Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications

Materials Science and Engineering C 72 (2017) 472–480

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Materials Science and Engineering C journal homepage: www.elsevier.com/locate/msec

Facile microwave-assisted synthesis of Te-doped hydroxyapatite nanorods and nanosheets and their characterizations for bone cement applications I.S. Yahia a,b, Mohd Shkir a,⁎, S. AlFaify a, V. Ganesh a, H.Y. Zahran a,b, Mona Kilany c,d a

Advanced Functional Materials & Optoelectronics Laboratory (AFMOL), Department of Physics, Faculty of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia Nano-Science & Semiconductor Labs, Metallurgical Lab., Department of Physics, Faculty of Education, Ain Shams University, Roxy, 11757 Cairo, Egypt c Department of Biology, Faculty of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia d Department of Microbiology, National Organization for Drug Control and Research (NODCAR), Cairo, Egypt b

a r t i c l e

i n f o

Article history: Received 22 June 2016 Received in revised form 19 September 2016 Accepted 21 November 2016 Available online 23 November 2016 Keywords: Hydroxyapatite Nano-rods XRD/FE-SEM Linear absorption coefficient FTIR/Raman spectroscopy Dielectric properties Biomaterial

a b s t r a c t In this work, the authors have fabricated the nanorods and nanosheets of pure and Te-doped HAp with different Te concentrations (0.04, 0.08, 0.16, 0.24 wt%) by microwave-assisted technique at low temperature. The crystallite size, degree of crystallinity and lattice parameters are calculated. FE-SEM study confirms that the fabricated nanostructures are nanorods of diameter about 10 nm in undoped and at low concentration of Te doping. However, at and higher concentration, it becomes nanosheets of about 5 nm thickness. X-ray diffraction, FT-IR and FTRaman studies shows that the prepared products are of HAp and Te has been successfully incorporated. From EDX the Ca/P molar ratio of the pure HAp is about 1.740, while this ratio for 0.04, 0.08, 0.16, 0.24 wt% Te doped is about 1.53, 1.678, 1.724, 1.792, respectively. Crystallite size was found to be increased with Te doping from 15 nm to 62 nm. The value of dielectric constant is found to be enhanced at higher concentrations of Te. The values of linear absorption coefficient were also determined and show that the prepared material with Te doping is more absorbable than pure and will be highly applicable in radiation detection applications. Furthermore, the antimicrobial potential of pure and Te doped HAp was examined against some Gram- negative and positive bacteria and fungi by agar disk diffusion method. The results demonstrated that the antimicrobial activity of Te doped HAp is stronger than that of pure HAp where it exhibited the highest activity against Bacillus subtilis N Candida albicans N Shigella dysenteriae. © 2016 Elsevier B.V. All rights reserved.

1. Introduction Hydroxyapatite (HA) is an excellent non-toxic material with uncountable applications in the field of biomedical as well as optoelectronics. It has many applications in retarding the multiplication of cancer cells, as implant biomedical materials in orthopedic and dental treatments, prostheses, repair of bone defects, bone augmentation, coating the metallic implants and filling of bone gaps and shows excellent biocompatibility, bioactivity osteoconductivity and affinity etc. [1–11]. It was also used as catalyst in chromatography or gas sensor, water purification, luminescence, fertilizers production and drug carrier [12,13]. It is well known that HAp has a structure that facilitate some ion incorporations such as K+, Ag+, Na+, Mn2+, Ni2, Cu2, Co2, Sr2, Ba2, Pb2, Cd2, Y3, La3, Fe2, Zn2, Mg2, Ce3, Al3, P, Si, V, Cr, (CO23 −) and F−, Cl−, O2−, OH−, Br− can substitute Ca2 +, (PO34 −) and (OH−) ions, respectively [14–21] in to its crystalline lattice that results in remarkable change of mechanical and biological properties. HAp crystallize in hexagonal ⁎ Corresponding author. E-mail addresses: [email protected], [email protected] (M. Shkir).

