Photocatalytic Performances of Ag3PO4 Polypods ... - ACS Publications

Subscriber access provided by UNIV OF CONNECTICUT

Article

Facile synthesis of polypod-like Ag3PO4 particles and its application in pollutant degradation under natural indoor weak light irradiation Fei Teng, Zailun Liu, and An Zhang Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b00735 • Publication Date (Web): 25 Mar 2015 Downloaded from http://pubs.acs.org on April 1, 2015

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.

Environmental Science & Technology 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 28

Environmental Science & Technology

TOC 56x45mm (96 x 96 DPI)

ACS Paragon Plus Environment


1

Facile Synthesis of Polypod-like Ag3PO4 Particles and Its Application in

2

Pollutant Degradation under Natural Indoor Weak Light Irradiation

3 4

FEI TENG,* ZAILUN LIU, AN ZHANG

5

Jiangsu Engineering and Technology Research Center of Environmental Cleaning Materials

6

(ECM), Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control

7

(AEMPC), Jiangsu Joint Laboratory of Atmospheric Pollution Control (APC), Collaborative

8

Innovation Center of Atmospheric Environment and Equipment Technology (AEET), School of

9

Environmental Science and Engineering, Nanjing University of Information Science & Technology

10

，219 Ningliu Road, Nanjing 210044, China; Email: tfwd@ 163.com (F. Teng); Phone/Fax:

11

+86-25-58731090

12 13

Abstract

14

Today, it is still a big challenge for Ag3PO4 to be applied in practices mainly due to the low

15

stability resistant to light irradiation, although it is an efficient photocatalyst. Herein, Ag3PO4

16

polypods are prepared by a facile precipitation method, and we have also investigated the

17

degradation reaction of pollutants driven under indoor weak light. It is amazing that under indoor

18

weak light irradiation, rhodamine B (RhB) can be completely degraded by Ag3PO4 polypods after

19

36 h, but only 18% of RhB by N-doped TiO2 after 120 h; and that under indoor weak light

20

irradiation, the degradation rate (0.08099 h-1) of RhB by the polypods are 46 times higher than that

21

(0.00173 h-1) of N-doped TiO2. The high activity of Ag3PO4 polypods are mainly attributed to the ACS Paragon Plus Environment 1

Page 2 of 28

Page 3 of 28


22

three-dimensional branched nanostructure and high-energy {110} facets exposed. Surprisingly,

23

after three cycles, Ag3PO4 polypods show a higher stability under indoor weak light than under

24

visible light irradiation, while Ag3PO4 have been decomposed into Ag under visible light

25

irradiation.

26

Keywords: Nanostructures; Polypod; Crystal growth; Ag3PO4

27 28

Introduction

29

Semiconductor photocatalysis is one of the most promising ways to solve current energy and

30

environment problems (1-3). From energy-saving and environmental protection viewpoint, it is still

31

a big challenge for photocatalysis to utilize indoor natural weak light to cleaning indoor

32

environmental pollution, without needing an extra artificial optical condenser system. Up to now,

33

nevertheless, there is still short of efficient photocatalysts to meet this requirement. Recently, silver

34

orthophosphate (Ag3PO4) photocatalyst has attracted considerable interest, which has been

35

demonstrated to be an highly active photocatalyst for the degradation of organic pollutants and the

36

oxidation of water under visible light irradiation (4,5). Strikingly, Ag3PO4 photocatalyst is reported

37

to have a high quantum efficiency of 90% at the wavelengths longer than 420 nm (6). Thus, Ag3PO4

38

could be expected to be a promising catalyst driven by indoor natural weak light-driven for the

39

cleaning of environmental pollutants, but not dependent on artificial light source.

40

To date, many efforts have been devoted to improving their photoelectric and photocatalytic

41

properties, e.g., semiconductor coupling (6-9) and polymer composites (10). It is well known that

42

the photocatalytic and photo-electric properties of photocatalysts are greatly affected by the

43

morphology and the active facets exposed (5,11-16). For example, Ye et al. (5) have synthesized

44

Ag3PO4 rhombic dodecahedronsACS andParagon cubes, Plus and Environment they have demonstrated that the rhombic 2


Page 4 of 28

45

dodecahedrons with the active {110} facets exposed have a much higher activity than the cubes

46

with the exposed {100} facets for the degradation of rhodamine B (RhB). Moreover, they have

47

reported that Ag3PO4 concave trisoctahedrons with the high-index facets exposed have the

48

improved photocatalytic activity (14). Besides, Wang et al. (15) have reported that Ag3PO4 crystals

49

with the exposed {111} facets have the improved photocatalytic properties. Recently, our groups

50

have also reported that the Ag3PO4 tetrapods with the high-energy {110} facets exposed have a

51

higher photocatalytic activity than the irregular one (16). To the best of our knowledge,

52

nevertheless, only the limited micro/nanostructures have been reported for Ag3PO4 so far (5,11-16).

