Fig. 2
N2 isotherms and micropore distributions of typical samples. a Samples activated at different temperatures (black square UFA-2-600, red circle UFFA-2-500, blue up-triangle UFFA-2-600, dark cyan down-triangle UFFA-2-700, magenta left-triangle UFFA-2-800). b Samples activated with different amounts of KOH (black square UFFA-1-600, red circle UFFA-2-600, blue up-triangle UFFA-3-600, dark cyan down-triangle UFFA-4-600). c Micropore distribution of typical samples investigated by N2 adsorption at low relative pressure of below 0.03 (black square UFA-2-600, red circle UFFA-1-600, blue up-triangle UFFA-2-600, dark cyan down-triangle UFFA-2-800)