One -pot synthesis and characterization of Zn -doped [616953]

Materials Chemistry and Physics
Manuscript Draft

Manuscript Number: MATCHEMPHYS -D-17-00950

Title: One -pot synthesis and characterization of Zn -doped
hydroxyapatite/graphene na nocomposites

Article Type: Full Length Article

Keywords: one -pot synthesis; Zn -doping; hydroxyapatite; graphene;
composite

Abstract: Zn -doped hydroxyapatite/graphene (Zn -doped HA/GP) composite was
successfully in situ synthesized by one -pot hydr othermal treatment for
the first time, and was studied through experimental analysis and density
functional theory calculations. The effects of a series of Zn contents
(0mol%, 1mol%, 5mol%, 10mol% and 20mol%) on the HA crystal structure, the
morphology and composition of composites were also investigated. The
obtained doped composites were analyzed and characterized by the
techniques of field emission scanning electron microscopy (FESEM) coupled
with energy dispersive X -ray detector (EDX), X -ray diffraction (XRD),
Fourier transform infrared spectroscopy (FT -IR), transmission electron
microscopy (TEM) and Raman spectroscopy. Density functional theory
calculations of Zn -doped HA showed that the replacement of Zn ions in HA
crystal lattice could cause the OH – group to move off the c axis toward
the Zn ions and become closer to the PO43 – group, resulting in the
formation of hydrogen -bond between OH – and PO43 – groups. The morphology
of Zn-doped HA/GP composite showed that Zn -doped HA grains with molar
fraction of 1 mol% Zn are intimately attached on the surface of graphene
whereas the amounts of Zn -doped HA attached on the GP surface reduce
obviously and the interfacial interactions are weakened accordingly as
the Zn doping amount increased from 5 to 20 mol%, which indicates that
the low crystallinity of Zn -doped HA particles due to an increasing Zn
content may have a negative effect on interfacial interaction between Zn –
doped HA and GP.

Graphical Abstract

Highlights:

*Zn-doped hydroxyapatite /graphene composites were synthesized by one-pot
hydrothermal treatment for the first time .

*DFT calculations showed that the doping of Zn ions in HA/GP could result in the
formation of hydrogen bond ing.

*TEM ima ges showed HA nanoparticles were uniformly dispersed on the surface of
graphene and exhibited fine rod-like morphology .

*The increasing contents of Zn doping tend to have a negative effect on interfacial
interaction between Zn -doped HA and graphene. Highlights (for review)

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65 1 One-pot synthesis and characterization of Zn -doped hydroxyapatite/graphe ne
nanocompos ites
Qiuhua Yuana,, Jianbo Wua, Caoping Qina, Anping Xua, Ziqiang Zhanga, Yaning Linb, Zehui Chena, Songxin Lina,
Zhiyang Yuanc, Xiangzhong Rena, Peixin Zhanga
aCollege o f Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, China
bCollege of Science, China University of Petroleum, Qingdao 266580, China
cShenzhen (Nanshan) Concord College of Sino -Canada, Shenzhen 518052, China

Abstract
Zn-doped h ydroxyapatite/graphene (Zn -doped HA/GP) composite was
successfully in situ synthesized by one-pot hydrothermal treatment for the first time,
and was studied through experimental analysis and d ensity functional theory
calculations . The effects of a series o f Zn contents ( 0mol%, 1mol%, 5mol%, 10mol%
and 20mol% ) on the HA crystal structure , the morphology and composition of
composites were also investigated. The obtained doped composites were analyzed and
characterized by the techniques of field emission scanning electron microscopy
(FESEM) coupled with energy dispersive X -ray detector (EDX) , X-ray diffraction
(XRD) , Fourier transform infrared spectroscopy (FT -IR), transmission electron
microscopy (TEM) and Raman spectroscopy . Density functio nal theory calculations
of Zn-doped HA showed that the replacement of Zn ions in HA crystal lattice could
cause the OH- group to move off the c axis toward the Zn ions and become closer to
the PO 43- group, resulting in the formation of hydrogen -bond betwee n OH- and PO 43-
groups . The morphology of Zn -doped HA/GP composite showed that Zn -doped HA
grains with molar fraction of 1 mol% Zn are intimate ly attach ed on the surface of
graphene whereas the amounts of Zn -doped HA attached on the GP surface reduce
obvio usly and the interfacial interactions are weakened accordingly as the Zn doping
amount increased from 5 to 20 mol% , which indicates that the low crystallinity of
Zn-doped HA particles due to an increasing Zn content may have a negative effect on

