Ostwald ripening behind the hierarchical structure evolution of titanium phosphate

Abstract

Control over nano- and microstructure of metal oxide materials is increasingly important, as it allows for fine-tuning their functionality. Material science provided a plethora of template and template-free methods to synthesize substrates with developed morphology, high crystallinity, and large specific concentration of reactive centers. Titanium phosphates (TiP), a wide group of materials composed of earth-abundant elements, are a versatile platform for the 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 nanocrystalline units produced substrates with a significant surplus in functionality. Although further studies in this direction seem perspective, little work was devoted to controlling features of the TiP hierarchical structure. Here, we report on a screening of general thermodynamic parameters of the hydrothermal synthesis of microspherical titanium phosphate. TiP microspheres change in size according to the Ostwald ripening mechanism with full retention of hierarchical structure. Deviations from this mechanism observed at high concentrations of phosphoric acid are explained in relation to the features of the constituting elements of the microspheres.