Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Nanocrystalline hydroxyapatite prepared under various pH conditions R. Palanivelu, A. Mary Saral, A. Ruban Kumar ⇑ School of Advanced Sciences, VIT University, Vellore 632014, Tamil Nadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Ultrasonic irradiation is very effective
for HAP nanoparticle synthesis. PEG600, pH values plays a vital role in
determining the morphology of HAP. pH value 9 is suitable for HAP nano
particle synthesis.
a r t i c l e
i n f o
Article history: Received 29 January 2014 Received in revised form 1 April 2014 Accepted 7 April 2014 Available online 18 April 2014 Keywords: Biocompatibility Ultrasonic irradiation Polyethylene glycol Nanocrystalline
a b s t r a c t Hydroxyapatite (HAP) has sovereign biomedical application due to its excellent biocompatibility, chemical and crystallographic similitude with natural human bone. In this present work, we discussed about the role of pH in the synthesis of calcium phosphate compound using calcium nitrate tetrahydrate and diammonium hydrogen phosphate as starting materials by chemical precipitation method assisted with ultrasonic irradiation technique. 5% polyethylene glycol (PEG600) is added along with the precursors under various pH condition of 7, 9 and 11 respectively. The functional group analysis, crystallized size and fraction of crystallized size are confirmed using Fourier Transformation Infra-Red spectroscopy and X-ray diffraction pattern. Morphological observations are done by scanning electron microscope. The results revealed the presence of nanocrystalline hydroxyapatite at pH above 9. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Hydroxyapatite [HAP, Ca10(PO4)3(OH)2] is the well-known substitute material for damage teeth and bones of human skeletal system due to its specific properties such as biocompatibility, osteointegrity and osseous inductivity [1–3]. Nanostructured HAP offers a variety of solutions for different clinical requirements, such as drug delivery [4], hard tissue replacement [5] and bone filling cement [6]. In additionally, HAP is an important catalytic material ⇑ Corresponding author. Tel.: +91 9443107659; fax: +91 0416 2242092. E-mail addresses: (A. Ruban Kumar).
[email protected],
http://dx.doi.org/10.1016/j.saa.2014.04.014 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
[email protected]
for organic chemical reactions [7]. All these biomedical and other potential applications are dependent on the crystallize size, morphology and microstructure [8,9]. During recent years, many researchers developed different techniques used to synthesis the HAP nanoparticles including sol–gel, co-precipitation and ultrasonic irradiation, microwave irradiation method, microemulsion [10–14]. In these methods, ultrasonic irradiation process is very effective for morphology changes because of ultrasonic process induces the emulsification and homogenization effects obtained through of interaction ultrasonic waves with in a liquid medium and these two effects are responsible for morphological differences and ordered structures [15]. The ultrasonic process is another important route to fast
38
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
synthesis of nanomaterials and it creates from the acoustic cavitation physical effects [16]. On the other hand, HAP is synthesized by ultrasonic freeze-drying method to obtain the spherical particles. In this spherical shape synthesis HAP nanoparticles have better rheological properties than other conventional methods particles [17–19]. When compared to other conventional methods ultrasonic irradiation synthesis has its own importance due to the short period of time, narrow particle size distribution and small crystallize size, high purity [20]. The present work investigates the combined effect of 5% concentration of PEG600, role of pH fixing the Ca/P ratio and ultrasound irradiation on the formation of nanocrystalline HAP. A precipitation method assisted with ultrasonic horn bath is used. Study on the effect of pH, ultrasonic process on the crystalline size, morphology and functional of groups of the synthesized PEG-HAP matrixes are carried out.
