Microparticle Synthesis by Fe-EDTA Hydrothermal Decomposition

Article pubs.acs.org/crystal

FeCO3 Microparticle Synthesis by Fe-EDTA Hydrothermal Decomposition Marius Chirita*,† and Adrian Ieta‡ †

Department of Nanocrystal Synthesis, National Institute for Research and Development in Electrochemistry and Condensed Matter, Timisoara, Plautius Andronescu Str. No. 1, RO-300224, Timisoara, Romania ‡ Department of Physics, State University of New York at Oswego, Oswego, New York, United States ABSTRACT: We developed a new procedure for synthesizing highly crystalline FeCO3 by hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea, starting from ferric ammonium sulfate and Na4EDTA as the main precursors. Single phase FeCO3 microcrystals with a size in the range of 50−200 μm have been obtained after high pressure−temperature treatment time between 15 and 26 h at 230 and 250 °C. Without changing the concentrations of the precursors and synthesis temperature, we have investigated the kinetics of phase transitions between 2 and 40 h of high pressure−temperature treatment time. A transition from hematite (in the first 4 h) to magnetite microoctahedrons with superparamagnetic behavior at room temperature, via a single phase of iron carbonate microcrystals, has been recorded.

1. INTRODUCTION FeCO3 belongs on the trigonal crystal system, having the Fe2+ ions in 6-coordination with the O atoms of the CO3 group. The C atoms are situated in a plane surrounded by its three neighboring O atoms.1 Its crystals are rhombohedral in shape. Because of its implications upon the geological sequestration of CO2,2 the thermodynamics of iron carbonate (FeCO3) has been studied in many research fields, such as geology,3,4 oceanography,5,6 and sedimentology.7,8 A very interesting application in crystallography is the potential of the iron carbonate to be used as a precursor to prepare Fe3O4 and Fe2O3 crystals9,10 by partial or total oxidation of Fe2+ ions to Fe3+ ions, respectively. Studies of the thermal decomposition of the FeEDTA complex indicate a temperature of about 140 °C11 for this process; the kinetics of EDTA decomposition is presented in refs 12 and 13. In accordance with ref 14, Fe(OH)3−EDTA autoclavation was conducted at chelate decomposition in the temperature interval of 180−275 °C. Magnetite crystalline structures were found up to 275 °C, and no free chelates were detected in the system, proving complete decomposition. In concordance with ref 15, the hematite final product was obtained at 200 °C, and the maghemite final product was obtained at 250 °C when an aqueous solution of [FeEDTA]- at pH = 4 was used. A method for the synthesis of hematite nanoparticles with a particle size average of 42 nm by hydrothermal decomposition of the Fe-EDTA complex at 230 °C in the presence of urea and H2O2 has been reported by us.16 Also, we have developed an experimental procedure for synthesizing magnetite microoctahedrons in the 15−45 μm range (along the ⟨001⟩ axis), with superparamagnetic behavior at room temperature by © 2011 American Chemical Society

hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea.17,18 Continuing our previous studies, the present experimental procedure is focused on the hydrothermal synthesis of iron carbonate microparticles in a pure crystalline structure, by hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea, starting from Fe(III)-ferric ammonium sulfate (FAS) and Na4EDTA as the main precursors. Also, maintaining the concentration unchanged for the precursors at 250 °C, we investigated the kinetics of phase transitions between 2 and 40 h of high pressure−temperature treatment time. Keeping the same concentrations for the precursors, we dropped the temperature by 20 °C and we repeated the entire synthesis at 230 °C, in 2 h increments from 2 to 26 h.

2. EXPERIMENTAL METHODS 2.1. Synthesis. Chemicals: FeNH4(SO4)2·12H2O, Na4EDTA, and urea of analytical purity, supplied by Fluka (Sigma-Aldrich). The following procedure of chemical preparation was followed: First, we prepared an aqueous solution of 1.05 × 10−1 M of FAS and then an aqueous solution of 1.05 × 10−1 M Na4EDTA. These two solutions were stirred continuously, and finally the aqueous 9.71 × 10−1 M of urea was mixed with the previous one while stirring continuously. The Fe(III)-EDTA complex formation was indicated when the color changed from purple to dark red.14 The pH was established to 6.0 by dropwise addition of 5% HCl solution, which led to a change in color from dark red to coral. This solution was transferred into a number of 14 Teflon-lined stainless-steel autoclaves and was heated up to 250 °C by a rate of 1.7 °C/min. The autoclaves were removed, one by one, every 2 h in the range between 2 and 40 h. Received: October 2, 2011 Revised: November 21, 2011 Published: December 5, 2011 883

