Large-pore mesoporous silica FDU-12 was synthesized and functionalized with silane coupling agents bearing methacrylate and diamino groups. Diamino-functionalized FDU-12/polyamide 6 and methacrylate-functionalized FDU-12/poly(methyl methacrylate) nanocomposites were prepared via in situ polymerization approach. These two synthesized nanocomposites were used as potential adsorbents for the removal of Cd2+ cations from aqueous media. The impact of different adsorption factors affecting the adsorption process was investigated, and isotherm and kinetic studies were conducted to gain a better understanding of adsorption mechanisms involved in the removal process of Cd2+ by the adsorbents. Experimental and computational results demonstrated that the adsorbents have acceptable performance for Cd2+ uptake.