Materials and methods Ca(NO3)24H2O (99% pure), (NH4)2HPO4 (99% pure) and ammonia solution, polyethylene glycol (PEG600) were procured from Merck (Germany), and used without any further purification. Hydroxyapatite was synthesized under three different pH conditions (7, 9 and 11). Initially to start with, the HAP was synthesis for neutral pH (pH = 7), with 1 M of Ca (NO3)24H2O and 5% concentration of PEG(600) dissolved in 100 ml of de-ionized water and this solution was stirred with the help of magnetic stirrer at 400 rpm for 8 h to ensure proper molecular interaction. This mixture was transformed into heavy duty beaker and place inside ultrasonic horn bath (E-Chrom ultrasonic horn, operated 22 kHz frequency) at 85% amplitude with pulse duration of 10 s ON and 2 s OFF, for the time period of 30 min. The same process was repeated for six intervals with the time gap 5 min. As the solution reaches the said temperature 100 ml of 0.6 M of (NH4)2HPO4 solution was added dropwise to the above mixture and the pH of the overall solution was maintained neutral pH (pH = 7) until a slurry was obtained, the obtained slurry was allowed to settle for a week in closed beakers at room temperature. The obtained sediment was washed with double distilled water and ethanol of HPLC grade twice to remove nitrate ions and other organic impurities, and dried in a hot air oven at 80 °C for 10 h in order to obtain a fine powder nature. The above said procedure was repeated for the pH values of 9 and 11. Powder X-ray diffraction results were carried out by Bruker D8 advanced diffractometer using source 2.2 kW Cu as anode and ceramic X-ray tube with Cu Ka radiation of wavelength (k = 0.15418 nm). The 2h range was from 20° to 55° in steps 0.02° and count time 0.2 s. The XRD spectrums obtained for the samples at various pH condition compared with ASTM standards and the crystallite size (Xs) was determined by using Debye–Scherrer formula [21].
Xs ¼
Result and discussion Fig. 1 shows the XRD pattern of synthesized HAP at three different pH conditions under the influence of 5% PEG(600), which act as organic modifier. It was evident from Fig. 1(a) which shows the diffraction peak pertaining to HAP synthesized at pH = 7 shows three crystalline phases pertaining to octa calcium phosphate (OCP) at 26.5° in (1 2 2) plane, Dicalcium phosphate (DCP) at 29.5° in (1 1 3) plane and HAP at 31.7° in (2 1 1) plane. Fig. 1(b) and (c) corresponds to the pH values of 9 and 11 respectively, it was apparent that the peaks pertaining to OCP and DCP disappear completely indicating the presence of pristine HAP, which was in accordance with the JCPDS data (no. 09-0432). The 2h values in Fig. 1(b) and (c) at 23.0°, 25.9°, 28.9° and 31.7°, 32.9°, 34.1° corresponds to miller indices planes (1 1 1), (0 0 2), (2 1 0), and (2 1 1), (3 0 0), (2 0 2) respectively. The said peaks were found to possess low intensity in Fig. 1(a), which could be attributed to the deficiency of calcium and higher crystalline size. The high intensity peaks appearing between 25° and 35° in Fig. 1(b) and (c) shows peak broadening indicating the crystallite size below 40 nm. FT-IR spectra of the as-prepared HAP powders in the presence of 5% PEG(600) with various pH condition as shown in Fig. 2(a–c). The peaks in the range of 3500 cm1 and 634 cm1 show the presence of hydroxyl functional groups (O–H) in the samples. Peak at 1030 cm1 indicates the presence of PO3 and the peak at 603 cm1 and 4 1 563 cm showed the presence of (P–O) sustained the bending vibration modes. The broaden peaks appeared in above 3100 cm1, which was clearly indicated HAP particle absorbed water molecule. The role of pH and the organic modifier could not be predicted from FTIR spectra. The surface morphology of synthesized HAP at various pH conditions like 7, 9 and 11 are taken using SEM and the micrographs shown in Figs. 3–5 respectively. The micrographs of the sample synthesized at pH = 7 revealed the presence of rod like structure. Micrographs of pH 9 and 11 show the presence spherical shape morphology at nanorange. The EDAX spectra confirmed the Ca/P as 1.67. Ultrasonic irradiation creates cavitation effects in an aqueous medium stimulate chemical reactivity producing heterogeneous reactions between Ca2+ and Po3 4 . This ultrasonic radiation process was effective on the Ph condition like 9 and 11 but not in the neutral pH 7. In the neutral pH, the reaction medium was inactive and Ca2+, PO3 4 ions releasing rate was slow from the precursor solution to form calcium deficient hydroxyapatite. Due to this the agglomeration of particles was less in pH 7. At high pH level like 9 and 11, the Ca2+ and PO3 4 ions mobility rate was high so that attracted very fast which leads to
0:9k b cos h
where b is the full width half maximum, (taken from the selected diffraction maximum intensity peaks, in radian), k is the wave length Cu Ka radiation source (k = 0.15404 nm) and h is the angle of diffraction (in degrees). Fourier transform infrared (FTIR) spectroscopy was recorded by the KBr pellet technique using SHIMADZU IRAFFINITY spectrometer for the range 400–4000 cm1; it was used to investigate the bonding nature of synthesized HAP particle. A morphological study of the obtained HAP particle was analyzed by Quanta 200 FEG scanning electron microscope (SEM/EDAX).
