Facile phase selective synthesis of α- and β-AgVO₃: a comparative study of their structural, morphological and...

AgVO₃ is a low bandgap semiconductor (∼2 eV) crystallizing in a metastable (α) phase or a thermodynamically stable (β) phase, each exhibiting distinct properties. Despite their photocatalytic potential, synthesizing phase pure α and β-AgVO₃ in a simple, reproducible manner remains a challenge. In this study, facile and repeatable synthesis routes are introduced for both phases. The α phase is obtained via a low-temperature precipitation method, while the β-phase is synthesized through a hydrothermal process at 120-160 °C. A comprehensive comparison of the structural, morphological, optical, and photocatalytic properties of both phases is conducted. Both exhibit a monoclinic structure and a rod-like morphology; however, the α phase shows a unique tree-like morphology with nanorod growth on microrods. Differential scanning calorimetry (DSC) analysis on α-AgVO₃ over three heating and cooling cycles and high-temperature X-ray diffraction show that the α-to-β phase transition is an irreversible exothermic process occurring between ∼200 and 240 °C. The complete electronic band structures of both phases were also determined, with the valence and conduction band positions for the α- and β-phase samples determined to be (1.13, -0.94 eV) and (0.92, -1.08 eV) versus NHE, respectively. The unique morphology of α-AgVO₃ contributes to its enhanced photocatalytic activity. Interestingly, and in contrast to previous reports favoring the β-phase, the α-phase demonstrates superior photocatalytic efficiency, achieving complete degradation of rhodamine B within 90 minutes, while the β-phase reaches 89% degradation after 180 minutes. This finding challenges the conventional assumption that the β-phase always outperforms the α-phase and suggests that morphology and surface structure can play a more critical role than crystallinity in determining photocatalytic performance.