High purity β-Bi2O3 preparation by thermal decomposition of tartrates published by Ural Federal University eISSN 2411-1414 chimicatechnoacta.ru ARTICLE 2023, vol. 10(3), No. 202310304 DOI: 10.15826/chimtech.2023.10.3.04 1 of 7 High purity β-Bi2O3 preparation by thermal decomposition of tartrates Evgeniya V. Timakova ab * , Tatiana E. Timakova ab , Liubov I. Afonina ab a: Department of Chemistry and Chemical Technology, Novosibirsk State Technical University, Novosibirsk 630073, Russia b: Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the RAS, Novosibirsk 630090, Russia * Corresponding author: timakova@solid.nsc.ru This paper belongs to the RKFM'23 Special Issue: https://chem.conf.nstu.ru/. Guest Editors: Prof. N. Uvarov and Prof. E. Aubakirov. Abstract The processes of oxidative thermolysis of bismuth(III) DL-tartrate BiC4H3O6 obtained by the interaction of high-purity basic bismuth(III) ni- trates [Bi6O4(OH)4](NO3)6·H2O and [Bi6O5(OH)3](NO3)5·3H2O with DL- tartaric acid solution have been investigated. The products of precipitation have been studied by methods of X-ray diffraction and thermal analysis, IR and Raman spectroscopy and chemical analysis. The staging of thermal transformation processes has been determined. Morphological studies and grain size analysis of initial precursors and final products of their thermal transformations have been carried out. The possibility of obtaining fine crystalline powders of tetragonal bismuth(III) oxide modification β-Bi2O3 by oxidative thermolysis of DL-BiC4H3O6 has been shown. Keywords basic bismuth(III) nitrate DL-tartaric acid X-ray diffraction thermal transformations β-bismuth(III) oxide fine-crystal powders Received: 28.06.23 Revised: 28.07.23 Accepted: 31.07.23 Available online: 03.08.23 Key finding ● Fine crystalline powders of high purity tetragonal bismuth(III) oxide β-Bi2O3 were obtained from the decomposition of the precursor DL-BiC4H3O6 synthesized from basic bismuth(III) nitrates. © 2023, the Authors. This article is published in open access under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). 1. Introduction Tartrates are widely used as precursors for the prepara- tion of fine crystalline and nanodispersed powders of met- als, their oxides [1–4] and mixed oxide materials [5–8] by thermolysis in inert and oxidizing atmospheres. Bismuth tartrate precursors are also used to produce bismuth ox- ides [9] and bismuth-based materials [10, 11]. We have investigated the thermal decomposition of bismuth tar- trate [Bi(NO3)(C4H4O6)]·3H2O obtained by adding a bis- muth solution in nitric acid to a solution of L(+)-tartaric acid [12]. It has been shown that thermolysis of [Bi(NO3)(C4H4O6)]·3H2O in air atmosphere for 6 h at 300 °C with preliminary holding at lower temperatures produces a mixture of tetragonal bismuth(III) oxide and bismuth(III) oxocarbonate β-Bi2O3/(BiO)2CO3. With in- creasing temperature, a β→α phase transition occurs and the final decomposition product is the monocline modifi- cation, α-Bi2O3. Monophase fine crystalline powders of tetragonal bismuth oxide β-Bi2O3 were obtained by oxida- tive thermolysis of bismuth(III) tartrate BiC4H3O6·H2O for 6 h at 280 °C. BiC4H3O6·H2O is an X-ray amorphous com- pound obtained by multiple washing of [Bi(NO3)(C4H4O6)]·3H2O with water. Direct precipitation of BiC4H3O6·H2O from nitric acid solutions does not pro- vide effective purification from nitrate ions, and obtaining this compound by multiple washings with water [Bi(NO3)(C4H4O6)]·3H2O is a lengthy process. Therefore, it is of interest to consider the process of obtaining BiC4H3O6·H2O by treating solid bismuth precursors with tartaric acid solution. It is reasonable to consider basic bismuth(III) nitrates as precursors for obtaining bismuth tartrate. It has been shown [13] that bismuth precipitation in the form of basic nitrates, during the hydrolytic processing of technological nitric acid solutions prepared from metallic bismuth of Bi1 grade and containing impurities of accompanying metals, allows high values of bismuth purification coefficients from impurities to be achieved. Hydrolysis at elevated temperatures not lower than 60 °C allows obtaining easily filterable precipitate of the composition [Bi6O4(OH)4](NO3)6·H2O (further basic bismuth(III) ni- trate) and separating it effectively from the mother liquor containing impurity metal ions. Washing this compound http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2023.10.3.04 mailto:timakova@solid.nsc.