Fig. 1. XRD pattern of HAP powder was synthesized different pH values (a) pH 7, (b) pH 9 and (c) pH 11.
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
39
Fig. 2. FTIR spectrum of synthesized HAP under various pH values (a) pH 7, (b) pH 9 and (c) pH 11.
Fig. 3. SEM micrographs of as-synthesized HAP at different pH condition pH 7.
agglomeration. At this stage PEG(600) was act as an encapsulating agent to stop the agglomeration process and retained the nanostructures. Figs. 4 and 5 show the spherical morphology of pure hydroxyapatite with pores in the middle. PEG–OH molecule easily attract Ca2+ ions from the calcium precursor solution to form the bond of PEG–O–Ca2–O–PEG [22]. Gopi et al. reported that the synthesis of hydroxyapatite in the presence of organic modifiers like glycine with acrylic acid with help of ultrasonic irradiation method for the achieving nanocrystalline structure [11].
Cao et al. discussed the power of ultrasonic irradiation in the synthesis of hydroxyapatite. Compared to the above works, in the present report we discussed about the role of pH in synthesizing the various compounds of calcium phosphate with Ca/P ratio and also proved the presence of nanocrystalline hydroxyapatite at pH 9 and pH 11 [19]. As per our knowledge, the role pH in the synthesis of calcium phosphate with the help of ultrasonic irradiation and polyethylene glycol is first of its kind reported by us.
40
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
Fig. 4. SEM micrographs of as-synthesized HAP at different pH condition at pH 9 with EDAX.
Fig. 5. SEM micrographs of as-synthesized HAP at different pH condition at pH 11 with EDAX.
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
Conclusion Nanocrystalline hydroxyapatite was synthesized successfully in the presence of 5% PEG by chemical precipitation method assisted with ultrasonic irradiation technique. At neutral pH (pH = 7), the reaction medium was inactive and the slow interaction of Ca2+, PO3 ions leads to form calcium deficient HAP. At pH 9 and 11, 4 the mobility of Ca2+ and PO3 4 ions high than leads to faster reaction rate. The encapsulating agent PEG controlled the process of agglomeration. The XRD results confirmed the presence of various compounds of calcium phosphate with respect to Ca/P. From this observation, (i) ultrasonic irradiation method was very effective in particle size reduction, (ii) pH value 9 is suitable for HAP nanoparticle synthesis with Ca/P ratio 1.67, and (iii) both ultrasonic irradiation process and pH values play a vital role in the formation of phase pure nanoparticles. Acknowledgement The authors thankful to VIT University for providing excellent research facilities. References [1] L.L. Hench, Bioceramics, J. Am. Ceram. Soc. 81 (1998) 1705–1728. [2] I.R. Gibson, W. Bonfield, J. Biomed. Mater. Res. 59 (2002) 697–708. [3] K. Cheng, W. Weng, G. Han, P. Du, G. Shen, J. Yang, J.M.F. Ferreira, Mater. Res. Bull. 38 (2003) 89–97.
