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Insight into the Influence of ZnO Defectivity on the Catalytic Generation of Environmentally Persistent Free Radicals in ZnO/SiO2Systems
- Source :
- The Journal of Physical Chemistry - Part C; September 2019, Vol. 123 Issue: 35 p21651-21661, 11p
- Publication Year :
- 2019
-
Abstract
- The present study aims at supplying a more in-depth picture of the generation of environmentally persistent free radicals (EPFRs) from phenol (PhOH) on ZnO/SiO2systems, by exploring the properties of ZnO nanoparticles (NPs) with different intrinsic defectivity grown on highly porous silica with a spherical (ZnO/SiO2_S) and wormlike morphology (ZnO/SiO2_W). In detail, besides an extensive structural, morphological, and surface investigation, the occurrence of inequivalent defect centers in the samples was tracked by photoluminescence (PL) experiments, which unveiled, for ZnO/SiO2_W, intense blue emissions possibly involving radiative recombination from Zniexcited levels to the valence band or to VZnlevels. Electron spin resonance (ESR) spectra corroborated these results and revealed a remarkably different behavior of the samples in the EPFR formation model reaction. In fact, upon PhOH contact, the ESR spectrum of ZnO/SiO2_S showed the exclusive presence of a weak isotropic signal ascribable to a PhenO•EPFR. Instead, for ZnO/SiO2_W, intense features associated with oxygen species in proximity of VO+, VZn–, and (VZn–)2–centers dominate the spectra, while a minor contribution of the PhenO•radical can be discovered only by signal simulation. These outcomes definitively envisage a role of the intrinsic defectivity of ZnO NPs on the final yield and stability of EPFR generation, with VO+and VZn–defects possibly involved in dissociative adsorption or oxidation processes at the oxide surface. Although this work focuses on ZnO, it is expected to foster a critical re-examination and integration of important results on other metal oxide/silica systems already reported in the literature, offering the chance to better evaluate the dependence of EPFR generation on the oxide defects chemistry.
Details
- Language :
- English
- ISSN :
- 19327447 and 19327455
- Volume :
- 123
- Issue :
- 35
- Database :
- Supplemental Index
- Journal :
- The Journal of Physical Chemistry - Part C
- Publication Type :
- Periodical
- Accession number :
- ejs50727186
- Full Text :
- https://doi.org/10.1021/acs.jpcc.9b06900