Facile synthesis of sunlight driven photocatalysts Zn0.9Ho0.05M0.05O (M = Pr, Sm, Er) for the removal of synthetic dyes from wastewater

Abstract

Currently, environmental pollution due to contaminants released from industries into clean water is a big challenge to maintain public health worldwide. The elimination of organic toxins, particularly organic dyes using semiconductor-mediated photocatalysis is an efficient technique. Herein, Zn0.9Ho0.05M0.05O (M = Pr, Sm, Er) photocatalysts were prepared by the co-precipitation method and characterized via state-of-art techniques to study the structural, optical, electrochemical, and morphological properties. XRD results confirmed that the grown ZnO-based catalysts have hexagonal wurtzite structures with high crystallinity and successful co-doping. FTIR and Raman analysis have shown the vibrational bands and optical phonon modes of ZnO in all catalysts with a small shift which further evident the co-doping. Roughly spherical morphology revealed by FE-SEM images with improvement by co-doping. The energy bandgap of grown ZnO depends on dopants and is decreased by co-doping compared to single-doped samples, as evident from UV-Visible analysis. The photocatalytic degradation experiment towards methyl orange (MO) and methylene blue (MB) dyes under sunlight exhibited that co-doped catalysts have higher efficiency against both dyes. Remarkably, Ho-Er co-doped catalyst degraded 99.7% MB and 84% MO dye under 60 min sunlight illumination with a higher apparent rate constant of 0.0975 and 0.028 min(-1), respectively, with stability up to 6th cycle against MB dye. The scavenger tests demonstrate that the major role in the enhanced photodegradation is superoxide (O-2*(-)) and hydroxyl (OH*) radicals. The boosted photocatalytic activity is due to the lower energy bandgap, and the higher flow of charge carrier (EIS results) led to the higher generation of reactive species. Moreover, these consequences revealed that the individual performance of ZnO could be boosted through rare earth elements co-doping to make it useful for environmental applications.