Synthesis and Photocatalytic Application of BiVO4 Nanocrystalline Functionalized by porphyrin with Two Different Crystalline Phases as an Efficient Photocatalyst

Porphyrins as a supermolecular compound and primary chromophores in photosynthesis, are nature's light harvesting system. Porphyrins capture a broad range of the solar spectrum due to their strong absorption band in both visible and near infrared regions. In the synthesis of bismuth vanadate (BiVO4) with monoclinic-tetragonal phases, NH4VO3 and Bi (NO3) 3.5H2O equimolar aqueous solution was mixed. PEG was added to the solution including Bi (NO3) 3.5H2O. The mixture was stirred for 1h and sonicated by ultrasonic for 30 min at room temperature. The yellow precipitate of BiVO4 was separated from the solution by centrifuging and was washed with distilled water and ethanol. The final production was dried in an oven at 60˚C. The resultant sample were calcined at 450˚C for 2h. Tetrakis (4-carboxyphenyl) porphyrin (TCPP) was prepared by reflaxing 4-Carboxybenzaldehyde and pyrrole in propionic acid.  The prepared sample was characterized by powder X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy (FT-IR). Photocatalytic activities of the BiVO4 sample were evaluated by the methyl orange decomposition under visible and UV light irradiation. The degradation was observed by the decrease in the absorbance peak studied by UV-Vis spectrophotometer. The results show that the behavior of photoinduced charges markedly depends on the crystalline phases of BiVO4 sample. The presence of interface in monoclinic-tetragonal heterophase provides a spatial condition for charge transfer, promotes the separation of photoinduced electron-hole pairs, and changes in the migration direction of photoinduced carriers. The results were shown under the irradiation of  UV light (λ > 400 nm),  25% of the methyl orange dye was destructed in the presence of the BiVO4 sample after 240 min, which is much higher than the irradiation of visible light.