Enhanced visible light photocatalytic non-oxygen coupling of amines to imines integrated with hydrogen production over Ni/CdS nanoparticles

Article abstract of DOI:10.1039/c8cy01326h

This work presents an efficient strategy for visible light-driven imine production through a photocatalytic non-oxygen coupling reaction of diverse amines dramatically boosted by hydrogen evolution over noble metal-free Ni/CdS nanoparticles. Thanks to the

Full text of DOI:10.1039/c8cy01326h

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Enhanced Visible light photocatalytic nonoxygen coupling of
amines to imines integrated with hydrogen production over
Ni/CdS Nanoparꢀcles†
Received 00th January 20xx,
Accepted 00th January 20xx
Weiwei Yu,a Di Zhang,a Xinwen Guo,a Chunshan Song,a,b Zhongkui Zhaoa,*
DOI: 10.1039/x0xx00000x
This work presents an efficient strategy for visible light driven imines production through
photocatalytic nonoxygen coupling reaction of diverse amines dramatically boosted by hydrogen
evolution over the noble-metal free Ni/CdS nanoparticles. Thanks to the integrating effect, close
to 100% conversion of benzylamine (75.2 h-1 of turnover frequency), 97% selectivity of imine with
21.4 mmol g-1 h-1 of hydrogen evolution rate (λ>420 nm) and 11.2% apparent quantum yield (450
nm, 10 mg catalyst) have been achieved at room temperature and ambient pressure. In
comparison with the use of common sacrificial agents like TEOA or Na2S/Na2SO3, by using coupling
of amines to imines, the H2 evolution rate increases two orders of magnitude. The
aforementioned integrating strategy has been extended to diverse amines, and the outstanding
photocatalytic performance for H2 and imines production was obtained. Besides, the catalyst can
be recycled several times without visible activity loss, suggesting a bright perspective for
sustainable chemistry and solar utilization. This new discovery may open a new horizon for
efficiently boosting solar hydrogen evolution and simultaneously clean producing diverse high
value-added fine chemicals under mild conditions.
www.rsc.org/
oxidation half-reaction to produce O2 can cause negative
aspects in achieving effective hydrogen evolution: (1) The H2
evolution half reaction is suppressed because of the O2 is a
1. Introduction
Solar-driven hydrogen evolution from water splitting via good electron acceptor. (2) The system–damaging reactive
semiconductive photocatalyst systems is an attractive and oxygen species can form through uncontrolled O2 reduction,
sustainable strategy to mitigate environmental issues and and most of the hydrogen evolution catalysts are O2 senstive.3
meet the increasing demands for energy.1 Great efforts have (3) The separation process of H2 and O2 increases energy
been devoted to exploiting highly solar water splitting systems consumption and limits commercial value of photocatalytic H2
over several decades. However, most semiconductor production. To efficiently restrain the oxidation half-reaction
photocatalysts suffer from a low H2 evolution efficiency due to and recombination of photogenerated electrons and holes,
the rapid recombination of photo-induced electrons and holes various hole-scavengers are employed, such as CH3OH4,
before the electrons migrating to the surface of catalysts for triethanolamine (TEOA),5 lactic acid,6 ascorbic acid,7
aqueous protons reducing reactions. In order to restrain the Na2S/NaSO3.8 However, such a method not only wastes the
recombination of photogenerated electron-hole pairs, noble oxidation energy of the photo-induced holes but also uses a
metals such as Pt, are always used as cocatalysts. Although the large amount of sacrificial reagents. Hence, it is desirable to
noble metals could boost the H2 evolution efficiency, due to replace the hole-scavengers with valuable organic
their scarcity and high cost, it is very important to develop transformations, which would efficiently boost both H2
noble-metal-free catalysts system.2 In addition, the water production from water splitting and simultaneously synthesis
of high value-added chemicals from organic transformations.
