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Project titleMesoporous hydroxyapatite powders containing tungstate or molybdate anions and iron cations as promising heterogeneous catalysts for oxidation of alcohols

AffiliationBaikov Institute of Metallurgy and Material Science, Russian Academy of Sciences,

Research area 09 - ENGINEERING SCIENCES, 09-203 - Phase equilibrium and transformations

Keywordshydroxyapatite, molybdate anion, tungstate anion, chemical synthesis, iron cation, hydrogen peroxide, anion-cation co-substitution, mesoporosity, electron paramagnetic resonance, phase composition, thermal stability, oxidation, green chemistry

Annotation
The increased requirements for environment preservation and the rational use of natural resources necessitate the introduction and development of new "green" chemical processes (including for industrial catalysis) that meet the strict requirements of environmental legislation. Selective oxidation of benzyl alcohol is one of the most important reactions of organic transformations for scientific research and industrial production. Nowadays, the industry oxidation of benzyl alcohol is performed in the presence of toxic stoichiometric oxidants, for example, chromates, permanganate, and chlorine-containing oxidants. The creation of a non-toxic and efficient catalyst is an urgent scientific task. The efficient and environmentally friendly oxidation of glycerol is also one of the most important goals of "green" chemistry. Glycerol is a cheap by-product of the biodiesel industry and seems a substantial environmental concern. The oxidation reactions of organic substrates under heterogeneous catalysts and hydrogen peroxide are one of the key components of "green" processes, characterized by "mild" conditions including relatively low temperature and resulting in the formation of only water during the processes. Recently, modified hydroxyapatites (HA) have been used as catalysts for the oxidation of organic substrates. Transition metals are introduced into the structure of hydroxyapatite, which can activate hydrogen peroxide both with the formation of the active radicals (iron, nickel, copper, manganese, cobalt) and with the formation of active peroxo complexes (derivatives of molybdenum, tungsten). The authors of this project [Goldberg, M. A., Akopyan, A. V., Gafurov, M. R., Makshakova, O. N., Donskaya, N. O., Fomin, A. S., ... & Komlev, V. S. (2021). Iron-Doped Mesoporous Powders of Hydroxyapatite as Molybdenum-Impregnated Catalysts for Deep Oxidative Desulfurization of Model Fuel: Synthesis and Experimental and Theoretical Studies. The Journal of Physical Chemistry C, 125(21), 11604-11619.] have shown the synergy effect of the iron and molybdenum combination in the HA catalyst for the oxidative desulfurization process of the model fuel. However, during the impregnation on the HA surface, molybdenum formed the separate phase of calcium molybdate, which led to a sufficient decrease of the catalyst specific surface, as well as resulted in the partial removal of molybdenum during the regeneration in the acetone. It is known that elements of group VI of the Mendeleev Periodic Table, including tungsten (W) and molybdenum (Mo) form the active peroxo complexes. In this regard, it is extremely interesting to obtain efficient and environmentally neutral catalysts based on the substituted tungstate-HA(WO4-HA) and molybdate-HA (MoO4-HA), in which active groups are introduced into the HA structure during the substitution of the hydroxyl and phosphate groups positions. Based on the results obtained in the author’s previous investigation, it is interesting to identify the physicochemical and catalytic characteristics of HA containing tungstate and molybdate anions and iron cations and when to compare the co-doped and Fe-impregnated powders. At the same time, there is no information on the synthesis of single-phase WO4-HA, MoO4-HA, as well as Fe-WO4-HA and Fe-MoO4-HA up to date. The precipitation from the aqueous solutions in glass vessels during the constant stirring is one of the most common laboratory methods for the powders synthesis, but it is rather difficult to scale it up for manufacturing. We have shown that the crystallization of materials after the precipitation during the ripening in the mother solution for 21 days ensures the production of mesoporous HA powders, which are characterized by the H3 type hysteresis loop. At the same time, the hydrothermal synthesis method could be considered as an alternative for obtaining the crystallized powders, while its zoom is a rather simpler technological problem. The solid-phase synthesis at high temperatures allows obtaining the larger crystals, in the contrast with the solution methods, and led to compare materials characteristics with nanosized mesoporous powders, as well as reveal the effect of material dispersion on their thermal stability. For a deep study of the structure of materials, it is supposed to reveal the paramagnetic properties of doped HA powders, which will result in establishing the presence of the radicals on the HA surface, and also evaluate the environment of tungstate, molybdate, and iron ions in the structure. The catalytic properties will be established from the point of view of the identification of the type and concentration of doping anions WO4-HA, MoO4-HA, as well as the co-doping of Fe-WO4-HA and Fe-MoO4-HA effect on the conversion, stability, and selectivity of the catalyst. For this purpose, the oxidation by hydrogen peroxide of alcohols - benzyl alcohol and glycerol will be conducted, and the optimal conditions for the substrates oxidation process, namely temperature, process time, solid/liquid ratio will be estimated.

