ZnS:Al-TiO2 Film for Solar-Light-Driven

Subscriber access provided by United Arab Emirates University | Libraries Deanship

Article

Stable and Flexible CuInS2/ZnS:Al-TiO2 Film for Solar Light-Driven Photodegradation of Soil Fumigant Lili Yan, Zhichun Li, Mingxing Sun, Guoqing Shen, and Liang Li ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b05587 • Publication Date (Web): 14 Jul 2016 Downloaded from http://pubs.acs.org on July 18, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

ACS Applied Materials & Interfaces is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ACS Applied Materials & Interfaces

1

Stable and Flexible CuInS2/ZnS:Al-TiO2 Film for

2

Solar

3

Fumigant

Light-Driven

Photodegradation

of

Soil

Lili Yan,† Zhichun Li, ‡ Mingxing Sun, § Guoqing Shen*,† and Liang Li*,‡

4 5

†

6

Shanghai 200240, China

7

‡

8

Dongchuan Road, Shanghai 200240, China

9

§

School of Agriculture and Biology, Shanghai Jiao Tong University, 800 Dongchuan Road,

School of Environmental Science and Engineering, Shanghai Jiao Tong University, 800

Shanghai Entry-Exit Inspection and Quarantine Bureau, 1208 Minsheng Road, Shanghai

10

200135, China

11

KEYWORDS: CuInS2/ZnS:Al QDs; TiO2; PET; Photocatalytic film; 1,3-Dichloropropene

12

13

14

15

ACS Paragon Plus Environment

1


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 2 of 32

16

ABSTRACT

17

Semiconductor quantum dots (QDs) are suitable light absorbers for photocatalysis because of

18

their unique properties. However, QDs generally suffer from poor photochemical stability

19

against air, limiting their applications in photocatalysis. In this study, a stable solar light-driven

20

QDs-containing photocatalytic film was developed to facilitate photocatalytic degradation of the

21

soil fumigant 1,3-dichloropropene (1,3-D). A highly stable CuInS2/ZnS:Al core/shell QDs

22

(CIS/ZnS:Al QDs) was synthesized by doping Al into the ZnS shell and controlling ZnS:Al shell

23

thickness; the CIS/ZnS:Al QDs was subsequently combined with TiO2 to form a CIS/ZnS:Al-

24

TiO2 photocatalyst. The optimized ZnS:Al shell thickness for 1,3-D photodegradation was

25

approximately 1.3 nm, which guaranteed and balanced the good photocatalytic activity and

26

stability of the CIS/ZnS:Al-TiO2 photocatalyst. The photodegradation efficiency of 1,3-D can be

27

maintained up to more than 80% after five cycles during recycling experiment. When

28

CIS/ZnS:Al-TiO2 was deposited as photocatalytic film on a flexible polyethylene terephthalate

29

substrate, over 99% of cis-1,3-D and 98% of trans-1,3-D were depleted as they passed through

30

the film during 15 h of irradiation under natural solar light. This study demonstrated that the

31

stable CIS/ZnS:Al-TiO2 photocatalyst both in powder and film form is a promising agent for

32

photodegradation and emission reduction of soil fumigants.

33 34 35 36


2

Page 3 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


37

INTRODUCTION

38

Semiconductor quantum dots (QDs) are suitable light absorbers for photocatalysis owing to their

39

extraordinary properties, such as tunable band gap, high extinction coefficient of light

40

absorption, and relatively high photostability compared with traditional organic dyes.1–5 To date,

41

a considerable amount of efforts has been devoted on researches to utilize QDs in sensitizing

42

TiO2, forming solar light-driven photocatalysts.6–8 However, some common narrowband gap

43

QDs, such as CdS, CdSe, and PbS, contain the toxic elements Cd and Pb. These core-only QDs

44

remain unstable, limiting their application in photocatalysis.9 Developing a stable, green, and

45

effective solar light-driven photocatalyst is an interesting endeavor. CuInS2 (CIS) QDs with a

46

band gap of 1.5 eV are emerging alternatives for these toxic conventional QDs. However, CIS

47

core also suffers from poor chemical-/photo-stability against air and moisture, limiting their

48

actual application.9 Therefore, the key issue in the application of CIS QDs in photocatalysis is

49

the need to improve their stability during photocatalytic reactions.

50

One common method that is proposed to be used to enhance the stability of CIS core involves

51

growing a protective shell to form core/shell QDs.10–13 This approach effectively eliminates

52

surface defects by reducing the number of dangling bonds on a surface, thereby improving

53

photostability.14 Furthermore, our previous work demonstrated an innovative approach to

54

drastically improve the photostability of QDs; this approach involves Al doping into a ZnS (Eg =

55

3.7 eV) shell; Al subsequently formed a self-passivation oxide layer (Al2O3) during light

56

irradiation.15,16 The conduction band edge of CIS is higher than that of TiO2, allowing the

57

electrons to energetically transfer to the lower conduction band of TiO2. This process leads to an

58

efficient and relatively long-charge separation by minimizing electron/hole recombination.17

59

However, Jiang et al. showed that shell thickness influences the efficiency of electron transfer.18


3


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 4 of 32

60

Sun et al. found that the electron transfer rate from CIS/ZnS QDs into porous TiO2 films

61

decreases exponentially with increasing shell thickness.19 The shell acts as a physical barrier that

62

may hinder the transfer of photogenerated electrons and holes from the core to the surface. 4

63

Moreover, the electrons and holes in this heterojunction structure are sequestered in the core and

64

become unavailable for photocatalytic reactions. Nevertheless, high-performance photocatalysts

65

require the electrons to effectively transfer to the outer surface.20 Thibert et al. observed that

66

CdSe/CdS QDs shows a higher photocatalytic activity for H2O reduction than CdSe core, and

67

this property is due to passivation of surface–deep trap states in core/shell QDs.20 In addition,

68

Huang et al. observed that growth of ZnS on CdS core can improve stability during

69

photocatalytic reaction and is advantageous for hydrogen generation.21 However, the effects of

70

shell and its thickness on photocatalytic reaction when CIS-based core/shell QDs is applied in

71

photocatalytic degradation of pollutants is rarely reported. Meanwhile, thickness significantly

72

affects the stability of QDs.22 Therefore, balancing the photocatalytic activity and stability of

73

photocatalysts by controlling shell thickness is a pivotal problem.

74

Moreover, for practical use, photocatalysts should be immobilized on the surface of a suitable

75

substrate given that immobilized photocatalysts can be separated and used for continuous

76

processes.23 Polyethylene terephthalate (PET) is one of the most widely used polymers. The

77

advantages of PET include its low cost, flexible properties, and high performance, such as high

78

transparency, high efficiency in gas barrier, high stability in dimension and good mechanical

79

property.24 PET has been used in photovoltaic fields, such as in dye- or QDs-sensitized solar

80

cells.25,26 To date, the use of photocatalysts based on QDs and TiO2 for photocatalysis in gas

81

phase is rarely reported. A heterojunction with a semiconductor can reduce TiO2 deactivation,


4

Page 5 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


82

particularly in the removal of volatile organic compounds (VOCs), owing to the formation of a

83

stable byproduct on a photocatalyst surface.27,28

84

In this study, we optimized the photocatalytic activity of CIS/ZnS:Al-TiO2 photocatalyst by

85

controlling the thickness of ZnS:Al shell during CIS/ZnS:Al QDs synthesis. The performance of

86

the soil fumigant 1,3-dichloropropene (1,3-D, which includes cis and trans isomers) in

87

photocatalytic degradation was evaluated. This fumigant, being a potential VOC in the formation

88

of photochemical smog (near-surface ozone), can lead to excessive atmospheric emission, which

89

can cause air pollution and pose potential risk to humans.29–32 Recycling experiments involving

90

these photocatalysts were performed to study the stability and reusability of these photocatalysts.