Nevertheless, the researches in this area remain extremely
rare. Kasap et al9 realized the photocatalytic reduction of
aqueous protons coupled to alcohol oxidation to aldehydes via
using a carbon nitride-molecular Ni catalyst system. Moreover,
10
Han et al
successfully integrated H2 production with the
transformation of biomass intermediates to the value-added
2b
aldehydes and acids. Very recently, Liu et al
realized H2
production coupling with benzylamine oxidation over MOF
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composites with Pt as cocatalyst. Unfortunately, no hydrogen 2.1 Chemicals
produces while the noble Pt cocatalyst is absent and the
Cadmium acetate ((CH3COO)2Cd·2H2O), nickel chloride
hexahydrate (NiCl2·6H2O), Cobalt chloride hexahydrate
(CoCl2·6H2O) and thioacetamide were purchased from Tianjin
Guangfu Fine Chemical Research Institute. Urea and Iron
chloride hexahydrate (FeCl3·6H2O) were purchased from
Tianjin Damao Chemical Reagent Factory. Ethylene glycol and
acetonitrile (CH3CN) were purchased from Tianjin Fuyu Fine
Chemicals Co. Ltd. HAuCl4·4H2O and H2PtCl6·6H2O were
purchased from Shenyang Nonferrous Metal Research
Institute. All the chemicals are analytical grade and directly
used without further processing. Deionized water was used in
all procedures and photocatalytic experiments were
implemented under nitrogen atmosphere.
incentive effects to hydrogen evolution by benzylamine
oxidation is worse than TEOA, besides the increase in
hydrogen evolution rate is desirable. It is very necessary to
design a more efficient noble-metal free catalyst system to
realize the coupling of visible light-driven hydrogen evolution
with amines oxidation.
Imines are important and valuable chemicals because of the
wide application as versatile intermediates for fine chemicals,
pharmaceuticals and agrochemicals.11 Great progress has been
made for the imines production in the past decade.12 From
economic and environment-friendly viewpoints, solar-driven
coupling of amines to imines using O2 as oxidant has been
regarded as a promising approach. To date, various catalysts
13
including supported Au catalysts on TiO2
or Au-Pd alloy
2.2 Preparation of the materials
nanoparticles on ZrO2 14, composite catalysts based on g-C3N4
The CdS NPs were prepared according to the previously
reported literature with some modifications.20 Briefly, 2 mmol
18
15, Nb2O5 16, WS2 17, WO3 and BiOBr 19 have been developed
to promote the photocatalytic aerobic oxidative coupling
reactions (Table S1). However, in the aforementioned
photocatalytic coupling systems, O2 is indispensable because
the superoxide radicals play a crucial role during the oxidative
coupling strategy of amines to imines. The aerobic oxidative
coupling of amines to imines is inevitably suffered from a risk
of handling an explosive mixture containing flammable organic
compounds and O2, which seriously limits the industrial
applications. Moreover, this aerobic oxidative coupling
strategy cannot be performed in anaerobic environment such
as reductive atmosphere or anaerobic bacteria breed.
Therefore, there is an urgent demand for developing an
efficient strategy to initiate a nonoxygen coupling of amines to
imines.
cadmium acetate (Cd(CH3COO)2·2H2O) and
6
mmol
thioacetamide were dissolved in 50 ml ethylene glycol by
ultrasonic processing. Above mixed solution was transferred
into an 80 ml Teflon-lined autoclave and maintained at 160
℃
for 18 h. Next, the autoclave was cooled to room temperature
and the orange precipitates were washed three times with
deionized water and once with absolute alcohol via
centrifugation. The final product was dried at 60
and grinded by using the agate mortar.
℃ in an oven
The g-C3N4 was synthesized by thermal polymerizing of urea
under N2 atmosphere. In detail, 5 g urea was placed in a quartz
boat and heated in N2 flow (30 ml/min) at 550
ramp rate of 5
min-1. The light yellow g-C3N4 was collected
by fully grinding.
℃ for 4 h with a
℃
Herein, we reported that visible light-driven H2 evolution
from water splitting integrating with nonoxygen coupling of
amines to their corresponding imines over the Ni/CdS
photocatalyst without using of noble metal. Owing to the
integrating effect between the two transformations, the
excellent H2 evolution rate and conversion of benzylamine
have been achieved under visible light irradiation. The H2
evolution rate boosting with benzylamine oxidation is two
orders of magnitude more than the traditional holes-
scavengers (TEOA or Na2S/NaSO3). The maximum hydrogen
evolution rate of 21.4 mmol h-1 g-1 and 11.2% optimized
apparent quantum yield (450 nm, only 10 mg catalyst being
used) associated with 100% conversion of benzylamine have
been achieved at room temperature and ambient pressure.
