Single-Crystalline Protrusion-Rich Indium Tin Oxide Nanoparticles with Colloidal Stability in Water for Use in Sustainable Coatings

Indium tin oxide (ITO) nanoparticles (NPs) with protrusions on their surfaces have been successfully obtained by solvothermal synthesis under high In3+ and Cl– concentrations. High-resolution transmission electron microscopy (HR-TEM) observations revealed that the ITO NPs with protrusions consisted of not a polycrystalline but a single-crystalline structure. The results suggested that the unique shape was produced by heterogeneous epitaxial nucleation on the growing surfaces of the ITO NPs in the presence of tetramethylammonium hydroxide (TMAH). Inhibition of homogeneous particle growth by adsorption of a large excess amount of Cl– ions on the surfaces of growing ITO NPs might play a critical role in the evolution of the unique protrusions. Compared to single-crystalline ITO NPs with a cubic shape, the ITO NPs thus obtained showed a high specific surface area and a low resistivity. Furthermore, the ITO NPs with protrusions exhibited an unprecedented high dispersion stability in water for a long period without the use of any dispersant. 1H nuclear magnetic resonance (NMR) relaxation (T2) measurements revealed that such high dispersion stability could be due to the shape-triggered increase in the hydrophilicity of the surfaces of the ITO NPs. The resulting ITO NP dispersions in water could be applied to prepare ITO thin films with low resistivity on a glass substrate. The behavior has great potential for application as sustainable coating materials to fabricate transparent conductive ITO thin films on flexible substrates under mild atmospheric conditions without usage of expensive production systems and harmful and environmentally undesirable chemicals.