Growth Mechanism of Surfactant-Free Size-Controlled Luminescent

Subscriber access provided by HACETTEPE UNIVERSITESI KUTUPHANESI

Article

Growth Mechanism of Surfactant-free Size-controlled Luminescent Hydroxyapatite Nanocrystallites Haoshuo Li, Lefu Mei, Haikun Liu, Yangai Liu, Libing Liao, and R. Vasant Kumar Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b00258 • Publication Date (Web): 20 Mar 2017 Downloaded from http://pubs.acs.org on March 26, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Crystal Growth & Design is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Crystal Growth & Design

Growth Mechanism of

Surfactant-free Size-controlled

Luminescent Hydroxyapatite Nanocrystallites Haoshuo Li1, Lefu Mei1*, Haikun Liu1, Yangai Liu1, Libing Liao1*, R Vasant Kumar2* 1

Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China. 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS, UK *

Author to whom correspondence should be addressed: Lefu Mei, Libing Liao, R

Vasant Kumar E-mail: [email protected], [email protected], [email protected]

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Abstract: Herein, a facile surfactant-free hydrothermal method assisted with coprecipitation has been explored in order to prepare size-controlled HAP nanorods, and the growth mechanism of HAP nanostructures has also been proposed. In this paper, the size of the HAP crystallites, ranging from 40 to 1500 nm, were controlled by varying the reaction conditions. Likewise, the experimental conditions can be changed to alter the shapes of the HAP nanostructures from nano-rods to nano-belts. Additionally, interesting optically properties were induced in nano-HAP by doping with rare earth elements. The samples doped with terbium and europium generated green and red orange emissions, respectively, under irradiation by blue light, which is popularly used for wound healing and skin disease treatment. Thus the doped HAP nanocrystals through the surfactant-free method have potential applications in blue phototherapy and photodynamic therapy.


Page 2 of 18

Page 3 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


1. Introduction Hydroxyapatite (HAP) has drawn growing attention over decades for use in the fields of materials science and biomedical engineering and more recently in nanotechnology owing to its excellent bioactivity and biocompatibility.1, 2 Synthetic HAP is usually used as the main constituent of hard tissue engineering in vertebrate because of its high chemical stability3, 4, especially HAP nanomaterials, making them suitable for bone and teeth substitutes5, 6. In view of above excellent properties, the HAP nanomaterials also are selected to be applied to drug delivery, biological probes and bioimaging by tailoring the size and morphology of the nanoparticles for each application7-10. For instance, the HAP nanoparticles with smaller size, especially less than 100 nm, are more likely to be ingested and internalized by living cells3. Spherical HAP particles are preferred as biological ceramics and drug delivery because of their high surface area11. HAP nanowhiskers could be used to coat the surface of Ti substrates as reinforcing agents in orthopedics and dentistry12,

13

. It is of great

importance to control the size and morphology of nanostructured HAP material while minimizing or avoiding any contaminants that can adversely affect biocompatibility and cause toxicity or inflammation. Based upon classical methods for nanoparticle synthesis, a series of methods are emerging to achieve the nano-HAP size and morphology variations. For example, hexadecyl trimethyl ammonium bromide (CTAB)3, glycol and butanol14 and urea and gelatin are used in the solvent during preparation to control the size distribution of the HAP particles and achieve various shapes of HAP particles. However, it is believed that organic additives will introduce toxic substances which can damage the bioactivity and biocompatibility of HAP. Removal of organic components may require high treatment temperatures which can adversely affect the morphology of the nanostructured HAP particles. Therefore, it is imperative to develop surfactant-free synthetic method at relatively low temperatures for controlling the size and shape of HAP nanoparticles. To our best knowledge, the method for controlling the sizes of HAP nanoparticles without organic additives has been scarcely reported. In this study, the size tunable HAP nanoparticles were successfully prepared via



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

surfactant-free hydrothermal method assisted with coprecipitation process, while retaining bioactivity and the biocompatibility of HAP. It is also shown that, in further advancing the potential use of nano-HAP in medical applications, the HAP nanorods emit bright green and red-orange light after doping with terbium and europium, respectively, upon excitation with blue light. This is of great significance as blue light is popularly used

for wound healing15 and to cure skin disease, such as acne

vulgaris16. While the penetrability of blue light is limited, the present as-prepared samples could potentially be developed for phototherapy and photodynamic therapy17, or as fluorescence labeling in therapy. 2. Experimental Section

2.1 Materials In the present study, the raw materials Ca(NO3)2·4H2O (99.0%) and Na2HPO4·12H2O (99.0%) were purchased from Xilong Chemistry Co., Ltd. (Guangdong, China). Eu(NO3)3·6H2O (99.99%) and Tb(NO3)3·6H2O (99.99%) were obtained from Aladdin industrial Corporation. In addition, the initial pH value of the solution was adjusted by NaOH (99.0%), ammonia solution (NH3, 25%) or Phosphoric acid (H3PO4, 85%) purchased from Modern Oriental Technology Development Co., Ltd. (Beijing, China). Deionized water and alcohol (99.7%) were also used as solvents in the synthesis process.

