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C: Surfaces, Interfaces, Porous Materials, and Catalysis
Synthesis of ZnIn2S4/CdS Heterostructure Based on Electrostatic Interaction Mechanism for the Indirect Photoelectrochemical Detection of Dopamine Hao Wang, Huili Ye, Bihong Zhang, Faqiong Zhao, and Baizhao Zeng J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05287 • Publication Date (Web): 10 Aug 2018 Downloaded from http://pubs.acs.org on August 13, 2018
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The Journal of Physical Chemistry
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Synthesis of ZnIn2S4/CdS Heterostructure Based on Electrostatic
2
Interaction Mechanism for the Indirect Photoelectrochemical
3
Detection of Dopamine
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Hao Wang1, Huili Ye1, Bihong Zhang, Faqiong Zhao, Baizhao Zeng*
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Key Laboratory of Analytical Chemistry for Biology and Medicine (Ministry of
6
Education), College of Chemistry and Molecular Sciences, Wuhan University, Wuhan
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430072, Hubei Province, P. R. China
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E-mail address:
[email protected] (BZ Zeng)
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Abstract
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A ZnIn2S4/CdS photocatalyst was synthesized based on an electrostatic interaction
12
mechanism and used to construct a photoelectrochemical (PEC) sensor for the highly
13
sensitive and selective detection of dopamine (DA). As CdS and ZnIn2S4 possessed
14
overlapped band potentials they could form heterojunction, which was favorable to
15
charge separation and photoelectrochemical conversion. Thus, the ZnIn2S4/CdS
16
composite showed better photoelectrochemical properties and higher photocatalytic
17
activity than ZnIn2S4 and CdS. When it was used for DA sensing in weak alkaline
18
solution, DA turned to polydopamine and acted as effective electron acceptor to make
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the anodic photocurrent decrease. Owing to adopting this detection strategy the
20
interference of coexistent reductive species (i.e. electron donor) was avoided
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effectively. Under the optimized conditions, the photocurrent change was linear to
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DA concentration in the range from 0.3 to 300 µM, and the detection limit was 0.1 1 ACS Paragon Plus Environment
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µM. The ZnIn2S4/CdS/ITO sensor was applied for the indirect detection of DA in
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urine samples and it presented good performance.
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1. Introduction
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As a typical II-III2-VI4 semiconductor, ternary sulfide photocatalyst ZnIn2S4 with
27
various morphologies (i.e. nanowires, flower-like microspheres and nanotubes) has
28
been synthesized by using different methods.1 The photocatalyst is eco-friend and can
29
be irradiated by visible-light, while most metal-oxide photocatalysts, like TiO2 and
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ZnO, are effective only under ultraviolet (UV) light.2 In addition, ZnIn2S4 is quite
31
stable in comparison with other metal chalcogenide semiconductors.3 For example,
32
CdS is unstable under light irradiation because of the strong oxidation capacity of
33
photogenerated
34
ZnIn2S4-based photocatalyst is applied in many fields, including charge storage,5
35
thermoelectricity6 and photocatalysis.7 However, the efficiency of pure ZnIn2S4 is far
36
from satisfaction due to the high recombination rate of photogenerated electron-hole
37
pairs.
holes,
which
is
known
as
photocorrosion.4
Accordingly,
38
To resolve this issue, a number of ZnIn2S4 based hybrid semiconductor
39
heterojunctions have been synthesized with expectation to improve its photocatalytic
40
performance. For example, Chai’s group fabricated a MWCNTs/ZnIn2S4 composite
41
for hydrogen production under visible-light irradiation.8 Peng et al. developed
42
ZnIn2S4-PVDF-poly-(MMA-co-MAA) composites for the degradation of methyl
43
orange with high photocatalytic activity.9 Liu and co-workers fabricated 2D ZnIn2S4
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nanosheet/1D TiO2 nanorod heterostructure arrays for the photoelectrochemical (PEC)
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splitting of water.10 We notice that ZnIn2S4 and CdS have overlapped band potentials,
46
and the ZnIn2S4/CdS heterostructure composite may present better PEC response 2 ACS Paragon Plus Environment
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under irradiation of visible light and higher charge separation efficiency than pure
48
ZnIn2S4 and CdS. However, up to now, ZnIn2S4 and its composites have not been
49
applied for the preparation of PEC sensors.
