Effect of ball milling with hydrogen peroxide or ammonia hydroxide on sorption performance of volatile organic compounds by biochar from different pyrolysis temperatures

Ball milling is a promising mechanochemical method for biochar modification to increase adsorption capacity to volatile organic compounds (VOCs). In this study, biochar derived from wheat straw at different pyrolysis temperatures (300 °C, 450 °C, and 600 °C) was modified by ball milling with H2O2 and NH4OH, respectively. The pristine and ball milled biochar were tested to adsorb aromatic VOCs (benzene, o-xylene, m-xylene, and p-xylene) through adsorption experiment with single adsorbate. The VOCs adsorption capacities onto biochar was 11.62–102.22 mg g−1. Ball milling effectively improved specific surface area (SSA) and total pore volume of biochar, and adsorption capacities increased 1.96–3.97 times compared to pristine biochar. Further, adsorption capacities of ball milled biochar pyrolyzed at 450 °C and 600 °C increased 1.33–1.64 times and 1.22–1.97 times by NH4OH modification, respectively. In addition, SSA and adsorption capacities of ball milled biochar derived from lower pyrolysis temperatures (300 °C and 450 °C) decreased by H2O2 modification, while adsorption capacities increased 1.18–1.99 times for ball milled biochar from 600 °C. The pseudo-second order model fitted better than pseudo-first order model for VOCs adsorption on ball milled biochar from 300 °C, while pseudo-first order model fitted better for ball milled biochar from 600 °C. VOCs adsorption mechanisms onto ball milled biochar included surface adsorption and partitioning. The results indicate that ball milling biochar with chemicals could be a promising modification method for VOCs adsorption.