Synthesis of high purity hydroxy sodalite nanoparticles via pore-plugging hydrothermal method for inorganic membrane development: Effect of synthesis variables on crystallinity, crystal size and morphology

Abstract

The effect of synthesis parameters on crystallinity, crystal size and morphology of hydroxy sodalite particles developed via the pore-plugging hydrothermal (PPH) synthesis method is reported in this study. The PPH method is promising in developing nanocomposite membrane materials with superior performance to those prepared from other methods. Towards developing high-quality nanocomposite sodalite/ceramic membrane for CO2 capture via the PPH method, obtaining high-purity sodalite (SOD) nanoparticles via PPH is essential. Thus effect of synthesis variables (e.g. ageing, interruption time, and synthesis temperature) on purity of as-prepared SOD crystals was investigated. A precursor solution with molar concentration of 5SiO2:0.5Al2O3:50Na2O:1005H2O was used in the synthesis. During the synthesis, 45 mL of the vigorously mixed precursor solution (with or without ageing) was poured into a Teflon-lined stainless-steel autoclave and subjected to PPH synthesis. Physico-chemical properties of the as-synthesized crystals were characterized with x-ray diffraction (XRD) for crystallinity and purity, scanning electron microscope (SEM) coupled with energy-dispersive x-ray spectrometer (EDS) for morphology and elemental composition, and Fourier transform infrared spectroscopy (FT-IR) for surface chemistry. In this study, the sizes of SOD crystals obtained was in the range of 227–493 nm and a percentage crystallinity of SOD crystals as high as 75% was obtained. When two interruptions of one hour each was introduced in the synthesis protocol (total synthesis time of 3.5 h), pure SOD crystals were obtained. The SEM images of this protocol revealed SOD crystals of typical thread ball aggregate similar to those reported in literature. Ageing the precursor prior to PPH was not instrumental to forming high-purity SOD crystals, and this could result in developing low-quality nanocomposite SOD/ceramic membranes via the PPH synthesis method. Furthermore, adjusting the synthesis temperature and interruption time of the PPH do have effect on the purity and crystallinity of the as-prepared SOD crystals.