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Spectroscopic investigations of nanohydroxyapatite powders synthesized by conventional and ultrasonic coupled sol–gel routes
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Spectrochimica Acta Part A 70 (2008) 1243–1245
Short communication
Spectroscopic investigations of nanohydroxyapatite powders synthesized by conventional and ultrasonic coupled sol–gel routes D. Gopi a,∗ , K.M. Govindaraju a , Collins Arun Prakash Victor a , L. Kavitha b , N. Rajendiran c a
Department of Chemistry, Periyar University, Salem 636011, Tamilnadu, India Department of Physics, Periyar University, Salem 636011, Tamilnadu, India c Department of Polymer Science, University of Madras, Chennai 600025, Tamilnadu, India b
Received 16 August 2007; received in revised form 18 January 2008; accepted 4 February 2008
Abstract In the present work, the synthesis and characterization of nano-HAP powders by a novel ultrasonic coupled sol–gel synthesis is reported. The obtained powders were sintered by conventional means at different temperatures. In addition to this, HAP powders prepared through the sol–gel method without the aid of the ultrasonic waves is also studied. The obtained nano-HAP powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. The results have proved that the nano-HAP powders synthesized by ultrasonic coupled sol–gel synthesis showed remarkable reduction in the particle size when compared with the conventional sol–gel method and hence these powders could be used as a coating material in biomedical applications. © 2008 Elsevier B.V. All rights reserved. Keywords: Biomaterials; Hydroxyapatite; Nanoparticle; Sintering; Ultrasonic
1. Introduction In recent years, hydroxyapatite (HAP, Ca10 (PO4 )6 (OH)2 ) nanoparticles had been studied with a great deal of interest in the biomedical applications due to its excellent osteophilic properties [1–7]. Synthetic nanohydroxyapatite finds its potential applications in bone, tooth replacement and drug delivery systems [8–11]. Earlier research on the development of HAP was mainly focused on controlling the stoichiometry of the products, and now with the development of nanotechnologies, a considerable interest is shown in controlling the morphology and size of HAP. Therefore, it is believed that the synthesis of nanoscale HAP with suitable size and morphology will certainly facilitate its clinical applications [12]. The properties of HAP prepared by various methods differ in their properties mainly due to the synthetic procedures, which in turn directly affect its bioactivity. Hence, a synthesis of pure HAP with controlled size and morphology is highly desirable. It has been well demonstrated that
∗
Corresponding author. Tel.: +91 427 2345766; fax: +91 427 2345124. E-mail address: [email protected] (D. Gopi).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.02.015
the sol–gel process offers good mixing of the starting materials and excellent chemical homogeneity of the resulting HAP [13] in comparison with conventional methods such as solid state reactions [14], wet precipitation [15] and hydrothermal synthesis [16]. Many researchers have observed that sintering method has provided a very versatile route for the preparation of uniform sized nano-HAP particles and enhanced densification of the nanoparticles due to greater surface area which in turn could improve the fracture toughness and other mechanical properties [17]. Moreover, nano-HAP is also expected to have a better bioactivity and thereby capable of interacting with the surrounding bone tissues [18] and bone formation which is known as osteo-induction. This paper deals with the preparation and spectral characterization of nano-HAP powders through an ultrasonic coupled sol–gel technique as a novel route for the synthesis. In addition to this HAP powders were also prepared by conventional sol–gel method without the ultrasonic irradiation and the results of two methods are compared. The present ultrasonic coupled sol–gel method is proved to be an effective method to prepare the nano-HAP powders with uniform size and distribution.
