Photocatalytic Dehydrogenation of Formic Acid on CdS Nanorods through Ni and Co Redox Mediation under Mild Conditions

Article abstract of DOI:10.1002/cssc.201800583

Selective release of hydrogen from formic acid (FA) is deemed feasible to solve issues associated with the production and storage of hydrogen. Here, we present a new efficient photocatalytic system consisting of CdS nanorods (NRs), Ni, and Co to liberate hydrogen from FA. The optimized noble-metal-free catalytic system employs Ni/Co as a redox mediator to relay electrons and holes from CdS NRs to the Ni and Co, respectively, which also deters the oxidation of CdS NRs. As a result, a high hydrogen production activity of 32.6 mmol h^?1 g^?1 from the decomposition of FA was noted. Furthermore, the photocatalytic system exhibits sustained H₂ production rate for 12 h with sequential turnover numbers surpassing 4×10³, 3×10³, and 2×10³ for Co–Ni/CdS NRs, Ni/CdS NRs, and CoCl₂/CdS NRs, respectively.

Full text of DOI:10.1002/cssc.201800583

Accepted Article
Title: Photocatalytic dehydrogenation of formic acid on CdS nanorods
through Ni and Co redox mediation under mild conditions
Authors: Muhammad Abdullah Khan, Zia-ur- Rehman, Jamal Abdul
Nasir, Muhammad Hafeez, Muhammad Arshad, Naveed Zafar
Ali, Ivo F Teixieira, and Ian McPherson
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ChemSusChem
10.1002/cssc.201800583
FULL PAPER
Photocatalytic dehydrogenation of formic acid on CdS nanorods
through Ni and Co redox mediation under mild conditions
[
a]
[b]
[c]
[c]
[d]
Jamal Abdul Nasir, Muhammad Hafeez, Muhammad Arshad, Naveed Zafar Ali, Ivo F. Teixeira,
[
d]
[a]
[e]
Ian McPherson Zia-ur-Rehman,* M. Abdullah Khan*
Abstract: Selective release of hydrogen from formic acid (FA) is
deemed feasible to solve issues associated with the release and
storage of hydrogen. Here, we present a new efficient photocatalytic
system consisting of CdS nanorods (NR), Ni, and Co to liberate
hydrogen from formic acid. The optimised noble metal free catalytic
system employs Ni/Co as a redox mediator to relay electrons and
holes from CdS-NR to the Ni and Co respectively, which also deters
the oxidation of CdS-NR. As a result, a high hydrogen production
HCOOH → CO + H
2
O
: ΔG = − 28.5 kJ mol−1
: ΔG = − 48.8 kJ mol−1
(1)
(2)
HCOOH → CO
2
+ H
2
Although the preferred dehydrogenation pathway, which yields H2
and CO ,is thermodynamically favoured, the competitive pathway
2
of dehydration that produces H Oand toxic CO also occurs. Since
a small amount of CO in H makes feed gas unsuitable for usage
in fuel cells, where it can poison the precious-metal H oxidation
catalyst (10 ppm for PEM fuel cells),[10] therefore a suitable
catalytic system that enables selective H production from FA is
necessary.
Most of the catalytic dehydrogenations of FA in homogeneous
reactions at ambient temperature, developed thus far, rely on
noble metal based organometallic complexes.[11] The notable
exceptions are the examples of iron catalyst systems capable of
2
2
2
-
1
-1
activity of 32.6 mmolh g from the decomposition of FA was noted.
Furthermore, the photocatalytic system exhibit sustained
production rate for 12 hours with sequential turnover numbers
H
2
2
3
3
3
surpassing 4×10 , 3×10 and 2×10 for Co-Ni/CdS-NR, Ni-CdS-NR
and CoCl /CdS-NR respectively.
2
dehydrogenating FA-to-H
activities comparable to the noble metal catalysts.