50
PEC sensor is a promising electroanalytical technique for low cost, rapid analysis,
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high sensitivity and simple instrumentation, it has attracted much attention of
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chemists and biologists.11 In the past few years, a number of PEC sensors were
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constructed for the detection of DA, and most of them were based on the traditional
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hole oxidation mechanism.12-14 Namely, DA acted as an effective electron donor for
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scavenging the photogenerated holes on the surface of semiconductor and inhibited
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the recombination of electron-hole pairs.15 However, little attention was paid on the
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construction of PEC sensors based on the interaction between electron acceptors in
58
solution and electrons from the photo-excited semiconductor, especially in PEC
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sensors based on n-type semiconductors.16 Previously, our group found that the
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cathodic photocurrent of Z-scheme BiOI-CdS photocatalyst significantly increased in
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an air-saturated electrolyte (O2 acted as an electron acceptor and facilitated the spatial
62
separation of charge carriers).17 What's more interesting, Wang et al developed an
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original strategy for DA detection, based on the decreased anodic photocurrent.18
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They found that the anodic photocurrent of CdS QDs decreased in the presence of DA,
65
due to the polydopamine (PDA), produced by the oxidation of DA, acted as electron
66
acceptor for the photoexcited CdS QDs, inhibiting the electron transfer from CdS
67
toward to the ITO electrode and leading to the decrease of photocurrent. However, the
68
photoelectrode material CdS QDs suffered from the high recombination rate of
69
photogenerated charge carriers and photocorrosion.19 Therefore, it is still necessary to
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improve the stability of photoactive materials and the separation efficiency of charge
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carriers. 3 ACS Paragon Plus Environment
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Motivated by these facts, a ZnIn2S4/CdS heterostructure composite was prepared
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based on an electrostatic interaction mechanism. The composite showed better
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photoelectrochemical property and higher photocatalytic activity than pure CdS and
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ZnIn2S4. The high photocatalytic activity resulted from the formation of
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heterogeneous junction, which accelerated the transfer of charge carriers at interface
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and inhibited their recombination effectively. DA easily turned to PDA in alkaline
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solution, and PDA could act as effective electron acceptor. Hence, it could inhibit the
79
transfer of photogenerated electrons to the ITO electrode, and made the anodic
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photocurrent significantly decrease. Thus, the anodic photocurrent of the as-prepared
81
ZnIn2S4/CdS/ITO decreased with increasing DA concentration. Therefore, it could be
82
used for the sensitive and selective detection of DA.
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2. Experimental
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2.1 Chemicals and apparatus
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Zn(CH3COO)2·2H2O,
InCl3·4H2O,
thioacetamide
(TAA),
CdCl2·2.5H2O,
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Na2S·9H2O, triethanolamine (TEA) and DA were obtained from Aladdin Chemistry
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Co., Ltd. (Shanghai, China). Tris(hydroxymethyl)aminomethane, hydrochloric acid,
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NaOH, uric acid (UA), glucose (Glu), ascorbic acid (AA), glutathione (GSH),
89
L-cysteine (Cys) and other reagents of analytical grade were provided by Sinopharm
90
Chemical Reagent Co., Ltd. (Shanghai, China), used without any further purification.
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A
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tris(hydroxymethyl)aminomethane and hydrochloric acid.
10
mM
Tris-HCl buffer
solution
(pH=8.5)
was
prepared
by
using
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The zeta potential was measured with a NanoZS90 Laser Particle Size and Zeta
94
Potential Analyzer (Malvern, England). Scanning electron microscopy (SEM) images
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were recorded with a field emission SEM (ZEISS SIGMA, Germany). X-ray
96
photoelectron spectra (XPS) were obtained using an ESCALAB 250Xi spectrometer
97
(Thermo Fisher Scientific Inc., USA). X-ray diffraction (XRD) patterns were obtained
98
using a Bruker D8 diffractometer (Germany) with Cu Kα radiation, over 2θ range of
99
15-70° at a scanning rate of 6° min-1. UV-visible diffuse reflectance spectra (DRS) of
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the samples were recorded with a UV-visible spectrophotometer (UV-3600, Shimadzu,
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Japan), BaSO4 was used as reflectance standard. The photoluminescence (PL) spectra
102
were measured with a Hitachi F-4600 fluorescence spectrophotometer (Tokyo, Japan)
103
at an excitation wavelength of 340 nm.