53

It still remains a big challenge to acquire Ag3PO4 with the other novel micro/nanostructures to

54

further improve its photocatalytic activity. The present question is that whether we can obtain the

55

other new nanostructures for Ag3PO4. Numerous studies (17) on Cu2O could provide us with the

56

positive answer, because both Ag3PO4 and Cu2O have the same bulk centre cubic (bcc) structures.

57

It is well known that various Cu2O micro/nanostructures have been achieved by the chemical

58

methods (17), for example, cubes, octahedrons, dodecahedrons, polyhedrons, nanowires,

59

nanocages, multipods, hierarchical and hollow structures, and so on. Recently, we have reported the

60

synthesis of the non-overlapped Ag3PO4 tetrapods (NOT), which are acquired under hydrothermal

61

conditions (16). The preparation is time-consuming and energy intensive. Therefore, we hold that it

62

is feasible to achieve novel Ag3PO4 nanostructures with greatly improved performances through an

63

innovative approach. On the other hand, it is still a big challenge for Ag3PO4 to be applied in

64

practices mainly due to the low stability resistant to light irradiation, although it is a highly efficient

65

photocatalyst.

66

Herein, the samples are synthesized by a simple precipitation reaction in a mixture containing

67

both tetrahydrofuran (THF) and water (W). Furthermore, we have mainly investigated the photo

68

degradation properties under indoor under weak light and visible light irradiation. It could be

ACS Paragon Plus Environment 3

Page 5 of 28


69

expected that a green and energy-saving cleaning approach could be developed using Ag3PO4 for

70

the cleaning of environmental pollutants under indoor natural weak light.

71

Experimental Section

72

Chemicals. All the chemicals are purchased from Shanghai Chemical Company, are of analytical

73

grade and used without further purification. The samples are synthesized by a simple precipitation

74

reaction, in which a mixture containing both tetrahydrofuran (THF) and water (W) is employed as

75

the solvent, phosphoric acid is used as the phosphorus source, and hexamethylenetetramine (HMT)

76

is added to adjust the pH value of the system.

77

Threefold-overlapped tetrapods (TOTs). Typically, 32 mL of deionized water was placed in a

78

breaker, and 8 mL THF was then added. 0.318 g Ag3NO4 was added into the mixed solvent above

79

under stirring. Then, 41 µL of 85 Wt.% H3PO4 was added drop wise to the solution above. Finally,

80

0.197 g of hexamethylenetetramine (HMT) was introduced into the above solution. The whole

81

process was carried out at room temperature under stirring. The color of the reaction mixture

82

changed from silvery white to golden yellow after injection of the HMT. After stirring for 5 min,

83

the yellow precipitation was collected, washed with deionized water for several times, and dried at

84

room temperature.

85

Three-dimensional towers (TDTs) and highly-branched tetrapods (HBTs). The same

86

procedures as above were taken, but the THF/W volumetric ratios were changed to 0:1 and 0.13:1

87

while the solvent volumes were kept same (40 mL) for TDT and HBT, respectively.

88

Non-overlapped tetrapods (NOTs). NOTs sample is synthesized as our previously reported

89

(16). Typically, 3 mmol of 85 Wt.% H3PO4 was dissolved in 80 mL of deionized water and 2.5

90

mmol of AgNO3 was added under stirring. Then, 37.5 mmol of urea were put into above solution.

91

The resulting precursor was transferred into a Teflon-lined stainless steel autoclave and maintained ACS Paragon Plus Environment 4


Page 6 of 28

92

at 80 oC for 24 h. After cooling to room temperature, the yellow precipitation was collected, washed

93

with deionized water several times, and dried overnight at 60 oC.

94

Bulk Ag3PO4. Bulk Ag3PO4 was synthesized as previously reported. Specifically, the

95

appropriate amounts of Na2HPO4 and AgNO3 powders were thoroughly ground until the initial

96

white changed to yellow. The sample is obtained by washing and drying as same above.

