In surface modification reaction, silanol groups are replaced with nonpo-lar hydrolytically stable Si (CH3)3 groups. A repulsive forceacts between the Si (CH3)3 groups, therefore the gels start to increase in volume, “spring back” and strengthen the pores(Rao et al., 2007). The FTIR analysis denotes that surface mod-ification reaction in the samples containing activated carbonwas completely done and the number of Si (CH3)3 groups in composite are more than that of pure silica aerogel. So theaverage pore diameter of composites is greater than that ofpure silica aerogel