Influence of annealing temperature on degradation efficiency and iron oxide transformations in CeO2/Fe-oxide sorbents

AIP Advances 11, 015308 (2021); https://doi.org/10.1063/9.0000133 11, 015308 © 2021 Author(s). Influence of annealing temperature on degradation efficiency and iron oxide transformations in CeO2/Fe-oxide sorbents Cite as: AIP Advances 11, 015308 (2021); https://doi.org/10.1063/9.0000133 Submitted: 15 October 2020 . Accepted: 23 November 2020 . Published Online: 05 January 2021 Ondrej Zivotsky, Jiri Lunacek, Yvonna Jiraskova, Jiri Bursik, Jakub Ederer, Pavel Janos, and Kristina Cabanova COLLECTIONS Paper published as part of the special topic on 65th Annual Conference on Magnetism and Magnetic Materials, 65th Annual Conference on Magnetism and Magnetic Materials, 65th Annual Conference on Magnetism and Magnetic Materials, 65th Annual Conference on Magnetism and Magnetic Materials and 65th Annual Conference on Magnetism and Magnetic Materials ARTICLES YOU MAY BE INTERESTED IN Intergranular interaction in nanocrystalline Ce-Fe-B melt-spinning ribbons via first-order reversal curve analysis AIP Advances 11, 015209 (2021); https://doi.org/10.1063/9.0000039 Quantum spin nematic liquid in the S = 1 antiferromagnetic chain with the biquadratic interaction AIP Advances 11, 015306 (2021); https://doi.org/10.1063/9.0000032 Structural and magnetic properties of iodide-mediated chemically synthesized L12 FePt3 nanoparticles AIP Advances 11, 015312 (2021); https://doi.org/10.1063/9.0000102 AIP Advances ARTICLE scitation.org/journal/adv Influence of annealing temperature on degradation efficiency and iron oxide transformations in CeO2/Fe-oxide sorbents Cite as: AIP Advances 11, 015308 (2021); doi: 10.1063/9.0000133 Presented: 2 November 2020 •Submitted: 15 October 2020 • Accepted: 23 November 2020 •Published Online: 5 January 2021 Ondrej Zivotsky,1,a) Jiri Lunacek,1Yvonna Jiraskova,2Jiri Bursik,2Jakub Ederer,3Pavel Janos,3 and Kristina Cabanova4,5 AFFILIATIONS 1Department of Physics, VSB-Technical University of Ostrava, 708 00 Ostrava, Czech Republic 2CEITEC IPM, Institute of Physics of Materials, AS CR, 616 62 Brno, Czech Republic 3Faculty of the Environment, University of Jan Evangelista Purkyne, 400 96 Usti nad Labem, Czech Republic 4Centre of Advanced Innovation Technologies, VSB-Technical University of Ostrava, 708 00 Ostrava, Czech Republic 5Faculty of Mining and Geology, VSB-Technical University of Ostrava, 708 00 Ostrava, Czech Republic Note: This paper was presented at the 65th Annual Conference on Magnetism and Magnetic Materials. a)Author to whom correspondence should be addressed: [email protected] ABSTRACT The microstructural and physical properties of magnetically separable CeO2(5 wt.%)/Fe-oxide sorbents, applicable for the decomposition of organophosphorus pesticides, are analyzed in dependence on calcination temperature. The sorbents are prepared using a two-step procedure: (1) synthesis of magnetite core from cheap and commercially available raw materials; and (2) the formation of cerium (III) carbonate by precipitation with the ammonium hydrogen carbonate, containing re-dispersed magnetite. The cerous carbonate/magnetite precursor is annealed in a muffle furnace at temperatures ranging from 473 to 1073K for 2 h to obtain the CeO2/Fe-oxide reactive sorbents. Structural characterization of the samples is performed using X-ray diffraction, scanning electron microscopy, Raman and Fourier transform infrared spectroscopy. Magnetic properties are obtained from hysteresis loops, field-cooled and zero-field-cooled curves, first-order reversal curve (FORC) diagrams, and Henkel plots. Sorbents exhibit an increase in coercivity from 0.2 kA/m to about 20 kA/m and a decrease in saturation magnetization from roughly 50 Am2/kg to 1 Am2/kg after