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Adsorption of polystyrene nanoplastics on sawdust-based activated carbons
Summary
This study tested activated carbon filters made from sawdust waste for their ability to remove nanoplastics from water. The best-performing filter, activated with potassium hydroxide, had a very high surface area and effectively captured polystyrene nanoplastics through chemical interactions. This low-cost, waste-derived approach could help reduce the amount of nanoplastics in drinking water, which is important because these tiny particles can cross into body tissues.
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.