41
[4] Wojciech L. Suchaneka, Kullaiah Byrappaa, Pavel Shuka, Richard E. Rimana, Victor F. Janasb, Kevor S. TenHuisen, Biomaterials 25 (2004) 4647–4657. [5] D. Gopi, J. Indira, L. Kavitha, S. Kannan, J.M.F. Ferreira, Spectrochim. Acta, Part A 77 (2010) 545–547. [6] M.P. Roudier, H. Vesselle, L.D. True, C.S. Higano, S.M. Ott, S.H. King, R.L. Vessella, Clin. Exp. Metastasis 20 (2003) 171. [7] S. Sebti, R. Tahir, R. Nazih, A. Saber, S. Boulaajaj, Appl. Catal., A 228 (2002) 155– 159. [8] G. Kawachi, S. Sasaki, K. Nakahara, E.H. Ishida, K. Ioku, Key Eng. Mater. 309– 311 (2006) (2006) 935–938. [9] A.N. Vasiliev, E. Zlotnikov, J. GKhinast, R.E. Riman, Scripta Mater. 58 (12) (2008) 1039–1042. [10] S. Bose, S.K. Saha, J. Am. Ceram. Soc. 86 (6) (2003) 1055. [11] R. Palanivelu, A. Ruban Kumar, Spectrochim. Acta: Mol. Biomol. Spectrosc. A 127 (2014) 434–438. [12] D. Gopi, J. Indira, L. Kavitha, M. Sekar, U. Kamachi Mudali, Spectrochim. Acta: Mol. Biomol. Spectrosc. A 93 (2012) 131–134. [13] A. Ruban Kumar, S. Kalainathan, A. Mary Saral, Cryst. Res. Technol. 45 (2010) 776–778. [14] Yuxiu Sun, Hua Yang, Dongliang Tao, Ceram. Int. 37 (2011) 2917. [15] Ravi Krishna Brundavanam, Zhong-Tao Jiang, Peter Chapman, Xuan-Thi Le, Nicholas Mondinos, Derek Fawcett, Gérrard Eddy Jai Poinern, Ultrason. Sonochem. 18 (2011) 697–703. [16] J.H. Bang, K.S. Suslick, Adv. Mater. 22 (2010) 1039–1059. [17] D.M. Liu, Ceram. Int. 24 (1998) 441–446. [18] E. Mavropoulos, A.M. Rossi, N.C.C. Rocha, G.A. Soares, J.C. Moreira, G.T. Moure, Mater. Charact. 5578 (2003) 1–5. [19] Li-yun Cao, Chuan-bo Zhang, Jian-feng Huang, Mater. Lett. 59 (2005) 1902– 1906. [20] G.E. Poinern, R.K. Brundavanam, N. Mondinos, Z.T. Jiang, Ultrason. Sonochem. 16 (2009) 469–474. [21] Y.X. Pang, X. Bao, J. Eur. Ceram. Soc. 23 (2003) 1697. [22] S.J. Kalita, A. Bhardwaj, H.A. Bhatt, Mater. Sci. Eng. C 27 (2007) 441–449.
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Nanocrystalline hydroxyapatite prepared under various pH conditions R. Palanivelu, A. Mary Saral, A. Ruban Kumar ⇑ School of Advanced Sciences, VIT University, Vellore 632014, Tamil Nadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Ultrasonic irradiation is very effective
for HAP nanoparticle synthesis. PEG600, pH values plays a vital role in
determining the morphology of HAP. pH value 9 is suitable for HAP nano
particle synthesis.
a r t i c l e
i n f o
Article history: Received 29 January 2014 Received in revised form 1 April 2014 Accepted 7 April 2014 Available online 18 April 2014 Keywords: Biocompatibility Ultrasonic irradiation Polyethylene glycol Nanocrystalline
a b s t r a c t Hydroxyapatite (HAP) has sovereign biomedical application due to its excellent biocompatibility, chemical and crystallographic similitude with natural human bone. In this present work, we discussed about the role of pH in the synthesis of calcium phosphate compound using calcium nitrate tetrahydrate and diammonium hydrogen phosphate as starting materials by chemical precipitation method assisted with ultrasonic irradiation technique. 5% polyethylene glycol (PEG600) is added along with the precursors under various pH condition of 7, 9 and 11 respectively. The functional group analysis, crystallized size and fraction of crystallized size are confirmed using Fourier Transformation Infra-Red spectroscopy and X-ray diffraction pattern. Morphological observations are done by scanning electron microscope. The results revealed the presence of nanocrystalline hydroxyapatite at pH above 9. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Hydroxyapatite [HAP, Ca10(PO4)3(OH)2] is the well-known substitute material for damage teeth and bones of human skeletal system due to its specific properties such as biocompatibility, osteointegrity and osseous inductivity [1–3]. Nanostructured HAP offers a variety of solutions for different clinical requirements, such as drug delivery [4], hard tissue replacement [5] and bone filling cement [6]. In additionally, HAP is an important catalytic material ⇑ Corresponding author. Tel.: +91 9443107659; fax: +91 0416 2242092. E-mail addresses: (A. Ruban Kumar).
[email protected],
http://dx.doi.org/10.1016/j.saa.2014.04.014 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.
