Exhaust gas is always pyrolysed from soft template and carbon precursor in the carbonization process to synthesize mesoporous carbon, resulting in environmental pollution and waste of energy. In this work, we describe a new method, referred to as a "pyrolysis-deposition'' strategy, for synthesis of mesoporous carbon nanospheres (MCNs) by using the exhaust gas pyrolysed from resin polymer as carbon precursor. The synthesis process is simply accomplished in one tube furnace, in which the exhaust gas is pyrolysed from resin polymer and synchronously deposits on Fe-containing hollow mesoporous silica nanospheres (Fe@ HMSNs) and converts to carbon under the catalysis of Fe. Highly dispersible MCNs with spherical morphology are obtained after removing Fe catalyst and etching silica. Some walnut-like carbon spheres with core-shell structure are also formed. The exhaust gas is fully utilized by converting to carbon and less exhaust gas emits into the air, which is advantageous to save energy and protect the environment. The resultant MCNs exhibit high specific surface area (1240 m(2) g(-1)), uniform mesoporous size (4.1 nm) and high performance for CO2 capture with a capacity of 2.36 and 4.76 mmol g(-1) at 1.0 bar under 25 and 0 degrees C, respectively.