104
PEC measurements were performed with a CHI 832C electrochemical workstation
105
(CH Instrument Co., Ltd, Shanghai, China). A PEC-10W Multifunctional LED Light
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Source System (Tianjin Brillante Technology Co., Ltd. China) was employed as the
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irradiation source; the distance was fixed at 10 cm between the light source and
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electrode surface. Photoelectrochemical tests were carried out at a constant potential
109
of 0 V (vs. Ag/AgCl). The supporting electrolyte was 10 mM Tris-HCl buffer solution.
110
All experiments were conducted at room temperature except mentioned other where.
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Electrochemical impedance spectroscopy (EIS) experiment was carried out on a CHI
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604D electrochemical workstation (Shanghai Chenhua Instrument Co. Ltd, China),
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the electrolyte was 0.1 M KCl containing 5.0 mM K3[Fe(CN)6]/K4[Fe(CN)6] (1:1),
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and the frequency range was from 100 kHz to 0.1 Hz at open circuit potential.
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2.2 Synthesis of lamellar ZnIn2S4
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The ZnIn2S4 was synthesized by a simple hydrothermal method.4 Briefly, 1 mmol
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Zn(CH3COO)2·2H2O and 2 mmol InCl3·4H2O were dissolved in 60 mL water, and
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then 6 mmol TAA was added into the solution. After stirring for 30 min, the mixture
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was transferred into a 100 mL Teflon-lined autoclave and was maintained at 160 ℃
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for 12 h. The product was collected by centrifugation and then washed for several
121
times with deionized water, ethanol, and dried at 60 ℃ for 12 h.
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2.3 Preparation of ZnIn2S4/CdS heterostructure
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The ZnIn2S4/CdS heterostructure was prepared according to an electrostatic
124
interaction mechanism as reported previously with a little modification.20 In brief,
125
0.0500 g ZnIn2S4 was dissolved in 30 mL water and 15 mL 0.10 M CdCl2 aqueous
126
solution was added drop-wisely under vigorous stirring. After stirring for 30 min, 45
127
mL 0.10 M Na2S aqueous solution was added slowly, stirred for another 30 min. The
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brown solid product, marked as ZnIn2S4/CdS, was washed for several times with
129
deionized water, ethanol, and dried at 60℃ in an oven overnight (Scheme 1). For
130
comparison, the volume of CdCl2 solution was changed (i.e. 5, 10, 20, 30 mL) and the
131
final products were labeled as ZnIn2S4/CdS-x (x= 1, 2, 4, 5), respectively. Pure CdS
132
was prepared using the same way but without ZnIn2S4.
133 134
Scheme 1. The synthesis of ZnIn2S4/CdS heterostructure by using an electrostatic interaction
135
mechanism.
136
2.4 Fabrication of photoelectrochemical sensor
137
Prior to modification, the ITO glass (1 cm × 2 cm) was cleaned by successive
138
sonication in NaOH solution (1 M), acetone, ethanolandpure water each for 20 min.
139
After being dried at 60 ℃ in an oven, 3M tape with a fixed area of 0.070 cm2 was
140
stuck on the ITO glass.21 Then, a 15 µL (1 mg mL-1) of aqueous dispersion of
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ZnIn2S4/CdS was dropped onto the ITO surface and dried at 60 ℃ to obtain
142
ZnIn2S4/CdS/ITO working electrode.
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3. Results and discussion
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3.1 Characterization of ZnIn2S4/CdS heterostructure
145
The obtained ZnIn2S4, CdS and ZnIn2S4/CdS heterostructure were characterized by
146
SEM and TEM (Figure 1). As can be seen, the ZnIn2S4 showed a lamellar structure
147
which was composed of two-dimensional nanosheets (Figure 1A and E), whereas CdS
148
displayed agglomerated-particles shape (Figure 1B and F). As to the ZnIn2S4/CdS,
149
CdS nanoparticles evenly distributed on the surface of ZnIn2S4 sheets (Figure 1C, D
150
and G). The zeta potential of ZnIn2S4 in water was -34.4 mV (Figure S1), indicating
151
that its surface carried negative charges.22 Thus Cd2+ was easily adsorbed by ZnIn2S4
152
and CdS nanoparticles tended to grow on the ZnIn2S4 sheets (Scheme 1).
