Hydrothermal carbonization plus pyrolysis produces microporous carbon material from biomass mixed with recyclable magnesium acetate template

Hard templates have been proven to be effective for generation of porous structures, but how to achieve sufficient contact of a solid template and solid biomass is an issue. Hydrothermal carbonization (HTC) involves structural re-construction of biomass via hydrolysis and re-polymerization processes, which might achieve more sufficient mixing of template/biomass. This was investigated herein by conducting HTC of cellulose (Cel), peach wood (PW), walnut shells (WS) with magnesium acetate (MC) at 180°C and subsequent pyrolysis at 800°C. Recycling MC from solid residual for multiple-round activation was also conducted. The results showed that the HTC pretreatment did remarkably enhance Specific surface area (S BET ) of resulting activated carbon (AC). For example, the S BET for AC-Cel-HTC was 727.4 m 2 /g while was 413.3 m 2 /g for AC-Cel, which was an increase by 76.0 %. The HTC-pyrolysis of WS also increased the S BET by 62.7 % (430.5 versus 246.6 m 2 /g from direct pyrolysis). Furthermore, more micropores were generated for ACs with HTC treatment (i. e. 30.0 % for AC-Cel-HTC and 10.7 % for AC-Cel). The HTC pretreatment resulted in better dispersion of MC on/in hydrochar, induced a certain degree of aromatization via removing partial aliphatic structures, and formed stable carbon skeleton for reserving micropores. ACs with HTC treatment possessed both abundant micropores for adsorption of phenol and mesopores for adsorption of methyl blue with quasi-first-order kinetic model. Additionally, MgO could effectively converted back to MC for use in several rounds of activation.