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D. Gopi et al. / Spectrochimica Acta Part A 70 (2008) 1243–1245
2. Materials and methods Calcium nitrate (Ca(NO3 )2 ·4H2 O), diammonium hydrogen phosphate ((NH4 )2 HPO4 ) and ethanol were used in the synthesis. All the chemicals used were of analytical grade and the solutions were prepared using deionized water. Diammonium hydrogen phosphate was dissolved in 1:1 ethanol/distilled water mixture and a stoichiometric amount of dissolved calcium nitrate was subsequently added dropwise into the hydrolyzed phosphate sol with continuous stirring for 1 h at 60 ◦ C. The two solutions were mixed in a Ca/P molar ratio of 1.67. The as-formed gel was aged for 16 h, washed with distilled water, dried and sintered at 300, 600 and 900 ◦ C in a muffle furnace for 4 h. In ultrasonically coupled synthesis, the gel formed by mixing the precursor solutions was allowed for ultrasonic agitation for 1 h at 60 ◦ C. The resulting powders were then washed, dried and sintered at 300, 600 and 900 ◦ C for 4 h to produce nano-HAP powders. Fourier transform infrared spectrometer (model: PerkinElmer 1600) was used in the wave number range of 4000–400 cm−1 to obtain the characteristic peaks of HAP powders. The structure and size of the HAP powder samples were characterized by X-ray diffraction (XRD) spectrometer (model: Bruker D8 Advance, Germany) and the morphology and size of the HAP powders was investigated by scanning electron microscope (SEM, JEOL, Japan). Fig. 2. The XRD patterns of nano-HAP powders synthesized by (i) sol–gel method and sintered for 4 h at (a) 300 ◦ C, (b) 600 ◦ C, and (c) 900 ◦ C; (ii) ultrasonic coupled sol–gel method and sintered for 4 h at (d) 300 ◦ C, (e) 600 ◦ C, and (f) 900 ◦ C.
3. Results and discussion
Fig. 1. The FT-IR spectra of nano-HAP powders synthesized by (i) sol–gel method and sintered for 4 h at (a) 300 ◦ C, (b) 600 ◦ C, and (c) 900 ◦ C; (ii) ultrasonic coupled sol–gel method and sintered for 4 h at (d) 300 ◦ C, (e) 600 ◦ C, and (f) 900 ◦ C.
Fourier transform infrared spectroscopy (FT-IR) spectra recorded for all the six samples are shown in Fig. 1(a–f). All the six spectra showed the formation of HAP as evident from the peaks. The bands at 1031 and 1097 cm−1 were due to the ν3 mode of phosphate group. The peak at 469 cm−1 was assigned to the ν2 phosphate mode and the bands at 563 and 603 cm−1 were due the ν4 phosphate mode. The spectrum also shows the ν1 PO4 3− mode peaks at 966 cm−1 [19]. The absorption band at 1635 cm−1 reflects H2 O bending mode and a broad peak at 3425 cm−1 indicates the adsorbed water. The OH stretching and bending modes are indicated by the peaks at 3567 and 637 cm−1 , respectively. The peaks found in the region of 1410–1450 cm−1 were due to carbonate groups, which is formed due to the entrapment of atmospheric carbondioxide during the stirring and calcination steps of the reaction. The FT-IR spectra obtained by the ultrasonic coupled method Fig. 1(f) shows no traces of impurities indicating that the synthesized powder was pure [20]. The XRD patterns of the HAP powders synthesized by conventional sol–gel method sintered at different temperatures are shown in Fig. 2(a–c). At low temperatures the spectrum showed some phases other than HAP such as TCP but on increasing the temperature the impurity phases gradually disappeared at 900 ◦ C. HAP powders obtained by ultrasonic coupled
D. Gopi et al. / Spectrochimica Acta Part A 70 (2008) 1243–1245
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Hence, this novel method is proved to be a successful way to synthesize nano-HAP powders. 4. Conclusions In the present work, the nano-HAP powders were achieved by ultrasonic coupled sol–gel synthesis. Presence of characteristic peaks of the phosphate and OH groups in FT-IR spectrum and the XRD data obtained all confirmed the formation of nano-HAP powders. Comparing the results of conventional and ultrasonically coupled synthesis of nano-HAP, it can be known that the nano-structured material synthesized by ultrasonic coupled synthesis possessed improved surface characteristics in terms of their size and morphologies. Moreover, sintering effects at various temperatures improved the phase purity and surface properties thereby making the as-synthesized material more compatible for bioactive coatings. Works on coating these powders over the implant surface and characterization of these coatings are yet to be carried out. Hence it could be concluded that this type of synthesis would always provide useful insights for designing good bioactive nano-HAP coatings with improved performance for the orthopedic implants. References
Fig. 3. The SEM micrographs of nano-HAP powder synthesized by (a) conventional sol–gel method and sintered at 900 ◦ C for 4 h. (b) Ultrasonic coupled sol–gel method and sintered at 900 ◦ C for 4 h.
