Synthesis Of Hydroxyapatite Nano-crystal Agglomerates By Template-assisted Biomineralization And Its Electrochemical Sensing Capability

Hydroxyapatite has been widely used as inorganic biomedical material. The unique3D network structure ensures its excellent electrochemical sensing capability. Among numerous synthesis methods, template-assisted biomineralization provides an effective way for regulating the morphologies and micro structures of HAp with advantages of environmentally friendly, simple process and low cost. Focused on this application area, HAp agglomerates with unique microstructure were fabricated by the template-assisted biomineralization method and the template-controlling mechanisum of morphology and microstructure has been investigated in detail. Furtherly, their electrochemical sensing capabilities towards toxic divaluent heavy metal ions, tervalence arsenic ions and organic molecules were researched respectively. The main contents of the present dissertation are listed as follows:1. A new natural biotemplate-assisted biomineralization method has been proposed to fabricate HAp agglomerates. Wherein, the natural bio-membrane and biomass was used as the templates in the biomineralization process respectively and the influences of them on the morphologies and microstructure of HAp agglomerates have been investigated systematically. It reveals that the biomembranes (egg-shell membranes and bamboo membrane) can regulate the crystal growth mainly by controlling the diffusion of reagent ions. The physical and chemical properties as well as functional groups can affect the nucleation process on the surface. Higher temperature and higher pH value can enhance the driving force for the formation of HAp, favor to its growth towards c-axis, following the "nucleation-dissolution recrystallization-self-assembly" mechanism. The organic matrix in natural eggshell has positive influences on the transformation to3D flower-like HAp agglomerate in a relatively fast way.2. A facile Nafion cathion-exchange membrane assisted strategy has been proposed for constructing multi-dimesional HAp nano-structure. Herein, seacucumber-like HAp agglomerates have been firstly prepared by this method, followed the "grow at the bottom" mechanism. On the other hand, a Nafion-assisted electrodeposition technology has been firstly applied for the fabrication. It was found that the parameters such as standard potential and microstructure of metal substrates, deposition temperature and voltage could obviously affect the deposition process. During this, the Nafion membrane plays important role in lowing the activation energy barrier for HAp and accelerating the formating reaction.3. A new determing technique has been developed via the electrochemical sensor modified by HAp assemblies with unique morphologies. The relationship between microstructure and the electrochemically sensing capability has also been researched, mainly attributes to the effect to the electro-catalytic kinetics. It suggested that the seacucumber-like HAp agglomerate with high surface area and adsorpting ability has excellent electrochemical sensing capability towards the toxic divalent heavy metal ions (Pb2+and Cd2+), with the sensitivity10-100times higher than those previously reported. Then it has been noticed that the crystal lattice structure of flower-like HAp agglomerate is crucial to the detection capabilities. Additionally,3D flower-like HAp agglomerates are explored to be a good candidate for the sensing of trace As3+. Moreover, it shows favourable electrochemical sensing behaviors towards harmful parhormone molecule (bisphenol A). This work is practically significant for the development of new electrochemical sensors with advantages of low cost, less energy consumption, easy preparation and high sensitivity.