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Preparation and characterization of Fe3O4 magnetic nanoparticles modified by perfluoropolyether carboxylic acid surfactant
Materials Letters 143 (2015) 38–40
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation and characterization of Fe3O4 magnetic nanoparticles modified by perfluoropolyether carboxylic acid surfactant Hongchao Cui, Decai Li n, Zhili Zhang School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Uninversity, Beijing 100044, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 17 October 2014 Accepted 5 December 2014 Available online 13 December 2014
Conventional surfactants-modified Fe3O4 magnetic nanoparticles (MNPs) are not satisfying in special areas, especially in corrosive and extreme temperature conditions. In this study, bare Fe3O4 MNPs were synthesized by co-precipitation without protective gas in atmosphere, and then modified by perfluoropolyether carboxylic acid surfactant (PCAS). Both the bare and the modified Fe3O4 MNPs were characterized. According to the results of characterization, the modified Fe3O4 MNPs are globular shaped and monodisperse whose average particle size decreased from 30 40 nm to 11 nm and in narrow distribution. In addition, characteristic peaks of PCAS and bare Fe3O4 both appear in FT-IR spectrum of modified Fe3O4 which suggest that Fe3O4 MNPs have been coated by PCAS. The surface coating won't alter Fe3O4 crystal morphology or superparamagnetism. However, it can slightly reduce saturation magnetization from 74.684 emu/g to 55.392 emu/g. The modified layer will be completely destroyed at near 380 1C. The mass ratio of the modified layer to bare Fe3O4 core is close to 39:53 according to thermal analysis. In summary, these results collectively showed that PCAS was successfully decorated at the surface of Fe3O4 MNPs and the performance of modified Fe3O4 MNPs has been greatly improved. & 2014 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 magnetic nanoparticle Perfluoropolyether carboxylic acid surfactant Surface modification Magnetic materials Nanocomposites Nanoparticles
1. Introduction Fe3O4 magnetic nanoparticles (MNPs) have been extensively investigated both for their scientific interests and technological applications. They have been widely used in ferrofluids [1], biomedicines [2], chemicals [3], magnetic records [4], catalysts [5] and electronic technique [6] due to their strong saturation magnetization (Ms) and good biological compatibility [7]. Surfactants used to modify Fe3O4 MNPs are hydrocarbons, such as oleic acid [1], lauric acid [8], SDBS [9], TEOS [10], PEG [11], TMMOS [12], etcetera. They are prone to react with other chemicals and can always be stripped off from Fe3O4 MNPs surface by organic solvents, then lose modification effect. In addition, conventional surfactants are strongly temperature dependent, Fe3O4 MNPs modified by these surfactants can't withstand extreme temperature such as -40 1C 250 1C, so the applications are limited. It is significant to introduce PCAS to functionalize Fe3O4 MNPs and protect them from chemical attack. PCAS with strong perfluorinated C-F bond is truly super-stable to acids, alkali, oxidation and reduction even at high temperatures[13]. The outstanding chemical and thermal stability of PCAS permit modified Fe3O4 MNPs
n
Corresponding author. Tel./fax: þ 86 10 51684006. E-mail address: [email protected] (D. Li).
http://dx.doi.org/10.1016/j.matlet.2014.12.037 0167-577X/& 2014 Elsevier B.V. All rights reserved.
applied in certain practical applications such as aerospace systems and chemical industry, where are too severe to survive for conventional surfactants.
2. Experiments Co-precipitation is a more tractable and efficient method to control size and composition of Fe3O4 MNPs than conventional approaches [8], and the reaction equation is Fe2 þ þ2Fe3 þ þ 8OH- ¼Fe3O4 þ4H2O. We conduct the experiment by an improved co-precipitation method without nitrogen or inert gases protection just directly exposed to the air for reaction. Considering Fe2 þ could be partially oxidized into Fe3 þ in atmosphere, so the molar ratio of Fe2 þ /Fe3 þ was adjusted to 1:1.75. 25% ammonia served as precipitant was added into the mixed solution of Fe2 þ and Fe3 þ at 60 1C with intensively agitation, the solution color immediately turned from red brown to black. The mixture was stirred for additional 20 min and half of the product solution was separated, rinsed, filtered and dried, then the bare Fe3O4 MNPs (BFMNPs) were prepared. The other half of the solution was sampled and heated up to 80 1C, then PCAS was added to the solution. The mixture was kept stirring for 2 h to obtain moderate coating.