reaction showed wide and high peaks indicating that the particle size is very small with good crystallinity (Fig. 2(d–f)). Compared with the conventional route, the ultrasonic coupled method is advantageous, as phase pure substance could be obtained in fairly quick time. The obtained patterns also matched well with the standard diffraction data (JCPDS No. 09-0432). Thus nano-HAP powders with superior quality were achieved by ultrasonic coupled sol–gel method at 900 ◦ C sintering temperature. The synthesized nano-HAP powder was also analysed by SEM technique. By comparing the micrographs of the nanoHAP powders obtained by conventional and ultrasonic coupled methods sintered at 900 ◦ C (Fig. 3(a and b)), it could be inferred that powders obtained through the ultrasonic coupled synthesis possesses improved structural features. Furthermore, the powders obtained through ultrasonic coupled method were of reduced and uniform size when compared with the powders prepared by conventional sol–gel method. The particle size obtained by the conventional sol–gel method was found to be in the range of 120–200 nm or even higher while the ultrasonic coupled synthesis resulted in powders of size ranging from 35 to 80 nm.
[1] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487–1570. [2] P. Layrolle, A. Ito, T. Tateishi, J. Am. Ceram. Soc. 81 (1998) 1421– 1428. [3] J.D. Currey, The Mechanical Adaptations of Bones, Princeton University Press, 1984. [4] S.F. Hulber, J.C. Bokros, L.L. Hench, J. Wilson, G. Heimke, High Tech Ceramics, Elsevier, Amsterdam, 1987, pp. 189–213. [5] D.C.R. Hardy, P. Frayssinet, Eur. J. Orthop. Surg. Traumatol. 9 (1999) 75–81. [6] R.M. Pilliar, M.J. Filiaggi, J.D. Wells, M.D. Grynpas, R.A. Kandel, Biomaterials 22 (2001) 963–972. [7] S.H. Maxian, J.P. Zawadsky, M.G. Dunn, J. Biomed. Mater. Res. 27 (1993) 111–117. [8] P.R. Menon, S.A. Napper, D.P. Mukherjee, Proceedings of the 1995 14th Southern Biomedical Engineering Conference, Shreveport, Louisiana, April, 1995, pp. 95–97. [9] M.L. Spence, M.G. McCord, Proceedings of the 1997 16th Southern Biomedical Engineering Conference, April, Mississippi, USA, 1997, pp. 257–259. [10] Y. Zhang, M.Q. Zhang, J. Biomed. Mater. Res. 55 (2001) 304–312. [11] Y. Zhang, M.Q. Zhang, J. Biomed. Mater. Res. 62 (2002) 378–386. [12] J.C. Elliott, E. Bres, P. Hardouin, Calcium Phosphate Materials, Fundamentals, Sauramps Medical, Montpellier, 1998, pp. 25–66. [13] C.J. Brinker, G.W. Scherrer, Sol–Gel Science: The Physics and Chemistry of Sol–Gel Processing, Academic Press, San Diego, 1990. [14] S.-H. Rhee, Biomaterials 23 (2002) 1147–1152. [15] Y. Liu, D. Hou, G. Wang, Mater. Chem. Phys. 86 (2004) 69–73. [16] Y. Wang, S. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Mater. Lett. 60 (2006) 1484–1487. [17] S. Nath, B. Basu, A. Sinha, Trends Biomater. Artif. Organs 19 (2006) 93–98. [18] T.J. Webster, C. Ergun, R.H. Doremus, R.W. Siegel, R. Bizios, Biomaterials 22 (2001) 1327–1333. [19] K.C. Blakeslee, R.A. Condrate, J. Am. Ceram. Soc. 54 (1971) 559–563. [20] A. Jillavenkatesa, R.A. Condrate Sr., J. Mater. Sci. 33 (1998) 4111– 4119.
