KOH is one of the most widely used activators for the synthesis of highly porous carbon. However, the strong causticity of KOH could cause serious equipment damage and safety issues at high temperature. In the current work, we presented the synthesis of porous carbons with large surface area using four different potassium salts (CH3COOK, KHCO3, K2CO3, and K2C2O4 center dot H2O) as mild but effective activators. Hydrochar prepared from the hydrothermal carbonization of glucosamine hydrochloride was used as carbon precursor. The carbons exhibited specific surface area up to 2403 m(2)/g. In order to reveal the different influences of nitrogen doping and textural properties under low and high pressure conditions, CO2 adsorption was tested with pressure up to 20 bar. At 1 bar, ultramicropore was the most determinant factor. Nitrogen doping also showed important influences, especially on the CO2/N-2 selectivity. At 20 bar, the carbon activated by KHCO3 showed CO2 uptakes of 26.24 (0 degrees C) and 18.63 mmol/g (25 degrees C). The experiment results indicated that the uptake at 20 bar correlated with the total surface area and total porosity of the carbon, and no apparent effects from nitrogen doping were observed. (C) 2020 Elsevier Inc. All rights reserved.