91

Finally, we designed a novel solar light-driven CIS/ZnS:Al-TiO2 photocatalytic film. The as-

92

prepared photocatalytic film was sandwiched in a glass reactor, which was used to investigate the

93

emission reduction of 1,3-D.

94

EXPERIMENTAL SECTION

95

Materials. Dodecanethiol (DDT, 98%), 1-octadecene (ODE, >90%), n-butylamine (>99%),

96

copper iodide (CuI, 99.95%), zinc acetate (Zn(Ac)2, 99%), oleylamine (90%), thioglycolic acid

97

(TGA, ≥98%), ethanolamine (99%), TiO2 (anatase, 25 nm), tetraethyl orthosilicate (TEOS,

98

99.99%), and poly (diallyl-dimethyl-ammonium chloride) (PDDA, low molecular weight 100–

99

200 kDa) 20% solution in water were provided by Aladdin Chemical (Shanghai, China).

100

Aluminum isopropoxide (Al(IPA)3, ≥98%) and oleic acid (OA, 90%) were purchased from

101

Sigma-Aldrich (St. Louis, MO, USA). Indium acetate (In(Ac)3, 99.99%) was obtained from Alfa

102

Aesar (Ward Hill, MA, USA). Acetone (HPLC grade) was obtained from Merck. 1,3-D (96%,

103

including 50:50 cis- and trans-1,3-D isomers) and titanium (IV) isopropoxide (TTIP, 98%) were

104

obtained from J&K Scientific Ltd (Beijing, China). All chemicals were used without further


5


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

105

Page 6 of 32

purification.

106

Synthesis of CIS/ZnS:Al QDs. The preparation of CIS/ZnS:Al QDs includes synthesis of

107

CIS QDs, preparation of Zn(OA)2 precursor, and coating of ZnS:Al. The details are described in

108

the Supporting Information.

109

Preparation of photocatalytic film. Cleaned PET was first submerged in a 1% (v/v) aqueous

110

solution of PDDA for 20 min, rinsed in DI water, and dried at room temperature. The details

111

SiO2 sol and TiO2 paste preparation are shown in the Supporting Information. The PET was

112

coated with two layers of prepared SiO2 through spin-coating and then dried at 80 °C for 2 h.

113

Subsequently, TiO2 layer was deposited on top of the SiO2 through spin-coating. The films were

114

dried at room temperature and subsequently at 80 °C for 1 h. The deposition of QDs solution was

115

then used in layer-by-layer deposition method.33 After coating each sub-layer, the PET film was

116

dipped into a methanol solution with 5% TGA for 30 s and completely rinsed with clean

117

methanol; the solvent was evaporated in the vacuum oven at 50 °C for 10 min. This process was

118

repeated for 10 times.

119

Characterization. Transmission electron microscopy (TEM) images of the synthesized QDs

120

and photocatalysts were obtained with JEM-2100 operated at 200 kV. The sizes of the QDs were

121

determined by using the software Nano Measurer 1.2.5. The sizes and shell thickness of the QDs

122

were determined by measuring the geometric diameter (d) and effective diameter (𝑑eff = 3 𝑑).34

123

The surface morphologies of the photocatalytic films were examined using a field emission

124

scanning electron microscope (SEM, FEI Nova NanoSEM 450) operated at 5 kV with a working

125

distance of 5 mm. X-ray diffraction (XRD) patterns were recorded on a Shimadzu XRD-6100

126

diffractometer. The elemental analysis of the photocatalyst was carried out using an inductively

127

coupled

2

plasma

optical

emission

spectroscopy

(ICP-PS3500DD,

Hitachi).

The


6

Page 7 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


128

photoluminescence (PL) intensities of QDs and photocatalysts were collected with a Gangdong

129

F-380 fluorescent spectrophotometer and Ocean Optics LS-450, respectively. UV-vis absorption

130

spectra of photocatalysts and films were collected on a Perkin-Elmer Lambda 750 UV/VIS/NIR

131

spectrometer. X-ray photoelectron spectroscopy (XPS) analysis was performed on a Thermo

132

Fisher Scientific ESCALAB 250Xi spectrometer with Al Kα radiation source (hv = 1486.8 eV).

133

Photocatalytic degradation of 1,3-D. A certain amount of CIS/ZnS:Al-TiO2 photocatalyst

134

was weighted into a 21 mL headspace vial. The vial was injected with 10 μL of 1,3-D (10.4

135

mmol L−1 in acetone) and immediately capped with a Teflon-faced butyl-rubber septum and an

136

aluminum cap (Agilent Technologies, Inc.). The bottom of the vial placed on a quartz glass was

137

irradiated under simulated solar light (Xeon lamp, CEL-S500, Aulight, Beijing, China, AM 1.5,

138

90 mw cm−2). The light density was monitored using CEL-NP2000 light power meter. No filter

139

was used. At certain time intervals, the vials were transferred into a freezer (−20 °C) and stored

140

for analysis. Acetone (5 mL) was added into each frozen vial, which was immediately capped

141

with a Teflon-faced butyl rubber septum and an aluminum cap. All sample vials were shaken for

142

1 h. The supernatants were filtered using a 0.22 μm nylon syringe filter, and an aliquot (1.0 mL)

143

was transferred to a 2.1 mL vial for 1,3-D analysis on an Agilent 6890N gas chromatograph (GC)

144

equipped with an Agilent 5973 mass selective detector. Separation was performed using a DB-5

145

MS capillary column (30 m × 250 μm × 0.25 μm). The inlet temperature was 250 °C, and the MS

146

source temperature was 230 °C. The initial oven temperature was set as 40 °C for 1 min and

147

ramped to 100 °C at a rate of 15 °C min−1 and then to 125 °C at a rate of 50 °C min−1. Under

148

these conditions, the retention times of cis- and trans-1,3-D were 3.11 and 3.40 min, respectively.

149

The performance of photocatalytic film was studied in two cylindrical borosilicate glass

150

reactors. Each reactor had an inside diameter and height of 8 and 4 cm, respectively, and


7


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 8 of 32

151

composed of one source chamber and one receiving chamber, respectively. The two glass

152

reactors were fitted together with a photocatalytic film sandwiched between them and the joint

153

was sealed with epoxy resin and scotch tape. The photocatalyst coating of the photocatalytic film

154

faced the source chamber. The middle of each glass reactor wall had a sampling port, which was

155

capped with a PTFE/silicone septum and an aluminum cap. The sampling ports were sealed with

156

adhesive aluminum tape.

157

1,3-D was introduced into a 400 mL glass cylinder where the air was to spike 0.08 ml of 1,3-D.

158

After equilibration for 30 min at room temperature, about 10 mL of 1,3-D gas was injected into

159

the source chamber by using a gastight syringe. The initial concentrations of cis- and trans-1,3-D

160

in the source chamber were 1.13 ± 0.01 and 0.63 ± 0.01 mg L−1, respectively. Subsequently, the

161

experiment was conducted under natural solar light between 9:30 a.m. and 14:30 p.m. The

162

average solar intensity was 42.3 mw cm−2 and the solar intensity fluctuations were minimal.