2.2 Synthesis of Pure and Doped Hydroxyapatite Nanoparticles Analytically pure Ca(NO3)2·4H2O and Na2HPO4·12H2O were used as raw material reagents. 0.003 mol of Na2HPO4·12H2O was dispersed in 30 ml of deionized water, and the pH of the solution was adjusted to 11.5 with 1 mol/L NaOH solution (or 25% ammonia solution). The pH of the solution was measured by the acidometer in the process. Then, 0.005 mol of Ca(NO3)2·4H2O was dispersed in 20 ml of deionized water, keeping the ratio of Ca/P at 1.67 identical to bone HAP. In the next step, the clear Ca(NO3)2 solution was mixed in Na2HPO4 solution drop by drop under stirring, allowing the mixture to form a white suspension with time. After the mixture was


Page 4 of 18

Page 5 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


stirred for 1 h, the suspension was transferred to an autoclave of 100 ml in volume and then heated at 200 oC for 8 h. After this, cooling the autoclave to room temperature, HAP was separated by centrifugation and washed by deionized water, and the obtained solids were dried at 60 oC for 12 h. In the synthesis for doping HAP, 5 ml of 0.01 mol/L Ln(NO3)3 (Ln = Tb, Eu ) solution was mixed with Ca(NO3)2 solution at the ratio of 1 : 100 for Ln: (Ca + Ln). After the pH of the above solution was adjusted to 10, the clear solution was dropwise added into the as-prepared Na2HPO4 solution with pH at 11.5. Rest of the procedure was identical to process described for the undoped HAP.

2.3 Characterization During the synthesis process, the initial pH value of the solution was measured using a pH meter (PHS-3C, INESA, China). The crystal structures of the as-prepared samples were characterized by X-ray diffraction (XRD, D8 Advance, Bruker, Germany) with a Cu Kα radiation (λ = 1.5406 Å) scanning from 10° to 70°. The Fourier transform infrared spectroscopy (FTIR) was obtained using a vacuum FT-IR spectrometer (VERTEX 80v, Bruker, Germany). The size and morphology of particles were observed on a scanning electron microscope (SEM, Nova NanoSEM 450, FEI, Canada) and a transmission electron microscope (TEM, JEM-2010, JEOL, Japan). Furthermore, the excitation and emission spectra of the doped HAP particles were recorded on a fluorescence spectrophotometer (F-4600, Hitachi, Japan) at room temperature.

3. Results and Discussion

3.1 Characteristics of pure HAP nanoparticles When the pH of the initial solution was adjusted to 11.5 by adding NaOH solution, the XRD patterns of HAP at different reaction time were investigated and are shown in Figure 1a. The x-ray diffraction patterns exhibit main peaks at 10.9°, 25.9°, 28.9°, 31.8°, 32.2°, 32.9°, 34.1°, 39.8°, 46.7° and 49.5°, corresponding respectively to (1 0



0), (0 0 2), (2 1 0), (2 1 1), (1 1 2), (3 0 0), (2 0 2), (3 1 0), (2 2 2) and (2 1 3) of HAP (JCPDS No.09-43218), which indicates that the as-prepared solids are pure HAP. From the reflections magnitude and the sharpness as shown in Figure 1a, it can be concluded that HAP particles with hydrothermal reaction for 12 h have better crystallinity than that for 8 h. The intensity ratio of the (0 0 2) and the (2 1 1) peaks, in comparison with the standard pattern, indicates a preferred orientation in the [0 0 2] direction19 of the samples made in this work, which correlates with rod-like morphology (SEM image shown later). FTIR analysis of the particles obtained under different reaction conditions were carried out and displayed in Figure 1b. The peaks at 560 and 603 cm-1 could be ascribed to the bending vibrations of PO43-, while those in the range of 940-1120 cm-1 (960, 1024 and 1090 cm-1) arise due to the asymmetric stretching vibrations in PO43- groups20, 21. In addition, the bands at 3575 and 632 cm-1 are attributed to OH- 14. The above results indicate that OH- and PO43- exist in the samples, which are consistent with the XRD results. Otherwise, no other obvious peaks between 1500 and 3000 cm-1, related to characteristic peaks of CH3, CH2, C=C and C≡C groups, could be observed in the FTIR spectra, indicating absence of organic contaminants.

