Ostwald ripening as a mechanism of hierarchical structural evolution of titanium phosphate

Control over nano- and microstructure of metal oxide materials is increasingly important, as it allows for fine-tuning their functionality. Therefore, material science provided a plethora of template and template-free methods to synthesize substrates with developed morphology, high crystallinity, and large specific surface. Despite significant advances in this field, there is no unified methodology and hence gen-eral consideration about mechanisms of sophisticated and hierarchically structured materials. Titanium phosphates (TiP), a wide group of materials composed of abundant elements, are a versatile platform for development of materials with customizable morphology and elemental composition. Ease of their synthesis and modification provided multiple sorbents, catalysts, energy capacitor electrodes, and polymer additives. Elaboration of hierarchical structures in titanium phosphates beyond the regular and uniform nanocrystal-line units produced substrates with a significant surplus in functionality. Although further studies in this di-rection seem promising, too little attention was focused on control features of TiP hierarchical structure. Here, the analysis of general thermodynamic parameters of hydrothermal synthesis of microspherical titanium phosphate has been carried out. The TiP microspheres change in size according to the Ostwald ri-pening mechanism with conservation of the hierarchical structure. The deviations from this mechanism, ob-served at high concentrations of phosphoric acid, are explained in relation to an active role of phosphate anions in the microsphere growth. Besides, the features of structural elements constituting the microspheres have been considered at more severe conditions of prolonged hydrothermal treatment.