Photocatalytic degradation of methyl green by doped zinc oxide thin layers under solar irradiation

The present work deals with methyl green (MG) dye degradation as a model of recalcitrant pollutants. To overcome the recovery cost of the photocatalyst powder, the suspensions are replaced by zinc oxide thin layers (ZnO and ZnO: Fe) deposited on glass substrates by the simple technique of Pyrolysis Spray, where free sunlight replaces the expensive artificial light sources. The use of iron-doped zinc oxide (ZnO:Fe) permits the shift of absorption spectrum toward longer wavelengths, thus allowing a b use of the of spectrum. Semiconductor optical characteristics (transmittance, energy gap) and photocatalytic degradation were determined using a UV-visible spectrophotometer. The catalysis reaction revealed a high dependency on pH, especially that of reaction medium. Alkalinization was found to accelerate degradation kinetics, while acidification slowed them down. The use of isobutanol indicates that the photocatalysis mechanism involves hydroxyl radicals. Iron (5 %) doping with ZnO made it possible to improve the photocatalytic degradation efficiency. The degradation rate varies from 55 % to 77 % over 60 min upon replacing the UV lamp by sunlight irradiation.