Development of nanostructured catalysts for catalytic oxidative water purification from organic impurities, including phenolic compounds published by Ural Federal University eISSN 2411-1414 chimicatechnoacta.ru ARTICLE 2023, vol. 10(3), No. 202310309 DOI: 10.15826/chimtech.2023.10.3.09 1 of 8 Development of nanostructured catalysts for catalytic oxidative water purification from organic impurities, including phenolic compounds Larissa R. Sassykova a * , Binara T. Dossumova a , Madina S. Ilmuratova a , Tatyana V. Shakiyeva a , Bedelzhan B. Baizhomartov a , Albina R. Sassykova b , Zhanar M. Zhaxibayeva c , Tleutai S. Abildin a a: Al-Farabi Kazakh National University, Almaty 050040 Kazakhstan b: Almaty Management College, Almaty 050000, Kazakhstan c: Abai Kazakh National Pedagogical University, Almaty 050010, Kazakhstan * Corresponding author: larissa.rav@mail.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 purpose of this work was to create magnetic nanocatalysts that could be used for the oxidation of organic water pollutants – phenol and its de- rivatives – and to determine the physicochemical characteristics of the catalysts. The development of such active nanocomposite catalysts would solve the environmental problem in the Republic of Kazakhstan in the field of wastewater treatment from organic impurities, including phe- nols, and would also contribute to the subsequent creation of domestic production of oxygen-containing compounds, since almost the entire spectrum of oxygen-containing compounds for various industries is im- ported into the Republic. Nanosized magnetic composites based on Fe and Co were obtained by chemical deposition, in some cases, using pol- yethyleneimine and polyvinylpyrrolidone. It was shown that the inter- action between nanoparticles and the polymer takes place in the case of a CoFe2O4 catalyst stabilized with polyvinylpyrrolidone or polyethylene- imine, which may indicate the efficient formation of nanocomposites. Ac- cording to the IR study, for the CoFe2O4 nanocomposite stabilized with polyvinylpyrrolidone, the absorption bands at 735, 663, 649, 626 cm –1 are natural vibrations for the composite nanoparticles embedded in a polyvi- nylpyrrolidone matrix. The synthesized nanocomposites were tested in the oxidation of phenol with oxygen. The results demonstrate that the catalysts are promising both for the purification of industrial wastewater from phenol and for the synthesis of oxygen-containing compounds in the liquid phase under mild conditions. Keywords oxidation catalysts nanoscale magnetic composites phenol wastewater aromatic hydrocarbons polyethylenimine polyvinylpyrrolidone Received: 02.07.23 Revised: 26.07.23 Accepted: 16.08.23 Available online: 22.08.23 Key findings ● Nanocomposites of Fe3O4, Fe-Co/Al2O3 and CoFe2O4 as well as CoFe2O4 stabilized with polyethylenimine or polyvi- nylpyrrolidone were synthesized. ● The prepared nanocomposites were studied by physicochemical research methods and tested in the oxidation reaction of phenol with oxygen. ● The efficiency of using Fe3O4, CoFe2O4 and CoFe2O4 stabilized with polyethylenimine in the oxidation of phenol with oxygen was established. © 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 Many reservoirs are polluted by phenolic wastewater from petrochemical and oil refineries, pulp and paper mills, chemical industry enterprises producing phenol or using it for the synthesis of other substances, plants and factories of pharmaceutical and forestry industries, and enterprises producing building materials, rubber, adhesives, plastics, http://chimicatechnoacta.ru/ https://doi.org/10.15826/chimtech.2023.10.3.09 mailto:larissa.rav@mail.ru http://creativecommons.org/licenses/by/4.0/ https://orcid.org/0000-0003-4721-9758 https://orcid.org/0000-0003-4126-2907 http://orcid.org/0000-0001-7773-6057 https://orcid.org/0000-0002-9664-442X https://orcid.org/0000-0002-3221-114X https://orcid.org/0000-0002-1806-522X https://orcid.org/0000-0002-5751-6791 