This integrating strategy concerning H2 generation from water
splitting associated with the nonoxygen coupling of
benzylamine to imine has been successfully extended to
diverse amines. Moreover, this research may open a new
window to simultaneously boosting both solar hydrogen
evolution and the production of diverse high value-added
chemicals under mild conditions.
The Ni/CdS was prepared by in situ photodeposition in a
mixed solution. Typically, 10 mg CdS and 6 μmol NiCl2·6H2O
contained in 0.15 ml H2O were dispersed in 2 ml CH3CN. Above
mixed solution was sealed in a flask (10 ml, Synthware) and
thoroughly replaced the air by N2 under stirring. Subsequently,
the mixture was irradiated with
a 300 W Xe lamp
(PLSSXE300/300UV, Perfectlight) with a 420 nm cut-off filter
for 5 min. The obtained Ni/CdS was kept in the mixed solution
in the flask under N2 atmosphere and directly used for
photocatalytic reactions. Adopted the above method, the Ni/g-
C3N4 was prepared by replacing CdS with g-C3N4, and the
Au/CdS, Pt/CdS, Fe/CdS and Co/CdS were obtained by
replacing NiCl2·6H2O with HAuCl4·4H2O, H2PtCl6·6H2O,
FeCl3·6H2O and CoCl2·6H2O, respectively. The theoretical
loading ratio of metal on CdS or g-C3N4 is 3.5 wt %.
2
.3. Characterization of materials
Scanning electron microscopy (SEM) images were obtained on
a JEOL JSM-5600LV SEM instrument and Transmission electron
microscopy (TEM) images were acquired on a JEM-2000EX
TEM instrument. X-ray diffraction (XRD) was conducted on a
D/Max 2400 diffractometer with monochromatic Cu Kα source.
X-ray photoelectron spectroscopy (XPS) measurements were
2. Experimental
performed on an ESCALAB 250 XPS system with
a
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monochromatic Al Kα X-ray source. The Brunauer-Emmett-
Teller (BET) method was utilized to calculate the specific
surface area, and the pore size distributions was calculated
from an adsorption branch of the isotherm via the Benjamin-
Johnson-Hui (BJH) model (3H-2000PS, BeiShiDe Instrument).
The UV-vis diffuse reflectance spectra (DRS) were recorded on
a JASCO V-550 UV-vis spectrometer.
2
.4 Photocatalytic performance test
Typically, 0.15 ml H2O and 3 ml CH3CN mixed solution
contained 0.5 mmol benzylamine were quickly added into the
above Ni/CdS mixed solution in the flask. Then the flask was
sealed and thoroughly replaced the air by N2 under stirring.
Subsequently, the mixture was illuminated by the Xe lamp for
a
certain time with continuous stirring. The reaction
temperature was kept at 20 oC by a circulating bath during the
experiment process. The generated H2 was quantified by a gas
chromatography (GC 9790 II, FuLi Instruments) equipped with
a thermal conductive detector (TCD) and nitrogen as the
carrier gas. The organic products were quantified by the GC
with a SE-54 capillary column (30 m × 0.32 mm × 0.50 μm),
flame ionization detector (FID), argon as the carrier gas and
trifluorotoluene as the internal standard. The qualitative
analysis of the products was performed by gas
Figure 1. (a) TEM and (b) HRTEM images of Ni/CdS, (c) XRD patterns of CdS and
the Ni/CdS, (d) Ni 2p spectra of Ni/CdS.
