Effect of pH and aging time on pore characteristics of dried silica xerogel

Abstract

Porous glasses with interconnected pores and voids offer unique properties, including high surface area, permeability, and controlled pore size distribution. This research focuses on the preparation of porous glasses through the sol-gel route, specifically investigating the influence of pH and aging time on the pore characteristics of Silica Xerogel. Xerogel is a porous structural material that can be obtained via the evaporative drying of any precursor’s wet gel. Sol-gel processing using tetraethyl orthosilicate (TEOS) as the precursor and HCl as the acid catalyst was employed to obtain porous silica glasses. By manipulating the pH and aging time, custom pore size distributions in the mesoporous or macroporous range were achieved. Scanning Electron Microscopy (SEM) analysis revealed interconnected porous morphologies, with the average pore size increasing linearly with aging time. Xerogel aged for 2 days exhibited a mesoporous structure, while those aged for 4 and 6 days showed a conversion to a macroporous structure. Varying the pH as well as the acid concentration of the catalyst during synthesis resulted in average pore sizes of ~ 31 nm and ~ 59 nm, with pH 3 favoring mesoporous structures and pH 6 enabling the synthesis of macroporous silica xerogel. A higher concentration of the acid catalyst (from 0.05 M to 0.1 M HCl) was found to promote faster gelation, resulting in a denser network with smaller pores.Elemental analysis confirmed the presence of silicon and oxygen as the main constituents in the porous silica xerogel. EDS mapping analysis provided a visual representation of the surface distribution of the elements of silica xerogel. X-ray Diffraction (XRD) confirmed their amorphous nature. The sol-gel method provides a versatile synthesis route for tailoring the microstructure and properties of the resulting materials. By modifying the synthesis parameters, materials with customized porosity can be obtained. Moreover, the sol-gel technique offers the advantage of direct synthesis of high-purity multi-component materials without the need for powder intermediates or costly vacuum-based processes. These findings highlight the potential of sol-gel synthesis for the development of functional materials with varied structures and porosity, catering to specificapplications such as liquid filters, batteries,sensors, support, capturer, matter transport and bio-scaffolds.