Effects of activation time and temperature on the performance of uniform-sized biochar for microplastic adsorption from wastewater

Abstract This study investigates the efficacy of biochar derived from Southern Yellow Pine for the removal of polystyrene (PS) microplastics (0.2 µm) from aqueous solutions. Raw biochar was produced via carbonization and subsequently activated using CO 2 at temperatures ranging from 550 to 850°C for activation times of 1–4 h, and was sieved into uniform-sized adsorbents between 300 and 425 μm. The effects of these activation parameters on the biochar's physicochemical properties and microplastic adsorption performance were systematically evaluated. Surface characterization through N 2 adsorption, ultimate and proximate analyses, and FTIR revealed that activation significantly enhanced the specific surface area and porosity. The Brunauer–Emmett–Teller (BET) surface area increased from 235.6 m 2 /g for raw biochar to a maximum of 600.2 m 2 /g for biochar activated at 850°C for 1h. Batch adsorption experiments demonstrated a strong correlation between surface area and adsorption capacity. The biochar activated at 850°C exhibited the highest microplastic removal efficiency of 99%, significantly outperforming the raw biochar and samples activated at lower temperatures. These findings highlight that thermal activation is a critical step for enhancing biochar’s properties and that tuning activation parameters, particularly temperature, is key to optimizing its performance for microplastic remediation in wastewater.