In this work, porous carbons were achieved from sustainable biomass lotus stalk. Unlike the common carbonization-activation two-step method, a facile one-step KOH activation procedure was explored to make the carbonaceous sorbents. The as-made adsorbents have advanced porous structures and hold superior CO2 uptake, up to 3.68 and 5.11 mmol/g at 1 bar, 25 and 0 degrees C, respectively. After carefully checking the relationship of CO2 uptake with each porous characteristic, the volume of narrow micropores is found to be the leading factor that determines the CO2 adsorption abilities of the adsorbents under ambient conditions. Moreover, the narrower pore size distribution is also preferential to the adsorption of CO2. Apart from the high CO2 uptake, these lotus stalk-derived adsorbents also possess extra excellent CO2 capture properties such as good recyclability, fast adsorption kinetics, reasonable CO2/N-2 selectivity, suitable heat of adsorption, and high dynamic adsorption capacity. These results demonstrate that these cost-effective carbonaceous adsorbents developed by the facile one-step method have potential in the application of actual CO2 capture.