Communications ADVANCED MATERIALSWe have shown that computational simulations, based on relatively simple models and simulation procedures, provide an effective procedure for rationalizing the orientation of guest species within layered double hydroxides. The results are in good agreement with those of experiment and suggest that further modeling of these materials would be beneficial.The preparation of improved adsorbent materials that can remove toxic metal ions from aqueous media is a continuing objective of environmental remediation efforts, particularly where there is a need to enhance the adsorption capacity and metal ion specificity. Materials advances in these areas can be expected to lead to more efficient remediation of contaminated effluent streams by fixed bed adsorption technologies.

A new approach to heavy metal ion adsorbents based on the covalent grafting of 3-mercaptopropylsilyl groups to the framework pore walls of mesoporous silica molecular sieves has been investigated with regard to hydroxyl group densities, channel dimensions, and morphologies. Two types of silicas were examined, namely, MCM-41 with an initially anionic silicate framework and HMS with an electrically neutral framework. The MCM-41 derivative was obtained through electrostatic S+X-I+ assembly, where S+ was a quaternary ammonium ion surfactant, X- was a halide, and I+ was the silica precursor derived from tetraethyl orthosilicate (TEOS) in acidic solution. HMS silicas were assembled by a S°I° pathway using alkylamines as surfactants (S°) and TEOS as the neutral silica source (I°). Prior to thiol functionalization of the mesostructures by a one-step grafting procedure, S+ was removed from MCM-41 by calcination, whereas for HMS, S° was removed by solvent extraction. The grafting process was much more effective for the functionalization of HMS than for MCM-41 owing to a higher surface concentration of surface hydroxyl groups. Consequently, the functionalized HMS derivative was able to bind quantitatively more Hg(II) ions from aqueous solution compared to MCM-41. The Hg(II) adsorption capacities for HMS were interpreted in terms of the size and accessibility of the framework pore structure.

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