Heavy metal ion (HgII) adsorbents with uniform mesopore channels were prepared by functionalizing SBA-15 and SBA-16 type ordered mesoporous silica samples with mercaptopropyl groups according to two routes: post synthesis grafting of pure mesoporous silica and direct functionalization by a co-condensation procedure. XRD, N2 adsorption-desorption measurements and 29Si solid state NMR spectroscopy were used to characterize the physico-chemical properties of the organic-inorganic hybrid materials and to investigate the different functionalization processes on the two types of ordered mesoporous silica SBA-15 and SBA-16 materials. Higher contents in organo-functional groups were achieved when following the one-step co-condensation route in comparison with the post-synthesis grafting. However, the evaluation of the diffusion rates of HgII species in the mesoporous solids by means of an electrochemical method showed faster binding rates for the post-synthesis grafted samples.