Tungsten Nanomaterials With Oxygen Vacancies As Efficient Photocatalysts And Photocolor Switching Agents

Semiconductor photocatalysis technology emerges as a “green technology” to remedy the problems resulting from the increasing energy shortages and environmental degradation.Recent studies on introduction of oxygen vacancies in semiconductor photocatalysts have shown great promise towards the increase in photo-response range as well as improved photoactivity.Herein,we have prepared Zn WO4 sample with oxygen vacancies(denoted as ZnWO_4-x)by the solvothermal treatment of Zn?NO₃?₃ and Na₂WO₄ in water/ethanol/PEG-400 solvent mixture,where ethanol might effectively work as a reducing agent to ensure removal of some oxygen atoms from ZnWO₄.The ZnWO_4-x sample is made up of nanorods having lengths of ⁵0 nm and diameters of ²0 nm.Furthermore,the synthesized brown ZnWO_4-x nanorods with oxygen vacancies exhibits the obviously broadened photoabsorption?UV-VisNIR?,compared with the tradition white ZnWO₄ nanorod with a UV absorption edge of 365 nm.Under UV or ultraviolet-visible-near-infrared?UV-Vis-NIR?light irradiation,ZnWO_4-x nanorods can photocatalytically degrade 91% or 78% tetracycline,higher than those?67% or 71%?by ZnWO₄ nanorods.The enhanced photocatalytic efficiency can be ascribed to the introduction of oxygen defects or oxygen vacancies which have been found to reduce photogenerated electron-hole pair recombination and narrow the band gap.Additionally,we prepared Bi₂WO₆ with oxygen vacancies for practical application in photoreversible color switching of methylene blue.Herein,we synthesized Bi₂WO₆ with oxygen vacancies(denoted as Bi₂WO_6-x)via the solvothermal treatment of Bi?NO₃?₃ and Na₂WO₄ in water/ethanol/PEG-400 solvent mixture,similar to the ZnWO_4-x above.The Bi₂WO_6-x sample exhibits a hierarchical structure comprising of ultrathin sheets of lengths ⁶00 nm and diameters ⁷ nm.Comparatively,pristine Bi₂WO₆ with a flower-like hierarchical structure has a diameter of ⁴ ?m.The Bi₂WO_6-x clearly shows a broadened photoabsorpton over the UV-Vis-NIR region with a subsequent bandgap reduction in comparison to pristine Bi₂WO₆.Furthermore,the Bi₂WO_6-x demonstrated efficient photoreversible color switching of methylene blue dye from blue to colorless?7 min,under visible light?and subsequently from colorless to blue?12 min,under UV light?over 5 cyclic tests.This notable photoreversible color switching can be attributed to the presence of oxygen vacancies that have enhanced photoactivity and improved the photo-redox reaction efficiency.