163

Gases were sampled with a gastight syringe from the source and receiving chambers for

164

subsequent analysis. 1,3-D concentration was determined on an Agilent 6890N GC-MS (Agilent

165

5973) and an interfaced HP7694E Headspace sampler. Separation was carried out using a DB-5

166

MS capillary column (30 m × 250 μm × 0.25 μm). The initial oven temperature of 40 °C was

167

held for 1 min and then increased to 56 °C at a rate of 2.5 °C min−1. The headspace sampler was

168

used under the following conditions: vial temperature, 80 °C; loop temperature, 90 °C; transfer

169

line temperature, 100 °C; and headspace vial equilibration time, 5.0 min. The retention times of

170

cis- and trans-1,3-D were 3.32 and 3.85 min−1, respectively.

171

RESULTS AND DISCUSSION

172

Characterization. Figure 1 shows the PL spectra and TEM images of the CIS core and

173

CIS/ZnS:Al QDs. Overgrowth of ZnS:Al shell led to a systematic blue shift of the PL spectra of


8

Page 9 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


174

CIS core, that is, from 708, 645, and 629 nm to 622 nm (Figure 1a); simultaneously, the PL

175

intensity considerably increased with increasing coating time. Compared with the size of CIS

176

core (2.65±0.27 nm, Figure 1b), that of CIS/ZnS:Al QDs considerably increased, and the ZnS:Al

177

shell thickness increased to 0.3, 1.3, and 1.6 nm at coating times of 30, 420, and 630 min,

178

respectively (Figures 1c–e). (a)

(b)

(c)

(d)

(e)

179 180

Figure 1. Evolution of PL spectra (a) and TEM images (b–e) of CIS core during growth of

181

ZnS:Al shell with increasing coating time of ZnS:Al from 0, 30, and 420 min to 630 min.

182

Figure 2a shows the diffractograms of TiO2, CIS/ZnS:Al-TiO2 photocatalyst and CIS/ZnS:Al

183

QDs. The typical diffraction peaks were found at 25.28°, 37.80°, and 48.05°, corresponding to

184

the (101), (004), and (200) planes of TiO2 nanoparticles, indicating that the TiO2 nanoparticles

185

are anatase structure according to JCPDS 21-1272. Addition of CIS/ZnS:Al QDs generated new

186

broad peaks located at 28.11°, 46.87°, and 55.29°, which can be attributed to the reflection

187

direction of CIS/ZnS:Al QDs.15 Details on the morphology of the obtained materials are shown

188

by the TEM images (Figures 2b–d). Compared with TiO2 without any treatment (Figure 2b),

189

many small nanoparticles were deposited on the surface of TiO2 nanoparticles (Figure 2d). The

190

coexisting lattice fringes of TiO2 nanoparticles and CIS/ZnS:Al QDs were evident in the intimate

191

contact observed in the HRTEM image (Figure 2c). Lattice fringe of 0.341 nm was

192

corresponding to the d-spacing value of the (101) plane of anatase TiO2 (JCPDS 21-1272). The


9


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 10 of 32

193

lattice fringe of the tetrahedral nanoparticle (red line circled) was 0.317 nm, corresponding to the

194

d-spacing value of the (112) plane from roquesite CIS (JCPDS 27-0159) or ZnS alloyed CIS.

195

Another lattice fringe of 0.232 nm in the Figure 2c inset could be related to the d-spacing value

196

(220) from sphalerite ZnS (JCPDS 05-0566).35 To better reveal the chemical states and

197

compositions of CIS/ZnS:Al-TiO2 photocatalyst, XPS analysis was further carried out and Figure

198

S1 shows the results. Elements of Ti, O, Cu, In, Zn, S, Al, and adventitious C existed in the

199

CIS/ZnS:Al-TiO2 photocatalyst (Figure S1a). In Figure S1b, two peaks for Ti 2p were observed

200

at 464.5 and 458.8 eV, assigned to Ti 2p1/2 and Ti 2p3/2, respectively, which was characteristic of

201

Ti4+ in anatase TiO2.36 Meanwhile, the peak for O 1s can be devolved into two peaks (Figure

202

S1c). The peak located at 529.9 eV was attributed to lattice oxygen, whereas the other peak at

203

531.9 eV was attributed to the surface adsorbed oxygen.37 The binding energy of Cu 2p1/2 and Cu

204

2p3/2 (Figure S1d) located at 952.0 and 932.2 eV was corresponding to chemical element state of

205

Cu+.38 The peaks of binding energy at 445.0 and 452.5 eV (Figure S1e) matched well with 3d

206

electron of In3+.38 The two peaks (Figure S1f) located at 163.2 and 162.0 eV were assigned to S

207

2p with a valence state of −2.39 The binding energy of Zn 2p1/2 and Zn 2p3/2 (Figure S1g) located

208

at 1044.9 and 1021.9 eV was corresponding to chemical state of Zn2+.40 The Al 2p peak (Figure

209

S1h) located at 74.6 eV could be associated with the formation of Al–O (Al–OH or Al2O3).15 In

210

addition, Figure S2 shows the Fourier transform infrared spectroscopy (FTIR) spectra in the

211

supporting information. The above characterization results by XRD, TEM, XPS, and FTIR can

212

demonstrate the successful deposition of CIS/ZnS:Al onto TiO2 nanoparticles. Moreover, based

213

on the XPS analysis, the Cu/In atomic ratio was close to 1 and the Zn/S atomic ratio was 0.79.

214

The major elements (Ti, Cu, Zn, and Al) of the photocatalyst were also analyzed by ICP-OES.

215

The results showed that the mass ratio of CIS/ZnS:Al QDs to CIS/ZnS:Al-TiO2 was 38.4% and


10

Page 11 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


216

the Al/Zn molar ratio was 0.106. Figure 2a (inset) shows the absorption spectra of CIS/ZnS:Al-

217

TiO2 photocatalyst. TiO2 absorbs in the near-UV region with an optical absorption threshold of

218

3.2 eV. Addition of CIS/ZnS:Al QDs can enhance adsorption in the visible region, which

219

underlies efficient harvesting of light energy. (a)

(c)

(b)

(d)

220 221

Figure 2. (a) XRD patterns and absorption spectra (inset) of TiO2, CIS/ZnS:Al-TiO2, and

222

CIS/ZnS:Al. (*) TiO2 and (#) CIS/ZnS:Al. (b) and (d) TEM images of TiO2 and CIS/ZnS:Al-

223

TiO2. (c) HRTEM image of CIS/ZnS:Al-TiO2. CIS/ZnS:Al QDs was synthesized with a ZnS:Al

224

shell thickness of 1.3 nm.

225

Figure 3 presents the SEM images of PET films. The morphology of the prepared PET films is

226

remarkably different. “Single-layer” indicated that the photocatalytic film consisted only of one

227

semi-transparent TiO2 layer (medium size) and QDs layer. “Double-layer” indicated that the

228

photocatalytic film consisted of two TiO2 layers and QDs layer. One of the two TiO2 layers was

229

transparent TiO2 layer (small size) and the other was opaque TiO2 layer (large size). Figure 4a

230

shows the XRD patterns of transparent and opaque TiO2. The broad peak at approximately 25°


11


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 32

231

(red line) of transparent TiO2 resulting from the TTIP hydrolysis can be indexed to the

232

amorphous TiO2. The other small, weak peaks can be attributed to the reflection direction of

233

crystalline TiO2.25 The opaque TiO2 (black line) contains peaks attributed to anatase (JCPDS 21-

234

1272) and rutile (JCPDS 78-1508). The average size of opaque TiO2 was approximately 25 nm,

235

which was calculated using the Scherrer equation. These TiO2 layers were obtained through

236

gradient centrifugation of TiO2 paste. The coating procedure resulted in a relatively even coating

237

of PET, formed from dispersing transparent TiO2 on the PET (Figure 3a). Addition of opaque

238

TiO2 and QDs layer resulted in a cracked film, and the border of the cracks was considerably

