Study on the Synthesis of Cyanex 301-Modified Fe2O3 Nanoparticles

Journal of Dispersion Science and Technology, 30:1203–1207, 2009Copyright # Taylor & Francis Group, LLCISSN: 0193-2691 print=1532-2351 onlineDOI: 10.1080/01932690802701796<strong>Study</strong> on the Synthesis of Cyanex 301-ModifiedFe 2 O 3 NanoparticlesHuaqiang Shi, Xiaodong Zhou, He Liu, Yusheng Lin, and Xun FuKey Laboratory of Eco-Chemical Engineering, Ministry of Education, College of Chemistry andMolecular Engineering, Qingdao University of Science and Technology, Qingdao, P. R. ChinaDownloaded By: [Fu, Xun] At: 09:11 9 August 2009Surface modified Fe 2 O 3 nanoparticles were successfully synthesized via different thermaltreatment of the Fe(OH) 3 precursor, which was obtained by the extraction-precipitation system.The Fe 3þ ions were extracted into hexane by the extractant first, then the extracted solutioncontaining Fe(III) complex was precipitated with NaOH solution. The obtained Fe(OH) 3 precursorwas given different thermal treatment, such as solvothermal reaction, an intense refluxingboiling tetralin and calcine at air, respectively. The obtained Fe 2 O 3 nanoparticles were characterizedby XRD, TEM, SEM, IR, UV-vis, and TG-DTG, respectively. The results showed thatFe 2 O 3 products were well modified by extractant, which could be well dispersed into organicsolvents to form the stable fluids.KeywordsChemical synthesis, composite, electron microscopy, magnetic material1. INTRODUCTIONFerrofluids is a unique and novel class of ferromagneticliquids in which inorganic magnetic materials are dispersedin a liquid to form a stable colloidal dispersion that exhibitsmagnetic properties when a magnetic field is applied. [1–3]Ferrofluids has important applications in the fileds suchas magnetocalor power cycle, [4] magnetoviscous effect, [5]magnetic imaging, [6] magnetic, [7] and magnetooptic datastorage media, [8] biology and medicine, [9] formation ofmultilayered magnetic films, [10] and so on.During the past few years, lots of methods for thepreparation of Fe 2 O 3 particles (not ferrofluids) have beenexplored, such as sol-gel method, [11] hydrothermal, [12]refluxing forced hydrolysis method, [13] and so on. Thecommon ferrofluids, comprising a colloidal dispersion ofmagnetite fine particles in an aqueous, were easily obtainedeither by acid peptization of magnetite or by immobilizationof small magnetiti particlees in the matrix of a watersoluble polymer. [14] Howerer, it is known to be a complexReceived 25 March 2008; accepted 17 April 2008.This work was financially supported by the foundation ofPh.D. subjects 2005, P. R. China (No. 20050426003) and theKey Laboratory Foundation of Eco-Chemical Engineering ofQingdao University of Science and Technology (No. KLECE2007-001). The authors thank Cytec Canada, Inc. for its kindlysupplying the extractant of Cyanex 301.Address correspondence to Xun Fu, Key Laboratory ofEco-Chemical Engineering, Ministry of Education, Collegeof Chemistry and Molecular Engineering, Qingdao Universityof Science and Technology, Qingdao 266042, P. R. China. E-mail:xunfu4483@hotmail.comproblem that how to prepare the ferrofuids in organicsolvents directly because of the coupling properties of theinsoluble particles and organic phase. In order to reduce thesurface energy of nanoparticles and enhance the dissolutioncapacity in organic solvent, the synthesis of organic–inorganic composite materials has been paid much attention.[15] Duo to the chemical structure of modifying agent,it could be adsorbed on the surface of the particles andsimultaneously become solvated by the organic solvent.Recently, a novel nonhydrolytic route based on the thermaldecomposition of iron complexes in the presence of a surfactanthas led to the formation of surface modified Fe 2 O 3nanoparticles that were soluble in organic solvents. [16] Cyanex301 (di-(2,4,4-trimethylpentyl) dithiophosphinic acid)is one of the industrial extractants and can extract a greatdeal of metals in a wide scope of aqueous acidity, [17] whosestructure is analogous to the classical surfactant. Due toits high activity, the extractant was adsorbed onto the surfaceof the particles, promoting the particles stabilization. [18]In this work, a simple method was described to preparesurface-modified magnetic Fe 2 O 3 nanoparticles. Theobtained Fe 2 O 3 nanoparticles was well modified by Cyanex301 and the obtained particles could be easily dispersed inorganic solvents to provide stable fluid.2. EXPERIMENTAL2.1. Extraction of Fe 3þ by Cyanex 301 and thePreparation of Fe(OH) 3 –Cyanex 301 PrecursorCyanex 301 was supplied by Cytec Co. of Canada andused without further purification. FeCl 3 6H 2 O and other1203