2
in acidic media exhibiting catalytic
Introduction
[12–16]
In addition,
the catalytic activity and selectivity are enhanced employing
Facile production of hydrogen at room temperature is an
important process due to its potential use as a clean fuel.[1] Apart
from process efficiency, a key challenge to the use of hydrogen in
mobile applications (i.e., fuel cells) is its safe storage and
additional base or/and additives.[17–20] Despite the substantial
progress, the inherent separation workup and recycling issues of
homogeneous catalytic systems, harsh operating conditions and
selectivity, and the requirement of additives may stymie their
practical realisation in device fabrication.[21–23] Similarly, host of
transport.[1–3] In this regard formic acid (FA, 4.4 wt% H
), readily
2
available from biomass through fermentation and pyrolysis, holds
significant promise as both a hydrogen supply and storage
noble metals based heterogeneous catalytic systems, with a
range of modifications, employed for low temperature release of
medium. The decomposition of FA produces gaseous H
2
with CO
back to FA
2
from FA were also found effective.[24–27] Apart from the
H
2
the only by-product.[4–6] With the hydrogenation of CO
2
sensitivity of these noble metals based catalyst to CO poisoning,
their prohibitive cost and low abundance limit their upscaling and
practical usage. Therefore, cost effective and stable catalytic
systems for efficient dehydrogenation of FA are still needed.
One exciting and sustainable way to drive the low temperature
splitting of FA is to harvest visible light on semiconductor surfaces.
The generated excitons (positive holes and electrons) can provide
necessary energy to activate organic molecules for their
conversion to products (FA do not absorb visible light). In spite of
the recent advances in heterogeneous/homogeneous catalysis
for the release of hydrogen from FA, examples of photocatalysis
are scarce and show substantially lower activities.[13,27–35] Only
recently, CdS has been identified as a potential candidate
now feasible under mild homogeneous conditions,[3,7–9]
complete fuel cycle can be imagined.
a
The chemical decomposition of FA proceeds via two distinct
reaction pathways, dehydration (1) and dehydrogenation (2).
[
a]
Jamal Abdul Nasir, Dr. Zia-ur-Rehman
Department of Chemistry, Quaid-i-Azam University, Islamabad
45320, Pakistan
E-mail: zrehman@qau.edu.pk
[b]
[c]
[d]
[e]
Dr. Muhammad Hafeez
Department of Chemistry, University of Azad Jammu and Kashmir,
Muzaffarabad, AJK Pakistan
Muhammad Arshad, Dr. Naveed Zafar Ali
Nanoscience and Technology Division, National Center for Physics,
Quaid-i-Azam University, Islamabad 45320, Pakistan
Dr. Ivo F. Teixeira, Dr. Ian McPherson
Inorganic Chemistry Laboratory, Department of Chemistry,
University of Oxford, Oxford, United Kingdom
* Dr. M. Abdullah Khan
2
material for photodecomposition of FA-to-H due to its low cost,
suitable valence and conduction band positions, and high visible
light activity.[30,35] However, the problem of fast recombination of
photo-generated charge carriers and its low tolerance to
+
2+
photooxidation i.e., CdS + 2 h → Cd + S hampers its effective
Renewable Energy Advancement Laboratory (REAL), Department
of Environmental Sciences, Quaid-i-Azam University, Islamabad
use. Efforts have been made to improve the photocatalytic
4
5320, Pakistan
efficiency of CdS-based photocatalysts by controlling their
E-mail: makhan@qau.edu.pk
[30,36]
morphology,
depositing
CdS
nanoparticles
on
[38–41]
polymers/membranes,[ and constructing heterojunctions,
37]
Supporting information for this article is given via a link at the end of
the document.
however, stability enhancement has received considerably less
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ChemSusChem
10.1002/cssc.201800583
FULL PAPER
attention. In a recent report Reisner et al. used capping agent-
S5a). For Cd 3d spectrum the binding energies agree well with
the values reported for the divalent cadmium in pure metal
sulphides (Figure S5b). The positions of S 2p1/2 and S 2p3/2 high
resolution XPS signals for the CdS sample are around 163.0 and
161.8 eV, respectively which are also consistent with literature
(Figure S5c). Further, Ni 2p core level peaks visible at 853.7 eV
stabilised CdS-quantum dots (QD) with a CoCl
2
co-catalyst for
the controlled decomposition of FA.[30] They observed impressive
-1 -1
2 2
catalytic FA-to-H activity (116 mmolH gcat h ) of CdS-QD/Co.