239

jagged, possibly indicating TiO2 and QDs accumulation in these areas (Figure 3e). A more

240

obvious cracked morphology was observed in the presence of double-layer film than in the

241

presence of single-layer film (Figure 3c); this phenomenon can be ascribed to the fact that the

242

former was coated with an addition TiO2 layer compared with the latter. This observation is

243

possibly caused by deposition of PDDA, producing a cracked film that covered nearly the entire

244

PET surface.41 Cracking can be prevented by precisely controlling the working conditions, such

245

as those in vacuum evaporation42,43 and ball-milling technique.44 Addition of QDs significantly

246

modified the morphology of TiO2, resulting in the presence of many bulges on the PET surface

247

(Figures 3d,f) compared with the morphology of the transparent TiO2 as shown in the SEM

248

image (Figure 3b). Particle distribution on the double-layer film became denser and more

249

obvious than that on the single-layer film. This relatively homogeneous distribution of TiO2 on

250

PET surface is possibly related to the presence of the positively charged CH3–N+(R)4 groups in

251

the PDDA film, which prefers the anchoring of negatively charged SiO2 particles (basicity) and

252

subsequently favors the attachment of TiO2 nanoparticles.41 QDs can be attached to TiO2

253

nanoparticles via the bifunctional linker molecule TGA.33 Furthermore, Figure 4b shows the UV-


12

Page 13 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


254

vis adsorption of single- and double-layer films, which can underlie efficient harvesting light

255

energy in the visible region. Figure 4b (inset) further demonstrates the digital photograph of

256

double-layer CIS/ZnS:Al-TiO2 photocatalytic film on the PET surface. Therefore, TiO2

257

nanoparticles and CIS/ZnS:Al QDs can be firstly successfully deposited on the PET surface. (a)

(b)

(c)

(d)

(e)

(f)

258 259

Figure 3. SEM images of selected areas of PET substrates coated with (a, b) transparent TiO2,

260

(c, d) single-layer film (semi-transparent TiO2 layer and QDs layer), (e, f) double-layer film

261

(transparent and opaque TiO2 layers as well as QDs layer).

262 263 264 265


13


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

Page 14 of 32

(b)

266 267

Figure 4. (a) XRD patterns of transparent and opaque TiO2 after centrifugation. “a” denotes

268

anatase and “r” denotes rutile. (b) UV-vis absorption spectra of photocatalytic films acquired in

269

transmission mode. Inset shows the digital photograph of double-layer photocatalytic film (PET

270

substrate, diameter of 8 cm, and thickness of 0.1 mm) prepared through spin-coating. Single-

271

layer denotes the photocatalytic film composed of semi-transparent TiO2 layer and QDs layer;

272

double-layer denotes the photocatalytic film composed of transparent and opaque TiO2 layers as

273

well as QDs layer.

274

Effect of ZnS:Al shell thickness during QDs synthesis on 1,3-D degradation. Figure 5a

275

shows the effect of ZnS:Al shell thickness on 1,3-D degradation during QD synthesis. The

276

degradation efficiencies of cis- and trans-1,3-D first increased with increasing ZnS:Al shell

277

thickness and peaked at 1.3 nm. The degradation efficiencies of cis- and trans-1,3-D increased

278

from 17.96% and 23.27% to 75.47% and 82.39%, respectively. The efficiencies decreased to

279

63.19% and 65.95% as the ZnS:Al shell thickness increased to 1.6 nm, respectively. The

280

efficiency when CIS/ZnS:Al-TiO2 photocatalyst was used for 1,3-D photodegradation was

281

higher by approximately 3.8-fold than that when using CIS-TiO2 photocatalyst. The

282

aforementioned phenomenon was related to the surface defects and to the band structure of the

283

resultant CIS/ZnS:Al core/shell QDs. Within a relatively short coating time, coating of ZnS and


14

Page 15 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


284

cation exchange occurred on the core/shell interface, significantly eliminating surface defects

285

and dangling bonds on CIS core, dramatically suppressing the non-irradiation recombination and

286

thereby drastically enhancing the PL quantum yield (QY).45 Moreover, diffusion of zinc into the

287

CIS core increased the band gap and formed a gradient alloy core/shell structure.10,15,46 This

288

gradient alloy core/shell structure was further verified by HCl etching of QDs (Figure S3 and

289

Table S3). This gradient core/shell structure resulted in the “smoothing” of the confinement

290

potential interfacial.45 The high-energy electrons in the core can easily tunnel through the ZnS

291

shell into TiO2. High PL QY indicates that most of the photogenerated holes and electrons can

292

recombine via the irradiation pathway (PL). After the combination of QDs with TiO2 and the

293

formation of heterojunction, the most photogenerated carriers separated on the interface and

294

electrons transferred to n-type TiO2, resulting in the high photodegradation efficiency mentioned

295

above. This transfer was significantly dependent on ZnS:Al shell thickness. When ZnS:Al shell

296

became too thick, the ZnS layer acted as a tunneling barrier, localizing the electrons and holes in

297

the CIS core and partially suppressing the transfer of electron into TiO2.47 Figure 5c demonstrates

298

the band alignment diagram of CIS/ZnS:Al-TiO2 photocatalyst. The conduction band edge of

299

CIS, which is higher than that of TiO2 effectively allowed the electrons to accumulate at the

300

lower conduction band of TiO2, minimizing electron/hole recombination.48 When the ZnS:Al

301

shell thickness was 1.3 nm, the electron transfer was easier than the ZnS:Al shell thickness of 1.6

302

nm.


15


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(a)

Page 16 of 32

(b)

(c)

303 304

Figure 5. (a) Effect of ZnS:Al shell thickness during QDs synthesis on the degradation

305

efficiency of 1,3-D. Experimental conditions: photocatalyst mass, 20 mg; solar light intensity, 90

306

mw cm−2; and irradiation time, 3 h. (b) Schematic of the CIS/ZnS:Al QDs structure. (c) Band

307

alignment diagram of CIS/ZnS:Al-TiO2 photocatalyst.

308

Moreover, the photocatalytic activity of the photocatalyst was compared with that of their

309

constituent TiO2 and CIS/ZnS:Al QDs (Table S1). The total 1,3-D degradation efficiency when

310

using CIS/ZnS:Al-TiO2 was 79.19%±3.38%, which is significantly higher than that when using

311

TiO2 (21.57%±3.92%). This result is mainly ascribed to the efficient harvesting of visible-light

312

energy resulting from addition of CIS/ZnS:Al QDs (Figure 2a, inset). Compared with

313

CIS/ZnS:Al QDs, CIS/ZnS:Al-TiO2 photocatalyst significantly improved the degradation

314

efficiency of cis-1,3-D from 58.31%±9.13% to 75.47%±1.90%. In addition, CIS/ZnS:Al QDs is

315

considerably more costly than TiO2. The CIS/ZnS:Al QDs/CIS/ZnS:Al-TiO2 mass ratio was

316

38.4%, indicating that the amount of CIS/ZnS:Al in CIS/ZnS:Al-TiO2 photocatalyst decreased


16

Page 17 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


317

by 61.6% compared with that of pure CIS/ZnS:Al QDs. These results indicated that CIS/ZnS:Al-

318

TiO2 photocatalyst resulted in high photocatalytic activity of 1,3-D.

