A series of novel porous adsorbent materials, that is, silica-gel supported low-generation amino-terminated polyamidoamine (PAMAM) (G1.0), were synthesized via the sol gel method using cetyltrimethylammonium bromide (CTAB) as the pore-directing agent and tetraethoxysilane (TEOS) as the cross-linking agent. The silica-containing precursor with PAMAM dendrimer (G1.0) was prepared via the divergent method. Their structures were characterized by Fourier transform infrared spectroscopy, elemental analysis, scanning electron microscopy, porous analysis, X-ray diffraction, and C-13 magic angle spinning NMR spectroscopy. Also investigated were influencing factors such as the content of functional groups, the pore-directing agent on their structures, and adsorption properties toward metal ions. Hg(II) was chosen as a representative metal ion to assess their adsorption capabilities and the utilization ratio of functional groups. The experimental results showed that the N contents of the samples with CTAB were lower, while the utilization ratios of N were higher, than those without CTAB. The pore-directing agent proved to be beneficial for the preparation of effective adsorbent for metal ions. The Hg(II) adsorption kinetics of the adsorbents followed the pseudo-second-order process at different temperatures. Langmuir and Freundlich isotherm models were both employed to analyze the experimental data with the former as the better fit. A temperature increase was also found to be beneficial for adsorption.