153 154
Figure 1. SEM images of (A) ZnIn2S4, (B) CdS and (C) ZnIn2S4/CdS heterostructure; (D)
155
enlarged SEM image of ZnIn2S4/CdS heterostructure. TEM images of (E) ZnIn2S4, (F) CdS and
156
(G) ZnIn2S4/CdS heterostructure.
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Figure 2A displayed the XRD patterns of ZnIn2S4, CdS and ZnIn2S4/CdS
158
heterostructure. The major diffraction peaks of pure ZnIn2S4 could be indexed to a
159
hexagonal phase of ZnIn2S4 (ICDD-JCPDS card NO.72-0773) with (006), (102), (108)
160
and (110) crystal planes at 2θ of 21.2°, 27.6°, 39.8° and 47.1°, respectively.23 All the
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diffraction peaks of the prepared CdS matched well with that of cubic CdS phase
162
(JCPDS no. 65-2887), with scattering angles of 26.5°, 44.2° and 52.2°, corresponding
163
to crystal planes (111), (220) and (311), respectively.24 The diffraction peaks of
164
ZnIn2S4 and CdS could be found in composite materials, but their intensity was weak,
165
indicating that their crystallinity decreased due to the influence by each other. It
166
meant that ZnIn2S4/CdS was not a simple mixture of ZnIn2S4 and CdS, but formed
167
heterojunction.25,26 The XPS analysis of ZnIn2S4/CdS heterostructure was performed
168
to investigate the elemental composition and the surface chemical states (Figure 2B).
169
As a result, elements Zn, In, Cd, and S were observed clearly. The measured binding
170
energies corresponding to Cd 3d5/2 and Cd 3d3/2 were 405.5 and 411.6 eV (Figure 2C)
171
respectively, meaning Cd was present as divalent ion. The peaks centered at 160.8 and
172
162.3 eV could be assigned to S2- (Figure 2E).27 For the In 3d spectra (Figure 2D), the
173
binding energies around 444.9 and 452.6 eV could be assigned to In 3d5/2 and In 3d3/2,
174
respectively. In addition, the high-resolution Zn 2p spectra (Figure 2F) displayed
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characteristic peaks at 1021.2 and 1045.1 eV, corresponding to Zn 2p3/2 and Zn 2p1/2,
176
respectively.28
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Figure 2. (A) XRD patterns of pure ZnIn2S4, CdS and ZnIn2S4/CdS heterostructure. XPS patterns
179
of the ZnIn2S4/CdS heterostructure: typical XPS survey (B), Cd 3d (C), In 3d (D), S 2p (E), and
180
Zn 2p (F) spectra.
181
Figure 3A revealed the UV-vis DRS of the as prepared samples, and they showed
182
strong photoabsorption to UV-visible light. ZnIn2S4 displayed a wider absorption
183
edge than CdS. The color of the ZnIn2S4, CdS and ZnIn2S4/CdS powders was shown
184
in Figure S2. The absorption edge of the ZnIn2S4/CdS was between those of CdS and
185
ZnIn2S4. The band gap (Eg) of ZnIn2S4/CdS was also between those of pure ZnIn2S4
186
and CdS, indicating the formation of heterostructure.29 The band gap of crystalline
187
semiconductor could be calculated from the classic Tauc approach by using the
188
following equation:30
189
(αhν) = A(hν- Eg)n/2
(1)
190
Where α, h, ν, A and Eg represent the absorption coefficient, Planck constant, light
191
frequency, proportional constant and band gap energy, respectively. The value of n is
192
a characteristics number of the transition in a semiconductor (for direct transition, n=1,
193
and for indirect transition, n=4). As reported, for the ZnIn2S4 semiconductor n=431 9 ACS Paragon Plus Environment
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194
and for CdS n=132. Herein the Eg values of ZnIn2S4 and CdS are calculated as 2.08
195
and 2.20 eV (Figure 3B), respectively. The CB and VB potentials of ZnIn2S4 and CdS
196
were estimated according to the empirical equations:33
197
EVB = X-E0 + 0.5 Eg
(2)
198
ECB = EVB - Eg
(3)
199
Where X is the absolute electronegativity of the semiconductor (Table S1a), Eg is the
200
band gap of the semiconductor and E0 is the energy of free electrons on the hydrogen
201
scale (about 4.5 eV). The X values for ZnIn2S4 and CdS are 4.86 and 5.19 eV,
202
respectively. The calculated values of VB and CB for ZnIn2S4 and CdS are listed in
203
Table S1b. The VB edge of CdS (1.79 eV) is more positive than that of ZnIn2S4 (1.40
204
eV), while the CB edge of ZnIn2S4 (-0.68 eV) is more negative than that of CdS
205
(-0.41 eV). This indicates ZnIn2S4 and CdS semiconductors possess overlapped band
206
potentials (Figure 3C) and they can form an effective heterojunction.34 Generally
207
speaking, a heterojunction of different semiconductors with matched energy levels is
208
favorable to charge separation and photoelectrochemical conversion.