[email protected]
for organic chemical reactions [7]. All these biomedical and other potential applications are dependent on the crystallize size, morphology and microstructure [8,9]. During recent years, many researchers developed different techniques used to synthesis the HAP nanoparticles including sol–gel, co-precipitation and ultrasonic irradiation, microwave irradiation method, microemulsion [10–14]. In these methods, ultrasonic irradiation process is very effective for morphology changes because of ultrasonic process induces the emulsification and homogenization effects obtained through of interaction ultrasonic waves with in a liquid medium and these two effects are responsible for morphological differences and ordered structures [15]. The ultrasonic process is another important route to fast
38
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
synthesis of nanomaterials and it creates from the acoustic cavitation physical effects [16]. On the other hand, HAP is synthesized by ultrasonic freeze-drying method to obtain the spherical particles. In this spherical shape synthesis HAP nanoparticles have better rheological properties than other conventional methods particles [17–19]. When compared to other conventional methods ultrasonic irradiation synthesis has its own importance due to the short period of time, narrow particle size distribution and small crystallize size, high purity [20]. The present work investigates the combined effect of 5% concentration of PEG600, role of pH fixing the Ca/P ratio and ultrasound irradiation on the formation of nanocrystalline HAP. A precipitation method assisted with ultrasonic horn bath is used. Study on the effect of pH, ultrasonic process on the crystalline size, morphology and functional of groups of the synthesized PEG-HAP matrixes are carried out.
Materials and methods Ca(NO3)24H2O (99% pure), (NH4)2HPO4 (99% pure) and ammonia solution, polyethylene glycol (PEG600) were procured from Merck (Germany), and used without any further purification. Hydroxyapatite was synthesized under three different pH conditions (7, 9 and 11). Initially to start with, the HAP was synthesis for neutral pH (pH = 7), with 1 M of Ca (NO3)24H2O and 5% concentration of PEG(600) dissolved in 100 ml of de-ionized water and this solution was stirred with the help of magnetic stirrer at 400 rpm for 8 h to ensure proper molecular interaction. This mixture was transformed into heavy duty beaker and place inside ultrasonic horn bath (E-Chrom ultrasonic horn, operated 22 kHz frequency) at 85% amplitude with pulse duration of 10 s ON and 2 s OFF, for the time period of 30 min. The same process was repeated for six intervals with the time gap 5 min. As the solution reaches the said temperature 100 ml of 0.6 M of (NH4)2HPO4 solution was added dropwise to the above mixture and the pH of the overall solution was maintained neutral pH (pH = 7) until a slurry was obtained, the obtained slurry was allowed to settle for a week in closed beakers at room temperature. The obtained sediment was washed with double distilled water and ethanol of HPLC grade twice to remove nitrate ions and other organic impurities, and dried in a hot air oven at 80 °C for 10 h in order to obtain a fine powder nature. The above said procedure was repeated for the pH values of 9 and 11. Powder X-ray diffraction results were carried out by Bruker D8 advanced diffractometer using source 2.2 kW Cu as anode and ceramic X-ray tube with Cu Ka radiation of wavelength (k = 0.15418 nm). The 2h range was from 20° to 55° in steps 0.02° and count time 0.2 s. The XRD spectrums obtained for the samples at various pH condition compared with ASTM standards and the crystallite size (Xs) was determined by using Debye–Scherrer formula [21].