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We dropped the temperature by 20 °C and repeated the entire synthesis at 230 °C, in 2 h increments from 2 to 26 h. Abrupt cooling with cold water ensured the freezing of phase transitions inside the autoclaves. All the pH measurements indicated a value between 9.4 and 9.5 for the final solutions. The obtained microparticles were filtrated, washed with bidistilled water, and dried at 60 °C in air. 2.2. Characterization. X’Pert PRO MPD difractometer (PANalytical) using Cu Kα radiation (λ = 0.15418 nm, Ni filter) in θ:θ configuration, assisted by the X’Pert Data Collector program for data collection was used to record the X-ray diffraction (XRD) patterns of powder samples. XRD patterns were identified using the PDF 4+ Database of JCPDS. The particles’ morphology was examined by means of scanning electron microscope FEI (Inspect S). Energy dispersive X-ray (EDAX) quantitative analysis was used to identify the elementary constituents of the sample. In addition, Fourier transform infrared (FT-IR) analysis was carried out by means of an IR-670PLUS (JASCO) spectrometer. Magnetic properties of the magnetite sample were examined by means of an AC hysteresigraph.19

hydrothermal treatment. The diffraction peaks of magnetite were indexed with the ICSD reference code: 01-079-0419. The SEM images reveal the rhombohedral morphology of the FeCO3 microcrystals synthesized after 22 h of high pressure−temperature treatment time. The sizes of the FeCO3 microcrystals are in the range of 50−200 μm and were evaluated following the SEM image (Figure 2).

3. RESULTS AND DISCUSSION The structural evolution from single phase of hematite to mixed phases of siderite and magnetite via single phase of siderite is presented in Figure 1. The crystalline structure of the FeCO3

Figure 1. XRD spectra of the products obtained after 4 h, 6 h, 16 h, 24 h, and 26 h of high pressure−temperature treatment time.

microparticles synthesized between 16 and 24 h of high pressure−temperature treatment time was confirmed by XRD analysis. All the spectra collected in this interval have the same characteristics as the presented spectra (Figure 1c,d), which indicates the presence of iron carbonate. In the XRD pattern (Figure 1c,d), all diffraction peaks were indexed to FeCO3, in agreement with the respective Inorganic Crystal Structure Database (ICSD) reference code: 01-083-1764. The spectrum in Figure 1c characterizes the sample obtained after 16 h of high pressure−temperature treatment time, and the spectrum presented in Figure 1d characterizes the sample obtained after 24 h of high pressure−temperature treatment time. The X-ray diffraction spectrum presented in Figure 1a characterizes the Fe2O3 crystalline phase present in the first 4 h of hydrothermal treatment. The diffraction peaks of hematite were indexed with the ICSD reference code: 01-087-1164. Figure 1b reveals the diffraction peaks of mixed phases of hematite and siderite after 6 h of hydrothermal treatment. Finally, Figure 1e represents the mixed phases of siderite and magnetite after 26 h of

Figure 2. SEM images of the FeCO3 microcrystals after 22 h of autoclavation at (top) 800× and (bottom) 3000× magnification.

The high purity of FeCO3 microcrystals synthesized between 16 and 24 h of high pressure−temperature treatment time was confirmed by EDAX analysis. All the spectra collected in this interval have the same characteristics as the presented spectra (Figure 3), which indicates the presence of iron and oxygen only, without any traces of Na, S, C, and N, which could result from EDTA and FAS decomposition. Figure 3 presents the EDAX spectra collected from FeCO3 microcrystals after 20 h (Figure 3a) and 24 h (Figure 3b) of hydrothermal treatment. 884

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hydrothermal treatment, when micrometric monodisperse magnetite with unusual superparamagnetic behavior (remanent magnetization 3 emu/g) at room temperature appears in the system (Figure 5).

Figure 3. EDAX spectra of FeCO3 microparticles after 16 h and 24 h of high pressure−temperature treatment time.

Additional confirmations of the composition and structure of the siderite resulted from FT-IR analysis are presented below, by checking the presence of the FeCO3 bond and of the vibrations of the Fe−O bond; the results are shown in Figure 4.

Figure 4. FT-IR spectrum of FeCO3 microcrystals after 22 h of high pressure−temperature treatment time. Figure 5. (Top) SEM image and (bottom) hysteresis loop of the final product after 40 h of high pressure−temperature treatment time.

