Characterization and Performance Analysis of Nanosilica Powders from Rice Hull Ash as Moisture Sorbents
Untreated and ethylene glycol (EG)-treated nanosilica powders were synthesized from rice hull ash and their sorption properties for water vapor were investigated. The morphology, elemental compositions, surface area and pore structures of the nanopowders were elucidated using scanning electron microscopy (SEM) and nitrogen adsorption-desorption modeling. SEM results showed that the particles were in agglomerated form with diameters of 62–84 nm and 41–65 nm for the untreated and the EG-treated nanosilica powders, respectively. Energy dispersive x-ray spectroscopy indicated that silicon was the most abundant element present in both samples.
The nitrogen sorption isotherms were categorized as type IV with H3 hysteresis loops by International Union of Pure and Applied Chemistry (IUPAC) classification. Surface area of untreated nanosilica powder was 48.11 m2 g-1, which was slightly more than that of EG-treated nanosilica powder (38.65 m2 g-1). Pore size distribution curves demonstrated the mesoporous nature of both samples. Water sorption isotherms of nanopowders at 5, 30 and 60 °C and relative humidity of 11–88% were determined using the static gravimetric method. The results were analyzed using the Guggenheim-Anderson-De Boer model.
The study showed that moisture sorption characteristics of both untreated and EG-treated nanosilica powders could be utilized as moisture sorbents at air relative humidity levels greater than 70% at all temperatures studied. Since nanosilica is widely used in many researches and with applications in different fields as sorbents and catalyst, these results on the water sorption characteristics of nanosilica powders will be beneficial for the processing and end-use applications of the nanoparticles.
Key Words: moisture sorbent, nanomaterial, nanopowder, nanosilica powder, nanotechnology, rice hull ash