Preparation Of Hydroxyapatite By Biomimetic Synthesis And Its Properties

Hydroxyapatite?HA?,possesses good biocompatibility,bioactivity,osteoconductivity,biodegradability and adsorption performance,is the major component of teeth and bone of vertebrate,which is also commonly used in biomedical field.However,few researchers focus their attention on the field of adsorption.Improtantly,the different excellent properties of HA are varying from its distinguishing shapes.This thesis aims to prepare HA with specific morphology and structure by biomimetic synthesis ways,and improve its adsorption performance for the treatment of wastewater.?1?HA with perforated porous structure was successfully synthesized using shell powder as the raw material by double interfacial diffusion method based on diffusion method in vitro simulation method.The discussion of ammonium hydroxide volume,calcium ion concentration and calcium source et al factors determines experimental conditions.The structure of obtained products was characterized by a series of instruments,such as X-ray diffraction,fourier transform infrared spectrograph,field-emission scanning electron microscopy,Transmission electron microscopy,particle size,Thermogravimetry and nitrogen adsorption–desorption analysis etc.Results indicate that the perforated porous structure of products is composed of nanosheets and has high specific surface area(up to188.5 m²·g^–1).It is could be used as an adsorbent for treating wastewater.Thus,investigation of adsorbing Sr²⁺in solution was further examined by discussing factors such as initial pH,ion strength,adsorbent dosage,contact time,initial Sr²⁺concentration and temperature,and three nonlinear kinetic models?pseudo-first-order,pseudo-second-order and general-models?,three nonlinear isothermal adsorption models?Langmuir,Freundlich and Liu models?,and the linear relation of thermodynamic were fitted.The results showed that the maximum adsorption capacity of HA was 45.36 mg·g^–1,and the removal rate is up to 98.94%at 313.15K;the kinetics and equilibrium adsorption data followed the nonlinear pseudo-second-order kinetic model and nonlinear Liu isotherm adsorption model during the adsorption process;and the adsorption process of Sr²⁺was endothermic,feasible,and spontaneous in nature as studied via thermodynamic analysis??G°<0,?H°>0,and?S°>0?.The enthalpy change(?H°<40 kJ·mol^–1)indicated that the adsorption process was mainly based on physical adsorption.In addition,a possible adsorption mechanism was proposed.Meanwhile,leaching and desorption experiments was used to evaluate recycling capacity.?2?HA with unique morphology and large specific surface area was synthesized by bacillus subtilis induction method,which was applied to the field of adsorption.The effects of factors,such as concentration of bacterial solution,reaction time and calcium ion concentration,were investigated to determine optimal experimental conditions:the concentration of bacterial liquid was 5.0×10⁸ cfu·mL^–1,the reaction time was 12 h,and the calcium ion concentration was 0.050 mol·L^–1.The obtained HA with porous morphology self-assembled by sheets,which were composed of nanoparticles,had average particle size of 0.66?m and higher specific surface area(196.7 m²·g^–1)under this condition,which was suitable for adsorption.The effects of factors including pH value,adsorbent dosage,ion strength,contact time,initial ion concentration and temperature on adsorption UO₂²⁺of HA were investigated,the linear and nonlinear fitting of the two kinetic models?pseudo-first-order and pseudo-second-order?,three nonlinear isotherm adsorption models?Langmuir,Freundlich and Liu models?and linear relationship of thermodynamic were performed.Meanwhile,the fitting parameters were calculated.The experimental results indicated that the equilibrium time was 120 min;the maximum adsorption capacity was 1025 mg·g^–1 and the maximum removal rate is 96.84%;the adsorption process kept consistent with the linear pseudo-second-order kinetic model and nonlinear Liu isotherm adsorption model;thermodynamic data(?G°<0,?H°=12.92 kJ·mol^–1,?S°=113.7 J·mol^–1·K^–1)could indicate that it was a spontaneous,endothermic and an increase of degrees of freedom process.The desorption rate of the desorption experiment was up to 97.97%,demonstrating the desorption effect was better.Meanwhile,the possible adsorption mechanism was also proposed.In this paper,the biomimetic synthesis method was successfully used to prepare HA with unique morphology and large specific surface area.This method is simple,controlling easily and strong feasibility.In sddition,it shows good adsorption effect and important potential significance in the field of wastewater treatment.