Taking these studies into account, herein, we report an efficient,
stable, noble metal-free photocatalytic system based on Ni
deposited on CdS nanorods (NR). Using CoCl
2
as a co-catalyst in
and 871.4 eV, attributed to NiO or Ni(OH)
of Ni onto the NRs surface (Figure S6d). Peaks around 861.0 eV
and 878 eV related to shakeup satellite features of NiO or Ni(OH)
are also present. Furthermore, EDX measurements confirm the
stoichiometric composition (%Cd 43.80; %S 56.20) and the
formation of pure CdS-NR with no other elemental impurity and
oxygen content within the limits (0.1%) of the technique (Figure
S7).
2
, indicate the presence
the reaction media we observe selective production of hydrogen
from FA under visible light irradiation at room temperature, with
no CO contamination. The CdS-NR catalyst is synthesised,
without the need for any additional stabilisation by surfactants, or
organic capping agents, through controlled thermolysis of
Cadmium(II) bis(dibutylcarbamodithioate) in ethylenediamine.
Then, by exploiting the redox potentials of Ni and Co relative to
the CdS-NR band-edge positions, electrons and holes are readily
2
2
shuttled from the CdS-NR to the Ni and CoCl , respectively. This
strategy impedes the oxidation of the CdS-NR, and imparts high
stability and enhanced photocatalytic activity over bare CdS-NR
2
or Ni deposited CdS-NR in the absence of CoCl .
Results and Discussion
The x-ray diffraction pattern of as prepared CdS-NR can be
refined primarily using the hexagonal wurtzite structure having
P63mc symmetry with lattice parameters a=b ~ 4.104(2) Å and c
~
6.668(4) Å (Figure 1a). A peak broadening of (002), (110), and
(
112) diffraction planes is also evident. Furthermore, relatively
intense narrower peak indicates that the (002) direction has a
longer crystal lattice than other crystal directions, consistent with
[
42]
nanorods growth along the c-axis.
In the case of the Ni-
deposited CdS sample, nanocrystals do not show any obvious Ni
peaks in the XRD pattern (Figure S3), due to its low loading (≤
2%). A representative high-resolution TEM (HRTEM) image
(
Figure 1b) of CdS-NR show high crystallinity with diameter ca. 7
nm and length ca. 80 nm. This is anticipated given the fact that
thermolysis of cadmium(II) bis(dibutylcarbamodithioate) directs
the extended growth of a stacked rods with sharp edges indicative
of crystalline structures.[42] The HRTEM analysis of many
randomly selected CdS-NR also showed directional orientation of
lattice fringes perpendicular to the rod axis (Figure 1c). Selected
area electron diffraction (SAED, Figure 1d) gave a clear diffraction
pattern and the lattice distances measured for the CdS-NR
amount to 0.37 nm and 0.667 nm, which correspond well with
lattice distances of the (100) and (001) planes, respectively, of
bulk CdS (JCPDS No: 01-080-0006) and is commensurate with
the lattice distances retrieved from Rietveld refinement of the
diffraction pattern. HRTEM of photo-deposited Ni sample shows
the presence of 2-4nm size particles at CdS-NRs surface (Figure
S4). Further, FTIR spectroscopic study of pristine NRs revealed
Figure 1. XRD patterns of (a) CdS-NR (JCPDS No. 01-080-0006). The TEM,
(b) HRTEM (c) images of CdS-NR with lattice fringes distances and SAED (d)
show high crystallinity of CdS-NR.
-1
For the production of H
2
from FA, CdS-NR 1.04 mM (150 μgmL ,
1
00 μL) were dispersed in sodium formate 3M in FA under visible
-2
light illumination (100 mWcm , λ > 420 nm, 25 °C) (Figure S8,
Table S1-S4). As seen from Figure 2, without any modification,
-1 -1
initial H
2
production rates of 1.34 mmolh g for CdS-NR were
observed. When photodeposited Ni-CdS-NR were used rates
-
1 -1
reached 22.8 mmolh g . The addition of CoCl
catalytic system ensued a marked increase to 32.6 mmolh g . It
was noted when CdS-NR and CoCl were present together the
catalytic system exhibited improved activity (14.2 mmol h g ) in
comparison to CdS-NR but lower than Ni/CoCl CdS-NR in
combination. Furthermore, analysis of the evolved gas by gas
chromatography reveals that the CO /H ratio remained below the
theoretical 1:1 stoichiometry, likely due to higher solubility of CO
2 2
.6H O to the
-1 -1
-1
-1
an attachment of C-H (2918 cm , 2854 cm ), N-H, (3284, 1591
-1
-1
2
cm ) and N-C=S (1461, 1008, 716 cm ) moieties at the CdS-NRs
surface (Figure S5). These species, generated during thermolysis
of Cd-complex, may provide the necessary thermodynamic
stabilisation required by the high surface energies of NRs facets.
