Electrogenerated singlet oxygen chemiluminescence during in situ transformation of nanostructured brushite to hydroxyapatite on Nafion film

Abstract

The nanostructures and phase transformations of calcium phosphates (CaPs) on the solid-water interface have attracted a great deal of recent interests in wide research fields. The structural water molecules or the coordinated hydroxyl (OH) are crucial points of consideration for the phase transformation and the production of redox active intermediates with electrochemically stable species. In this work, nanostructured brushite (DCPD, CaHPO4•2H2O) was assembled in situ on Nafion modified glassy carbon electrode (GCE) in Ca(NO3)2 and NaH2PO4 solution. Upon application of cyclic voltammetric (CV) scan, a strong electrogenerated chemiluminescence (ECL) was observed at 1.0 V vs Ag/AgCl in pH 7.4 phosphate buffer solution. Characteristic emission signals at 634 nm and 1268 nm manifested the generation of singlet oxygen. Raman spectroscopy and X-ray diffraction (XRD) spectrum evidenced phase transformation during CV scans, and entailed CV peaks showed the transformative immediate species were attributed to the ECL. This finding provides one insight into the intermediate species during the CaPs phase transformation. Furthermore, the method presented in this work also supplied a new route for singlet oxygen generation from earth abundant materials.