 Corresponding author.
E-mail address: yuanqiuh@szu.ed u.cn (Q. H. Yuan) *Manuscript
Click here to view linked References

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65 2 interfacia l interaction between Zn -doped HA and GP.
Keyword s: one-pot synthesis; Zn -doping; hydroxyapatite ; graphene; composite

1. Introduction
In recent years, the study in orthopedic biomaterials is a booming field owing to
their direct relationships to human he alth. Biomaterials used in orthopedic surgery can
be divided into three major classes of materials, namely, polymer s, metals or alloys
and ceramics [1]. Hydroxyapatite (HA, Ca10(PO 4)6(OH) 2), the most promising
bioceramic material analogous to calcium phospha te found in bone , has attracted a
significant amount of attention for a wide range of orthopedic applications due to its
excellent biocompatibility , bioactivity and osteoconductivity [2]. However, many
reports have mentioned the poor mechanical propertities of HA, such as low
brittleness and bending strength, which limits its utilization. To improve m echanical
performances of HA , inert materials like biopolymer [3], Ti-alloys [4], alumina [5],
yttria -stabilized zirconia [6], and carbon nano -materials [7], were employed as second
phase reinforcements . Among the carbon nanomaterials, graphene (GP) nano platelets,
formed by several layers of graphe ne with a thickness of up to 100 nm, possess
extraordinary electrical, thermal, and mechanical properties (e.g., intrinsic strength
130 GPa and Young’s modulus 0.5 -1 TPa) that have gained much attention recently as
reinforcing material [8-10].
More and more research ers have attempted to investigate the incorporation of GP
or its derivatives as reinforc ing materials in HA composites , including using in situ
synthesis method[ 11-13],spark plasma sintering technique [10,14] , chemical vapor
deposition [ 15], and electrospinning method [ 16]. In fact, most natural apatite s are
non-stoichiometric because of containing multiple trace elements . In order to meet the
requirements of practical clinical application , it is essential to add trace ions into
composites to enhance its biological performance. However, only a few studies have
investigated the effect of trace ions substitution on HA /GP composites. Janko vić et
al.[17] have studied silver/ hydroxyapatite/graphene composite coating produced by
electrophoretic deposition . The results showed that the presence of graphene exerted a

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65 3 toughing consequence and the silver based composite coating is potential for
biomedical application with antibacterial activity and noncytotoxicity . Baradaran et al.
[18] investigated the mechanical and biological properties Ni-doped HA mixed with
GP nanoplatelets . Their results indicated 1.5 wt.%, the ratio of GP nanoplatelets in
composite, was the optimum value for the growth and proliferation of osteoblast cell.
However, to the best of our knowledge, there are no reports on the effect of
incorporating Zn ions into HA/GP nanoplatelets composites.
This is the first work to successfully in situ synthesize Zn-doped HA/GP
nanocomposites by one -pot hydrothermal treatment . The obtained products were
characterize d by a series of methods such as XRD, FT -IR, FESEM, EDX, TEM ,
Raman spectroscopy , etc. The loca l structure of Zn incorporated into HA was
examined by an combination of experimental results with density functional theory
calculations . And the effects of incorporating Zn ions on the HA crystal structure , the
morphology and composition of the composite s were also studied.
2. Materials and methods
2.1 Chemical s and reagents
Ca(NO 3)2·4H 2O, (NH 4)2HPO 4 and Zn(NO 3)2·6H 2O were obtained from Aladdin
Industrial Corporation (Shanghai, China) . Graphene nanoplatelets w ere purchased
from Hunan Fenghua Material Dev elopment Co., Ltd . Sodium hydroxide (NaOH)
supplied by Tianjin Baishi Chemical E ngineering Co., Ltd. Ethanol were obtained
from Guangzhou Donghong Chemical Factory . All the received chemicals were of
analytical grade and were utilized without further purifi cation. D eionized water was
used throughout the synthetic process as a solvent to mix the salts as described in
stoichiometric quantities.
2.2 Preparation of Zn-doped HA /GP nanocomposite materials
Zn-doped HA/GP composite materials with 1 wt.% GP nanoplate lets were in situ
synthesized using one-pot hydrothermal treatment . The G P (40 mg) nanoplatelets ,
approximately 30–50 layers of G P monolayers were overlapped , were dispersed in 40
mL DI water by sonication for 5 min . The desired amounts of Ca(NO 3)•4H 2O and
Zn(NO 3)2•6H 2O were added into 40mL GP suspension . The molar ratios of

