Research On The Synthesis Of Hydroxyapatite-graphene Composites And Its Gas Sensing Property

Abstract:Hydroxyapatite(HA), as the main component of bone, has attracted more and more widely attention for its application in chemical sensing, due to its excellent adsorption capability. Hydroxyapatite-graphene composites are promising as a new generation of gas sensing materials with both excellent adsorption capability and conductivity. Biomimetic method and chemical precipitation method were adopted to fabricate nano-sized HA in situ on the functionalized graphene sheet functionalized with dopamine. The obtained composites were firstly applied in gas sensing successfully. The main contents of the present dissertation are listed as follows:1. After biomimetic mineralization, three dimensional micro spherical HA with a diameter of3μm being wrapped and interconnected by graphene flake can be observed. While with chemical precipitation method, the obtained HA is needle-like, with the size of60to120nm in length and5nm in diameter. During the process, the functional layer of polydopamine and the graphene flake can provide with nucleation sites for HA, and act as templates at the same time. The differences of the chemical micro-environments and the driving forces in the above methods lead to diverse morphologies of the products.2. It is convenient to control the composition, the morphology and the micro-structure of hydroxyapatite by adjusting the amount of functionalized graphene, the concentration of the reagents, the pH value and the temperature. In particular, amorphous HA with nano-spherical morphology can be obtained by increasing the amount of the functionalized graphene. The concentration of reagent, the pH value and temperature are directly linked to the driving force; as a consequence, these parameters have obvious influence on the composition and microstructure of the products.3. Hydroxyapatite-graphene composites show obvious response to several volatile gases at room temperature. The gas sensor property of the composites is much enhanced than that of pure graphene reduced by the same method. Specifically, the response sensitivity of the composites to ammonia is1.9-3.7times higher than that of graphene. Besides, the response sensitivity of composites obtained by biomimetic mineralization method is even much higher than its counterpart obtained by chemical precipitation method. The mechanism of the gas sensing property of the composites is proposed to be a synergism between the excellent adsorption capability of HA and electrical conductivity of grapheme. Specifically, HA can capture the molecules of the detecting gases effectively, and graphene can act as an excellent electron transmission medium.