H. Cui et al. / Materials Letters 143 (2015) 38–40
Finally, modified Fe3O4 MNPs (MFMNPs) were obtained after collecting, rinsing, filtering and drying. Morphology and composition of the as-synthesized samples were characterized by transmission electron microscopy (TEM, JEOL-2100), X-ray diffraction (XRD, Brucker D8), and Fourier transform infrared spectroscopy (FT-IR, Varian 3100) respectively. Magnetic property was analyzed by vibrating sample magnetometer (VSM, Lakeshore 7307), and thermal behavior was tested by thermogravimetry/differential scanning calorimeter (TG-DSC, Netzsch STA449 F3).
3. Results and discussion XRD patterns of BFMNPs and MFMNPs are shown in Fig. 1(a). The peaks at 2θ ¼30.01, 35.41, 43.11, 53.61, 56.91 and 62.41 can be indexed to (220), (311), (400), (422), (511) and (440) lattice planes, characteristic of Fe3O4 (JCPDS 19–0629), and no impurity peaks are observed. The average particle sizes of BFMNPs and MFMNPs estimated by Scherrer formula are 31.1 nm and 10.7 nm respectively. The pattern of MFMNPs is almost identical to that of BFMNPs, which suggests that modification won't change Fe3O4 crystal phase of inverse spinel structure. The widen peaks in XRD of MFMNPs caused by grain refinement [13] indicating that PCAS has been coated on BFMNPs and restricted the continuous growth of Fe3O4 crystals. FT-IR spectra of BFMNPs, pure PCAS and MFMNPs displayed in Fig. 1(b) show that the absorption peaks are mainly in the finger print region. Characteristic stretching vibration absorption peaks of Fe-O at 579 cm 1 both appeared in FT-IR of BFMNPs and MFMNPs. The peak at 1135 cm 1 can be assigned as –O- asymmetric absorption peak, and peaks at 1243 cm 1 and 982 cm 1 can be attributed to C-F strong stretching vibration absorption peaks, the one at 2353 cm 1 is typically asymmetric stretching vibration peak from CO2, and the one at 3401 cm 1 corresponds to bound water O-H stretching vibration absorption. All these peaks can be identified at the corresponding positions from FT-IR of pure PCAS. However, the strong peak at 1776 cm 1 of pure PCAS shifts to 1673 cm 1 in MFMNPs and becomes weaker, which is caused by the reaction of –COOH and –OH (adsorbed). The “–COOH” group in PCAS became “–COO-” and finally attached to BFMNPs surface, so the modification is chemical adsorption [14]. Characteristic peaks of both BFMNPs and pure PCAS can be observed in FT-IR of MFMNPs, which indicates Fe3O4 has been covered with PCAS. TEM images and size distribution histograms of BFMNPs and MFMNPs are illustrated in Fig. 2. Particle size of BFMNPs ranges
39
from 30 nm to 40 nm, the particles exhibit serious aggregation and can't be dispersed under ultrasonication as shown in Fig. 2 (a,b). Particle size of MFMNPs is between 8 14 nm and 11 nm on average which is in consistent with XRD results. MFMNPs are homogeneously dispersed without flocculation, spherical shaped and clear boundary as shown in Fig. 2(c,d). The inset in Fig. 2(c) is an HRTEM image of a single modified particle with a clear crystalline structure corresponding to lattice fringe (311) of Fe3O4. This implies that PCAS can enhance the crystallization of Fe3O4 and decrease the particle size significantly. Morphological differences between