https://crossmark.crossref.org/dialog/?doi=https://doi.org/10.15826/chimtech.2023.10.3.09&domain=pdf&date_stamp=2023-08-22 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 2 of 8 DOI: 10.15826/chimtech.2023.10.3.09 pesticides, phenol-formaldehyde resins [1–6]. Catalysts based on various metals, metal oxides, deposited systems, and magnetic composites based on metal oxides show good efficiency in the oxidation of phenol with oxygen [3, 4, 7–14]. The most promising catalysts are nanodisperse catalytic systems for the purification of industrial waters from organic impurities, including phenolic compounds. Such catalysts can provide a high rate of oxidation of phe- nolic pollutants and effective oxidation of organic com- pounds with various functional groups. A significant number of publications are devoted to the study of the properties and applications of magnetic materials based on iron oxides in their common modifications – hematite, maghemite, and magnetite. This is due to the lower tox- icity of nanoparticles and their acceptable magnetic properties when compared with similar compounds of nickel and cobalt [13, 15–19]. The oxidation of phenol with oxygen in the presence of a magnetically controlled ferromagnetic catalyst stabilized by polymers is charac- terized by higher efficiency, low activation energy and the absence of toxic compounds in aqueous solution. For example, Fe3O4 is an active particle of catalysts, and co- balt complexes forms stable π-complexes with aromatic compounds; due to the π-dative transfer of electrons from the central atom to π*-loosening C6H6 orbitals, they activate the multiple bonds of the ring more strongly and loosen the molecule. When the metal complex is bound to the polymer, some of the ligands in the complex are re- placed by functional groups of the polymer chain. One of the most promising preparative methods is the synthesis of nanoparticles using polyethyleneimine (PEI) or poly- vinylpyrrolidone (PVP) as a stabilizer due to their bio- compatibility and hypoallergenicity. PEI coatings contain many amino groups and form cationic complexes that actively react with negatively charged surfaces and sub- stances. PEI is a positively charged polymer. The authors of [20, 21] found the effectiveness of magnetofection in vivo when using iron oxide nanoparticles stabilized with PEI. The structural formula of PVP contributes to the fact that PVP acts as a surface stabilizer, dispersant and na- noparticle expansion modifier. PVP also has protective properties due to its unique structure. The PVP molecule contains a highly polar amide group, which provides hy- drophilic properties, as well as non-polar methyl groups, both in the skeleton and in the ring, which provide hy- drophobic properties [22]. The purpose of this work was to create magnetic nanocatalysts that could be used for the oxidation of or- ganic water pollutants – phenol and its derivatives – and to determine the physicochemical characteristics of the catalysts. 2. Experimental The following chemical reagents were used for the syn- thesis of magnetite and cobalt ferrite stabilized with PEI and PVP: iron (II) sulfate heptahydrate (FeSO4.7H2O) – “chemically pure”; iron (III) chloride hexahydrate (FeCl3·6H2O) – “chemically pure”; Co(NO3)2·6H2O – “chemically pure”; 25% aqueous solution of ammonia (NH4OH) – “chemically pure”. Co-deposition occurs in two stages: first, the nuclea- tion of crystals (when critical supersaturation is reached); second, the slow crystal growth through the process of diffusion of dissolved substances to the crystal surface. These two stages should be separated in order to avoid the formation of crystals during the growth period [5, 16, 23, 24]. According to a number of works [25–27], the creation of polyethyleneimine coatings on magnetic iron oxide nanoparticles is a difficult task due to the aggregation during the adsorption of this polymer. To increase the efficiency of the catalytic system in the oxidation of organic compounds, the surface of magnet- ite was treated with cobalt nitrate. In the series of