Photocatalytic Degradation of Methyl Green Dye Mediated by Pure and Mn-Doped Zinc Oxide Nanoparticles under Solar Light Irradiation

Abstract

Herein this study, pure and manganese- (Mn-) doped ZnO (2 wt. %) nanoparticles have been synthesized using the chemical precipitation method and characterized for the photodegradation of methyl green (MG) pollutant dye under natural sunlight. The structural analysis via XRD patterns has revealed that both intrinsic and Mn-doped ZnO (2 wt. %) samples have hexagonal wurtzite structures with appropriate phase purity, clearly indicating the absence of any external impurity. The incorporation of Mn in the host ZnO lattice has decreased the crystallite size (21.10 → 18.76 nm), and nanoparticle-type surface features with sizes in the 50–100 nm range have been observed through FESEM-based surface morphological studies. Both aforementioned observations have merit in providing more active area and a high surface area to volume ratio for photocatalytic reaction. The investigation of photophysical properties indicates that in Mn-doped ZnO nanoparticles, the absorption peak is blue-shifted by 5 nm (365 → 360 nm), due to the widening of the bandgap. The degradation kinetics of MG dye follow the pseudo-second-order kinetics, and the degradation efficiency has been observed to be 62.78% mediated by pure ZnO and 66.44% by Mn-doped ZnO (2 wt. %) photocatalyst under 60 minutes of sunlight irradiation. Specifically, the rate of photocatalytic reaction (K) ~0.01792 min-1 and $R^2$ ~0.97992 has been achieved for pure ZnO, whereas slightly higher (K) ~0.02072 min-1 and $R^2$ ~0.97299 have been observed for Mn-doped ZnO, respectively. Conclusively, the synergistic interactions with multiple charge transfer pathways, improvement of e−/h+ pair charge separation, improved surface area, and efficient generation of hydroxyl radicals are supposed to be responsible for the highly efficient photocatalytic activity of the Mn–doped ZnO photocatalyst for MG dye.