Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles

Anatase TiO 2 nanoparticles (NPs) have the potential to photocatalyse water splitting using UV light, to thus provide hydrogen fuel in a clean and sustainable manner. Such NPs have optical gaps covering a small range of relatively high energy solar photons, giving rise to low photo-efficiencies. Alt...

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Autores: Morales García, Ángel, Macià Escatllar, Antoni, Illas i Riera, Francesc, Bromley, Stefan Thomas
Tipo de recurso: artículo
Estado:Versión aceptada para publicación
Fecha de publicación:2019
País:España
Institución:Universidad de Barcelona
Repositorio:Dipòsit Digital de la UB
OAI Identifier:oai:diposit.ub.edu:2445/165146
Acceso en línea:https://hdl.handle.net/2445/165146
Access Level:acceso abierto
Palabra clave:Fotocatàlisi
Diòxid de titani
Nanopartícules
Photocatalysis
Titanium dioxide
Nanoparticles
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spelling Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticlesMorales García, ÁngelMacià Escatllar, AntoniIllas i Riera, FrancescBromley, Stefan ThomasFotocatàlisiDiòxid de titaniNanopartículesPhotocatalysisTitanium dioxideNanoparticlesAnatase TiO 2 nanoparticles (NPs) have the potential to photocatalyse water splitting using UV light, to thus provide hydrogen fuel in a clean and sustainable manner. Such NPs have optical gaps covering a small range of relatively high energy solar photons, giving rise to low photo-efficiencies. Although anatase NPs with 10-20 nm diameters thermodynamically prefer crystalline faceted morphologies, application of physico-chemical procedures can produce more rounded NPs with amorphous shells. Such engineered metastable core-shell NPs (so-called black TiO 2 NPs) have reduced band gaps due to shell-induced band edge broadening, resulting in higher photoactivities. For <5 nm diameters, TiO 2 NPs typically exhibit spherical-like NP morphologies, which also display enhanced photoactivity. For smaller NPs it is difficult to experimentally determine their thermodynamic stability and internal atomic structure, to help rationalise their higher photoactivities. Employing accurate electronic structure calculations, we establish the relative stability of spherical and faceted stoichiometric TiO 2 NPs with 1-3.4 nm diameters. Mirroring experimental preparation, simulated thermal annealing is found to significantly stabilise relaxed spherical cut anatase NPs. We find that the smallest spherical NPs become amorphized by annealing, but, for diameters >2 nm, annealing yields NPs with anatase-cores and amorphous-shells. Like larger black TiO 2 core-shell NPs, we confirm that our core-shell NPs are metastable relative to faceted anatase NPs and have significantly smaller optical gaps than faceted NPs. Our calculated gaps are in excellent agreement with experimental data, strongly supporting the validity of our NP models. Energy gap narrowing in these core-shell NPs is found to be due to broadening of valence band states induced by the amorphous shell, analogous to the mechanism proposed for black TiO 2 NPs. Our stoichiometric NPs also show that this band narrowing effect does not require the disordered shells to be non-stoichiometric or for incorporation of other atom types. Instead, we find that this effect mainly arises from 4-coordinated Ti atoms in the amorphous shell. Our careful and systematic computational investigation, using NP models of unprecedented realism, thus provides direct confirmation that the enhanced photoactivity in small spherical TiO 2 NP observed in experiment is due to the formation of metastable core-shell NPs with 4-coordinated Ti centresRoyal Society of Chemistry2019info:eu-repo/semantics/articleinfo:eu-repo/semantics/acceptedVersionapplication/pdfhttps://hdl.handle.net/2445/165146Articles publicats en revistes (Ciència dels Materials i Química Física)reponame:Dipòsit Digital de la UBinstname:Universidad de BarcelonaInglésVersió postprint del document publicat a: https://doi.org/10.1039/c9nr00812hNanoscale, 2019, vol. 11, num. 18, p. 9032-9041https://doi.org/10.1039/c9nr00812h(c) Morales-García, Ángel et al., 2019info:eu-repo/semantics/openAccessoai:diposit.ub.edu:2445/1651462026-05-27T06:46:51Z
dc.title.none.fl_str_mv Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
title Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
spellingShingle Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
Morales García, Ángel
Fotocatàlisi
Diòxid de titani
Nanopartícules
Photocatalysis
Titanium dioxide
Nanoparticles
title_short Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
title_full Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