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65 4 [Zn]/[Ca+Zn] •100(mol%) were 0 (undoped), 1, 5, 10 and 20 mol% and the samples
were labe lled as HA/GP , 1ZnHA /GP, 5ZnHA /GP, 10ZnHA /GP and 20ZnHA /GP,
respectively. This step was followed b y the drop -wise addition of Na2HPO 4 at the
speed of 2mL ·min-1 to keep the value of n(Ca+Zn)/n(P) as 1.67. The pH of the
suspension was adjusted to 10.5 by NaOH and then the suspension was stirred under
ambient conditions for 2 h. The final suspension was transferred into a 50mL Teflon
bottle, which is held in a stainless steel autoclave for hydrothermal reaction at 180 ℃
for 24 h. The autoclave was cooled down to room temperature. Samples were filtered
and washed by deionized water for three times , and then rinsed by ethyl alcohol once.
At last the samples were dried in an oven at 40 ℃ for 12 h .
2.3 Characterization
The phase composition of Zn-doped HA /GP samples was identified by X -ray
diffractrometry (Bruker AXS -D-8 ADV ANCE, Germany) ，which used a tube volta ge
of 40 kV and current of 40 mA in the 2θ ranging from 5°to 60°with Cu -Kα
radiation of 1.5406 Å. The functional group s of the composites were determined using
a Fourier transform infrared spectroscopy (FT -IR, Shimadzu IRAffinity), in a
frequency range of 4000-400 cm-1 using the KBr pellet technique . Microstructure of
the composites was characterized by transmission electron microscopy (TEM,
JEM -2100) and field emission scanning electron microscopy (FESEM , JSM-7800F ).
For the TEM characterization , the powder sample was dispersed in ethanol to form
dilute suspension which was treated by sonication, and a few drops of this suspension
were applied onto a carbon film supported by copper grid. Raman spectra were
carried out by a micro -Raman spectroscopy (InVia Ref lex, the excitation wavelength
of 514.5 nm).
2.4 Computational methods and models
Computer simulations have played an important role in the field of materials.
Simulations can provide an understanding of the structure –performance relationships
in materials , which in turn can help design better and more efficient experiment.
Density functional theory (DFT) has proved to be a powerful tool for users to study
the relationship between microstructure and property of the materials [19].

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65 5 The calculations were perfo rmed by Cambridge Serial Total Energy Package
(CASTEP) [20] based on the density functional theory (DFT). The GGA [21] with
PBE functional is used for the exchange correlation of electrons and the ultrasoft
pseudopotentials are employed. The kinetic energy cut-off of 430 eV was determined
to guarantee the convergence of total energies within an accuracy of 10-7 eV/atom.
The k -meshes were 3×3×6 for HA.
3. Results and discussion
3.1 FT-IR analysis of Zn -doped HA/GP composites
FT-IR spectra of Zn -doped HA/GP c omposites with various Zn fractions have
been shown in Fig. 1. The spectrum of the undoped HA/GP (Fig. 1a) shows broad
bands ranging from 3400 -3500 cm-1，corresponding to O -H stretching vibration of
adsorbed water molecules. The i ntense bands at 1104, 1033 and 962 cm-1 are due to
the stretching mode s of P-O and the bands at 603, and 565 cm-1 are attributed to the
bending modes O -P-O. The bands at 3570 and 632 cm-1 are the stretching and
bending bands, respectively, of the HA hydroxyl group. The absorption bands around
873 and 1419 -1455 cm-1 are assigned to CO 32- which implies that small portions of
the PO 43- groups are substituted by CO 32-, indicating the r eaction between HA and
carbon dioxide in the air. With increasing Zn fraction, the intensity of three P -O
stretching peaks (1104, 1033 and 962 cm-1) progressively decrease and become
obscure. In addition , the O -H stretching and bending peak s at 3570 and 63 2 cm-1
become weaker and much broade r, and for the sample of 20ZnHA/GP, the peak is
almost absent , this change may originate from the hydrogen -bond formation [ 22].
When Zn content increases up to 20 mol% , the distance s of oxygen atoms between
OH- and PO 43- groups are becoming closer than those between adjacent hydroxyl
groups so as to form hydrogen -bond more easily.
3.2 Density function theory (DFT) calculation s
As an initial guess, we use the crystallographic structure of HA reported by
Posner et al. and K ay et al. [23], with a hexagonal primitive cell of 44 atoms that has
two formula units of Ca 5(PO 4)3OH in a unit cell with space group P6 3/m. There are
two forms of Ca ions for Zn substitution: Ca1 (CaO 9) and Ca2 site (CaO 7). In order to

