The aim of this study is to exploit low-cost N-doped porous carbonaceous adsorbents with excellent CO2 adsorption properties. Herein, the N-enriched porous carbons were obtained through a single-step sodium amide activation of carbonized water chestnut shell at 400-500 degrees C. The optimal sample possesses high CO2 uptake of 4.50 mmol/g (25 degrees C) and 6.04 mmol/g (0 degrees C) at atmospheric pressure. Additionally, this sample displays high CO2/N-2 selectivity, stable cyclic ability, moderate CO2 isosteric heat of adsorption, fast CO2 adsorption rate, and high dynamic CO2 uptake. In addition to the two well-known factors i.e. volume of narrow micropore and N content, the pore size distribution is also found to play major role in deciding CO2 adsorption performance for these adsorbents. The features of excellent CO2 adsorption properties, low-cost raw materials, low reaction temperature and facile preparation demonstrate that these adsorbents are prospective in the application of CO2 capture.