97

N-doped TiO2 (NTs). Nitrogen doping was conducted as described previously (18). Typically,

98

0.5 g of Degauss P25 TiO2 powders was suspended in ethanol (5 mL). Then, urea (1 g) dissolved in

99

a mixture solvent of both 2.5 mL ethanol and 0.5 mL H2O was added into the suspension above.

100

The mixture was stirred and heated to completely evaporate the solvent, followed by calcination at

101

400 oC for 4 h in air.

102

Characterization. The crystal structures of the samples were determined by X-ray powder

103

polycrystalline diffractometer (Rigaku D/max-2550VB), using graphite monochromatized CuKα

104

radiation (λ= 0.154 nm), operating at 40 kV and 50 mA. The XRD patterns were scanned in the

105

range of 20-80o (2θ) at a scanning rate of 5o min-1. The samples were characterized on a scanning

106

electron microscope (SEM, Hitachi SU-1510) with an acceleration voltage of 15 keV. The samples

107

were coated with 5-nm-thick gold layer before observations. The texture properties of the samples

108

were measured by nitrogen sorption isotherms. The surface areas the samples were calculated by

109

the Brunauer-Emmett-Teller (BET) method. UV-Vis diffuse reflectance spectra (UV-DRS) of the

110

samples were obtained using a UV-vis spectrophotometer (UV-2550, Shimadzu, Japan).

111

Photocatalytic degradation reaction. Photocatalytic activities of the samples were evaluated

112

by photocatalytic decomposition of rhodamine B (RhB). Typically, the suitable amounts of powders

113

were put into a solution of RhB (100 mL, 10 mg L-1), which was irradiated with a 300W Xe arc

114

lamp equipped with an ultraviolet cut off filter to provide visible light (λ ≥ 420 nm). Because the

115

BET areas of HBTs, TDTs, TOTs, NOTs and Plus NTsEnvironment are 4.9, 3.2, 3.3, 3.1, 32.2 m2 g-1, 64 mg of ACS Paragon 5

Page 7 of 28


116

HBTs, 97 mg of TDTs, 94 mg of TOTs, 100 mg of NOTs and 96 mg of NTs are used in the

117

degradation, respectively. According to reference (19), the aim is to keep their surface areas same.

118

The degradation reactions are also carried out under indoor weak light irradiation, while keeping the

119

other conditions constant.

120

Results and Discussion

121

Effect of THF/W volumetric ratio. Figure 1 shows the typical scanning electron microscopy

122

(SEM) images of the samples prepared at different THF/W volumetric ratios. When the volume

123

ratio of THF/W is increased, the morphology of Ag3PO4 changes from three-dimensional towers

124

(TDTs) to highly-branched tetrapods (HBTs), threefold-overlapped tetrapods (TOTs), irregular

125

Ag3PO4. At 0:1, Three-dimensional towers (TDT) form, whose bifurcated angle between the shaft

126

and secondary branch is about 109o28' (Figure 1a). A few of fractured HBT are found in TDT

127

sample. At 0.13:1, the formed HBT sample has four stretched shafts, which further grow through

128

the secondary branching growth (Figure 1b). From the SEM images, we can observe that the four

129

shafts of HBT stretch along four [111] directions (16) and they have further branched through a

130

secondary growth process.

131

angles are also 109°28′. Nevertheless, these TOTs are distinct from the previously reported

132

unoverlapped tetrapods (13,15,16). The threefold-overlapped branches are parallel to one another

133

and their twelve arms are 5-8 µm × 500 nm. The twelve branches are about 5-8 µm in length and

134

500 nm in diameter. At too higher THF/W ratios (0.5:1, 1:1 and 1:0), however, the irregular samples

135

are obtained (Figure S1, seeing electronic supporting information (ESI)). It is clear that the THF/W

136

ratio plays a key role in the growth of Ag3PO4.

Figure 1c shows the uniform TOTs formed at 0.25:1, whose bifurcated

137

Figure 2A shows X-ray diffraction (XRD) patterns of the samples prepared at THF/W =0/1,

138

0.13/1 and 0.25/1. All diffraction peaks can be well indexed to the bcc Ag3PO4 (JCPDS No.

