Thermal evolution of Zn3(OH)2V2O7·2H2O to Zn-V-O family (Zn2(OH)(VO4), Zn3(VO4)2-α, ZnO and Zn3(VO4)2-β): A structural, optical and visible light photocatalytic study

Several compounds of the Zn-V-O family were prepared via a precipitation process followed by a hydrothermal process and a thermal treatment. The starting material (from the precipitation process), consisted of a single vanadium compound Zn ₃(OH) ₂V ₂O ₇·2H ₂O, hydrated zinc hydroxy-vanadate, these crystals were matured in a hydrothermal process at 200 °C producing the same phase but more crystalline. The material obtained calcined at 300, 500, 700 and 850 °C, resulted in the formation of four other Zn-V-O compounds (Zn ₂(OH)(VO ₄), Zn ₃(VO ₄) ₂-α, ZnO and Zn ₃(VO ₄) ₂-β), which evolved from the progressive dehydration and restructuring of the starting hydrated zinc hydroxy-vanadate compound (Zn ₃(OH) ₂V ₂O ₇·2H ₂ O). The samples obtained at different calcination temperatures (T _Calc ) were characterized in their structural, optical, morphological, textural and photocatalytic response. The relevant compound in photocatalysis, zinc vanadate Zn ₃V ₂O ₈ in heterojunction with ZnO, was synthetized to 500 and 700 °C. It was observed that the best photocatalytical response under visible illumination in the degradation of methylene blue (MB) was obtained with the material calcined at 500 °C, its reactivity against MB was preserved in multiple cycles of reuse and in different radical blocking conditions.