Investigation of photocatalytic properties of Cu & Rb Co-doped ZnO thin films via sol-gel spin coating method

This study outlines the synthesis and evaluation of pristine and Cu/Rb: ZnO thin films, developed via the sol-gel spin coating methodology. X-ray diffraction (XRD) analysis confirmed that all the thin films had a hexagonal wurtzite structure and a preferential orientation along the c-axis at various levels of doping (1, 3, and 5%). The maximum crystallite size was 18.88 nm at a doping concentration of 3%, and lower at 1% and 5% due to dopant-induced lattice distortion and strain effect. FESEM analysis demonstrates that the particle size of ZnO decreases systematically and consistently between the pristine (115 nm) and the 5% doped (60.14 nm) sample, and that the morphology grows more irregular and agglomerated with increasing dopant concentration. The successful inclusion of Cu and Rb into the ZnO matrix was confirmed by Energy Dispersive Spectroscopy (EDS). Moreover, the transmittance of Cu/Rb: ZnO thin films exceeded 50% in the visible spectrum. It is observed that the absorption edge is shifted to higher wavelengths (red shift) that correspond to a decrease in bandgap with the addition of 1 and 3 at% Cu/Rb: ZnO thin films, resulting in the narrowing of the bandgap to a minimum of 3.21 eV. A slight widening of the bandgap observed at 5 at% Cu/Rb concentration is attributed to the Burstein-Moss effect. Experiments of photocatalytic degradation revealed that doping greatly enhanced the activity in the UV light, and Cu/Rb: ZnO thin films had the highest rate of degrading methylene blue (39.39%), relative to 4.82% in pristine ZnO thin films. The findings highlight the possibilities of Cu/Rb: ZnO thin films in the treatment of wastewater and any other environmental application, as they have enhanced structural, optical, morphological, and photocatalytic properties.