Real-Time Multiscale Imaging of Heterogeneous Multistage Reactions: Insights into Nanoscale TiO₂ Synthesis

Area of Science:

• Materials Science
• Chemical Engineering
• Nanotechnology

Background:

• Hydrothermal synthesis is a key method for creating functional inorganic materials.
• Controlling product uniformity is challenging due to complex interactions between reactive species, solution chemistry, and nanoscale products.

Purpose of the Study:

• To resolve heterogeneity in hydrothermal synthesis across multiple length scales.
• To develop a novel strategy for observing reaction pathways and phase separations in real-time.

Main Methods:

• Combined in situ X-ray pair distribution function (PDF) and small-angle X-ray scattering (SAXS) for atomic and nanoscale structural analysis.
• Implemented a novel time-lapse optical imaging strategy to visualize heterogeneity and phase separations throughout the reaction.

Main Results:

• Identified multiple cycles of titanium dioxide (TiO₂) formation and separation during hydrothermal hydrolysis of TiCl₄.
• Observed differing TiO₂ characteristics in each formation-separation cycle, contributing to product nonuniformity.
• Demonstrated that the combined techniques can reveal heterogeneity across atomic to macroscopic scales.

Conclusions:

• The developed imaging strategy offers an efficient in situ method to study reaction evolution under varying conditions.
• This approach advances the understanding and control of functional inorganic material synthesis, particularly for polymorphic products like TiO₂.