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Synthesis of hydroxyapatite particles in catanionic mixed surfactants template
Materials Chemistry and Physics 131 (2011) 132–135
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Synthesis of hydroxyapatite particles in catanionic mixed surfactants template Nesa Esmaeilian Tari, Mohammad M. Kashani Motlagh ∗ , Beheshteh Sohrabi Department of Chemistry, Iran University of Science and Technology, Resalat Square, Hengam Street, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 18 January 2011 Received in revised form 26 July 2011 Accepted 29 July 2011 Keywords: Nanostructures Precipitation Surface properties Electron microscopy
a b s t r a c t Different morphologies of nano hydroxyapatite particles, Ca10 (PO4 )6 (OH)2 (HAP) are prepared by precipitation method using CaCl2 and H3 PO4 (water phase) and the mixture of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and anionic one sodium dodecyl sulfate (SDS) as template. The mixture of these surfactants in two regions of cationic-rich and anionic-rich form the various aggregations as template. The results show that by changing the ratio of cationic to anionic surfactant in the mixture the morphology of the nano HAP can be controlled. The nano structure of products is studied by the means of X-ray diffraction (XRD), Fourier transmission infrared spectrometer (FT-IR) and scanning electron microscopy (SEM). With this system we could synthesize nano particles of hydroxyapatite with high crystallinity and least agglomeration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Hydroxyapatite (HAP) has been widely studied as an important biocompatible material because of its chemical similarity to the natural calcium phosphate mineral present in a biological hard tissue [1–4]. HAP also finds applications in others fields of industrial or technological interests as catalyst in chromatography or gas sensor [5], water purification, fertilizers production and drug carrier [6]. Properties of HAP, including bioactivity, biocompatibility, solubility, sinterability, castability, fracture toughness and absorption can be tailored over wide ranges by controlling the particle composition, size and morphology [7–9]. The morphology of calcium phosphate nanoparticles made by traditional methods as chemical co-precipitation [10], sol–gel [11], spray-pyrolysis [12], hydrothermal synthesis [13], emulsion processing [13], mechano-chemical method [14], and autocombustion methods [15], are needle-like, sheet-like, or spherical which are not more than 300 nm in length. Surfactant based template systems have a lot of promise to synthesize nano crystalline materials. The investigations show that surfactants are assumed to be very efficient templates for controlling particle size and shape [16]. Also, organic additive and templates with complex functionalization patterns are found to control the nucleation, growth and alignment of inorganic crystals has been widely applied for biomimetic synthesis of inorganic materials with controllable morphologies [17]. The mixtures of cationic/anionic surfactants are of great interest from both practical and fundamental viewpoints. Such mixtures
∗ Corresponding author. Tel.: +98 2173912704; fax: +98 2177491204. E-mail address: [email protected] (M.M. Kashani Motlagh). 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.07.078
exhibit strong synergism between the surfactants because of electrostatic attraction between the oppositely charged head groups besides hydrophobic interaction between the alkyl tails [18]. Molecular assembly of the mixed surfactants can form a variety of structures such as cylindrical micelles, vesicles, and planar bilayers depending on the molar mixing ratio in the solution, because the Columbic interaction between the hydrophilic parts of anionic and cationic surfactants causes formation of quasi-double-chained composites, whose properties are greatly different from those of single-component systems [19]. Also, our investigations showed that with changing concentration of CTAB or SDS in the cationicrich and anionic-rich regions revealed a phase transition from vesicles to mixed micelles [20,21]. Differences in the lengths of the CTAB and SDS hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phase), and vesicles form spontaneously over a wide range of compositions in both cationic-rich and anionic-rich solutions. In this paper we used the mixed cationic–anionic surfactants in two regions of cationic-rich and anionic-rich as template and studied the effect of mixed surfactant template on the structure and properties of the resulting HAP nano particles. 2. Materials and methods HAP nanopowders were synthesized using the micelle as a template system where the mixture of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the template. Also for comparison SDS was used lonely as a template. Calcium chloride (CaCl2 , Merck) and phosphoric acid (H3 PO4 85%, Merck) were used as calcium and phosphorus sources, respectively. 0.6 mol of phosphoric acid and the mixture of SDS and CTAB with the ratio of 99:1 (%w w−1 ) (anionic-rich) and 1:99 (%w w−1 ) (cationic-rich) in the second experience were dissolved in 25 ml de-ionized water and 25 ml of ethanol was added to the solution while SDS was used in the third experience as the same. The pH was adjusted at 12 using sodium hydroxide. 1 mol of CaCl2 was dissolved into 50 ml
N.E. Tari et al. / Materials Chemistry and Physics 131 (2011) 132–135
Fig. 1. XRD pattern of HAP samples: (1) SDS:CTAB; 1:99, (2) SDS:CTAB; 99:1, (3) SDS.
