Elsevier

Catalysis Today

Volume 335, 1 September 2019, Pages 78-90
Catalysis Today

Charge carrier trapping, recombination and transfer during TiO2 photocatalysis: An overview

https://doi.org/10.1016/j.cattod.2018.10.053Get rights and content

Highlights

  • Analytic methods to study the charge carrier dynamics are introduced.

  • The fates of charge carrier trapping and recombination are understood.

  • Various interfacial charge transfer processes are discussed case-by-case.

Abstract

Heterogeneous photocatalysis mediated by semiconducting TiO2 has attracted continuous interest during the past decades and has shown great potentials in environmental remediation and solar energy conversion. Basically, photocatalysis is initiated by the TiO2 excitation. The generated charge carriers undergo trapping, recombination, and interfacial transfer before proceeding the redox reaction at TiO2 surface. Monitoring the charge carrier dynamics is of particulate importance for understanding the underlying mechanism and designing efficient photocatalysts. This review overviews the recent progress in characterization of charge carrier dynamics. We will present the analytic techniques for monitoring the fate of charge carriers at each elementary photocatalytic step, including charge carrier generation, trapping and recombination inside the photocatalyst, as well as the interfacial charge transfer. The charge carrier dynamics at TiO2/H2O interface, hole transfer reactions for O2 production, and photocatalytic oxidation of organic compounds and nitric oxides, and electron transfer reactions for photocatalytic reduction of viologens and metal ions are addressed, aiming at a deeper understanding of photocatalytic process.

Section snippets

Basic principles of semiconductor photocatalysis

According to literature surveys by Serpone et al. [1,2], the term photocatalysis firstly appeared in 1910 in a textbook of photochemistry. In 1911 a study about Prussian blue bleaching over illuminated ZnO particles was reported. Research in semiconductor photocatalysis grew in 1960–1970s and has surged since late 1980s. Up to now semiconductor photocatalysis has been developed as a versatile technology applicable in environmental remediation and solar energy conversion [[3], [4], [5], [6], [7]

Characterization techniques

Exploring the charge carrier kinetics is essential for understanding the photocatalytic mechanism occurring at semiconductor surface. Herein two key characterization techniques, namely, time-resolved spectroscopy and electron paramagnetic resonance (EPR) spectroscopy, are briefly introduced. The former technique is applied to monitor the charge carrier dynamics, while the latter is useful to identify the paramagnetic species formed upon reaction of the charge carriers.

Charge carrier trapping

The photogenerated charge carriers can be trapped in either in bulk or on the surface. In generally, surface trapping at either the subsurface or the surface region is preferred in semiconductor nanoparticles [70]. The temporal species including trapped holes, trapped electrons, and free electrons are the main states for charge carriers during the trapping stage. By using TAS in a wide wavelength range from 400 to 2500 nm, Yoshihara et al. [77] found that trapped holes and electrons are

Interfacial charge carrier transfer dynamics

After charge carrier separation the valence band holes and conduction band electrons can initialize the redox reactions. Photocatalytic reaction is a typical surface reaction. Adsorption-kinetic models, and, specifically, the Langmuir-Hinshelwood (L-H) model, are commonly applied to describe photocatalytic mineralization reactions [112]. Accordingly, it can be deduced that the photocatalytic reaction generally behaves as a pseudo-first-order reaction in kinetics, and its efficiency relies on a

Summary and perspective

We have overviewed recent progress in dynamics of interfacial electron transfer in photocatalysis with the assistants of various analytic techniques. Charge carrier generation, trapping, recombination, and interfacial transfer have been briefly described to illustrate how interfacial electron transfer perspectives can provide unique insights into the field of photocatalysis and motivate more knowledge sharing in research to cover major aspects of photocatalysis from fundamentals to

Acknowledgements

This work is supported by the National Nature Science Foundation of China (No. 51772094), Fundamental Research Funds for the Central Universities (No. JB2016ZZD04) and Beijing Natural Science Foundation (No. 2172052)

References (151)

  • R. Katoh et al.

    Transient absorption spectra of nanocrystalline TiO2 films at high excitation density

    Chem. Phys. Lett.

    (2010)
  • F. Wilkinson et al.

    The use of diffuse reflectance laser flash photolysis to study primary photoprocesses in anisotropic media

    Tetrahedron

    (1987)
  • P.R. Patil et al.

    Transient photoconductivity measurements of ultrasonic spray pyrolyzed tungsten oxide thin films

    Mater. Res. Bull.

    (2000)
  • Z. Wang et al.

    Probing paramagnetic species in titania-based heterogeneous photocatalysis by electron spin resonance (ESR) spectroscopy—A mini review

    Chem. Eng. J.

    (2011)
  • I.R. Macdonald et al.

    In situ EPR studies of electron trapping in a nanocrystalline rutile

    J. Photochem. Photobiol. A

    (2010)
  • I.R. Macdonald et al.

    EPR studies of electron and hole trapping in titania photocatalysts

    Catal. Today

    (2012)
  • K.Y. Jung et al.

    Photoluminescence and photoactivity of titania particles prepared by the sol–gel technique: effect of calcination temperature

    J. Photochem. Photobiol. A

    (2005)
  • A. Yamakata et al.

