Abstract
Fluorescein and rhodamine B modified mesoporous silica particles were synthesized by post-grafting and co-condensation approaches. The materials exhibited different pore size distributions, particle shapes and sizes. The materials were characterized by nitrogen sorption, scanning electron microscopy and fluorescence spectroscopy. The Förster resonance energy transfer between the selected dye pair was explored for the different materials by exposure to various concentrations of gaseous ammonia. A logarithmic increase in rhodamine B emission with increasing ammonia concentration was observed for both post-grafted and co-condensed materials. The dye accessibility by ammonia gas in the silica framework of mesoporous materials was evaluated by using a flow cell gas sensor setup built in-house. Response to ammonia gas and recovery with nitrogen gas are explained by comparing the structure properties and dye loading of the materials. The post-grafted dye modified silica showed better performance in terms of reversibility and recovery.
Highlights
Mesoporous silica can be functionalized with organic functional groups, allowing this versatile material to be used in many applications, in particular the separation and adsorption of gaseous species
The relatively narrow pore size distribution (PSD) is typical for SBA-15 particles (SBAs) that has a small tail extending in to the microporous range (Fig. 4).[35]
CoCo SBA FR LD showed a broad PSD with a width at half maximum of about 9 nm and a pore size of about 10 nm (Fig. 4)
Summary
Mesoporous silica can be functionalized with organic functional groups, allowing this versatile material to be used in many applications, in particular the separation and adsorption of gaseous species. Postsynthetic functionalization is favored over co-condensation if the groups to be integrated are not sufficiently stable under the harsh conditions of mesoporous silica synthesis, or if more regular silicates with a narrower pore size distribution (PSD) are desired.[14] One drawback of grafting is that the entire surface may not be accessible, which leads to an inhomogeneous distribution with more grafted groups on the external surface and near the pore. Fluorescein and rhodamine constitute an established dye pair that exhibits Förster resonance energy transfer (FRET), a phenomenon that describes the nonradiative transfer of energy between two chromophores under appropriate conditions.[24] the influence on the FRET activity was investigated for each material by immobilizing in a xerogel film and recording fluorescence spectra in the absence and presence of gaseous ammonia. The accessibility of the dyes to NH3 is discussed on the basis of gas sensor measurements in a gas flow cell optical sensor setup
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