Transmittance (a.u.)

(A) 2 h-ammonia

3575

HAP: JCPDS No.09-432

603 632 560

HAP-8 h

(B) 8 h-NaOH

960

HAP-12 h

1090

(222) (213)

(C) 12 h-NaOH (310)

(202)

(002) (210)

(100)

(b)

(211) (112) (300)

(a)

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 6 of 18

1024

10

20

30

40

50

60

70

4000

3600

3200

2800

2θ (degree)

2400

2000

1600

1200

800

400

-1

Wavenumber (cm )

Figure 1. (a) XRD pattern of pure nano-HAP obtained at 200 oC for different hydrothermal time; (b) FTIR spectra of pure nano-HAP obtained at 200 oC: (A) reaction time of 2h using ammonia solution; reaction time of (B) 8h, (C) 12h using NaOH solution.

SEM image in Figure 2 shows the morphology of the HAP particles synthesized at 200 oC when the pH of initial solution was adjusted to 11.5 using NaOH solution.


Page 7 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


After hydrothermal treatment for 8 h, most HAP particles (Figure 2a) appeared as short rods within the length ranging from 150 to 300 nm and the width from 30 to 50 nm, while a small number of rods are up to 500 nm. In addition, a number of short rods are anchored to one long rod and they are oriented nearly along the long rod. This suggests that, when a long rod is growing, secondary (and even tertiary) rods are formed as nuclei on the longer rod surface. When the hydrothermal reaction time is increased to 12 h, the HAP crystals are belt-like with lengths of 600-1500 nm and widths of 50-100 nm, as shown in Figure 2b. In this case, they are more randomly oriented in different directions, accounting further growth of the crystal grains with longer time. All the morphologies of the nano-HAP correspond with the XRD results that the particles grow along one preferred crystallographic direction.

(a)

(b)

400 nm

Figure 2. SEM images of HAP nanoparticles obtained at 200 oC: (a) reaction time 8h, (b) reaction time 12h.

To further investigate microscopic morphology and structural information at higher magnification, TEM was used and the results are shown in Figure 3. As Figure 3a shows, the HAP nanorods with clear outline in the picture have excellent crystallinity, which tallies with the XRD analysis. The TEM patterns of the nanorods/nanobelts with a width about 40-60 nm are accordant with the conclusion of the SEM observation. Moreover, the hexagonal/trigonal microcrystals could be observed in Figure 3a, which are similar to ZnO microcrystals. Figure 3b provides a detailed lattice picture of a single HAP nanorod recorded by HRTEM, and the insert is a magnified detail. As Figure 3b shows, the cross-like crystal planes were observed clearly, and the characteristic spacing which is parallel to the length direction was



measured as 0.47 nm corresponding to that of the (1 1 0) plane in the hexagonal HAP crystal. The characteristic spacing, which is parallel to the width direction, was measured as 0.34 nm and it corresponds to d-spacing of the (0 0 2) planes. So, the TEM results are in excellent agreement with the XRD patterns showing preferred orientation growth in the (0 0 2) direction. (b)

(a)

0.34nm

0.47nm

Figure 3. (a) TEM images of HAP nanoparticles obtained via hydrothermal condition for 12 h;(b) HRTEM image of rectangular area in Figure (a) and the insert is magnified image.

pH=7 pH=9

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 18

pH=10 pH=11

HAP: JCPDS No. 09-432

10

20

30

40

50

60

70

2θ (degree)

Figure 4. XRD pattern of pure nano-HAP obtained at 200 oC for 8h in the solution at different initial pH values with NaOH or H3PO4 solution.

According to the structural results, it is confirmed that the as-prepared solids are hexagonal HAP, and the particles grow along the c-axis direction. A mechanism is put forward to explain this phenomenon in the literature22. In their study, OH- ions firstly concentrate on the (1 1 0) plane because of its higher surface energy than other planes,