http://dx.doi.org/10.1016/j.msec.2016.11.074 0928-4931/© 2016 Elsevier B.V. All rights reserved.

crystal structure with lattice parameters a = b = 0.9418 nm, c = 0.6884 nm with unit cell volume V = 0.5288 nm3 [22–24]. Several reports are available on the preparation of HAp nanostructures by different methods such as chemical co-precipitation, sol–gel process, spraypyrolysis, hydrothermal synthesis, emulsion or micro-emulsion routes, gel method, microwave [25–32]. The sol–gel method is useful for the synthesizing of HAp, because this method has many advantages, containing high product purity and low synthesis temperature [23,26,33, 34]. However, the microwave technique has the advantage of homogenous internal and volumetric heating at rapid rates [35–41] and found to be better than conventional heating to achieve high crystalline nanostructure materials. As per the current available literature there is no study has been made on Te doped HAp so far. However, the Te/TeO2 has been widely doped in different kind of materials such as SnO2, ZnO, glassy systems etc. and found to enhance their key properties for future device applications [42–45]. Hence, due to such influence of Te/TiO2 on the key properties we have also aimed to fabricate the nanostructures of HAp with different concentrations of Te-doping (0.04, 0.08, 0.16, 0.24 wt%) via a microwave heating process - a rapid and cost effective route [35,36,

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46] and study its effect on crystallinity, crystalline structure, phase composition, morphology, vibrational, dielectric and radiation detection and biomedical properties etc. and the obtained results are discussed here. The increases of morbidity and mortality caused by pathogenic bacteria and fungi are very high and researchers worldwide are searching new alternative therapies and new drugs to reduce these infections. New therapeutic and prophylactic strategies are urgently required to prevent microbial infection. HAp represent a new generation of antimicrobial materials [47–51]. Therefore, it is expected that a hybrid material constituted of Te doped hydroxyapatite will exhibit improved mechanical, biological, and antimicrobial properties, thus making it an excellent candidate for numerous biomedical applications. 2. Experimental details 2.1. Materials For the fabrication of Te doped HAp nanostructures, Calcium nitrate tetrahydrate [Ca(NO3)2. 4H2O], ammonium hydrogen phosphate ADP (NH4H2PO4), cetyltrimethylammonium bromide (CTAB), ammonium hydroxide (NH4OH) and potassium tellurite (K2TeO3) were purchased from Sigma Aldrich and used without further purifications. 2.2. Synthesis of Te doped HAp nanostructure For the synthesis of undoped and Te doped HAp nanostructures, we have used the following procedure: 1) In 100 ml of double distilled water, the calculated amount of 0.5 M calcium nitrate tetrahydrate [Ca(NO3)2. 4H2O] and 0.3 M ammonium hydrogen phosphate ADP (NH4H2PO4) were dissolved separately in two beakers by continuous stirring (800 rpm) at constant temperature i.e. 90 °C. In the prepared solution of Calcium nitrate tetrahydrate, ADP was added gradually. Further a surfactant named cetyltrimethyl ammonium bromide (CTAB) was added to the prepared solution for controlling the structure morphology of HAp. To set the pH about 10 of the readied solution we have added the ammonium hydroxide by continuous stirring for at least 1 h and one more hour stirring was done to achieve the white precipitate. The different concentrations (0.04, 0.08, 0.16, 0.24 wt%) of Te doping have been done in the prepared solution in terms of potassium tellurite. The finally prepared solutions were subjected to microwave irradiation to get the complete synthesis of undoped and Te doped HAp. For microwave irradiation the Anton Paar microwave [Multiwave Pro 1500 W (IEC 705)] operated at fixed power ~700 watt and temperature 145 °C for 20 min has been used to have fast and rapid thermal shock to form the exact crystalline phase of HAp. At the end of the microwave process all the prepared precipitates were cleaned using distilled water and alcohol for several times to remove any unwanted impurity. Finally the as-prepared powders were dried at 100 °C for 24 h. 2.3. Characterization methods X-ray diffraction patterns of undoped and Te doped HAp nanostructure samples were carried out using a X-ray diffractometer of Shimadzu LabX XRD-6000 with CuKα (λ = 1.5406 Å) radiation, operated at 30 mA and 40 kV at the scan rate of 0.2°/m over the angular range of 10° to 90° at 300 K. The recorded XRD data was analyzed using the Shimadzu software attached with XRD and pdf2 library for the matching process. The morphology of the fabricated nanostructures was studied using a field emission scanning electron microscope (FE-SEM) (JSM-7500 F; JEOLJapan). FT-IR spectra was also recorded using THERMO SCIENTIFIC, DXR FT-IR spectrometer by KBr pallet method in the wavenumber range of 4000–400 cm− 1. The FT-Raman spectra was also recorded using a THERMO SCIENTIFIC, DXR FT-Raman spectrometer accompanied with microscope in the wavenumber range of 1500–50 cm− 1, the excitation wavelength was 532 nm and laser power 2 mW. The dielectric constant, loss and ac conductivity measurement were