annealing at 973K. This deterioration of magnetic properties is caused by the transformationofmagnetiteandmaghemiteintoweaklyferromagnetichematite,withatypicalpeakinFORCdiagramandaMorintransition at about 200K. The degradation efficiency towards parathion and paraoxon methyl is about 30% for samples annealed from 473K to 773K. ©2021 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/9.0000133 I. INTRODUCTION In recent years, cerium dioxide (CeO2) has been used in a variety of applications, either as a pure compound or as a part of various composites. Cerium dioxide is conventionally applied in catalytic applications,1special sensors and absorbents,2and antioxidants,3 and it is also currently emerging in cancer therapy4and as a reactive sorbent.5Emerging applications are related usually to its nanocrystalline forms – nanoceria. There are various preparation methods of ceriumdioxide,involvingforexamplesol-gel,homogeneoushydrolysis, hydrothermal synthesis, and precipitation methods.6CeO2in its bulk form is diamagnetic but, at decreasing grain size below approx. 15nm, its ferromagnetic behavior is under intensive investigations over the world. It was shown recently that not only paramagnetic Ce3+next to diamagnetic Ce4+ions and/or the oxygen vacancies7influence the magnetic behavior but also a small amount of magnetic iron-based impurities detected in CeO28,9 can be a reason for it. Moreover, a trace amount of iron, typically at the level of several ppm, was found and confirmed by several experimental methods9in the Ce-sources used for the CeO2production. Recently developed a new kind of magnetically separable sorbent, formed from grains of iron oxide decorated by CeO2 AIP Advances 11, 015308 (2021); doi: 10.1063/9.0000133 11, 015308-1 © Author(s) 2021 AIP Advances ARTICLE scitation.org/journal/adv nanocrystallites10 was successfully applied in the decomposition of organophosphorus pesticides and chemical warfare agents. These investigations revealed that the degradation efficiency of sorbents depends on the CeO2amount, and its crystallinity, which can be influenced by its method of preparation including calcination.11 On the other hand, the magnetic properties of CeO2are mainly governed by the strong magnetizations of the iron oxides and their phase transformations with increasing annealing temperature. This paper discusses the preparation, microstructural, and physical characterization of magnetically separable CeO2(5 wt.%)/ Fe-oxide powder sorbents across a wide range of annealing temperatures (Ta) from 473K to 1073K. Further we demonstrate the sorbents degradation capabilities using selected pesticides. Such a complex study of these composite materials has not yet been presented. In addition to conventional characterization techniques, involving X-ray diffraction, electron microscopy, and hysteresis loops, magnetic interactions are studied using first-order reversal curves (FORCs) and Henkel plots. The degradation efficiency towards parathion and paraoxon methyl exhibits a dependence on Ta. II. EXPERIMENTAL We prepared a series of magnetically separable sorbents, consisting of iron oxide serving as a magnetically separable core or carrier, and cerium oxide serving as an active constituent capable of destroying dangerous chemicals. The magnetite core was synthesized by the co-precipitation of the Fe2+and Fe3+salts from cheap and commercially available raw materials. Subsequently, the core was re-dispersed in a solution containing 5 wt.