Xs ¼
Result and discussion Fig. 1 shows the XRD pattern of synthesized HAP at three different pH conditions under the influence of 5% PEG(600), which act as organic modifier. It was evident from Fig. 1(a) which shows the diffraction peak pertaining to HAP synthesized at pH = 7 shows three crystalline phases pertaining to octa calcium phosphate (OCP) at 26.5° in (1 2 2) plane, Dicalcium phosphate (DCP) at 29.5° in (1 1 3) plane and HAP at 31.7° in (2 1 1) plane. Fig. 1(b) and (c) corresponds to the pH values of 9 and 11 respectively, it was apparent that the peaks pertaining to OCP and DCP disappear completely indicating the presence of pristine HAP, which was in accordance with the JCPDS data (no. 09-0432). The 2h values in Fig. 1(b) and (c) at 23.0°, 25.9°, 28.9° and 31.7°, 32.9°, 34.1° corresponds to miller indices planes (1 1 1), (0 0 2), (2 1 0), and (2 1 1), (3 0 0), (2 0 2) respectively. The said peaks were found to possess low intensity in Fig. 1(a), which could be attributed to the deficiency of calcium and higher crystalline size. The high intensity peaks appearing between 25° and 35° in Fig. 1(b) and (c) shows peak broadening indicating the crystallite size below 40 nm. FT-IR spectra of the as-prepared HAP powders in the presence of 5% PEG(600) with various pH condition as shown in Fig. 2(a–c). The peaks in the range of 3500 cm1 and 634 cm1 show the presence of hydroxyl functional groups (O–H) in the samples. Peak at 1030 cm1 indicates the presence of PO3 and the peak at 603 cm1 and 4 1 563 cm showed the presence of (P–O) sustained the bending vibration modes. The broaden peaks appeared in above 3100 cm1, which was clearly indicated HAP particle absorbed water molecule. The role of pH and the organic modifier could not be predicted from FTIR spectra. The surface morphology of synthesized HAP at various pH conditions like 7, 9 and 11 are taken using SEM and the micrographs shown in Figs. 3–5 respectively. The micrographs of the sample synthesized at pH = 7 revealed the presence of rod like structure. Micrographs of pH 9 and 11 show the presence spherical shape morphology at nanorange. The EDAX spectra confirmed the Ca/P as 1.67. Ultrasonic irradiation creates cavitation effects in an aqueous medium stimulate chemical reactivity producing heterogeneous reactions between Ca2+ and Po3 4 . This ultrasonic radiation process was effective on the Ph condition like 9 and 11 but not in the neutral pH 7. In the neutral pH, the reaction medium was inactive and Ca2+, PO3 4 ions releasing rate was slow from the precursor solution to form calcium deficient hydroxyapatite. Due to this the agglomeration of particles was less in pH 7. At high pH level like 9 and 11, the Ca2+ and PO3 4 ions mobility rate was high so that attracted very fast which leads to
0:9k b cos h
where b is the full width half maximum, (taken from the selected diffraction maximum intensity peaks, in radian), k is the wave length Cu Ka radiation source (k = 0.15404 nm) and h is the angle of diffraction (in degrees). Fourier transform infrared (FTIR) spectroscopy was recorded by the KBr pellet technique using SHIMADZU IRAFFINITY spectrometer for the range 400–4000 cm1; it was used to investigate the bonding nature of synthesized HAP particle. A morphological study of the obtained HAP particle was analyzed by Quanta 200 FEG scanning electron microscope (SEM/EDAX).
Fig. 1. XRD pattern of HAP powder was synthesized different pH values (a) pH 7, (b) pH 9 and (c) pH 11.
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
39
Fig. 2. FTIR spectrum of synthesized HAP under various pH values (a) pH 7, (b) pH 9 and (c) pH 11.
Fig. 3. SEM micrographs of as-synthesized HAP at different pH condition pH 7.
agglomeration. At this stage PEG(600) was act as an encapsulating agent to stop the agglomeration process and retained the nanostructures. Figs. 4 and 5 show the spherical morphology of pure hydroxyapatite with pores in the middle. PEG–OH molecule easily attract Ca2+ ions from the calcium precursor solution to form the bond of PEG–O–Ca2–O–PEG [22]. Gopi et al. reported that the synthesis of hydroxyapatite in the presence of organic modifiers like glycine with acrylic acid with help of ultrasonic irradiation method for the achieving nanocrystalline structure [11].
Cao et al. discussed the power of ultrasonic irradiation in the synthesis of hydroxyapatite. Compared to the above works, in the present report we discussed about the role of pH in synthesizing the various compounds of calcium phosphate with Ca/P ratio and also proved the presence of nanocrystalline hydroxyapatite at pH 9 and pH 11 [19]. As per our knowledge, the role pH in the synthesis of calcium phosphate with the help of ultrasonic irradiation and polyethylene glycol is first of its kind reported by us.
40
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
Fig. 4. SEM micrographs of as-synthesized HAP at different pH condition at pH 9 with EDAX.
Fig. 5. SEM micrographs of as-synthesized HAP at different pH condition at pH 11 with EDAX.