319

Stability and reusability of the photocatalyst. The stability and reusability of the

320

photocatalyst can influence the photocatalytic film. The good reusability of the photocatalytic

321

film is advantageous in fumigation degradation, reducing the processing and waste disposal costs

322

of field fumigants. As mentioned above, doping Al into the ZnS shell can further improve the

323

photostability of QDs by forming a passivation oxide layer during light irradiation. We thus

324

compared the photocatalytic activity of CIS/ZnS:Al-TiO2 photocatalyst with that of CIS/ZnS-

325

TiO2 photocatalyst under simulated solar light, which can evaluate the stability and reusability of

326

the photocatalyst.

327 328

Figure 6. Recycling activities of CIS/ZnS:Al-TiO2 (black column) and CIS/ZnS-TiO2

329

photocatalysts (diagonal column) for 1,3-D photodegradation (left, cis-1,3-D; right, trans-1,3-D).

330

Experimental conditions: photocatalyst mass, 50 mg; solar light intensity, 90 mw cm−2, and

331

irradiation time for each cycle, 5 h.

332

Recycling experiments were conducted using an equal amount of CIS/ZnS:Al-TiO2 and

333

CIS/ZnS-TiO2 photocatalysts. The photocatalysts were collected, washed, precipitated by

334

acetone, and dried in vacuum at 60 °C for 1 h after each cycle. The degradation efficiencies of

335

both catalysts deceased with increasing recycling cycles (Figure 6). The same trends were


17


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 32

336

observed between the two isomers of 1,3-D. During recycling, the CIS/ZnS:Al-TiO2

337

photocatalyst always resulted in high photocatalytic degradation efficiencies of cis- and trans-

338

1,3-D. The efficiencies can be maintained by more than 80% after five cycles. The degradation

339

efficiency using CIS/ZnS:Al-TiO2 photocatalyst decreased at a slower rate than that when using

340

CIS/ZnS-TiO2 photocatalyst, specifically after the third cycle. An extremely significant

341

difference between CIS/ZnS:Al-TiO2 and CIS/ZnS-TiO2 photocatalysts (p < 0.01) was observed

342

in the fourth and fifth cycle, as revealed by using SPSS software (version 19.0, SPSS Inc.,

343

Chicago, IL, USA). This significant difference can be ascribed to the photostability difference of

344

the QDs. After each cycle, the remnant PL intensity of the CIS/ZnS:Al-TiO2 photocatalyst was

345

correspondingly stronger than that of CIS/ZnS-TiO2 photocatalyst (Figure 7). After five cycles,

346

the remnant PL intensity of CIS/ZnS:Al-TiO2 photocatalyst was maintained at approximately 90%

347

of the initial PL intensity. By contrast, the PL intensity of CIS/ZnS-TiO2 photocatalyst was

348

approximately 65% of the initial value. Huang et al.21 reported that the presence of ZnS shell can

349

significantly improve the photostability of CdS NCs by preventing photocorrosion of CdS NCs.

350

It also can improve the stability during photocatalytic reactions. Therefore, photostability of the

351

photocatalyst can imply to some extent the stability and reusability of the photocatalyst.

352

Reduction in photostability indicates the photodegradation of the photocatalyst itself. Doping of

353

Al into the ZnS shell improved the photostability of CIS/ZnS QDs.15 The ZnS:Al shell not only

354

considerably reduced surface defects but also yielded a highly photostable CIS/ZnS:Al structure,

355

which further improved the stability of CIS/ZnS:Al-TiO2 photocatalyst. However, the initial

356

degradation efficiency when using CIS/ZnS:Al-TiO2 photocatalyst was lower than that when

357

using CIS/ZnS-TiO2 photocatalyst. Kim et al. found that an Al overlayer can retard electron

358

transfer into the dye in a dye-sensitized TiO2 with an initial thin coating of Al2O3.49 Rao et al.


18

Page 19 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


359

reported that Al in the CIS/ZnS:Al QDs could be further oxidized into Al2O3, which formed a

360

passivation oxide layer during light irradiation.15 Thus, Al2O3 prevented electron transfer to the

361

outer surface to some extent. PL lifetime of these two photocatalysts were recorded using a

362

steady-state and time-resolved fluorescence spectrofluorometer (QM/TM/IM, PTI, USA) (Table

363

S2). The lifetime of CIS/ZnS:Al-TiO2 (307.5 ns) was longer than that of CIS/ZnS-TiO2 (287.2

364

ns), which further verified the slower electron transfer rate in the CIS/ZnS:Al-TiO2. Therefore,

365

this new approach involving doping of Al into ZnS shell not only can enhance the stability of the

366

photocatalyst but also maintain photocatalytic activity.

367 368

Figure 7. Photostability of CIS/ZnS:Al-TiO2 and CIS/ZnS-TiO2 photocatalysts after each cycle.

369

1,3-D degradation on photocatalytic film under natural solar light. Figure 8 shows the

370

degradation of 1,3-D on photocatalytic films under natural solar light. The control used was a

371

PET substrate without any nanocomposite. In the source chamber, 1,3-D rapidly disappeared in

372

the presence of single- and double-layer films. By contrast, a slight reduction was observed in

373

the control treatment and was possibly caused by penetration into the receiving chamber through

374

the PET substrate. In the receiving chamber, the concentrations of cis- and trans-1,3-D remained

375

lower in the single- and double-layer films than in the control. The photocatalytic films are

376

obviously effective for 1,3-D photocatalytic degradation and for controlling emission of 1,3-D

377

from the source chamber into the receiving chamber.


19


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 20 of 32

378

Within 15 h of irradiation, approximately 75% of cis-1,3-D and 79% of trans-1,3-D

379

disappeared in the single-layer film in the source chamber (Figure 8a). Over 99% of cis-1,3-D

380

and 98% of trans-1,3-D were depleted using the double-layer film, and a nearly complete

381

disappearance was reached during the irradiation period (Figure 8a). As shown in Figure 3f, the

382

double-layer film is rough and displays obvious presence of aggregates, which served as light-

383

scattering centers. This layer can improve the light-harvesting behavior of light-sensitive

384

materials, such as QDs.50 This phenomenon can also be verified using the UV-vis absorption

385

spectra of the two photocatalytic films acquired in transmission mode (Figure 4b). The double-

386

layer film showed higher absorbance than the single-layer film at wavelength lower than 550 nm.

387

Moreover, 1,3-D can be degraded using CIS/ZnS:Al-TiO2 photocatalyst. The photocatalytic

388

degradation of 1,3-D in the presence of photocatalytic films probably resulted in the

389

disappearance of 1,3-D in the source chamber. The concentration of 1,3-D as a function of time

390

in the source chamber was fitted using a pseudo-first-order model to investigate the

391

disappearance characteristic of 1,3-D on the photocatalytic films. The equations are as follows:51

392

ln

393

𝑡1/2 =

394

where C0 is the initial 1,3-D concentration, C is the concentration at any time (t), k is the pseudo-

395

first-order rate constant, and t1/2 is the half-life. This kinetic equation is the simplification of

396

Langmuir–Hinshelwood kinetic expression, which is commonly used to explain the kinetics of

397

heterogeneous catalysis.52 Table 1 shows the obtained first-order rate constants (k) and half-life

398

(t1/2). The fitting curves of cis-1,3-D and trans-1,3-D were included in the Supporting

399

Information (Figure S4). The correlation coefficients at different levels were higher than 0.95,

400

indicating that 1,3-D degradation kinetic could be considered a pseudo-first-order model. t1/2 of

𝐶0 𝐶

= 𝑘t

(1)

ln2

(2)

𝑘


20

Page 21 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


401

1,3-D in the presence of the double-layer film was shorter than that in the presence of the single-

402

layer film (Table 1). t1/2 of the cis- and trans-1,3-D decreased from 7.6 h to 3.3 h and from 6.5 h

403

to 2.7 h, respectively. These values were much lower than the values of 1.7–53 days in the

404

aerobic soil.53 Degradation of 1,3-D by the photocatalytic film was more rapid compared with the

405

long t1/2 of 52 and 12 days for cis- and trans-1,3-D under atmospheric condition.54 In addition,

406

the trans isomer dissipated more rapidly than the cis isomer. The higher dissipation rate is

407

possibly caused by direct reaction of trans-1,3-D with nucleophilic groups, such as –NH2, –SH,

408

and –COOH.55 These groups may react rapidly with trans but not with cis isomer because of

409

steric difference.55 In the present synthesis of CIS/ZnS:Al QDs, CIS/ZnS:Al QDs were capped

410

with ligands, such as DDT and OA, which contain –SH and –COOH groups, respectively.

