mesoporous structure favors the increase of the active sites and the utilization of
photon, thus improving its photocatalytic activity and further promoting the research
and the extensive applications of g-C 3 N 4 materials. Therefore, great efforts have
been devoted to synthesizing and studying mesoporous g-C 3 N 4 (MCN). In this
chapter, the development of MCN in recent years has been reviewed, including
the preparation and modifications of it. Firstly, we introduced four main different
preparation methods of MCN, which are soft-template method [25], hard-template
method [26], template-free method [27], and sol–gel method [28]. These synthesis
methods using different precursors and strategies make the as-prepared products
possess different pore regularity and other properties. After that, the modification
methods of MCN, which can lead to further improvement of photocatalytic activity
and the broaden of applications, were presented. In the end, a short summary of
MCN as well as its application prospects was provided.
14.2 The Preparation of MCN
The synthesis of bulk g-C 3 N 4 is quite simple by calcinating precursors at high
temperature to create a thermal polymerization reaction. The kinds of the precursors
are various and abundant, including urea, cyanamide, dicyandiamide, melamine,
carbon tetrachloride, ethylenediamine, ammonium thiocyanate, hexamethylenetetramine, and so on. In the process of high-temperature polymerization, the main
reactions for the precursor represented by cyanamide are shown in Fig. 14.1 [27].
Figure 14.1 shows that the reactions contain the two processes of polyaddition
and polycondensation. Firstly, the precursor polymerizes to melamine. Secondly, a
condensation occurs through removing ammonia from melamine to form the g-C 3 N 4
polymer. The results of X-ray analysis and differential scanning calorimetry (DSC)
demonstrated that in the process of the thermal polymerization, melamine can be
found in the products at 350
C, while the melamine rearranges to form tris-s-triazine
when the temperature arises to around 390
C. The condensation process of the triss-triazine unit to polymers, networks, and potentially the final g-C 3 N 4 occurs at the
temperature of ~520
C, with the material becoming unstable slightly above 600
C.
Heating to 700
C causes the residue-free disappearance of the material via generating nitrogen and cyano fragments. This reaction process may relate to the cohesive
energy, which was proved by the theoretical calculations results. As shown in
Fig. 14.2, the cohesive energy of the molecules increases along with the polyaddition
path [27].
The preparation of MCN includes not only the abovementioned reactions for the
preparation of bulk g-C 3 N 4 but also an additional step to generate the mesoporous
structure. The reported preparation methods of MCN are not as abundant as that of
bulk g-C 3 N 4 , which are summarized as follows.
346
14 Synthesis and Modifications of Mesoporous g-C 3 N 4 Photocatalyst
photon, thus improving its photocatalytic activity and further promoting the research
and the extensive applications of g-C 3 N 4 materials. Therefore, great efforts have
been devoted to synthesizing and studying mesoporous g-C 3 N 4 (MCN). In this
chapter, the development of MCN in recent years has been reviewed, including
the preparation and modifications of it. Firstly, we introduced four main different
preparation methods of MCN, which are soft-template method [25], hard-template
method [26], template-free method [27], and sol–gel method [28]. These synthesis
methods using different precursors and strategies make the as-prepared products
possess different pore regularity and other properties. After that, the modification
methods of MCN, which can lead to further improvement of photocatalytic activity
and the broaden of applications, were presented. In the end, a short summary of
MCN as well as its application prospects was provided.
14.2 The Preparation of MCN
The synthesis of bulk g-C 3 N 4 is quite simple by calcinating precursors at high
temperature to create a thermal polymerization reaction. The kinds of the precursors
are various and abundant, including urea, cyanamide, dicyandiamide, melamine,
carbon tetrachloride, ethylenediamine, ammonium thiocyanate, hexamethylenetetramine, and so on. In the process of high-temperature polymerization, the main
reactions for the precursor represented by cyanamide are shown in Fig. 14.1 [27].
Figure 14.1 shows that the reactions contain the two processes of polyaddition
and polycondensation. Firstly, the precursor polymerizes to melamine. Secondly, a
condensation occurs through removing ammonia from melamine to form the g-C 3 N 4
polymer. The results of X-ray analysis and differential scanning calorimetry (DSC)
demonstrated that in the process of the thermal polymerization, melamine can be
found in the products at 350
C, while the melamine rearranges to form tris-s-triazine
when the temperature arises to around 390
C. The condensation process of the triss-triazine unit to polymers, networks, and potentially the final g-C 3 N 4 occurs at the
temperature of ~520
C, with the material becoming unstable slightly above 600
C.
Heating to 700
C causes the residue-free disappearance of the material via generating nitrogen and cyano fragments. This reaction process may relate to the cohesive
energy, which was proved by the theoretical calculations results. As shown in
Fig. 14.2, the cohesive energy of the molecules increases along with the polyaddition
path [27].
The preparation of MCN includes not only the abovementioned reactions for the
preparation of bulk g-C 3 N 4 but also an additional step to generate the mesoporous
structure. The reported preparation methods of MCN are not as abundant as that of
bulk g-C 3 N 4 , which are summarized as follows.
346
14 Synthesis and Modifications of Mesoporous g-C 3 N 4 Photocatalyst