Expected results
A systematic study on the synthesis of mesoporous anion-substituted (tungstate-HA(WO4-HA) and molybdate-HA (MoO4-HA)) hydroxyapatite (HA) powders with a specific surface area of at least 100 m2/g by precipitation from aqueous solutions and hydrothermal methods, as well as crystallized powders by the solid-phase method will be performed. The influence of the process conditions on the obtained materials’ physicochemical parameters (chemical and phase composition, crystal lattice parameters, specific surface area, type of mesoporosity and pore volume, morphology, etc.) will be evaluated, their thermal stability at temperatures up to 1200 °C will be investigated. The conditions for obtaining single-phase materials will be found. The effect of tungstate and molybdate anions on the paramagnetic properties of doped HA will be revealed, and the valences of doping elements will be determined. Based on the results of the analysis of electron-nuclear interactions, the values of anisotropic dipole-dipole splittings will be calculated, which allow us to estimate the distance to the surrounding nuclei and, accordingly, the position of the impurity ions. Double anion (tungstate or molybdate)-cationic (iron) substituted mesoporous HA powders will be synthesized by the precipitation from aqueous solutions and hydrothermal methods, and the conditions for obtaining single-phase materials will be established. The synthesized anion-substituted HA powders will be impregnated by iron salts solutions saturation with the following heat treatment for iron ions introduction. The phase composition of the obtained cation-anion-containing HA powders will be determined, the morphology, texture characteristics, distribution of calcium, phosphorus, tungsten/molybdenum, and iron elements on the surface of the powders will be studied. The dominant mechanisms for spin-lattice and spin-spin (phase coherence) of anionic impurities relaxation, as well as radiation-induced centers in the temperature range from 297 K to 10 K will be established. These allow us to estimate the distribution degree (homogeneous or inhomogeneous) of the introduced anionic and cationic impurities within the HA sample, evaluate the processes of interionic interaction in co-doped HA, and the imperfection of the crystal lattice. The active acid sites and the acidity of the resulting powders will be characterized by H2 temperature-programmed reduction and temperature-programmed desorption of ammonia. The influence of the technological parameters of the benzyl alcohol and glycerol oxidation process (temperature, duration, catalyst/ oxidants ratio) on the degree of conversion, the product selectivity, and the regeneration ability of the catalysts based on molybdate- and tungstate-substituted HA, and also iron-molybdate- and iron-tungstate-containing HA will be investigated. The significance of the obtained results is determined by the solution of the complex problem of new heterogeneous catalysts creation for "green" processes, namely, for the oxidation of benzyl alcohol and glycerol with hydrogen peroxide under mild conditions - at a relatively low temperature and with the formation of exclusive water in the reaction process based on the most stable calcium phosphate – HA, which will be capable form the active peroxo complexes due to the presence of - molybdate - and - tungstate anions. For the solution of this problem, one should determine the effect of the synthesis method and parameters on the physicochemical properties of powders, as well as on their paramagnetic characteristics which led to establishing the formation of the tungstate- and molybdate-substituted, double anion-cation-substituted HA structure features, and to reveal the relationship between the concentration of doping anions, and also co-doping anions and an iron cation, textural characteristics of materials, their morphology and catalytic activity in the reactions of hydrogen peroxide oxidation of benzyl alcohol as a model compound. For the first time, studies will be carried out on the oxidation of glycerol with hydrogen peroxide in the presence of a single-phase (not being a carrier, but acting as a catalyst) material based on hydroxyapatite.

