Year-end Sale % OFF 
Abstract
Pure and Ce-modified ZnO nanosheet-like polycrystalline samples were successfully synthesized by a simple and fast microwave-based process and tested as photocatalytic materials in environmental remediation processes. In an attempt to clarify the actual relationships between functionality and atomic scale structure, an in-depth characterization study of these materials using a battery of complementary techniques was performed. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM), energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS), photoluminescence spectroscopy (PL) and UV–Visible absorption spectroscopy were used to evaluate the effect of Ce ions on the structural, morphological, optical and photocatalytic properties of the prepared ZnO nanostructures. The XRD results showed that the obtained photocatalysts were composed of hexagonal, wurtzite type crystallites in the 34–44 nm size range. The SEM and TEM showed nanosheet-shaped crystallites, a significant fraction of them in contact with bundles of randomly oriented and much smaller nanoparticles of a mixed cerium–zinc phase with a composition close to Ce0.68Zn0.32Ox. Importantly, in clear contrast to the prevailing proposals regarding this type of materials, the STEM-XEDS characterization of the photocatalyst samples revealed that Ce did not incorporate into the ZnO crystal lattice as a dopant but that a heterojunction formed between the ZnO nanosheets and the Ce–Zn mixed oxide phase nanoparticles instead. These two relevant compositional features could in fact be established thanks to the particular morphology obtained by the use of the microwave-assisted hydrothermal synthesis. The optical study revealed that in the ZnO:Ce samples optical band gap was found to decrease to 3.17 eV in the samples with the highest Ce content. It was also found that the ZnO:Ce (2 at.%) sample exhibited the highest photocatalytic activity for the degradation of methylene blue (MB), when compared to both the pure ZnO and commercial TiO2-P25 under simulated sunlight irradiation. The kinetics of MB photodegradation in the presence of the different photocatalysts could be properly described using a Langmuir–Hinshelwood (LH) model, for which the ZnO:Ce (2 at.%) sample exhibited the highest value of effective kinetic constant.
Highlights
Nowadays, extensive efforts and various strategies have been developed to control the increasing amounts and variety of water pollutants linked to the disposal of industrial waste
This fact does not rule out the possibility that this type of phases was present, since they could have formed at a concentration and size too low to be detectable in the X-ray diffraction experiment
The present results show that the improvements in the photocatalytic activities in the ZnO:Ce systems were not related to changes in the band structure of ZnO due to rare earth (RE) dopping or to an interaction between the band structures at the CeO2 /ZnO hererojunctions
Summary
Extensive efforts and various strategies have been developed to control the increasing amounts and variety of water pollutants linked to the disposal of industrial waste. In a more recent paper [28], the formation of nanosized CeO2 /ZnO heterojunctions have been proposed to rationalize the optical and photocatalytic performance of Ce-modified ZnO materials with Ce contents below 10 at.% In this case, the composition of the Ce-containing phase decorating the surface of the ZnO aggregates was investigated by means of energy-dispersive X-Ray spectroscopy-scanning transmission electron microscopy (STEM-XEDS). As far as we know, the preparation of the Ce-modified ZnO photocatalysts via a microwave-assisted hydrothermal process and the characterization of their photocatalytic performance under simulated sunlight irradiation have to date not been reported, despite the very interesting features which characterize this route, such as low cost, short synthesis times and mild temperature conditions. The photocatalytic performances of TiO2 –P25, ZnO and the microwave-assisted hydrothermal Ce-modified ZnO photocatalysts under simulated sunlight irradiation were compared
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