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0002-7015-9231 https://orcid.org/0000-0003-0564-8992 https://orcid.org/0000-0002-5606-3022 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2023.10.3.04&domain=pdf&date_stamp=2023-08-03 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 2 of 7 DOI: 10.15826/chimtech.2023.10.3.04 with water results in hydrolytic decomposition to form the [Bi6O5(OH)3](NO3)5·3H2O. As a result of recrystallization, the final product is effectively purified from metal impuri- ties captured in the volume of microcrystals during the precipitation of the primary hydrolysis product. The use of [Bi6O4(OH)4](NO3)6·H2O and [Bi6O5(OH)3](NO3)5·3H2O as precursors for further treatment with carboxylic acids or alkaline reagents makes this process widely applicable for the synthesis of high-purity bismuth compounds for engi- neering and medicine. The aim of this work was the synthesis of high purity bismuth(III) tartrate by the reaction "basic bismuth(III) nitrates – tartaric acid solution" followed by the produc- tion of tetragonal β-Bi2O3. 2. Experimental All reagents (acids, bases and salts) in this work were of analytical grade and were used without further purification. Metallic bismuth Bi1 (Kazzinc, GOST (State Standard) 10928–90) was used. The metal contents were (wt.%): 99.1 bismuth, 0.71 lead, 1.0·10–3 zinc, 1.0·10–3 antimony, 3.3·10–3 copper, 1.0·10–1 silver, 2.0·10–4 arsenic, 1.0·10–3 iron and 1.0·10–4 tellurium. Bismuth stock solution in nitric acid (420 g∙l–1 bismuth and 100 g·l–1 free HNO3) was prepared by dissolving technical bismuth oxide, obtained according to ref. [14], in nitric acid with the concentration of 7 mol·l–1. The hydrolytic precipita- tion of bismuth from nitric acid solution, as well as investiga- tion of "solid precursor – carboxylic acid solution" processes were carried out in fluoroplastic or glass vessels equipped with stirrers and thermostatically controlled in water baths. Hydrate tetrahydroxo-tetraoxo-hexabismuth(III) hex- anitrate of [Bi6O4(OH)4](NO3)6·H2O was prepared by add- ing 50 ml of distilled water heated to 55–60 °C to 50 ml of bismuth nitrate solution with stirring, then 36 ml of am- monium carbonate solution with a concentration of 2.5 mol·l–1 to pH = 1. The mixture was stirred for 30 min and allowed to stand for 1 h. The mother liquor was sepa- rated from the sediment by decantation, the sediment was washed with 150 ml of nitric acid solution with a concen- tration of 0.1 mol·l–1 for 30 min at 60 °C. Trihydrate trihy- droxo-pentaoxo-hexabismuth(III) pentanitrate of the com- position [Bi6O5(OH)3](NO3)5·3H2O was obtained by wash- ing the precipitate twice with 150 ml of distilled water for 30 min at 60 °C. For the synthesis of bismuth(III) tartrate 10 g of fresh- ly prepared basic bismuth(III) nitrates [Bi6O4(OH)4](NO3)6·H2O or [Bi6O5(OH)3](NO3)5·3H2O was stirred for 10 min in 90 ml distilled water to the resulting mixture was added the required amount of tartaric acid C4H6O6. The molar ratio of tartrate ions to bismuth was 1.1. The resulting mixture was stirred for 1–2 h at 70 °C. The resulting precipitate was filtered off, washed 2 times with distilled water at the synthesis temperature and dried in air. Bismuth(III) oxocarbonate of the composition (BiO)2CO3 was obtained by treating [Bi6O4(OH)4](NO3)6·H2O or [Bi6O5(OH)3](NO3)5·3H2O with ammonium carbonate solution at pH ≥ 8 and 25 °C [13]. Chemical determination of macro