Page 7 of 8
Dalton Transactions
DOI: 10.1039/C5DT04901F
nitrogen activation (Figure 10d insert).
nitrogen photofixation ability. With the ZnMoCdS mass
CdS, MoCdS and ZnCdS were prepared using the same
method and metal molar ratio. Figure 11a compares the nitrogen 60 exhibits the highest NH4 generation rate under visible light,
percentage of 80%, the asꢀprepared heterojunction photocatalyst
+
photofixation performance of CdS, MoCdS and ZnCdS. The
which is 13.5ꢀfold and 1.75ꢀfold greater than those of individual
gꢀC3N4 and ZnMoCdS. This outstanding nitrogen photofixation
ability is attributed to the synergy effect of heterojunctions and
sulfur vacancies. Not only ZnMoCdS but other ternary
+
5
NH4 generation rate are 0.19, 0.70 and 1.01 mg·Lꢀ1·hꢀ1·gcatꢀ1 for
CdS, MoCdS and ZnCdS, obviously lower than asꢀprepared
ternary metal sulfide ZnMoCdS. Considering the sulfur vacancies
are regarded as the active centers for nitrogen photofixation, the 65 metal sulfide can combine with gꢀC3N4 to form the heterojunction
+
NH4 generation rate should be highly dependent on the amount
catalyst to promote the separation rate of electronsꢀholes.
10 of sulfur vacancies. More metal components causes the more
crystal lattice defects, leading to the formation of more sulfur
Acknowledgment
vacancies. The actual atomic ratio obtained by ICP is CdS0.98
,
This work was supported by National Key Technology R & D
Programme of China (No. 2012ZX07505ꢀ001), National Natural
70 Science Foundation of China (No. 41571464), Education
Department of Liaoning Province (No. L2014145),
Environmental Science and Engineering Innovation Team of
Liaoning Shihua University ([2014]ꢀ11), and Students’
Innovation Fund Project of China.
Mo0.11Cd0.89S1.06 and Zn0.12Cd0.92S0.98 for CdS, MoCdS and
ZnCdS, respectively. The difference of the theoretical and actual
15 number of sulfur atoms stands for the concentration of sulfur
+
vacancies. It is noted that the NH4 generation rates of CdS,
MoCdS and ZnCdS are linearly related to the concentration of
sulfur vacancies (Figure 11a insert), confirming the significantly
important role of sulfur vacancies on nitrogen photofixation.
20
75 Notes and references
15
12
9
6
5
4
3
2
1
0
(a)
(b)
1.0
0.8
0.6
0.4
0.2
0.0
College of Chemistry, Chemical Engineering, and Environmental
Engineering, Liaoning Shihua University, Fushun 113001, China, Eꢀmail:
hushaozhenglnpu@163.com; fylilnpu@163.com; Tel: 86ꢀ24ꢀ56860865
MoNiCdS-CN(20%)
NiZnCdS-CN(20%)
ZnCdS
MoCdS
R=0.990
0.00
0.02
0.04
0.06
0.08
Surfur vacancies concentration
MoNiCdS
NiZnCdS
6
25
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4
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time / h
time / h
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Figure 11. Nitrogen photofixation performance over asꢀprepared
30 catalysts under visible light.
In addition, MoNiCdS and NiSnCdS were also prepared using
the same method and metal molar ratio. ICP results show that the
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35 Ni0.13Sn0.10Cd0.85S1.13, indicating sulfur vacancies are also formed
in these ternary metal sulfides. The asꢀprepared ternary
atomic
ratio
is
Mo0.11Ni0.12Cd0.87S1.15
and
metal sulfide combined with gꢀC3N4 to form the heterojunction
catalyst MoNiCdSꢀCN(20%) and NiSnCdSꢀCN(20%). Nitrogen
photofixation performance shown in Figure 11b indicates that the
+
ꢀ1
40 NH4 generation rate are 2.5 and 1.84 mg·Lꢀ1·hꢀ1·gcat for
MoNiCdSꢀCN(20%) and NiSnCdSꢀCN(20%), obviously higher
than that of CN, MoNiCdS and NiSnCdS (0.26, 1.47 and 1.18
mg·Lꢀ1·hꢀ1·gcatꢀ1). This result indicates that not only ZnMoCdS
but other ternary metal sulfide can combine with gꢀC3N4 to form
45 the heterojunction catalyst to promote the separation rate of
electronsꢀholes.
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Conclusions
A novel gꢀC3N4/ZnMoCdS heterojunction photocatalysts with
outstanding nitrogen photofixation ability under visible light were
50 prepared by hydrothermal postꢀtreatment. Strong electronic
coupling exists between two components in the gꢀ
C3N4/ZnMoCdS heterojunction photocatalysts, leading to more
effective separation of photogenerated electronꢀhole pairs and
faster interfacial charge transfer. The sulfur vacancies on ternary
55 metal sulfide not only serve as active sites to adsorb and activate
N2 molecules but also promote interfacial charge transfer from
catalyst to N2 molecules, thus significantly improving the
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