MeFe2O4 ferrites, where Me is Fe2+, Co2+, Ni2+, Cu2+and etc.), cobalt ferrite (CoFe2O4) has the highest cubic magnetocrystalline anisotropy, which is why cobalt ni- trate was chosen. Synthesis of CoFe2O4 was carried out through the fol- lowing stages: 1) mixing of the aqueous solutions of FeCl3·6H2O and Co(NO3)2·6H2O; 2) slow heating of the mixture to 353 K; 3) dripping 25% ammonia solution into the mixture with intense stirring and constant control of the crucial parameters (solution pH, mixture temperature); 4) mixing the resulting composite for another 40 minutes. As a result, a very rapid formation of a dark brown suspension occurred. Nanosized magnetic composites stabilized with PVP (Mw = 10,000) and based on Fe3O4, CoFe2O4 were obtained by chemical deposition. Nanocrystals of iron magnetite (Fe3O4) stabilized with PVP were obtained by chemical co- precipitation of the corresponding salts: ferrous and ferric iron ions in an alkaline solution [16, 28–30]. The synthesis was carried out separately in water in an aqueous solution with PVP (Mw = 10,000). The composition and structure of the synthesized cata- lysts were determined by SEM, Mossbauer and IR-Fourier spectroscopy. A Vertex 70v IR Fourier spectrometer (Bruker, Germany) with a computer-based system for re- cording and processing spectra was used. The reactions of phenol with oxygen on the nanocom- posites stabilized with PEI were carried out according to a widely used method described in the scientific litera- ture, including our previous works [5, 16, 23, 24], in a duck-type thermostated glass reactor. During and after the experiment, the samples of intermediate and final products were analyzed for the presence of phenol and benzoquinone by UV and IR spectroscopy. https://doi.org/10.15826/chimtech.2023.10.3.09 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 3 of 8 DOI: 10.15826/chimtech.2023.10.3.09 3. Results and discussion 3.1. Results of physicochemical studies For the Fe-Co/Al2O3 sample (Figure 1), according to the SEM analysis, areas with an increased iron content were found, which confirms the results of the elemental analy- sis (Figure 2, Table 1). In the diffraction pattern of the Fe-Co/Al2O3 sample (Figure 3), the signals related to iron oxide, cobalt in the region of 2θ = 50–55°, and a shoulder corresponding to the unknown phase in the region 2θ = 40–45° are seen. The diffraction peaks for cobalt oxide correspond to Co3O4 spinel [28, 29, 31–33] (Table 2). Detection of hydrocarbon by elemental analysis in the case of a CoFe2O4 catalyst stabilized with PVP shows that there is an interaction between nanoparticles and poly- mer, indicating efficient formation of nanocomposites (Figure 4, Table 3) [34, 35]. According to an IR study, for the CoFe2O4 nanocomposite stabilized with PVP, the ab- sorption bands in the region of 600–800 cm–1 are due to the stretching vibrations of the Fe–O bond in oxides. The absorption bands at 735, 663, 649, 626 cm–1 are natural vibrations for composite nanoparticles embedded in a pol- yvinylpyrrolidone matrix. Table 1 Elemental analysis of the Fe-Co /Al2O3 sample. Spectrum Na2О Al2О3 Cl Fe2О3 CoО Total 1 0.21 71.33 0.00 19.90 8.56 100.00 2 0.34 94.07 0.00 4.20 1.39 100.00 3 0.36 93.36 0.00 4.63 1.66 100.00 4 0.23 95.77 0.00 1.38 2.62 100.00 5 0.36 98.29 0.00 0.09 1.26 100.00 6 0.23 98.30 0.00 0.08 1.38 100.00 Average 0.29 91.95 0.00 5.05 2.81 100.00 Table 2 The diffraction date of the Fe-Co /Al2O3 and nanocompo- site with PEI samples. Sample Reflections, Å Phase Fe-Co/Al2O3 3.48, 2.37, 2.08, 1.74, 1.60, 1.51, 1.40, 1.37, 1.23, 1.18 Al2O3 (ASTM 71- 1123). 2.71, 2.51, 2.20, 1.84, 1.69, 1.59, 1.48, 1.45, 1.30 hematite α-Fe2O3 (ASTM 13-534). 5.52, 4.28, 2.85, 2.76, 2.71, 2.55, 2.51, 2.37, 2.13, 2.06, 1.43, 1.23 Co3O4 (ASTM 80- 1535). nanocomposite with PEI 2.96, 2.53, 2.09, 1.71, 1.61, 1.48, 1.32, 1.27 γ-Fe2O3 (ASTM 5- 637). 