Influence of Phosphor Precursors on the Morphology and Purity of Sol–Gel-Derived Hydroxyapatite Nanoparticles Kh.Yousefi 1*, A.R.Khalifeh 2

Advances in Applied NanoBio-Technologies 2021, Volume 2, Issue 2, Pages: 49-52

J. Adv. Appl. NanoBio Tech.

Journal web link: http://www.jett.dormaj.com https://doi.org/10.47277/AANBT/2(2)52

Influence of phosphor precursors on the morphology and purity of sol–gel-derived hydroxyapatite nanoparticles Kh.Yousefi 1*, A.R.Khalifeh 2

1 Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran. 2 Department of Inspection, Shiraz Petrochemical Complex, Shiraz, Iran.

Abstract In this study nano crystalline hydroxyapatite (HA) particles were produced by both sol-gel and precipitation methods. For this purpose calcium nitrate tetra hydrate (Ca(NO3)2·4H2O) was selected as calcium precursors and three types of phosphorus precursors such as acid phosphoric (H3PO4) , triethyl phosphate (C2H5O)3PO and pentad oxide phosphorus (P2O5) were chosen. The produced powders were characterized by X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results show that although hydroxyapatite can be produced by all phosphorus precursors used in the current research, the purity of HA obtained from penta oxide phosphorus and phosphoric acid is higher than that of triethyl phosphate. The SEM micrographs prove that the morphology of nano-HAP depends on the type of phosphorus precursor .The HAP prepared from acid phosphoric was spherically shaped whereas the one from triethyl phosphate is needle like and from penta oxide phosphorus was found to be Pyramidal in shape.

Keywords: Hydroxyapatite, Sol-gel, Precipitation, Phosphor preceusor.

1 Introduction1 including Biocompatibility and degradation, depend on particle Hydroxyapatite is a ceramic which most important feature is morphology, purity and particle size[22, 23]. So in this study the bioactive, so it can establish chemical bond with tissue and different phosphor materials were used and purity and therefore it has a wide application in medicine and dentistry [1, 2]. morphology of obtained phases were compared with each other. It has been used for the construction of orthopedic implants, porous scaffold, filling bone defects, making dental implants, 2 Material and methods dental fillings, and etc [3, 4]. Several different HA synthesis 2.1 Material techniques have been developed in recent years. To obtain HA Materials that were used in three tests have been listed in Table with good morphology, nano particle size, and high purity, 1. efficient production methods should be considered [5-7]. These techniques include mechanochemical synthesis [5, [8, 9], various Table 1: Used materials type of wet chemistry techniques such as direct precipitation from Test Calcium Phosphor Solvent aqueous solutions [6], electrochemical deposition [10], sol–gel [11],and hydrothermal synthesis [12]. Among these methods, sol– No presursor presursor gel synthesis of HA ceramics has recently attracted much Test 1 Ca(NO3)2.4H2O H3PO4 water attention, due to its many advantages which include high product purity, homogeneous composition, and low synthesis temperature Test 2 Ca(NO3)2.4H2O P2O5` Ethanol [13]. But in sol-gel method many parameters affect properties of Test 3 Ca(NO3)2.4H2O (C2H5O)3PO Ethanol + product. These parameters are hydrolyzing time, aging time, temperature reaction, types of precursor and so on [14, 15]. water Researchers have been carried out many investigations to improve the sol-gel method. Effects of parameter changes such as hydrolyzing time [16, 17], aging time [18, 19], temperature 2.2 Methods reaction [20], calcium precursor [21]. Also in sol-gel method, Three type of phosphor precursors were used in this study. In different phosphor precursor are used which affect hydrolyzing test 1, first 0.25M H3PO4 was prepared in distilled water. 0.1M and aging time. As a result, they affect HA properties but the effect calcium nitrate tetra hydrate was prepared by completely of phosphor precursor not yet has been studied. Features of HA, dissolving in distilled water. This calcium solution was slowly

Corresponding author: Kh.Yousefi, Department of Materials Science and Engineering, School of Engineering, Shiraz University, Shiraz, Iran. E-mail: [email protected] 49

Advances in Applied NanoBio-Technologies 2021, Volume 2, Issue 2, Pages: 49-52

added to the acid solution. This solution was stirred for 3 h and kept 48 h for ageing at room temperature. The product was white Thrietyl phosphate solve in ethanol precipitated .This sample was named S1. The processes is schematically shown in Figure 1. In test 2, a designed amount of phosphoric pentoxide (P2O5, Increase water to solution for hydrolyzes Merck) was dissolved in absolute ethanol. A designed amount of calcium nitrate tetra hydrate (Ca (NO3)2·4H2O, Merck) was also Hydrolyze at room temperature for 24 hr dissolved in absolute ethanol to form a 1.67 mol/l solution. The solutions were mixed in a Ca/P molar ratio of 1.67 as an initial mixed precursor solution. The mixture was stirred for about 3 h at Added Ca(NO ) ·4H O to solution room temperature and the solution was kept 48 h at room 3 2 2 temperature. Here a white transparent gel was obtained. This sample was named S2. String for 24 hr at room temperature In test 3, triethyl phosphate ((C2H5O) 3 PO, TEP,) diluted in ethanol and an appropriate amount of water was added then it was stirred for 24 h to be hydrolyzed. This solution was added to String for 24 hr in room tetempercher solution Ca (NO3)2·4H2O. This mixture was stirred for 3h and was kept 48h at room temperature. The flow chart of the synthesis Aging for 24 hr is depicted in Fig. 2.