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65 6 investigate which form of Ca ion is more likely to be replace d by Zn ion in HA, the
positions of Ca1 and Ca2 replaced by Zn ions were processed by self -consistent -field
(SCF) calculations respectively. The calculated results show that the energy of Zn
substitution in the Ca2 ( -854.701 Ha) is lower than that of Zn in the Ca1 ( -854.696
Ha), so the Zn ion is more likely to replace Ca2 in the doping process. This result
agrees with the studies by Tang et al.[24] and Terra et al.[25] that Zn energetically
prefers the Ca2 site.
The ca lculated lattice parameters of HA and Zn -doped HA are listed in Table 1
together with experimental data reported in the literature s. From Table 1 we can see
that the cell parameters after the minimization of HA were found to be a=b=9.531 Å
and c=6.881 Å, in excellent agreement with in 1.5% error of experiment al values [23].
Our calculations of lattice parameters of HA are in good accordance with other
literatures [26,27] . And it is evident that the doping of Zn atoms can affect the lattice
structure of HA. T he lattice parameter s of Zn -doped HA are larger than th ose of the
pure HA .
In order to find out the influence of Zn atoms on the lattice structure of HA, the
local distribution s of atoms of HA structure where Zn atoms doped were analyzed and
showed in Fig . 2. From the relaxed geometry of F ig. 2b we can see that the HA crystal
structure after doping Zn atoms exhibits obvious changes , namely, the OH- group
adjacent to Zn atoms tends to move off the c axis toward the Zn atoms where the
Zn-OH distance is 2.042 Å. The distance between the OH- group and PO 43- group is
2.814 Å, which becomes smaller as compared to the original distances in HA of 2.999
Å. We believe the phenomenon that the O atom of the OH- group was dragged by the
Zn atoms out from the c axis may result in the formation of hydrogen -bond between
the OH- group and PO 43- group. And this could explain the decreasing of the
intensit ies of the OH- and PO 43- peaks in FT-IR spectra (Fig. 1) .
3.3 XRD characterization of undoped and Zn-doped HA powder s
XRD patterns, shown in Fig 3, were utilized to monitor the structural changes
that occurred in novel composites of graphene and Zn -doped hydroxyapatite. The
pattern of undoped HA/GP (Fig. 3a) shows high intensity HA peaks at crystal planes

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65 7 (002), (211), (112), and (300), corresponding to 2θ =25.957°, 31.834°, 32.262°,
32.944° respectively , which are in good agreement with HA standard JCPDS database
(PDF#09 -0432) . Compared with undoped HA/GP, the XRD peaks drastically became
broader and less intense (especially in the range of 30<2θ<35° ) as the Zn
concentration increased from 1 to 20 mol% . Since the ionic radius of Zn2+ (0.074 nm)
is much smaller than that of Ca2+(0.106 nm), the replacement of Zn ions in the HA
structure will distort the lattice . This indicates t hat the crystallinity of the apatite
significantly decreases with increasing Zn fraction , which is consistent with our
previous result s[28]. When the Zn content reached 20 mol% , the apatite structure was
no longer kept and became amorphous and indistinct. M oreover, there are no traces of
the graphene peaks due to small content GP and the presence of strong HA peaks in
the vicinity, whereas GP presence can be confirmed by the analysis of FESEM , TEM
and Raman. This demonstrates that the incorporation of the GP has no influence on
the stability of HA. Furthermore , the lack of GP peaks in the XRD is most likely
relevant to the layered structure of the GP with irregular arrays of atoms in three
dimensions [29].
3.4 FESEM characterization of Zn-doped HA/GP composi tes
Fig.4 shows the FESEM images of graphene nanoplatelets and the
as-synthesized Zn -doped HA/GP composites in situ by one -pot hydrothermal
treatment. The initial graphene nanoplatelets (Fig. 4a) reveal that GP monolayers are
overlapped (about 30 -50 layers ). The morphologies of pure HA/GP sample were
shown in Fig. 4b. After stirring during preparation, multilayer GP are scattered into
small sheets. It can be clearly found that HA crystallites were randomly dispersed on
the surface of GP sheets . The HA grain s have not been removed from GP sheets even
by successive water washings, which means that the pure HA grains are closely
adhered to both sides of GP sheets. Additionally, Liu et al. [ 29] reported that there was
a strong and coherent interfacial bond ing between the GP surface and the (300) plane
of HA. The morphology of Zn -doped HA/GP composite with molar fraction of 1
mol% Zn (Fig. 4c) still shows HA grains and grapheme sheets are tightly attached
together . The corresponding EDX micrograph, shown as inset i n Fig. 4c, exhibits that