Page 9 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


which had the effect of obstructing Ca2+ and PO43- to prevent the growth of HAP nucleus parallel to (1 1 0) direction. While the (0 0 2) plane has lower surface energy, which would not prevent the growth of HAP nucleus. Therefore, the HAP crystals prefer to grow into rods or belts in the alkaline condition. When the initial pH value of the solution was reduced lower than 11.5, as Figure 4 shows, the characteristic peaks of the monetite (CaHPO4) appear in XRD patterns, and the peak intensity is higher and higher with the initial pH value ranging from 11 to 7. The results indicate that the high concentration of OH- is conducive to the formation of HAP instead of monetite, which was previously reported23. The growth mechanism of a single HAP crystal is depicted in Figure 5a. According to the crystal structure of HAP where OH- locates in the channel parallel to c-axis24, 25, OH- could firstly arrange themselves along c-axis in the hydrothermal solution, as shown in Figure 5a(II). The similar conclusion was reported in the literature26 about the growth of zinc oxide crystal with hexagonal symmetry. It could be speculated that, when the concentration of OH- is high enough, they would also gather on the polar faces such as (0 0 2), which could inhibit the extension of the crystal nucleus in the c-axis. The growth mechanism of HAP crystals is described in Figure 5a(I). In addition, Figure 5b shows the transformation of morphology of HAP particles during the process of growth. When the initial solution was stirred, the agglomerate precursors were firstly formed (as section 1). Then, the precursors were gradually separated by the bubbles in the boiling hydrothermal solution and, meanwhile, the microcrystals formed on the precursors (as section 2). With the reaction time increase, the microcrystals are further separated from each other and began to grow independently. While the reaction time is 8 h, the crystals had grown in to distinct rod-like morphology (as section 4). The transformation of morphology of HAP particles are displayed in the inserts, which corresponds to the above growth process.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

OHNH3

Ca2+ PO43-

Page 10 of 18

(b)

1 precursor

NH 3

Gas

c NH 3 • H 2 O NH + OH

2

Liquid

c − 4

−

3

c-axis

c-axis

4

HA crystal

(I) Ammonia solution

(II) NaOH solution

HAP crystal

OH-

PO43-

Ca2+

Figure 5. Schematic diagrams of (a) growth mechanism of single HAP crystal and (b) growth process of HAP particles (the inserts are TEM images of HAP obtained for (2) 0.5h, (3) 1h, (4) 8h).

Since OH- has a significant impact in the morphology and size of HAP, ammonia solution was used for adjusting the alkalinity and substitution NaOH solution in the follow work, and the stirring rate was appropriately increased. Figure 6 displays the SEM images of nano-HAP particles obtained at 200 oC for different reaction time when the pH of the initial solution was kept at 11.5. After hydrothermal treatment for 8 h, the obtained HAP nanorods (Figure 6a) ranging from 80 nm to 180 nm in length are only about 40 nm in width (as Figure 6c displayed). Compared to the particles (Figure 6a) which were obtained by NaOH supplying OH-, the nanorods (Figure 6a) assisted with ammonia in the process display smaller size. But the particles were more cohesive together. When hydrothermal treatment time is decreased to 2 h and the initial stirring rate was further increased, the dimension of most particles (Figure 6b) range from 60 nm to 100 nm in length and from 30 nm to 40 nm in width (as Figure 6d displayed), which means that the HAP nanorods with reaction time 2 h are of more uniform morphology and smaller dimension19. This phenomenon could be explained by the idea that ammonia solution could provide more stable alkalinity in the hydrothermal solution than NaOH solution. When the temperature was increased from room temperature to 200 oC, the ammonia gradually volatilized from the solution and kept the gas pressure nearly constant. Figure 5a(I) depicts the mutual transformation between ammonia and OH- would take place in the hydrothermal process. So, OH-


Page 11 of 18

was constantly consumed and supplied in the reaction, which made a significant effect on the growth of HAP crystal grain. In addition, pure HAP could be prepared in the solution with initial pH = 9 using ammonia solution22, while it could not synthetized when the initial pH = 10.5 was in the NaOH solution27, which may be a proof for the above conclusion. On the basis of above results, the size of HAP particles could be controlled by alkaline reagent and the reaction time of hydrothermal treatment, just as summarized in Figure 7. For the reaction time of 8 h, the nanoparticles as-prepared using ammonia solution have smaller sizes than those reached using NaOH solution. Besides, the size and morphology of nanoparticles could be controlled by adjusting the reaction time.

(b)

(a)

200 nm

100 nm

50

45 40

(c)

(d) 40

35

Number (%)

30

Number (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


25 20 15 10

30

20

10

5

0

0 80

100

120

140

Length (nm)

160

180

40

60

80

100

120

Length (nm)

Figure 6. SEM image of pure HAP assisted with ammonia in the process: (a) reaction time of 8 h, (b) reaction time of 2 h; (c) size distribution of the particles in Figure (a) and (d) size distribution of the particles in Figure (b).


ammonia 12 11.5 11

2

long belts

rods

short rods

0

Page 12 of 18

NaOH

8 Reaction Time / h

12

Figure 7. Schematics of the size of HAP controlled by the pH and time.

