In situ synthesis of three dimensional graphene-hydroxyapatite nano powders via hydrothermal process

doi:10.1016/j.matchemphys.2018.10.023

Materials Chemistry and Physics

Volume 222, 15 January 2019, Pages 251-255

https://doi.org/10.1016/j.matchemphys.2018.10.023 Get rights and content

Highlights

•
The hydrothermal process led to the reduction of graphene oxide.
•
The hydrothermal process resulted in the synthesis of hydroxyapatite nano-rods.
•
Graphene oxide sheets were assembled together and a 3D rGO structure was formed.
•
In hydrothermal conditions, the hybrid powder of 3DG coated with hydroxyapatite nano rods was synthesized.

Abstract

In this study, in situ formation of three dimensional graphene-hydroxyapatite using graphene oxide, calcium nitrate tetra hydrate, and diammonium hydrogen phosphate solutions in a chemical synthesis system was investigated. First, the solutions were mixed and calcium phosphate was precipitated on graphene oxide sheets followed by performing a hydrothermal method at 180 °C, 2.2 MPa, pH = 11, and 6 h. The latter process resulted in the formation of three dimensional graphene while it was coated on hydroxyapatite nanorods. The synthesized powders were characterized in two steps for calcium phosphate-graphene oxide powders before hydrothermal process and three dimensional graphene-hydroxyapatite powders after hydrothermal process with Fourier-Transform Infrared spectroscopy (FT-IR), Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Energy Dispersive Spectroscopy (EDS), and Raman spectroscopy. The results of XRD and FTIR analysis showed that in the first step, di-calcium phosphate dehydrates were formed on graphene oxide sheets and converted to hydroxyapatite after the hydrothermal process. Raman spectroscopy analysis and FTIR confirmed that graphene oxide has been reduced in the hydrothermal process. Also, microscopic images confirmed the three-dimensional structure of graphene after hydrothermal process. Finally, the results showed that the hydrothermal method leads to the formation of a high crystalline hydroxyapatite nanorods that cover the surface of the three dimensional graphene.

Introduction

With the aging population, the number of patients with osteoporosis will increase, so there is a need for better treatments for the patient and the affected bones. About 70% of the bone ingredients contain calcium phosphate, so calcium phosphates are good materials for repairing damaged bones. These materials have good biocompatibility and bioactivity [1].

Hydroxyapatite, with the chemical formula of [Ca₁₀(PO₄)₆(OH)₂], is one of the most widely used as calcium phosphate compounds in tissue engineering. The ratio of calcium to phosphate in hydroxyapatite is 1.67 and is very similar to bone tissue [2,3]. Researchers have made great efforts to improve the biological and mechanical properties of hydroxyapatite. These efforts have been largely based on changing the shape and dimensions of powders, structure, or addition of a reinforcing phase to these materials [4,5]. So far, many methods have been reported for the synthesis of hydroxyapatite. Among them, the hydrothermal method has always been of interest due to its speed, quality, and control capability [6].

Graphene, a two-dimensional material, recently attracted the attention of researchers due to its osteoconductivity and good biocompatibility [[7], [8], [9]]. Several reports have been published on the use of two dimensional graphene as a reinforcing phase in hydroxyapatite-based composites. Zhang et al. [10] have worked on hydroxyapatite/mesoporous graphene/carbon nanotubes hybrid membranes for regenerative medicine, studying biological properties of the composite materials and achieved good results. Other studies have also been published on the synthesis of reduced graphene oxide-hydroxyapatite composites, and in some of them sintering properties of the synthesized powder have been investigated [[11], [12], [13], [14]]. In most of the research, two-dimensional graphene has been used as filler in the final composite materials [[15], [16], [17]].