Annotation of the results obtained in 2022
According to the results of the first year of the project, the methods of synthesis by precipitation from aqueous solutions (PAS) and hydrothermal method (HM) have been developed for obtaining molybdate- (MoO4-HA) and tungstate-containing (WO4-HA) hydroxyapatite powders (HA) with dopant content up to 10 mol % by phosphate anion. Also, powders of pure HA were received by both methods, as a control. The HM synthesis process conditions varied from 120 to 180 °C in temperature, 60 to 1440 min duration, and 200 to 1000 kPa in reactor pressure. Comparing both synthesis methods showed that 1) the synthesis method does not affect the powder elemental composition; 2) the limits of single-phase powder materials' existence were determined depending on the synthesis method: for MoO4-HA up to 2.5 mol.% by PAS and up to 1.5 mol.% by HM; for WO4-HA up to 1.5 mol.% by PAS. HM synthesis did not form WO4-HA single-phase materials; 3). the application of HM allows us to obtain the powders with higher crystallization degrees compared to the samples synthesized by PAS; the increase of HM treatment temperature resulted in the further growth of powders' crystallization degree, which practically did not change after ripening in mother solutions. At the same time, the ripening in mother solutions provided a significant increase in crystallinity degree for the PAS powders. Also, the state of functional groups was established by infrared spectroscopy and the formation of HA structure for doped materials was shown. The investigation of textural characteristics showed that the specific surface area (S) increased (up to 117.8 m2/g) with the MoO4 concentration growth up to 5 mol.% with its further decrease for the PAS powders. The total pore volume increased as the MoO4-anion content increased - up to 0.6163-0.6196 cm3/g, the average pore diameter also increased and reached 20.8 nm. The powders containing WO4-anions had the highest S value at the WO4 content of 2.5 mol % - 129.8 m2/g. A further increase in the WO4-anion content leads to a sharp decrease in S to 74.3 m2/g, which is accompanied by a decrease in porosity from 0.5089 to 0.3833 cm3/g. The average pore size ranged from 14.3 nm (2.5 % WO4) to 20.4 (1.0 % WO4). The HM synthesis materials are characterized by a lower S (no more than 72.6 m2/g with 1 mol.% WO4, 120 min, 120°C). An increase in the concentration of introduced anion leads first to an increase and then to a decrease in S value. After aging in the mother liquor for 21 days, an increase in S and an increase in the total pore volume as well as a decrease in the volume of micropores are observed. It may be noted that the temperature and duration increase of HM treatment contributes to the reduction of S. The effect of dopants on the particle morphology was revealed by transmission electron microscopy. The introduction of anions leads to the appearance of particles 100 nm in size, belonging to either CaWO4 or CaMoO4 in a HA matrix consisting of particles 7-10 nm for the powders obtained by PAS, and 20 nm for the powders obtained by HM. It was found that before the second phase, the dopants were uniformly distributed in the powders. The electron paramagnetic resonance method was used to determine spin-spin (T2) and spin-lattice (T1) relaxation times for all investigated samples. Spin-lattice relaxation times of PAS powders are significantly shorter (T1 = 10 μs) than those for HM samples, indicating a more amorphous structure of HA and MoO4-HA samples. The hyperfine interaction (HFI) constant with the concentration of impurity anions increased to 67.7 Gs, with calculations showing that the change was due to the isotropic contribution of the HFI with the preservation of the dipole-dipole splitting. This result is important because the introduction of a large number of WO4 anions does not lead to significant distortions in the crystal lattice. However, the charge difference between the