Photocatalytic Degradation Of Methylene Blue Over Ag-loaded BiVO₄ Photocatalysts

BiVO₄ has been recognized as a photocatalst for water splitting and pollutant degradation under visible light irradiation.In this dissertation, we prepared the Ag-loaded BiVO₄ photocatalyst (Ag-BiVO₄) . In general, noble metal loading on photocatalysts can improve their photocatalytic activities. In this study, Ag has been loaded on BiVO₄ by deposited method from AgNO₃ solution. The optical, physical, chemical properties of silver loaded BiVO₄ are explored with different techniques, such as XRD, TEM, SEM, TG-DSC, DRS and IR. The photocatalytic performance of the Ag-BiVO₄ catalyst is applied to the model photodegradation of methylene blue (MB) under visible light and UV irradiation. The relationship between the structure of Ag-BiVO₄ and photocatalytic properties is elucidated. The other objectives of this study were as follows: (1) to compare the photocatalytic degradation rate of MB on BiVO₄ with the Ag-BiVO₄ catalyst and investigate the optimal content of Ag loading under visible light and UV irradiation. (2) to study the influence of various parameters such as the content of Ag loading BiVO₄, the initial MB concentration, pH, etc. on the MB removal under visible light and UV irradiation. (3) to study the degradation process of MB by BiVO₄ and Ag-BiVO₄ under visible light irradiation and UV irradiation.Under visible light irradiation, the results demonstrated that the MB was degraded effectively by more than 99% within 3 h. The presence of Ag significantly enhanced the MB degradation and the optimal content of Ag was 3 wt.%. It is confirmed that the calcination temperature on Ag-BiVO₄ is very important for the photocatalytic activity and the highest removal of MB was obtained by calcination at 100℃. The UV-Vis spectral analysis showed that blue shift resulting from N-demethylation of MB occurred accompanied with oxidative degradation. Furthermore, the degradation of MB using Ag-BiVO₄ followed the first-order reaction kinetic model under different initial concentration of MB and pH. While, under UV irradiation, the results indicate that using 2 g/ L Ag-BiVO₄ with 3 wt.% of Ag content, more than 95% MB (initial concentration 10 mg/L) could be removed at the pH of 7．2 for 2 h.Compare the absorption spectral temporal changes of MB by Ag-BiVO₄(3 wt.%) under visible light with UV irradiation, it is found that the blue shift in maximum absorption wavelength under visible light irradiation is larger. It is illuminated that under visible light irradiation the Ag-BiVO₄ showed the higher photodegradation efficiency than UV irradiation.In order to explain the relationship of the catalysts structure and the photocatalytic activities, all the catalysts were characterized by XRD ect. techniques. It is showed that the Ag-BiVO₄ treated at low calcined temperature indicated the highest photocatalytic activity. With the increasing calcinations temperature, the more Ag formed, thus decreased the degradation rate of MB.