Spectrochimica Acta Part A 70 (2008) 1243–1245
Short communication
Spectroscopic investigations of nanohydroxyapatite powders synthesized by conventional and ultrasonic coupled sol–gel routes D. Gopi a,∗ , K.M. Govindaraju a , Collins Arun Prakash Victor a , L. Kavitha b , N. Rajendiran c a
Department of Chemistry, Periyar University, Salem 636011, Tamilnadu, India Department of Physics, Periyar University, Salem 636011, Tamilnadu, India c Department of Polymer Science, University of Madras, Chennai 600025, Tamilnadu, India b
Received 16 August 2007; received in revised form 18 January 2008; accepted 4 February 2008
Abstract In the present work, the synthesis and characterization of nano-HAP powders by a novel ultrasonic coupled sol–gel synthesis is reported. The obtained powders were sintered by conventional means at different temperatures. In addition to this, HAP powders prepared through the sol–gel method without the aid of the ultrasonic waves is also studied. The obtained nano-HAP powders were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and scanning electron microscopic (SEM) techniques. The results have proved that the nano-HAP powders synthesized by ultrasonic coupled sol–gel synthesis showed remarkable reduction in the particle size when compared with the conventional sol–gel method and hence these powders could be used as a coating material in biomedical applications. © 2008 Elsevier B.V. All rights reserved. Keywords: Biomaterials; Hydroxyapatite; Nanoparticle; Sintering; Ultrasonic
1. Introduction In recent years, hydroxyapatite (HAP, Ca10 (PO4 )6 (OH)2 ) nanoparticles had been studied with a great deal of interest in the biomedical applications due to its excellent osteophilic properties [1–7]. Synthetic nanohydroxyapatite finds its potential applications in bone, tooth replacement and drug delivery systems [8–11]. Earlier research on the development of HAP was mainly focused on controlling the stoichiometry of the products, and now with the development of nanotechnologies, a considerable interest is shown in controlling the morphology and size of HAP. Therefore, it is believed that the synthesis of nanoscale HAP with suitable size and morphology will certainly facilitate its clinical applications [12]. The properties of HAP prepared by various methods differ in their properties mainly due to the synthetic procedures, which in turn directly affect its bioactivity. Hence, a synthesis of pure HAP with controlled size and morphology is highly desirable. It has been well demonstrated that
∗
Corresponding author. Tel.: +91 427 2345766; fax: +91 427 2345124. E-mail address: [email protected] (D. Gopi).
1386-1425/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2008.02.015
the sol–gel process offers good mixing of the starting materials and excellent chemical homogeneity of the resulting HAP [13] in comparison with conventional methods such as solid state reactions [14], wet precipitation [15] and hydrothermal synthesis [16]. Many researchers have observed that sintering method has provided a very versatile route for the preparation of uniform sized nano-HAP particles and enhanced densification of the nanoparticles due to greater surface area which in turn could improve the fracture toughness and other mechanical properties [17]. Moreover, nano-HAP is also expected to have a better bioactivity and thereby capable of interacting with the surrounding bone tissues [18] and bone formation which is known as osteo-induction. This paper deals with the preparation and spectral characterization of nano-HAP powders through an ultrasonic coupled sol–gel technique as a novel route for the synthesis. In addition to this HAP powders were also prepared by conventional sol–gel method without the ultrasonic irradiation and the results of two methods are compared. The present ultrasonic coupled sol–gel method is proved to be an effective method to prepare the nano-HAP powders with uniform size and distribution.