BFMNPs and MFMNPs can be ascribed from three aspects: First, Fe3 þ and Fe2 þ were supersaturated in solution, and innumerable crystal nuclei generated instantaneously once precipitant was added. Additionally, the heat released during Fe3O4 crystallization accelerated crystal growth. Second, both large specific surface area and attraction between magnetic dipoles lead to BFMNPs spontaneous aggregation. Third, PCAS not only blocked crystals growth by firm chemical adsorption [14] on the surface, but also prevented particles agglomeration by steric hindrance of PCAS long chain. Consequently, the PCAS layer restrained the growth of BFMNPs and promoted the dispersion. TG-DSC results of BFMNPs and MFMNPs are shown in Fig. 3. Below 100 1C, the mass losses are 5.97% and 7.65%, respectively, corresponding to the amount of absorbed water on particle surfaces. From 100 1C to 800 1C, BFMNPs hardly have mass loss while MFMNPs have 39.03% mass loss which is caused by thermal decomposition of PCAS. PCAS completely breaks down at 380 1C, in accordance with Kissa [15]. The mass ratio of PCAS layer to bare Fe3O4 is close to 39:53, calculated on mass loss. According to DSC results also exhibited in Fig. 3, both samples have four obvious exothermic peaks at 34 1C, 123 1C, 254 1C and 590 1C for BFMNPs, and 42 1C, 186 1C, 330 1C and 608 1C for MFMNPs. The positive peak shifts of MFMNPs compared with BFMNPs imply that thermal-oxidative stability has been improved after modification. Peak area of 330 1C becomes larger than 254 1C after modification is due to huge amount of heat released from PCAS decomposition. The peaks at 254 1C and 590 1C of BFMNPs and 330 1C and 608 1C of MFMNPs show strong exothermic reactions while no obvious mass loss in both TG curves, which can be attributed to phase transition of Fe3O4. Fe3O4 to γ-Fe2O3 at 320 1C, γ-Fe2O3 to α-Fe2O3 at 600 1C [16,17], where, magnetism finally disappears. From the analysis above, the functionalization of BFMNPs with PCAS can reinforce their thermal-oxidative stability. Magnetic properties of BFMNPs and MFMNPS were measured by VSM at 300 K, shown in Fig. 4. Both magnetization curves are
Fig. 1. XRD patterns (a) and FT-IR spectra (b) of BFMNPs and MFMNPs.
40
H. Cui et al. / Materials Letters 143 (2015) 38–40
Fig. 2. TEM images and size distribution histograms of BFMNPs (a, b) and MFMNPs (c,d).
surfactants [18]. Third, Ms is proportional to particle size [19], and smaller particles can be obtained because of PCAS coating.
4. Conclusions Without protective gas, Fe3O4 MNPs were fabricated by coprecipitation and further modified by PCAS. Upon modification, average particle size decreased to 10 nm, Fe3O4 MNPs are in homogeneous dispersion with inverse spinel structure. Additionally, the modification can decrease Ms from 74.684 emu/g to 55.392 emu/g. PCAS is completely decomposed at 380 1C. The mass ratio of PCAS to bare Fe3O4 is close to 39:53. Acknowledgments Fig. 3. TG-DSC of BFMNPs (a) and MFMNPS (b).
This study has been supported by Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT Nos.243071529), NSFC of China (Nos.51375039,61271049), and Beijing Natural Science Foundation (Nos. 4142046). References
Fig. 4. Magnetization curve of BFMNPS and MFMNPs.