139

06-0505) and no impurities phases are found, Plus confirming the formation of phase-pure Ag3PO4. ACS Paragon Environment 6


Page 8 of 28

140

Furthermore, we have calculated the intensity ratios of (222)/(110) and (222)/(200) peaks of TDTs

141

(Figure 2B). The peak intensity ratios of (222)/(110) and (222)/(200) are 2.86 and 2.83,

142

respectively; whereas 1.43 and 1.47 for the bulk one (Figure S2, seeing ESI). The results mean that

143

{111} crystal facets may preferentially grow. We have tried to perform the high-resolution

144

transmission electron microscopy to determine its growth direction. However, our attempt is

145

unsuccessful because the Ag3PO4 crystals are too large and unstable under irradiation with

146

high-energy electrons. Nevertheless, several researchers have demonstrated that the branches of

147

Ag3PO4 tetrapods grow preferentially along the [111] direction (13,15,16). Herein, we could only

148

assume that the crystals grow preferentially along the [111] direction. Moreover, Yu et al. have

149

revealed the correlation of the ZnO tetrapods with the growth orientation (20).

150

Effects of pH value and reaction temperature. First, the HMT-dependent experiments have been

151

performed to understand the role of HMT, while keeping the THF/W volumetric ratio at 0.25:1 at

152

30 oC.

153

values. Under strong acidic conditions, we hold that at pH values low than 0.21, phosphorous

154

source mainly exists as the molecular form of H3PO4. Thus, Ag3PO4 can not form without adding

155

HMT. We have found that with increasing the HMT amount, the pH value of the system increases

156

from 0.21 to 4.82 due to the hydrolysis of HMT (Table S1 of ESI). As a result, Ag3PO4 can form

157

only in a certain molar ratio range of HMT/Ag(I) (Figure 4). At 0.5:1 (HMT/Ag(I)), TOTs form, on

158

which a few nanoparticles attaches (Figure 4A). Although TOTs can also form at 0.75:1, almost no

159

any nanoparticles attach on their surfaces (Figure 4B). At 1:1, the pitted tetrahedrons form (Figure

160

4C); and at 1.25:1 and 1.5:1, the formed samples are poly-armed Ag3PO4 (Figure 4D). It is clear

161

that the HMT amount added has also a great influence on the morphology of Ag3PO4.

It is obviously observed from Figure 3 that H3PO4 has four existing forms at different pH

162

On base of the results above, we hold that it is the pH value that has changed the existing form

163

and distribution of phosphate ions, namely, more PO43- ions exist at high pH values (21). Hence the

164

nucleation and growth rates of Ag3PO4 greatly increase with the HMT amount added. As a result, ACS Paragon Plus Environment 7

Page 9 of 28


165

the branching growth of Ag3PO4 becomes pronounced, leading to the formation of poly-armed

166

sample.

167

Moreover, the temperature-dependent experiments are also performed (Figure 5). The results

168

show that the non-overlapped Ag3PO4 tetrapods (NOT) form at 15 and 20 oC, which have the wide

169

leaves (Figure 5(A,B)). At 30 and 45 oC, the threefold-overlapped Ag3PO4 tetrapods (TOTs) form

170

(Figure 5(C,D)). It seems that TOTs form from the NOTs with wide leaves. It is reasonable that the

171

wide leaves are metastable due to the high surface energy. At high temperatures, the wide leaves

172

may split and grow into the overlapped branches through the dissolution and re-crystallization

173

processes. At low temperatures, the tetrapods with wide leaves form; with increasing the

174

temperature, each wide leaf of tetrapods gradually transform into three independent branches, and

175

finally become overlapped tetrapods.

176

Generally, crystal formation is determined by the thermodynamics and kinetics of growth. Thus

177

various parameters, including intrinsic crystal structure, nature and concentration of precursor,

178

molecule adsorption, temperature, time, and the other moieties present in solution such as counter

179

ions and foreign metal ions, can greatly affect the final crystal (22). Obviously, these factors are

180

closely interdependent and cannot be considered independently. It seems that the crystals form

181

through the complicated process of dissolution – recrystallization – splitting growth. It is reasonable

182

that reaction temperature generally has a significant influence on the kinetics and thermodynamics

183

of nucleation and growth, leading to different morphologies.

184

Formation mechanism of Ag3PO4. On base of the results above, a plausible growth mechanism is

185

proposed as follows. First, THF, as an aprotic, polar solvent, can strongly solvate Ag(I) ions,

186

resulting in a slow diffusion rate of Ag(I) ion. Moreover, a large spatial obstacle will exist by the

187

solvating shells of THFs, which can reduce the collision reaction of both Ag(I) with PO43-. As a

188

result, the secondary branching growth of the shaft is refrained, as demonstrated by the fact that the

189

sub-branches of HBTs are shorter than those of TDTs (Figures 1C vs. 1A). The sub-branches of ACS Paragon Plus Environment 8


Page 10 of 28

190

TDT can fully grow without THF. Limited by small space close to the center of a tetrapod, the

191

fully-grown sub-branches of the four shafts will intersect and squeeze one another and finally the

192

shafts snap off, leading to the formation of TDTs with long sub-branches (Figure 1A).

