TY - JOUR

T1 - Importance of Surfaces and Many-Body Absorption Spectra for C-Doped TiO2 Photocatalysts

AU - Curti, Mariano

AU - Mendive, Cecilia B.

AU - Bredow, Thomas

AU - Bahnemann, Detlef W.

N1 - Funding Information: M.C. is grateful to the Deutscher Akademischer Austauschdienst (DAAD, Germany) together with the Ministerio de Educación, Cultura, Ciencia y Tecnología (Argentina) for his ALEARG scholarship. C.B.M. is member of the research staff of Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). The calculations presented here were mainly carried out on the LUIS cluster system at the Leibniz Universität Hannover, Germany. T.B. thanks the University of Bonn for providing computer time on the Bonna cluster and the LUIS for providing additional computational resources. The studies performed in the laboratory “Photoactive nanocomposite materials” were supported by Saint-Petersburg State University (ID: 73032813). Finally, the authors wish to thank the anonymous reviewer who highlighted the importance of convergence in the G0W0-BSE calculations, thus allowing us to realize the key role of the theory level on these results.

PY - 2021/11/4

Y1 - 2021/11/4

N2 - Heterogeneous photocatalytic processes, in which a photocatalyst absorbs light to produce redox-active electron-hole pairs, have strong prospects of application in light energy conversion and environmental remediation. Although considerable efforts have been dedicated to the development of new photocatalysts, nanoparticulated anatase TiO2 continues to be the reference system. Its limited light absorption properties have been addressed in different ways, and among these, doping with heteroatoms (e.g., C or N) is a simple and efficient (although poorly understood) strategy. In the case of C-doping, although a significant number of computational works have described its major features, there are still conflicting reports on the local coordination of C, on the thermodynamic feasibility of the doping process, and on the optical properties of the doped material. Here, by considering surfaces instead of bulk anatase, we demonstrate that the C-doped structures are stabilized by up to 5 eV, indicating a spontaneous doping process across a broad range of oxygen pressures. Furthermore, we show that the calculated absorption spectrum for the most stable configuration, Ti-by-C substitution, is strongly dependent on the theory level: while semiempirical calculations indicate a red shift with respect to pristine TiO2, calculations at the highest achievable level (qpGW0-BSE [Bethe-Salpeter equation] without the Tamm-Dancoff approximation [TDA]) show no visible light absorption. In addition, we find that the commonly used TDA introduces a significant shift to the calculated spectra of the doped (but not the pristine) material. These results have two important implications that can be generalized to other systems: (i) a correct estimation of changes in optical properties upon doping may require theory levels higher than G0W0-BSE(TDA) and (ii) thermodynamic parameters determined from doping bulk structures may significantly deviate when considering surfaces, of relevance for nanoscaled materials.

AB - Heterogeneous photocatalytic processes, in which a photocatalyst absorbs light to produce redox-active electron-hole pairs, have strong prospects of application in light energy conversion and environmental remediation. Although considerable efforts have been dedicated to the development of new photocatalysts, nanoparticulated anatase TiO2 continues to be the reference system. Its limited light absorption properties have been addressed in different ways, and among these, doping with heteroatoms (e.g., C or N) is a simple and efficient (although poorly understood) strategy. In the case of C-doping, although a significant number of computational works have described its major features, there are still conflicting reports on the local coordination of C, on the thermodynamic feasibility of the doping process, and on the optical properties of the doped material. Here, by considering surfaces instead of bulk anatase, we demonstrate that the C-doped structures are stabilized by up to 5 eV, indicating a spontaneous doping process across a broad range of oxygen pressures. Furthermore, we show that the calculated absorption spectrum for the most stable configuration, Ti-by-C substitution, is strongly dependent on the theory level: while semiempirical calculations indicate a red shift with respect to pristine TiO2, calculations at the highest achievable level (qpGW0-BSE [Bethe-Salpeter equation] without the Tamm-Dancoff approximation [TDA]) show no visible light absorption. In addition, we find that the commonly used TDA introduces a significant shift to the calculated spectra of the doped (but not the pristine) material. These results have two important implications that can be generalized to other systems: (i) a correct estimation of changes in optical properties upon doping may require theory levels higher than G0W0-BSE(TDA) and (ii) thermodynamic parameters determined from doping bulk structures may significantly deviate when considering surfaces, of relevance for nanoscaled materials.

UR - http://www.scopus.com/inward/record.url?scp=85118933231&partnerID=8YFLogxK

U2 - 10.1021/acs.jpcc.1c08416

DO - 10.1021/acs.jpcc.1c08416

M3 - Article

AN - SCOPUS:85118933231

VL - 125

SP - 24263

EP - 24272

JO - Journal of Physical Chemistry C

JF - Journal of Physical Chemistry C

SN - 1932-7447

IS - 43

ER -