Chapter 7
The Preparation and Applications
of g-C 3 N 4 /TiO 2 Heterojunction Catalysts
7.1 Introduction
Nowadays, there have been two global problems all the society is facing, environmental pollution and energy shortage, which have caused great harm to human
health and life. To solve these problems, photocatalysis as an effective approach
has attracted widespread concern of researchers. In this approach, by utilizing
photocatalysts, light as a clean excitation power can be used to induce a series of
catalytic reactions, with regard to environment and energy, such as photocatalytic
degradation of pollutants in water [1–4], removal of indoor harmful gases [5],
reduction of CO 2 [6–8], as well as splitting of water to produce H 2 and O 2 [9].
In many of the photocatalysts studied, TiO 2 has been widely recognized as the
most potential one due to its merits of low cost, good stability, nontoxicity, and so on
[10–13]. However, the conventional TiO 2 has shortcomings in the following two
aspects: (1) the large bandgap (~3.2 eV) can only absorb UV light with λ 387 nm,
and the absorption of visible light is almost zero, which leads to the low utilization
efficiency of sunlight, and (2) the recombination rate of photo-generated electron–
hole pairs is high, greatly limiting the photocatalytic performance of TiO 2 . At
present, various methods for the improvement of the photocatalytic activity of
TiO 2 have been reported, such as metal and nonmetal oxide loading [14, 15],
noble metal deposition [16, 17], nonmetal element doping [18, 19], modifications
of morphology, and so on [20–23]. These methods can broaden the absorption
wavelength of TiO 2 and enhance the absorption efficiency of solar light in some
extent. But the recombination of photo-generated electrons and holes results in a
lower quantum yield, further seriously affecting the catalytic activity of the catalysts.
Heterojunction catalyst is one of the hot spots in catalytic field in recent years,
which usually consists of two different semiconductors contacting with each other to
form the structure of heterojunction. The heterojunction structure can promote the
transfer of the photo-generated electrons and holes in opposite direction, greatly
improving the effective utilization rate of the excitons. Therefore, heterojunction
© Springer Nature Singapore Pte Ltd. 2018
J. Zhang et al., Photocatalysis, Lecture Notes in Chemistry 100,
https://doi.org/10.1007/978-981-13-2113-9_7
173
The Preparation and Applications
of g-C 3 N 4 /TiO 2 Heterojunction Catalysts
7.1 Introduction
Nowadays, there have been two global problems all the society is facing, environmental pollution and energy shortage, which have caused great harm to human
health and life. To solve these problems, photocatalysis as an effective approach
has attracted widespread concern of researchers. In this approach, by utilizing
photocatalysts, light as a clean excitation power can be used to induce a series of
catalytic reactions, with regard to environment and energy, such as photocatalytic
degradation of pollutants in water [1–4], removal of indoor harmful gases [5],
reduction of CO 2 [6–8], as well as splitting of water to produce H 2 and O 2 [9].
In many of the photocatalysts studied, TiO 2 has been widely recognized as the
most potential one due to its merits of low cost, good stability, nontoxicity, and so on
[10–13]. However, the conventional TiO 2 has shortcomings in the following two
aspects: (1) the large bandgap (~3.2 eV) can only absorb UV light with λ 387 nm,
and the absorption of visible light is almost zero, which leads to the low utilization
efficiency of sunlight, and (2) the recombination rate of photo-generated electron–
hole pairs is high, greatly limiting the photocatalytic performance of TiO 2 . At
present, various methods for the improvement of the photocatalytic activity of
TiO 2 have been reported, such as metal and nonmetal oxide loading [14, 15],
noble metal deposition [16, 17], nonmetal element doping [18, 19], modifications
of morphology, and so on [20–23]. These methods can broaden the absorption
wavelength of TiO 2 and enhance the absorption efficiency of solar light in some
extent. But the recombination of photo-generated electrons and holes results in a
lower quantum yield, further seriously affecting the catalytic activity of the catalysts.
Heterojunction catalyst is one of the hot spots in catalytic field in recent years,
which usually consists of two different semiconductors contacting with each other to
form the structure of heterojunction. The heterojunction structure can promote the
transfer of the photo-generated electrons and holes in opposite direction, greatly
improving the effective utilization rate of the excitons. Therefore, heterojunction
© Springer Nature Singapore Pte Ltd. 2018
J. Zhang et al., Photocatalysis, Lecture Notes in Chemistry 100,
https://doi.org/10.1007/978-981-13-2113-9_7
173