1204 H. SHI ET AL.Downloaded By: [Fu, Xun] At: 09:11 9 August 2009chemicals used in this work are analytical purity. First,FeCl 3 aqueous solution (with definite concentration) isextracted into hexane by the extractant Cyanex 301 atVo=Va ¼ 1. The distribution ratio is determined from theFe 3þ concentrations in the aqueous solutions before andafter extraction. After phase separation, the organic phasecontaining Fe(III)-Cyanex 301 complex is precipitateddirectly with NaOH solution under strong stirring. Uponthe addition of NaOH, the color of the organic phaseturned gradually from black to brown or red. Afterevaporation of the solvents, the red substance is washedwith hot acetone and ethanol alternatively, and dryingat 70 C.2.2. Preparation of Fe 2 O 3 Nanoparticles via theThermal TreatmentThe obtained Fe(OH) 3 –Cyanex 301 precursor was givendifferent thermal treatment to obtain suface modifiedFe 2 O 3 nanoparticles.1. Thermal refluxing: The Fe(OH) 3 –Cyanex 301 precursorwas suspended in 40 ml tetralin and the suspension wassubjected to an intense refluxing (at the boiling pointof tetralin 210 C) under argon flow for 9 hours. Theobtained brown solution was cooled to room temperatuenaturelly and an excess of acetone was added intoit. A brown precipitate formed immediately, whichwas isolated by centrifugation.2. Calcining: The obtained Fe(OH) 3 –Cyanex 301 precursorwas calcined in a tube at 600 C at air for 2 hoursand the red powder was obtained.3. Solvothermal process: 35 mL of the above organic phasecontaining Fe(OH) 3 –Cyanex 301 precursor was transferredinto a 50 ml Teflon-lined stainless autoclave.The red samples were obtained in autoclave after thereaction was went on for 24 hours at 180 C. The aboveFe 2 O 3 particles were filtered, washed, dried, anddispersed into organic solvents again with the help ofultrasonic.3. RESULTS AND DISCUSSIONEqual volumes of 0.04 mol L 1 FeCl 3 aqueous solutionand 0.10 mol L 1 Cyanex 301 hexane were mixed, shakenfor several minutes and equilibrated longer than 24 hoursat room temperature. The concentrations of Fe 3þ ions inthe aqueous solutions before and after extraction weredetermined by EDTA titration. It could been confirmedthat the extraction ratio reached about 100% and theFe 3þ ions in the aqueous solution was efficiently transferredinto hexane in our preliminary experiments.Figure 1 showed the XRD patterns of the as-preparedFe(OH) 3 -Cyanex 301 precursor (a), Fe 2 O 3 particles afteran intense influxing in boiling tetralin (b) and calcined at600 C (c) of the precursor. It could be seen that theobtained precursor (a) was Fe(OH) 3 according to theJCPDS card (No. 34-1266) although the crystallinity wasrelatively poor. The XRD patterns showed three broadweak envelope at about 2h ¼ 16 , 34 , and 62 , whichapproximately indexed to (200), (400), and (002) crystalgraphicplanes. The crystallinity of the products could begreatly improved by different thermal treatments. Themain peaks of the influxed (b) and the calcined (c) samplesmatched well with the standard positions JCPDS cardNo. 25-1402 and No. 33-664, respectively.Figure 2 showed the TEM, SEM images, and the relatedelectron diffraction (ED) patterns of the as-preparedFe(OH) 3 –Cyanex 301 precursor (a), Fe 2 O 3 nanoparticlesafter an intense influxing (b), calcined at 600 C (c, d) andsolvothermal process (e) of the above precursor. It couldbe seen that the Fe(OH) 3 –Cyanex 301 precursor (a) wasmainly made up of sphere-like polycrystal materials, whichwas formed from radially aligned Fe(OH) 3 . After anintense influxing (b), the radially aligned Fe(OH) 32.3. Characterization of Surface ModifiedFe 2 O 3 NanoparticlesThe morphologies and size of the Fe 2 O 3 nanoparticleswere observed by transmission electron microscopy(TEM; JEM-2000EX, Japan) and scanning electron microscopy(SEM; JSM-5600LV, Japan). The x-ray powderdiffraction (XRD) pattern of the products was recordedby employing a Rigaku (Japan) D=max r-A x-ray diffractometerwith Cu=Ka radiation (k ¼ 0.15418 nm). The solidsamples were also characterized with ultraviolet-visibleabsorption spectra (UV-vis; 756CRT, China), infraredray (IR; 510P, USA) and thermal gravimetric analysis(TG; TG-209, Germany), respectively.FIG. 1. XRD patterns of the as-prepared Fe(OH) 3 –Cyanex 301 precursor(a), Fe 2 O 3 nanoparticles after influx in tetralin (b) and calcinedat 600 C (c) of the precursor.