solution containing de-ionized water and ethanol. This solution was added drop wise into the phosphorous-surfactant solution mixed under vigorous stirring, yielding a milky suspension. The suspension was stirred for half an hour. It was then aged for 48 h. After that the precipitate was filtered off and washed with de-ionized water and ethanol for several times. A gel-like paste was obtained, which was dried in an
133
Fig. 2. FT-IR spectra of synthesized hydroxyapatite: (1) SDS:CTAB; 1:99, (2) SDS:CTAB; 99:1, (3) SDS. oven at 100 ◦ C for 20 h. The powder was then calcinated in a furnace at 650 ◦ C for 5 h, yielding a white powder. The morphologies of the as-prepared HAP were observed by a scanning electron microscopy (SEM) (Cambridge-S365) equipped with energy-disperse X-ray spectroscopy. The powder X-ray diffractometer using Cu K␣ (siemens D500) and Fourier
Fig. 3. Scanning electron microscopy for synthesized HAP in (1, 2) mixture of surfactants (SDS:CTAB, 99:1), (3, 4) (SDS:CTAB, 1:99), (5, 6) SDS.
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Fig. 4. The strong interaction between the sulfate groups of SDS and the Ca2+ ions in the presence of alcohol on the surface of HAP particles.
transform infrared (FTIR) spectroscopy (shimadzu, KBr pellet technique) were used to identify the quality and composition of hydroxyapatite.
3. Results and discussion The wide angle (2 > 10◦ ) X-ray diffraction patterns of the obtained samples is shown in Fig. 1. The diffraction peaks correspond to the standard characteristic peaks of hexagonal HAP. There is a high consistency between the data from our samples and that from the standard data base, with lattice dimensions of a = b = 0.9414 nm, c = 0.6879 nm (space group p63 /m, JCPDS No. 09-0432). No other impurity was observed in the XRD pattern, indicating the chief inorganic phase of the sample is HAP crystal. The average crystal size precipitates was estimated by using the simple Scherrer equation: D=
k [ˇ1/2 cos ]
where D is the size in A˚ measured using reflection (2 1 1), k the shape ˚ factor equal to 0.9, the wavelength of X-rays equal to 1.5418 A, the diffraction angle equal to 31.8 for the reflection (2 1 1), and ˇ1/2 is defined as diffraction peak width at half height, expressed in radians. By this equation the crystal size of samples 1, 2 and 3 are 57, 52 and 57 nm, respectively. Fig. 2 shows the FT-IR spectra of the samples. The peak at 3420 cm−1 is attributed to the v2 bending mode of adsorbed water [22]. The stretching vibration band of OH− is observed at 3569 cm−1 [23]. Two adsorption bands at 561 and 601 cm−1 are ascribed to the v4 bending mode of PO4 3− [23]. The characteristic band at 1024 and 1091 cm−1 are related to the stretching vibration of PO4 3− . The band at 951 cm−1 is assigned to v1 stretching mode of PO4 3− . The typical splitting peaks at 567 and 603 cm−1 derived from the v4 phosphate mode [24]. The FT-IR results indicate that no surfactant molecules are incorporated in the HAP. Fig. 3(1–6) shows the SEM images of the HAP nanoparticles in SDS/CTAB, CTAB/SDS and SDS templates, respectively. They reveal that the overall morphology of the obtained powders at anionicrich region (SDS:CTAB, 99:1) (Fig. 3 1, 2) solution is rod like. Our investigations show that SDS micelles are more unstable than CTAB micelles, due to their precipitation because of the strong repulsion between sulfate groups of SDS. Therefore, we added alcohol to SDS solutions. According to Fig. 4, alcohol is modeled as a “spacer” that dilutes the charge density at the micelle–water interface, thereby