The infrared spectrum of siderite is characterized by four prominent absorption bands at 1823.36 cm−1, 1419.35 cm−1, 865.88 cm−1, and 736.67 cm−1, respectively. According to refs 20 and 21, these bands are caused by the CO3 groups in the crystals. The minor peak at 681.71 can be attributed to the same CO3 groups in the crystals21 or to the absorption band caused by the HCO3 groups, according to Miller et al.22 In the vicinity of 437.02 cm−1, the absorption band is characteristic of Fe−O vibrations.23 The chemistry of the Fe(III)-EDTA complexes’ formation and decomposition at different temperatures is presented in our previous work.16−18,24 Maintaining the concentration unchanged for the precursors at 250 °C, we investigated here the kinetics of crystalline phase transitions between 2 and 40 h of high pressure−temperature treatment time. In the first 4 h, the synthesis product was hematite only. Between 6 and 14 h, mixed phases of hematite and siderite were found in autoclaves. Between 16 and 24 h, single phase siderite was found as the final product. After high pressure−temperature treatment time longer than 26 h, mixed phases of siderite and magnetite coexist until 40 h of

Having the same concentrations for precursors, we dropped the temperature by 20 °C and we repeated the entire synthesis at 230 °C and intervals between 2 and 26 h. What is significantly different between syntheses at 230 and 250 °C is that, in the first case, the iron carbonate and nanometric hematite coexist in mixed phases between 4 and 26 h. In the second case, hematite completely disappears after 8 h of thermal treatment, and sometimes magnetite appears in a very small quantity, to coexist with siderite between 8 and 18 h of hydrothermal treatment. In both cases, pure siderite, rhombohedral in shape, with sizes in the range of 50−200 μm, can be extracted after careful washing (for hematite removal) or magnetic separation (for magnetite removal). The behavior of precursors at 230 °C between 26 and 38 h of high pressure−temperature treatment time was presented in our previous work,17 and we did not observe any main differences in the evolution of the precursors system in this interval of time (26−38 h) between 230 and 250 °C. As in our previous study,17 after 40 h of hydrothermal treatment the final product was micrometric monodisperse magnetite in the single 885

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(4) Fisher, Q. J.; Raiswell, R.; Marshall, J. D. Siderite concretions from nonmarine shales (westphalian A) of the pennines England: controls of their growth and composition. J. Sediment. Res. 1998, 68, 1034−1045. (5) Jensen, L.; Boddum, J. K.; Tjell, J. C.; Christensen, T. H. The solubility of rhodochrosite (MnCO3) and siderite (FeCO3) in anaerobic aquatic environments. Appl. Geochem. 2002, 17, 503−511. (6) Ptacek, C. J.; Reardon, E. J. Solubility of siderite (FeCO3) in concentrated NaCl and Na2SO4 solutions at 25 °C. Water−Rock Interact. 1992, 181−183. (7) James, H. L. Chemistry of the iron-rich sedimentary rocks. In Data of Geochemistry, U. S. Geological Survey Professional Paper 440-W; U. S. Government Printing Office: Washington, DC1966. (8) Smith, H. J. Equilibrium in the system: ferrous carbonate, carbondioxide and water. J. Am. Chem. Soc. 1918, 40, 879−883. (9) Xuan, S.; Chen, M.; Hao, L.; Jiang, W.; Gong, X.; Hu, Y.; Chen, Z. Preparation and characterization of microsized FeCO3, Fe3O4 and Fe2O3 with ellipsoidal morphology. J. Magn. Magn. Mater. 2008, 320, 164−170. (10) LauerH. V.MingD. W.GoldenD. C.Thermal characterization of Fe3O4 nanoparticles formed from poorly crystalline siderite. Lunar Planet. Sci. 2005, XXXVI, Part 12. (11) Diatlova, N. M.; Bikhman, B. I.; Belskaya, L. B.; Gurevich, M. Z.; Tevlin, S. A. Teploenergetika 1966, 13−56. (12) Motekaitis, R. J; Cox, B.; Taylor, P.; Arthure, N. D.; Martell, A. E.; Miles, B.; Tvedt, T. J. Thermal degradation of EDTA chelates in aqueous solution. Can. J. Chem. 1982, 60, 1207−1213. (13) Gabelica, Z.; Charmot, A.; Vataj, R.; Soulimane, R.; Barrault, J.; Valange, S. Thermal degradation of iron chelate complexes adsorbed on mesoporous silica and alumina. J. Therm. Anal. Calorim. 2009, 445−454. (14) Diatlova, N. M.; Bikhman, B. I.; Belskaya, L. B.; Gurevich, M. Z.; Tevlin, S. A. Teploenergetika 1966, 13−56. (15) Szilagyi, P. A. Study of iron-chelates in solid state and aqueous solutions using Mossbauer spectroscopy. Ph.D. Thesis, Université de Toulouse, 2007; pp 32−40. (16) Chirita, M.; Banica, R.; Ieta, A.; Grozescu, I. Fe-EDTA thermal decomposition, a route to highly crystalline hematite (Alpha Fe2O3) nanoparticle synthesis. Part. Sci. Technol. 2010, 28, 1−9. (17) Chirita, M.; Banica, R.; Ieta, A.; Grozescu, I. Superparamagnetic unusual behavior of micrometric magnetite monodisperse monocrystals synthesized by Fe-EDTA thermal decomposition. Part. Sci. Technol. 2011, DOI: 10.1080/02726351.2011.585220. (18) Chirita, M.; Banica, R.; Sfarloaga, P.; Ieta, A.; Grozescu, I. A short route of micrometric magnetite synthesis via Fe-EDTA thermal decomposition. Semiconductor Conference (CAS), 2010 International 2010, 2, 391−394. (19) Mihalca, I.; Ercuta, A. J. Optoelectron. Adv. M 2003, 5, 245. (20) Huang, C. K.; KerrP. F., Infrared study of the carbonate minerals. Am. Mineral. 1960, 4.5, 311−324. (21) Halford, R. S. Motions of molecules in condensed systems: 1. Selection rules, relative intensities, and orientation efiects for Raman and infrared spectra. J. Chem. Phys. 1946, 14, 8−15. (22) Miller, F. A.; Wilkins, C. H. Infrared spectra and characteristic frequequencies of inorganic ions. Anal. Chem. 1952, 24, 1253−1294. (23) Jiang, W.; Wu, Y.; He, B.; Zeng, X.; Lai, K.; Gu, Z. J. Colloid Interface Sci. 2010, 347, 1−7. (24) Chirita, M.; Banica, R.; Ieta, A.; Bucur, A.; Sfirloaga, P.; Ursu, D. H.; Grozescu, I. Highly crystalline FeCO3 microparticle synthesis by hydrothermal decomposition of Fe-EDTA complex. Am. Inst. Phys. Conf. Proc. 1262/2010, 124.