209
Electrochemical impedance spectroscopy (EIS) is widely applied to investigate the
210
electron-transfer efficiency.35 In this case, it was also used to characterize the
211
electrode change. Figure 3D presented an overview of the semicircular Nyquist plots
212
for the CdS/ITO and ZnIn2S4/CdS/ITO. The EIS of CdS/ITO showed big diameter,
213
reflecting the poor electrical conductivity of CdS. As to the ZnIn2S4/CdS, its
214
charge-transfer resistance was much smaller than that of CdS. The reason was that the
215
amount of CdS was relative less in ZnIn2S4/CdS.36, 37
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Figure 3. (A) UV-Vis diffuse reflectance spectra of ZnIn2S4, CdS and ZnIn2S4/CdS; (B) plots of
218
(αhν)1/2 vs. photon energy (hν) for ZnIn2S4 and (αhν)2 vs. photonenergy (hν) for CdS; (C) band
219
structure diagram for ZnIn2S4/CdS; (D) EIS of CdS/ITO and ZnIn2S4/CdS/ITO.
220
3.2 Possible mechanism of charge transfer
221
The possible mechanism for the PEC sensing of DA is displayed in Figure 4, which
222
is different from the traditional hole oxidation mechanism. Under irradiation (LED,
223
490-500 nm), electrons are excited from the occupied VB to the empty CB of ZnIn2S4,
224
leaving holes in the VB. The photogenerated electrons in the CB of ZnIn2S4 transfer
225
to CB of CdS and produce anodic photocurrent. Meanwhile, holes are transported in
226
the opposite direction to the heterojunction interface. Thus, the efficient spatial
227
separation of carriers is achieved. The addition of TEA can scavenge photogenerated
228
holes and amplify the anodic photocurrent signal. In addition, after adding DA in this
229
weakly alkaline solution (Tris-HCl, pH = 8.5), the formed PDA with abundant BQ
230
groups can act as electron acceptor and inhibit charge separation, hence the anodic
231
photocurrent significantly decreases. The inhibition by BQ may be related to the 11 ACS Paragon Plus Environment
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formation of recombination complex, in which photo-induced electrons transfer from
233
the CB of the photocatalyst to the LUMO of BQ.27, 38 The photocurrent change (∆I:
234
Isample–Iblank) depends on the amount of PDA produced by DA oxidation. Therefore,
235
this enables the indirect detection of DA.
236 237
Figure 4. Possible charge separation diagrams and the response mechanism of ZnIn2S4/CdS
238
heterojunction to DA.
239
3.3 PEC activity and PEC response of ZnIn2S4/CdS/ITO sensor
240
Linear sweep voltammogram (LSV) was recorded in 0.10 M Na2SO4 aqueous
241
solution with light on and off, and the ZnIn2S4/CdS photoanode exhibited higher
242
photocurrent than pure ZnIn2S4 and CdS under visible light illumination (Figure 5A).
243
This was attributed to the inhibition of CdS immobilized on the surface of ZnIn2S4 to
244
the recombination of electron–hole pairs.
245
The photocurrent responses of the electrodes under LED illumination were
246
explored (Figure 5B). We can see that all electrodes responded rapidly under the
247
irradiation of visible light. The ZnIn2S4/CdS/ITO showed enhanced photocurrent
248
response than pristine ZnIn2S4/ITO and CdS/ITO. The photocurrent density was
249
further enhanced by the addition of TEA because of its hole-trapping ability (Figure
250
5C). As a result, there was a large scale left for the photocurrent response of DA. The 12 ACS Paragon Plus Environment
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PEC responses of ZnIn2S4/ITO and CdS/ITO to 30 µM DA were shown in Figure 5D,
252
the ∆I were 0.25 and 1.05 µA cm-2, respectively, which were smaller than that of
253
ZnIn2S4/CdS/ITO (i.e. 5.12 µA cm-2). That was to say, the ZnIn2S4/CdS composite
254
had more favorable and sensitive response to DA.