% of cerium (III) nitrate, and cerium (III) carbonate was prepared by precipitation with ammonium hydrogen carbonate. The cerous carbonate/magnetite precursor was annealed (calcined) in a muffle furnace at temperatures Taranging from 473 to 1073K for 2 h to obtain the CeO2/Fe-oxide – type reactive sorbents. Testing of the effectiveness of the sorbents was performed using the pesticides parathion methyl and paraoxon methyl in aprotic and aqueous environments. Sample morphology was studied using a TESCAN LYRA 3XMUFEG/SEMscanningelectronmicroscopewithanaccelerating voltage of 20 kV, equipped with an X-Max80 Oxford Instruments detector for energy-dispersive X-ray (EDX) analysis. An X’PERT PRO diffractometer, with the capacity to produce Co Kαradiation (λ=0.17902nm), was used for diffractogram measurements in the range of 2θ=20○−135○, steps =0.01○, and time per step 5s. The Rietveld structure refinement method12 using the HighScore Plus program and the ICSD database13 was applied to analyze the relative volume of phases and their basic parameters: lattice parameters and mean microdomain size. Fourier transform infrared (FTIR) spectra were obtained by a Nicolet iS50 spectrometer using the single reflection mode on diamond crystal (32 scans, 4cm-1 resolution). The measurements were performed using far-infrared spectroscopy (400−4000cm-1), a technique highly suited to inorganic samples. Raman spectra were obtained using a Smart Raman microscopy system XploRA™across the entire range of wavenumbers from 100 to 4000cm−1. A 50×objective and a laser excitation of 532nm were used. The laser spot diameter was approximately 0.5 μm, which allows a particle/aggregate spot analysis. The magnetic properties of powder samples were determined usingavibrating-samplemagnetometer(VSM)andaPhysical Property Measurement System (PPMS). The VSM was used to measure room temperature (RT) virgin and magnetization curves, with a maximum applied magnetic field of 1600 kA/m, and to construct first-order reversal curve (FORC) diagrams with a step of 8 kA/m between two adjacent FORCs. PPMS was used to obtain field-cooled (FC)and zero-field-cooled(ZFC) curvesin thetemperature rangeof 2−293K and in a magnetic field of 8 kA/m. III. RESULTS AND DISCUSSION A. Structural studies The morphology of the CeO2/iron-oxide powdered samples calcined at 673K and 1073K, as well as the qualitative distribution of elements in particles visualized in maps, are shown in Fig. 1. The Ceand Fe-rich oxides do not differ significantly in size in the sample annealed at 673K. Treatment at higher temperatures resulted in particle agglomeration and the formation of larger grains. The Rietveld analysis of X-ray diffractograms across the whole range of calcination temperatures involved the use of ICSD data sheet 28753 for CeO2(a=b=c=0.5411nm), 26410 for magnetite (a=b =c=0.83941nm), 35643 for maghemite (a=b=0.833996nm, c=0.83220nm), and 15840 (a=b=0.5038nm, c=1.3772nm) for hematite (see Table I). The progress of the refinement was monitored by the R-values,12 Rp, Rwp, Rexp, and by the S-indicator reflecting a “goodness-of-fit.” The final R-values varied across the whole range of the samples around 2.8 %, 4.4 %, 1.7 %, respectively. The Sindicator has ranged between 1.9 and 3.4 and the RBraggs parameters obtained for individual phases round 1.6 % (CeO2), 3.0 % (Fe3O4), 1.9 % (γFe2O3), and 4.3 % (α-Fe2O3). The results were accepted as reasonable. The analysis of magnetite and maghemite patterns using the mentioned data sheets was possible, but the similarity of lattice parameters did not allow their unique determination. Therefore, using the data sheet for maghemite was better in differentiating between both oxides. Notably, a certain degree of uncertainty in real representation of both oxides exists. The infrared spectra of the prepared samples presented in Fig. 1(c) supports the results from XRD and SEM. The sorbents annealed at temperatures of 873–1073K show two peaks at 518cm-1 and 436cm-1 that are close to the stretching vibrations of the FeO bond in hematite.14 Conversely, for the samples annealed below 873K, only one peak shifted to 