Enhanced adsorption of polystyrene nanoplastics by cetyltrimethylammonium bromide surface-modified magnetic rice straw biochar: Efficient performance and adsorption mechanisms

Nanoplastics, characterized by their small size, high diffusion, and stability, have attracted wide attention worldwide as a new potentially threatening pollutant. In this study, magnetic rice straw biochar modified with cetyltrimethylammonium bromide (CTAB) was prepared and utilized for the adsorption removal of polystyrene nanoparticles (PSNPs, <100 nm). The characteristics and adsorption performance of CTAB modified magnetic biochar (MBC-CTAB) were systematically investigated using characterization techniques and batch adsorption experiments. The grafting of alkyl chains onto the biochar surface through surfactant modification improved the surface activity and adsorption capacity of the magnetic biochar towards nanoplastics. Moreover, the application of an external magnetic field facilitated the rapid separation and recovery of MBC-CTAB. MBC-CTAB exhibited a removal efficiency of 99.56 % for 20 mg/L PSNPs, with a maximal adsorption capacity of 54.07 mg/g at 298 K. The presence of anions such as HPO42- and CO32- as well as dissolved organic compounds like humic acid creates significant competition between PSNPs, thereby inhibiting the adsorption capacity of MBC-CTAB towards PSNPs. The mechanism of MBC-CTAB for nanoplastics adsorption can be attributed to electrostatic interaction, hydrophobic interactions, pore filling, and surface complexation. This study demonstrates the feasibility of using surfactant-modified biochar for the adsorption of nanoplastics, providing a promising option for the development of new pollutant treatment technologies and the mitigation of the adverse impacts of nanoplastics on the environment and ecosystems.