thioacetamide (see Figure S1a for the SEM image of CdS).20
The metallic Ni NPs were supported on the surface of CdS NPs
(Ni/CdS) via an in situ photodeposition method in a mixed
solvent (CH3CN/H2O) with the NiCl2·6H2O as Ni source (Figure
S1b for the SEM image of Ni/CdS).21 Figure 1a and b show
typical transmission electron microscope (TEM) and high-
resolution TEM (HRTEM) images of the as-synthesized Ni/CdS
catalyst, indicating that the Ni NPs are successfully decorated
on the surface of CdS NPs. The X-ray diffraction (XRD) patterns
(Figure 1c) confirm that the CdS NPs with a mixed crystalline
phases consisting of cubic (PDF#65-2887) and hexagonal
(PDF#41-1049) planes. No visible diffraction peaks
corresponding to Ni or nickel compounds in the XRD pattern of
Ni/CdS can be resolved because of its low loading or
amorphous Ni. The chemical states of the elements of Ni/CdS
were estimated by X-ray photoelectron spectra (Figure 1d and
Figure S2). From Figure 1d, based on references,10,21 the fitted
peak appearing at 852.1 eV can be assigned to metallic Ni, and
the peaks occurring at 853.2 and 856.2 eV can be ascribed to
NiO and NiCl2, respectively. The big peak at around 858.2 cna
be assigned to Ni satellite. The surface area of CdS NPs is 24.2
m2 g-1 and the N2 adsorption-desorption isotherms display type
IV isotherms with H3 hysteresis loop suggesting the existence
of mesopores (Figure S3a).22 The BJH analysis indicates that
CdS NPs owns a wide pore size distribution and the major pore
size is centered at 43 nm (Figure S3b), resulting from the
accumulation of CdS NPs.
chromatography-mass
spectrometry
(GC-MS,
mass
HP6890/5973MSD, Agilent) equipped with
a
spectrometry detector. By similar experimental process, the
photocatalytic performance of Ni/CdS nanoparticles for visible
light driven nonxygen coupling of diverse amines integrated
with H2 production was measured. TON was calculated on the
basis of photodeposited Ni molar amount, while hydrogen
evolution rate was obtained based on the dosage of CdS
1
photocatalyst. H nuclear magnetic resonance (NMR) spectra
of products were record product was recorded at 25 oC in
CD3CN by a 500 MHz spectrometer (Bruker AVANCE III 500).
The cycle experiments were performed by directly adding
substrate and H2O after each cycle. The AQYs were performed
similar to the above for photocatalytic performance test while
2.5 mmol benzylamine and 0.5 ml H2O were added. Different
wavelengths of visible light (420, 450, 520 and 600 nm) as light
sources were obtained by using band-pass filters. The optimal
hydrogen production rate was obtained by measuring the
hydrogen yield per 15 mins. Area of irradiation was ca. 6.0 cm2.
The light intensity was determined by
a PL-MW2000
photoradiometer (Perfectlight). The AQY was calculated as
follows:
2 × amount of H 2 molecules evolved
AQY [%] =
× 100
The photocatalytic performance of the as-synthesized
Ni/CdS catalyst and the supported diverse metals catalysts on
CdS for H2 production integrated with nonxygen coupling of
benzylamine under different reaction conditions are
summarized in Table 1. Initially, the photocatalytic activity of
Ni/CdS was verified under N2 atmosphere with visible light
irradiation. To our delight, a H2 production rate of 12.94 mmol
h-1 g-1 associated with 94% conversion of benzylamine (45.41
number of incident photons
3. Results and discussion
The CdS nanoparticles (NPs) were synthesized through a facile
glycol thermal sulfuration process of cadmium acetate by
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(entry 10), although Pt is a well-known cocatalyst for highly-
efficient hydrogen evolution reaction from water splitting.
Moreover, using g-C3N4 as support, only 5% conversion of
benzylamine and 85% of imine selectivity with trace H2
production can be achieved (entry 12). The result indicates Pt
cannot effectively abstract hydrogen from substrates which is
consistent with previous literature that Pt cannot adsorb
hydrogen from alcohol.23 The aforementioned results strongly
suggest that the synergistic effect between metallic Ni and CdS
Table 1. Visible light-driven nonoxygen coupling of benzylamine to imine with H2
Production.a
Entry
Catalyst
Conv.
[%]
Sel.
