The effect of synthesis parameters on structure and properties of silica xerogels

Abstract

Introduction Sol gel derived silica matrices have many promising features such as high homogeneity, product purity, chemical and physical stability and porosity. These porous materials with nanosized pores enable loading of numerous biologically active substances into matrices. Objective The aim of this study was to investigate the effect of synthesis parameters on structure of silica xerogels. Methods The effect of two different catalysts (NH4OH and HCl), drying temperature and water content on properties of xerogels were studied. Chemical composition and structure of xerogels were analyzed by Fourier Transfer Infrared Radiation (FTIR) and Scanning Electron Microscopy (SEM), respectively. Specific surface area and pore size of xerogels were examined by BET. Results FTIR results confirmed the forming of Si-O-Si bonds which proved condensation of silanols. According to results, acid-base catalyst, lower temperature for drying and lower water content caused to form crack free xerogels. SEM results showed that acid-base catalyzed xerogels were more porous and pores of acid-base catalyzed xerogels were cylindrical while acid catalyzed xerogels had plate like pores. BET results represented that using higher drying temperature, higher water content and acid-base catalyst increased pore size of xerogel. Also BET results proved that these xerogels had nanosized pores( 4nm). Conclusion We conclude that different active substances can be entrapped in xerogels by changing synthesis parameters and achieving different pore sizes.