CYANEX 301-MODIFIED Fe2O3 NANOPARTICLES 1205Downloaded By: [Fu, Xun] At: 09:11 9 August 2009above could be easily dispersed into organic solvents.While the obtained Fe 2 O 3 sample (e) was of sheet-likestructure with size of about 100200 nm after solvothermaltreatment at 180 C, which ED pattern shows that thesamples were polycrystals.Figure 3 showed the IR spectra of the as-preparedFe(OH) 3 –Cyanex 301 precursor (a), Fe 2 O 3 nanoparticlesafter an intense influxing (b) and calcined (c) of the aboveprecursor. The absorption peaks at 2955 cm 1 and2395 cm 1 were attributed to the stretched vibration ofC–H and S–H, respectively. The absorption peaks at1475 cm 1 and 1365 cm 1 were attributed to the splittingof tert-butyl. The absorption peaks at 488 cm 1 and612 cm 1 were attributed to the P–S–H and P¼S in extractantCyanex 301. [19] The typical peaks in Cyanex 301 mostexisted in Fe(OH) 3 precursor (a) and Fe 2 O 3 nanoparticles(b, c), indicating that Cyanex 301 adsorbed on the surfaceof Fe 2 O 3 particles could not be washed off totally. The stabilizingfunction is expected to be similar to that of thiolligands. Moreover, as shown in Figure 3a, the frequencyseparation between 1508 and 1355 cm 1 indicates that theCyanex 301 molecule bind the surface iron centers inchelating of bridging mode of coordination. The bands at600 cm 1 and 464 cm 1 were indicative of an iron oxidehydroxide network. [20] After thermal treatment of Fe(OH) 3 –Cyanex 301 precursor, the characteristic bands of theCyanex 301 groups were still observable, while an enhancementof the band at 600 cm 1 was also observed. Theseresults unveil the preservation of the organophilic sheatharound the magnetic solid and also the formation of ironoxide network. [21]Figure 4 shows the UV-vis absorption spectra of theas-prepared Fe(OH) 3 –Cyanex 301 precursor (a), Fe 2 O 3nanoparticles after an intense influxing (b) and calcined(c) of the precursor. The absorption band at about215 nm in (a) should be attributed to the bond of P¼S inFIG. 2. TEM and SEM images of the Fe(OH) 3 –Cyanex 301 precursor(a), Fe 2 O 3 nanoparticles after influxing (b), calcined (c, d) andsolvothermal treatment (e).disappeared and the hydrolysis sample was polycrystalFe 2 O 3 nanoparticles with the diameter of about 100 nm.As shown in (c, d), the single crystal Fe 2 O 3 nanoparticleswith the diameter of less than 100 nm have been obtainedafter calcination at 600 C. Due to the good modificationeffect of Cyanex 301, the obtained Fe 2 O 3 samples mentionFIG. 3. IR spectra of the Fe(OH) 3 –Cyanex 301 precursor (a), Fe 2 O 3particles after influxing (b) and calcined (c) of the precursor.