The XPS survey spectrum of the Ni/CdS-NR sample also confirms
the elemental coexistence of Ni, Cd, and S as expected (Figure
-1 -1
2
2
2
2
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ChemSusChem
10.1002/cssc.201800583
FULL PAPER
over H
trap containing 10M NaOH was employed to capture CO
2
in FA, as observed previously.[30] In addition, when a base
from
In order to evaluate the stability of the photocatalytic system, long-
2
term continuous evolution of H
2
from FA using Ni-CoCl
2
/CdS-NR
the gas mixture from the catalytic reaction, a nearly 50% reduction
in volume was noted. The GC analysis of gas treated with the
base trap also confirmed the absence of CO and thus excluded
the possibility of competing dehydration reaction over CoNi/CdS-
NR during the course of the reaction. This clearly demonstrates
the usefulness of our photocatalytic system for selective release
was performed. After 18h, 285 mmol of H
2
had been evolved
(Figure 3b). This value is significant as the system does not
require any organic polymers or capping agents for stabilisation,
or expensive noble-metal catalysts or ultraviolet light for activation.
The turnover number (TON) based on the amount of metallic Ni
and Co was estimated to be ca. 1.06 ×105 after 18 h, clearly
showing the high efficiency of the photocatalytic system. In
2
of H from FA free of fuel-cell inhibitors.
2
general, typical thermal H release pathways slow rapidly with the
decrease in solution pH, due to the release of proton in medium
(a dependence of catalyst activity on pH, the pH > 3.8
corresponding to the pKa of FA favours the FA decomposition)[23]
however in this case no such deactivation was recorded over a
prolonged period. When, particle aggregation was monitored in
situ by UV/Vis spectroscopy, a 11 nm red-shift was noted for CdS-
250
200
150
100
CdS-NR
Co/CdS-NR
Ni/CdS-NR
Co-Ni/CdS-NR
2
NR (Figure S11). However, in the case of Ni and CoCl loaded
CdS-NR sample no change was observed during the course of
the reaction. In addition, a blue shift due to the etching effect of
the acidic medium that may result in a decrease in size of the
particles was also absent, while XRD of the Ni/CdS-NR after the
reaction show no marked change in diffraction pattern.
5
0
0
0
2
4
6
8
10
12
2-
Furthermore, the susceptibility of sulfide ions (S ) to oxidation by
Time/h
photogenerated holes, which is accompanied by the leaching of
Cd2+ ions into the solution, was estimated by complexometric
titration experiments. No change in colour of the solution infers
the absence of Cd (II) ions in the reaction medium to a detection
Figure 2. Visible light driven FA decomposition to hydrogen over CdS-
-
2
−1
NR. λ>420 nm, 100 mWcm , 1.04 mM CdS (150 μgmL ), 1.25 mM NiCl
.75 mM CoCl .6H O and 3.0 M NaHCO in 2.0 mL FA.
2 2
·6H O,
0
2
2
2
-1
limit of 0.003 ppm or ≤ 3 µg L . These results indicate that the
photocatalyst remains stable and intact in redox conditions
We performed controlled experiments using visible light
irradiation, λ ≥ 420 nm, at room temperature and pressure. For
reference, maintaining the same conditions, in the absence of
light or photocatalyst, no product formation was detected. The
8
7
6
5
4
3
2
1
0
300
250
285
Ni/CdS-NR
Co/CdS-NR
265
a
b
2
42
212
addition of NiCl
CdS-NR also did not show any activity towards FA-to-H
2
or CoCl
2
to the reaction mixture in absence of
. The
2
00
185
2
150
100
dependence of catalytic reaction on light was confirmed by
varying the light intensity (Figure S9, Table S5). A slight increase
in activity with increased light intensity was recorded. For λ ≥ 420
nm the maximum external quantum yield was 15.57ꢀ% using 1mM
aqueous CdS-NR solution (Table S6). When the full solar
spectrum without the cut off filter was used a 30% increase in the
catalytic activity was observed. This observation infers that the
reaction is facilitated by visible light and ultraviolet light is not
necessary for photocatalytic reaction. Although the initial FA
concentration seems to have no effect, the variation in
concentration of sodium formate (0.5M-3.0M) resulted in an
8
8
5
0
0
3
2
0
.0 0.5 1.0 1.5 2.0 2.5
0
3
6
9
12 15 18
c/mM
time/h
Figure 3. Effects of co-catalysts on the photocatalytic decomposition of FA by
varying loading of CoCl and NiCl , (b) Long-term photocatalytic H generation
from FA/SF solution using Ni-Co/CdS-NR.
