Ultrasonic Spray Chemistry
The controlled heteroatom bonding (C-X) of nanostructured materials has received much attention over the past decade owing to their unique chemical, electrical, magnetic, and optical properties. Among the nanostructured materials, carbon nanomaterials (CNMs) and conjugated mircroporous polymers (CMPs) have shown great promise as energy conversion and storage materials owing to their electrical conductivity of extended π-conjugation backbone, bipolar operational flexibility, and large specific surface area. However, the sp2-hybridized network in these materials is thermodynamically very stable; therefore, complex processes and/or harsh conditions are required to achieve heteroatom doping, such as chemical vapor deposition, atomic layer deposition, plasma treatment, and layer-by-layer cross-linking. Taken together, the formation of carbon-heteroatom bonds under mild reaction conditions remains a major challenge.
In our group, we present ultrasonic spray chemistry (USC) which is the combined system of cavitation and nebulization. This cavitational implosion is very localized and transient with a temperature of ~5000 K and a pressure of ~1000 bar. Such conditions permit a range of chemical reactions that are normally inaccessible. Furthermore, USC can also enhance the surface energy of reactant by generation of the heated droplet of mist, thus the chemical synthesis and nanostructuring of the materials can be achieved simultaneously. To demonstrate the C-X bonding by USC, we built up the library of heteroatom doped carbon nanomaterials (X-CNMs) for application into energy storage system and electro-catalyst. The synthesized X-CNMs showed high performances in both of metal-free energy storage material and electro-catalyst fields. Furthermore, the simplicity and continuous process of USC could be a major breakthrough in processability issue of CMPs. Considering the encouraging these results, USC still has an opportunity for the expansion of the applied materials and research area.
Keywords: ultrasonic spray chemistry, heteroatom bonding, carbon nanomaterials, conjugated microporous polymer
1) H.T. Kim et al. Adv. Mater. 29, 1702747 (2017)