Aging for 48hr Ca(NO3)2.4H2O H3PO4

Drying at 100 overnight

Calcination at 600 for 2 hr

Calcium solution Phosphor solution Figure 2. Flow chart of hydroxyapatite preparation test 3.

3 Results and discussions 3.1 XRD analysis. Mixing When phosphoric acid is used as the phosphorus precursor Stiring at 50 for 3 hours immediately after the addition of calcium solution to phosphate solution, a white precipitate was obtained. The reaction involved in the formation of HA during the precipitation preparation can be expressed as follows:

H3PO4 + 3NH4OH = (NH4)3PO4 + 3H2O (1)

Precipitation 6(NH4)3 PO4 + 10Ca (NO3)2. 4H2O = Ca10 (PO4)6(OH)2 + and aging for 24 hours 20NH4NO3 (2)

The formation of 20mol NH4NO3 (ammonium nitrate) by product was removed by repeated washing with double distilled water. Figure 3 shows the XRD spectrum taken from test 1 sample. Graph a (pre-wash sample) confirmed that main phase is ammonium Calcination before nitrate and hydroxyapatite phase is minimal. But the only peak in Calcination after washing washing the graph b (washed sample) is hydroxyapatite that these results confirm that the phase of ammonium nitrate is dissolved in water. But when the precursor alkoxide triethyl phosphate or colloidal Figure 1. Flow chart of hydroxyapatite preparation in test 1. P2O5 are used after a few hours that solution was stirred, it transfers to concentrated solution and, over time, a given clear gel The products of three tests were dried at 80 for 24h in oven then forms, which this time aging depends on the test conditions. Figure were calcined at 600 temperatures for 2 h using an electrical 4 shows the XRD pattern of production of three tests.XRD Pattern furnace with heating rate of 10 c/min. shows that S1 and S2 are only Hydroxyapatite but S3 is In order to study the phase evolution and formation of crystalline hydroxyapatite and impurities such as carbonate calcium (CaCo3). HA, the produced powders were analysed by using IR The second product (S3) shows incomplete reaction between pre- spectroscopy (Buck 500, KBr) in the range of 500–4000 cm−1. materials calcium and phosphorus. Triethyl phosphates, is an Phase identification of the calcined gels was performed using the alkoxide precursor with a slow speed of hydrolysis. So its X-ray diffractometer (XRD, Philips, X’pert Pro, CuK_) at a incomplete hydrolysis leads to a lack of response between pre- scanning speed of 1◦ 2θ min−1 from 10◦ to 60◦. Scanning electron materials phosphorus and calcium [16]. Hydrolysis reaction of microscopy (SEM, S 360, Oxford-England) was used for triethyl phosphate (TEP) proceeds as follows: morphology analysis of products. 50

Advances in Applied NanoBio-Technologies 2021, Volume 2, Issue 2, Pages: 49-52

OP(OC2H5)3 +H2O → OP(OC2H5)3−x (OH) x +xC2H5OH (3) Therefore, in order to reduce the impurities, the time of hydrolysis should be increased so that hydrolyze thriethyl phosphate can be done completely and aging time should also be increased, so that the reaction between the precursor materials is fully done [10]. In contrast, P2O5 is a colloidal precursor and in a short time, the reaction between the raw materials is completely done. The reaction between phosphoric acid and the calcium nitrate which is based on deposition methods does not require time for hydrolysis and at a short time hydroxyapatite can be produced.

3.2 FTIR analyse FT–IR patterns presented in figure 5 confirm the formation of HA calcined at 600°C. Three produced materials in the three tests have some similar bands that the bands at 3570 and 632cm belong to the vibration of hydroxyl (O–H) group, the bands at 1089 ,1044 and 960 cm are the characterization of phosphate stretching vibration and the bands observed at 601 ,570 and 473cm are due to the phosphate being in vibration. But the three samples are different at some peaks IR. S3 has bands at1648, 1454 and 874 which are carbonat peaks that show this sample has impurity of carbonat. In contrast, S1 and S2 have only carbonatis peaks at 1648 which shows carbonate impurity in these two samples is low.

Figure 3. XRD patterns of sample S1calcined in (a) pre-washed (b) washed sample.

Figure 5. IR spectrum collected from sample S1, S2, S3 wavenumber range of 500–4000 cm−1.

3.3 Morphological analysis Fig. 6 shows the SEM micrographs of S1, S2 and S3. The morphology of the powders indicates that it is composed of agglomerates with wide particle size distributions. Powder Figure 4. XRD patterns of sample S1 ,S2, S3 (a) S3 (b) S2 (c) S1. synthesized from acid phosphoric was found to be spherical agglomerates whereas the powder synthesized from thrietyl After protonation of the alkoxide ligands (–OR) and removal phosphate is needle shape and P2O5 leads to pyramid shape. of the charged ligand (–OR) +, P–(OR) hydrolyzed forms P–(OH) Difference morphology is due to the difference of nucleation and and following interaction with Ca precursor develops the apatite growing [19]. When acid phosphoric has been used, santysis is structure. Since calcium nitrate is dissolved in water to form ionic precpitition and growing is the same in all direction, therefore derivative; the reaction may proceed as follows: morphology is spherical. But when thrietyle phosphate and panta oxid phosphor were used, the method of production is sol gel in OP(OEt)3−x (OH)x +Ca2+ +NO3→ (NO3)− (OH)–Ca–O– which interaction between precursors is at molecular scale. So nuclition and growth are different at various directions. As a result, PO(OEt)3−x +H++C2H5OH + H2O (4) morphology should be pyramid or needle like. 51

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