3.2 Applications of HAP nanoparticles The nanoparticles doped with metal ion were frequently reported for high-performance optical applications.28,

29

Meanwhile, Tb3+, Eu3+ and Ca2+ have

similar ion radii and coordination environment.30,

31

Thus, terbium and europium

could be doped into hydroxyapatite with the dimension below 100 nm, which has been widely observed in recent works32-36. Figure 8 shows that the XRD patterns of the doped particles are in accord with the standard pattern of pure HAP, indicating the particles are still HAP in structure. Moreover, the following excitation and emission spectra (Figure 9) of the doped HAP indicate that the particles have photoluminescence properties, while the pure HAP is not fluorescent.

HAP: 0.01 Eu Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

pH of initial solution


HAP: 0.01 Tb

HAP: JCPDS No.09-432

10

20

30

40

50

60

2θ (degree)

Figure 8. XRD patterns of doped HAP nanoparticles.


70

Page 13 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 9a exhibits the excitation wavelength of Tb-doped HAP mostly ranging from 300 nm to 400 nm (in ultraviolet region) with a peak at 376 nm. In Figure 9b, the emission wavelength at 488, 543, 583 and 621 nm accord with 5D4-7Fj (j=6, 5, 4, 3) transitions of Tb3+, respectively37,

38

, and the peak at 543 nm is strongest one,

indicating that the solids are emitting green light. Though the solids mainly absorb UV-light, they could also absorb the light with wavelength at 484 nm. The insert in Figure 9b shows the PL spectrum of Tb-doped HAP with excitation wavelength at 484 nm, which still retains quite a large intensity. The blue light with wavelength at 484 nm would not kill living cells, which had been applied in biological experiments31, 35, 37

. Figure 9c depicts the PLE spectrum of Eu-doped HAP, which reveals that the

excitation light with wavelength at 393 nm could be absorbed adequately. Figure 9d shows the emission wavelength at 573, 590, 613, 650 and 697 nm due to the 5D0-7Fj (j=0, 1, 2, 3, 4) transitions of Eu3+, respectively39-41. And the emission peak located in 613 nm indicates that the particles emit the red-orange light primarily. As Tb-doped HAP, Eu-doped HAP could also absorb the blue light at 464 and 500 nm, indicating that Eu-doped HAP could also be applied in the biological field34-36,

42

. The PL

spectrum with excitation wavelength at 464 nm (the insert in Figure 9d) also retains large intensity, which indicates that the fluorescence property of Eu-doped HAP is also good.



(a)

λem = 543 nm

376 369

160000

Intensity (a.u.)

Intensity (a.u.)

90000

351 60000 484

30000

339

316

(b)

60000 5

543

λ ex= 376 nm

120000

30000

80000

0

583

5

550

D 4 -7 F 6 488

5

40000

350

400

450

621

600

D 4- 7F 4

5

583

0 300

λ ex= 484 nm

543

7

D4 - F 5

442

650

7

D 4- F 3 621

0

500

500

550

Wavelength (nm)

600

650

Wavelength (nm) 15000

40000

(c)

393 nm

80000

λ em = 613 nm

Intensity (a.u.)

20000 382 nm 464 nm 318 nm

500 nm

7

613 nm

350

400

450

500

550

5000

697

D0- F1

590 nm

40000

0 550

600 5

650

700

7

D0- F4

20000

5

7

D0- F0

5

0 550

7

D0- F3

573 nm

0 300

5

λex = 464 nm

7

D0- F2

60000

362 nm

573 590

10000

30000

10000

613

(d) λex = 393 nm 5

Intensity (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 14 of 18

697 nm

650 nm 600

Wavelength (nm)

650

700

750

Wavelength (nm)

Figure 9. Excitation and emission spectra of doped HAP: (a) PLE spectrum of Tb-doped HAP with emission wavelength at 543nm, and (b) PL spectrum with excitation wavelength at 376 nm (the insert is PL spectrum with excitation wavelength at 484 nm); (c) PLE spectrum of Eu-doped HAP with emission wavelength at 613nm, (d) PL spectrum with excitation wavelength at 393 nm (the insert is PL spectrum with excitation wavelength at 464 nm).