473

performed using Keithley 4200-SCS characterization system in the high frequency range from 3 kHz to 10 MHz at room temperature. The linear absorption coefficient was determined by measuring the values of the initial intensity of radiation before attenuation (Io) and the final intensity after attenuation (I) using NaI detector 1.5 PX 1.5/2.0 IV (REXON, components, Inc., USA) attached with universal computer spectrometer UCS-20. In this measurement, we have placed the detector in such way between radioactive point source and the detector window so that the detection of any radiation coming directly from the source and scattered from the surroundings can be minimized, to remove the scattered radiation we have designed Lead collimator. The gamma ray source (Cs-137) of energy (662 keV) and (Am-241) of energy (59.5 keV) were used for irradiating the samples for 100 s duration of time at room temperature. The antimicrobial activity of pure hydroxyapatite and telluriumdoped hydroxyapatite was detected by agar disk diffusion method using Müller-Hinton agar medium [32]. All materials were steam sterilized at 115 °C for 15 min. A volume of 15 ml sterile culture medium was evenly inoculated with Gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus and Micrococcus sp.), Gram-negative bacteria (P. aeruginosa, Klebseilla sp. and Shigella dysenteriae) and Candida albicans. Twenty-five mg disks of pure hydroxyapatite and tellurium-doped hydroxyapatite were put onto the Petri dishes surface. Then after the Petri dishes were incubated at 37 °C for 24 h. The inhibition zones were measured in millimeter and the assay was performed in triplicate. 3. Results and discussion 3.1. Nanostructure structure analysis To confirm the nanostructure morphology and elemental composition of pure and Te-doped HAp the FE-SEM/EDS micrographs/patterns were captured and shown in Fig. 1. The presence of Te has been confirmed from EDS pattern. SEM analysis confirms that the fabricated nanostructure of pure and 0.04% Te-doped is nanorods of diameter about 10 nm, however for 0.08, 0.16 and 0.24% Te doped it is nanosheets of thickness about 5 nm. The Ca/P molar ratio of the pure HAp is about 1.740, while this ratio for (0.04, 0.08, 0.16, 0.24 wt%) Te doped is about 1.53, 1.678, 1.724 and 1.792, respectively. The change in the ratio was observed with the addition of Te, this is also may be due to ionic substitution and may attributed to crystal defect. The obtained results are in good agreement with the earlier reports [52]. 3.2. Phase and crystal structure analyses Fig. 2 shows the recorded X-ray diffraction patterns of all the prepared nanostructures. The X-ray diffraction data was used to confirm the crystalline structure, crystalline phase and crystallinity of pure and Te-doped HAp nanostructures. From this figure, it is clear that the prepared nanostructure are well crystalline and has Hydroxyapatite phase, with hexagonal crystal structure and found in good correlation with JCPDS# 09-0432 and also confirmed from the peaks observed in all diffraction patterns correspond to the (100), (002), (211), (300), (202), (310), (222), (213), (004) and (304) planes, respectively. The main phase of Hydroxyapatite was observed in all the samples however with Te doping some peaks of TeO2 (JCPDS# 11-0693) were also observed due to doping at higher concentrations only. The diffraction peaks of TeO2 confirm the inclusion of Te in the crystalline matrix of HAp. The lattice parameters (a and c) and unit cell volume (V) of the prepared nanostructure were determined using the following relations [53]: 1 2