OH group and the impurity anions leads to a change in the electron density distribution of the impurity centers. According to the electron-nuclear double resonance data: 1). it was found that the introduction of MoO4 and WO4 anions in a wide concentration range does not lead to significant structural changes. However, from the point of view of HA fine structure, there is a change in local electron density distribution within the crystal lattice, which is of fundamental importance at the moment; 2). The local nuclear environment of impurity centers contains signals from structural ions/atoms with characteristic HA hyperfine splitting. A high-resolution high-frequency spectrometer study reveals a small scatter in the g-factor and isotropic contact Fermi contribution to the electron-nuclear coupling. Despite the introduction of impurities in large quantities, the degree of crystallinity and symmetry of the sample is maintained. Acidity has been investigated by thermally programmed ammonia desorption and revealed: the low-temperature area up to 300 °C reflects desorption of physically adsorbed ammonia molecules (weak acid sites); the high-temperature area (above 400 °C) corresponds to ammonia desorption adsorbed on strong acid sites. For the substituted samples the additional signal appearance in contrast to the initial HA in the weak acid sites area (at 203 °C for WO4-HA and at 207 °C for MoO4-HA) was fixed. At the same time, the ratio of weak acid sites to strong ones remains unchanged for MoO4-HA and slightly decreases for WO4-HA. The total number of acid sites in the substituted catalysts increases almost twice as much as in the pure HA. Thus, the addition of small amounts of MoO4 and WO4-anions to the HA structure significantly increases its acidity, which has a positive effect on the activities of such materials in the oxidation reactions of various substrates. According to the thermo-programmed reduction of catalysts by hydrogen, the modification of HA by MoO4 anions leads to an increase in the number of oxidation sites associated with MoO3 reduction. The small peak with a maximum of around 300 °C for HA-1%WO4 can be attributed to the reduction of polytungsten compounds. The peaks at 700, 815 °C as well as the peak which starts at 880 °C are related to WO3 reduction. The activity of PAS HA, MoO4-HA, and WO4-HA in the reaction of selective oxidation of benzyl alcohol to benzaldehyde was investigated. It was shown that the catalysts of the following components have the highest activity: 1%MoO4-HA, 2.5%MoO4-HA, and 7.5%WO4-HA, in the presence of which more than 40% substrate conversion with 100% target product selectivity was achieved. Varying of amount from 0,05 to 5 wt. % of pointed catalyst compositions has allowed to determine the most active composition of catalyst - 2,5%MoO4-HA and its dosage 0,1 wt. % at which maximum substrate conversion of 59% with an output of benzaldehyde 25% was reached. At the same time, idle oxidation of benzyl alcohol with hydrogen peroxide in the absence of the catalyst did not exceed 19% conversion with a benzaldehyde yield of 15%. Oxidation in the presence of pure HA was 25% of alcohol conversion. Diffusion limitations were found to be minimized when a speed of more than 650 rpm was achieved. It has been revealed that the selectivity of benzyl alcohol oxidation is influenced not only by the process temperature but also by the dosage of the catalyst. The optimum temperature of the oxidation process is 30 °С and the dosage is 0,1 wt. %, at which 100 % selectivity on benzaldehyde is obtained, has been determined. The dependence of alcohol conversion on the amount of oxidizer shows an increase in substrate conversion and aldehyde yield, which is associated with an increase in the concentration of generated peroxocomplexes. Increasing the reaction time up to 6 h has no positive effect on the oxidation process. The catalyst is easily regenerated and can be reused within 5 cycles.