“S” shaped, lacking hysteresis, remanence or coercivity, which implies that modification won't alter superparamagnetism. However, modification reduced Ms from 74.684 emu/g to 55.392 emu/g, which can be explained by three aspects: first, PCAS as a non-magnetic material lowered magnetization per unit mass. Second, random spin caused by coating reduced magnetic orientation and weakened the interaction between particles, which have been observed using other
[1] Kholmetskii AL, Vorobyova SA, Lesnikovich AI, Mushinskii VV, Sobal NS. Mater Lett 2005;59:1993–6. [2] Laurent S, Forge D, Port M, Roch A, Robic C, Vander Elst L, et al. Chem Rev 2008;108:2064–110. [3] Hu A, Yee GT, Lin W. JACS 2005;127:12486–7. [4] Frey NA, Peng S, Cheng K, Sun S. Chem Soc Rev 2009;38:2532–42. [5] Lee KU, Kim MJ, Park KJ, Kim M, Kwon OJ, Kim JJ. Mater Lett 2014;125:213–7. [6] Arico AS, Bruce P, Scrosati B, Tarascon J-M, Van Schalkwijk W. Nat Mater 2005;4:366–77. [7] Oh JK, Park JM. Prog Polym Sci 2011;36:168–89. [8] Mamani JB, Costa-Filho AJ, Cornejo DR, Vieira ED, Gamarra LF. Mater Charact 2013;81:28–36. [9] Lee HH, Yamaoka S, Murayama N, Shibata J. Mater Lett 2007;61:3974–7. [10] Chen H, Wang Y, Qu J, Hong R, Li H. Appl Surf Sci 2011;257:10802–7. [11] Yang J, Zou P, Yang L, Cao J, Sun Y, Han D, et al. Appl Surf Sci 2014;303:425–32. [12] Cha HG, Kim CW, Kang SW, Kim BK, Kang YS. J. Phys. Chem. C 2010;114:9802–7. [13] Goya G, Berquo T, Fonseca F, Morales MJ. Appl Phys 2003;94:3520–8. [14] Maity D, Agrawal D J. Magn Magn Mater 2007;308:46–55. [15] Kissa E. Fluorinated Surfactants and Repellents. 2nd ed. New York: Marcel Dekker Inc; 2001. [16] Cornell Rochelle M, Schwertmann U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses. 1st ed. New York: John Wiley & Sons; 1996. [17] Sun S, Zeng H, Robinson DB, Raoux S, Rice PM, Wang SX, et al. JACS 2004;126:273–9. [18] Yamaura M, Camilo R, Sampaio L, Macedo M, Nakamura M, Toma H. J Magn Magn Mater 2004;279:210–7. [19] Dormann JL, Fiorani D. Magnetic properties of fine particles. University of Michigan: North-Holland; 1992.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Preparation and characterization of Fe3O4 magnetic nanoparticles modified by perfluoropolyether carboxylic acid surfactant Hongchao Cui, Decai Li n, Zhili Zhang School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong Uninversity, Beijing 100044, PR China
art ic l e i nf o
a b s t r a c t
Article history: Received 17 October 2014 Accepted 5 December 2014 Available online 13 December 2014
Conventional surfactants-modified Fe3O4 magnetic nanoparticles (MNPs) are not satisfying in special areas, especially in corrosive and extreme temperature conditions. In this study, bare Fe3O4 MNPs were synthesized by co-precipitation without protective gas in atmosphere, and then modified by perfluoropolyether carboxylic acid surfactant (PCAS). Both the bare and the modified Fe3O4 MNPs were characterized. According to the results of characterization, the modified Fe3O4 MNPs are globular shaped and monodisperse whose average particle size decreased from 30 40 nm to 11 nm and in narrow distribution. In addition, characteristic peaks of PCAS and bare Fe3O4 both appear in FT-IR spectrum of modified Fe3O4 which suggest that Fe3O4 MNPs have been coated by PCAS. The surface coating won't alter Fe3O4 crystal morphology or superparamagnetism. However, it can slightly reduce saturation magnetization from 74.684 emu/g to 55.392 emu/g. The modified layer will be completely destroyed at near 380 1C. The mass ratio of the modified layer to bare Fe3O4 core is close to 39:53 according to thermal analysis. In summary, these results collectively showed that PCAS was successfully decorated at the surface of Fe3O4 MNPs and the performance of modified Fe3O4 MNPs has been greatly improved. & 2014 Elsevier B.V. All rights reserved.