540cm-1 is clearly visible. According to Refs. 15 and 16 the peak at 540cm-1 could correspond to the Fe-O bond in maghemite or magnetite. The presence of CeO2cannot be conclusively confirmed or ruled out by FTIR analysis alone because Ce-O stretching vibrations should be observed in a band around 520cm-1 17 being close to that of iron oxides. Therefore, cerium dioxide was locally detected using Raman spectroscopy (not presented), where the sharp peak at 435cm-1 corresponds well to the values reported in Ref. 18. Both the selected pesticides, parathion and paraoxon methyl, are decomposed quickly in the presence of reactive sorbents, producing 4-nitrophenol as the main degradation product. Fig. 1(d) shows that a maximum degradation efficiency of about 30% is obtained for sorbents with 5 wt.% CeO2annealed at 473–773K. Moreover, our latest results confirm that degradation efficiency can be increased to 90% by adding more cerium dioxide. AIP Advances 11, 015308 (2021); doi: 10.1063/9.0000133 11, 015308-2 © Author(s) 2021 AIP Advances ARTICLE scitation.org/journal/adv FIG.1.Scanningelectronmicroscopy(SEM) imagesandenergy-dispersiveX-ray(EDX)distribution mapsofFe,Ce,andO ofthesamplesannealedat673K(a)and1073K (b). Fourier transform infrared (FTIR) spectra(c) and degradation efficiency towards parathion and paraoxon methyl (d) as a function of annealing temperature. B. Magnetic measurements The magnetic properties of sorbents with 5 wt.% CeO2are presented in Fig. 2 and Table II. Although the prepared samples are composite materials, bulk magnetic measurements using VSM and PPMS detect predominantly strong iron oxide responses, which are several orders of magnitude higher than that of cerium dioxide. CeO2is typically diamagnetic at RT, or weakly ferromagnetic with a small magnetization at saturation about one thousandth of an Am2/kg.8 TABLE I. Results of Rietveld analysis of sorbents annealed at temperature Ta; phase content (A), lattice parameters (a,b,c), microdomain size (d). CeO2Fe3O4γ-Fe2O3α-Fe2O3 TaAa=b=c d Aa=b=c d Aa=b c d Aa=b c d (K) (%) (nm) (nm) (%) (nm) (nm) (%) (nm) (nm) (nm) (%) (nm) (nm) (nm) 473 5.4 0.5394 3.2 42.9 0.8368 8.3 51.7 0.8341 0.8299 11.8 ... ... ... ... 573 4.8 0.5413 3.4 28.4 0.8333 11.7 66.8 0.8391 0.8258 8.3 ... ... ... ... 673 5.3 0.5411 6.4 32.5 0.8331 14.6 62.2 0.8402 0.8247 8.7 ... ... ... ... 773 5.0 0.5408 8.4 25.7 0.8383 7.8 61.6 0.8329 0.8322 11.3 7.7 0.5031 1.3736 40.3 873 4.2 0.5408 10.4 ... ... ... 3.3 0.8368 0.8323 11.5 92.5 0.5034 1.3751 41.9 973 4.6 0.5408 12.3 ... ... ... ... ... ... ... 95.4 0.5034 1.3747 47.4 1073 4.7 0.5409 14.0 ... ... ... ... ... ... ... 95.3 0.5035 1.3748 51.3 AIP Advances 11, 015308 (2021); doi: 10.1063/9.0000133 11, 015308-3 © Author(s) 2021 AIP Advances ARTICLE scitation.org/journal/adv FIG. 2. Magnetic properties of sorbents with 5 wt.% CeO2. (a) Magnetization curves measured at different annealing temperatures Ta. (b) Field-cooled (FC) and zero-field-cooled (ZFC) curves of samples annealed at 673K and 1073K (inset). First-order reversal curves (FORCs) of sorbents annealed at (c) 673K, (d) 873K, and (e) 1073K. Room temperature hysteresis loops [subplot Fig. 2(a)] at annealing temperatures of 473−773K exhibit low coercive fields and a similar magnetization of about 50 Am2/kg at an applied magnetic field of 1600 kA/m (M1600). These high values of M1600 reflect the main contribution of magnetite and maghemite (see Table I). The slightly lower value of M1600 but 7 times higher coercivity was obtained in previous study of the magnetite with 20 wt.