Immobilization of cadmium ions to synthesis hierarchical flowerlike cadmium phosphates microspheres and their application in the degradation of organic pollutants under light irradiation

Abstract

The treatment of wastewater especially that contaminated by heavy metals and/or organic pollutants by a green, cost-efficient and robust route is highly desirable. Herein, by addition of phosphates to immobilize cadmium ions, hierarchical flowerlike Cd₅H₂(PO₄)₄·4H₂O microspheres were successfully prepared by nanosheet formation and following self-assembly at room temperature without additive assistance. The influence of experimental parameters such as pH value and raw materials (cadmium ions and phosphate ions) on the morphology and crystal structure of the products was studied. Hierarchical Cd₅(PO₄)₂P₂O₇ was readily obtained by calcination of the Cd₅H₂(PO₄)₄·4H₂O precursor. The microstructures of the products were characterized by X-ray power diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), N₂ adsorption–desorption (BET), and UV-vis diffuse reflectance spectroscopy (DRS). The as-prepared Cd₅H₂(PO₄)₄·4H₂O and Cd₅(PO₄)₂P₂O₇ possessed a wide band gap energy of 5.56 eV and ca. 5.00 eV, respectively. Owing to the strong oxidation/reduction ability and the unique hierarchical structure, hierarchical Cd₅(PO₄)₂P₂O₇ microspheres exhibited excellent photocatalytic activity and durability for the degradation of organic pollutants (rhodamine B, RhB) under UV light irradiation. The main reactive species and the photocatalytic mechanism of Cd₅(PO₄)₂P₂O₇ towards RhB degradation were also discussed.