4. Conclusions

In this study, the HAP nanoparticles were prepared via a hydrothermal method assisted by a coprecipitation process without any organic additives, which preserves the bioactivity and biocompatibility of HAP. Moreover, the HAP length ranging from 40 to 1500 nm was controlled by adjusting the alkaline agent and the reaction time in hydrothermal condition, and the morphologies changed from rods to belt-like ones with increasing reaction time. The formation of pure HAP phase was confirmed by XRD patterns and FTIR spectra, which also prove that there are no organic contaminants in the obtained HAP. Furthermore, the growth mechanism of single HAP crystal and the growth process of HAP particles are explained. In addition, the


Page 15 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


rods of size less than 100 nm were partially doped with Ln (Ln = Tb, Eu). And the doped nanometer particles could respectively emit green and red-orange light when excited by blue light. Due to biocompatibility and fluorescence, doped nano-HAP offers important potential applications in blue-light phototherapy and fluorescence labeling.

Acknowledgment

This present work was supported by the National Natural Science Foundations of China (Grant No. 51672257), the Fundamental Research Funds for the Central Universities (Grant No. 2652016051 and 2652016083), the State Scholarship Fund of China Scholarship Council (CSC). The authors are deeply grateful to Dr. Jinzhong Zhang for both criticisms and fruitful suggestions. Reference