Publications

1. Goldberg M.A., Antonova O.S., Donskaya N.O., Fomin A.S., Murzakhanov F.F., Gafurov M.R., Konovalov A.A., Kotyakov A.A., Leonov A.V., Smirnov S.V., Obolkina T.O., Kudryavtsev E.A., Barinov S.M., Komlev V.S. Effects of Various Ripening Media on the Mesoporous Structure and Morphology of Hydroxyapatite Powders Nanomaterials, №3, Т.13, С.418 (year - 2023) https://doi.org/10.3390/nano13030418

2. Khayrutdinova D.R., Goldberg M.A., Antonova O.S., Krokhicheva P.A., Fomin A.S., Obolkina T.O., Konovalov A.A., Akhmedova S.A., Sviridova I.K., Kirsanova V.A., Sergeeva N.S., Barinov S.M., Komlev V.S. Effects of Heat Treatment on Phase Formation in Cytocompatible Sulphate-Containing Tricalcium Phosphate Materials Minerals, Т.13, №2. С.147 (year - 2023) https://doi.org/10.3390/min13020147

3. O.N. Makshakova, M.R. Gafurov, M.A. Goldberg The mutual incorporation of Mg2+ and CO32- into hydroxyapatite: a DFT study Materials, Т.15, №24. С.9046 (year - 2022) https://doi.org/10.3390/ma15249046

4. Donskaya N.O. МОЛИБДАТ ЗАМЕЩЕННЫЙ ГИДРОКСИАПАТИТ ДЛЯ КАТАЛИТИЧЕСКОГО ПРИМЕНЕНИЯ Сборник трудов XIX Российской ежегодной конференции молодых научных сотрудников и аспирантов «Физико химия и технология неорганических материалов» (с международным участием), С. 125 (year - 2022)

5. Donskaya N.O. Сравнение методов получения молибдат-замещенного гидроксиапатита Сборник тезисов докладов Международной научной конференции студентов, аспирантов и молодых учёных «Ломоносов-2023», - (year - 2023)

6. Donskaya N.O., Goldberg M.A., Fomin A.S., Antonova O.S. ПОЛУЧЕНИЕ И СВОЙСТВА МОЛИБДАТ-ЗАМЕЩЕННОГО ГИДРОКСИАПАТИТА ДЛЯ КАТАЛИТИЧЕСКОГО ПРИМЕНЕНИЯ XIII Конференция молодых ученых по общей и неорганической химии: Тезисы докладов конференции, Москва, 2023. – 366 с., С.88 (year - 2023)

7. Donskaya N.O., Goldberg M.A., Fomin A.S., Antonova O.S., Konovalov A.A., Komlev V.S. СИНТЕЗ И СВОЙСТВА ВОЛЬФРАМАТ-ЗАМЕЩЕННОГО ГИДРОКСИАПАТИТА Инновационные материалы и технологии : материалы Междунар. науч.-техн. конф. молодых ученых, г. Минск, 21–23 марта 2023 г. – Минск : БГТУ, 2023. – 405 с., С.264 (year - 2023)

8. Goldberg M.A. МОЛИБДАТ ЗАМЕЩЕННЫЙ ГИДРОКСИАПАТИТ, ПОЛУЧЕННЫЙ ГИДРОТЕРМАЛЬНЫМ СПОСОБОМ Сборник трудов XIX Российской ежегодной конференции молодых научных сотрудников и аспирантов «Физико химия и технология неорганических материалов» (с международным участием), С.120 (year - 2022)

9. Goldberg M.A., Valeev D.V., Donskaya N.O., Fomin A.S., Antonova O.S., Konovalov A.A., Komlev V.S. ГИДРОТЕРМАЛЬНЫЙ СИНТЕЗ МОЛИБДАТ- ЗАМЕЩЕННОГО МЕЗОПОРИСТОГО ГИДРОКСИАПАТИТА XIII Конференция молодых ученых по общей и неорганической химии: Тезисы докладов конференции, Москва, 2023. – 366 с., С.15 (year - 2023)