2.70, 2.53, 1.84, 1.48, 1.45, 1.30, 1.18 α -Fe2O3 (ASTM 13-534) 2.98, 2.73, 1.38 ε-Fe2O3 (ASTM 16- 653) 4.29, 2.87, 2.73, 2.65, 2.38, 2.36, 2.04, 1.43, 1.23 Co3O4 (ASTM 80- 1535) Figure 1 Results of SEM analysis: CoFe2O4 (a), Fe-Co/Al2O3 (b). Figure 2 X-ray fluorescence analysis of the samples: Fe- Co/Al2O3 (a); CoFe2O4 (b); CoFe2O4/PEI (c). https://doi.org/10.15826/chimtech.2023.10.3.09 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 4 of 8 DOI: 10.15826/chimtech.2023.10.3.09 Figure 3 The diffraction patterns of: Fe-Co/Al2O3 sample (a); CoFe2O4 composite (b); CoFe2O4/PEI composite (c). Table 2 Elemental analysis data of the CoFe2O4 catalyst stabilized with PVP. Element number Element symbol Element name Atomic conc. Weight conc. 6 C Carbon 24.869 10.600 8 O Oxygen 42.794 24.300 26 Fe Iron 23.157 45.900 27 Co Cobalt 9.180 19.200 Bands characteristic of PVP at 1657 cm–1 (amide Raman band), 1498, 1461, 1423, and 1372 cm–1 (deformation vibra- tions of CH2 groups in the pyrrolidone cycle) and 1287 cm–1 (Amide III–C–H bending vibrations) were found in the pol- ymer matrix with slight shifts compared to pure PVP [36, 37]. This probably indicates that PVP forms a composite together with the ferrite nanocrystals. Thus, the inclusion of CoFe2O4 nanoparticles in the PVP matrix leads to a shift of some absorption bands in the nanocomposites. https://doi.org/10.15826/chimtech.2023.10.3.09 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 5 of 8 DOI: 10.15826/chimtech.2023.10.3.09 3.2. Testing of the synthesized nanocomposites in the oxidation of phenol The synthesized nanocomposites were tested in the oxida- tion reaction of phenol with oxygen (Figure 5). Catalytic activity of the magnetic nanocomposites with composition Fe3O4, CoFe2O4 and CoFe2O4/PEI was checked in the pro- cess of phenol oxidation (Cphenol = 0.003 mol/L). Brief interpretation of the IR spectra of phenol and reac- tion products after oxidation with oxygen in the presence of a CoFe2O4/PEI nanocomposite (Figure 6): For phenol: IR spectrum: valence oscillations OH – in the area 3385–3610 cm–1, 3390–3395 cm–1; valence vibra- tions of C–O are in the fields of 1220–1232 cm–1 and 1240– 1245 cm–1. Figure 4 Results of physicochemical studies of the CoFe2O4 cata- lyst stabilized with PVP: SEM image (FW: 17 μm, Mode: 10 kV – Image, Detector: BSD Full) (a); X-ray fluorescence spectrum (b). Figure 5 Oxidation of phenol with oxygen: oxidation on systems of different composition (a): Fe3O4 (1); CoFe2O4 (2); CoFe2O4/PEI (3); oxidation on CoFe2O4/PEI at different reaction temperatures (b): 303 K (1), 313 K (2), 323 K (3), 333 K (4) and 343 K (5). Figure 6 The results of the analysis of the reaction medium for the oxidation of phenol with oxygen: IR spectrum of the starting materi- al, phenol, before the reaction (a); IR spectrum of the final sample after the phenol oxidation reaction (b); UV spectra: pure phenol (c); after 1 hour of oxidation (d); after 2 hour of oxidation (e). https://doi.org/10.15826/chimtech.2023.10.3.09 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 6 of 8 DOI: 10.15826/chimtech.2023.10.3.09 UV spectrum data: 210 (ε = 6200 L/mol·cm) and 270 nm (ε = 1450 L/mol·cm). There are absorption bands characteristic of phenol in the region 192–194/210– 2011/265–270 nm (Figure 6a). The results of IR and UV spectroscopy indicate the presence of CH in the aromatic ring and C=C double bonds, as well as valence vibrations of C=O groups of car- bonyl compounds [16, 38–42]. The absorption band of double bonds C=C was found at 3050–3060 cm–1. The oscillation band of hydroxyl groups of hydroquinone, the intermediate product of phenol oxi- dation is at 3420–3425 cm–1. The vibrations in the C=O bonds of the carbonyl group of benzoquinones were at 1676 cm–1, 1648 cm–1 (intense band). The vibration bands of the C–H and C–C bonds of the quinone ring are at 1365 cm–1 and 1312 cm–1. The UV spectrum of the sample during the reaction shows bands in the 207–210/213 nm region (Figure 6b) and a plateau in the 270–275 nm region [16, 40–42]. Thus, according to the UV and IR spectroscopy data, the magnetic composites have good catalytic activity dur- ing the oxidation of phenol with oxygen. It was concluded that among the magnetic nanocomposites of the Fe3O4, CoFe2O4 and CoFe2O4/PEI compositions, the most efficient oxidation of phenol is observed in the presence of the CoFe2O4/PEI nanocomposite. 