Communication
bination kinetics. Time-resolved fluorescence indicates decays
with short and long lifetimes depending on the preparation
Abstract: A stable noble-metal-free hydrogen evolution
photocatalyst based on graphite carbon nitride (g-C N )
[
9]
3
4
method, lifetimes that range from 5–10 ns to 50–100 ns.
Precious metals such as Pt are always needed as co-catalysts
to increase the lifetime of the charge carrier and achieve
was developed by a molecular-level design strategy.
Surface functionalization was successfully conducted to in-
troduce a single nickel active site onto the surface of the
[
7a,10]
practical applications.
To make g-C N an economically feasible and useful catalyst,
semiconducting g-C N . This catalyst family (with less than
3
4
3
4
0
.1 wt% of Ni) has been found to produce hydrogen with
considerable efforts have been devoted to making the catalyst
more efficient. Up to now, doping is the most important
a rate near to the value obtained by using 3 wt%
platinum as co-catalyst. This new catalyst also exhibits
very good stability under hydrogen evolution conditions,
without any evidence of deactivation after 24 h.
[
7,11]
method to enhance the catalyst efficiency;
other methods
[
12]
including increasing the surface area of C N , and the utiliza-
3
4
[
13]
tion of sensitizer. However, the noble metal Pt is essentially
the co-catalyst needed in all these method, which greatly
limits the application of g-C N4 in water splitting. Recently,
3
Due to the global energy crisis and environmental pollution,
hydrogen is poised to be a very important clean energy
a few examples have shown that co-catalysts other than Pt can
be used in the g-C N hydrogen-evolution system. These in-
3
4
[
1]
II
[13a]
[14]
[15]
vector. Photocatalytic hydrogen production from water by
using semiconductor catalysts has received considerable atten-
clude [Ni (PPh {NPhCH P(O)(OH) } ) ]Br ,
MoS2, NiS, and
2
2
2 2 2
2
[
16]
Ni(OH)2, yet all these have only moderate hydrogen evolu-
tion rates, low stability, and fast loss of reactivity. In the case of
[2]
tion in the past few decades, and various kinds of photo-
based water-splitting catalysts suitable for natural light have
been developed. These include inorganic materials such as
NiS or Ni(OH) , the co-catalyst is needed in large amounts.
2
More recently, one report showed that carbon quantum dots
can work as the co-catalyst for g-C N to give stable hydrogen
[
3]
[4]
[5]
[2e]
metal oxides, nitrides, sulfides, phosphides, and organo-
3
4
[1d,6a]
[17]
metallic complexes of Ru, Pt, and Os.
However, most of
evolution at a moderate rate.
these materials contain expensive noble metals or poisonous
metals as co-catalysts, which may hinder their widespread
The mechanism of carbon nitride photocatalyzed hydrogen
evolution usually involves the following: upon absorption of
a photon with energy equal to or higher than the band gap of
the semiconductor g-C N , photogenerated electrons migrate
[6]
application for economic and environmental reasons.
In the last few years, a graphite-like organic polymeric
carbon nitride (g-C N ) has attracted increasing interest owing
3
4
to the surface and are trapped by the Pt nanoparticles deposit-
ed on the surface; these produce the hydrogen by electroly-
3
4
to its photocatalytic activity for hydrogen production from
water under visible-light irradiation and in the presence of
[
18]
sis. The activity of the catalyst comes from the few locations
in which the active sites are structurally distinct from the bulk
g-C N ; thus, the dispersion of Pt on the surface can greatly
[
7]
a sacrificial reagent. This material is cheap, easy to synthesize,
and environmental friendly. In fact, g-C N is one of the oldest
3
4
3
4
[
10]
synthetic polymers, reported for the first time by Liebig in
influence the catalyst efficiency. However, it is still difficult to
improve the catalysts performance based on a reasonable
structure–activity relationship alone.
[8]
1
834, which was known as melon at first. Unlike graphite,
g-C N is a semiconductor material with an optical band gap
3
4
[
7a]
of 2.7 eV.
However, g-C N itself exhibits a very low activity in water
Based on a long-term study of the surfaces of organometal-
[
19]
lic catalysts, we developed a noble-metal-free water-splitting
catalyst by using the molecular-level design strategy of graft-
ing single active hydrogen evolution sites onto the surface of
g-C N . Owing to the specific location and direct chemical
3
4
À1
splitting, with a typically efficiency lower than 1 mmolh for
H evolution in the presence of triethanolamine as a sacrificial
2
reagent. This is due to the relatively fast electron–hole recom-
3
4
bonding, enhanced catalytic efficiency can be expected for the
photogeneration of electrons, which can then move directly to
the catalytic center. The surface of g-C N is terminated with
[
a] Dr. Y. Chen, Dr. B. Lin, Dr. W. Yu, Dr. H. Wang
Physical Sciences and Engineering Department
King Abdullah University of Science & Technology
3
4
NH2 groups; these are potential sites for anchoring the
catalytic center. However, because of their chemical inertness,
no successful design of such a catalyst has been reported yet.
g-C N is constructed of repeated tri-s-triazine units, which
2
3955-6900 Thuwal (Saudi Arabia)
[
b] Dr. Y. Chen, Prof. K. Takanabe, Prof. J.-M. Basset
Catalysis Center, Physical Sciences and Engineering Department
King Abdullah University of Science & Technology
3
4
2
3955-6900 Thuwal (Saudi Arabia)
E-mail: lin.bin@kaust.edu.sa
c] Prof. Y. Yang
have similar chemical properties to triazine. Based on our pre-
[
20]
vious experiences with the synthesis of triazine derivatives,
we introduced a conjugate triazine unit with a NiS moiety
(C N S Ni) to the surface of g-C N (Figure 1). NiS is known to
[
3
3
2
3
4
Department of Chemistry, Zhejiang Sci-Tech University
Hangzhou, 310018, (P. R. China)
be a good electrolytic hydrogen-evolution material, and a
conjugated aromatic ring is poised to enhance the electron
transfer. Thus, a noble-metal-free hydrogen-evolution catalyst
with enhanced efficiency can be expected.
[
d] S. M. Bashir, Prof. H. Idriss
SABIC-CRI at KAUST, 23955-6900, Thuwal (Saudi Arabia)
E-mail: IdrissH@sabic.com
We investigated the reactivity of the NH group on the g-
2
C N surface at first. The alkylation reaction of g-C N was per-
3
4
3
4
Chem. Eur. J. 2015, 21, 10290 – 10295
10291
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim