Preparation And Properties Of In Situ Synthesized Hydroxyapatite/Polyacrylonitrile Composite Adsorption Materials

The HAp powder and in-situ synthesized HAp/PAN composite bead were prepared using the methods of precipitation and inverse microemulsion from stock solutions of (NH4)2HPO4and Ca(NO3)2-4H2O. The in-situ synthesized HAp/PAN composite fiber was prepared via the precipitation method. The forming process and synthetic route of fibers made through the precipitation approach were discussed. The synthesis conditions were discussed via orthogonal optimization. X-ray diffraction (XRD), Fourier transform infrared spectroscopy(FTIR), scanning electron microscopy(SEM), particle size measurement, thermal analysis were employed to analyze the morphology, structure, adsorption properties, thermal properties, strength of synthesized HAp powder and in-situ synthesized HAp/PAN composite materials.The aging mode in which the HAp/PANcomposite bead aged in water for24h after formation in water was more conducive to HAp synthesis. The inorganic phase in composite materials was mainly HAp with low crystallinity. The bending mode of phosphate groups belong to HAp was observed at563.3cm-1,601.9cm-1and1031.4cm-1in composite bead. The peak at2244.4cm-1is assigned to nitrile group in PAN. The peaks of carbonyl group at1630.7cm-1and1739cm-1were caused by the hydrolysis of PAN in ammonia water. The large particle size of synthesized HAp with a wide size distribution obtained via precipitation method ranged from0.5μm to6.5μm. Smaller size and more uniform distribution of HAp particles about200nm were observed in PAN/HAp composite bead using precipitation method. The result of thermal analysis showed the weight loss of composite materials was mainly caused by thermal decomposition of PAN. Gross mass fraction of HAp in composite bead and composite fiber was calculated, which was close to the theoretical value. High adsorption capacity of216.82mg/g was acheived for synthesized HAp particles at Cd2+concentration of about679.96mg/L. The adsorption amount of HAp/PAN composite bead and HAp/PAN composite fiber were41.83mg/g and27.31mg/g, respectively. Higher strength of composite fiber of1.36cN/dtex compared with neat PAN fiber was obtained owing to the synthesized HAp with small particle size and uniform distribution for reinforcing PAN.Comparing with the first synthetic route, the synthesized HAp in composite bead has lower crystallinity, smaller particle size, uniformer distribution and higher adsorption amount in the second synthetic route.It was more advantageous for synthesized HAp with smaller particle size and more uniform distribution to increase the amount of PAN matrix and reduce the concentration of precursors. Through the analysis of orthogonal optimization, good adsorption of in-situ synthesized HAp/PAN composite beads via the precipitation method can be obtained at the Ca2+concentration of0.25mol/L, synthesis temperature of60℃, coagulation bath temperature of10℃, aging time of48h, aging pH value of12. The adsorption kinetics of HAp/PAN composite bead conformed to the pseudo-second-order kinetic model. After24h, the adsorption of composite bead reached equilibrium with the cadmium adsorption amount of62.55mg/g under the conditions of the temperature of25℃and initial Cd2+concentration of about749mg/L and the theoretical adsorption amount was63.81mg/g. The thermodynamics of HAp/PAN composite bead correlated with Langmuir isotherm model and the maximum adsorption amount was148.43mg/g.The average grain diameter of synthesized HAp via inverse microemulsion method was about398nm, and the particle size distribution was relatively uniform. Larger size of HAp particles about600nm was observed in PAN/HAp composite bead. At the Cd2+concentration of about950.2mg/L, the synthesized HAp has higher adsorption amount towards Cd2+of326.27mg/g, and lower adsorption amount of22.38mg/g of composite bead was obtained due to larger particle size of HAp in composite bead and produced byproducts.