NMR Characterisation of the Organic/SiO 2 Interfaces in Templated Porous Silica.
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0984-MM14-06
NMR Characterisation of the Organic/SiO2 Interfaces in Templated Porous Silica. Niki Baccile, Guillaume Laurent, Thierry Azaïs, and Florence Babonneau LCMCP, Université Pierre et Marie Curie-Paris6; CNRS, 4 place Jussieu, Paris, 75005, France
ABSTRACT This paper illustrates the use of a 1H-29Si-1H double CP sequence to investigate different organic/SiO2 interfaces in templated porous silica. The advantage of this sequence is to selectively edit, in a one-dimensional experiment, the protons that are in close proximity with the Si surface sites. In order to maximize the polarization transfer efficiency, some experiments have been recorded at lower temperature (238 K). Examples will concern surfactant/silica interactions in mesostructured silicas and the behavior of benzoic acid and 4-methoxychlorophenol, a common pesticide, encapsulated in mesoporous silica. INTRODUCTION Mesoporous silicas with long range ordered porosity appear as very attractive host matrices for a large variety of organic molecules. The possibility to obtain well ordered porous network can facilitate the diffusion of species; the pore size can be tuned by a proper choice of the templating agent and thus be adapted to the size of the guest molecules; the surface can be easily functionalized by a large range of organic groups, in order to tune the host-guest interactions. These materials are currently exploited to develop specific adsorbents for air and water pollutant filtering [1] but little attention has been addressed so far to the behavior of the pollutant within the porous host network. This is obviously an important issue to consider for further materials recycling. Another field of applications that is currently explored is the controlled release of drugs such as ibuprofen [2]. In that case, the possibility to encapsulate large amounts of drugs up to 400 mg/g of SiO2 is definitely a key argument. Additionally, a suitable functionalization of the silica surface can provide a way to control the drug release rate by playing with the drug-surface interactions [3]. In such applications, the interactions between the guest molecules and the silica surfaces need to be better characterized, and high-resolution solid state NMR is one of the main techniques to investigate the organic-inorganic interfaces. However, few studies have been published so far on this topic. They have been mainly focused on the characterization of surfactant/silica interfaces in the as-synthesized templated silicas. Extremely valuable information can be extracted from 29Si{1H} heteronuclear correlation HETCOR experiments [4], on the spatial proximity between the organic moieties and the silica surface. Variation of contact time, tCP (time during which the magnetization transfer occurs between the two dipolar coupled spin systems) can be used to explore increasing inter-nuclei distances. However, these two-dimensional experiments are rather time consuming, especially at moderate static magnetic field. We have thus developed a sequence based on a 1H-29Si-1H double
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