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

Abstract

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.

Photocatalytic Activity of Fibrous Ti/Ce Oxides Obtained by Hydrothermal Impregnation of Short Flax Fibers

“…The fibrous photocatalysts were prepared by calcination of the impregnated biotemplates in air in an electric furnace at 600 °C for 30 min. The calcination temperature was in accordance with our previous study that revealed the best photocatalytic activity for fibrous TiO 2 samples was prepared at 600 °C [ 28 ]. The Ti/Ce oxides denoted as TiO 2 –3% Ce and TiO 2 –5% Ce, where 3 and 5 wt.% were the Ce(NO 3 ) 3 ∙6H 2 O concentrations in the precursor solutions.…”

“…The morphologies of the biotemplated TiO 2 –3% Ce and TiO 2 –5% Ce samples were studied by SEM, see Figure 2 . The SEM images of flax fiber and TiO 2 samples were published previously in [ 28 ]. The particles of all the photocatalysts had a similar fibrous structure replicating the texture of the flax template.…”

“…The precursor solutions with titanium and cerium polyhydroxy complexes were prepared in the following way. First, we made a solution of titanium hydroxy complexes by hydrolyzing titanium chloride TiCl 4 (Sigma-AldrichRus, Moscow, Russia) at room temperature by the technique described in [ 28 ]. For that purpose, we added TiCl 4 dropwise to a 6M HCl solution until the Ti 4+ concentration reached 4.92 M. Then, this solution was slowly diluted with distilled water under constant stirring until the Ti 4+ concentration was 0.56 M. This solution was aged for 3 h at 20 °C leading to the formation of titanium polyhydroxy complexes.…”

“…Short flax fibers were used as a biotemplate in this work [ 28 ]. The biotemplate was impregnated with the precursor solutions in an autoclave for 5 h at 115 °C and a pressure of 170 kPa.…”

“…We have earlier reported a method for the preparation of TiO 2 using short flax fibers as a template. As is known, the amount of waste in flax straw processing can reach 75%, as only long flax fibers are used for making linen fabrics, and short fibers are not suitable for these purposes [ 28 ]. Flax fibers have a multimeric structure with pores and capillaries and possess higher acid resistance than other cellulose materials; they are most suitable for the biomimetic synthesis of ceramic fibers based on strongly acidic precursor solutions.…”