A facile one-pot melting-assisted and solvent-free method was successfully developed for the first time for preparing nitrogen-containing polymers. Followed by activation at temperatures ranging from 600 to 800 degrees C led to the formation of N-rich microporous carbons possessing narrow pore size distribution (ca. 0.5-3 nm), high specific surface area (ca. 1021.4-3657.0m(2) g(-1)), large pore volume (ca. 0.43-2.00 cm(3) g(-1)) and high nitrogen content (ca. up to 5.11 wt%). Particularly, the porous carbons exhibited outstanding CO2 adsorption capacity of 2.65 and 7.38 mmol g(-1) at 273 K and 0.15 and 1 bar, respectively; meanwhile, it also exhibited extremely large CO2 storage capacity of 22.06 mmol g(-1) at 298 K and 20 bar. Moreover, the outstanding CO2/N-2, CO2/CH4 and CH4/N-2 selectivity up to 36.5, 6.9 and 5.1 at 298 K and 1 bar were achieved. The determinant factors on CO2 capture at 0.15, 1 and 20 bar were carefully investigated. Furthermore, this method could be 10-fold scaled up to produce almost identical high-performance carbons. For real-world applications, pressure/vacuum swing adsorption (P/VSA) working capacity, gas-mixture transit breakthrough experiment, and recycle feasibility are evaluated. Thus, these novel materials are promising candidates for CO2 capture from dilute gas mixtures.