Agricultural waste biochar after potassium hydroxide activation: Its adsorbent evaluation and potential mechanism

The agricultural waste (Goji branch) was pyrolyzed into biochars with one-step potassium hydroxide (KOH) activation under different processing conditions. The biochars were first characterized in structural features and functional groups and then evaluated for adsorptive performance with methylene blue as a model pollutant. Different adsorption models were applied to fit the adsorption process and reveal the possible mechanisms. The adsorption capacity was found to strongly correlate (R² = 0.9642) with the surface area of the biochars, among which biochar K_50%W_29%C-700 (pyrolysis at 700 °C in the presence of 50 % KOH and 29 % water) possessed the largest surface area (1378 m²/g) and exhibited the highest adsorption capacity (769 mg/g) compared to its homologous products. Biochar K_50%W_29%C-700 also showed excellent recyclability and potent adsorption capacity toward other common organic pollutants. The results suggest that traces of water in agricultural wastes could significantly intensify the KOH-involved activation efficiency of producing porous biochar.