Keywords: Fe3O4 magnetic nanoparticle Perfluoropolyether carboxylic acid surfactant Surface modification Magnetic materials Nanocomposites Nanoparticles
1. Introduction Fe3O4 magnetic nanoparticles (MNPs) have been extensively investigated both for their scientific interests and technological applications. They have been widely used in ferrofluids [1], biomedicines [2], chemicals [3], magnetic records [4], catalysts [5] and electronic technique [6] due to their strong saturation magnetization (Ms) and good biological compatibility [7]. Surfactants used to modify Fe3O4 MNPs are hydrocarbons, such as oleic acid [1], lauric acid [8], SDBS [9], TEOS [10], PEG [11], TMMOS [12], etcetera. They are prone to react with other chemicals and can always be stripped off from Fe3O4 MNPs surface by organic solvents, then lose modification effect. In addition, conventional surfactants are strongly temperature dependent, Fe3O4 MNPs modified by these surfactants can't withstand extreme temperature such as -40 1C 250 1C, so the applications are limited. It is significant to introduce PCAS to functionalize Fe3O4 MNPs and protect them from chemical attack. PCAS with strong perfluorinated C-F bond is truly super-stable to acids, alkali, oxidation and reduction even at high temperatures[13]. The outstanding chemical and thermal stability of PCAS permit modified Fe3O4 MNPs
n
Corresponding author. Tel./fax: þ 86 10 51684006. E-mail address: [email protected] (D. Li).
http://dx.doi.org/10.1016/j.matlet.2014.12.037 0167-577X/& 2014 Elsevier B.V. All rights reserved.
applied in certain practical applications such as aerospace systems and chemical industry, where are too severe to survive for conventional surfactants.
2. Experiments Co-precipitation is a more tractable and efficient method to control size and composition of Fe3O4 MNPs than conventional approaches [8], and the reaction equation is Fe2 þ þ2Fe3 þ þ 8OH- ¼Fe3O4 þ4H2O. We conduct the experiment by an improved co-precipitation method without nitrogen or inert gases protection just directly exposed to the air for reaction. Considering Fe2 þ could be partially oxidized into Fe3 þ in atmosphere, so the molar ratio of Fe2 þ /Fe3 þ was adjusted to 1:1.75. 25% ammonia served as precipitant was added into the mixed solution of Fe2 þ and Fe3 þ at 60 1C with intensively agitation, the solution color immediately turned from red brown to black. The mixture was stirred for additional 20 min and half of the product solution was separated, rinsed, filtered and dried, then the bare Fe3O4 MNPs (BFMNPs) were prepared. The other half of the solution was sampled and heated up to 80 1C, then PCAS was added to the solution. The mixture was kept stirring for 2 h to obtain moderate coating.
H. Cui et al. / Materials Letters 143 (2015) 38–40
Finally, modified Fe3O4 MNPs (MFMNPs) were obtained after collecting, rinsing, filtering and drying. Morphology and composition of the as-synthesized samples were characterized by transmission electron microscopy (TEM, JEOL-2100), X-ray diffraction (XRD, Brucker D8), and Fourier transform infrared spectroscopy (FT-IR, Varian 3100) respectively. Magnetic property was analyzed by vibrating sample magnetometer (VSM, Lakeshore 7307), and thermal behavior was tested by thermogravimetry/differential scanning calorimeter (TG-DSC, Netzsch STA449 F3).