reducing the electrostatic repulsion between the ionic head groups (sulfate groups in SDS) so the micelles become stable. It is shown that the alcohol is preferentially partitioned into the regions of lower curvature, where it is more efficient in relieving the electrostatic strain. Also, the presence of SDS had greatly influenced the morphology of the product due to a strong interaction between the sulfate groups of SDS and the Ca2+ ions in the solution and on the surface of HAP particles (Fig. 4) [24–26]. Since, hydrocarbon chain length of SDS is lower than CTAB therefore; channels diagonal in hydroxyapatite rods in presence of SDS are smaller than CTAB. However the morphology of HAP in anionic-rich region, due to the presence of CTAB and neutralizing opponent charges is more oriented than in the solution of SDS (Fig. 3(3)) and CTAB only [27,28]. Also, nanosheet forms in cationic-rich region can be explained by the SDS monomers, because of electric charges of cationic surfactant was neutralized by the charges on SDS ions. We propose here a mechanism for the formation of HAP nanoparticles in the compositions containing the anionic surfactant. Earlier studies show that the sulfate groups are able to interact with calcium ions present in an aqueous solution. Surfactant molecules in micelles or emulsion droplet interact with Ca2+ ions to form zwitterions structures [17,25,26]. These numerous calcium-rich domains lead to the fast formation of HAP particles upon contact with phosphate ions in the aqueous phase. The reaction between H3 PO4 and CaCl2 in the micelles is deemed to be rapid because of the localized Ca2+ -concentration effect. In addition, the positional stabilization of Ca2+ ions within each zwitterions structure as a result of the electrostatic interaction effect by SDS molecules favors the formation of ordered HAP crystals. In the case of CTAB/SDS, the growth mechanism is more complicated because the chemical reaction of the CTAB and SDS competitively takes place. The HAP nanosheets are suggested to form by competitive reactions of the passivation and the micelle formation [29]. 4. Conclusion HAP nanopowders were synthesized using the micelle as a template system where the mixture of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with different ratio were used as the template in order to investigate the effect of mixed surfactant on the morphology of synthesized particles. In other experience HAP nano particles was synthesized in the
N.E. Tari et al. / Materials Chemistry and Physics 131 (2011) 132–135
presence of SDS as template. Data reveal that the overall morphology of the obtained powders at anionic-rich region (SDS:CTAB, 99:1) solution is rod like, but in the presence of cationic rich region (SDS:CTAB, 1:99) the resulted particles was sheet like which because of the interaction of surfactants with opposite charges. The resulted HAP nano particles in the presence of SDS were rod like but their morphology was less oriented than anionic-rich region. Our experience shows that the type of surfactant has great effect on the morphology of synthesized particles. References [1] S.V. Dorozhkin, M. Epple, Biological and medical significance of calcium phosphates, Angew. Chem. Int. Ed. 41 (2002) 3130. [2] G. Bezzi, G. Celotti, E. Landi, T.M.G. La Torretta, I. Sopyan, A. Tampieri, A novel sol–gel technique for hydroxyapatite preparation, Mater. Chem. Phys. 78 (2003) 816–824. [3] H. Ehrlich, P.G. Koutsoukos, K.D. Demadis, O.S. Pokrovsky, Modern strategies for the isolation of organic frameworks, Micron 40 (2009) 169–193. [4] W. Suchanek, M. Yoshimura, Processing and properties of hydroxyapatitebased biomaterials for use as hard tissue replacement implants, J. Mater. Res. 13 (1998) 94. [5] J. Torrent-Burgues, T. Boix, J. Fraile, R. Rodriguez-Clemente, Hydroxyapatite precipitation in a semibatch process, Cryst. Res. Technol. 