Hydrophilicity enhancement of low-temperature lignocellulosic biochar modified by physical–chemical techniques

Creation of oxygen-containing functional groups on the biochar surface can highly improve its hydrophilicity and amend its behaviour in aquatic systems. Hydrogen peroxide, ozone, potassium permanganate and nitrogen acid were most usually used reagents for the surface oxidation. On the contrary, biochar activation by strong acids can be a costly process at the industrial scale and can raise environmental problems due to the disposal of activated carbon. Hence, there is a need to search for cheaper and cleaner products for the modification of biochar. For this reason, weak acids, such as solution of rhamnolipids or rainfall water solution, can be used. In this study, it was found that lower size biochar particles had higher wettability compared to larger size particles, since it was categorized as slightly hydrophobic (2.67 s). Steam of average concentration of rhamnolipid solution (20 mg/l) had the highest effect on the enhancement of biochar surface area (15.2 m2/g) and satisfactory impact on the reduction of initial hydrophobicity (4210 s). Biochar modified with increased concentration of nitric acid solution (from 65 to 20%) wettability was in accordance with the increase of surface area (from 4210 to 3907 s and from 1.27 to 4.36 m2/g).