Apart from Au and Pd nanoparticles, Pt nanoparticles were also homogenously
loaded in the mesoporous channels of MCN by Wen-sheng Dong et al. [49] The
synthesized materials were used for the selective oxidation of glycerol with molecular oxygen in base-free aqueous solution, showing high conversion efficiency and
selectivity. Shijiao Sun et al. also synthesized similar composites of MCN and Pt
nanoparticles [50]. The Pt nanoparticles with a diameter of 3–4 nm were loaded on
the MCN support. The as-prepared composites were applied as bifunctional air
electrodes, showing improved electrochemical performances with good round-trip
efficiency as high as 87% through the examination with an all-solid-state Li-air
battery.
14.3.2 Metallic Oxide Loading
In addition to the noble metal deposition, the metallic oxide has also been loaded into
the ordered mesoporous channels of MCN material. The metallic oxide improves the
photocatalytic activity of MCN via the formation of the heterojunction structure,
which can efficiently increase the separation rate of photo-generated electrons and
holes.
Jie Xu et al. prepared vanadia-loaded MCN catalysts by a wet impregnation
method using NH 4 VO 3 as a precursor and mesoporous carbon nitride as a support.
The modified MCN materials exhibited remarkable catalytic performance for the
hydroxylation of benzene to phenol in the presence of H 2 O 2 , which was attributed to
the high dispersion of vanadia species and the benzene-activation capability of
MCN. Due to the inbuilt and unique tri-s-triazine moieties, benzene was chemically
adsorbed and then activated on the catalytic surface of MCN through an electron
transfer from HOMO of C 3 N 4 to LUMO of benzene. In this path, the high surface
areas and the rich mesopores of MCN materials upgraded the amount of adsorbed
benzene molecules. On the other hand, V
4+ species that dispersed on the surface of
MCN were oxidized to radical-containing V
5+ species by H 2 O 2 , simultaneously
generating H 2 O. And then the as-produced V
5+ species reacted with the activated
benzene, thus yielding the target phenol. The possible path of the reaction is shown
in Fig. 14.12 [51].
Kamalakannan Kailasam et al. reported mesoporous carbon nitride–tungsten
oxide composites (CN/WO 3 ) and applied it to photocatalytic hydrogen evolution.
MCN/WO 3 composite showed very high photocatalytic activity for the evolution of
hydrogen from water with sacrificial electron donors under the irradiation of visible
light. The higher activity could be ascribed to the high surface area as well as
synergetic effect between the WO 3 and the carbon nitrides which led to improved
charge separation rate through a photocatalytic solid-state Z-scheme mechanism, as
shown in Fig. 14.13 [52]. After modification with WO 3, the photo-generated holes in
the valance band (VB) of g-C 3 N 4 and the photo-generated electrons in the conduction band (CB) of WO 3 would recombine at the interface, leaving the electrons in the
CB of g-C 3 N 4 and holes in the VB of WO 3. Therefore, the overall separation
358
14 Synthesis and Modifications of Mesoporous g-C 3 N 4 Photocatalyst
loaded in the mesoporous channels of MCN by Wen-sheng Dong et al. [49] The
synthesized materials were used for the selective oxidation of glycerol with molecular oxygen in base-free aqueous solution, showing high conversion efficiency and
selectivity. Shijiao Sun et al. also synthesized similar composites of MCN and Pt
nanoparticles [50]. The Pt nanoparticles with a diameter of 3–4 nm were loaded on
the MCN support. The as-prepared composites were applied as bifunctional air
electrodes, showing improved electrochemical performances with good round-trip
efficiency as high as 87% through the examination with an all-solid-state Li-air
battery.
14.3.2 Metallic Oxide Loading
In addition to the noble metal deposition, the metallic oxide has also been loaded into
the ordered mesoporous channels of MCN material. The metallic oxide improves the
photocatalytic activity of MCN via the formation of the heterojunction structure,
which can efficiently increase the separation rate of photo-generated electrons and
holes.
Jie Xu et al. prepared vanadia-loaded MCN catalysts by a wet impregnation
method using NH 4 VO 3 as a precursor and mesoporous carbon nitride as a support.
The modified MCN materials exhibited remarkable catalytic performance for the
hydroxylation of benzene to phenol in the presence of H 2 O 2 , which was attributed to
the high dispersion of vanadia species and the benzene-activation capability of
MCN. Due to the inbuilt and unique tri-s-triazine moieties, benzene was chemically
adsorbed and then activated on the catalytic surface of MCN through an electron
transfer from HOMO of C 3 N 4 to LUMO of benzene. In this path, the high surface
areas and the rich mesopores of MCN materials upgraded the amount of adsorbed
benzene molecules. On the other hand, V
4+ species that dispersed on the surface of
MCN were oxidized to radical-containing V
5+ species by H 2 O 2 , simultaneously
generating H 2 O. And then the as-produced V
5+ species reacted with the activated
benzene, thus yielding the target phenol. The possible path of the reaction is shown
in Fig. 14.12 [51].
Kamalakannan Kailasam et al. reported mesoporous carbon nitride–tungsten
oxide composites (CN/WO 3 ) and applied it to photocatalytic hydrogen evolution.
MCN/WO 3 composite showed very high photocatalytic activity for the evolution of
hydrogen from water with sacrificial electron donors under the irradiation of visible
light. The higher activity could be ascribed to the high surface area as well as
synergetic effect between the WO 3 and the carbon nitrides which led to improved
charge separation rate through a photocatalytic solid-state Z-scheme mechanism, as
shown in Fig. 14.13 [52]. After modification with WO 3, the photo-generated holes in
the valance band (VB) of g-C 3 N 4 and the photo-generated electrons in the conduction band (CB) of WO 3 would recombine at the interface, leaving the electrons in the
CB of g-C 3 N 4 and holes in the VB of WO 3. Therefore, the overall separation
358
14 Synthesis and Modifications of Mesoporous g-C 3 N 4 Photocatalyst