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Hollow microparticles are important materials, offering a larger surface area and lower density than their solid counterparts. Furthermore, their inner void space can be exploited for the encapsulation and release of guest species in a variety of applications. Herein, we present phosphazene-based silica hollow microparticles prepared via a surfactant-free sol-gel process through self-assembly of the alkoxysilyl-containing polymer in water–ethanol solution. Solely, a silane-derived polyphosphazene was used as the precursor for the microparticle formation, without additional classical silica sources. These novel hollow silica-based microparticles were prepared without surfactant, using a designed amphiphilic polyphosphazene for the particle formation made by two components, a hydrophilic unit consisting of 3-mercaptopropyl(trimethoxysilane), and a hydrophobic unit (dodecanethiol) attached to the double bonds from the poly(allylamine)phosphazene backbone via a thiol-ene photoreaction. Due to these two functionalities, a "vesicle"-like self-assembled structure was formed in the reaction medium, which could be then utilized for the microparticle preparation. The influence of NaOH during the synthesis was shown to affect the size and the wall thickness of the microparticles. This effect may enhance the possibilities to tailor such microparticles for drug delivery purposes or for future controlled release of other substances, such as drugs, fragrances, or anticorrosive pigments. [ABSTRACT FROM AUTHOR]

Fluorescent organic-inorganic mesoporous hybrid materials have been prepared and characterised, and their behaviour against nitroaromatic explosives have been tested. MCM-41 silica was used as an inorganic scaffold and pyrene ( P derivative containing trialkoxysilane moieties), dansyl and fluorescein ( D and F derivatives also containing trialkoxysilane groups, respectively) fluorophores have been anchored on hybrid materials by a co-condensation method to obtain a homogenous distribution of dyes into the pores of the support. Six sensing materials have been prepared, of which SP, SD, SF were hydrophilic and SPh, SDh, SFh were hydrophobic. Template-free hydrophilic materials ( SP, SD, SF) were obtained after repeated NH4NO3/ethanol extractions under temperature from as-synthesised ( MP, MD and MF supports, respectively) solids. Hydrophobic materials (SPh, SDh, SFh) were prepared by using excess 1,1,1,3,3,3-hexamethyldisilazane with template-free hydrophilic ( SP, SD and SF) materials. The six final materials displayed the typical emission bands of the grafted fluorophores. In particular, SP and SPh show the typical pyrene monomer (370-420 nm) and excimer (430-600 nm) emissions. SD and SDh exhibit the broad dansyl fluorescence band in the 450-600 nm range, whereas solids SF and SFh present sharp fluorescein emission centred at 525 nm. The fluorescent behaviour of the six final materials was tested in the presence of explosives (pentaerythritol tetranitrate (PETN), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), nitrobenzene (NB), 1,3,5-trinitrobenzene (TNB), 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT), 2,4,6-trinitrophenylmethylnitramine (Tetryl) and picric acid (PA)). Only nitroaromatic compounds were able to induce emission quenching. As a general trend, the quenching degree depended on the nature of the final material. The best response was obtained with explosives PA and Tetryl, which were able to significantly quench the emission of the sensing supports. The observed quenching was ascribed to the π-π stacking interactions between the electron-donor fluorophores and the electron-withdrawing nitroaromatic explosives. When using SPh for Tetryl and PA, the limits of detection were 8.5 and 1.4 ppm, respectively, whereas they were 14.4 and 1.2 ppm for SDh. Principal component analysis algorithms were applied to the fluorescence measurements taken with the six hybrid materials and the seven explosives. The obtained score plot showed well-defined clusters for the seven explosives tested. Finally, solid SDh was applied to detect trace amounts of Tetryl in soil samples with good results. [ABSTRACT FROM AUTHOR]

Porous organosilica microparticles consisting of silane-derived cyclophosphazene bridges were synthesized by a surfactant-mediated sol-gel process. Starting from the substitution of hexachlorocyclotriphosphazene with allylamine, two different precursors were obtained by anchoring three or six alkoxysilane units, via a thiol-ene photoaddition reaction. In both cases, spherical, microparticles (size average of ca. 1000 nm) with large pores were obtained, confirmed by both, scanning and transmission electron microscopy. Particles synthesized using the partially functionalized precursor containing free vinyl groups were further functionalized with a thiol-containing molecule. While most other reported mesoporous organosilica particles are essentially hybrids with tetraethyl orthosilicate (TEOS), a unique feature of these particles is that structural control is achieved by exclusively using organosilane precursors. This allows an increase in the proportion of the co-components and could springboard these novel phosphorus-containing organosilica microparticles for different areas of technology. [ABSTRACT FROM AUTHOR]