255 256
Figure 5. (A) Linear sweep voltammograms of (a) CdS/ITO, (c) ZnIn2S4/CdS/ITO and (d)
257
ZnIn2S4/ITO, (b) ZnIn2S4/CdS/ITO in dark. Solution composition: 10 mM Tris-HCl buffer
258
solution (pH = 8.5) containing 0.050 mM TEA; (B) PEC response curves of (a) ZnIn2S4/ITO, (b)
259
CdS/ITO, (c) ZnIn2S4/CdS/ITO in Tris solution, and (d) ZnIn2S4/CdS/ITO in Tris solution
260
containing 0.050 mM TEA; (C) PEC response curves of ZnIn2S4/CdS/ITO in 10 mM Tris-HCl
261
buffer solution (pH = 8.5) containing 0.050 mM TEA (a), 0.050 mM TEA and 30 µM DA (b), 0
262
mM TEA and 0 µM DA (c), and 30 µM DA (d). Bias potential: 0 V (vs. Ag/AgCl), with on-off
263
illumination of 490-500 nm LED light; (D) PEC response of ZnIn2S4/ITO (a, b) and CdS/ITO (c, d)
264
in blank solution (a, c) containing DA (b, d); (E) Illuminated open circuit potential of CdS/ITO
265
and ZnIn2S4/ITO in 0.10 M Na2SO4 solution; (F) Decay of open circuit potential in dark.
266
In order to make the electron transport mechanism clear, the open-circuit
267
voltage-decay process was recorded (Figure 5D). The electron-hole pairs
268
recombination caused Voc decay. The decay lifetime of the accumulated electrons can
269
be related to the drop in the potential using the following equation:39
270
τ = (kBT/e)(dVoc/dt)-1
(4)
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271
Where kBT is the thermal energy, e is the positive elementary charge, and dVoc/dt is
272
the first-order time derivation of the Voc. Figure 5E shows the calculated τ as a
273
function of Voc. It is clear that the ZnIn2S4/CdS heterostructure has longer electron
274
lifetime in comparison with the pure ZnIn2S4. This proves that the introduction of CdS
275
promotes the interfacial charge transfer efficiently and makes the photogenerated
276
electron lifetime increase. It is consistent with the observation in PL spectra (in Figure
277
S3). The ZnIn2S4/CdS displays lower PL emission than the pristine ZnIn2S4,
278
indicating that the modification of CdS enables the effective separation of
279
photogenerated charge carriers. This contributes to the good PEC and photocatalytic
280
performance.10
281
3.4 Influence of CdS content
282
To evaluate the influence of CdS content, the SEM images and transient
283
photocurrent responses of the ZnIn2S4/CdS and ZnIn2S4/CdS-x (x=1, 2, 4, 5) modified
284
electrodes were recorded (Figure S4 and Figure S5). It could be observed that the
285
amount of CdS particles on the surface of ZnIn2S4 sheets gradually increased with
286
increasing the precursor concentration of CdS, and at last most of the ZnIn2S4 sheets
287
were covered. The photocurrent increased significantly with increasing the content of
288
CdS (curves a-c), and the ZnIn2S4/CdS/ITO displayed the highest photocurrent
289
response. When the content of CdS was further increased, the photocurrent declined
290
significantly (curves c-e). When the CdS content was too low, the charge separation
291
was poor and photocurrent was small. When it was too high the transport of carriers
292
was hindered and attenuation occurred due to the charge recombination, thus the
293
overall photocurrent decreased. In this case, the ZnIn2S4/CdS heterostructure
294
displayed best PEC performance and was chosen as electrode modification material.
