PhC-2024

E.A. Bogdanova^1,2, V.M. Skachkov¹, K.V. Nefedova^1
1 Institute of Solid State Chemistry of the Ural Branch of RAS
² JSC Giredmet

Abstract: The article discusses the possibility of obtaining a hardened composite material with a porous structure based on nanostructured hydroxyapatite (HAP) synthesized by precipitation from a solution. The new material by the mechanochemical synthesis of hydroxyapatite with aluminum, silicon, nickel, hafnium and titanium was obtained. The synthesized samples are certified using modern physical and chemical methods of analysis. The influence of the qualitative and quantitative composition of the composite on the sintering processes and the strength characteristics of the studied samples is shown. It has been experimentally established that the Ca₁₀(PO₄)₆(OH)₂ – 15%CaF₂-15%TiO_x. system is the most promising for the development of biocomposites based on it. Composite materials of this composition have a dense uniform structure with a high degree of crystallinity, with developed porosity, and are a promising material for further research in order to introduce it into medical practice. The possibility of practical application of the obtained composite material as a component of a bioactive coating is evaluated. A patent application has been filed for the developed composite material.
Keywords: hydroxyapatite, fluorapatite, titanium oxide, calcium fluoride, sintering, composite biomaterials, microhardness, bioactive coating

C.D. Bui¹, S.S. Nalimova¹, Z.V. Shomakhov², A.M. Guketlov², S.S. Buzovkin¹, A.A. Rybina^1
1 Saint Petersburg Electrotechnical University «LETI»
² Kabardino-Balkarian State University named after H.M. Berbekov

Abstract: Type II ZnO/Zn₂SnO₄ heterostructure was considered for gas sensor applications. ZnO nanorods surrounded by a Zn₂SnO₄ shell were grown on the surface of BI2 substrate with sputtered electrical contacts (sensor plat-form) by the hydrothermal synthesis method. Gas-sensitive properties were investigated on different gas analytes (isopropanol, ethanol, and acetone) using a combined laboratory setup allowing for resistivity response and electrical impedance spectroscopy measurements. At an operating temperature of 150°C, the sample showed optimum sensitivity to acetone (1000 ppm) and the R_a/R_g ratio reached a value of 11. The variation of the impedance plot based on the results of measurements in the presence of acetone vapors at an operating temperature of 200°C shows consistent changes. This operating temperature showed a clearer optimization compared to other studies where the sensor operating temperature ranged from 300 to 450°C. In addition, the energy band diagram of the ZnO/Zn₂SnO₄ heterostructure was presented and the acetone detection mechanism was discussed. The structure of the ZnO/Zn₂SnO₄ nanorods causes an improved response due to the chemisorption of oxygen on the surface of the Zn₂SnO₄ shells.
Keywords: zinc oxide, zinc stannate, hydrothermal method, gas sensor, acetone detection, ZnO/Zn2SnO4

S.A. Gerk, O.A. Golovanova
Dostoevsky Omsk State University

Abstract: Composites based on hydroxyapatite and natural biopolymers are promising materials for bone grafting. In this work, samples of hydroxyapatite were synthesized by chemical precipitation from aqueous solutions in the presence of high molecular weight hyaluronic acid (0,4-0,8 wt.%). The resulting powders are represented by carbonate-containing nanohydroxyapatite and contain 89-98 wt.% of polysaccharide. A correlation has been established between the content of hyaluronic acid in the mother solution and the crystal chemical, structural and morphological characteristics of the samples. It was revealed that, in comparison with the hydroxyapatite sample, in viscoelastic media of the polysaccharide, powders are formed that have a smaller parameter a of the hydroxyapatite crystal lattice, close in value to the stoichiometric phase. With an increase in the content of hyaluronic acid in the mother solution, the crystallinity, crystallite sizes and specific surface area of the composites decrease; their average value is 16 nm and 47 m²/g. Samples based on nanohydroxyapatite and polysaccharide consist of oval-lamellar agglomerated particles. At the maximum content of hyaluronic acid in the model solution, amorphized round conglomerates, dense in structure, are formed. The synthesized composites can be used in medical practice as osteoconductive implants, as well as to create nanoencapsulated drug delivery systems.
Keywords: nanohydroxyapatite, hyaluronic acid, composites, polymers; crystal chemical parameters, morphology

E.S. Kartashynska^1,2
1 L.M. Litvinenko Institute of Physical Organic and Coal Chemistry
² Donetsk National Technical University

Abstract: The paper presents a comparative analysis of quantum chemical semiempirical methods for calculation of the binding thermodynamic parameters for C_nH_2n+2 alkanes (n=6–14) and polyaromatic hydrocarbons of the coronene series as model structures of the graphene surface. Two types of orientation of alkane molecules are considered depending on the relative position of the C–C–C «zigzag» plane of alkanes within the polyaromatic hydrocarbons plane: parallel and perpendicular. The parallel arrangement of alkane molecules on the polyaromatic hydrocarbon surface is revealed to be more energetically advantageous than the perpendicular one. The enthalpy, entropy, and Gibbs energy of alkane formation and binding to polyaromatic hydrocarbons are calculated using the PM3, RM1, PM6-DH2, PM6-D3H4, and PM7 methods. It is shown that the first two methods are improper for describing the intermolecular C–H/π interactions in alkane – polyaromatic hydrocarbon systems, since the Gibbs binding energy estimated in them has positive values, which is inconsistent with the available literature data. The use of the PM6 method with DH2 correction for dispersion interactions and hydrogen bonds is optimal. The values of binding enthalpy in alkane – tricircumcoronene complexes calculated using PM6-DH2 and RM6-D3H4 methods are in good agreement with experimental data on the enthalpy of adsorption of alkanes on the graphite/graphene surface, as well as data from molecular dynamic modeling. However, according to the Gibbs binding energy in the considered alkane complexes with parallel and perpendicular orientation of alkanes on tricircumcoronene, only the PM6-DH2 method gives values that correspond in the best way to the available data on the energy preference of such complexes.
Keywords: alkanes, polyaromatic hydrocarbons, adsorption, enthalpy, absolute entropy, Gibbs binding energy, C–H/π interactions, semiempirical methods