% CeO2after calcination at 673K.19 The ZFC–FC curves presented for the sample calcined at 673K are shown in Fig. 2(b). The maximum of the ZFC curve, denoted as blocking temperature (≈221K), corresponds tothe smallestsize ofparticles in the sample. Below this temperature the transition to superparamagnetic behaviour occurs. In contrast, the point at which the ZFC and FC curves separate (≈275K) is denoted as an irreversible temperature, which represents the largest particles. A difference between these characteristic temperatures can betakenasameasureoftheparticlesizedistributioninthemeasured assembly. The marked decrease in the RT magnetization of the samples calcined at 873, 973, and 1073K is caused by the transformation of ferrimagnetic magnetite and maghemite to hematite, exhibiting TABLE II. Room temperature magnetic properties of sorbents with 5 wt.% CeO2obtained from hysteresis loops and Henkel plots,showingadependenceonannealingtemperatureTa;magnetizationatamagneticfieldof1600kA/m(M1600),remanent magnetization (Mr), coercive field (Hc), and peak position (ΔM,ΔH) from the Henkel plots. Ta(K) M1600 (Am2/kg) Mr(Am2/kg) Hc(kA/m) ΔM(Am2/kg) ΔH(kA/m) 473 54.09 0.32 0.23 0.07 25.02 573 52.95 0.29 0.21 0.05 25.14 673 52.42 0.30 0.22 0.06 25.18 773 48.85 0.23 0.18 0.06 25.22 873 6.14 0.19 1.07 0.04 180.16 973 1.14 0.20 18.25 0.03 203.72 1073 1.07 0.20 21.53 0.03 203.95 AIP Advances 11, 015308 (2021); doi: 10.1063/9.0000133 11, 015308-4 © Author(s) 2021 AIP Advances ARTICLE scitation.org/journal/adv canted antiferromagnetic order at RT. The higher temperatures of calcination contribute also to an increase in particle size which is reflectedinhighervaluesofcoercivity(seeTableII).TheRThysteresis loop of the sample annealed at 1073K is presented in the inset of subplotFig.2(a).Theloopembodies a typical ferromagneticreversal known as “wasp pas” followed by a linear increase in magnetization athigherfields, correspondingtoantiferromagneticorder.Themagnetization M1600 about 1 Am2/kg is higher as compared to those in Ref. 19 obtained for the composition with 20 wt. % CeO2calcinated under the same conditions. Here the value 0.41 Am2/kg is much closer as to the saturation magnetization of hematite nanoparticles (0.21−0.29 Am2/kg) as to the bulk crystals (0.38 Am2/kg).20 It seems that mutual ratio of iron-oxide/CeO2affect the magnetic behavior and should be further studied from a viewpoint of large surfaces of small particles and interactions among them. The Morin transition, obtained here between 200K and 220K [inset of subplot Fig. 2(b)], corresponds to assembly of small particles (confirmed by XRD) and it agrees with Ref. 21. FORC diagrams provide an important tool for investigating the magnetic properties of materials, especially particle systems; they are computed from a class of partial magnetic hysteresis loops and represent a map of the magnetic response of all particles in a sample, with irreversible magnetizations, in terms of the coercivity (switching field) Hc=Hsw and magnetic interaction field distribution Hu=Hint.22 FORC diagrams of samples annealed at 673K, 873K, and 1073K are presented in subplots Figs. 2(c)-2(e) and were calculated using the special program tool doFORC, which is a portable application, made using only free libraries and freely available to the scientific community (for details see Ref. 23). Fig. 2(c) shows the sample with a very low value of coercivity, corresponding to the presence of a magnetite and maghemite mixture (see Tables I and II). If the FORCs are measured in the large region of Hc=0−400 mT and Hu=±100 mT, with the step of 8 kA/m, the diagram contains no visible peaks [blue color in subplot Fig. 2(c)]. Clear contours are visible only in the high-resolution FORC diagram, when both the region and the step are reduced towards the low Hc[inset of subplot Fig. 2(c)]. The FORC maximum is approximately Hc∼0.3 mT, Hu∼-6 mT, whereas a negative value of Hu corresponds to the presence of a local interaction field. Figures 2(d) and 2(e) are completely different, showing clear