[%]
H2 rate
[mmol h-1 g-1]
1
2b
3c
4d
5e
6
Ni/CdS
Ni/CdS
Ni/CdS
Ni/CdS
Ni/CdS
-
94
16
-
96
95
-
12.94
1.29
0.02
0.06
0
plays
a crucial role in improving the photocatalytic
-
-
performance for coupling of benzylamine to imine with
simultaneous hydrogen production from water splitting. Ni
serves as active sites for hydrogen evolution on CdS
photocatalyst, which promotes the consumption of
photogenerated electrons. Moreover, Ni serves as active sites
for photocatalytic reaction on CdS photocatalyst, by which not
only promotes the migration of photogenerated electrons but
also activates substrates.21 As a consequence, the synergistic
effect between CdS and Ni exists, which efficiently promotes
the photocatalytic nonoxygen coupling of amines to imines
integrated with hydrogen production over Ni/CdS
Nanoparticles. In a word, we unveil an efficient combination
strategy for boosting visible light-driven hydrogen evolution
from water splitting integrated with nonoxygen coupling of
benzylamine to imine over Ni/CdS photocatalyst. The
nonoxygen coupling of benzylamine to imine efficiently utilizes
photogenerated holes, which boosts the H2 evolution
simultaneously. On the other hand, the consumption of
photoinduced electrons by H2 generation can efficiently inhibit
the recombination of photoinduced charge carriers. As a
consequence, both H2 evolution and the benzylamine
oxidation are dramatically promoted.
0
-
0
-
0
7
CdS
8
10
97
85
94
98
83
1.73
0.43
0.86
trace
0.09
trace
8
Au/CdS
Co/CdS
Pt/CdS
Fe/CdS
Ni/g-C3N4
9
9
32
17
4
10
11
12
5
[a] Reaction conditions: benzylamine (0.5 mmol), CdS nanoparticle (10 mg),
NiCl2.H2O (6 μmol), mixed solvent (5 mL CH3CN/0.3 mL H2O), nitrogen
atmosphere, λ > 420 nm, 1.85 W Xe lamp. The rate of H2 evolution was
calculated for 1h. [b] CH3CN as solvent (in absence of H2O). [c] 0.5 mmol
TEOA instead of benzylamine. [d] Na2S/Na2SO3 (0.15 mmol/0.35 mmol)
instead of benzylamine and the mixed solvent is 4.15 mL CH3CN/1.15 mL
H2O. [e] Without light irradiation.
mmol h-1 g-1 of benzylamine oxidation rate) and 96% selectivity
of imine are obtained (entry 1), while no transformation takes
place under either no visible light irradiation (entry 5) or the
absence of Ni/CdS catalyst (entry 6) conditions. From GC-MS
spectra of reaction mixture, the main by-products can be
confirmed to be dibenzylamine and trace benzaldehyde. The
conversion of benzylamine and H2 production rate dropped
sharply in the absence of H2O under nonoxygen nitrogen
atmosphere (entry 2). From Table S1, similar results can be
seen over diverse catalysts, the conversion of amines with
nonoxygen atmosphere is fall badly compared with aerobic
atmosphere. When the benzylamine were replaced with same
amount of sacrificial agents as TEOA or Na2S/Na2SO3, H2
evolution rate decrease two orders of magnitude to 0.02 mmol
h-1 g-1 and 0.06 mmol h-1 g-1 (entry 3, entry 4), which indicated
that the H2 evolution stimulating effect of benzylamine is much
better than TEOA and Na2S/Na2SO3 which are usual sacrificial
agents for photocatalytic H2 production in our catalytic
reaction condition. The result is very different from the H2
production coupling with selective benzylamine oxidation over
MOF composites with Pt cocatalyst.2b In that work, with the
same amount of benzylamine as TEOA, H2 evolution rate
decreases from 0.59 mmol h-1 g-1 to 0.33 mmol h-1 g-1. To
perform the reaction over individual CdS NPs results in a H2
production rate of 1.73 mmol h-1 g-1, and only 8% conversion
with 10% selectivity for imine (83% of 2-amino-2-
phenylacetamide, 7% of dibenzylamine; entry 7). Other
supported metal catalysts, such as Au/CdS, Co/CdS, Pt/CdS,
and Fe/CdS are less effective than Ni/CdS (entry 8-11). More
interestingly, trace H2 over Pt/CdS catalyst can be generated
The time courses for H2 production integrated with the
nonoxygen coupling of benzylamine to imine using Ni/CdS NPs
are shown in Figure 2a and 2b. The reaction conditions are the
same as those described in Table 1 unless otherwise noted. As
presented in Figure 2a, the conversion of benzylamine sharp
increases with the extending reaction time up to 1 h ( 94% of
conversion with 95 ± 2% of selectivity), and then it begins to
slightly increase along with the further extending reaction time.
