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/SiO2 systems, 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 Zni excited levels to the valence band or to VZn levels. 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.

D'Arienzo, M., Mostoni, S., Crapanzano, R., Cepek, C., Di Credico, B., Fasoli, M., et al. (2019). Insight into the Influence of ZnO Defectivity on the Catalytic Generation of Environmentally Persistent Free Radicals (EPFRs) in ZnO/SiO2 Systems. JOURNAL OF PHYSICAL CHEMISTRY. C, 123(35), 21651-21661 [10.1021/acs.jpcc.9b06900].

Insight into the Influence of ZnO Defectivity on the Catalytic Generation of Environmentally Persistent Free Radicals (EPFRs) in ZnO/SiO2 Systems

D'Arienzo, M
Primo
;
Mostoni, S
Secondo
;
CRAPANZANO, ROBERTA;Di Credico, B;Fasoli, M;Vedda, A;Villa, I;Scotti, R
Ultimo
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/SiO2 systems, 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 Zni excited levels to the valence band or to VZn levels. 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.
Articolo in rivista - Articolo scientifico
ZnO Defectivity, Environmentally Persistent Free Radicals
English
2019
123
35
21651
21661
partially_open
D'Arienzo, M., Mostoni, S., Crapanzano, R., Cepek, C., Di Credico, B., Fasoli, M., et al. (2019). Insight into the Influence of ZnO Defectivity on the Catalytic Generation of Environmentally Persistent Free Radicals (EPFRs) in ZnO/SiO2 Systems. JOURNAL OF PHYSICAL CHEMISTRY. C, 123(35), 21651-21661 [10.1021/acs.jpcc.9b06900].
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/240091
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