Aerogels with large surface areas and adjustable pore structures serve as ideal thermal transpiration materials. Gas molecules can flow from the cold to the hot side of a channel subjected to a temperature gradient when molecular flow dominates gas transport. Our lab has synthesized silica, cellulose, chitosan, and polyimide aerogels with various pore structures. We have studied the 3D tortuous pore structure, Knudsen effect correlations, and explored potential applications for volatile organic compound (VOC) degradation and air pollution particle detection.