The wide Bi–O and P–O bond length of BiPO 4 exhibits a high photocatalytic activity for photocatalytic degradation of organic pollutants. For the BiPO 4, the Bi atom and the P atom are surrounded by eight oxygen atoms and four oxygen atoms, respectively. The BiPO 4 and Ag 3PO 4 are monoclinic phase with space group P21/n (14) and cubic phase with space group P-43n (218), respectively. Figure 2d,e show the crystal structures of BiPO 4 and Ag 3PO 4, respectively. In this case, this phenomenon may be due to the fact that CQDs do not react with oxygen in the reactor to form carbon dioxide. In our previous study, the carbon can suppress the formation of M-ferrite and α-Al 2O 3 phase prepared by a polyacrylamide gel method. The structure analysis shows that the introduction of CQDs in the Ag 3PO 4/BiPO 4 composites obviously accelerate the formation of Ag 3PO 4 and BiPO 4. For the CQDs/Ag 3PO 4/BiPO 4 composite, the intensity of the diffraction peaks is sharper than that for Ag 3PO 4/BiPO 4. In addition to the XRD characteristic peaks of the Ag 3PO 4 phase, the XRD characteristic peaks of BiPO 4 are also observed in these composites. The main XRD diffraction peaks of the Ag 3PO 4/BiPO 4 and CQDs/Ag 3PO 4/BiPO 4 composites are similar to those of pure Ag 3PO 4, indicating that the host lattice of Ag 3PO 4 in these composites undergoes no change. Figure 2c shows the XRD patterns of Ag 3PO 4/BiPO 4 and CQDs/Ag 3PO 4/BiPO 4. The XRD diffraction peaks of Ag 3PO 4 and BiPO 4 can be ascribed to JCPDF#06-0505 and JCPDF#15-0767, respectively. The result indicates that the theoretically simulated values are in good agreement with the observed XRD diffraction peaks. The black curves, red curves, vertical olive lines, and blue lines represent the observed XRD peaks, theoretically estimated curves, Bragg peaks, and difference between the observed values, and theoretically estimated values of XRD diffraction peaks, respectively. For the Ag 3PO 4 and BiPO 4 samples, the XRD curves were fitted using the Jade 6.0 package. Photocatalytic Testingįigure 2a,b show the XRD patterns of Ag 3PO 4 and BiPO 4, respectively. The sinusoidal voltage pulse was used for the EIS measurement (amplitude: 5 mV frequency range: 10 −2–10 5 Hz). A 0.2 V bias voltage was used during the transient photocurrent measurement. The used light source was a 200 W xenon lamp emitting simulated sunlight. The used electrolyte was 0.1 mol L −1 Na 2SO 4 aqueous solution. The slurry mixture was homogeneously coated on the surface of fluorine-doped tin oxide (FTO) thin film (effective area: 1 × 1 cm 2), and subjected to drying 60 ☌ for 5 h. The working electrode was prepared as follows: 15 mg of the photocatalyst, 0.75 mg of polyvinylidene fluoride (PVDF), 0.75 mg of carbon black and 1 mL of 1-methyl-2-pyrrolidione (NMP) were mixed together to form uniform slurry. A CST 350 electrochemical workstation (Wuhan Corrtest Instruments Co., Ltd., Wuhan, China) equipped with a three-electrode cell configuration was used to study the electrochemical impedance spectroscopy (EIS) and photocurrent response of the samples. The electrochemical properties of the samples were investigated according to the method reported in the literature. In recent years, silver phosphate (Ag 3PO 4) based composite photocatalysts, such as Bi 4Ti 3O 12/Ag 3PO 4, Ag 3PO 4/NaTaO 3, MoS 2/Ag 2S/Ag 3PO 4, Ag 3PO 4/Bi 2WO 6, Ag 3PO 4/Cu 2O, TiO 2/Ag 3PO 4/bentonite, Co 3(PO 4) 2/Ag 3PO 4, and Ag 3PO 4/BiFeO 3 have been extensively studied due to their excellent photocatalytic activity for photocatalytic degradation of the organic pollutions under visible light irradiation. ![]() Therefore, it is desirable to develop novel photocatalysts with high visible-light utilization for degradation of organic pollutions in wastewater. Recently, although great progress has been made in the field of photocatalysis, only few photocatalysts can effectively use visible light in the degradation of organic pollutions. The photocatalytic degradation of organic pollutants in wastewater is an attractive, environmentally friendly and green method that offers a way to harness solar power efficiently and convert them into non-toxic degradation products.
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