Adsorption of modified polystyrene nanoplastics on biomass-derived activated carbons: A study of ball mill activation

This study focuses on synthesizing activated carbons using lignin and sawdust as precursors, with FeCl₃ employed as an activating agent, aimed at adsorbing of modified polystyrene nanoparticles. The impact of ball milling during the impregnation process was evaluated, revealing that the best results were obtained with a milling time of 10 min. This method resulted in activated carbons with enhanced porosity compared to those synthesized without milling. However, extending the milling time adversely affected the performance, likely due to heat generated by friction in the ball mill, which caused excessive dehydration and impeded the proper carbonization process. The activated carbons demonstrating the best performance were L-10 (derived from lignin) with a BET surface area of 1258 m² g^-1, and S-10 (derived from sawdust) with 1072 m² g^-1. The materials exhibited high adsorption capacities of 70.08 and 65.77 mg g^-1 for polystyrene nanoparticles (PSNPs) with L-10 and S-10 carbons, respectively. These results align with the higher surface areas of the adsorbent materials, emphasizing the crucial role of porosity in adsorption efficiency. Notably, the pore sizes of the activated carbons were smaller than the diameter of the PSNPs, minimizing diffusion effects and concentrating adsorption activity on the external surfaces. In addition, the adsorption process was governed by electrostatic interactions, with additional contributions from π-π interactions between the aromatic structures of the activated carbon and the benzene rings of the polystyrene. When examining polystyrene nanoparticles modified with amino and carboxyl groups, L-10 and S-10 exhibited higher affinity for amine-functionalized polystyrene while showing repulsion toward carboxyl-functionalized polystyrene.