quantities of Bi(III) in solutions was carried out by titration with complexon III solution in the presence of xylenol orange indicator. Micro quantities of Bi(III) were determined by photocolor- imetric method using potassium iodide. Carbon, nitrogen and hydrogen contents in the obtained samples were de- termined by modified Pregle method with gravimetric termination. The phase compositions of the samples were analyzed using X-ray diffraction technique (XRD) on a diffractome- ter (Bruker D8 Advance, Germany) using Cu Kα radiation (λ = 1.5418 Å). X-ray diffraction data were collected in scanning mode at a scanning speed of 0.5°·min–1 in the range of 4° < 2θ < 70°. Phase analysis was performed us- ing the ICDD PDF-4 database (2011). The IR absorption spectra in the range 400–4000 cm–1 were recorded with a IR-Fourier spectrometer Tensor 27 (Bruker, Germany). The samples were prepared as tablets with calcined KBr. Raman spectra were taken on a T64000 spectrometer (Horiba Jobin Yvon, Japan) with an Ar+ laser (wavelength 514.5 nm, Z(XY)-Z geometry). Microstructure of the samples was studied by scanning electron microscopy (SEM) using a Hitachi TM 1000 Scanning Electron Micro- scope. Thermal analysis of the samples was carried out on a synchronous thermoanalytical complex STA 449 F1 Jupiter (Netzsch) dynamically under heating in an Ar/O2 atmos- phere (80/20; O2 10 ml·min−1; Ar 40 ml∙min−1). Samples weighing 20–50 mg were placed in crucibles of Pt – 10% Rh alloy and heated at a rate of 10 deg·min–1 to 350– 500 °C. The mass spectra of the gaseous products formed in the course of the heat treatment were recorded in the multi-ion detection mode at m/z of 18 and 44 with a QMS 403D quadrupole mass spectrometer (Netzsch). Particle size analysis of powders was performed using a la- ser particle size analyzer Microsizer 201A (VA Instalt, Russia). 3. Results and Discussion 3.1. Synthesis and characterization of bismuth DL-tartrate According to the XRD analysis, the treatment of freshly precipitated [Bi6O4(OH)4](NO3)6·H2O (Figure 1, curve 1) with a solution of L(+)-tartaric acid at a molar ratio of n(C4H4O62–/Bi3+) = 1.1 at 70 °C within 1 h leads to the for- mation of a mixture of [Bi6O4(OH)4](NO3)6·H2O [13] and [Bi6O5(OH)3](NO3)5∙3H2O (ICDD 000-48-0575) (Figure 1, curve 2). Increasing the exposure time to 2 h gives [Bi6O5(OH)3](NO3)5∙3H2O (Figure 1, curve 3). When [Bi6O5(OH)3](NO3)5∙3H2O is treated with L(+)-tartaric acid solution, the initial precursor remains as a synthesis product. Thus, in the system "basic bismuth(III) nitrates - https://doi.org/10.15826/chimtech.2023.10.3.04 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 3 of 7 DOI: 10.15826/chimtech.2023.10.3.04 solution of L(+)-tartaric acid" under the chosen condi- tions, bismuth tartrate is not formed. Considering the possibility of using the racemic form of tartaric acid for the synthesis of tartrate precursors [15–17], we chose DL-tartaric acid to obtain bismuth tartrate. According to the XRD data, the treatment of basic bis- muth(III) nitrates with DL-tartaric acid solution at n = 1.1 and temperature 70 °C for 1–2 h leads to the formation of bismuth tartrate of a BiC4H3O6 composition (Figure 1, curve 4), which is confirmed by the data of chemical anal- ysis, content in %: Bi – 60.1 (theor. 58.7); C – 12.7 (13.5) and H – 0.75 (0.84). DL-BiC4H3O6 has a low degree of crys- tallinity: an intense reflex is observed on the diffracto- gram of the compound at d/n = 6.57 Å (2θ = 13.46°), other reflexes are broadened and have low intensity. The analysis of IR and Raman spectra of DL-tartaric acid and its bismuth salt allowed us to conclude the form of the presence of tartaric acid residues in DL-BiC4H3O6 and the way of their connection with metal atoms. The assignment of vibrational bands in the IR and Raman spectra of DL- BiC4H3O6 was carried out in comparison with the spectra of DL-tartaric acid based on literature data [18, 19]. Tartaric acid can form complex