Characterization and quantification of electron donating capacity and its structure dependence in biochar derived from three waste biomasses

Biochar has shown a unique electrochemical property being involved in various redox reactions in soil and water. In this study, the electron donating capacities (EDCs) of biochar pyrolyzed at 200-800 degrees C from pine wood, barley grass and wheat straw were investigated by using the mediated electrochemical oxidation method. The EDC values for all biochar were in the range of 0.18-1.83 mmol e(-) (g biochar)(-1), showing the increase as the temperature increased from 200 degrees C to 400 degrees C, the decrease from 400 degrees C to 650 degrees C, and then increase from 650 degrees C until to 800 degrees C. At low and intermediate temperatures of 200 650 degrees C, the EDCs were mainly attributed to the phenolic hydroxyl groups, while the conjugated pi-electron system associated with aromatic structure dominated the EDCs of biochar at the high temperatures of over 650 degrees C. The barley grass- and wheat straw-derived biochar had higher EDCs than the pine wood-derived biochar, resulting from the higher phenolic hydroxyl groups in the former samples than the latter one. In conclusion, the reductive property of biochar was mainly attributed to both phenolic hydroxy group and conjugated pi-electron system associated with aromatic structure, depending on the pyrolytic temperature and feedstock source. The results will help us to obtain a complete view on the role of biochar in biogeochemical redox reactions and consider developing biochar with controlled redox properties for specific environmental applications such as electron shuttle and catalyst material. (C) 2018 Elsevier Ltd. All rights reserved.