The surface properties of ACS biochar are shown in Table 2. The carbonization degree of biochar could be evaluated by H/C, while the polarity index was suggested by O/C and (O þ N)/C atomic weight ratios. The H/C, O/C and (O þ N)/C ratios of the biochar were 0.61, 0.20 and 0.28, respectively. The average pore diameter (PD) of
ACS was approximately 3.83 nm, which lay within the range of mesoporous. In addition, the values of SSA, TPV and MV of the ACS biochar were 341.05 cm2 /g, 0.22 cm3 /g and 0.16 cm3 /g, respectively, which were much higher than those for common biochar.