of the former were very broad, while those of the latter were highly uniform and
narrow [29].
Haoran Li et al. reported a facile soft-template method for the preparation of
boron- and fluorine-doped MCN materials. It was found that 1-butyl-3methylimidazoliumtetrafluoroborate (BmimBF 4 ), as a commercially available
room-temperature ionic liquid, was a unique soft template for the preparation of
boron- and fluorine-enriched MCN, in which an organic precursor, such as
dicyandiamide (DCDA), self-condensed to form carbon nitride in the presence of
BmimBF 4 . Their experimental results revealed that ionic liquids were good soft
templates, which were generally defined as organic salts with a <100
C melting
point. They inherited many features of inorganic molten salts, including the excellent
chemical and thermal stability as well as negligibly small vapor pressure and the
convenience of being liquid in ambient conditions [30].
Soft-template method possesses the advantages such as easy operation, simple
equipment, and low cost. The exploration of new soft templates is essential for the
further applications of the soft-template method for the synthesis of MCN materials.
Meanwhile, the soft-template method has drawbacks. For example, it cannot always
strictly control the size and morphology of the as-prepared products, limiting the
catalytic performance of the final MCN materials.
14.2.2 Hard-Template Method
In the hard-template method, the templates with mesopores are firstly synthesized,
which are usually mesoporous silica materials like SBA-15. Then, the precursor
solution of g-C 3 N 4 such as urea solution is perfused into the mesopores of the
as-prepared template, and the precursor will transfer into g-C 3 N 4 in the pore channels by the high-temperature calcination. After removing the template, MCN is
obtained.
Ajayan Vinu et al. prepared MCN by a typical hard-template method. In their
synthesis process, mesoporous silica SBA-15 [31] was added to a mixture of
ethylenediamine and carbon tetrachloride. After the reflux of the silica framework,
MCN with uniform mesopores and high photocatalytic activity was obtained
[32]. Zhongkui Zhao et al. also synthesized MCN by using SBA-15 as a hard
template. Their experimental results showed the specific surface area and pore
volume and N content of the obtained MCN had a tight relationship with the chosen
precursor. By using hexamethylenetetramine as the precursor, the obtained MCN
was highly ordered, with ultrahigh specific surface area of 1116 m
2 g
À1 and pore
volume of 1.54 cm
3 g
À1 . The procedure for the synthesis is presented in Fig. 14.4
[33]. In addition to changing the precursor, it is also demonstrated that the specific
pore volume as well as the pore diameter can also be controlled by simply adjusting
the structure of the SBA-15 template. Ajayan Vinu et al. successfully prepared MCN
with tunable pore diameters by using SBA-15 materials with different pore diameters as templates via a simple polymerization reaction between carbon tetrachloride
14.2 The Preparation of MCN
349
narrow [29].
Haoran Li et al. reported a facile soft-template method for the preparation of
boron- and fluorine-doped MCN materials. It was found that 1-butyl-3methylimidazoliumtetrafluoroborate (BmimBF 4 ), as a commercially available
room-temperature ionic liquid, was a unique soft template for the preparation of
boron- and fluorine-enriched MCN, in which an organic precursor, such as
dicyandiamide (DCDA), self-condensed to form carbon nitride in the presence of
BmimBF 4 . Their experimental results revealed that ionic liquids were good soft
templates, which were generally defined as organic salts with a <100
C melting
point. They inherited many features of inorganic molten salts, including the excellent
chemical and thermal stability as well as negligibly small vapor pressure and the
convenience of being liquid in ambient conditions [30].
Soft-template method possesses the advantages such as easy operation, simple
equipment, and low cost. The exploration of new soft templates is essential for the
further applications of the soft-template method for the synthesis of MCN materials.
Meanwhile, the soft-template method has drawbacks. For example, it cannot always
strictly control the size and morphology of the as-prepared products, limiting the
catalytic performance of the final MCN materials.
14.2.2 Hard-Template Method
In the hard-template method, the templates with mesopores are firstly synthesized,
which are usually mesoporous silica materials like SBA-15. Then, the precursor
solution of g-C 3 N 4 such as urea solution is perfused into the mesopores of the
as-prepared template, and the precursor will transfer into g-C 3 N 4 in the pore channels by the high-temperature calcination. After removing the template, MCN is
obtained.
Ajayan Vinu et al. prepared MCN by a typical hard-template method. In their
synthesis process, mesoporous silica SBA-15 [31] was added to a mixture of
ethylenediamine and carbon tetrachloride. After the reflux of the silica framework,
MCN with uniform mesopores and high photocatalytic activity was obtained
[32]. Zhongkui Zhao et al. also synthesized MCN by using SBA-15 as a hard
template. Their experimental results showed the specific surface area and pore
volume and N content of the obtained MCN had a tight relationship with the chosen
precursor. By using hexamethylenetetramine as the precursor, the obtained MCN
was highly ordered, with ultrahigh specific surface area of 1116 m
2 g
À1 and pore
volume of 1.54 cm
3 g
À1 . The procedure for the synthesis is presented in Fig. 14.4
[33]. In addition to changing the precursor, it is also demonstrated that the specific
pore volume as well as the pore diameter can also be controlled by simply adjusting
the structure of the SBA-15 template. Ajayan Vinu et al. successfully prepared MCN
with tunable pore diameters by using SBA-15 materials with different pore diameters as templates via a simple polymerization reaction between carbon tetrachloride
14.2 The Preparation of MCN
349