Preparation of perfluoro-1,3-propanedisulfonic acid/Nafion/silica hybrid nanoparticles-thermally stable Nafion in these silica hybrid nanoparticles even after calcination at 800 °C

Abstract

Perfluoro‐1,3‐propanedisulfonic acid (PFPS)/Nafion/silica hybrid particles were prepared by the sol–gel reactions of PFPS with tetraethoxysilane and silica nanoparticles in the presence of Nafion under alkaline conditions. These obtained composites exhibited a good dispersibility and stability in not only water but also traditional organic media such as methanol, ethanol, 1,2‐dichloroethane, tetrahydrofuran, and dimethyl sulfoxide. Dynamic light scattering measurements and field‐emission scanning electron microscopy show that these hybrid particles are nanometer size‐controlled fine particles before and even after calcination at 800 °C. Nafion/silica hybrid nanoparticles were also prepared in the absence of PFPS under similar conditions. The weight of original Nafion markedly dropped around 350 °C and decomposed gradually, reaching 0% around 450 °C, and Nafion in the Nafion/silica nanocomposites exhibited a similar weight loss behavior to that of the original one. However, Nafion/PFPS/silica hybrid nanoparticles were found to exhibit no weight loss corresponding to the contents of Nafion and PFPS in the silica gel matrices even after calcination at 800 °C. It was demonstrated that the pH value (3.77 at 25 °C) of Nafion/PFPS/silica hybrid nanoparticles after calcination is smaller than that (5.66 at 25 °C) before calcination, and this hybrid nanoparticles exhibited a higher proton conductivity (5.8 × 10−3 S/cm at 85 °C) than that (4.1 × 10−3 S/cm at 85 °C) before calcination. In addition, Nafion/PFPS/silica hybrid nanoparticles after calcination at 800 °C were applied to the Friedel‐Crafts acylation of thiophene with acetic anhydride to give the expected 2‐acetylthiophene, of whose yield was similar to that before calcination under similar conditions. These findings suggest that Nafion in PFPS/silica hybrid nanoparticle cores should exhibit a nonflammable characteristic even after calcination at 800 °C to act as an effective acid catalyst. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1869–1877

Preparation and properties of fluorinated aliphatic alcohols/silica nanocomposites – Application to the encapsulation of anatase titanium oxide nanoparticles into these composite cores

“…In fact, we have already succeeded in preparing new fluoroalkyl end-capped oligomer/silica nanocomposites through the encapsulation of silica nanoparticles as guest molecules into fluoroalkyl end-capped oligomeric nanoparticle cores, and fluoroalkyl end-capped oligomers containing higher acidic protons such as sulfo groups formed by the nanocomposite reactions in the presence of tetraethoxysilane (TEOS) and silica nanoparticles under alkaline conditions afforded no weight loss behavior at 800°C; although the corresponding oligomer containing carboxyl groups can exhibit a usual weight loss after calcination corresponding to the content of the oligomer in the composite matrices [28]. Low molecular weight fluorinated surfactants such as perfluoro-1,3-propanedisulfonic acid (PFPS) were also applied to the nanocomposite reactions with TEOS in the presence of silica nanoparticles under alkaline conditions to give no weight loss corresponding to the content of PFPS in the silica nanocomposite cores even after calcination at 800°C [29,30]. It was suggested that the smooth dehydrofluorination between the sulfonic acid protons (higher acidic protons) and fluorines in fluorinated oligomers catalyzed by both ammonia and silica nanoparticles should proceed to give hydrogen fluoride, and this hydrogen fluoride can react with silica nanoparticles to afford ammonium hexafluorosilicate [31][32][33].…”