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 Zn3(OH)2V2O7·2H2O, 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 (Zn2(OH)(VO4), Zn3(VO4)2-α, ZnO and Zn3(VO4)2-β), which evolved from the progressive dehydration and restructuring of the starting hydrated zinc hydroxy-vanadate compound (Zn3(OH)2V2O7·2H2O). The samples obtained at different calcination temperatures (TCalc) were characterized in their structural, optical, morphological, textural and photocatalytic response. The relevant compound in photocatalysis, zinc vanadate Zn3V2O8 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.