Biomorphic Fibrous TiO2 Photocatalyst Obtained by Hydrothermal Impregnation of Short Flax Fibers with Titanium Polyhydroxocomplexes

A biomimetic solution technology for producing a photocatalytic material in the form of biomorphic titanium oxide fibers with a hierarchical structure using short flax fiber as a biotemplate is proposed. The impregnation of flax fibers intensified under hydrothermal conditions with a precursor was performed in an autoclave to activate the nucleation of the photoactive TiO2 phases. The interaction between precursor and flax fibers was studied by using infrared spectroscopy (IR) and differential scanning calorimetry/thermogravimetry analysis (DSC/TG). The morphology, structure, and textural properties of the TiO2 fibers obtained at annealing temperatures of 500–700 °C were determined by X-ray diffraction analysis, scanning electron microscopy, and nitrogen adsorption/desorption. It is shown that the annealing temperature of the impregnated biotemplates significantly affects the phase composition, crystallite size, and porous structure of TiO2 fiber samples. The photocatalytic activity of the obtained fibrous TiO2 materials was evaluated by using the decomposition of the cationic dye Rhodamine B in an aqueous solution (concentration 12 mg/L) under the influence of ultraviolet radiation (UV). The maximum photodegradation efficiency of the Rhodamine B was observed for TiO2 fibers annealed at 600 °C and containing 40% anatase and 60% rutile. This sample ensured 100% degradation of the dye in 20 min, and this amount significantly exceeds the photocatalytic activity of the commercial Degussa P25 photocatalyst and TiO2 samples obtained previously under hydrothermal conditions by the sol-gel method.