N.A. Klychkov¹, V.V. Simakov¹, I.V. Sinev¹, V.V. Efanova², A.M. Zakharevich^1
1 Saratov State University
² Volga State Transport University

Abstract: The paper presents the results of a study on the sensitivity of gas-sensing zinc oxide ZnO film nanostructures at room temperature. The aim of the research was to investigate the effect of ambient humidity on the conductivity of ZnO samples and their response to ethanol vapor in the presence of water vapor. It has been discovered that zinc oxide films are responsive to both water and ethanol vapor at room temperature, across a broad range of concentrations (5% to 50% saturated vapor). The study found that repeated exposure to water vapor can lead to changes in the conductivity of zinc oxide samples when they are exposed to dry air. Additionally, pre-annealing the samples at 400°C can help to replicate the concentration-dependent response of gas-sensitive structures to water vapor. Hysteresis was observed in the relationship between concentration and response to water vapor, in the range of 5% to 90% of the relative humidity. This can be explained by the capillary condensation of water vapor within the mesopores of zinc oxide layers. As the humidity of a gas sample containing ethanol increased, the response values and detection limit for ethanol decreased in the gas-air mixture for ZnO samples. Statistical analysis using the principal component method showed the potential for classifying dry and humid gas samples with ethanol vapor in air. Data processing was used to eliminate the influence of the background humidity on the calibration curve for gas-sensitive ZnO samples, demonstrating the effectiveness of this method.
Keywords: zinc oxide, sol-gel technology, semiconductor gas sensor, ethanol response, gas sensitivity, room temperatures, humidity effect

N.A. Klychkov, V.V. Simakov, I.V. Sinev
Saratov State University

Abstract: An experimental and theoretical study was conducted on the temperature dependence of the conductivity of zinc oxide (ZnO) layers in dry air and ethanol. The study found that the conductivity of ZnO depends non-linearly on temperature, and its type varies depending on experimental conditions. Scanning speed directly affects the type of the temperature dependence, with a local minimum in conductivity between 250±5°C at a scanning rate of 0,4°C/min. However, monotonic dependencies are observed at slower scanning rates, such as 30°C/min, and a mechanism is proposed to explain the effect of the scanning velocity on the type of dependency. This mechanism involves the process of the thermal activation of oxygen molecules to form atomic oxygen at adsorption sites. The key idea behind this mechanism is that atomic oxygen forms deeper acceptor levels on zinc oxide surfaces compared to molecular oxygen. At a high scanning rate, the relaxation time for filling the surface with adsorbed oxygen is significantly longer than the experimental time. Therefore, metastable «frozen» states of atomic forms of adsorbed oxygen appear on the surface of zinc oxide layers. As a result, metastable «frozen» states of adsorbed atoms appear on the surface of zinc oxide layers. Based on calculations using this model, we propose a method for reducing the number of nonequilibrium atomic oxygen states by heating samples in a reducing medium.
Keywords: zinc oxide, semiconductor gas sensor, gas sensitivity at room temperature, temperature dependence of conductivity, oxygen dissociation, surface acceptor, Schottky double barrier model

V.K. Krut’ko¹, L.Yu. Maslova¹, V.A. Suchok², O.N. Musskaya¹, A.I. Kulak^1
1 Institute of General and Inorganic Chemistry of the NAS of Belarus
² Limited Liability Company «Medbiotech»

Abstract: The dynamics of cisplatin release and its mixture with hydroxyapatite from bioinert templates based on carbon felt and polyethylene were studied. Changing the polyethylene and carbon felt layer ratio in the templates influenced the volumetric concentration of cisplatin and the duration of its release. The diffusion of cisplatin from the samples was limited by the number of polyethylene layers. After crystallization at 800°C, the phase composition of hydroxyapatite-α is 65% hydroxyapatite and 35% α-tricalcium phosphate, and hydroxyapatite-αβ consists of 50% hydroxyapatite, 35% α- and 15% β-tricalcium phosphate. Long-term (44 days) release was observed in templates with 2-3 layers of carbon felt and 3-4 layers of polyethylene, and it was slowed when using mixtures with hydroxyapatite (58 days). The appending of hydroxyapatite/cisplatin mixtures into the template with varying amounts of hydroxyapatite phases and α-/β-tricalcium phosphates slowed the release of cisplatin by 14 days, totaling 58 days, due to the sorption and/or binding of cisplatin to calcium phosphates.
Keywords: cisplatin, hydroxyapatite, tricalcium phosphate, carbon felt, bioinert template, release