Development of Environmental Ceramic Materials via Microwave-Assisted Hydrothermal Processing

We focused on the unique properties of microwave irradiation, namely rapid and selective heating, and applied them to the hydrothermal synthesis of ceramic particles, including zeolites from coal fly ash, spherical mesoporous silica and pudding-like ZnO microcrystals. Microwave irradiation enables rapid molecular-level heating of solutions, significantly reducing reaction times compared with conventional hydrothermal synthesis. Moreover, microwave-assisted hydrothermal processes are believed to enhance solute dissolution more effectively than conventional heating. These characteristics can lead to distinctive effects, such as enhanced crystal growth, changes in the resulting crystalline phases, and particle size reduction. Because microwave absorption depends on the dielectric loss coefficient of the solvent, selective heating can be achieved. Utilizing this feature, we developed spherical particles and unique ZnO crystals by selectively heating droplets in a water-in-oil (W/O) emulsion under microwave irradiation. This paper reports these results.