2
2
2
2
increase in H generation rates from 0.177±0.04 to 0.845 ±0.09
-1
-1
To establish the reactive species involved in this new
photocatalytic system, a series of experiments was performed. A
decrease in intensity of the steady state photoluminescence (PL)
and the change in time-decay curve of PL, measured from the
characteristic emission peak of each sample (Figure 4a, b),
indicate efficient charge separation and transfer, and suppression
of the recombination rate in the optimised photocatalytic reaction
system. For all the samples a broad PL emission peak around 510
nm–660 nm is seen. This emission is a likely outcome of
recombination of shallow trapped electrons present within the
defect states of CdS-NR with holes in the valence band or shallow
mmolh g (Figure S10, Table S7). This may be due to a buffering
+
effect in the vicinity of CdS, after FA is oxidised to CO
2
+ 2H . This
may also promote the adsorption of HCOO, which is often how
FA interacts with metal/metal oxides.[31,43] Furthermore, it was
found that the gas production from 1.0 M sodium formate alone
was too little to be measured. Figure 3a, shows the change in
amount of H
was found that optimal concentrations of 1.2 mM of NiCl
mM CoCl lead to the substantial increase in activity for FA photo
assisted dehydrogenation over CdS-NR (Table S8-9).
2
produced by varying the loadings of Ni and Co. It
2
and 0.75
2
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ChemSusChem
10.1002/cssc.201800583
FULL PAPER
holes trap states near the valence band. Besides, as the PL data
were obtained from the respective reaction mixtures, in the case
of Co/CdS-NR only a slight change of PL was noted (Figure 4a).
Whereas the TRPL signal of Co/CdS-NR, in particular, remained
almost unaltered. Although the hole transfer to cobalt is
energetically favourable (Figure 4c), the XPS analysis of the
sample confirmed the absence of deposited Co on CdS-NR
surface. Therefore, presumably due to the transitory nature of
cobalt coordination or interaction with the CdS-NR combined with
competing quenching of holes between FA and Co (relative
concentration of FA is very high than that of Co concentration) is
the reason for unchanged PL signal. Figure 3c, portrays an
overview of the redox potentials of FA with respect to the positions
of Co-Ni/CdS-NR band edges.[44,45] It can be seen that all the
component are suitably positioned where differences in redox
potentials, in theory, may potentially support catalytic reaction to
proceed. Although Ni 2p XPS profile (Figure 4d) with binding
to the photocatalyst system. Results show only a small change in
the amount of H
2
produced. It suggests that in photocatalytic
decomposition of FA H
2
evolution is likely limiting the reaction rate.
To exclude the possibility of Ni2 (NiO) as an activity species in
photocatalytic process, Ni-CdS-NR sample was collected and
exposed to the air. When recharged, keeping all others conditions
+
-1 -1
unaltered, a clear decrease in activity was noted (2 mmolh g ).
To determine the role of CoCl , active catalyst was separated by
centrifugation after a reaction of one hour. The obtained catalyst
was then recharged, this time without adding CoCl , and it was
2
2
observed that the activity was comparable to CdS-NR. This
suggests that Co is not deposited on CdS-NR and remains in the
reaction medium and the observed improved activity is
presumably through the transitory contact with the CdS-NR
forming bound Co-hole-formate species. The XPS analysis of the
sample also confirmed the absence of deposited Co on CdS-NR
surface. The improved catalysis is, therefore, due to the
cooperative redox mediation of Ni0 and Co3+ where both the
reductive and oxidative half reactions are enhanced.
