Insights into optimized synthesis conditions of hollow microspheres of silica for water vapor adsorption

Abstract

Hollow microspheres of silica were synthesized with different ethanol/water ratios (0.4, 1.0, 2.0 and 6.0) to assess the influence of this parameter on the morphology/porosity of the samples and thus on their water adsorption capacity. The samples were characterized by N2 at 77 K and CO2 at 273 K adsorption isotherms, scanning electron microscopy, transmission electron microscopy and water vapor isotherms at 298, 313 and 328 K. The textural properties of the samples were slightly different: as the ethanol/water ratio increases, the pore volume and specific surface area decrease and the structure of the samples evolves into a well-defined spherical arrangement. In addition, water adsorption capacity of the samples was similar to that of commercial adsorbents used for gas drying at high relative pressures, but significantly lower at low relative pressures. Moreover, varying of the ethanol/water ratio did not lead to a noticeable improvement in the water adsorption capacity at low relative pressures and hence these samples are not suitable for deep gas drying. On the other hand, as they require less energy to be regenerated, HMS are alternatives to be considered in less demanding situations, such as coarse drying and water harvesting from air.