Effects of chloride and oxygen ions in rutile TiO2 nanorod synthesis by the molten-salt method

Abstract

Rutile TiO₂ nanorods have been extensively employed in numerous fields owing to their distinctive morphology, exceptional physical and chemical properties, and biocompatibility. A considerable number of researchers have reported the synthesis method of molten salt for high-aspect-ratio rutile TiO₂ nanorods. Nevertheless, their crystal phase and crystal growth mechanism remain enigmatic. In this investigation, rutile TiO₂ nanorods were synthesized from anatase TiO₂, potassium chloride, and potassium carbonate at 1173 K. The effects of Cl⁻ and O²⁻ on the crystal transformation and growth were further meticulously investigated by integrating experimental results, morphological prediction, and relevant adsorption energy calculation data. It was discovered that Cl⁻ could facilitate the crystal phase transformation from anatase TiO₂ to rutile TiO₂. The ratio of Cl⁻ to anatase TiO₂ ranging from 5.8 : 12 to 9.2 : 12 is beneficial to forming rutile TiO₂ nanorods. But, a portion of blocky rutile TiO₂ still exists in the final product. Moreover, O²⁻ is conducive to forming potassium titanate (K₂Ti_xO_2x+1) nanorods, which inhibit the conversion of anatase TiO₂ to rutile TiO₂. The combination of Cl⁻ and O²⁻ under the conditions of precisely controlling the molar ratio of Cl⁻/O²⁻ within 4.14 to 9.20 is conducive to the synthesis of rutile TiO₂ nanorods. The results provide a good reference for precisely controlling the synthesis of rutile TiO₂ nanorods to achieve the desired properties.