The volume expansion effect of amine supported on mesoporous silica during CO2 adsorption process was found for the first time through well-designed experiments and was further confirmed by theoretical calculations. It was found that the residual pore volume of mesocellular silica foam (MCF) based solid amine sorbent (tetraethylenepentamine (TEPA) supported on MCF) gradually decreased with the increase of CO2 uptake. Moreover, the surface area, the average diameters of window and cell of MCF show a similar changing trend. This is due to the volume expansion effect of TEPA during CO2 adsorption process, i.e., the total volume of reaction products of TEPA and CO2 is larger than that of pure TEPA. The products are very sticky and almost lose the liquidity totally even at 80 degrees C. The sticky products and the volume expansion effect may increase the mass transfer resistance and are not beneficial to higher CO2 uptakes especially for solid amine sorbent with higher amine loading due to the decrease of pore size and the residual pore volume. DFT calculations based on simple models also indicate that the total volume of the generated products is much larger than that of unreacted amine, further confirming the volume expansion effect of amine during CO2 adsorption process. DFT calculations also indicate that the volume is even doubled in the presence of moisture. The volume expansion effect of solid amine sorbent found in this study may help to design the sorbent with high CO2 capture performance and less the mass transfer resistance. (C) 2020 Elsevier Inc. All rights reserved.