295
3.5 Photoelectrochemical detection of DA
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The ZnIn2S4/CdS heterostructure modified ITO electrode was applied to the
297
quantitative determination of DA. As shown in Figure 6A-B, the photocurrent
298
decreased with increasing DA concentration. The photocurrent change was
299
proportional to the logarithm of DA concentration in a wide range of 0.3 to 300 µM,
300
the linear regression equation was ∆I/µAcm-2 = - 5.158﹣3.019 log c/µM with a
301
correlation coefficient of 0.9982. The detection limit was 0.1 µM. Some reported DA
302
PEC sensors were listed in Table 1 for comparison, and the linear range and detection
303
limit of the sensor could meet the practical needs.
304 305
Figure 6. (A) Photocurrent response of the ZnIn2S4/CdS/ITO in the presence of 0, 0.3, 1.0, 3.0, 10,
306
30, 100, 300 µM DA (from a to h); (B) linear relationship between response photocurrent and
307
logCDA; (C) photocurrent response stability of the ZnIn2S4/CdS/ITO in 10 mM Tris-HCl buffer
308
solution (pH=8.5) containing 0.050 mM TEA; (D) comparison of the photocurrent responses of 30
309
µM AA, UA, Cys, GSH, Glu and DA. Applied potential: 0 V (vs. Ag/AgCl).
310
To evaluate the reproducibility, five electrodes were prepared under the same
311
conditions and 50 µM DA was determined. A relative standard deviation (RSD) of 5.3%
312
(n=5) was obtained. The repeatability was investigated by monitoring 50 µM DA
313
using one modified electrode, and the RSD of the photocurrent was 4.1% (n=5). The 15 ACS Paragon Plus Environment
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314
stability of the PEC sensor was examined, as shown in Figure 6C, no obvious change
315
of photocurrent response was observed in 400 s, indicating the chemical and optical
316
properties of the sensor kept almost unchanged. The photocurrent responses of foreign
317
species, such as AA, UA, Cys, GSH and Glu, were recorded and compared with that
318
of DA (Figure 6D). It was interesting, these foreign species presented very low PEC
319
response under the same conditions. The high stability and selectivity should be
320
ascribed to the good photoactive material used and the unique response mechanism.
321
Finally, the ZnIn2S4/CdS/ITO was applied to the detection of DA in human urine
322
samples. The determination results are listed in Table S2. As can be seen, the
323
recovery and precision are satisfactory, indicating that the PEC sensor is promising in
324
the indirect detection of DA in real samples.
325
Table 1 Comparison of various DA PEC sensors.
PEC sensors
Role of DA
Linear range(µM)
LOD (µM)
Reference
G-C3N4/TiO2
electron donor
0.1-50
0.02
40
CuTsPc/TiO2
electron donor
4-810
0.5
41
TiO2 NPs
electron donor
0.002
42
WO3-ITO
electron donor
53-80 85-155
0.3
14
ZnIn2S4/GR
electron donor
0.01-20
0.001
43
0.4-10
0.17
18
0.3-300
0.1
This work
0.2-200 200-5000
PDA as electron CdTe-FTO
ZnIn2S4/CdS
acceptor PDA as electron acceptor
326 327
4. Conclusion
328
A ZnIn2S4/CdS heterostructure with good PEC properties was synthesized, based
329
on an electrostatic interaction mechanism. The overlapped band potentials and fast 16 ACS Paragon Plus Environment
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330
interfacial charge transfer made the photogenerated electron lifetime increase. Thus,
331
the resulting ZnIn2S4/CdS/ITO showed good PEC and photocatalytic performance.
332
When it was used for the PEC sensing of DA, it showed high sensitivity and
333
selectivity. During the detection process, DA turned to PDA and acted as effective
334
electron acceptor to inhibit the charge transfer and make the anodic photocurrent
335
decrease. The PEC sensor could detect 0.1 µM DA with a linear range of 0.3 to 300
336
µM.
337
338
Author Information
339
Corresponding Author
340
*E-mail address:
[email protected] (BZ Zeng)
341
Author Contributions
342
1
343
the final version of the manuscript.
344
Supporting information
345
The Zeta potential of ZnIn2S4, digital pictures of products, PL spectra, SEM images of
346
ZnIn2S4/CdS-x, photoelectrochemical response curves of ZnIn2S4/CdS-x.
347
Acknowledgement
H.W. and H.Y. contribute equally to this work and all authors have given approval to
348
The work was supported by the National Natural Science Foundation of China
349
(Grant No. 21675117). The authors appreciate the Analytical and Testing Center of
350
WHU for the help in material characterization. 17 ACS Paragon Plus Environment
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