(1) Liao, C. J.; Lin, F. H.; Chen, K., Shao; Sun, J. S. Thermal decomposition and reconstitution of hydroxyapatite in air atmosphere. Biomaterials 1999, 20, 1807-1813. (2) Jarcho, M. Calcium phosphate ceramics as hard tissue prosthetics. Clin. Orthop. Relat. R. 1981, 57, 259-278. (3) Cai, Y. R.; Liu, Y. K.; Yan, W. Q.; Hu, Q. H.; Tao, J. H.; Zhang, M.; Shi, Z. L.; Tang, R. K. Role of hydroxyapatite nanoparticle size in bone cell proliferation. J. Mater. Chem. 2007, 17, 3780-3787. (4) Hu, Q. H.; Tan, Z.; Liu, Y. Effect of crystallinity of calcium phosphate nanoparticles on adhesion, proliferation, and differentiation of bone marrow mesenchymal stem cells. J. Mater. Chem. 2007, 17, 4690-4698. (5) Dorozhkin, S. V. Bioceramics of calcium orthophosphates. Biomaterials 2010, 31, 1465-1485. (6) Chen, H.; Gao, J.; Su, S.; Zhang, X.; Wang, Z. A Visual-Aided Wireless Monitoring System Design for Total Hip Replacement Surgery. IEEE T. Biomed. Cric. S. 2015, 9, 227-236. (7) Ketaki, D.; M. Monsoor, S.; Sutapa, R. R.; Meenal, K. Self-Activated Fluorescent Hydroxyapatite Nanoparticles: A Promising Agent for Bioimaging and Biolabeling. ACS Biomater. Sci. Eng. 2016, 2, 1257–1264. (8) Wang, C.; Liu, D.; Zhang, C. Defect-Related Luminescent Hydroxyapatite-Enhanced Osteogenic Differentiation of Bone Mesenchymal Stem Cells Via an ATP-Induced cAMP/PKA Pathway. ACS Appl. Mater. Interfaces 2016, 8, 11262–11271. (9) Koirala, M. B.; Nguyen, T. D.; Pitchaimani, A.; Choi, S. O.; Aryal, S. Synthesis and Characterization of Biomimetic Hydroxyapatite Nanoconstruct Using Chemical Gradient across Lipid Bilayer. ACS Appl. Mater. Interfaces 2015, 7, 27382-27390. (10) Zhang, X.; Liu, M.; Wang, B.; Chen, H.; Wang, Z. A Wide Measurement Range and Fast Update Rate Integrated Interface for Capacitive Sensors Array. IEEE T. Circ. S. 2014, 61, 2-11.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(11) Ma, Y.; Zhang, J.; Guo, S.; Shi, J.; Du, W.; Wang, Z.; Ye, L.; Gu, W. Biomimetic mineralization of nano-sized, needle-like hydroxyapatite with ultrahigh capacity for lysozyme adsorption. Mater. Sci. Eng. C 2016, 68, 551-556. (12) Teshima, K.; Wagata, H.; Sakurai, K.; Enomoto, H.; Mori, S.; Yubuta, K.; Shishido, T.; Oishi, S. High-Quality Ultralong Hydroxyapatite Nanowhiskers Grown Directly on Titanium Surfaces by Novel Low-Temperature Flux Coating Method. Cryst. Growth Des. 2012, 12, 4890-4896. (13) Peng, Q.; Zhang, C.; Zhao, X.; Sun, X.; Li, F.; Chen, H.; Wang, Z. A Low-Cost UHF RFID System With OCA Tag for Short-Range Communication. IEEE T. Ind. Electron. 2015, 62, 4455-4465. (14) Guang, S.; Ke, F.; Shen, Y. Controlled Preparation and Formation Mechanism of Hydroxyapatite Nanoparticles under Different Hydrothermal Conditions. J. Mater. Sci. Technol. 2015, 31, 852-856. (15) Hawkins, D.; Houreld, N.; Abrahamse, H. Low Level Laser Therapy (LLLT) as an Effective Therapeutic Modality for Delayed Wound Healing. Ann. N.Y. Acad. Sci. 2005, 1056, 486-493. (16) Papageorgiou, P.; Katambas, A.; Chu, A. Phototherapy with blue (415 nm) and red (660 nm) light in the treatment of acne vulgaris. Br. J. Dermatol. 2000, 142, 973–978. (17) Dai, T.; Tegos, G. P.; Zhiyentayev, T.; Mylonakis, E.; Hamblin, M. R. Photodynamic therapy for methicillin-resistant Staphylococcus aureusinfection in a mouse skin abrasion model. Laser Surg. Med. 2010, 42, 38-44. (18) Ma, T.; Xia, Z.; Liao, L. Effect of reaction systems and surfactant additives on the morphology evolution of hydroxyapatite nanorods obtained via a hydrothermal route. Appl. Surf. Sci. 2011, 257, 4384-4388. (19) Guo, X. Y.; Xiao, P.; Liu, J.; Shen, Z. J. Fabrication of Nanostructured Hydroxyapatite via Hydrothermal Synthesis and Spark Plasma Sintering. J. Am. Ceram. Soc. 2005, 88, 1026-1029. (20) Han, G. S.; Lee, S.; Kim, D. W.; Kim, D. H.; Noh, J. H.; Park, J. H.; Roy, S.; Ahn, T. K.; Jung, H. S. A Simple Method To Control Morphology of Hydroxyapatite Nano- and Microcrystals by Altering Phase Transition Route. Cryst. Growth Des. 2013, 13, 3414-3418. (21) Santos, C.; Almeida, M. M.; Costa, M. E. Morphological Evolution of Hydroxyapatite Particles in the Presence of Different Citrate:Calcium Ratios. Cryst. Growth Des. 2015, 15, 4417-4426. (22) Padmanabhan, S. K.; Balakrishnan, A.; Chu, M. C.; Lee, Y. J.; Kim, T. N.; Cho, S. J. Sol–gel synthesis and characterization of hydroxyapatite nanorods. Particuology 2009, 7, 466-470. (23) Eliaz, N.; Sridhar, T. M. Electrocrystallization of Hydroxyapatite and Its Dependence on Solution Conditions. Cryst. Growth Des. 2008, 8, 3965-3977. (24) Bhat, S. S.; Waghmare, U. V.; Ramamurty, U. First-Principles Study of Structure, Vibrational, and Elastic Properties of Stoichiometric and Calcium-Deficient Hydroxyapatite. Cryst. Growth Des. 2014, 14, 3131-3141. (25) Dorozhkin, S. V. Amorphous calcium (ortho)phosphates. Acta Biomater. 2010, 6, 4457-4475. (26) Dakhlaoui, A.; Jendoubi, M.; Smiri, L. S.; Kanaev, A.; Jouini, N. Synthesis, characterization and optical properties of ZnO nanoparticles with controlled size and morphology. J. Cryst. Growth 2009, 311, 3989-3996. (27) An, L.; Li, W.; Xu, Y.; Zeng, D.; Cheng, Y.; Wang, G. Controlled additive-free hydrothermal synthesis and characterization of uniform hydroxyapatite nanobelts. Ceram. Int. 2016, 42, 3104-3112. (28) Zou, R.; Huang, J.; Shi, J.; Huang, L.; Zhang, X.; Wong, K.-L.; Zhang, H.; Jin, D.; Wang, J.; Su, Q. Silica shell-assisted synthetic route for mono-disperse persistent nanophosphors with enhanced in vivo recharged near-infrared persistent luminescence. Nano Res. 2017, 1-13. (29) Mao, Z.; Chen, J.; Li, J.; Wang, D. Dual-responsive Sr2SiO4: Eu2+-Ba3MgSi2O8: Eu2+, Mn2+


