The Novel Formation of Ordered and Varied Silica-Imidazole Complexes from Silicic Acid

Abstract

Fixed quantities of silicic acid in isopropyl alcohol were treated with varying amounts of imidazole in the same solvent, left closed till complexation was complete (∼7 days) and the resulting gels on slow evaporation (∼30 days) afforded glassy solids, ranging from nodules to tubules, as seen by scanning electron microscope (SEM). In another strategy where soluble oligomers of silica along with monomers can be present and the reaction conditions remaining the same, rectangular cubes of varying sizes were secured. In the view of the significance and potential utility of this novel finding, only duplicate runs, which essentially afforded similar SEM are included here. Elemental analysis established the presence of imidazole in the complexes and their percentage composition was computed using thermo gravimetric analysis (TGA). FTIR showed organics, presence of hydrogen-bonded imidazole, Si‒O‒Si bonds, and complete absence of Si‒O‒C bonds. It is suggested that a pattern where hydrogen-bonded imidazole with itself and the polymer, is entombed in the polymerized silicic acid. Domains having such a profile most likely lead to the observed morphology.The present work vastly widens the scope for silicic acid—guest complexation and holds potential to discover a range of silica harboring materials.

GRAPHICAL ABSTRACT

Keywords:

• Silicic acid-imidazole complexation in isopropanol to spherical nodules
• tubules
• rectangular cubes

Acknowledgements

We thank Dr. J. S. Yadav, Director, IICT for his encouragement and the Department of Biotechnology, New Delhi for financial assistance.