+
2
energy maxima at 553 eV shows the presence of both Ni and
0
Ni species at the photocatalyst surface. The substantial increase
in FA-to-H
XPS results infer the reduction of Ni to Ni (ECB of CdS = -0.45
V; E Ni /Ni = -0.25 V) in reaction media by photogenerated
2
activity for Ni/CdS-NR, quenching of PL signal and the
To highlight the significance of this noble metal free Co-Ni/CdS-
NR based photocatalytic system, a comparison with selected
recent and important catalysts developments for FA-to-H are
2
2+
0
0
2+
0
electrons at the conduction band of CdS-NR. This band offset
shown in Table 1.
0
between CdS-NR and Ni provides a conduit for electrons to pass
from CdS to Ni . The observed Ni2+ peak in the sample is due to
exposure of the sample to air while collecting and drying, prior to
the measurements.
0
Table 1. Comparison of selected catalysts for the photocatalytic
conversion of FA-to-H .
2
Light /
Activity[a]
EQY /%
Lifetime
Photocatalyst
Ref.
-
1 -1
λ (nm)
mmolh g
420 nm
h
2
2
1
1
50
00
50
00
1.0
0.8
[
46]
-
-
-
-
CdS-NR
CdS-NR
AuPd/TiO
2
Solar irr.
17.7
15.6
˃ 10
a
b
Co/CdS-NR
Ni/CdS-NR
Co-Ni/CdS-NR
Co/CdS-NR
Ni/CdS-NR
Co-Ni/CdS-NR
[Fe
3
(CO)12]+P
tpy
[13]
[28]
Solar irr.
2.7
n/a
n/a
˃ 24
˃ 60
[b]
Ph
3
0
0
0
0
.6
.4
.2
.0
2
Cu O
˃ 420
0.155
[35]
[30]
[47]
Pd/C
QD-
3
N
4
≥ 400
53.4
n/a
˃ 6
5
0
0
21.2 ±
˃
420
116 ± 14
˃ 168
MPA/CoCl
2
2.7
CdS-NR
˃ 420
˃ 420
˃ 420
˃ 420
0.22
4.46
1.22
4.26
n/a
13.9
21.4
n/a
n/a
˃ 50
˃ 30
˃ 3
4
00
500
600
(nm)
700
800
0
5
10
t / (ns)
15
20
25
[
[
[
47]
38]
48]
Pt-CdS-NR
Pt-CdS QD
Pt-CdS-TNT

1
0
.34 ±
.13
This
work
This
work
This
work
This
work
CdS/NR
≥ 420
≥ 420
≥ 420
n/a
n/a
n/a
˃ 12
˃ 12
˃ 12
Co/CdS-NR
Ni/CdS-NR
14.2 ± 2
22.8 ± 2
Co-Ni/CdS-NR
≥ 420
32.6 ± 5
15.57
˃ 18
[
a] To compare, published data was converted into gravimetric activity,
considering molar amount of hydrogen generated per hour of illumination and
per gram of the photocatalyst; [b] tpy=2,2’:6’,2”-terpyridine; n/a
= not
available.
Figure 4. (a) Steady state and (b) Time resolved photoluminescence decay
curve of CdS-NR based photocatalytic systems. (c) The band edge positions of
CdS-NR and the relative positions of redox potionals of Ni2+/Ni , Co /Co
0
2+
3+
V
Conclusions
NHE and FA and (d) Ni 2p XPS spectra of the CdS-NR.
In conclusion, we have demonstrated an efficient visible light
driven hydrogen production from FA using an inexpensive
photocatalyst system under mild conditions. The redox mediation
of Ni and Co leads to the better mobility of photogenerated
electron and holes away from the photocatalyst surface, improved
Furthermore, experiments were performed at a constant donor
concentration and an irradiation time of 6 h, to determine the
effect of different types of electron donors having differences in
energy positions (i.e., methanol, ethanol and formic acid) relative
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ChemSusChem
10.1002/cssc.201800583
FULL PAPER
catalytic efficiency, and tolerance to the photooxidation. We
envisage that this example of cooperative photocatalysis will stir
new interest for the employment of other heterogeneous catalysts
in a related manner.