d

2

¼

4 h þ hk þ k 3 a2

2

!

2

þ

l c2

ð1Þ

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Fig. 1. (a) EDX patterns of Te doped and (b) SEM micrographs of undoped and Te doped HAp.

V ¼ 0:866 a2 c

ð2Þ

where, the symbols are having their usual meanings. The calculated values of the crystal lattice parameters of undoped and Te-doped HAp nanostructures are listed in Table 1 and found to be in close

approximation with earlier reports [18,54]. The degree of crystallinity (Xc) was obtained using the following eq. [55]:

X c ¼ 1−

V 112 =300 I300

ð3Þ

I.S. Yahia et al. / Materials Science and Engineering C 72 (2017) 472–480

70

# (114)

# (204)

0.24% Te # (220)

80

90

* Ca5(PO4)3OH

#(204)

The calculated crystallite size, dislocation density and lattice strain for all the prepared nanostructures are given in Table 1. It is clear from the data presented in Table 1 that the average grain size of undoped and Te doped HAp are found in the range from 15 to 62 nm.

* Ca5(PO4)3OH # TeO2

3.3. Vibrational spectroscopy analysis

0.08% Te

20

30

40

Pure [Ca5(PO4)3OH]

50

(304)

(004)

(213)

(222)

(310)

(300)

(211)

(202)

(100)

(002)

0.04% Te

10

60

70

80

90

2θ Fig. 2. XRD pattern of undoped and Te-doped HAp nanostructures.

where V112/300 is the intensity of the hollow between (112) and (300) planes, and I300 is the intensity of the peak belongs to (300) plane. The calculated average value of Xc for all the specimens has been given in Table 1. It is clear from Table 1 that the lattice parameters and unit cell volume were affected by adding the Te content in to HAp lattice. The lattice parameters were found to be reduced with increasing the Te doping, such kind of observation were also reported by other on HAp [56]. The value of degree of crystallinity has no systematic change with Te doping as it was found to be decreased at low concentration and increased at higher concentrations of Te doping. The higher value of Xc shows that the crystallinity has been enhanced due to Te inclusion in the crystalline matrix of HAp, such results were also reported by others [18,57]. The crystallite or crystallite size (L) was calculated for all the prepared nanostructures by the Scherer's eq. [53,58] using the FWHM of the diffraction peaks: L¼

where λ is the X-ray wavelength (nm), β is the full width at half maximum of the peak in radian and θ is the Braggs' angle in degree. The lattice strain and dislocation density were also calculated using θ the following relations [37]: and ϵ ¼ β cos and δ ¼ D12 . 4

# TeO2

0.16% Te #(114)

# (212)

60

#(220)

# (004)

#(212)

# (103)

50

#(200)

*(211)

#(102)

*

# (200)

# (102) (211)

40

Intensity, (a.u.)