title_fullStr Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
title_full_unstemmed Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
title_sort Understanding the interplay between size, morphology and energy gap in photoactive TiO2 nanoparticles
dc.creator.none.fl_str_mv Morales García, Ángel
Macià Escatllar, Antoni
Illas i Riera, Francesc
Bromley, Stefan Thomas
author Morales García, Ángel
author_facet Morales García, Ángel
Macià Escatllar, Antoni
Illas i Riera, Francesc
Bromley, Stefan Thomas
author_role author
author2 Macià Escatllar, Antoni
Illas i Riera, Francesc
Bromley, Stefan Thomas
author2_role author
author
author
dc.subject.none.fl_str_mv Fotocatàlisi
Diòxid de titani
Nanopartícules
Photocatalysis
Titanium dioxide
Nanoparticles
topic Fotocatàlisi
Diòxid de titani
Nanopartícules
Photocatalysis
Titanium dioxide
Nanoparticles
description Anatase TiO 2 nanoparticles (NPs) have the potential to photocatalyse water splitting using UV light, to thus provide hydrogen fuel in a clean and sustainable manner. Such NPs have optical gaps covering a small range of relatively high energy solar photons, giving rise to low photo-efficiencies. Although anatase NPs with 10-20 nm diameters thermodynamically prefer crystalline faceted morphologies, application of physico-chemical procedures can produce more rounded NPs with amorphous shells. Such engineered metastable core-shell NPs (so-called black TiO 2 NPs) have reduced band gaps due to shell-induced band edge broadening, resulting in higher photoactivities. For <5 nm diameters, TiO 2 NPs typically exhibit spherical-like NP morphologies, which also display enhanced photoactivity. For smaller NPs it is difficult to experimentally determine their thermodynamic stability and internal atomic structure, to help rationalise their higher photoactivities. Employing accurate electronic structure calculations, we establish the relative stability of spherical and faceted stoichiometric TiO 2 NPs with 1-3.4 nm diameters. Mirroring experimental preparation, simulated thermal annealing is found to significantly stabilise relaxed spherical cut anatase NPs. We find that the smallest spherical NPs become amorphized by annealing, but, for diameters >2 nm, annealing yields NPs with anatase-cores and amorphous-shells. Like larger black TiO 2 core-shell NPs, we confirm that our core-shell NPs are metastable relative to faceted anatase NPs and have significantly smaller optical gaps than faceted NPs. Our calculated gaps are in excellent agreement with experimental data, strongly supporting the validity of our NP models. Energy gap narrowing in these core-shell NPs is found to be due to broadening of valence band states induced by the amorphous shell, analogous to the mechanism proposed for black TiO 2 NPs. Our stoichiometric NPs also show that this band narrowing effect does not require the disordered shells to be non-stoichiometric or for incorporation of other atom types. Instead, we find that this effect mainly arises from 4-coordinated Ti atoms in the amorphous shell. Our careful and systematic computational investigation, using NP models of unprecedented realism, thus provides direct confirmation that the enhanced photoactivity in small spherical TiO 2 NP observed in experiment is due to the formation of metastable core-shell NPs with 4-coordinated Ti centres
publishDate 2019
dc.date.none.fl_str_mv 2019
dc.type.none.fl_str_mv info:eu-repo/semantics/article
info:eu-repo/semantics/acceptedVersion
format article
status_str acceptedVersion
dc.identifier.none.fl_str_mv https://hdl.handle.net/2445/165146
url https://hdl.handle.net/2445/165146
dc.language.none.fl_str_mv Inglés
language_invalid_str_mv Inglés
dc.relation.none.fl_str_mv Versió postprint del document publicat a: https://doi.org/10.1039/c9nr00812h
Nanoscale, 2019, vol. 11, num. 18, p. 9032-9041
https://doi.org/10.1039/c9nr00812h
dc.rights.none.fl_str_mv (c) Morales-García, Ángel et al., 2019
info:eu-repo/semantics/openAccess
rights_invalid_str_mv (c) Morales-García, Ángel et al., 2019
eu_rights_str_mv openAccess
dc.format.none.fl_str_mv application/pdf
dc.publisher.none.fl_str_mv Royal Society of Chemistry
publisher.none.fl_str_mv Royal Society of Chemistry
dc.source.none.fl_str_mv Articles publicats en revistes (Ciència dels Materials i Química Física)
reponame:Dipòsit Digital de la UB
instname:Universidad de Barcelona
instname_str Universidad de Barcelona
reponame_str Dipòsit Digital de la UB
collection Dipòsit Digital de la UB
repository.name.fl_str_mv
repository.mail.fl_str_mv
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score 15.300724

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