It was clearly demonstrated that all the APACs display type-IV isotherms with obvious hysteresis loops above the relative pressure range of 0.4, indicating the well- pronounced development of mesopores. According to the IUPAC classification, the hysteresis loops can be classified as type H4, revealing the existence of slit-shaped mesopores. The surface textural parameters are summarized in Table 1S and Table S2. It is evident that that the BET surface area of APACs was higher than APAC-0-600-60 (223 m 2 /g, char which was prepared by the pyrolysis of Enteromorpha at 600 °C for 1 h). And the carbon yield of APACs was much higher than APAC-0-600-60 (32.4%). These results suggested that using APP as activating agent was efficient to pro- duce activated carbon with high yield and porosity. Furthermore, the average pore diameter of all the APACs was above 3 nm. The ratios of mesopore volume to total pore volume were more than 60%. It is evident that that ammonium polyphosphate is effective in producing carbon with higher mesopore volume and large pore diameter. Compared to other previous reports, the synthesis procedure in this study was more simple and much less expensive.