411

Similarly, these groups can participate in degradation and preferentially react with trans isomer,

412

which accelerated the degradation rate relative to that of the cis isomer.

413

After 15 h of irradiation, the concentrations of cis- and trans-1,3-D using the control in the

414

receiving chamber were 0.23 and 0.16 mg L−1, respectively (Figure 8b). The concentrations of

415

cis- and trans-1,3-D in the presence of the single- and double-layer films were 0.16 and 0.12 mg

416

L−1, respectively (Figure 8b). These values remained lower than that in the presence of the

417

control, indicating that the photocatalytic film was relatively less permeable than the control film.

418

In a previous report, two outer layers and an inner layer of HDPE were constructed using

419

activated materials to control the emission.56 By contrast, our fabricated film consisted only of

420

one PET coated with CIS/ZnS:Al-TiO2 photocatalyst, which can effectively control the

421

penetration of 1,3-D into the receiving chamber.


21


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 32

(b)

(a)

422 423

Figure 8. (a) Disappearance of cis- and trans-1,3-D concentrations over time in the source

424

chamber. (b) Concentrations of cis- and trans-1,3-D over time in the receiving chamber.

425

Experimental conditions: solar light intensity, 42.3 mw cm−2; and irradiation time, 15 h. Single-

426

layer (Single) denotes the photocatalytic film composed of semi-transparent TiO2 layer and QDs

427

layer; double-layer (Double) denotes the photocatalytic film composed of transparent and opaque

428

TiO2 layers as well as QDs layer.

429 430

Table 1 Equilibrium Time, Rate Constant (k), Half-life (t1/2) of 1,3-D in Permeability Reactors Fumigant cis-1,3-D trans-1,3-D

PET film single-layer double-layer single-layer double-layer

k (h-1) 0.092 0.211 0.106 0.256

t1/2 (h) 7.6 3.3 6.5 2.7

R2 0.9573 0.9776 0.9684 0.9898

431 432

CONCLUSION

433

This study provided a basis for efficient extended VOCs photodegradation by using the as-

434

prepared CIS/ZnS:Al-TiO2 photocatalyst both in its powder and film forms. The photocatalytic

435

activity and stability of CIS/ZnS:Al-TiO2 photocatalyst for 1,3-D photodegradation can be


22

Page 23 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


436

balanced by controlling the thickness of ZnS:Al shell. The optimized ZnS:Al shell thickness was

437

approximately 1.3 nm. The results of recycling experiment showed that the degradation

438

efficiency of 1,3-D remained higher than 80% after five cycles. Using the developed flexible

439

CIS/ZnS:Al-TiO2 photocatalytic film, over 99% of cis-1,3-D and 98% of trans-1,3-D can be

440

degraded in the source chamber. Therefore, the proposed photocatalytic film can be effectively

441

utilized to photodegrade and to control the emission of the soil fumigant. In addition, the film

442

can maintain high reusability because the photostability of QDs can be improved by doping Al

443

into the ZnS shell. Further researches should be conducted to understand the effect of the doping

444

level of Al on the photocatalytic activity of CIS/ZnS:Al-TiO2 photocatalyst. Moreover, the effect

445

of the quality and shapes of the CIS/ZnS:Al QDs on the photocatalytic activity should be

446

evaluated.

447

ASSOCIATED CONTENT

448

Supporting Information

449

The supporting information includes the following: details on synthesis of CIS/ZnS:Al QDs,

450

preparation of CIS/ZnS:Al-TiO2 photocatalyst, preparation of SiO2 sol and TiO2 paste, etching of

451

CIS/ZnS:Al QDs, Table S1-S3 as well as Figure S1-S4. This material is available free of charge

452

via the Internet at http://pubs.acs.org.

453

AUTHOR INFORMATION

454

Corresponding Author

455

*(G. Q. Shen) E-mail: [email protected]. Tel.: +86 21 34206143.

456

*(L. Li) E-mail: [email protected]. Tel.: +86 21 54747567.

457

Notes


23


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 24 of 32

458

The authors declare no competing financial interest.

459

ACKNOWLEDGMENT

460

This work was supported by the National Natural Science Foundation of China (NSFC 21477075,

461

21271179), and the national key research and development plan (2016YFD0800207).

462

REFERENCES

463

(1) El-Sayed, M. A. Small is Different: Shape-, Size-, and Composition-Dependent

464

Properties of Some Colloidal Semiconductor Nanocrystals. Acc. Chem. Res. 2004, 37, 326–

465

333.

466 467

(2) Zhang, W. J.; Zhong, X. H. Facile Synthesis of ZnS−CuInS2−Alloyed Nanocrystals for a Color-Tunable Fluorchrome and Photocatalyst. Inorg. Chem. 2011, 50, 4065–4072.

468

(3) Xie, Y.; Ali, G.; Yoo, S. H.; Cho, S. O. Sonication-Assisted Synthesis of CdS

469

Quantum-Dot-Sensitized TiO2 Nanotube Arrays with Enhanced Photoelectrochemical and

470

Photocatalytic Activity. ACS Appl. Mater. Interfaces 2010, 2, 2910–2914.

471

(4) Zhu, H. M.; Song, N. H.; Lian, T. Q. Controlling Charge Separation and

472

Recombination Rates in CdSe/ZnS Type I Core-Shell Quantum Dots by Shell Thicknesses.

473

J. Am. Chem. Soc. 2010, 132, 15038–15045.

474

(5) Bera, R.; Kundu, S.; Patra, A. 2D Hybrid Nanostructure of Reduced Graphene

475

Oxide-CdS Nanosheet for Enhanced Photocatalysis. ACS Appl. Mater. Interfaces 2015, 7,

476

13251–13259.

477

(6) Xue, C.; Wang, T.; Yang, G. D.; Yang B. L.; Ding, S. J. A Facile Strategy for the

478

Synthesis of Hierarchical TiO2/CdS Hollow Sphere Heterostructures with Excellent Visible

479

Light Activity. J. Mater. Chem. A 2014, 2, 7674–7679.


24

Page 25 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


480

(7) Wang, C. J.; Thompson, R. L.; Baltrus, J.; Matranga, C. Visible Light Photoreduction

481

of CO2 Using CdSe/Pt/TiO2 Heterostructured Catalysts. J. Phys. Chem. C Lett. 2009, 1, 48–

482

53.

483 484

(8) Ratanatawanate, C.; Tao, Y.; Balkus Jr, K. J. Photocatalytic Activity of PbS Quantum Dot/TiO2 Nanotube Composites. J. Phys. Chem. C 2009, 113, 10755–10760.

485

(9) Pons, T.; Pic, E.; Lequeux, N.; Cassette, E.; Bezdetnaya, L.; Guillemin, F.; Marchal,

486

F.; Dubertret, B. Cadmium-Free CuInS2/ZnS Quantum Dots for Sentinel Lymph Node

487

Imaging with Reduced Toxicity. ACS Nano 2010, 4, 2531–2538.