1244
D. Gopi et al. / Spectrochimica Acta Part A 70 (2008) 1243–1245
2. Materials and methods Calcium nitrate (Ca(NO3 )2 ·4H2 O), diammonium hydrogen phosphate ((NH4 )2 HPO4 ) and ethanol were used in the synthesis. All the chemicals used were of analytical grade and the solutions were prepared using deionized water. Diammonium hydrogen phosphate was dissolved in 1:1 ethanol/distilled water mixture and a stoichiometric amount of dissolved calcium nitrate was subsequently added dropwise into the hydrolyzed phosphate sol with continuous stirring for 1 h at 60 ◦ C. The two solutions were mixed in a Ca/P molar ratio of 1.67. The as-formed gel was aged for 16 h, washed with distilled water, dried and sintered at 300, 600 and 900 ◦ C in a muffle furnace for 4 h. In ultrasonically coupled synthesis, the gel formed by mixing the precursor solutions was allowed for ultrasonic agitation for 1 h at 60 ◦ C. The resulting powders were then washed, dried and sintered at 300, 600 and 900 ◦ C for 4 h to produce nano-HAP powders. Fourier transform infrared spectrometer (model: PerkinElmer 1600) was used in the wave number range of 4000–400 cm−1 to obtain the characteristic peaks of HAP powders. The structure and size of the HAP powder samples were characterized by X-ray diffraction (XRD) spectrometer (model: Bruker D8 Advance, Germany) and the morphology and size of the HAP powders was investigated by scanning electron microscope (SEM, JEOL, Japan). Fig. 2. The XRD patterns of nano-HAP powders synthesized by (i) sol–gel method and sintered for 4 h at (a) 300 ◦ C, (b) 600 ◦ C, and (c) 900 ◦ C; (ii) ultrasonic coupled sol–gel method and sintered for 4 h at (d) 300 ◦ C, (e) 600 ◦ C, and (f) 900 ◦ C.
3. Results and discussion
Fig. 1. The FT-IR spectra of nano-HAP powders synthesized by (i) sol–gel method and sintered for 4 h at (a) 300 ◦ C, (b) 600 ◦ C, and (c) 900 ◦ C; (ii) ultrasonic coupled sol–gel method and sintered for 4 h at (d) 300 ◦ C, (e) 600 ◦ C, and (f) 900 ◦ C.
Fourier transform infrared spectroscopy (FT-IR) spectra recorded for all the six samples are shown in Fig. 1(a–f). All the six spectra showed the formation of HAP as evident from the peaks. The bands at 1031 and 1097 cm−1 were due to the ν3 mode of phosphate group. The peak at 469 cm−1 was assigned to the ν2 phosphate mode and the bands at 563 and 603 cm−1 were due the ν4 phosphate mode. The spectrum also shows the ν1 PO4 3− mode peaks at 966 cm−1 [19]. The absorption band at 1635 cm−1 reflects H2 O bending mode and a broad peak at 3425 cm−1 indicates the adsorbed water. The OH stretching and bending modes are indicated by the peaks at 3567 and 637 cm−1 , respectively. The peaks found in the region of 1410–1450 cm−1 were due to carbonate groups, which is formed due to the entrapment of atmospheric carbondioxide during the stirring and calcination steps of the reaction. The FT-IR spectra obtained by the ultrasonic coupled method Fig. 1(f) shows no traces of impurities indicating that the synthesized powder was pure [20]. The XRD patterns of the HAP powders synthesized by conventional sol–gel method sintered at different temperatures are shown in Fig. 2(a–c). At low temperatures the spectrum showed some phases other than HAP such as TCP but on increasing the temperature the impurity phases gradually disappeared at 900 ◦ C. HAP powders obtained by ultrasonic coupled
D. Gopi et al. / Spectrochimica Acta Part A 70 (2008) 1243–1245
1245
Hence, this novel method is proved to be a successful way to synthesize nano-HAP powders. 4. Conclusions In the present work, the nano-HAP powders were achieved by ultrasonic coupled sol–gel synthesis. Presence of characteristic peaks of the phosphate and OH groups in FT-IR spectrum and the XRD data obtained all confirmed the formation of nano-HAP powders. Comparing the results of conventional and ultrasonically coupled synthesis of nano-HAP, it can be known that the nano-structured material synthesized by ultrasonic coupled synthesis possessed improved surface characteristics in terms of their size and morphologies. Moreover, sintering effects at various temperatures improved the phase purity and surface properties thereby making the as-synthesized material more compatible for bioactive coatings. Works on coating these powders over the implant surface and characterization of these coatings are yet to be carried out. Hence it could be concluded that this type of synthesis would always provide useful insights for designing good bioactive nano-HAP coatings with improved performance for the orthopedic implants. References
Fig. 3. The SEM micrographs of nano-HAP powder synthesized by (a) conventional sol–gel method and sintered at 900 ◦ C for 4 h. (b) Ultrasonic coupled sol–gel method and sintered at 900 ◦ C for 4 h.