*(002)

# (110) # (111)

30

* (002)

20

#(110) #(111)

10

475

0:9λ βcosθ

ð4Þ

3.3.1. FT-Raman analysis The recorded FT-Raman spectrum of undoped and Te-doped HAp nanostructure samples has been presented in Fig. 3(a). Firstly, here we discuss the bands observed in pure HAp as follows: the band observed at 1072 and 1040 cm−1 are assigned to triply degenerated asymmetric stretching mode of PO4. The main peak with high intensity at 961 cm−1 is assigned to totally symmetric stretching vibration of tetrahedral PO4 group of P\\O bond in HAp [59,60]. Further the band observed at 589 and 432 cm−1 are assigned to triply and doubly degenerated bending modes of PO4 group of O\\P\\O bond. The above assigned bands in the 0.04 wt% Te doped HAp are observed at 1070, 1045, 960, 589, 427 cm−1, in 0.08 wt% Te doped HAp are observed at 1068, 1040, 959, 590, 430 cm−1, in 0.16 wt% Te doped HAp are observed at 1040, 960, 592, 391 cm−1, and in 0.24 wt% Te doped HAp are observed at 1041, 960, 591, 390 cm−1. The peak at 432 in pure has been slightly shifted to the lower wavenumber in the low concentration Te-doped samples however at higher concentration it was shifted by 40 cm− 1 i.e. at 390 cm−1 which may be assigned to O\\P\\O bending modes of HPO24 − group of calcium phosphate [59]. Some new broad and sharp bands are also observed due to Te doping centered at 762, 769, 781, 782 cm−1in all however at higher concentrations (i.e. 0.16 and 0.24%) some new bands are also occurred centered at 173, 147, 121 and 60 cm− 1 which are due to the presence of TeO2 phase in HAp [61], this is also confirmed in X-ray analysis. 3.3.2. FT-IR analysis The recorded FT-IR spectrum of undoped and Te-doped HAp nanostructure samples has been shown in Fig. 3(b), respectively. From this figure, it is clear that all the bands of HAp are present in all the recorded spectra [59,60,62]. The vibrational bands observed at 1034, 603 and 565 cm− 1 are assigned to phosphate group. The sharp bands 3569 cm−1and a weak one at 633 cm−1 are related to the characteristic modes of hydroxyl group. It is clear from figure that with Te doping the intensity of some bands is increasing and decreasing as well. The wide bands centered at 3421 cm−1 and 1636 cm− 1 are associated with

Table 1 Lattice parameters, average values of crystallite size, dislocation density, lattice strain and degree of crystallinity of undoped and Te-doped HAp nanostructures. Samples

a = b, c = and V

Crystallite size (nm)

Dislocation density (nm)−2

Lattice strain

Xc

PHAp

a = b = 0.942288822(nm) c = 0.688757271 (nm) V = 0.529624132 (nm3) a = b = 0.935102118 (nm) c = 0.683504216 (nm) V = 0.518326117 (nm3) a = b = 0.940654662 (nm) c = 0.68851037 (nm) V = 0.510313088 (nm3) a = b = 0.785963152 (nm) c = 0.574492472 (nm) V = 0.330884147 (nm3) a = b = 0.794045898 (nm) c = 0.580400481 (nm) V = 0.347012695 (nm3)

15.9780

4.811E-03

2.313E-03

0.4878

20.4461

6.184E-03

2.502E-03

0.0833

17.3949

3.912E-03

1.734E-02

0.1176

49.8475

2.152E-03

1.143E-03

0.1667

62.3718

4.275E-04

6.759E-04

0.5385

0.04 wt% Te_HAp

0.08 wt% Te_HAp

0.16 wt% Te_HAp

0.24 wt% Te_HAp

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7000

(a)

0.24wt% Te_HAp

(b) 60

Raman intensity (a.u.)