10. Kucheryaev K.A., Antonova O.S., Goldberg M.A., Konovalov A.A., Fomin A.S. СИНТЕЗ ПОРОШКОВОГО ГИДРОКСИАПАТИТА В СРЕДЕ ПОЛИВИНИЛОВОГО СПИРТА XIII Конференция молодых ученых по общей и неорганической химии: Тезисы докладов конференции, Москва, 2023. – 366 с., С.344 (year - 2023)

11. - Способ получения порошкового однофазного вольфрам-содержащего гидроксиапатита методом химического соосаждения -, 2023112018 (year - )

Annotation of the results obtained in 2023
Studies have been carried out on the synthesis of hydroxyapatite using solid phase or heterophase methods. It was found that using the solid phase method it is not possible to obtain monophase HA without impurities using the equipment available at IMET RAS. A heterophase method with elements of mechanical activation (MCA) was developed for the production of single-phase HA, including dry MCA in a planetary mill and additional MCA in a distilled water environment. Molybdate-containing HA (MoO4-HA) and tungstate-containing HA (WO4-HA) with an introduced anion concentration of 0.5 and 1.0 mol% were obtained using the proven method. According to X-ray phase analysis (XRD), all the materials obtained are single phase and belong to the apatite structure. With the introduction of MoO4 and WO4 and a further increase in the dopant concentration, a decrease in the degree of crystallinity of the apatite phase is observed. The introduction of WO4 contributes to a greater decrease in the degree of crystallinity compared to MoO4.The size of the coherent scattering regions also decreases with increasing dopant concentration, as does the crystal lattice parameter a and the parameter c. The adsorption-desorption isotherms of HA, MoO4-HA and WO4-HA indicate the formation of mesoporous powders. The materials have a specific surface area (Ssp) of at least 70 m2/g. Scanning electron microscopy (SEM) shows that the materials form agglomerates of 0.5 to 5.0 microns. Heat treatment of the powders from 300 to 1200 °C resulted in partial thermal decomposition of the apatite phase with the formation of β-trichalcium phosphate (β-TCP). According to the IR spectroscopy data, vibrations of OH groups are preserved for all samples up to 1200°C, indicating the preservation of the apatite structure. For all samples, the intensity of vibrations of CO3 groups decreases significantly with increasing heat treatment temperature and disappears after 900 ℃. The thermal stability of HA, MoO4-HA and WO4-HA obtained by precipitation from aqueous solutions (PSA) in Phase 1 of the project was investigated. After the calcination at 300 and 600°C, powders retain the structure of either pure HA or a composite of HA and CaMoO4 or CaWO4. At 900°C, the main phase in the powders obtained after 1 day of ageing was β-TCP. Materials aged in mother solutions for 21 days were characterised by the preservation of HA and the formation of α-trichalcium phosphate (α-TCP) at 900 °C. When the powders were calcined at 1200°C, CaO was formed in the materials due to dehydration of the apatite phase and its recrystallisation into α-TCP and β-TCP. Thermogravimetry (TG), differential scanning calorimetry (DSC) with mass spectroscopy were carried out on pure HA, MoO4-HA and WO4-HA materials obtained by precipitation from aqueous solutions (ASP) and MCA. It was found that H2O and CO2 are released when the powders are heated, regardless of the composition and synthesis method of the materials. Pure HA showed no significant weight loss of 1.3% in the temperature range of 300-1050 °C; the main process was the crystallisation of the apatite phase and the removal of adsorbed substances from the highly developed surface of the powders. After 1050 °C, HA starts to lose chemically bound water and shows an increase in the dehydroxylation rate with increasing temperature. From 1200 °C, XRD shows the appearance of CaO impurity and the formation of β-TCP, corresponding to the thermal decomposition of HA. Mass loss increases for MoO4-HA, which is associated with a large volume of pores and substances adsorbed on the surface. Thermal decomposition of the apatite phase starts at lower temperatures. For concentrations up to 2.5 mol% MoO4, the formation of CaMoO4 and β-TCP occurs from 600 ℃; for high molybdate concentrations (5 and 10 mol%), α-TCP and CaMoO4 are formed at temperatures below 1050 ℃.Further gradual mass loss began at 1050 °C and was associated with the removal of carbonate, the transformation of the apatite structure into TCP and CaO, and the release of lattice oxygen from CaMoO4. MoO4-HA shows an earlier onset of the exothermic peak associated with water loss and crystallisation of CaMoO4. The intensity of the DSC peaks increased with increasing MoO42- content. A study of WO4-HA showed a similar