National Research Tomsk State University, Tomsk, Russia:

E. S. Lyutova, Associate Professor at the Department of Inorganic Chemistry, Faculty of Chemistry, Candidate of Technical Sciences, e-mail: lyutova.tsu@mail.ru
A. O. Soltanova, Undergraduate Student, Faculty of Chemistry
L. P. Borilo, Professor at the Department of Inorganic Chemistry, Faculty of Chemistry, Doctor of Technical Sciences

This paper examines bioactive spherical composites synthesized on the basis of Tokem-250 cation exchanger for the TiO₂ – P₂O₅/CaO system from alcohol solutions by sol-gel method. The frame of the material is represented by TiO₂ – P₂O₅, whereas the inside is filled with Ca²⁺ (a Tokem-250 with Ca²⁺ sample with an applied sol). The carboxylic cation exchanger Tokem-250 is highly selective in relation to Ca²⁺ ions and thus it can potentially be used for making biomaterials as calcium is one of the building materials for bone tissue. A comprehensive study has been carried out to determine the effect that the composition of both the initial components and binders can have on the properties of bioactive spherical TiO₂ – P₂O₅/CaO composites synthesized on the basis of Tokem-250 cation exchanger. The concentration of the components in the system has no impact on the properties of the resulting composites. The main stages have been identified of how the composites get formed. Stage 1: up to 235 ^oC – water is removed; Stage 2: from 235 to 600 ^oC – alcohol burns off, nitrates decompose and the cationite matrix disintegrates; Stage 3: from 600 to 1,000 ^oC — the sample crystallizes. The following heat treatment conditions have been identified that would be applicable to the samples: drying at 60 ^oC, annealing at 150, 250, 350 ^oC for 30 minutes each, at 600 ^oC for 6 hours and at 800 ^oC for 1 hour. Samples annealed at 800 ^oC have a crystalline structure, and the following oxide phases were registered: CaO, P₂O₅, TiO₂ and Ti₂O₃, as well as CaTiO₃ (perovskite). Lewis basic centers (Ti – O) dominate the surface of the synthesized composites. The studied composites have the ability to form an apatite-like layer and can be recommended for further study of biological properties. Polyvinyl alcohol and gelatin can be used as a binder.
Support for this research was provided under the Tomsk State University Development Programme Priority-2030.

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