orbitals (FMOs), molecular electrostatic potential (MEP), natural bond orbitals (NBOs), electrostatic potential (ESP), and Mulliken population, play a crucial role in the study of adsorption behaviour. In this paper, the developments in DFT calculations of the properties of cellulose-based materials, as well as the applications and technical factors related to the removal of HM ions and HM composite pollutants, are reviewed. Furthermore, our team has focused on DFT approaches such as the sequential investigation of adsorption structure -> functional groups -> key elements. This sequential approach was used to assess the removal of HM ions and complexation-decomplexation-recomplexation processes related to the adsorption of HM composite pollutants to provide insights and methods supporting the development and substantive application of cellulose-based materials.