phase, having octahedral morphology and unusual superparamagnetic behavior at room temperature. Our preliminary research has shown that by changing some synthesis conditions, for example, autoclavation time between 12 h and 22 h and synthesis temperature between 230 and 250 °C, particle size may be controlled within the range of 10−200 μm. For a precise control of the particle’s dimension, additional experiments have to be done. In future investigations, our attention will be focused on the synthesis of micrometric iron oxides (hematite, magnetite, and maghemite) by thermal treatment of our synthesized FeCO3 microcrystals presented here.

4. CONCLUSION We developed a new procedure for synthesizing highly crystalline FeCO3 microparticles by hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea, starting from ferric ammonium sulfate and Na4EDTA as the main precursors. Without changing the concentrations of the precursors and synthesis temperature, we investigated the kinetics of phase transitions in the interval between 2 and 40 h of high pressure−temperature treatment. Single phase FeCO3 microcrystals with sizes in the range of 50 μm to 200 μm were obtained after high pressure−temperature treatment time between 15 and 26 h at 230−250 °C. The synthesis of pure iron carbonate microparticles was confirmed using X-ray powder diffraction and EDAX investigation. A transition from single phase of hematite (after the first 4 h) to single phase of magnetite microoctahedrons (after 40 h) with superparamagnetic behavior at room temperature, via single phase of iron carbonate microcrystals was recorded. The present investigation has demonstrated the possibility of synthesizing microsize iron carbonate particles, having rhombohedral morphology, starting from Fe3+ ions only and using the hydrothermal decomposition of the Fe(III)-EDTA complex in the presence of urea.

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AUTHOR INFORMATION

Corresponding Author

*Tel.: 0040256494413; e-mail: [email protected].

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ACKNOWLEDGMENTS The authors would like to thank Dr. Radu Banica, Dr. Aurel Ercuta, Dr. Cecilia Savii, Dr. Zoltan Szabadai, Dr. Alexandra Bucur, Dr. Paula Sfarloaga, and Dr. Ioan Grozescu for helpful discussions and technical support. This work was supported by Project PN 09 34 01 01 of the Ministry of Research and Education in Romania. Program: Modern Contributions in Energy and Health. Objective: Research in nanostructurate materials and physicochemical processes at nanometric scale.

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REFERENCES

(1) Nagai, T.; Ishido, T.; Seto, Y.; Nishio-Hamane, D.; Sata, N.; Fujino, K. Pressure-induced spin transition in FeCO3-siderite studied by X-ray diffraction measurements. Joint AIRAPT-22 & HPCJ-50 IOP Publishing. J. Phys.: Conf. Ser. 2010, 215, 012002. (2) Testemale, D.; Dufaud, F.; Martinez, I.; Bénezeth, P.; Hazemann, J.-L.; Schott, J.; Guyot, F. An X-ray absorption study of the dissolution of siderite at 300 bar between 50 °C and 100 °C. Chem. Geol. 2009, 259, 8−16. (3) Silva, C. A. R.; Liu, X.; Millero, F. J. Solubility of sidertie (FeCO3) in NaCl solutions. J. Solution Chem. 2002, 31, 97−108. 886

dx.doi.org/10.1021/cg201309k | Cryst. Growth Des. 2012, 12, 883−886