compounds with metals due to carboxylic and alcohol (oxy) groups, so it is neces- sary to analyze the characteristic vibrational bands of these functional groups. Calculations of the vibrational spectrum of tartaric acid [18] showed that only the stretching vibrations of OH, CH, and C=O groups are spe- cific in shape and wavenumbers, while the other vibra- tions are strongly mixed. Therefore, let us consider in de- tail the changes observed in the spectrum of the salt as compared to the spectrum of the acid. In the spectra of DL-tartaric acid (Figures 2 and 3, curve 1) the presence of OH-groups involved in the for- mation of intermolecular hydrogen bonding is indicated by a broad band in the range of 3650–3280 cm–1, divided into two components at 3413 (IR), 3408 (Raman) and 3365 (IR), 3354 (Raman), assigned to the stretching vibrations of ν(O–H) alcohol and carboxyl groups, respectively [18]. Stretching vibrations of the C=O bond of dimeric carboxyl groups linked by intermolecular hydrogen bonds corre- spond to a strong band at 1743 (IR), 1690 (Raman) cm–1 and those involved in intramolecular hydrogen bonds at 1635 (IR), 1653 (Raman) cm–1. These bands are not record- ed in the spectrum of bismuth salt (Figures 2 and 3, curve 2). In the above spectra bands related to asymmetric νas(COO–) and symmetric νs(COO–) stretching vibrations of ionized COO– groups at (cm–1): 1595, 1555 (IR ); 1583, 1558 (Raman) and 1404, 1362 (IR); 1404, 1363 (Raman) respectively are present, which denotes substitution of protons in the carboxyl groups of carboxylic acid by Bi- containing cation. Presence of several asymmetric and symmetric bands of carboxylate ions indicates different structural functions performed by them. The broad band in the range of 3650-3300 cm–1 in the IR spectrum refers to alcohol groups not substituted by bismuth cation and involved in intermolecular hydrogen bonds. In the range of 1460-1200 cm–1 several bands of in- plane bending vibration β(OH) overlapping with in-plane bending β(C–H) are observed in acid spectra (Figures 2 and 3, curve 1): the medium and strong bands 1455, 1401 (IR) and 1457, 1391 (Raman) refer to in-plane bending vi- bration of alcohol groups, and weak bands 1327 (IR), 1330 (Raman) to carboxyl groups [18]. In the spectra of the acid (Figures 2 and 3, curve 1), the bands of stretching vibrations ν(C–H) at 2971, 2912 (IR) and 2972, 2923 (Raman) cm–1 are observed. In the spectra of the salt (Figures 2 and 3, curve 2) these vibrations correspond to bands at 1289, 1258 (IR) and 1283, 1263 (Raman) cm–1. In the IR spectrum of the acid a series of strong and medium bands belonging to in-plane bending vibrations of β(C–C–H) at 1291, 1257, 1238, 1220 cm–1 (Figure 2, curve 1) are observed. In the Raman spectrum these bands are ob- served at wavenumbers of 1263, 1245, 1219 cm–1 (Figure 3, curve 1), these vibrations also overlap with in-plane bend- ing vibrations of hydroxyl groups [18]. When the protons of OH-groups are substituted by bismuth cation, the dis- appearance of several bands, decrease of intensity and broadening of bands registered at 1289, 1258 (IR) and 1283, 1263 (Raman) cm–1 are observed in the spectra of salt (Figures 2 and 3, curve 2). Figure 1 X-ray powder diffraction patterns of the initial [Bi6O4(OH)4](NO3)6·H2O (1) and treated by L(+)- (2, 3) and DL- (4) C4H6O6. Synthesis conditions: 70 °C, n = 1.1, 1 h (2, 4), 2 h (3). Figure 2 IR spectra of DL-C4H6O6 (1) and DL-BiC4H3O6 (2). https://doi.org/10.15826/chimtech.2023.10.3.04 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 4 of 7 DOI: 10.15826/chimtech.2023.10.3.04 In the acid spectrum strong bands at 1142 (IR) and 1151 (Raman) cm–1 related to the stretching vibrations of ν(C– O) carboxyl groups are observed. For alcohol groups, these vibrations appear as a strong band in the IR spectrum at 1095 cm–1 and a weak band in the Raman spectrum at 1089 cm–1 [18]. At replacement of protons of carboxylic and alcohol groups by bismuth