Adsorption of polystyrene nanoplastics on sawdust-based activated carbons

The rapid increase in global plastic production has led to the significant accumulation of plastic waste in aquatic environments. Nanoplastics, defined as particles <1 μm in size, have been detected in various water bodies, raising environmental and health concerns due to their persistence and challenges in management. This research examines the adsorption efficiency of sawdust-derived activated carbons (ACs) for polystyrene nanoplastics (PSNPs). Several agents were investigated in chemical activation, including the use of phosphoric acid (H 3 PO 4 ), ferric chloride (FeCl 3 ), and potassium hydroxide (KOH). Different carbonaceous adsorbents with varying textural properties and points of zero charge (pH PZC ) were synthesized. S-Char exhibited no porosity and a basic surface (pH PZC of 10.3). S-H 3 PO 4 achieved a BET surface area of 837 m 2 ·g −1 , predominantly mesoporous, and had an acidic surface (pH PZC of 3.0); S-FeCl 3 demonstrated a BET surface area of 451 m 2 ·g −1 , mainly microporous, with a pH PZC of 5.9; S-KOH presented the highest BET surface area of 1037 m 2 ·g −1 , meso-microporous, and a pH PZC of 6.3. The adsorption kinetics were best represented by the pseudo-second-order model, indicating that the adsorption process is predominantly governed by chemical interactions. Notably, the adsorption capacity of S-KOH increased with temperature, underscoring the endothermic nature of the process. Adsorption isotherms of S-KOH, determined at temperatures of 25, 50, and 75 °C, conformed well to the Sips model, with a maximum adsorption capacity of 40.84 mg·g −1 at 75 °C. The enthalpy and entropy of adsorption were calculated to be 6.99 kJ·mol −1 and − 3.27 J·mol −1 ·K −1 , respectively, suggesting an endothermic reaction and a decrease in randomness at the solid-liquid interface during adsorption. Breakthrough curves were generated at various adsorption temperatures, fitting accurately to a logistic-type equation representative of the Bohart-Adams, Thomas, and Yoon-Nelson models. • Sawdust-based activated carbons were prepared by chemical activation. • The activated carbons were used for the adsorption of nanoplastic particles. • S-KOH demonstrated the highest adsorption efficiency. • Maximum adsorption capacity of 40.84 mg·g −1 has been obtained at 75 °C. • Kinetics, equilibrium, and breakthrough adsorption tests were performed.