behaviour of the materials during the heating. At a WO4 content of 1.0-2.5%, the materials exhibited behaviour close to that of pure HA, as confirmed by the similarity of the DSC and TG curves. The main difference is the appearance of a bend in the TG curves at 830-850 °C, which is associated with the almost complete removal of structural carbonate according to the IR data. In the presence of CaWO4 in materials containing 5.0 and 7.5 mol% WO42-, the weight loss was increased and a corresponding peak appeared in the DSC curves at 522 °C. This process is related to the removal of oxygen from the CaWO4 lattice. The weight loss also increases after 1200 °C due to the decomposition of HA. A study of the thermal stability of materials obtained by MCA showed the similarity of the nature of the mass loss and DSC curves to materials containing the lowest concentrations of dopants obtained by OVR. This is due to the achievement of similar phase and texture characteristics of the powders. Magnetic resonance spectroscopy methods in electron spin echo detection mode for tungstate anions, when measuring the transverse relaxation time, revealed the predominant mechanism of spin-spin interaction T2 between equivalent impurity centres. An increase in the spin-lattice relaxation time T1 with increasing WO4 concentration further confirms the low degree of deformation of the HA structure (i.e. high crystallinity). Measurements of the relaxation rate of HA samples with molybdate anions, carried out over a wide temperature range (from 297 K to 10 K), made it possible to identify and delimit three main relaxation regions, establishing for each interval its own mechanisms of energy transfer (electronic magnetisation) from the spin system to the hydroxyapatite crystal lattice. The main mechanisms of longitudinal relaxation include "direct" and Raman two-phonon processes. The impregnation of HA, MoO4-HA (2.5 mol%) and WO4-HA (7.5 mol%) obtained by OVR with iron ions was carried out. As a result of impregnation with a Fe(NO3)3 solution, the phase composition of the powders does not change; the monophase structure of apatite (HA and MoO4-HA) or a composite material of HA and CaWO4 (WO4-HA) is preserved. A low concentration of applied iron (1 and 5 wt%) does not lead to the formation of Fe2O3 and a change in the parameters of the crystalline cell of the apatite phase. According to IR spectroscopy, the vibrations of the PO4 groups remain practically unchanged; the intensity of the vibrations of the OH groups slightly decreases in the case of MoO4-HA and WO4-HA and increases in the case of pure HA. This indicates different changes in the structure of HA during impregnation: for MoO4-HA and WO4-HA the process of improvement of the structure of apatite occurs, which is expressed by an increase in the intensity of OH vibrations, while for pure HA the opposite process is observed. For all impregnated powders there was a tendency for S to decrease as the amount of iron on the surface increased from over 71 to 61 m2/g. The total pore volume decreased from 0.53 to 0.19 cm3/g and the average diameter increased. According to SEM data, the impregnated powders consist of agglomerates larger than 10 microns. According to transmission electron microscopy, the particle size ranged from 13 to 40 nm and the morphology was predominantly lamellar, irrespective of the powder composition. The particle length to width ratio decreased from 2:1 for HA to ~1.4:1 for 7.5WO4HA. According to energy dispersive mapping mode analysis data, iron particles are uniformly distributed on a matrix of Ca, P, O as well as Mo and W in substituted iron impregnated materials. Electron diffraction data show only HA and CaMoO4 or CaWO4 phases in the materials. The activity of iron-impregnated mesoporous powders based on HA, WO4-HA and MoO4-HA as catalysts for the peroxide oxidation of benzyl alcohol to benzaldehyde was investigated. It was found that the impregnation of iron to the surface of substituted HAs negatively affects the efficiency of benzyl alcohol oxidation compared to the original molybdate-substituted sample. A study of the kinetics of decomposition of H2O2 as an oxidant showed an intense decomposition of H2O2 in the presence of synthesised iron-impregnated samples, apparently due to the presence of iron particles on the surface of HA. 5Fe/MoO4-HA was found to have the highest activity, in the presence of which 36% conversion of benzyl alcohol and 70% selectivity for the desired product, benzaldehyde, are achieved. Optimal conditions for the oxidation of benzyl alcohol to benzaldehyde in the presence of 5Fe/MoO4-HA were selected: temperature 80°C, time 30 min, amount of catalytic additive 1 wt%, molar ratio H2O2:benzyl alcohol = 10:1.