cation, these bands in bis- muth salt spectra (Figures 2 and 3, curve 2) shift to the region of lower wavenumbers and additionally the third band appears, which is connected with C–O–Bi bond for- mation and participation of oxygen of non-dissociated al- cohol group in bismuth cation coordination. In the region of 1150-850 cm–1, the stretching vibra- tions ν(C–C) are recorded as bands of medium intensity at 984, 918, 889, 868, 831 (IR) and 991, 900, 889, 873, 833 (Raman) cm–1 (Figures 2 and 3, curve 1). These bands are mixed with stretching and deformation vibrations of C–O bonds [18]. Therefore, changes are also observed in this region in the salt spectrum, consisting in a decrease in the number of vibration bands and a change in their intensity. Thus, in the IR spectrum of salt (Figure 2, curve 2) bands are observed: weak at 1003 cm–1 and medium at 925 cm–1; in the Raman spectra (Figure 3, curve 2) these vibrations appear as medium and weak bands at 1006 and 925 cm–1 respectively. Оut-of-plane bending vibrations δ(C–C=O) include bands at 831–482 cm–1 in the spectra of acid (Fig- ures 2 and 3, curve 1) [18]. These bands are not registered in the salt spectra. The strong band at 818 cm–1 (Figure 2, curve 2) in the IR spectrum of salt and weak bands at 827, 817 cm–1 in the Raman spectrum (Figure 3, curve 2) are related to scissor vibrations of the carboxylate ion δs(COO–) [19]. The presence of two δs(COO–) bands in the Raman spectrum confirms the different structural functions of carboxylate ions. A strong band in the IR spectrum of the salt at 719 cm–1 refers to the torsional vibrations of δτ(COO–) [20]. Stretching vibrations ν(Bi–O) include an intense band at 486 cm–1 with the shoulder at 476 cm–1 [21] in the infrared spectrum of the salt (Figure 2, curve 2). These vibrations are recorded in the Raman spectrum (Figure 3, curve 2) as a strong band with two maxima at 483 and 475 cm–1, which indicate the unequal formation of metal-oxygen bonds. The absence of in-plane bending vi- brations β(OH) bands of water molecules at 1630– 1600 cm–1 indicates the formation of anhydrous salt [22]. Thus, the proposed composition of BiC4H3O6 for bis- muth DL-tartrate is in agreement with the physicochemi- cal studies carried out and also confirmed by IR and Ra- man spectroscopy. 3.2. Thermal analysis of bismuth DL-tartrate Thermal analysis data in Ar/O2 atmosphere also confirm the composition of the synthesized compound (Figure 4): it is stable up to 220 °C and does not contain crystalliza- tion water. This fact indicates the possibility of drying DL- BiC4H3O6 samples at a temperature of 100–150 °С during their industrial preparation and the possibility of long- term storage at room temperature. Further thermolysis of DL-BiC4H3O6 samples proceeds with exothermic effect in the temperature range 230–280 °C. Its maximum observed around 275 °C is related to tartrate ions decomposi- tion/oxidation; according to mass spectrometry, it is ac- companied by water and carbon dioxide removal. The minimum on the TG curve at 265 °C indicates the formation of metallic bismuth as a result of its reduction by carbon of tartrate ions, a further increase in mass is associated with the oxidation of metallic bismuth to oxide. In parallel, the decomposition of bismuth(III) oxocar- bonate resulting from the thermolysis of bismuth tartrate also proceeds. According to mass spectrometry, these pro- cesses are accompanied by the release of carbon dioxide. Thus, the process of oxidative thermolysis of DL-BiC4H3O6 is rather complicated and the effects on the DSC curve at temperature ≥345 °C corresponding to the phase transi- tion of tetragonal modification β-Bi2O3 into monocline α- Bi2O3 [23], indicate only a mixture of α- and β-Bi2O3 as a result of non-isothermal linear heating of the sample. The total mass loss of salt decomposition to Bi2O3 is 34.5% and agrees with the theoretical value (34.55%). Figure 3 Raman spectra of DL-C4H6O6 (1) and DL-BiC4H3O6 (2). Figure 4 The TG-DSC curves of DL-BiC4H3O6 and MS signals of H2O and CO2. https://doi.org/10.15826/chimtech.2023.10.3.04 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 5 of 7 DOI: 10.15826/chimtech.2023.10.3.04 According to XRD data (Figure 5, curve 1), the samples DL-BiC4H3O6 aged in air at 280 °C for 6 h represent a mix- ture of α-, β-Bi2O3 and metallic bismuth. A decrease of an- nealing temperature to 240–270 °C also leads to the for- mation of the specified mixture of substances. The DL- BiC4H3O6 samples were successively keeping at tempera- tures of 200, 220 and 240 °C. According to XRD data, holding the sample at 200 °C for 3 h does not lead to sig- nificant changes. Its diffractogram (Figure 5, curve 2) co- incides with the initial one for DL-BiC4H3O6 (Figure 1, curve 4). Further heating of sample at 220 °C for 3–6 h leads to its amorphization (Figure 5, curve 3). In the infrared spectrum of this sample, the vibrational bands of DL-BiC4H3O6 (Figure 6, curves 1 and 2) are not observed. At the same time, the bands typical for bis- muth(III) oxocarbonate of (BiO)2CO3 composition appear (Figure 6, curve 3). Thus, we can assume the formation of X-ray amorphous (BiO)2CO3 during keeping of DL- BiC4H3O6 at 220 °C. This assumption is confirmed by fur- ther exposure of the sample at 240 °C. On the diffracto- gram of this sample (Figure 5, curve 4) the (BiO)2CO3 (ICDD 000-41-1488) reflexes are observed at the back- ground of X-ray amorphous halo. On the basis of the stud- ies carried out, the following scheme can be proposed for obtaining β-Bi2O3. The samples of DL-BiC4H3O6 are succes- sively kept at 220 °C for 3–6 h and then at 280 °C for 3–6 h. As a result, the single-phase samples of β-Bi2O3 are obtained (ICDD 010-77-5341, Figure 5, curve 5). According to SEM data, [Bi6O4(OH)4](NO3)6·H2O pre- cipitated from nitric acid solutions by ammonium car- bonate is well formed short prismatic crystals with the largest single crystal size in the basic plane of 3–10 µm and 1–3 µm thick (Figure 7a). As a result of washing [Bi6O4(OH)4](NO3)6·H2O with water, the obtained [Bi6O5(OH)3](NO3)5·3H2O, is an elon- gated prismatic crystal with a length in the basic plane of 4–20 µm, width of 2–8 µm and thickness of 1–3 µm (Figure 7b). In the subsequent step of the treatment of freshly prepared basic bismuth(III) nitrates with DL-tartaric acid solution, the resulting DL-BiC4H3O6 samples are aggre- gates of 5–30 µm, consisting of needle-like particles of 1-3 µm length and 0.1–0.3 µm thickness, both synthesized from [Bi6O4(OH)4](NO3)6·H2O (Figure 7c) and from [Bi6O5(OH)3](NO3)5·3H2O (Figure 7d). The β-Bi2O3 samples obtained by oxidative thermolysis inherit the morphology of DL-BiC4H3O6, also presenting aggregates of different sizes (Figure 7e, f). For the synthesized powders DL-BiC4H3O6 and the β- Bi2O3 samples obtained from them, their particle size dis- tribution was analyzed, the results of which are shown in Figure 8. Table 1 shows the values of average particle/aggregate size (DI), the values of their standard deviations (σ), the degree of asymmetry of particle distribution (Sk) calculat- ed by "geometric" method [24] and the value of 50 wt.% particle/aggregate size (D50). Figure 5 X-ray powder diffraction patterns of DL-BiC4H3O6 sam- ples aged at different temperatures. Exposure temperature: 280 (1), 200 (2), 220 (3), 240 (4), 220 and then 280 °C (5). Cur- ing times: 6 h (1), 3 h (2–4), 6 h (5). Figure 6 IR spectra of DL-BiC4H3O6 (1), DL-BiC4H3O6 incubated at 220 °C for 6 h (2) and (BiO)2CO3 (3). Figure 7 SEM images of the initial [Bi6O4(OH)4](NO3)6·H2O (a), [Bi6O5(OH)3](NO3)5·3H2O (b); samples DL-BiC4H3O6 (c, d) synthesized from (a) and (b); samples β-Bi2O3 (e, f) obtained from (c) and (d). https://doi.org/10.15826/chimtech.2023.10.3.04 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 6 of 7 DOI: 10.15826/chimtech.2023.10.3.04 Figure 8 Grain size frequency histograms of DL-BiC4H3O6 (1, 2) synthesized from [Bi6O4(OH)4](NO3)6∙H2O (1) and [Bi6O5(OH)3](NO3)5∙3H2O (2) and β-Bi2O3 (3, 4) obtained from (1) and (2) samples. Table 1 Results of grain size analysis for samples of DL-BiC4H3O6 and β-Bi2O3. Samples D50, µm DI, µm σ, µm Sk Precursor 1: DL-BiC4H3O6 from Bi6O4(OH)4](NO3)6·H2O 12.0 10.67 2.24 –0.50 β-Bi2O3 from precursor 1 9.80 8.98 2.08 –0.41 Precursor 2: DL-BiC4H3O6 from Bi6O5(OH)3](NO3)5∙3H2O 7.78 5.93 2.62 –0.48 β-Bi2O3 from precursor 2 6.87 5.93 2.42 –0.41 The obtained values of the standard deviation σ are in a range of 2.00–4.00 μm, indicating a wide particle size distribution [24]. Assessment of the symmetry of the dis- tribution curves by the degree of asymmetry (|Sk|<0.5) shows that the asymmetry is insignificant for all samples [24]. The analysis of the obtained results shows that the particle size distribution in the studied samples is close to normal. This suggests that the processes of DL-BiC4H3O6 synthesis from basic bismuth(III) nitrates occur in condi- tions close to equilibrium and are accompanied by recrys- tallization processes. The results of grain size analysis of DL-BiC4H3O6 and β- Bi2O3 powders are in agreement with the electron micros- copy data and indicate smaller particle/aggregate sizes in samples synthesized using [Bi6O5(OH)3](NO3)5·3H2O. 4. Limitations This work continues our previous research on the prepara- tion of bismuth compounds with optically active and inac- tive isomers of oxyacids [25]. This direction in bismuth chemistry is poorly studied. At the same time, it opens up the possibility of using new synthesized compounds in engineering and medicine. 5. Conclusions Treatment of high-purity basic bismuth(III) nitrates with DL-tartaric acid solution at molar ratio of tartrate ions to bismuth equal to 1.1 and temperature of 70 °C resulted in bismuth(III) tartrate of BiC4H3O6 composition. It has been shown that the process of oxidative thermolysis of DL-BiC4H3O6 includes a stage of formation of bis- muth(III) oxocarbonate (BiO)2CO3 and metallic bismuth. After consecutive incubation of DL-BiC4H3O6 samples in air atmosphere at 220 °C for 3–6 h and then at 280 °C for 3–6 h, fine crystalline powders of tetragonal β-Bi2O3, in- heriting the morphology of the initial tartrates, were obtained. ● Supplementary materials No supplementary materials are available. ● Funding This work was performed in accordance with the thematic plans of Novosibirsk State Technical University (TP- KhKhT-1_23) and Institute of Solid State Chemistry and Mechanochemistry, Siberian Branch of the RAS (121032500064-8). ● Acknowledgments The authors would like to express their gratitude to the Core Facilities VTAN NSU for the equipment provided for the registration of Raman spectra and to the Chemical Re- search Centre of N.D. Zelinsky Institute of Organic Chem- istry SB RAS for the spectral (IR) measurements. ● Author contributions Conceptualization: E.V.T. Data curation: L.I.A., E.V.T. Formal Analysis: T.E.T., L.I.A. Funding acquisition: E.V.T., L.I.A. Investigation: T.E.T., E.V.T., L.I.A. Methodology: E.V.T., L.I.A. Project administration: E.V.T. Resources: E.V.T., L.I.A. Software: E.V.T., T.E.T. Supervision: E.V.T., L.I.A. Validation: L.I.A., T.E.T. Visualization: E.V.T., L.I.A. Writing – original draft: E.V.T. Writing – review & editing: E.V.T., L.I.A. ● Conflict of interest The authors declare no conflict of interest. https://doi.org/10.15826/chimtech.2023.10.3.04 Chimica Techno Acta 2023, vol. 10(3), No. 202310304 ARTICLE 7 of 7 DOI: 10.15826/chimtech.2023.10.3.04 ● Additional information Author IDs: Evgeniya V. Timakova, Scopus ID 25032239000; Tatiana E. Timakova, Scopus ID 57929100400; Liubov I. Afonina, Scopus ID 7006080705. Websites: Novosibirsk State Technical University, https://www.nstu.ru/; Institute of Solid State Chemistry and Mechanochemis- try, http://www.solid.nsc.ru/. References 1. Amrani MA, Alrafai HA, Al-nami SY, Labhasetwar NK, Qasem A. 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