Chemically engineered biochar – Effect of concentration and type of modifier on sorption and structural properties of biochar from wood waste

Abstract The main aim of study was a) preparation of biochars (BCs) engineered chemically with various reagents including base (NaOH), as well as mineral (HCl, HNO3, H2SO4) and organic (CH3COOH) acids, b) determination of type and concentration effect of the modifier on surface properties of the BCs, and c) assessment of optimal modification conditions regarding environmental aspects. Results showed that modifiers used at the lowest concentration (0.001 M and 0.01 M) changed the BCs properties insignificantly. Modification with 0.1–1.0 M NaOH caused increase of value of surface area (by 21–82%) and volume of pores from 5 to 40 nm (by 109–239%). Acidic modifiers at 0.1–1.0 M enhanced the number of acidic functional groups, mainly lactonic ones. The best effect was obtained for BCs treated with CH3COOH and H2SO4, revealing an elevation of acidic structures by 13–17% and by 9–15%, respectively. The largest enhancement of basic groups occurred for the BCs treated with increasing concentration of NaOH (by 21–154%) and CH3COOH (by 2–50%). The pH of the modified BCs was drastically reduced/elevated after treating with the highest acid/base concentrations, which suggests considering compromise between the best chemical properties of BC and its safe use, e.g. selection of the BC modified with 0.1 M modifier.