To exploit fully, the inherent properties of graphene sheets are often assembled into functional architectures with three dimensional interconnected porous microstructures. The three dimensional graphene based materials show many excellent characteristics including increased chemical stability and flexibility. Recently, a great deal of research has been done for the synthesis of three dimensional graphene. One of the applications of three dimensional graphene is its use in tissue engineering as scaffolds [18,19]. So far, various methods for the synthesis of three dimensional graphene have been used including sugar blowing assisted reduction and interconnection of graphene oxide [20], use of metal oxide as cross linker [21], the hydrothermal method and the use of the nickel template [22,23]. The three-dimensional graphene that is synthesized by these methods is achieved by self assembling graphene sheets together and in fact displaying two-dimensional graphene properties in some extent in three dimensions [24].

In the last five years, various studies have been done to synthesize powders and composites that hydroxyapatite and three dimensional graphene are their main phases. In a number of published reports, the hydrothermal method has been used [8,12]. This method has always been considered, as it leads to the formation of in situ hybrid powders. In some of these reports, the hydrothermal method has been introduced separately, while in this work, the in situ formation of 3D graphene synthesized by hydrothermal process [[25], [26], [27]].

Although the published reports are useful and introduce the properties of synthesized powders, however, in none of the reports, hydrothermal synthesis details have been investigated and the formed structures after precipitation in the initial step of the process is unknown. So, the purpose of this study is to synthesize a three dimensional graphene-hydroxyapatite nano structure powders via hydrothermal process and to find the mechanism for hybrid powders formation.

Section snippets

Materials and methods

Calcium nitrate tetrahydrate (Ca(NO₃)₂·4H₂O, ≥ 99.0%) and Diammonium hydrogenphosphate ((NH₄)₂HPO₄, ≥99.0%) were purchased from Sigma Aldrich. Graphene oxide colloid was purchased from Abalonyx (Norway).

For the hydrothermal process, a set up shown schematically in Fig. 1, was designed and manufactured in this work. The volume of the PTFE container is 330 cc.

For synthesis of nano powders, solutions containing calcium and phosphorus are prepared with calcium to phosphorus ratio of 1.67. For this

Results and discussion

Fig. 2 shows the mechanism of nano powder formation by hydrothermal method. At the beginning of the process (Fig. 2a,b), Calcium ions (Ca²⁺) added to graphene oxide colloid are absorbed into carboxyl groups (-COOH or COO-) due to electrostatic interactions between calcium ions and functional groups located on the graphene oxide surface [28]. This phenomenon makes the subsequent reactions, which lead to the formation of calcium phosphates; tend to be more heterogeneous nucleation than

Conclusions

The three dimensional graphene-hydroxyapatite nanocomposite powders were well synthesized in this study. The results of the XRD analysis showed that the primary powder, formed by the reaction of the precipitation of the reactants, is mainly DCPD formed on the surface of the graphene oxide. After the hydrothermal process, the monoclinic structure of DCPD has changed to the hydroxyapatite hexagonal structure. This issue is known in microscopic images. The FTIR analysis also confirms this phase

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View full text

In situ synthesis of three dimensional graphene-hydroxyapatite nano powders via hydrothermal process

Highlights

Abstract

Introduction

Section snippets

Materials and methods

Results and discussion

Conclusions

Mater Sci Eng C Mater Biol Appl.

J. Mech. Behav. Biomed. Mater.

Carbon

Carbon

Ceram. Int.

Adv. Colloid Interface Sci.

J. Eur. Ceram. Soc.

Synth. Met.

Carbon

Thin Solid Films

Ceram. Int.

Ceram. Int.

Calcium phosphates in biomedical applications: materials for the future

Mater. Today

Main properties of nanocrystalline hydroxyapatite as a bone graft material in treatment of periodontal defects, A review of literature

Biotechnol. Biotechnol. Equip.

Preparation and properties of nanoparticles of calcium phosphates with various Ca/P ratios

J. Res. Natl. Inst. Stand Technol.

Silk fibroin/hydroxyapatite composites for bone tissue engineering

Biotechnol. Adv.

Hydrothermal synthesis of hydroxyapatite

J. Phys. Conf.

Graphene: a versatile platform for nanotheranostics and tissue engineering

Prog. Mater. Sci.