488

(10) Li, L.; Daou, T. J.; Texier, I.; Kim Chi, T. T.; Liem, N. Q.; Reiss, P. Highly

489

Luminescent CuInS2/ZnS Core/Shell Nanocrystals: Cadmium-Free Quantum Dots for in

490

Vivo Imaging. Chem. Mater. 2009, 21, 2422–2429.

491

(11) Song, W. S.; Kim, J. H.; Yang, H. Silica-Embedded Quantum Dots as

492

Downconverters of Light-Emitting Diode and Effect of Silica on Device Operational

493

Stability. Mater. Lett. 2013, 111, 104–107.

494

(12) Song, W. S.; Jang, E. P.; Kim, J. H.; Jang, H. S.; Yang, H. Unique Oxide Overcoating

495

of CuInS2/ZnS Core/Shell Quantum Dots with ZnGa2O4 for Fabrication of White Light-

496

Emitting Diode with Improved Operational Stability. J. Nanopart. Res. 2013, 15, 1462.

497 498 499 500

(13) Park, J.; Kim, S. W. CuInS2/ZnS Core/Shell Quantum Dots by Cation Exchange and Their Blue-Shifted Photoluminescence. J. Mater. Chem. 2011, 21, 3745–3750. (14) Reiss, P.; Protiere, M.; Li, L. Core/Shell Semiconductor Nanocrystals. Small 2009, 5, 154–168.

501

(15) Rao, P. H.; Yao, W.; Li, Z. C.; Kong, L.; Zhang, W. Q.; Li, L. Highly Stable

502

CuInS2@ZnS:Al Core@Shell Quantum Dots: the Role of Aluminium Self–Passivation.


25


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

503

Page 26 of 32

Chem. Commun. 2015, 51, 8757–8760.

504

(16) Li, Z. C.; Yao, W.; Kong, L.; Zhao, Y. X.; Li, L. General Method for the Synthesis of

505

Ultrastable Core/Shell Quantum Dots by Aluminum Doping. J. Am. Chem. Soc. 2015, 137,

506

12430–12433.

507

(17) Peng, Z. Y.; Liu, Y. L.; Chen, K. Q.; Yang, G. J.; Chen, W. Fabrication of the

508

Protonated Pentatitanate Nanobelts Sensitized with CuInS2 Quantum Dots for Photovoltaic

509

Applications. Chem. Eng. J. 2014, 244, 335–342.

510 511

(18) Jiang, Z. J.; Kelley, D. F. Effects of Inhomogeneous Shell Thickness in the Charge Transfer Dynamics of ZnTe/CdSe Nanocrystals. J. Phys. Chem. C 2012, 116, 12958–12968.

512

(19) Sun, J. H.; Zhao, J. L.; Masumoto, Y. Shell-Thickness-Dependent Photoinduced

513

Electron Transfer from CuInS2/ZnS Quantum Qots to TiO2 Films. Appl. Phys. Lett. 2013,

514

102, 053119.

515

(20) Thibert, A.; Frame, F. A.; Busby, E.; Holmes, M. A.; Osterloh F. E.; Larsen, D. S.

516

Sequestering High-Energy Electrons to Facilitate Photocatalytic Hydrogen Generation in

517

CdSe/CdS Nanocrystals. J. Phys. Chem. Lett. 2011, 2, 2688–2694.

518

(21) Huang, L.; Wang, X. L.; Yang, J. H.; Liu, G.; Han, J. F.; Li, C. Dual Cocatalysts

519

Loaded Type I CdS/ZnS Core/Shell Nanocrystals as Effective and Stable Photocatalysts for

520

H2 Evolution. J. Phys. Chem. C 2013, 117, 11584–11591.

521

(22) Zhang, H. C.; Ye, Y. H.; Zhang, J. Y.; Cui, Y. P.; Yang, B. P.; Shen, L. Effects of Core

522

Size and Shell Thickness on Luminescence Dynamics of Wurtzite CdSe/CdS Core/Shell

523

Nanocrystals. J. Phys. Chem. C 2012, 116, 15660–15666.

524

(23) Matsuzawa, S.; Maneerat, C.; Hayata, Y.; Hirakawa, T.; Negishi, N.; Sano, T.

525

Immobilization of TiO2 Nanoparticles on Polymeric Substrates by Using Electrostatic


26

Page 27 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

526 527 528


Interaction in the Aqueous Phase. Appl. Catal., B 2008, 83, 39–45. (24) Zeng, K.; Bai, Y. P. Improve the Gas Barrier Property of PET Film with Montmorillonite by In Situ Interlayer Polymerization. Mater. Lett. 2005, 59, 3348–3351.

529

(25) Zhang, D. S.; Yoshida, T.; Oekermann, T.; Furuta, K.; Minoura, H. Room-

530

Temperature Synthesis of Porous Nanoparticulate TiO2 Films for Flexible Dye-Sensitized

531

Solar Cells. Adv. Funct. Mater. 2006, 16, 1228–1234.

532

(26) Li, F. S.; Son, D. I.; Cho, S. H.; Kim, W. T.; Kim, T. W. Flexible Photovoltaic Cells

533

Fabricated Utilizing ZnO Quantum Dot/Carbon Nanotube Heterojunctions. Nanotechnology

534

2009, 20, 155202.

535

(27) Weon, S.; Choi, W. TiO2 Nanotubes with Open Channels as Deactivation-Resistant

536

Photocatalyst for the Degradation of Volatile Organic Compounds. Environ. Sci. Technol.

537

2016, 50, 2556–2563.

538

(28) Tan, T. H.; Scott, J.; Ng, Y. H.; Taylor, R. A.; Aguey-Zinsou, K. F.; Amal, R.

539

Understanding Plasmon and Band Gap Photoexcitation Effects on the Thermal-Catalytic

540

Oxidation of Ethanol by TiO2-Supported Gold. ACS Catal. 2016, 6, 1870–1879.

541

(29) Luo, L. F.; Yates, S. R.; Ashworth, D. J.; Xuan, R. C.; Becker, J. O. Effect of Films

542

on 1,3-Dichloropropene and Chloropicrin Emission, Soil Concentration, and Root-Knot

543

Nematode Control in a Raised Bed. J. Agric. Food Chem. 2013, 61, 2400–2406.

544

(30) Ashworth, D. J.; Ernst, F. F.; Xuan, R. C.; Yates, S. R. Laboratory Assessment of

545

Emission Reduction Strategies for the Agricultural Fumigants 1,3-Dichloropropene and

546

Chloropicrin. Environ. Sci. Technol. 2009, 43, 5073–5078.

547

(31) Gan, J.; Yates, S. R.; Crowley, D.; Becker, J. O. Acceleration of 1,3-Dichloropropene

548

Degradation by Organic Amendments and Potential Application for Emissions Reduction. J.


27


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

549

Page 28 of 32

Environ. Qual. 1998, 27, 408–414.

550

(32) Zheng, W.; Papiernik, S. K.; Guo, M. X.; Yates, S. R. Competitive Degradation

551

Between the Fumigants Chloropicrin and 1,3-Dichloropropene in Unamended and Amended

552

Soils. J. Environ. Qual. 2003, 32, 1735–1742.

553 554

(33) Sun, Z. H.; Sitbon, G.; Pons, T.; Bakulin, A. A.; Chen, Z. Y. Reduced Carrier Recombination in PbS-CuInS2 Quantum Dot Solar Cells. Sci. Rep. 2015, 5, 10626.

555

(34) Zhong, H. Z.; Lo, S. S.; Mirkovic, T.; Li, Y. C.; Ding, Y. Q.; Li, Y. F.; Scholes, G. D.