R. Palanivelu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 131 (2014) 37–41
Conclusion Nanocrystalline hydroxyapatite was synthesized successfully in the presence of 5% PEG by chemical precipitation method assisted with ultrasonic irradiation technique. At neutral pH (pH = 7), the reaction medium was inactive and the slow interaction of Ca2+, PO3 ions leads to form calcium deficient HAP. At pH 9 and 11, 4 the mobility of Ca2+ and PO3 4 ions high than leads to faster reaction rate. The encapsulating agent PEG controlled the process of agglomeration. The XRD results confirmed the presence of various compounds of calcium phosphate with respect to Ca/P. From this observation, (i) ultrasonic irradiation method was very effective in particle size reduction, (ii) pH value 9 is suitable for HAP nanoparticle synthesis with Ca/P ratio 1.67, and (iii) both ultrasonic irradiation process and pH values play a vital role in the formation of phase pure nanoparticles. Acknowledgement The authors thankful to VIT University for providing excellent research facilities. References [1] L.L. Hench, Bioceramics, J. Am. Ceram. Soc. 81 (1998) 1705–1728. [2] I.R. Gibson, W. Bonfield, J. Biomed. Mater. Res. 59 (2002) 697–708. [3] K. Cheng, W. Weng, G. Han, P. Du, G. Shen, J. Yang, J.M.F. Ferreira, Mater. Res. Bull. 38 (2003) 89–97.
41
[4] Wojciech L. Suchaneka, Kullaiah Byrappaa, Pavel Shuka, Richard E. Rimana, Victor F. Janasb, Kevor S. TenHuisen, Biomaterials 25 (2004) 4647–4657. [5] D. Gopi, J. Indira, L. Kavitha, S. Kannan, J.M.F. Ferreira, Spectrochim. Acta, Part A 77 (2010) 545–547. [6] M.P. Roudier, H. Vesselle, L.D. True, C.S. Higano, S.M. Ott, S.H. King, R.L. Vessella, Clin. Exp. Metastasis 20 (2003) 171. [7] S. Sebti, R. Tahir, R. Nazih, A. Saber, S. Boulaajaj, Appl. Catal., A 228 (2002) 155– 159. [8] G. Kawachi, S. Sasaki, K. Nakahara, E.H. Ishida, K. Ioku, Key Eng. Mater. 309– 311 (2006) (2006) 935–938. [9] A.N. Vasiliev, E. Zlotnikov, J. GKhinast, R.E. Riman, Scripta Mater. 58 (12) (2008) 1039–1042. [10] S. Bose, S.K. Saha, J. Am. Ceram. Soc. 86 (6) (2003) 1055. [11] R. Palanivelu, A. Ruban Kumar, Spectrochim. Acta: Mol. Biomol. Spectrosc. A 127 (2014) 434–438. [12] D. Gopi, J. Indira, L. Kavitha, M. Sekar, U. Kamachi Mudali, Spectrochim. Acta: Mol. Biomol. Spectrosc. A 93 (2012) 131–134. [13] A. Ruban Kumar, S. Kalainathan, A. Mary Saral, Cryst. Res. Technol. 45 (2010) 776–778. [14] Yuxiu Sun, Hua Yang, Dongliang Tao, Ceram. Int. 37 (2011) 2917. [15] Ravi Krishna Brundavanam, Zhong-Tao Jiang, Peter Chapman, Xuan-Thi Le, Nicholas Mondinos, Derek Fawcett, Gérrard Eddy Jai Poinern, Ultrason. Sonochem. 18 (2011) 697–703. [16] J.H. Bang, K.S. Suslick, Adv. Mater. 22 (2010) 1039–1059. [17] D.M. Liu, Ceram. Int. 24 (1998) 441–446. [18] E. Mavropoulos, A.M. Rossi, N.C.C. Rocha, G.A. Soares, J.C. Moreira, G.T. Moure, Mater. Charact. 5578 (2003) 1–5. [19] Li-yun Cao, Chuan-bo Zhang, Jian-feng Huang, Mater. Lett. 59 (2005) 1902– 1906. [20] G.E. Poinern, R.K. Brundavanam, N. Mondinos, Z.T. Jiang, Ultrason. Sonochem. 16 (2009) 469–474. [21] Y.X. Pang, X. Bao, J. Eur. Ceram. Soc. 23 (2003) 1697. [22] S.J. Kalita, A. Bhardwaj, H.A. Bhatt, Mater. Sci. Eng. C 27 (2007) 441–449.
