Boosting the sunlight irradiation and methylene blue dye degradation over ZnO doped with N and C elements

This article aims at preparing ZnO nanoparticles and doping with nitrogen (N) and carbon (C) nonmetals via sol-gel method followed by the calcination in N2 and air media to mitigate the fast electron-hole pairs recombination drawbacks and improve the visible light photocatalytic activity of pure ZnO under sunlight irradiation. The influence of dopant content of N-and C-N doped ZnO on the photodegradation of methylene blue (MB) dye was investigated. To compare doped samples properties with ZnO bare, techniques such as X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), fourier transform infrared (FTIR), Brunauer, Emmett and Teller (BET) surface area, and UV-Vis diffuse reflectance spectroscopy (DRS) were employed. Wurtize hexagonal structure of ZnO with good crystallinity of nanoparticles (NPs) ranged between 15.5 and 45.8 nm was confirmed by XRD. However, entering N into ZnO lattice decreased the crystallite size whereas doping with C-N enhanced the crystallite size of ZnO. Through SEM, ZnO NPs appeared as spherical morphology and FTIR showed the characteristic absorption bands related to Zn-O stretching and bending vibration modes with symmetric stretching vibration of O-C=O and-C-O groups were detected in FTIR. The bandgap value of ZnO was decreased from 3.07eV to 2.83eV upon doping with 40%N/ZnO(air). Pure ZnO exhibited 100% degradation of MB at 180 min, and ZnO doped with the highest concentrations of N and C-N dopants showed a full degradation of MB dye at 60 and 90 min, respectively. Thereof, the 40% N/ ZnO(air) material exhibited the higher visible-light activity compared with 40%C-N/ZnO(N2), where a complete photodegradation of MB dye was obtained at 60min.This superior photoactivity for 40%N/ZnO catalyst is due to their capability in reducing the electron-hole pair recombination arising from its smaller bandgap energy value.