Influence of synthesis parameters on the crystalline, structural, textural, optical and photocatalytic properties of alpha and beta polymorphs of AgVO3 nanorods

摘要

The influence of synthesis conditions on the formation of alpha and beta polymorphs of AgVO3, their crystalline, structural, textual and optical properties and photocatalytic activity for dye degradation was investigated. The as-prepared polymorphs were characterized by using XRD, FTIR, EDX, SEM, TEM, HRTEM, XPS, BET and UV-vis. analyses. The analytical results indicated that a metastable alpha-AgVO3 was formed in the precipitation method, whereas it was irreversibly converted into thermodynamically stable beta-AgVO3 by a hydrothermal method at 120 degrees C. The hydrothermal treatment was found to be decisive for the formation of beta-form with high crystallinity and phase purity. The increase of hydrothermal temperature to 150 degrees C and 180 degrees C could not contributed to a significant variation in the crystalline, structural, textural and optical properties of the beta-AgVO3. Moreover, a plausible mechanism for the phase transformation was briefly discussed. A combination of the needle and rodlike nanostructures of alpha form was completely changed to nanorods in beta form after hydrothermal treatment. The optical band gap of alpha and beta AgVO3 polymorphs was found to be 1.91 eV and 1.98 eV respectively. The photocatalytic activity of the silver vanadates for the degradation of Rhodamine B indicated that beta-AgVO3 nanorods were better than alpha-AgVO3 polymorphs. This could be attributed to the significant effects of its stable crystalline structure rather than specific surface area. Moreover, due to the reduced grain boundaries in beta-form, their electron-hole recombination rate was lowed compared to a form. The degradation efficiency reached to 56% within 180 min under visible light irradiation. However, the increase of hydrothermal temperature does not have a significant effect in the photocatalytic activity. Moreover, the beta-AgVO3 nanorods were successfully reused for five cycles of photodegradation.