Close to 100 % of conversion and 97 % of selectivity for
benzylamine transformation can be obtained for 1.5 h. From
Figure 2b, the time course for H2 production basically agrees
with the conversion of benzylamine showed in Figure 2a. It is
easily understandable for the increasing H2 produced volume
along with the extending reaction time up to 90 min. More
interesting, 21.4 mmol h-1 g-1 of maximum high hydrogen
evolution rate at 45 min of reaction time can be obtained. The
decreasing hydrogen evolution rate along with the extending
reaction time results from the gradually decreasing
benzylamine concentration.10 The apparent quantum yield
(AQY) values for H2 evolution over Ni/CdS photocatalyst under
various wavelengths of visible light are demonstrated in Figure
2c. The catalyst owns higher AQY value at 450 nm to be 11.2%.
To explore the plausible mechanism of the photocatalytic
converting of benzylamine to imine coupled to H2 production
over Ni/CdS NPs, a series of control experiments were
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Figure 3. Recyclability in (a) conversion and selectivity as well as (b) the produced
H2 amount for oxygen-free transformation of benzylamine to imine coupled to
hydrogen production over Ni/CdS catalyst under visible light irradiation. Reaction
conditions: benzylamine (0.5 mmol), CdS nanoparticle (10 mg), NiCl2.H2O (6
μmol), mixed solvent (5 mL CH3CN/0.3 mL H2O), nitrogen atmosphere, λ>420 nm,
20 oC, 1.5 h. Note: 0.5 mmol of benzylamine was added per cycle experiments
(blue bar charts), 0.7 mmol of benzylamine was added (green bar chart).
imine over Ni/CdS with H2O assistance is proposed and
illustrated in Scheme 1. The electrons are excited from the
valence band (VB) of CdS to its conduction band (CB) and leave
corresponding holes at the VB under light irradiation. The
electrons rapidly transfer to Ni NPs and reduce aqueous
protons to H2. The carbon cationic species produced by the
holes coupled with benzylamine to produce the desired
imine.2b The ratio of H2 and coupling product towards
benzylamine show a good stoichiometric relationship on the
basis of the proposed mechanism of reaction (Figure S4).
Furthermore, the durability of the as-synthesized Ni/CdS
catalyst was tested by cycle experiments. Figure 3 shows the
results of visible light-driven nonoxygen coupling of
benzylamine to imine integrated with hydrogen evolution in
the presence of H2O. From Figure 3a, no visible decrease in
photocatalytic properties for the coupling of benzylamine to
imine half-reaction after 4 cycles can be observed. However,
the H2 production half-reaction shows a gradual decline during
cycle experiments (blue bar charts; Figure 3b), which is mainly
because of part of photoinduced electrons are consumed via
reducing Ni2+ to Ni due to Ni is easily oxidized when adding
substrates during the cycle experiments. However, the H2
production half-reaction shows a gradual decline during cycle
experiments (blue bar charts; Figure 3b), which is mainly
because of the Ni on the surface of CdS was easily oxidized
(similar to Raney Ni) when adding substrates during the cycle
experiments and part of photoinduced electrons are
consumed via reducing Ni2+ to Ni. The H2 volume could be
regained when the more benzylamine (increase from 0.5 to 0.7
mmol) are used (green bar chart), which further confirms the
above supposed reaction mechanism.
Figure 2. (a) Conversion and selectivity with (b) produced H2 volume and H2
evolution rate towards nonoxygen transformation of benzylamine to imine
coupled to H2 production over Ni/CdS catalyst in the presence of H2O under
visible light irradiation. The bars in Figure 2b denote the rate of H2 evolution
averaged over 15 min of visible light irradiation. (c) Ultraviolet-visible diffuse
reflectance spectrum of the CdS NPs and wavelength-dependent AQY values
towards H2 evolution over Ni/CdS catalyst (2.5 mmol benzylamine and 0.5 ml
H2O were added). (d) Photocatalytic performance of Ni/CdS under various
reaction conditions: BA denotes as benzylamine.
implemented (Table 1 and Figure 2d). No H2 was detected
when benzylamine was absent in the reaction system, which
shows clearly the synergistic effect between H2 production on
the Ni cocatalyst and benzylamine conversion plays a critical
role in improving the photocatalytic activity of Ni/CdS.