reaction showed wide and high peaks indicating that the particle size is very small with good crystallinity (Fig. 2(d–f)). Compared with the conventional route, the ultrasonic coupled method is advantageous, as phase pure substance could be obtained in fairly quick time. The obtained patterns also matched well with the standard diffraction data (JCPDS No. 09-0432). Thus nano-HAP powders with superior quality were achieved by ultrasonic coupled sol–gel method at 900 ◦ C sintering temperature. The synthesized nano-HAP powder was also analysed by SEM technique. By comparing the micrographs of the nanoHAP powders obtained by conventional and ultrasonic coupled methods sintered at 900 ◦ C (Fig. 3(a and b)), it could be inferred that powders obtained through the ultrasonic coupled synthesis possesses improved structural features. Furthermore, the powders obtained through ultrasonic coupled method were of reduced and uniform size when compared with the powders prepared by conventional sol–gel method. The particle size obtained by the conventional sol–gel method was found to be in the range of 120–200 nm or even higher while the ultrasonic coupled synthesis resulted in powders of size ranging from 35 to 80 nm.
[1] L.L. Hench, J. Am. Ceram. Soc. 74 (1991) 1487–1570. [2] P. Layrolle, A. Ito, T. Tateishi, J. Am. Ceram. Soc. 81 (1998) 1421– 1428. [3] J.D. Currey, The Mechanical Adaptations of Bones, Princeton University Press, 1984. [4] S.F. Hulber, J.C. Bokros, L.L. Hench, J. Wilson, G. Heimke, High Tech Ceramics, Elsevier, Amsterdam, 1987, pp. 189–213. [5] D.C.R. Hardy, P. Frayssinet, Eur. J. Orthop. Surg. Traumatol. 9 (1999) 75–81. [6] R.M. Pilliar, M.J. Filiaggi, J.D. Wells, M.D. Grynpas, R.A. Kandel, Biomaterials 22 (2001) 963–972. [7] S.H. Maxian, J.P. Zawadsky, M.G. Dunn, J. Biomed. Mater. Res. 27 (1993) 111–117. [8] P.R. Menon, S.A. Napper, D.P. Mukherjee, Proceedings of the 1995 14th Southern Biomedical Engineering Conference, Shreveport, Louisiana, April, 1995, pp. 95–97. [9] M.L. Spence, M.G. McCord, Proceedings of the 1997 16th Southern Biomedical Engineering Conference, April, Mississippi, USA, 1997, pp. 257–259. [10] Y. Zhang, M.Q. Zhang, J. Biomed. Mater. Res. 55 (2001) 304–312. [11] Y. Zhang, M.Q. Zhang, J. Biomed. Mater. Res. 62 (2002) 378–386. [12] J.C. Elliott, E. Bres, P. Hardouin, Calcium Phosphate Materials, Fundamentals, Sauramps Medical, Montpellier, 1998, pp. 25–66. [13] C.J. Brinker, G.W. Scherrer, Sol–Gel Science: The Physics and Chemistry of Sol–Gel Processing, Academic Press, San Diego, 1990. [14] S.-H. Rhee, Biomaterials 23 (2002) 1147–1152. [15] Y. Liu, D. Hou, G. Wang, Mater. Chem. Phys. 86 (2004) 69–73. [16] Y. Wang, S. Zhang, K. Wei, N. Zhao, J. Chen, X. Wang, Mater. Lett. 60 (2006) 1484–1487. [17] S. Nath, B. Basu, A. Sinha, Trends Biomater. Artif. Organs 19 (2006) 93–98. [18] T.J. Webster, C. Ergun, R.H. Doremus, R.W. Siegel, R. Bizios, Biomaterials 22 (2001) 1327–1333. [19] K.C. Blakeslee, R.A. Condrate, J. Am. Ceram. Soc. 54 (1971) 559–563. [20] A. Jillavenkatesa, R.A. Condrate Sr., J. Mater. Sci. 33 (1998) 4111– 4119.