Influences of impregnation ratio and activation time on ultramicropores of peanut shell active carbons

•Peanut shell active carbons containing ultramicropores were made by KOH activation.•We studied effects of impregnation ratio (IR) and activation time on ultramicropores.•Increasing IR varied ultramicropore volume (V<0.7 nm) and ultramicropore fraction.•Prolonging the activation time varied ultramicropore fraction, not varying V<0.7 nm.•The highest V<0.7 nm was obtained by activation for 1–2 h using an IR of 2.

We studied effects of impregnation ratio and activation time on ultramicropores of KOH-activated peanut shell active carbons (ACs). The ultramicropores were characterized in terms of ultramicropore volume (V<0.7 nm), ultramicropore fraction (V<0.7 nm/Vt), and pore size distribution. The ultramicropores of the ACs were mostly in the range of 0.45–0.70 nm. Increasing the impregnation ratio from 1 to 3 first increased the V<0.7 nm and V<0.7 nm/Vt, and then decreased them. Prolonging the activation time from 1 h to 2 h resulted in a minimum V<0.7 nm/Vt, but hardly affected the V<0.7 nm. The AC with the highest V<0.7 nm (0.11 ml/g) was obtained by activation for 1–2 h at an impregnation ratio of 2. The V<0.7 nm bore a linear relationship with the CO2 uptakes at 0.1 and 0.2 bar (0 °C). This research was significant for preparation of ACs with developed ultramicropores.