Amorphous and crystalline silica nanoparticles recovered from polymer-silica hybrid films

Abstract

This work is concerned with thermal recovery of sol-gel-prepared mesoporous silica nanoparticles, SiO2 NPs, from organic (aramid or chitosan)−inorganic (SiO2 network) hybrid films. Aramid-SiO2 hybrid films are divided into bonded aramid-SiO2 hybrid (B-Ar-Si) and unbonded aramid-SiO2 hybrid (UB-Ar-Si) films. In bonded hybrid films, a coupling agent (3-isocyanatopropyl)triethoxysilane (ICTEOS) is added to study its effect on the SiO2 network formation and dispersion of the prepared NPs. The same study was carried out using the biodegradable chitosan as the polymer (Cs-Si). The hybrid films were calcined at 500, 800 and 1100 °C to study the effect of temperature on surface area, morphology, porosity and particles size. EDS and FTIR were used to confirm the composition of the hybrid films and NPs, while XPS analysis proved that the surfaces of NPs are made up of silicon and oxygen atoms of SiO2. Surface area and porosity of NPs were tested using N2 sorption analysis and confirmed the synthesis of porous (as high as 1.20 cm3/g) high specific surface area (as high as 810 m2/g) NPs. The prepared SiO2 NPs have a spherical form with particles as tiny as 3 nm and a tendency to sinter at high temperatures, according to SEM, AFM, TEM, HRTEM, and XRD data. Additionally, even at high temperatures, UB-Ar-Si and B-Ar-Si hybrid films produced amorphous SiO2 NPs, but larger NPs recovered from Cs-Si hybrids produced crystalline phases (α-quartz or β-cristobalite), controlled by the used SiO2% in the hybrid films and by the recovery temperature.