S. G. Karchevskii

Introduction. Additive manufacturing of hydroxyapatite (HA) ceramics is considered a promising approach to creating personalized bone implants. However, highly loaded photopolymer suspensions assume precise composition and exposure conditions to ensure stable printing and product quality. The present study aims to develop a photopolymer suspension based on HA of in-house synthesis for the additive production of ceramic implants using DLP 3D printing. Materials and methods. HA is synthesized by coprecipitation and hydrothermal synthesis methods in aqueous solutions of calcium and phosphate salts. The powder is milled and fractionated for assessing the morphology and element composition using scanning electron microscopy and energy-dispersive X-ray fluorescence analysis, respectively. A photopolymer suspension with 60 wt. % of the inorganic phase, developed based on the synthesized HA, contains acrylate monomers, photoinitiating system and dispersing additives. In addition, photopolymerization is studied on a DLP 3D printer at different UV radiation powers and exposure times. Results and discussion. The synthesized well-crystallized HA has lamellar and nanostructured morphology, as well as developed porosity; the predominance of calcium and phosphorus without significant toxic impurities is confirmed. At a radiation power of 40 mW/cm², the optimal exposure time of 6–10 s ensures the formation of uniformly hardened layers with a thickness of about 0.7–0.9 mm and a thickness plateau at a further increase in exposure time. Conclusion. The obtained data indicate that the combination of controlled HA morphology and specially selected photopolymer matrix provides sufficient polymerization depth and layer stability required for DLP printing of complex geometries. High specific surface area and porosity of HA further enhance its potential in tissue engineering. The developed photopolymer suspension based on HA of in-house synthesis demonstrates suitability for DLP 3D printing and can be used as a basis for creating personalized ceramic implants in traumatology, orthopedics, neurosurgery, and maxillofacial surgery.

A series of catalysts were prepared from a granulated hierarchical (micro–meso–macroporous) NaY_h zeolite: NaY_h, H-NaY_h, H-Y_h, Li-NaY_h, K-NaY_h, Ca-NaY_h, Mg-NaY_h, and La-NaY_h. Their physicochemical properties were characterized, and their catalytic activity and product selectivity were investigated in the aromatization of isophorone. The highest performance in the synthesis of 3,5-dimethylphenol was achieved in the presence of K-NaY_h, the catalyst distinguished both by the highest basicity among the tested samples and by low concentrations of weak Brønsted acid sites and Lewis acid sites. This sample exhibited a 3,5-dimethylphenol selectivity of 78.6% at an isophorone conversion of 98.9%. H-Y_h, H-NaY_h, Ca-NaY_h, Mg-NaY_h, and La-NaY_h provided the highest possible isophorone conversion (up to 100.0% at 400°C and 1 h^–1), with the reaction products mainly consisting of dimethylbenzenes and trimethylbenzenes (their selectivity reached up to 72.9 wt %). In the presence of low-activity samples (NaY_h and Li-NaY_h), the predominant products were methylbenzenes (dimethylbenzenes and trimethylbenzenes, 26.6–30.9%) and isophorone derivatives (β-isophorone and dihydroisophorone, 30.5–33.0%).

The catalytic performance (activity and selectivity) of a FAU-type hierarchical NaY_h zeolite, as well as of a series of modified samples, was investigated in the homocondensation of acetone. The modified samples were prepared from NaY_h by ion exchange of Na⁺ for cations of alkali (Li⁺, K⁺), alkaline-earth (Ca²⁺, Mg²⁺), transition (Co²⁺, Ni²⁺), and rare-earth (La³⁺) metals, as well as by decationation (H-NaY_h, HY_h). The predominantly acidic zeolites (Ca-NaY_h, Mg-NaY_h, Co-NaY_h, Ni-NaY_h, La-NaY_h, H-NaY_h, and HY_h) promoted the formation of acetic acid and mesitylene even at 250°C. The zeolites that contained alkali metal cations (Na⁺, Li⁺, and K⁺) exhibited activity only when the temperature was elevated. Starting from 350°C, NaY_h and Li-NaY_h promoted the formation of acetic acid. In contrast, the performance of K-NaY_h under heating was characterized by the absence of acetic acid formation and a smooth increase in the selectivity towards isophorone (up to 23%) and mesitylene (up to 18%). Over the range of 400–450°C, in the presence of K-NaY_h, secondary isophorone transformations were intensified, resulting in the formation of 3,5-xylenol as the main product with a selectivity of 32%.

The physicochemical properties of a series of catalysts based on granulated Na-Yh zeolite with the hierarchic (micro–meso–macro) pore structure (Na-Yh, HNa-Yh, MgO/Na-Yh, La₂O₃/Na-Yh, TiO₂/Na-Yh) and the activity and selectivity of these catalysts in isophorone aromatization were studied. MgO/Na-Yh and La₂O₃/Na-Yh zeolites with high content of basic sites and low content of Brønsted acid sites are the most effective in the synthesis of 3,5-dimethylphenol: The 3,5-dimethylphenol formation selectivity reaches 63–69% at 87–94% isophorone conversion. In the presence of Na-Yh zeolite containing both acid and base sites, the prevalent reactions are isophorone isomerization and synthesis of trimethylbenzenes. The modification of Na-Yh with titanium oxide leads to an increase in the content of acid sites on the TiO₂/Na-Yh surface and to the prevalence of the aromatization to form trimethylbenzenes. In the presence of HNa-Yh containing a set of the strongest Brønsted and Lewis acid sites, isophorone transforms into a mixture of polymethylbenzenes.

The catalytic properties of mesoporous amorphous titanosilicate Ti–Si in acetone homocondensation at 250–350°С and mass feed space velocity of 0.5–10 h^–1 were studied. The acetone conversion was 13–52 wt %, and the selectivity with respect to mesitylene was 52–70 wt %. A kinetic model based on the experimentally developed scheme of chemical transformations was constructed; it includes 10 steps and takes into account the effect of water. The retrieval of the kinetic parameters was implemented in the form of a global optimization problem, which allowed determination of the kinetic constants, adsorption constant, activation energy, and heat of adsorption of water.