36 (2001) 1075–1082. [6] J. Arensds, J. Chistoffersen, M.R. Chistoffersen, H. Eckert, Calcium hydroxyapatite precipitated from an aqueous solution, J. Cryst. Growth 84 (1987) 515–532. [7] Y. Wang, Sh. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Hydrothermal synthesis of hydroxyapatite nanopowders using cationic surfactant as a template, Mater. Lett. 60 (2006) 484. [8] H. Arami, M. Mohajerani, M. Mazloumi, R. Khalifehzadeh, A. Lak, S.K. Sadrnezhaad, Rapid formation of hydroxyapatite nanostrips via microwave irradiation, J. Alloys Compd. 469 (2009) 391–394. [9] R.Z. Legeros, Calcium Phosphates in Oral Biology and Medicine, Karger, Basel, Switzerland, 1991. [10] L. Yan, Y.D. Li, Z.X. Deng, J. Zhuang, X.M. Sun, Surfactant-assisted hydrothermal synthesis of hydroxyapatite nanorods, Int. J. Inorg. Mater. 3 (2001) 633. [11] D.M. Liu, T. Troczynski, W.J. Tseng, Water-based sol–gel synthesis of hydroxyapatite: process development, Biomaterials 22 (2001) 1721–1730. [12] K. Itatani, T. Tsugawa, T. Umeda, Y. Musha, I.J. Davies, S. Koda, Preparation of submicrometer-sized porous spherical hydroxyapatite agglomerates by ultrasonic spray pyrolisis technique, J. Ceram. Soc. Jpn. 118 (2010) 462–466.
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[13] M.H. Cao, Y.H. Wang, C.X. Guo, et al., Preparation of ultrahigh-aspect-ratio hydroxyapatite nanofibers in reverse micelles under hydrothermal conditions, Langmuir 20 (2004) 4784. [14] S. Modes, P. Lianos, Luminescence probe study of the conditions affecting collodial semiconductor growth in reverse micelles and water-in-oïl microemulsions, J. Phys. Chem. 93 (1989) 5854. [15] M.L. Curri, A. Agostiano, L. Manna, et al., Synthesis and characterization of CdS nanoclusters in a quaternary microemulsion the role of cosurfactant, J. Phys. Chem. B 104 (2000) 8391. [16] Y. Wu, S. Bose, Nanocrystalline hydroxyapatite: micelle template synthesis and characterization, Langmuir 21 (2005) 3232. [17] H. Tang, J. Yu, X. Zhao, D.H.L. Ng, Influence of PSSS on the morphology and polymorph of calcium carbonate in the ethanol water mixed system, J. Alloys Compd. 463 (2008) 343–349. [18] J. Zhao, J. Liu, J. Jiang, Intraction between anionic and cationic gemni surfactants at air/water interface and in aqueous bulk solution, Colloids Surf. A: Physicochem. Eng. Aspects 350 (2009) 141–146. [19] T. Ohkubo, T. Ogrura, H. Sakai, M. Abe, Synthesis of highly-ordered mesoporous silica particles using mixed cationic and cationic surfactants as templates, J. Colloid Interf. Sci. 312 (2007) 42–46. [20] B. Sohrabi, H. Gharibi, S. Javadian, M. Hashemianzadeh, A new model to study the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture, J. Phys. Chem. B 111 (2007) 10069–10078. [21] B. Sohrabi, H. Gharibi, B. Tajik, S. Javadian, M. Hashemianzadeh, Molecular interaction of cationic and anionic surfactants in mixed monolayers and aggregates, J. Phys. Chem. B 112 (2008) 14869–14876. [22] A. Siddharathan, T.S. Sampath Kumar, S.K. Seshadri, Synthesis and characterization of nanocrystalline apatites from eggshells at different Ca/P ratios, Biomed. Mater. 4 (2009) 045010. [23] Y. Wang, S. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Hydrothermal synthesis of hydroxylapatite nanopowders using cationic surfactant as a template, Mater. Lett. 60 (2006) 1484. [24] H. Wang, L. Zhai, Y. Li, Tiejun Shi, Preparation of irregular mesoporous hydroxyapatite, Mater. Res. Bull. 43 (2008) 1607. [25] J. Yu, H. Tang, B. Cheng, Influence of PSSS additive and temperature on morphology and phase structures of calcium oxalate, J. Colloid Interf. Sci. 288 (2005) 407. [26] M. Lei, W.H. Tang, L.Z. Cao, P.G. Li, J.G. Yu, Effect of (sodium 4-styrene sulfonate) on morphology of calcium carbonate particles, J. Cryst. Growth 294 (2006) 358. [27] Y. Li, W. Tjandra, K.C. Tam, synthesis and characterization of nanoporous hydroxyapatite using cationic surfactants as templates, Mater. Res. Bull. 43 (2008) 2126–2318. [28] Y. Wang, S. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Hydrothermal synthesis of hydroxyapatite nanopowders using cationic surfactants as a template, Mater. Lett. 60 (2006) 1484–1487. [29] H. Usui, The effect of surfactants on the morphology and optical properties of precipitated wurtzite ZnO, Mater. Lett. 63 (2009) 1489–1492.
Contents lists available at ScienceDirect
Materials Chemistry and Physics journal homepage: www.elsevier.com/locate/matchemphys
Synthesis of hydroxyapatite particles in catanionic mixed surfactants template Nesa Esmaeilian Tari, Mohammad M. Kashani Motlagh ∗ , Beheshteh Sohrabi Department of Chemistry, Iran University of Science and Technology, Resalat Square, Hengam Street, Tehran, Iran
a r t i c l e
i n f o
Article history: Received 18 January 2011 Received in revised form 26 July 2011 Accepted 29 July 2011 Keywords: Nanostructures Precipitation Surface properties Electron microscopy
a b s t r a c t Different morphologies of nano hydroxyapatite particles, Ca10 (PO4 )6 (OH)2 (HAP) are prepared by precipitation method using CaCl2 and H3 PO4 (water phase) and the mixture of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and anionic one sodium dodecyl sulfate (SDS) as template. The mixture of these surfactants in two regions of cationic-rich and anionic-rich form the various aggregations as template. The results show that by changing the ratio of cationic to anionic surfactant in the mixture the morphology of the nano HAP can be controlled. The nano structure of products is studied by the means of X-ray diffraction (XRD), Fourier transmission infrared spectrometer (FT-IR) and scanning electron microscopy (SEM). With this system we could synthesize nano particles of hydroxyapatite with high crystallinity and least agglomeration. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Hydroxyapatite (HAP) has been widely studied as an important biocompatible material because of its chemical similarity to the natural calcium phosphate mineral present in a biological hard tissue [1–4]. HAP also finds applications in others fields of industrial or technological interests as catalyst in chromatography or gas sensor [5], water purification, fertilizers production and drug carrier [6]. Properties of HAP, including bioactivity, biocompatibility, solubility, sinterability, castability, fracture toughness and absorption can be tailored over wide ranges by controlling the particle composition, size and morphology [7–9]. The morphology of calcium phosphate nanoparticles made by traditional methods as chemical co-precipitation [10], sol–gel [11], spray-pyrolysis [12], hydrothermal synthesis [13], emulsion processing [13], mechano-chemical method [14], and autocombustion methods [15], are needle-like, sheet-like, or spherical which are not more than 300 nm in length. Surfactant based template systems have a lot of promise to synthesize nano crystalline materials. The investigations show that surfactants are assumed to be very efficient templates for controlling particle size and shape [16]. Also, organic additive and templates with complex functionalization patterns are found to control the nucleation, growth and alignment of inorganic crystals has been widely applied for biomimetic synthesis of inorganic materials with controllable morphologies [17]. The mixtures of cationic/anionic surfactants are of great interest from both practical and fundamental viewpoints. Such mixtures
