Biomass-based grading porous carbon and preparation method thereof

The invention discloses a biomass-based grading porous carbon and a preparation method thereof. The method comprises the following steps of shearing and sieving the biomass raw materials to 20 to 80 meshes; adding the materials into a double-salt system water solution; performing stirring; performing low-temperature hydro-thermal method pre-carbonization treatment for 5 to 20h at 180 to 300 DEG C;performing washing and filtering to obtain a pre-carbonization product; then raising the temperature to 600 to 1000 DEG C in inert atmosphere; performing carbonization activation treatment for 0.5 to8h; performing acid washing, alkali washing or ultrasonic treatment on the obtained product; then washing the materials by water to the neutral state; performing drying to obtain the biomass-based grading porous carbon. The hydrothermal carbonization is performed during the pre-carbonization; the double-salt system is used as a salt template and a pre-hole-forming agent; the adverse conditions are provided for the subsequ