It is very challenging to prepare biomass-derived porous carbons with well-confined ultramicropores. Traditionally, biomass-derived carbons, via a chemical activation process, possess wide pore size distributions from micropores to macropores. Outstanding BET surface area of 2676 +/- 107 m(2) g(-1) was obtained with excellent CO2 uptake of 6.15 and 2.26 mmol g(-1) under 1 and 0.15 bar at 273 K. Furthermore, the outstanding CO2/N-2, CO2/CH4, and CH4/N-2 selectivities of 43.5, 7.4, and 5.9 were obtained on an OTS-1-550 at 298 K and 1 bar. The pore size effect on CO2 capture and gas-separation performance was carefully investigated, indicating that the ultramicropores (<1 nm) governed the CO2 adsorption capacity at 1 bar. Also, the vacuum wing adsorption (VSA) processes and breakthrough experiments have confirmed their practical application potential.