The Electrochemistry And Analytical Application Of Magnesium Phosphates Based On Their Hydration Process

Magnesium phosphate（MgPs）is an important type of biological materials which has a wide range of applications in the field of biomedicine.The hydration of MgPs is of great significance to its formation and application,while the electrochemical oxidation activity and the function of water molecules that is influenced by Mg²⁺ions and phosphate ions have not been studied yet.This article explored the electrochemical behavior of MgPs formation and their hydration process,and constructed a detection platform for phosphate ions based on its H₂O activity.The main achievements in this paper are listed as follows:（1）The more initial magnesium source in incubating solution,the more favorable the formation of MgHPO₄·3H₂O in the condition of pH 7.4,and the higher phosphorus source content,the more conductive to the formation of Mg₃（PO₄）₂·5H₂O and Mg₃（PO₄）₂·8H₂O phases.The incubating solution can form MgHPO₄·3H₂O under the circumstance of pH 7.4,and slowly transform to Mg₃（PO₄）₂·5H₂O.The increasement of pH speeds up the phase transition procedure.It is observed that the structure of the surrounding phosphate radicals is constantly changing,during the MgPs phase transition process,until the MgPs forms a stable phase.（2）The MgHPO₄·3H₂O was assembled on the MWCNT/Nafion modified glassy carbon electrode,namely the prepared MgPs/MWCNT/Nafion electrode.The coordinated H₂O is generated by MgHPO₄·3H₂O in the solution,which forms coordinated hydroxide（OH^-）under the action of phosphate deprivation.The combinative OH^-appears an obvious electrochemical oxidation peak with electrical stimulation.After adding free Mg²⁺ions,it promotes the generation of more coordinated H₂O and OH^-,which realizes direct electrochemical detection of phosphate ions in the range of 0.1μM to 10μM.The concentration of phosphate ions is proportional to the current height of the oxidation peak.In addition,the MgPs/MWCNT/Nafion electrode displays good selectivity,which is not affected by other anions during the detection of phosphate.（3）The MgPs/MWCNT/Nafion in Mg-rich state was successfully assembled in-situ on the MWCNT/Nafion modified electrode.Raman spectroscopy,infrared spectroscopy,X-ray diffraction and energy dispersive X-ray spectroscopy confirmed the formation of MgPs in the magnesium-rich state.The electrochemical oxidation peaks at different potentials and intensities were observed in different buffer solutions.In pH 7.4 phosphate buffer solution,it was proved that the oxidation peaks of the modified electrode at 0.7 and 1.0 V vs Ag/Ag Cl were enhanced with the prolonging of incubation time and the increasement of the content of Mg²⁺ions in the initial medium.Data analysis of infrared spectroscopy and X-ray photoelectron spectroscopy verified the difference in the content and state of the formed MgPs coordinated H₂O,which resulted in the conversion of coordinated H₂O through coordinated OH^-to bound OOH under the promotion of phosphate,and then released oxygen.This discovery provides direct experimental evidence for the electrochemical oxidation mechanism of water,and also offers a rich source of inorganic materials for the electrochemical oxidation of water.