Publications

1. M.A. Goldberg, N.O. Donskaya, D.V. Valeev, A.S. Fomin, F.F. Murzakhanov, A.V. Leonov, A.A. Konovalov, O.S. Antonova, A.A. Shoppert, E.A. Kudryavtsev, M.R. Gafurov, S.M. Barinov, V.S. Komlev Mesoporous molybdate-substituted hydroxyapatite nanopowders obtained via a hydrothermal route Ceramics International, Н.50, Т.10, С.17404-17418 (year - 2024) https://doi.org/10.1016/j.ceramint.2024.02.229

2. M. Goldberg , D. Valeev, N. Donskaya, A. Fomin, O. Antonova, A. Konovalov, V. Komlev Mesoporous hydroxyapatite powders containing molybdate anions obtained by the hydrothermal method as a promising heterogeneous catalyst BOOK OF ABSTRACTS ELEVENTH INTERNATIONAL CONFERENCE ON RADIATION, NATURAL SCIENCES, MEDICINE, ENGINEERING, TECHNOLOGY AND ECOLOGY (RAD 2023) 19–23.06.2023 | HERCEG NOVI, BOOK OF ABSTRACTS ELEVENTH INTERNATIONAL CONFERENCE ON RADIATION, NATURAL SCIENCES, MEDICINE, ENGINEERING, TECHNOLOGY AND ECOLOGY (RAD 2023) 19–23.06.2023 | HERCEG NOVI, p.53 (year - 2023) https://doi.org/10.21175/rad.abstr.book.2023.13.1

3. M.A. Goldberg, N.O. Donskaya, A.S. Fomin, O.S. Antonova, A.A. Konovalov, E.A. Eseva, P.D. Polikarpova, A.V. Akopyan, V.S. Komlev The Oxidation of Benzyl Alcohol in the Presence of Mesoporous Molybdate-Contained Hydroxyapatite Powders Book of oral abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, p.39, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE (year - 2023)

4. N.O. Donskaya, M.A. Goldberg, A.S. Fomin, O.S. Antonova, A.A. Konovalov, E.A. Eseva, P.D. Polikarpova, A.V. Akopyan, V.S. Komlev. The Oxidation of Benzyl Alcohol in the Presence of Mesoporous Tungsten-Contained Hydroxyapatite Powders Book of oral abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, Book of oral abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, p.50 (year - 2023)

5. O.S. Antonova, K.A. Kucheryaev, M.A. Goldberg, A.V. Leonov, A.S. Fomin Preparation of Hydroxyapatite Powders by The Heterophase Method with Elements of Mechanochemical Activation Book of poster abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, p.28, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE (year - 2023)

6. К.А. Кучеряев, О.С. Антонова, М.А. Гольдберг, А.А. Коновалов, А.С. Фомин Synthesis of Powder Hydroxyapatite in Polyvinylpyrrolidone Medium Book of poster abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, Book of poster abstract, 6th International Conference on Physical Chemistry & Functional Materials 13-14 June 2023 Firat University ELAZIĞ / TÜRKİYE, p.27 (year - 2023)

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