Roles of Phosphoric Acid in Biochar Formation: Synchronously Improving Carbon Retention and Sorption Capacity

Pretreatment of biomass with phosphoric acid (H3PO4) for biochar production was expected to improve carbon (C) retention, porosity structure, and the sorption ability of biochar. This study investigated the interaction of phosphorus with the C structure to elucidate the mechanisms by which H3PO4 simultaneously captured C and created micropores. Sawdust was soaked in diluted H3PO4 and dried for pyrolytic biochar generation at 350, 500, and 650°C. Results showed that H3PO4 pretreatment resulted in 70 to 80% of biomass C retention in biochar, compared with only about 50% remaining without pretreatment. The specific surface area and total pore volume of the H3PO4–pretreated biochar were 930 m2 g−1 and 0.558 cm3 g−1, respectively, compared with