Diverse effects of microwave heating on anatase crystallization in ionothermal synthesis of nanostructured TiO2

This article examines anatase crystallization in the ionothermal synthesis [sol gel method in the presence of ionic liquid (IL)] of nanostructured TiO2 under microwave (MW) irradiation. MW heating can lead to rapid temperature increase of chemical reactions. In this study, we found that rapid temperature increasing effects on anatase crystallization were diverse and dependent on initial water concentration, MW irradiation time, and IL concentration. The results indicated that higher anatase crystallinity was obtained at high water amount irrespective of IL concentration. However, at lower water amounts, higher anatase crystallinity occurred only when MW heating was applied after the mixtures reacted for certain duration, especially at lower initial temperature and at a specific IL concentration. Different MW heating effects on the hydrolysis–condensation reaction and the post-treatment stage under MW/IL conditions can explain this diversity. Heating characteristics of IL/water mixtures under MW irradiation were also discussed.