Growth, properties and photocatalytic degradation of congo red using Gd: ZnO thin films under visible light

Pristine ZnO thin films, as well as 1, 2, 3 and 4 at.% Gd:ZnO thin films, were synthesized via a spray pyrolysis approach on glass substrates and different analysis methods were used to explore the effect of Gd ion doping on the structural, morphological, chemical, and optical characteristics. The presence of functional groups and chemical bonds ascribed to ZnO were confirmed by Fourier transform infrared spectroscopy (FTIR) measurement. The presence of Zn, O, and Gd in the formed pristine and Gd:ZnO thin films was confirmed using EDX analysis and elemental mapping investigations, which was further validated using X-ray photoelectron spectroscopy (XPS) analysis that indicated the existence of Gd in the layers with Gd in the + 3 state. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis revealed that the films are polycrystalline with a hexagonal wurtzite structure, and surface morphology changed with increasing Gd content. The ultraviolet-visible (UV-Vis) spectrophotometer for all films shows good visible transmittance averaging 60-80% and their band gap energy (E-g) ranging between 3.24 and 3.26 eV. The photocatalytic proprieties of the films were carried out by assessing the degradation efficiency of the dye Congo red (CR) under visible light. The results show that Gd:ZnO films with different Gd contents have better catalytic degradation efficiencies than pristine ZnO.