Ball milling biochar with ammonia hydroxide or hydrogen peroxide enhances its adsorption of phenyl volatile organic compounds (VOCs)

Pristine biochar (CN600), ball-milled biochar (CN600-BM), H2O2 modified BM-biochar (CN600-O), and NH4OH modified BM-biochar (CN600-N) derived from corn stalk were applied to adsorb phenyl volatile organic compounds (VOCs). H2O2 and NH4OH modification of BM-biochar significantly improved its physicochemical characteristics and adsorption abilities. The specific surface area of CN600-O increased 2.05 and 1.23 times compared to CN600 and CN600-BM, respectively; while CN600-N increased 2.41 and 1.45 times, respectively. In addition, the ball milled biochars, especially CN600-O, showed higher acidity and polarity than CN600. The VOC adsorption amount onto biochars was 10.96–130.21 mg/g. CN600-O and CN600-N had high uptake of the VOCs and reached 100.07–111.79 mg/g and 110.49–130.21 mg/g, respectively. CN600-N showed the best performance with P-xylene adsorption up to 130.21 mg/g. VOC adsorption onto the CN600-O and CN600-N were mainly governed by surface adsorption and associated with morphology characteristics of the biochars as well as VOC properties such as boiling point and molecular size. Five cycles of adsorption-desorption experiments showed that CN600-O and CN600-N had good reusability with the reuse efficiencies of 88.01 %–92.21 % and 92.19 %–95.39 %, respectively. The results indicate that O- and N-doped ball-milled biochars are promising in adsorption for effective and sustainable VOC removal.