Study on the hydrolysis and crystallization mechanism of nano-titanium dioxide based on supercritical hydrothermal synthesis

To address the severe challenges of environmental pollution and energy shortages, nano-TiO2, as a core photocatalytic material, is in urgent demand for applications in environmental remediation and new energy development. Its photocatalytic performance strongly depends on crystal phase and microstructure. However, conventional synthesis methods struggle to achieve precise control over particle size, crystal phase, and dispersity, often involving complex processes that hinder industrial-scale application. Supercritical hydrothermal synthesis (SCHS), with its advantages of rapid nucleation and environmental friendliness, offers a novel pathway for producing high-performance nano-TiO2. In this study, a continuous-flow SCHS system was employed to systematically investigate the effects of precursor type, concentration, and solvent system on the morphology, crystal phase, and crystallinity of nano-TiO2. The results demonstrate that using tetrabutyl titanate under neutral conditions enables the preparation of anatase-phase single-crystal TiO2with an average particle size of 9.98 nm and excellent dispersity. By adjusting the precursor concentration, it was found that a low concentration of 0.01 mol l-1could suppress Ostwald ripening, thereby optimizing particle uniformity. Furthermore, replacing ethanol with butanol as the solvent significantly reduced particle surface tension due to the interfacial dispersion effect of butanol, yielding a minimum particle size of 7.70 nm at an alcohol-to-water ratio of 3:7. Combined with thermodynamic simulations, the hydrolysis-crystallization mechanism and crystal phase formation pathway of nano-TiO2were elucidated. This research provides critical parameters and theoretical support for the industrial production of high-quality nano-TiO2using SCHS technology.