∗ Corresponding author. Tel.: +98 2173912704; fax: +98 2177491204. E-mail address: [email protected] (M.M. Kashani Motlagh). 0254-0584/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.matchemphys.2011.07.078
exhibit strong synergism between the surfactants because of electrostatic attraction between the oppositely charged head groups besides hydrophobic interaction between the alkyl tails [18]. Molecular assembly of the mixed surfactants can form a variety of structures such as cylindrical micelles, vesicles, and planar bilayers depending on the molar mixing ratio in the solution, because the Columbic interaction between the hydrophilic parts of anionic and cationic surfactants causes formation of quasi-double-chained composites, whose properties are greatly different from those of single-component systems [19]. Also, our investigations showed that with changing concentration of CTAB or SDS in the cationicrich and anionic-rich regions revealed a phase transition from vesicles to mixed micelles [20,21]. Differences in the lengths of the CTAB and SDS hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phase), and vesicles form spontaneously over a wide range of compositions in both cationic-rich and anionic-rich solutions. In this paper we used the mixed cationic–anionic surfactants in two regions of cationic-rich and anionic-rich as template and studied the effect of mixed surfactant template on the structure and properties of the resulting HAP nano particles. 2. Materials and methods HAP nanopowders were synthesized using the micelle as a template system where the mixture of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the template. Also for comparison SDS was used lonely as a template. Calcium chloride (CaCl2 , Merck) and phosphoric acid (H3 PO4 85%, Merck) were used as calcium and phosphorus sources, respectively. 0.6 mol of phosphoric acid and the mixture of SDS and CTAB with the ratio of 99:1 (%w w−1 ) (anionic-rich) and 1:99 (%w w−1 ) (cationic-rich) in the second experience were dissolved in 25 ml de-ionized water and 25 ml of ethanol was added to the solution while SDS was used in the third experience as the same. The pH was adjusted at 12 using sodium hydroxide. 1 mol of CaCl2 was dissolved into 50 ml
N.E. Tari et al. / Materials Chemistry and Physics 131 (2011) 132–135
Fig. 1. XRD pattern of HAP samples: (1) SDS:CTAB; 1:99, (2) SDS:CTAB; 99:1, (3) SDS.
solution containing de-ionized water and ethanol. This solution was added drop wise into the phosphorous-surfactant solution mixed under vigorous stirring, yielding a milky suspension. The suspension was stirred for half an hour. It was then aged for 48 h. After that the precipitate was filtered off and washed with de-ionized water and ethanol for several times. A gel-like paste was obtained, which was dried in an
133
Fig. 2. FT-IR spectra of synthesized hydroxyapatite: (1) SDS:CTAB; 1:99, (2) SDS:CTAB; 99:1, (3) SDS. oven at 100 ◦ C for 20 h. The powder was then calcinated in a furnace at 650 ◦ C for 5 h, yielding a white powder. The morphologies of the as-prepared HAP were observed by a scanning electron microscopy (SEM) (Cambridge-S365) equipped with energy-disperse X-ray spectroscopy. The powder X-ray diffractometer using Cu K␣ (siemens D500) and Fourier
Fig. 3. Scanning electron microscopy for synthesized HAP in (1, 2) mixture of surfactants (SDS:CTAB, 99:1), (3, 4) (SDS:CTAB, 1:99), (5, 6) SDS.