contours with one central peak (Hc=175 mT, Hu=0 mT) in the large region. This demonstrates the predominance of the hematite formed via the transformation of magnetite and maghemite above Ta=773K (see Table I). The shape of the diagram and its spreading in the direction of the Huaxis indicate presence of the local interaction field distribution of the predominantly single domain particles (SDP). Themagnetic interactions of the samples were further analyzed using Henkel plots usually constructed using the relation between the isothermal remanence (IRM) and DC demagnetization curves.24 In this paper we used some simplifications from the Ref. 25 and the Henkel plots were obtained from virgin and hysteresis loops at RT. For all samples, the Henkel plots are convex curves, indicating the presence of negative (dipolar) magnetostatic interactions. The strongest interactions are observed at the peak position ΔH,ΔM; particular values are summarized in last two columns of Table II. It is evident that, while the interaction strengths (ΔM) are similar for all samples, the position of the ΔHparameter shifts to higher magneticfields,whenhematiteisformedatannealingtemperatureabove 773K. Moreover, in agreement with Ref. 24 the position of the central peak of the FORC diagram is very close to the ΔHvalue. IV. CONCLUSIONS We summarize the following main conclusions from our study: (1) We have successfully prepared magnetically separable CeO2(5wt.%)/Fe-oxide sorbentsinawiderangeof annealing temperatures Tafrom 473K to 1073K. The sorbents exhibit maximum degradation efficiency of about 30% towards parathion and paraoxon methyl at Ta=473-773K. Degradation efficiency can be increased by adding more cerium dioxide. (2) SEM and EDX analysis indicate that the sorbents contain a mix of grains of different sizes; some are enriched with Ce, and others are Ce depleted. XRD results show that the transformation of magnetite and maghemite to hematite starts at 773K and finishes at 973K. The microdomain size of CeO2 and hematite gradually increases with increasing Ta. (3) The magnetic properties of sorbents annealed at 473-773K are: A low coercive field, a high magnetization at a magnetic field of 1600 kA/m (M1600), and blocking and irreversible temperatures of about 221K and 275K. The strongest magnetostatic interactions occur at low magnetic fields. (4) The magnetic properties of sorbents annealed at 873-1073K are: An increase in the coercive field and a decrease of M1600 at RT caused by the predominant contribution of hematite, hysteresisloopsconsistingofferromagneticreversalfollowed by a linear increase in magnetization, corresponding to antiferromagnetic order; a Morin transition at about 200K, and the strongest magnetostatic interactions at higher magnetic fields. ACKNOWLEDGMENTS This work was funded by the Ministry of Education Youth and Sports of the Czech Republic via the following projects: No. CZ.02.1.01/0.0/0.0/17 048/0007399 (ERDF/ESF New Composite Materials for Environmental Applications), SP2020/45, and No. LM2018124 (NanoEnviCz Research Infrastructure). DATA AVAILABILITY The data that support the findings of this study are available from the corresponding author upon reasonable request. REFERENCES 1I. Luisetto, S. Tuti, and E. Di Bartolomeo, Int. J. Hydrogen Energy 37, 15992 (2012). 2N. Izu, W. Shin, N. Murayama, and S. Kanzaki, Sens. Actuators B Chem. 87, 95 (2002). 3A. Garzón-Manjón, A. Aranda-Ramos, B. Melara-Benítez, I. Bensarghin, J. Ros, S. Ricart, and C. Nogués, Bioconjugate Chem. 29, 2325 (2018). 4E. Nourmohammadi, H. Khoshdel-sarkarizi, R. Nedaeinia, M. Darroudi, and R. Kazemi Oskuee, Mat. Sci. Eng.: C 109, 110533 (2020). 5P.Janos,P. Kuran, M. Kormunda, V. Stengl, T. M. Grygar, M. Dosek, M.Stastny, J. Ederer, V. 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