Page 16 of 18

Page 17 of 18

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


composite phosphor to human eyes and plant chlorophylls applications for general lighting and plant lighting. Chem. Eng. J. 2016, 284, 1003-1007. (30) Wang, K. The analogy in chemical and biological behaviour between non-essential ions compared with essential ions. S. Afr. J. Chem. 1997, 50, 232-239. (31) Frederick, S. R. Terbium (III) and europium (III) ions as luminescent probes and stains for biomolecular systems. Chem. Rev. 1982, 82, 541-552. (32) Zavala-Sanchez, L. A.; Hirata, G. A.; Novitskaya, E.; Karandikar, K.; Herrera, M.; Graeve, O. A. Distribution of Eu2+ and Eu3+ Ions in Hydroxyapatite: A Cathodoluminescence and Raman Study. ACS Biomater. Sci. Eng. 2015, 1, 1306-1313. (33) Rosticher, C.; Viana, B.; Maldiney, T.; Richard, C.; Chanéac, C. Persistent luminescence of Eu, Mn, Dy doped calcium phosphates for in-vivo optical imaging. J. Lumin. 2016, 170, 460-466. (34) Xie, Y.; He, W.; Li, F.; Perera, T. S.; Gan, L.; Han, Y.; Wang, X.; Li, S.; Dai, H. Luminescence Enhanced Eu(3+)/Gd(3+) Co-Doped Hydroxyapatite Nanocrystals as Imaging Agents In Vitro and In Vivo. ACS Appl. Mater. Interfaces 2016, 8, 10212-10219. (35) Hui, J. F.; Zhang, X. Y.; Zhang, Z. C. Fluoridated HAp: Ln3+ (Ln=Eu or Tb) nanoparticles for cell-imaging. Nanoscale 2012, 4, 6967-6970. (36) Chen, F.; Zhu, Y. J.; Zhang, K. H.; Wu, J.; Wang, K. W.; Tang, Q. L.; Mo, X. M. Europium-doped amorphous calcium phosphate porous nanospheres: preparation and application as luminescent drug carriers. Nanoscale Res. Lett. 2011, 6, 67. (37) Li, L.; Liu, Y.; Tao, J. Surface Modification of Hydroxyapatite Nanocrystallite by a Small Amount of Terbium

Provides a Biocompatible Fluorescent Probe. J. Phys. Chem. C 2008, 112, 12219-12224.

(38) Atuchin, V. V.; Aleksandrovsky, A. S.; Chimitova, O. D.; Krylov, A. S.; Molokeev, M. S.; Bazarov, B. G.; Bazarova, J. G.; Xia, Z. Synthesis and spectroscopic properties of multiferroic β′ -Tb2(MoO4)3. Opt. Mater. 2014, 36, 1631-1635. (39) Shi, P.; Xia, Z.; Molokeev, M. S.; Atuchin, V. V. Crystal chemistry and luminescence properties of red-emitting CsGd1-xEux(MoO4)2 solid-solution phosphors. Dalton Trans. 2014, 43, 9669-9676. (40) Atuchin, V. V.; Aleksandrovsky, A. S.; Chimitova, O. D.; Gavrilova, T. A.; Krylov, A. S.; Molokeev, M. S.; Oreshonkov, A. S.; Bazarov, B. G.; Bazarova, J. G. Synthesis and Spectroscopic Properties of Monoclinic α-Eu2(MoO4)3 J. Phys. Chem. C 2014, 118, 15404-15411. (41) Zhang, J.; Gong, S.; Yu, J.; Li, P.; Zhang, X.; He, Y.; Zhou, J.; Shi, R.; Li, H.; Peng, A.; Wang, J. Thermally Stable White Emitting Eu3+ Complex@Nanozeolite@Luminescent Glass Composite with High CRI for Organic-Resin-Free Warm White LEDs. ACS Appl. Mater. Interfaces 2017, 9, 7272-7281. (42) Xie, Y.; Perera, T. S.; Li, F.; Han, Y.; Yin, M. Quantitative Detection Method of Hydroxyapatite Nanoparticles Based on Eu(3+) Fluorescent Labeling in Vitro and in Vivo. ACS Appl. Mater. Interfaces 2015, 7, 23819-23823.



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 18

For Table of Contents Use Only

Growth Mechanism of

Surfactant-free Size-controlled

Luminescent Hydroxyapatite Nanocrystallites Haoshuo Li1, Lefu Mei1*, Haikun Liu1, Yangai Liu1, Libing Liao1*, R Vasant Kumar2* 1

Beijing Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China. 2 Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, CB3 0FS, UK

0.34nm

1 1

precursor

0.47nm

2 2 3

3

4

4 HAP crystal

OH-

PO43-

Ca2+

a facile surfactant-free hydrothermal method assisted with coprecipitation has been explored in order to prepare size-controlled HAP nanorods, and the growth mechanism of HAP nanostructures has also been proposed.


Growth Mechanism of Surfactant-Free Size-Controlled Luminescent

Recommend Documents