6000 5000

50

0.16wt% Te_HAp

40

T (%)

4000 0.08wt% Te_HAp

3000 2000

0.04wt% Te_HAp

1000

PHAp

20 10

0 1400

1200

30

1000

800

600

Raman shift (cm-1)

400

200

0 4000

PHAP 0.04wt% Te_HAp 0.08wt% Te_HAp 0.16wt% Te_HAp 0.24wt% Te_HAp 3500

2000

Wavenumber (cm-1)

1500

1000

500

Fig. 3. (a) FT-Raman spectra and (b) FT-IR spectra of undoped and Te doped HAp nanostructures.

water molecule which was absorbed in the prepared samples or in KBr pallets. The vibrational bands of carbonate groups are observed at 1457 and 1404 cm−1 which may be incorporated at the precipitation stage. The triply degenerated asymmetric stretching modes of P\\O band of the phosphate group is observed at 1092 cm−1. The vibration band observed at 962 cm− 1 is assigned to non-degenerated symmetric stretching mode of P\\O band of phosphate group. The band observed at 472 cm−1 is assigned to double degenerated bending modes of O\\P\\O bonds of phosphate group. The band observed at 878 cm−1 is assigned to the characteristic peaks of hydrogen phosphate group. The peaks were also found to be minutely shifted and broadened as compared to pure HAp which gives the clear indication of Te doping in the crystalline matrix of HAp as it was also confirmed by EDX and X-ray analysis. These results confirm the highly purity of the synthesized material. 3.4. Dielectric and ac electrical conductivity analyses It is well known that the bone is a dielectric materials [63] and the field of electromagnetic which are non-invasive techniques. These have been applied from last few decades in many applications such as in bone growth or fracture healing [64,65]. The dielectric studies on HAp is well documented in the literature which are key for the application of HAp in the fabrication of biological sensors and acceleration of healing in bone fracture with electromagnetic field [66,67]. Therefore it is very important to study such properties from which we can have the information about amount of charges stored, defects, and may be used for bone repairing applications. For calculating the dielectric constant (ε1), dielectric loss (ε2) and total ac conductivity (σtot.ac) parameters, we have applied the following relations [21,68]: Cd εο A

ð5Þ

ε2 ¼ tanδ  ε 1

ð6Þ

ε1 ¼

σ tot:ac ¼

d ZA

at room temperature has been presented in Fig. 4(a). From which it is clear that the relative permittivity is frequency dependent and all samples shows similar behavior. As at low frequency the value of ε1 is found to be decreased with increasing frequency up to 1 MHz where as from 1 MHz to 5 MHz, it is almost constant. The observation of high dielectric constant in low frequency range is may be due to the contribution of electronic, ionic, dipolar and space charge polarizations as it depends on the frequencies [69]. The value of ε1 is found to be enhanced due to Te doping in HAp at higher concentrations (i.e. 0.16 and 0.24 wt%), however, at lower concentrations (i.e. 0.04 and 0.08 wt%) this value is decreasing which is good correlation with the earlier report on Cd doped HAp [21]. The values of dielectric constant is found to be higher than the previously reported values on Fe doped HAp as well as other [39, 70]. This change in ε1 value is may be due to Te ion which cause a high dielectric polarization and this will help us to spread the electromagnetic fields in bone fractures to heal of bone fractures. The similar behavior was observed for dielectric loss (ε2) with the applied frequencies [see Fig. 4(b)]. The plot of alternating current conductivity (σac) has been presented in Fig. 4(c) from which it is clear that the value of σac is found to be increased with frequency in pure as well as doped samples and follows the universal power law. The value of frequency exponent s was also calculated for all the samples from the slope of linear part of the curve lnσac vs. lnω and found to be between 1 and 1.008 for pure and doped samples as shown in Fig. 4(d). It is clear that the s values are found to be almost equal to unity as all the synthesized nanostructures lacked measurable direct current conductivity. The s value is found in between 0.6 and 1 for ionic conducting materials [71] and the theoretical limit of it is about 1. The value of s has a physical significance that if the value of s≤ 1 then the hopping motion involves a translation motion with a sudden hopping whereas if the value of s≥ 1, the hopping motion involves localized hopping. The value of s is found to be increased at low concentration of Te however at higher concentrations it is almost same to the pure HAp. The values of the dielectric constant, and ac conductivity are in good agreement with previous reports and these parameters are also found to be affected by doping [70,72].

