Photocatalytic degradation of methylene blue dye by porous zinc oxide nanofibers prepared via electrospinning: When defects become merits

Zinc oxide nanofibers consisting of interconnected polycrystalline nanoplatelets were produced via electrospinning followed by calcination and cooling at fast rates in order to obtain defect-rich hollow nanostructures. The produced nanofibers were evaluated as a photocatalyst for the degradation of methylene blue under 350 nm UV irradiation obtaining a fast reaction kinetics (rate constants: 2.86⋅10–2 min–1 and 6.06⋅10–2 min–1, by the use of 0.1 mg mL–1 and for 1.0 mg mL–1 photocatalyst in 15 µM aqueous solution, respectively). The thorough nanomaterial characterization and the comparison with ZnO photocatalysts with different morphology, particle size, crystallinity and defect density and location allowed identifying the influential factors. Defects located at the nanoplatelet connection interface (mainly oxygen- and zinc-vacancies) play a key role, in line with the recently assessed crucial importance of the grain boundaries in the photocatalyst design. The investigated nanofibers outperform most state-of-art electrospun pure zinc oxide photocatalysts.