556

Noninjection Gram-Scale Synthesis of Monodisperse Pyramidal CuInS2 Nanocrystals and Their

557

Size-Dependent Properties. ACS Nano 2010, 4, 5253–5262.

558

(35) Chen, C. W.; Wu, D. Y.; Chan, Y. C.; Lin, C. C; Chung, P. H.; Hsiao, M.; Liu, R. S.

559

Evaluations of the Chemical Stability and Cytotoxicity of CuInS2 and CuInS2/ZnS Core/Shell

560

Quantum Dots. J. Phys. Chem. C 2015, 119, 2852–2860.

561 562

(36) Mayer, J. T.; Diebold, U.; Madey, T. E.; Garfunkel, E. Titanium and Reduced Titania Overlayers on Titanium Dioxide (110). J. Electron Spectrosc. Relat. Phenom. 1995, 73, 1–11.

563

(37) Hou, D. F.; Hu, X. L.; Hu, P.; Zhang, W.; Zhang, M. F.; Huang, Y. H. Bi4Ti3O12

564

Nanofibers–BIOI Nanosheets p–n Junction: Facile Synthesis and Enhanced Visible-Light

565

Photocatalytic Activity. Nanoscale 2013, 5, 9764–9772.

566

(38) Li, T. T.; Li, X. Y.; Zhao, X. D.; Shi, Y, Teng, W. Fabrication of n-type CuInS2 Modified

567

TiO2 Nanotube Arrays Heterostructure Photoelectrode with Enhanced Photoelectrocatalytic

568

Properties. Appl. Catal., B 2014, 156–157, 362–370.

569

(39) Chang, J.; Waclawik, E. R. Controlled synthesis of CuInS2, Cu2SnS3 and Cu2ZnSnS4

570

Nano-Structures: Insight into the Universal Phase Selectivity Mechanism. CrystEngComm 2013,

571

15, 5612–5619.


28

Page 29 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


572

(40) Hou, Y.; Li, X. Y.; Zhao, Q. D.; Quan, X.; Chen, G. H. Electrochemical Method for

573

Synthesis of a ZnFe2O4/TiO2 Composite Nanotube Array Modified Electrode with Enhanced

574

Photoelectrochemical Activity. Adv. Funct. Mater. 2010, 20, 2165–2174.

575

(41) Sánchez, B.; Coronado, J. M.; Candal, R.; Portela, R.; Tejedor, I.; Anderson, M. A.;

576

Tompkins, D.; Lee, T. Preparation of TiO2 Coatings on PET Monoliths for the Photocatalytic

577

Elimination of Trichloroethylene in the Gas Phase. Appl. Catal., B 2006, 66, 295–301.

578

(42) Lopes, F. V. S.; Miranda, S. M.; Monteiro, R. A. R.; Martins, S. D. S.; Silva, A. M.

579

T.; Faria, J. L.; Boaventura, R. A. R.; Vilar, V. J. P. Perchloroethylene Gas-Phase

580

Degradation over Titania-Coated Transparent Monoliths. Appl. Catal., B 2013, 140–141,

581

444–456.

582 583 584 585

(43) Rao, K. N. Studies on Thin Film Materials on Acrylics for Optical Applications. Bull. Mater. Sci. 2003, 26, 239–245. (44) Weerasinghe, H. C.; Huang, F. Z.; Cheng, Y. B. Fabrication of Flexible Dye Sensitized Solar Cells on Plastic Substrates. Nano Energy 2013, 2, 174–189.

586

(45) García-Santamaría, F.; Chen Y. F.; Vela, J.; Schaller, R. D.; Hollingsworth, J. A.;

587

Klimov, V. I. Suppressed Auger Recombination in “Giant” Nanocrystals Boosts Optical

588

Gain Performance. Nano lett. 2009, 9, 3482–3488.

589

(46) Li, L.; Pandey, A.; Werder, D. J.; Khanal, B. P.; Pietryga, J. M.; Klimov, V. I.

590

Efficient Synthesis of Highly Luminescent Copper Indium Sulphide-Based Core/Shell

591

Nanocrystals with Surprisingly Long-Lived Emission. J. Am. Chem. Soc. 2011, 133, 1176–

592

1179.

593

(47) McDaniel, H.; Fuke, N.; Makarov, N. S.; Pietryga, J. M.; Klimov, V. I. An Integrated

594

Approach to Realizing High-Performance Liquid-Junction Quantum Dot Sensitized Solar


29


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

595 596

Page 30 of 32

Cells. Nat. Commun. 2013, 4, 2887. (48) Lin, Y. H.; Zhang, F.; Pan, D. C.; Li, H. X.; Lu, Y. F. Sunlight-Driven

597

Photodegradation

of

Organic

Pollutants

Catalyzed

598

Nanocomposites. J. Mater. Chem. 2012, 22, 8759–8763.

by

TiO2/(ZnS)x(CuInS2)1−x

599

(49) Kim, W.; Tachikawa, T.; Majima, T.; Choi, W. Photocatalysis of Dye-Sensitized TiO2

600

Nanoparticles with Thin Overcoat of Al2O3: Enhanced Activity for H2 Production and

601

Dechlorination of CCl4. J. Phys. Chem. C 2009, 113, 10603–10609.

602

(50) Ito, S.; Chen, P.; Comte, P.; Nazeeruddin, M. K.; Liska, P.; Péchy, P.; Grätzel, M.

603

Fabrication of Screen-Printing Pastes from TiO2 Powders for Dye-Sensitised Solar Cells.

604

Prog. Photovoltaics 2007, 15, 603–612.

605

(51) Xie, R. Y.; Zhang, L. P.; Xu, H.; Zhong, Y.; Sui, X. F.; Mao, Z. P. Fabrication of Z-

606

Scheme Photocatalyst Ag-AgBr@Bi20TiO32 and Its Visible-Light Photocatalytic Activity for

607

the Degradation of Isoproturon Herbicide. J. Mol. Catal. A: Chem. 2015, 406, 194–203.

608 609

(52) Kumar, K. V.; Porkodi, K.; Rocha, F. Langmuir-Hinshelwood Kinetics-a Theoretical Study. Catal. Commun. 2008, 9, 82–84.

610

(53) Ashworth, D. J.; Yates, S. R.; Van Wesenbeeck, I. J.; Stanghellini, M. Effect of Co-

611

Formulation of 1,3-Dichloropropene and Chloropicrin on Evaporative Emissions from Soil.

612

J. Agric. Food Chem. 2015, 63, 415–421.

613

(54) Tuazon, E. C.; Atkinson, R.; Winer, A. M.; Pitts Jr, J. N. A Study of the Atmospheric

614

Reactions of 1,3-Dichloropropene and Other Selected Organochlorine Compounds. Arch.

615

Environ. Contam. Toxicol. 1984, 13, 691–700.

616

(55) Guo, M. X.; Papiernik, S. K.; Zheng, W.; Yates, S. R. Effects of Environmental

617

Factors on 1,3-Dichloropropene Hydrolysis in Water and Soil. J. Environ. Qual. 2004, 33,


30

Page 31 of 32

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

618


612–618.

619

(56) Xuan, R. C.; Yates, S. R.; Ashworth, D. J.; Luo, L. F. Mitigating 1,3-

620

Dichloropropene, Chloropicrin, and Methyl Iodide Emissions from Fumigated Soil with

621

Reactive Film. Environ. Sci. Technol. 2012, 46, 6143–6149.

622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638


31


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

639

Page 32 of 32

TOC Graphic

640 641


32

ZnS:Al-TiO2 Film for Solar-Light-Driven

Recommend Documents