CYANEX 301-MODIFIED Fe2O3 NANOPARTICLES 1207procedure. The obtained Fe 2 O 3 nanoparticles were wellmodified by Cyanex 301 and could be dispersed well intoorganic solvents again due to the high affinity with nonpolarsolvent with the R groups in Cyanex 301. Thismethod provides a good idea for preparing ferrofluidsdirectly in organic solvent for industry.Downloaded By: [Fu, Xun] At: 09:11 9 August 2009FIG. 6. TEM images of the Fe 2 O 3 nanoparticles obtained in 1 mol L 1(a) and 4 mol L 1 (b) NaOH solution.3.1. Solubility of the Surface Modified Fe 2 O 3Nanoparticles in Organic SolventsThe as-prepared Fe 2 O 3 nanoparticles modified withCyanex 301, which were obtained from an intense influxingin boiling tetralin of the Fe(OH) 3 -Cyanex 301 precursor.With the help of ultrasonic, the obtained Fe 2 O 3 nanoparticlescould be dispersed easily into organic solvents, such ashexane and toluene. In hexane solvent, the dissolutionprocess proceeds rapidly and leads to clear and transparentbrown organosols. There was no obvious precipitate afterthe obtained brown organosols was centrifugating at3000 r=min for 30 minutes and it remain stable even aftermore than 2 month in our lab at room temperature. Theabove results were well in agreement with the IR, UV,and TG-DSC analysis results. When the as-prepared surfacemodified Fe 2 O 3 nanoparticles after calcined at 600 Cwere redispersed into hexane solvent, the dissolution capacitydecreased obviously and there is a little of precipitateafter a centrifugating process. It was considered that someR groups in Cyanex 301 on the surface of Fe 2 O 3 nanoparticleswas decomposed during the calcined process. Thismight imply that the R groups in Cyanex 301 have a higheraffinity with nonpolar solvent.4. CONCLUSIONSurface modified Fe 2 O 3 nanoparticles were successfulllysynthesized via the different thermal treatments from theFe(III)–Cyanex 301 precursor, such as solvothermal reactionin Teflon-lined stainless autoclave, an reflux in boilingtetralin for 9 hours and calcine at 600 C under air for2 hours. The extractant Cyanex 301 acted as phase transferagent and surface modifying agent during the wholeREFERENCES[1] Tronc, E., Chanéac, C., and Jolivet, J.P. (1998) J. Solid StateChem., 139(1): 93–104.[2] Wormuth, K. (2001) J. Colloid Interface Sci., 241(2):366–377.[3] De Cuyper, M. and Noppe, W. (1996) J. Colloid InterfaceSci., 182(2): 478–482.[4] Jing, Z.H. and Wu, S.H. (2004) J. Solid State Chem.,177(4–5): 1213–1218.[5] Hall, W.F. and Busenberg, S.N. (1969) J. Chem. Phys., 51(1):137–144.[6] Goto, K. and Sakurai, T. (1977) Appl. Phys. Lett., 30(7):355–356.[7] Speliotis, D.E. (1997) In Magnetic Hysteresis in NovelMagnetic Materials, edited by G.C. Hadjipanayis; NATOASI Series, Ser. E: Applied Sciences; Dordrecht, Germany:Kluwer: vol. 338, p. 259.[8] Sellmayer, D.J. In Nanophase Materials-Synthesis-Properties-Applications, edited by G.C. Hadjipanayis andW. Siegel NATO ASI Series, Ser. E: Applied Sciences;Dorcrect, , Germany: Kluwer, vol. 260, p. 537.[9] Arshady, R. (1993) Biomaterials, 14(1): 5–15.[10] Meldrum, F.C., Kotov, N.A., and Fendler, J.H. (1994)J. Phys. Chem., 98(17): 4506–4510.[11] da Costa, G.M., De Grave, E., de Bakker, P.M.A., andVandenberghe, R.E. (1994) J. Solid State Chem., 113(2):40–412.[12] Hiroyuki, I. and Sugimoto, T. (2003) J. Colloid Interface Sci.,265(2): 283–295.[13] Wei, Y., He, H.L. (1997) Acta Physico-Chimica Sinica, 13(6):564–568.[14] Yokoi, H. and Kantoh, T. (1993) Bull. Chem. Soc. Jpn.,66(5): 1536–1541.[15] Motte, L., Petit, C., Boulanger, L., Lixon, P. and Pileni, M.P.(1992) Langmuir, 8(4): 1049–1053.[16] Bourlinos, A.B., Simopoulos, A., and Petridis, D. (2002)Chem. Mater., 14(2): 899–903.[17] Sole, K.C. and Feather, A.M. (2005) Hydrometallurgy,78(1–2): 52–78.[18] Song, X.Y., Sun, S.X., Zhang, W.M., and Yin, Z.L. (2004)J. Colloid Interface Sci., 273(2): 463–469.[19] Chen, J., Jiao, R.Z., and Zhu, Y.J. (1996) Chin. J. Appl.Chem., 13(2): 45–48.[20] Deacon, G.B. and Phillips, R. (1980) Coord. Chem. Rev.,33(3):227–250.[21] Nasrazadan, S. (1997) Corros. Sci., 39(10–11):1845–1859.