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65 8 the main elements existing in the sample are C, Ca, P, O and Zn, indicat ing there are
no other impurities in the sample. However, the micrographs of Zn -doped HA/GP
composite s tend to change after doping Zn. The amount s of HA grains adhered to the
GP surface were reduced as the Zn doping content increased from 5 to 20 mol%
(Fig.4d-f). For high molar fractions of Zn -doping samples, due to more amorphous
phase, its u ndeveloped structure might weaken the interfacial interaction between Zn
doped HA and graphene.
3.5 TEM characterization of Zn-doped HA/GP composites
TEM microphotograph s for the as -synthesized Zn -doped HA/GP composite s
which are HA/GP, 1ZnHA/GP, 5ZnHA/GP, 10ZnHA/GP and 20ZnHA/GP are shown
in Fig. 5 respectively. Fig. 5a disp lays free standing HA nanoparticles of the undoped
HA/GP sample. The aggregate consisting of numerous fine rod -like HA particles with
an av erage length of about 75 nm and diameter of about 25 nm can be distinguished.
As verified from Fig. 5b, HA grains were uniformly decorated or dispersed on the
rumple surface of GP. It seems that the addition of GP could reduce the aggregation of
these parti cles to a certain extent. Fig. 5c shows there is no obvious influence on the
composite morphology in low concentration of Zn doping (molar fraction of 1mol%
Zn). The apatite morphology in 10ZnHA/GP sample (Fig. 5e) is no longer sustained
and shows an amorph ous phase. Furthermore, t he TEM image of 20ZnHA/GP sample
(Fig. 5f) reveals the typical morphology of amorphous phase and the total
agglomeration of precipitates on the wrinkled GP background. This suggests that the
growth of Zn -doped HA crystal was inhibi ted by increasing Zn content. As combined
with the XRD and SEM results, it seems that lower crystallinity of particles could
exert a negative effect on interfacial interaction between Zn -doped HA and GP
nanoplatelets.
3.6 Raman characterization of Zn-doped HA/GP composites
Raman analysis was employed to identify the existence and property of the G P
nano platelets in the composit es. Both of the typical D band at 1355 cm-1 and G band
at 1585 cm-1 in undoped HA/GP sample were observed in Fig. 6b, together with
characteristic peaks of HA at 4 27, 589 and 96 0 cm-1, which are associated with the

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65 9 doubly degenerate bending mode v2(PO 43-), triply degenerate bending mode v3(PO 43-)
and totally symmetric stretching mode v1(PO 43-), respectively . The D band
corresponds to t he presence of defective graphitic carbon on the GP edges and the G
band is a characteristic feature of the in -plane vibration of sp2 carbon atoms [30]. The
intensity ratio of the D to G bands (I D/IG) is used to measure the degree of disorder
and the avera ge size of the sp2 domains. The I D/IG ratio for the GP nanoplatelets is
0.853, whereas the ratios for the undoped HA/GP, 10ZnHA/GP and 20ZnHA/GP
composite powder were 0.864, 0.871 and 0.903 respectively . The composite samples
tend to have higher ID/IG comp ared with the GP nanoplatelets, which indicates an
increase in the defect density in the GP due to the decrease in crystallinity .
4. Conclusion
Zn-doped HA/GP nanocomposite was successfully in situ synthesized by
one-pot hydrothermal treatment for the fir st time. The obtained samples were
characterized by the techniques of XRD , FT-IR, FE-SEM , EDX , TEM and Raman
spectroscopy. The results of d ensity functional theory calculations showed that Zn
ions replaced partial Ca ions and entered HA crystal lattice, which could cause the
OH- group to move off the c axis toward the Zn ion and become closer to the PO 43-
group, resulting in the formation of hydrogen -bond between OH- and PO 43- groups .
The synthetic HA nanoparticles were uniformly dispersed on the surface of graphene
and exhibited fine rod-like morphology with an average length of about 75 nm and
diameter of about 25 nm . And the increasing contents of Zn doping tend to inhibit the
growth of the HA crystallites , and thus form low crystallinity of HA grains on the
surface of graphene, which may have a negative effect on interfacial interaction
between Zn -doped HA and GP .
Acknowledgements
This work was financially supported by the National Natural Science Foundation
of China (grant #21471102, #20971088) and Shenz hen Government’s Plan of Science
and Technology (grant #JCYJ20150525092941007).
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65 14 Tables
Table 1. The lattice parameters of the optimized HA and Zn -doped HA.