ð7Þ 3.5. Linear absorption coefficient

σ tot:ac ¼ σ dc þ Bωs

ð8Þ

where εο is the permittivity of free space (εο = 8.854 × 10−12 F·m−1), C, d, Z and A are the capacitance, thickness, impedance and area of studied sample, respectively. Here σdc is the direct current conductivity, B is a constant, ω is the angular frequency and s is an frequency exponent. Also, the ac electrical conductivity, σac = Bωs. The plot of variation of relative permittivity (ε1) values as a function of the applied frequency

It is very important to have the information about the effect of gamma radiation on the bone of human body for future application to prevent it. Hence, here our aim to study the linear absorption coefficient is due to its importance as gamma absorption properties of materials for various applications in the field of science, technology, agriculture and human health. Hence, we have studied the absorption properties of the prepared nanorods and nanosheets using gamma radiation

I.S. Yahia et al. / Materials Science and Engineering C 72 (2017) 472–480 12

36

(a)

32

Pure HAP Te 2_HAP Te 3_HAP Te 4_HAP Te 5_HAP

(b)

Pure HAP 0.04wt% Te _HAP 0.08wt% Te _HAP 0.16wt% Te _HAP 0.24wt% Te _HAP

10

Dielectric loss, (ε2)

34

Dielectric constant, ε1)

477

30 28 26 24 22

8

6

4

2 20 18

0 0

1M

2M

3M

4M

5M

6M

7M

8M

9M

10M

0.0

2.0M

4.0M

f, (Hz) -4

8.0M

10.0M

1.008

(c)

-5

(d) Frequency exponent (s)

-6

σac, (siemens/m)

6.0M

f, (Hz)

-7 -8 -9 -10

Pure HAP 0.04wt% Te _HAP 0.08wt% Te _HAP 0.16wt% Te _HAP 0.24wt% Te _HAP

-11 -12 -13 -14 10

11

12

13

14

,

15

16

17

18

19

1.005

1.002

0.999

0.996 0.00

20

0.05

0.10

0.15

0.20

0.25

Te Concentrations (wt%)

ω (ω in Hz)

Fig. 4. Plots of variation of (a) Dielectric constant (b) dielectric loss, (c) ac conductivity and (d) frequency exponent for undoped and Te-doped HAp nanostructures.

8

Cs Am

(b)

7

x1/2 (cm)

6 5 4 3 2 1 0 0.00

0.05

0.10

0.15

0.20

0.25

Te Concentrations (%)

25

Cs Am

(c)

x10 (cm)

20

15

10

5

0 0.00

0.05

0.10

0.15

0.20

0.25

Te Concentrations (%) Fig. 5. Plots of variation of (a) linear attenuation coefficient, (b) half value layer and (c) tenth value layer of pure and Te doped HAp nanorods and nanosheets.

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technique at twp radiation source named Cs-137 (at 662 keV) and Am241 (at 59.5 keV). The absorption of radiation is defined by the following relation:

Test Microbe

I ¼ I ο e−μx

ð9Þ

where Iο is the intensity as counts of radiation during a certain time duration without any absorber/material, I is the counted intensity under the same time with a thickness x of absorber/prepared pure and Te doped HAp samples between the radiation source and detector and μ is the linear absorption coefficient. The calculated values of μ for pure and Te doped HAp are presented in Fig. 5 (a). It is clearly visible that the value of μ is increasing many times with increasing the Te concentrations from 0.109 to 2.512 when measure with Cs-137 source and 0.884 to 5.132 cm−1 when measured with Am-241. Further, it is also valuable to calculate the exponential absorption of photons as halfthickness, x1/2, or half-value layer (HVL) and tenth-value layer (TVL). The HVL is known as the thickness of prepared absorbing nanorods and nanosheets is defined as [73]: ln

2

3

4

5

13 0 13 14 15 11 0 0

25 11 15 17 15 12 12 10

30 15 17 19 17 14 13 15

35 30 18 25 18 16 15 25

40 45 20 28 22 20 17 30

antimicrobial abilities have been achieved by adding the tellurium with different concentrations the higher the concentration of tellurium the higher the antimicrobial activity. These results are in conformity with that of [74,75].