PicoQuant GmbH). The samples were excited using a 405 nm laser pulse
at a frequency of 32 MHz. XPS analysis was performed using a micro-
focused monochromatic Al K-Alpha X-ray source having a spot size of 700-
micron. The source was operated at 15 KeV at constant analyser energy
(CAE) 100 eV for survey scans and 20 eV for high resolutions scans. The
charge neutralisation was applied using a combined low energy / ion flood
source to avoid the charging effects. The data acquisition was performed
with Matrix software and data analysis was performed with Igor pro along
with XPS fit procedures. The curve fitting of spectra was done using
Gaussian-Lorentsian line shape after performing the background
corrections. For photocatalysis Xenon lamp (750 W, 45 A) equipped with
Experimental Section
Materials. All chemicals were of high purity grade and used without further
purification. Formic acid (LR grade >90%) was purchased from Sigma
-
2
an average light intensity (100 mWcm ) with a cut off filter (λ > 420) was
2
used as an illumination source. Detailed analyses for H , CO, and CO ,
Aldrich. Sodium formate was synthesised by reacting Na
acid in 1:2 molar ratio. 3.0 M sodium formate solutions, 0.75 mM
CoCl .6H O, and 1.25 mM NiCl .6H O solutions were prepared in formic
2 3
CO with Formic
2
were performed on Shimadzu GC2014 gas chromatograph (GC) equipped
with a thermal conductivity detector (TCD) and flame ionisation detector
2
2
2
2
acid to give a total volume of 20 mL. All solvents were of analytical grade,
and distilled water was used in all photocatalytic experiments.
2
(FID)-Methanator (detection limit: 40 ppm for CO). H generation was
measured relative to its standard peak. The H formation rate was
2
calculated as the molar amount of hydrogen generated per hour of
illumination rate and per gram of Cd-NRs.
Preparation of CdS-NR. Sodium dibutylcarbamodithioate was prepared
according to a reported method. [49] Stoichiometric amount of NaOH (1.18
g, 0.029 mol) was added to react with dibutylamine, (5 mL, 0.029 mol) in
methanol (30 mL), followed by drop wise addition of equivalent moles of
methanolic solution of CS
2
(1.75 mL, 0.029 mol) at 0°C. Cd(NO
3 2 2
) .4H O
Authors Contributions
(0.616g, 0.002 mol) and sodium dibutyldithiocarbamate (Figure S1) (1g,
0
.004 mol) were added in methanol in 2:1. The immediately formed
Jamal Abdul Nasir carried out material synthesis testing and
analysis. M Hafeez made contributions to the synthesis. M.
Arshad did XPS, N. Z. Ali did XRD refining. I. F. Teixeira and I. M.
Pherson contributed to the characterisations and analysis. M.
Abdullah Khan and Zia-ur-Rehman initiated, supervised and
coordinated the research. All authors discussed the results and
commented on the manuscript.
precipitate
of the synthesised complex, cadmium(II)
bis(dibutylcarbamodithioate), was filtered off, washed and dried (Figure
S2). Monodisperse CdS nanorods without any capping agent were
prepared according to literature procedure (Scheme S1).[42]. Cadmium(II)
bis(dibutylcarbamodithioate) served as a single source precursor and
ethylenediamine as a decomposing solvent. The complex was thermalised
in two neck flask using ethylenediamine (10 mL) by a gradual increase in
temperature to the decomposition point (118 °C) with constant stirring.
Yellow coloured CdS-NR thus obtained were then dispersed in methanol,
filtered off, repeatedly washed with methanol, and dried. For Ni
Keywords: CdS nanorods • Formic acid dehydrogenation •
redox mediation • photocatalytic hydrogen production •
photodeposition and Co loading onto CdS-NR prior to photocatalytic H
generation, NiCl and CoCl (0.05 to 2.5 mM) were suspended in aqueous
2
2
2
dispersed solution of CdS-NR. In the case of Ni, under 30 min of visible
light illumination a colour change of reaction mixture from yellow to a light
green was observed, while, no change in colour for Co, was noticed.
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FULL PAPER
Table of Contents
FULL PAPER
[
a]
Jamal Abdul Nasir, Muhammad
Hafeez,[ Muhammad Arshad, Naveed
Zafar Ali,[c] Ivo F. Teixeira, Ian
McPherson[d] Zia-ur-Rehman,* M.
Abdullah Khan*[e]
b]
[c]
Efficient
visible
light
diversion
[d]
dehydrogenation of formic acid over
CdS nanorods through cooperative
redox mediation of Ni and Co, is
achieved at room temperature.
[a]
Page No. – Page No.
Photocatalytic dehydrogenation of
formic acid on CdS nanorods through
Ni and Co redox mediation under mild
conditions
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