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65 15 Table 1. The lattice parameters of the optimized HA and Zn -doped HA.
Structure HA Zn-doped HA
Lattice Parameter( Å)
(Present)
Expt./Cal. a=b=9.531
c=6.881
a=b=9.58[2 6]
c=6.88
a=b=9.52[2 7]
c=6.87 a=9.537,b=9.534
c=6.896
–

–

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65 16 Figure Captions
Fig. 1. FTIR spectra of undoped and Zn -doped HA/GP powders with varied molar
fractions of Zn: HA/GP (a), 1ZnHA/GP (b), 5ZnHA/GP (c), 10ZnHA/GP (d) and
20ZnHA/GP(e) .
Fig. 2. Crystallographic lattice structure of undoped HA(a) and Zn-doped HA(b)
crystal.
Fig. 3. XRD Pattern s of undoped and Zn -doped HA/GP composites with varied molar
fractions of Zn: HA/GP (a), 1ZnHA/GP (b), 5ZnHA/GP (c), 10ZnHA/GP (d) and
20ZnHA/GP(e) .
Fig. 4. FESEM images of graphene nanoplatelets(a) and Zn -doped HA/GP composite
with varied molar fractions of Zn: HA/GP(b), 1ZnHA/GP(c), 5ZnHA/GP(d),
10ZnHA/GP(e) and 20ZnHA/GP(f). EDX of 1ZnHA/GP sample is shown as insets.
Fig. 5. TEM micrographs of obtained samples: HA/GP (a and b), 1ZnHA/GP(c),
5ZnHA/GP(d), 10ZnHA/GP(e) and 20ZnHA/GP(f) .
Fig. 6. The Raman spectra of GP nanoplatelets (a), undoped HA/GP(b),
10ZnHA/GP(c) and 20ZnHA/GP(d) composites.

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65 17
4000 3500 3000 2500 2000 1500 1000 500OH-

CO32-CO32-
OH-e
d
c
bTransmittance/a.u. a
PO43-
Wavenumber/cm-1
Fig. 1. FTIR spectra of undoped and Zn -doped HA/GP powders with varied molar fractions of
Zn: HA/GP (a), 1ZnHA/GP (b), 5ZnHA/GP (c), 10ZnHA/GP (d) and 20ZnHA/GP(e) .

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65 18
Fig. 2. Crystallographic lattice structure of undoped HA(a) and Zn-doped HA (b) crystal.

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65 19
10 20 30 40 50 60PDF#09-0432-HAd
c
b
ae
(210)(102)
(004)(123)(222)(311)(200)
(301)
(310)(212)(202)(300)(211)(111)(112)
(002) Fig. 3. XRD Pattern s of undoped and Zn -doped HA/GP composites with varied molar fractions
of Zn: HA/GP (a), 1ZnHA/GP (b), 5ZnHA/GP (c), 10ZnHA/GP (d) and 20ZnHA/GP(e) .

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65 20

Fig. 4. FESEM images of graphene nanoplatelets (a) and Zn -doped HA/GP composite with
varied molar fractions of Zn: HA/GP (b), 1ZnHA/GP (c), 5ZnHA/GP (d), 10ZnHA/GP (e) and
20ZnHA/GP(f) . EDX of 1ZnHA/GP sample is shown as insets. a b
c d
e f

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65 21

Fig. 5. TEM micrographs of obtained samples: HA/GP (a and b ), 1ZnHA/GP (c), 5ZnHA/GP (d),
10ZnHA/GP (e) and 20ZnHA/GP(f) . a b
f d c
e

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65 22
500 1000 1500 2000 2500d
c
aG bandD bandv3(PO43-)v1(PO43-)

v2(PO43-) b
Raman shift / cm-1Intensity / a.u.Fig. 6. The Raman spectra of GP nanoplatelets (a), undoped HA/GP(b), 10ZnHA/GP(c) and
20ZnHA/GP(d) composites.