ð9aÞ

for calculating the value of x1/2 it can be written as follows: ln 2 μ

ð10Þ

correspondingly, the tenth-value layer (TVL) is expressed as: x1 =10 ¼ TVL ¼

Bacillus subtilis Micrococcus sp. Staphylococcus aureus P mirabilis Shigella dysenteriae Klebseilla sp. P aeruginosa Candida albicans

Inhibition Zone (mm) Pure hydroxyapatite

4. Conclusions

I −μx ¼ Iο

x1 =2 ¼ HVL ¼

Table 2 The relationship between the antimicrobial property and concentration of telluriumdoped hydroxyapatite.

ln 10 μ

ð11Þ

The values of HVL and TVL can be determined by using the values of μ from Eqs. (10) & (11) and the calculated values of HVL and TVL are shown in Fig. 5(b) and (c), respectively against Te concentration. From this figure it can be seen that the values of HVL and TVL are reduced as the concentration of Te increased. Te-doped HAp can weakened the electromagnetic gamma radiation inside the body and can be used in other radiation shielding applications. 3.6. Antimicrobial analysis It was observed that tellurium improved the antimicrobial property of hydroxyapatite making it an excellent candidate for numerous biomedical applications. Fig. 6 cleared that both pure hydroxyapatite and tellurium-doped hydroxyapatite exhibited antimicrobial effect against some pathogenic Gram-negative bacteria, Gram-positive bacteria and yeast. Table 2 showed that Gram-positive bacteria are more susceptible than Gram-negative bacteria. Hydroxyapatite endowed with

Successful synthesis of pure and Te-doped Hydroxyapatite nanorods and nanosheets has been achieved by microwave irradiation technique. The main phase of HAp was confirmed by X-ray diffraction analysis with a small amount of TeO2 at the higher concentrations. The calculated values of average grain size are found to be increased from 15 nm in pure to 62 nm in doped samples however all are in nano-meter range. The lattice parameters and unit cell volume are found to be slightly varied due to Te doping. The value of degree of crystallinity is found to be enhanced with Te doping in HAp samples. The scanning electron microscopy study confirms that the fabricated nanostructure of pure and 0.04 wt% Te doped is nanorods of diameter about 10 nm however for 0.08, 0.16 and 0.24 wt% Te doped it is nanosheets of thickness about 5 nm. The detailed FT-Raman and FT-IR analysis has been done and confirms the fundamental mode of vibrations of HAp as well as presence of Te in HAp samples and found to be in good correlation with X-ray results. The value of relative permittivity is found to be enhanced at higher concentration of Te doping in HAp. The increment in the values of ac conductivity has been observed with frequency and follows the universal power law. The value of frequency exponent was also calculated and found to be increased at low concentrations of Te however at higher concentrations it is almost same to the pure HAp. Furthermore, the radiations study has been performed and shows that the values of linear absorption coefficient has been enhanced due to Te doping. It may wakened the electromagnetic radiation and can be used in radiation shielding applications. Hydroxyapatite endowed with antimicrobial abilities have been achieved by adding the tellurium with different concentrations the higher the concentration of tellurium the higher the antimicrobial activity.

Fig. 6. Antimicrobial activity of pure hydroxyapatite (P) and tellurium doped hydroxyapatite with different concentrations (2 (0.04% wt), 3 (0.08% wt), 4 (0.16% wt) and 5 (0.24% wt)) against (A) Bacillus subtilis, (B) Candida albicans and (C).

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