Synthesis And Characterization Of The Structure And Adsorption Properties Of Doped Hydroxyapatite

In this paper, undoped hydroxyapatite (HAP), carbon-doped hydroxyapatite(CHAP) and Mg-doped hydroxyapatite (MgHAP) were synthesized by sol-glemethod, in which taking calcium nitrate tetrahydrate, phosphoric acid, ammoniumbicarbonate and magnesium nitrate hexahydrate as calcium source, phosphorussource and magnesium source respectively. Studied the pH of precursors system,the calcination temperature optimum and the mole rate of doped ions, in order tofind the optimun conditions of synthesizing hydroxyapatite. The synthesizedhydroxyapatites were characterized by X-ray diffraction (XRD), scanning electronmicroscopy (SEM), IR spectroscopy (FTIR), BET specific surface areacharacterization. Using the synthesized HAP, CHAP, MgHAP conducted theexperiments of adsorbing aqueous copper ions and fluoride ions under differentconditions to investigate the mechanism of hydroxyapatite adsorption.The optimum conditions of synthesizing hydroxyapatite that precursor systempH is10, the calcination temperature is650℃. For CHAP and MgHAP whendoping as n (C)/n (P)=0.1, n (Mg)/n (Ca+Mg)=0.1, single phase is obtained,the grain size is at the nanoscale (less than100nm).The experiments result of adsorbing aqueous copper ions shows the process canbe described by proposed second-order equation and Langmuir isotherm, whichindicated that the adsorption process was a kind of chemical adsorption. Theadsorption capacity of HAP、CHAP and MgHAP were19.64mg/g,31.01mg/g,35.51mg/g respectively. The pH influence experiment and the analysis of Ca2+、Mg2+and Cu2+concentration after reaction showed that when initial pH=5theadsorption mechanism was ion exchange, when initial pH=2~4the adsorptionmechanism was ion exchange and physical adsorption, in which the dissolution ofhydroxyapatite existed. XRD analysis of the reaction products shows in HAP andCHAP there were no new phase no matter initial pH=5or3, but in MgHAP therewas a large number of tricalcium phosphate, which was caused due to the smallerradius of the magnesium ions.The experiments result of adsorbing aqueous fluoride ions shows the processcan be described by proposed second-order equation and Langmuir isotherm, whichindicated that the adsorption process was a kind of chemical adsorption. Asorptioncapacity of HAP, CHAP and MgHAP were1.82mg/g,1.69mg/g and1.10mg/grespectively. XRD analysis result of the reaction products ascertain no new phaseformed. The adsorption process was dissolution-precipitation reactions and ionexchange reactions joint action is concluded from the result combined with previousstudies.