A Metatitanic Acid Particulate Xerogel: Green Synthesis, Structure Determination, and Detailed Characterization

The manuscript focuses on an original method of preparation of metatitanic acid when only environmentally safe base substances are used in the synthesis process. The synthesis is based on the reaction of solid titanyl sulfate in an aqueous solution of sodium hydroxide. This method allows for (i) a full preservation of the morphology of the starting titanyl sulfate and (ii) a preparation of metatitanic acid substances with specific parameters. This can be achieved via a precise control of the alkali metal/titanyl sulfate ratio resulting in substances with varying contents of alkali metals or even sulfate anions. The prepared metatitanic acid then also contains very small weakly crystalline particles (2-3 nm) and forms pseudomorphic aggregates whose shape and dimensions correspond to those of the starting titanyl sulfate. These aggregates exhibit regular nanoporosity with a high surface area of up to 500 m²·g^-1, have no tendency to form colloids, and are mechanically highly resistant even by high-energy ultrasound. The characterization of the resulting products is done via their chemical composition and methods of structural analysis, as well as by electron microscopy and local analysis. The mechanism of product formation is discussed based on the structure of the precursor, including the so far unknown structure of metatitanic acid.