Immobilization of cadmium ions to synthesis hierarchical flowerlike cadmium phosphates microspheres and their application in the degradation of organic pollutants under light irradiationElectronic supplementary information (ESI) available: N2 adsorption-desorption isotherms and pore-size distribution of Cd5(PO4)2P2O7 (T500 and T700), comparative photocatalytic activity of samples under the irradiation of visible light (λ > 400 nm), SEM image of Cd5(PO4)2P2O7 (T400) irregular nanoparticles. See D

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 Cd 5 H 2 (PO 4 ) 4 ·4H 2 O 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 Cd 5 (PO 4 ) 2 P 2 O 7 was readily obtained by calcination of the Cd 5 H 2 (PO 4 ) 4 ·4H 2 O 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), N 2 adsorption-desorption (BET), and UV-vis diffuse reflectance spectroscopy (DRS). The as-prepared Cd 5 H 2 (PO 4 ) 4 ·4H 2 O and Cd 5 (PO 4 ) 2 P 2 O 7 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 Cd 5 (PO 4 ) 2 P 2 O 7 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 Cd 5 (PO 4 ) 2 P 2 O 7 towards RhB degradation were also discussed. Hierarchical flowerlike Cd 5 H 2 (PO 4 ) 4 ·4H 2 O and Cd 5 (PO 4 ) 2 P 2 O 7 microspheres were prepared by cadmium ion immobilization followed by an annealing treatment. Cd 5 (PO 4 ) 2 P 2 O 7 was applied as a novel photocatalyst toward dye degradation under light irradiation.