Compared with the reaction with adequate H2O (0.3 mL)
added, a much lower photocatalytic activity for converting of
benzylamine and rate of hydrogen evolution are obtained in
absence of additional H2O (the crystal water of NiCl2·6H2O and
acetonitrile solvent containing H2O provide a spot of H2O for
reaction). The result shows that H2O is an important reaction
component during the catalytic process. On the basis of the
above experiment results,
a plausible mechanism for
photocatalytic nonoxygen strategy for integrating H2
production with the nonoxygen coupling of benzylamine to
After having demonstrated the outstanding photocatalytic
performance in nonoxygen coupling of benzylamine to
corresponding imine integrated with H2 evolution under visible
light irradiation, we also explored the feasibility of the
developed integrating strategy for the transformation of a
series of structurally diverse aryl amines (Table 2). The various
aryl amines tend to give their corresponding imines with
excellent activity and selectivity integrating with outstanding
hydrogen evolution activity, suggesting the expandable
strategy developed in this work.
Scheme 1. Plausible reaction mechanism over Ni/CdS nanoparticles under visible
light irradiation.
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photocatalytic performance was obtained. Besides, the
catalyst can be recycled several times without visible catalytic
activity loss, suggesting a bright perspective for sustainable
chemistry and solar utilization. This work not only realizes
highly efficient visible light-driven hydrogen evolution
integrated with nonoxygen coupling of amines to their imines
but also opens a new avenue to integrating highly efficient
synthesis of organic chemicals under mild conditions with solar
fuel generation.
Table 2. Visible light-driven hydrogen production integrating with the nonxygen
coupling of various amines to their corresponding imines over Ni/CdS NPs
photocatalyst.a
No
.
Con.
[%]
Sel.
[%]
H2
Substrate
Product
[ml]
1b
2
99
98
92
90
97
97
96
95
4.1
4.1
3.0
3.1
Conflicts of interest
There is no conflict to declare.
3
Acknowledgements
4c
This work was financially supported by the National Natural
Science Foundation of China (U1610104 and 21676046), the
Chinese Ministry of Education via the Program for New
Century Excellent Talents in Universities (NCET-12-0079), and
the Natural Science Foundation of Liaoning Province (grant no.
2015020200).
5
6
7
99
98
96
95
95
97
3.7
4.3
3.3
Notes and references
1
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In summary, we have unveiled that H2 production was
dramatically boosted by integrating with nonoxygen coupling
of diverse amines to imines over noble-metal free Ni/CdS
photocatalyst under visible light irradiation. Thanks to the
integrating effect between the two reactions, the catalyst
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DOI: 10.1039/C8CY01326H
Enhanced Visible light photocatalytic nonoxygen coupling of amines
to imines integrated with hydrogen production over Ni/CdS
Nanoparticles†
Weiwei Yu,a Di Zhang,a Xinwen Guo,a Chunshan Song,a,b Zhongkui Zhao,a,*
a State Key Laboratory of Fine Chemicals, PSU-DUT Joint Center for Energy Research,
School of Chemical Engineering, Dalian University of Technology, Dalian 116024, China.
E-mail: zkzhao@dlut.edu.cn
b EMS Energy Institute, PSU-DUT Joint Center for Energy Research and Department of
Energy & Mineral Engineering, Pennsylvania State University, University Park,
Pennsylvania 16802, United States
Nonoxygen coupling of amines to imines smoothly takes place initiated by hydrogen
evolution over Ni/CdS nanoparticles with visible light. Thanks to the integrating effect
between the nonoxygen coupling of benzylamine and the solar-driven reduction of aqueous
protons, the outstanding catalytic performance was achieved. The integrating strategy has
been extended to coupling of diverse amines to their corresponding imines.