3. Results and discussion XRD patterns of BFMNPs and MFMNPs are shown in Fig. 1(a). The peaks at 2θ ¼30.01, 35.41, 43.11, 53.61, 56.91 and 62.41 can be indexed to (220), (311), (400), (422), (511) and (440) lattice planes, characteristic of Fe3O4 (JCPDS 19–0629), and no impurity peaks are observed. The average particle sizes of BFMNPs and MFMNPs estimated by Scherrer formula are 31.1 nm and 10.7 nm respectively. The pattern of MFMNPs is almost identical to that of BFMNPs, which suggests that modification won't change Fe3O4 crystal phase of inverse spinel structure. The widen peaks in XRD of MFMNPs caused by grain refinement [13] indicating that PCAS has been coated on BFMNPs and restricted the continuous growth of Fe3O4 crystals. FT-IR spectra of BFMNPs, pure PCAS and MFMNPs displayed in Fig. 1(b) show that the absorption peaks are mainly in the finger print region. Characteristic stretching vibration absorption peaks of Fe-O at 579 cm 1 both appeared in FT-IR of BFMNPs and MFMNPs. The peak at 1135 cm 1 can be assigned as –O- asymmetric absorption peak, and peaks at 1243 cm 1 and 982 cm 1 can be attributed to C-F strong stretching vibration absorption peaks, the one at 2353 cm 1 is typically asymmetric stretching vibration peak from CO2, and the one at 3401 cm 1 corresponds to bound water O-H stretching vibration absorption. All these peaks can be identified at the corresponding positions from FT-IR of pure PCAS. However, the strong peak at 1776 cm 1 of pure PCAS shifts to 1673 cm 1 in MFMNPs and becomes weaker, which is caused by the reaction of –COOH and –OH (adsorbed). The “–COOH” group in PCAS became “–COO-” and finally attached to BFMNPs surface, so the modification is chemical adsorption [14]. Characteristic peaks of both BFMNPs and pure PCAS can be observed in FT-IR of MFMNPs, which indicates Fe3O4 has been covered with PCAS. TEM images and size distribution histograms of BFMNPs and MFMNPs are illustrated in Fig. 2. Particle size of BFMNPs ranges
39
from 30 nm to 40 nm, the particles exhibit serious aggregation and can't be dispersed under ultrasonication as shown in Fig. 2 (a,b). Particle size of MFMNPs is between 8 14 nm and 11 nm on average which is in consistent with XRD results. MFMNPs are homogeneously dispersed without flocculation, spherical shaped and clear boundary as shown in Fig. 2(c,d). The inset in Fig. 2(c) is an HRTEM image of a single modified particle with a clear crystalline structure corresponding to lattice fringe (311) of Fe3O4. This implies that PCAS can enhance the crystallization of Fe3O4 and decrease the particle size significantly. Morphological differences between BFMNPs and MFMNPs can be ascribed from three aspects: First, Fe3 þ and Fe2 þ were supersaturated in solution, and innumerable crystal nuclei generated instantaneously once precipitant was added. Additionally, the heat released during Fe3O4 crystallization accelerated crystal growth. Second, both large specific surface area and attraction between magnetic dipoles lead to BFMNPs spontaneous aggregation. Third, PCAS not only blocked crystals growth by firm chemical adsorption [14] on the surface, but also prevented particles agglomeration by steric hindrance of PCAS long chain. Consequently, the PCAS layer restrained the growth of BFMNPs and promoted the dispersion. TG-DSC results of BFMNPs and MFMNPs are shown in Fig. 3. Below 100 1C, the mass losses are 5.97% and 7.65%, respectively, corresponding to the amount of absorbed water on particle surfaces. From 100 1C to 800 1C, BFMNPs hardly have mass loss while MFMNPs have 39.03% mass loss which is caused by thermal decomposition of PCAS. PCAS completely breaks down at 380 1C, in accordance with Kissa [15]. The mass ratio of PCAS layer to bare Fe3O4 is close to 39:53, calculated on mass loss. According to DSC results also exhibited in Fig. 3, both samples have four obvious exothermic peaks at 34 1C, 123 1C, 254 1C and 590 1C for BFMNPs, and 42 1C, 186 1C, 330 1C and 608 1C for MFMNPs. The positive peak shifts of MFMNPs compared with BFMNPs imply that thermal-oxidative stability has been improved after modification. Peak area of 330 1C becomes larger than 254 1C after modification is due to huge amount of heat released from PCAS decomposition. The peaks at 254 1C and 590 1C of BFMNPs and 330 1C and 608 1C of MFMNPs show strong exothermic reactions while no obvious mass loss in both TG curves, which can be attributed to phase transition of Fe3O4. Fe3O4 to γ-Fe2O3 at 320 1C, γ-Fe2O3 to α-Fe2O3 at 600 1C [16,17], where, magnetism finally disappears. From the analysis above, the functionalization of BFMNPs with PCAS can reinforce their thermal-oxidative stability. Magnetic properties of BFMNPs and MFMNPS were measured by VSM at 300 K, shown in Fig. 4. Both magnetization curves are
Fig. 1. XRD patterns (a) and FT-IR spectra (b) of BFMNPs and MFMNPs.
40
H. Cui et al. / Materials Letters 143 (2015) 38–40
Fig. 2. TEM images and size distribution histograms of BFMNPs (a, b) and MFMNPs (c,d).
surfactants [18]. Third, Ms is proportional to particle size [19], and smaller particles can be obtained because of PCAS coating.
4. Conclusions Without protective gas, Fe3O4 MNPs were fabricated by coprecipitation and further modified by PCAS. Upon modification, average particle size decreased to 10 nm, Fe3O4 MNPs are in homogeneous dispersion with inverse spinel structure. Additionally, the modification can decrease Ms from 74.684 emu/g to 55.392 emu/g. PCAS is completely decomposed at 380 1C. The mass ratio of PCAS to bare Fe3O4 is close to 39:53. Acknowledgments Fig. 3. TG-DSC of BFMNPs (a) and MFMNPS (b).
This study has been supported by Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT Nos.243071529), NSFC of China (Nos.51375039,61271049), and Beijing Natural Science Foundation (Nos. 4142046). References
Fig. 4. Magnetization curve of BFMNPS and MFMNPs.
“S” shaped, lacking hysteresis, remanence or coercivity, which implies that modification won't alter superparamagnetism. However, modification reduced Ms from 74.684 emu/g to 55.392 emu/g, which can be explained by three aspects: first, PCAS as a non-magnetic material lowered magnetization per unit mass. Second, random spin caused by coating reduced magnetic orientation and weakened the interaction between particles, which have been observed using other
[1] Kholmetskii AL, Vorobyova SA, Lesnikovich AI, Mushinskii VV, Sobal NS. Mater Lett 2005;59:1993–6. [2] Laurent S, Forge D, Port M, Roch A, Robic C, Vander Elst L, et al. Chem Rev 2008;108:2064–110. [3] Hu A, Yee GT, Lin W. JACS 2005;127:12486–7. [4] Frey NA, Peng S, Cheng K, Sun S. Chem Soc Rev 2009;38:2532–42. [5] Lee KU, Kim MJ, Park KJ, Kim M, Kwon OJ, Kim JJ. Mater Lett 2014;125:213–7. [6] Arico AS, Bruce P, Scrosati B, Tarascon J-M, Van Schalkwijk W. Nat Mater 2005;4:366–77. [7] Oh JK, Park JM. Prog Polym Sci 2011;36:168–89. [8] Mamani JB, Costa-Filho AJ, Cornejo DR, Vieira ED, Gamarra LF. Mater Charact 2013;81:28–36. [9] Lee HH, Yamaoka S, Murayama N, Shibata J. Mater Lett 2007;61:3974–7. [10] Chen H, Wang Y, Qu J, Hong R, Li H. Appl Surf Sci 2011;257:10802–7. [11] Yang J, Zou P, Yang L, Cao J, Sun Y, Han D, et al. Appl Surf Sci 2014;303:425–32. [12] Cha HG, Kim CW, Kang SW, Kim BK, Kang YS. J. Phys. Chem. C 2010;114:9802–7. [13] Goya G, Berquo T, Fonseca F, Morales MJ. Appl Phys 2003;94:3520–8. [14] Maity D, Agrawal D J. Magn Magn Mater 2007;308:46–55. [15] Kissa E. Fluorinated Surfactants and Repellents. 2nd ed. New York: Marcel Dekker Inc; 2001. [16] Cornell Rochelle M, Schwertmann U. The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses. 1st ed. New York: John Wiley & Sons; 1996. [17] Sun S, Zeng H, Robinson DB, Raoux S, Rice PM, Wang SX, et al. JACS 2004;126:273–9. [18] Yamaura M, Camilo R, Sampaio L, Macedo M, Nakamura M, Toma H. J Magn Magn Mater 2004;279:210–7. [19] Dormann JL, Fiorani D. Magnetic properties of fine particles. University of Michigan: North-Holland; 1992.