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Fig. 4. The strong interaction between the sulfate groups of SDS and the Ca2+ ions in the presence of alcohol on the surface of HAP particles.
transform infrared (FTIR) spectroscopy (shimadzu, KBr pellet technique) were used to identify the quality and composition of hydroxyapatite.
3. Results and discussion The wide angle (2 > 10◦ ) X-ray diffraction patterns of the obtained samples is shown in Fig. 1. The diffraction peaks correspond to the standard characteristic peaks of hexagonal HAP. There is a high consistency between the data from our samples and that from the standard data base, with lattice dimensions of a = b = 0.9414 nm, c = 0.6879 nm (space group p63 /m, JCPDS No. 09-0432). No other impurity was observed in the XRD pattern, indicating the chief inorganic phase of the sample is HAP crystal. The average crystal size precipitates was estimated by using the simple Scherrer equation: D=
k [ˇ1/2 cos ]
where D is the size in A˚ measured using reflection (2 1 1), k the shape ˚ factor equal to 0.9, the wavelength of X-rays equal to 1.5418 A, the diffraction angle equal to 31.8 for the reflection (2 1 1), and ˇ1/2 is defined as diffraction peak width at half height, expressed in radians. By this equation the crystal size of samples 1, 2 and 3 are 57, 52 and 57 nm, respectively. Fig. 2 shows the FT-IR spectra of the samples. The peak at 3420 cm−1 is attributed to the v2 bending mode of adsorbed water [22]. The stretching vibration band of OH− is observed at 3569 cm−1 [23]. Two adsorption bands at 561 and 601 cm−1 are ascribed to the v4 bending mode of PO4 3− [23]. The characteristic band at 1024 and 1091 cm−1 are related to the stretching vibration of PO4 3− . The band at 951 cm−1 is assigned to v1 stretching mode of PO4 3− . The typical splitting peaks at 567 and 603 cm−1 derived from the v4 phosphate mode [24]. The FT-IR results indicate that no surfactant molecules are incorporated in the HAP. Fig. 3(1–6) shows the SEM images of the HAP nanoparticles in SDS/CTAB, CTAB/SDS and SDS templates, respectively. They reveal that the overall morphology of the obtained powders at anionicrich region (SDS:CTAB, 99:1) (Fig. 3 1, 2) solution is rod like. Our investigations show that SDS micelles are more unstable than CTAB micelles, due to their precipitation because of the strong repulsion between sulfate groups of SDS. Therefore, we added alcohol to SDS solutions. According to Fig. 4, alcohol is modeled as a “spacer” that dilutes the charge density at the micelle–water interface, thereby
reducing the electrostatic repulsion between the ionic head groups (sulfate groups in SDS) so the micelles become stable. It is shown that the alcohol is preferentially partitioned into the regions of lower curvature, where it is more efficient in relieving the electrostatic strain. Also, the presence of SDS had greatly influenced the morphology of the product due to a strong interaction between the sulfate groups of SDS and the Ca2+ ions in the solution and on the surface of HAP particles (Fig. 4) [24–26]. Since, hydrocarbon chain length of SDS is lower than CTAB therefore; channels diagonal in hydroxyapatite rods in presence of SDS are smaller than CTAB. However the morphology of HAP in anionic-rich region, due to the presence of CTAB and neutralizing opponent charges is more oriented than in the solution of SDS (Fig. 3(3)) and CTAB only [27,28]. Also, nanosheet forms in cationic-rich region can be explained by the SDS monomers, because of electric charges of cationic surfactant was neutralized by the charges on SDS ions. We propose here a mechanism for the formation of HAP nanoparticles in the compositions containing the anionic surfactant. Earlier studies show that the sulfate groups are able to interact with calcium ions present in an aqueous solution. Surfactant molecules