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

Abstract

The influence of synthesis conditions on the formation of α and β 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 α-AgVO3 was formed in the precipitation method, whereas it was irreversibly converted into thermodynamically stable β-AgVO3 by a hydrothermal method at 120 °C. The hydrothermal treatment was found to be decisive for the formation of β-form with high crystallinity and phase purity. The increase of hydrothermal temperature to 150 °C and 180 °C could not contributed to a significant variation in the crystalline, structural, textural and optical properties of the β-AgVO3. Moreover, a plausible mechanism for the phase transformation was briefly discussed. A combination of the needle and rod-like nanostructures of α form was completely changed to nanorods in β form after hydrothermal treatment. The optical band gap of α and β 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 β-AgVO3 nanorods were better than α-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 β-form, their electron-hole recombination rate was lowed compared to α 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 β-AgVO3 nanorods were successfully reused for five cycles of photodegradation.