    Morphology-sensitive trapping states of photogenerated charge carriers on SrTiO3 particles studied by time-resolved visible to mid-IR absorption spectroscopy: The effects of molten salt flux treatments

    J. Photochem. Photobiol. A

    (2015)
  • Y. Bessekhouad et al.

    Synthesis of photocatalytic TiO2 nanoparticles: optimization of the preparation conditions

    J. Photochem. Photobiol. A

    (2003)
  • N. Serpone et al.

    On the genesis of heterogeneous photocatalysis: a brief historical perspective in the period 1910 to the mid-1980s

    Photochem. Photobiol. Sci.

    (2012)
  • J.M. Coronado

    A historical introduction to photocatalysis

  • A. Hagfeld et al.

    Light-induced redox reactions in nanocrystalline systems

    Chem. Rev.

    (1995)
  • A.L. Linsebigler et al.

    Photocatalysis on TiO2 surfaces: Principles, mechanisms, and selected results

    Chem. Rev.

    (1995)
  • J. Schneider et al.

    Understanding TiO2 photocatalysis: Mechanisms and materials

    Chem. Rev.

    (2014)
  • H. Zhang et al.

    Photoelectrocatalytic materials for environmental applications

    J. Mater. Chem.

    (2009)
  • J.H. Pan et al.

    Porous photocatalysts for advanced water purifications

    J. Mater. Chem.

    (2010)
  • M. Cargnello et al.

    Solution-phase synthesis of titanium dioxide nanoparticles and nanocrystals

    Chem. Rev.

    (2014)
  • D. Chen et al.

    Recent progress in the synthesis of spherical titania nanostructures and their applications

    Adv. Funct. Mater.

    (2013)
  • X.W. Lou et al.

    Hollow micro-/nanostructures: synthesis and applications

    Adv. Mater.

    (2008)
  • G. Liu et al.

    Titanium dioxide crystals with tailored facets

    Chem. Rev.

    (2014)
  • X. Lai et al.

    Recent advances in micro-/nano-structured hollow spheres for energy applications: From simple to complex systems

    Energy Environ. Sci.

    (2012)
  • F. Zhu et al.

    Hierarchical TiO2 microspheres: synthesis, structural control and their applications in dye-sensitized solar cells

    RSC Adv.

    (2012)
  • N.G. Park et al.

    Comparison of dye-sensitized rutile- and anatase-based TiO2 solar cells

    J. Phys. Chem. B

    (2000)
  • D.O. Scanlon et al.

    Band alignment of rutile and anatase TiO2

    Nat. Mater.

    (2013)
  • X. Chen et al.

    Titanium dioxide nanomaterials: synthesis, properties, modifications, and applications

    Chem. Rev.

    (2007)
  • Hengzhong Zhang et al.

    Understanding polymorphic phase transformation behavior during growth of nanocrystalline aggregates

    J. Phys. Chem. B

    (2000)
  • T.A. Kandiel et al.

    Tailored titanium dioxide nanomaterials: Anatase nanoparticles and brookite nanorods as highly active photocatalysts

    Chem. Mater.

    (2010)
  • M. Monai et al.

    Brookite: Nothing new under the sun?

    Catalysts

    (2017)
  • M.C. Ceballos-Chuc et al.

    Influence of brookite impurities on the raman spectrum of TiO2 anatase nanocrystals

    J. Phys. Chem. C

    (2018)
  • J.J.M. Vequizo et al.

    Trapping-induced enhancement of photocatalytic activity on brookite TiO2 powders: Comparison with anatase and rutile TiO2 powders

    ACS Catal.

    (2017)
  • Q. Tay et al.

    Enhanced photocatalytic hydrogen production with synergistic two-phase anatase/brookite TiO2 nanostructures

    J. Phys. Chem. C

    (2013)
  • L. Liu et al.

    Photocatalytic CO2 reduction with H2O on TiO2 nanocrystals: Comparison of anatase, rutile, and brookite polymorphs and exploration of surface chemistry

    ACS Catal.

    (2012)
  • H. Hu et al.

    Hierarchical tubular structures constructed from ultrathin TiO2(B) nanosheets for highly reversible lithium storage

    Energy Environ. Sci.

    (2015)
  • D. Xu et al.

    From titanates to TiO2 nanostructures: Controllable synthesis, growth mechanism, and applications

    Sci. China Chem.

    (2012)
  • H. Breil et al.

    Di(cyclooctatetraene)titanium and tri(cyclooctatetraene)dititanium

    Angew. Chem. Int. Ed.

    (1966)
  • H. Liu et al.

    Mesoporous TiO2-B microspheres with superior rate performance for lithium ion batteries

    Adv. Mater.

    (2011)
  • S. Liu et al.

    Nanosheet-constructed porous TiO2-B for advanced lithium ion batteries

    Adv. Mater.

    (2012)
  • M.R. Hoffmann et al.

    Environmental applications of semiconductor photocatalysis

    Chem. Rev.

    (1995)
  • S. Kohtani et al.

    Reactivity of trapped and accumulated electrons in titanium dioxide photocatalysis

    Catalysts

    (2017)
  • D. Gong et al.

    In situ mechanistic investigation at the liquid/solid interface by attenuated total reflectance FTIR: ethanol photo-oxidation over pristine and platinized TiO2 (P25)

    ACS Catal.

    (2011)
  • Cited by (379)

    View all citing articles on Scopus
    1

    These authors have equal contribution to this work.

    View full text