in micelles or emulsion droplet interact with Ca2+ ions to form zwitterions structures [17,25,26]. These numerous calcium-rich domains lead to the fast formation of HAP particles upon contact with phosphate ions in the aqueous phase. The reaction between H3 PO4 and CaCl2 in the micelles is deemed to be rapid because of the localized Ca2+ -concentration effect. In addition, the positional stabilization of Ca2+ ions within each zwitterions structure as a result of the electrostatic interaction effect by SDS molecules favors the formation of ordered HAP crystals. In the case of CTAB/SDS, the growth mechanism is more complicated because the chemical reaction of the CTAB and SDS competitively takes place. The HAP nanosheets are suggested to form by competitive reactions of the passivation and the micelle formation [29]. 4. Conclusion HAP nanopowders were synthesized using the micelle as a template system where the mixture of cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) with different ratio were used as the template in order to investigate the effect of mixed surfactant on the morphology of synthesized particles. In other experience HAP nano particles was synthesized in the
N.E. Tari et al. / Materials Chemistry and Physics 131 (2011) 132–135
presence of SDS as template. Data reveal that the overall morphology of the obtained powders at anionic-rich region (SDS:CTAB, 99:1) solution is rod like, but in the presence of cationic rich region (SDS:CTAB, 1:99) the resulted particles was sheet like which because of the interaction of surfactants with opposite charges. The resulted HAP nano particles in the presence of SDS were rod like but their morphology was less oriented than anionic-rich region. Our experience shows that the type of surfactant has great effect on the morphology of synthesized particles. References [1] S.V. Dorozhkin, M. Epple, Biological and medical significance of calcium phosphates, Angew. Chem. Int. Ed. 41 (2002) 3130. [2] G. Bezzi, G. Celotti, E. Landi, T.M.G. La Torretta, I. Sopyan, A. Tampieri, A novel sol–gel technique for hydroxyapatite preparation, Mater. Chem. Phys. 78 (2003) 816–824. [3] H. Ehrlich, P.G. Koutsoukos, K.D. Demadis, O.S. Pokrovsky, Modern strategies for the isolation of organic frameworks, Micron 40 (2009) 169–193. [4] W. Suchanek, M. Yoshimura, Processing and properties of hydroxyapatitebased biomaterials for use as hard tissue replacement implants, J. Mater. Res. 13 (1998) 94. [5] J. Torrent-Burgues, T. Boix, J. Fraile, R. Rodriguez-Clemente, Hydroxyapatite precipitation in a semibatch process, Cryst. Res. Technol. 36 (2001) 1075–1082. [6] J. Arensds, J. Chistoffersen, M.R. Chistoffersen, H. Eckert, Calcium hydroxyapatite precipitated from an aqueous solution, J. Cryst. Growth 84 (1987) 515–532. [7] Y. Wang, Sh. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Hydrothermal synthesis of hydroxyapatite nanopowders using cationic surfactant as a template, Mater. Lett. 60 (2006) 484. [8] H. Arami, M. Mohajerani, M. Mazloumi, R. Khalifehzadeh, A. Lak, S.K. Sadrnezhaad, Rapid formation of hydroxyapatite nanostrips via microwave irradiation, J. Alloys Compd. 469 (2009) 391–394. [9] R.Z. Legeros, Calcium Phosphates in Oral Biology and Medicine, Karger, Basel, Switzerland, 1991. [10] L. Yan, Y.D. Li, Z.X. Deng, J. Zhuang, X.M. Sun, Surfactant-assisted hydrothermal synthesis of hydroxyapatite nanorods, Int. J. Inorg. Mater. 3 (2001) 633. [11] D.M. Liu, T. Troczynski, W.J. Tseng, Water-based sol–gel synthesis of hydroxyapatite: process development, Biomaterials 22 (2001) 1721–1730. [12] K. Itatani, T. Tsugawa, T. Umeda, Y. Musha, I.J. Davies, S. Koda, Preparation of submicrometer-sized porous spherical hydroxyapatite agglomerates by ultrasonic spray pyrolisis technique, J. Ceram. Soc. Jpn. 118 (2010) 462–466.
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