4. Limitations The magnetic properties of stabilized magnetic composites are determined by many factors, such as the chemical composition, the type of crystal lattice, the size and shape of particles, and the interaction of particles with the sur- rounding polymer matrix. By changing the size, shape, composition, and structure of nanoparticles, it is possible, within certain limits, to control the magnetic characteristics of materials based on them. However, it is not always possible to control all these fac- tors during the synthesis of nanoparticles of approximately the same size and chemical composition, which means that the properties of stabilized magnetic composites may differ. During synthesis, magnetite can be oxidized to ma- ghemite, but it tends not to oxidize completely even during prolonged heating. In the process of obtaining nanoparti- cles, the question of their stabilization always arises, which limits the further growth of the solid phase. There- fore, it is difficult to determine the optimal reaction condi- tions, including the type of reaction, solvent, temperature and surfactants, in particular polymers, which react selec- tively at the resulting phase boundary. 5. Conclusions It is known that good results in the purification of indus- trial wastewater from phenol can be obtained by using catalysts. Among the most promising catalysts are nano- dispersed catalytic systems and magnetic composites based on metal oxides. Within the framework of this re- search the nanocomposites of Fe3O4, Fe-Co/Al2O3 and CoFe2O4 were synthesized. The composites of CoFe2O4 sta- bilized with polyethylenimine or polyvinylpyrrolidone were prepared and used for oxidation of phenol with oxy- gen. According to IR-spectroscopy, there was the presence of C=O bonds of the carbonyl group of benzoquinone and C–H and C–C bonds of the quinone ring in the products of phenol oxidation with oxygen. Based on the results of phenol oxidation, it can be concluded that magnetic com- posites based on iron and cobalt immobilized by polymers are promising catalysts for wastewater treatment from organic compounds, including phenol, as well as for the targeted synthesis of oxygen-containing compounds. ● Supplementary materials No supplementary materials are available. ● Funding This research has been funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan, grant No. AP14870308 “Development of tech- nology for catalytic petrochemical synthesis of oxygen- containing compounds from aromatic hydrocarbons in the presence of nanoscale magnetic composites”. ● Acknowledgments None. ● Author contributions Conceptualization: B.T.D., L.R. S. Data curation: L.R. S., T.V. S. Formal Analysis: L.R. S., A. R. S. Funding acquisition: T.V. S. Investigation: B.T.D., M.S.I., Z.M. Z., B.B.B. Methodology: B.T.D., L.R. S., B.B.B. Project administration: T.V. S. Resources: T.V. S., L.R. S. Software: L.R.S., A. R. S., T.S.A. Supervision: T.V. S., B.T.D. Validation: L.R. S., B.T.D. Visualization: A. R. S., Z.M. Z., M.S.I., T.S.A. Writing – original draft: L.R. S., B.T.D. Writing – review & editing: L.R. S. ● Conflict of interest The authors declare no conflict of interest. ● Additional information Author IDs: Larissa R. Sassykova, Scopus ID 56178673800; https://doi.org/10.15826/chimtech.2023.10.3.09 https://www.scopus.com/authid/detail.uri?authorId=56178673800 Chimica Techno Acta 2023, vol. 10(3), No. 202310309 ARTICLE 7 of 8 DOI: 10.15826/chimtech.2023.10.3.09 Binara T. Dossumova, Scopus ID 57210592713; Madina S. Ilmuratova, Scopus ID 57262368200; Tatyana V. Shakiyeva, Scopus ID 55911739700; Bedelzhan B. Baizhomartov, Scopus ID 55911858500; Albina R. Sassykova, Scopus ID 57220005479; Zhanar M. Zhaxibayeva, Scopus ID 57224865951; Tleutai S. Abildin, Scopus ID 6506476435. 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