N,Nb-codoping has recently been proposed as a promising strategy to enhance the activity of nanostructured TiO2 under visible irradiation. Here, we suggest a possible electronic mechanism to account for the observed visible absorption improvement. The effects of N and Nb species on the electronic, crystallographic, and morphological properties of TiO2 were deeply investigated both experimentally (HRXRPD, EXAFS, EDX, BET, SEM, EPR, and DRS) and theoretically (DFT). We found a significant synergism between N and Nb species, while EXAFS, HR-XRPD, and DFT simulations provided compelling evidence for the Nb substitutional position in anatase. At variance with interstitial, substitutional Nb can transfer an electron to low-energy valence states of the N codopant near the valence band. This intrinsic charge compensation mechanism is substantiated by EPR, which shows a reduction of the paramagnetic bulk N species signal in N,Nb-codoped samples. DRS analysis of N,Nb-codoped samples shows a slight reduction of the apparent band gap and a significantly increased visible-light absorbance. This effect is due to the shallow midgap states created by Nb (below conduction band) and N (above valence band). DFT results suggest that substitutional Nb ions transfer electrons to low-lying guest N states within the band gap, eventually enhancing the light absorption.

Unraveling the cooperative mechanism of visible-light absorption in bulk N,Nb codoped TiO2 powders of nanomaterials / C. Marchiori, G. Di Liberto, G. Soliveri, L. Loconte, L. Lo Presti, D. Meroni, M. Ceotto, C. Oliva, S. Cappelli, G. Cappelletti, C. Aieta, S. Ardizzone. - In: JOURNAL OF PHYSICAL CHEMISTRY. C. - ISSN 1932-7447. - 118:41(2014 Oct 07), pp. 24152-24164. [10.1021/jp507143z]

Unraveling the cooperative mechanism of visible-light absorption in bulk N,Nb codoped TiO2 powders of nanomaterials

G. Di Liberto;G. Soliveri;L. Loconte;L. Lo Presti
;
D. Meroni
;
M. Ceotto;C. Oliva;S. Cappelli;G. Cappelletti;C. Aieta
Penultimo
;
S. Ardizzone
Ultimo
2014

Abstract

N,Nb-codoping has recently been proposed as a promising strategy to enhance the activity of nanostructured TiO2 under visible irradiation. Here, we suggest a possible electronic mechanism to account for the observed visible absorption improvement. The effects of N and Nb species on the electronic, crystallographic, and morphological properties of TiO2 were deeply investigated both experimentally (HRXRPD, EXAFS, EDX, BET, SEM, EPR, and DRS) and theoretically (DFT). We found a significant synergism between N and Nb species, while EXAFS, HR-XRPD, and DFT simulations provided compelling evidence for the Nb substitutional position in anatase. At variance with interstitial, substitutional Nb can transfer an electron to low-energy valence states of the N codopant near the valence band. This intrinsic charge compensation mechanism is substantiated by EPR, which shows a reduction of the paramagnetic bulk N species signal in N,Nb-codoped samples. DRS analysis of N,Nb-codoped samples shows a slight reduction of the apparent band gap and a significantly increased visible-light absorbance. This effect is due to the shallow midgap states created by Nb (below conduction band) and N (above valence band). DFT results suggest that substitutional Nb ions transfer electrons to low-lying guest N states within the band gap, eventually enhancing the light absorption.
Nb,N-doped TiO2 ; microstructure ; nanostructure ; point defects ; DFT calculations ; EPR measurements
Settore CHIM/02 - Chimica Fisica
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/241116
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