193

We hold that the adsorption of THF on the surface of Ag3PO4 is another important factor. Since

194

the oxygen atom of THF molecule has two pairs of unshared electrons, THF molecules are easy to

195

adsorb on Ag(I)-enriched facets of Ag3PO4 nanocrystals through the coordination of Ag(I) with the

196

oxygen of THF (5). As a result, the growth rate of Ag(I) ion-enriched facets, i.e. {110}, may be

197

reduced greatly. With further increasing the THF amount, the growth of sub-branches is inhibited

198

significantly. As a result, the uniform TOTs form at 0.25:1 (Figures 1C and 4). At too high THF/W

199

ratios (0.5:1, 1:1, 1:0), AgNO3 can not completely dissolve in the system, leading to the formation

200

of irregular particles (Figure S1, seeing ESI). To conclude, THF plays a vital role in the growth of

201

Ag3PO4, which needs extensive research in future.

202

Degradation performance of Ag3PO4 polypods under visible light irradiation The

203

photocatalytic activities of the typical samples have been investigated using the degradation of

204

rhodamine B (RhB) as the probe reaction (Figure 6). Herein, N-doped TiO2 (NT) is also prepared to

205

compare with Ag3PO4. Because the BET areas of HBTs, TDTs, TOTs, NOTs and NTs are measured

206

to be 4.9, 3.2, 3.3, 3.1, 32.2 m2 g-1, their amounts used in the degradation of RhB are 64, 97, 94, 100

207

and 9.6 mg, respectively. The aim is to keep their surface areas same according to the reference (19).

208

Moreover, we have measured the absorption spectra of RhB with irradiation time. It is obvious that

209

RhB has been destroyed, characterized by the disappearance of the maximum absorbance of RhB at

210

553 nm (Figure 7). The apparent reaction rate constants are 1.1335, 0.6936, 0.4008, 0.2199 and

211

0.0078 min-1 for HBT, TDT, TOT, NOT and NT, respectively (Figure 6B). The apparent rate

212

constants of HBT, TDT, TOT and NOT are 144.3, 87.9, 50.4 and 27.2 times higher than that of NT,

213

respectively, indicating the high photocatalytic activity of Ag3PO4 (4). For the Ag3PO4 samples,

214

their activity orders are HBT > TDT > TOT > NOT. On one hand, the percentages of the {110}


Page 11 of 28


215

facets exposed are calculated to be 99%, 97%, 90% and 87% for HBT, TDT, TOT and NOT,

216

respectively. Taking their same surface areas into account, their different activities can be mainly

217

attributed to the active {110} facets exposed. Many researchers (4,5,13,14,16) have reported that the

218

surface energies of {110} and {100} facets are 1.31 and 1.12 J/m2; respectively; and further

219

demonstrated that the high-energy {110} facets have a higher photocatalytic activity than the {100}

220

and {111} facets for the degradation of RhB. On the other hand, the ultraviolet-visible diffuse

221

reflectance spectra (UV-DRS) reveal that three Ag3PO4 samples can absorb the visible light with a

222

wavelength shorter than 510 nm, which have the same absorption edge, indicating their same band

223

gap energy (Figure 8). However, the absorbencies of both polypods are about 2.5 times higher than

224

the bulk, which may favor to improve the photo activity. The high absorbencies of the former two

225

samples can be attributed to their three-dimensional microstructures, which favors for the

226

repeatedly reflections and absorptions of irradiation light (the inset of Figure 8) (17,23).

227

Degradation performance of Ag3PO4 polypods under natural indoor weak light We have

228

investigated the indoor weak light-driven degradation performances of Ag3PO4 polypod structures

229

(Figure 9). It is amazing that under indoor weak light irradiation, 100% RhB has been degraded

230

after 36 h, while only 18% can be degraded by N-doped TiO2 after 120 h (Figure 9a). The apparent

231

reaction kinetic constant (0.08099 h-1) of Ag3PO4 polypods is 46.8 times higher than that (0.00173

232

h-1) of N-doped TiO2 (Figure 9b). Besides, the complete mineralization of RhB dye by Ag3PO4 has

233

been confirmed by using the organic carbon (TOC) test, infrared spectroscopy (IR), UV-Vis

234

absorption spectra and mass spectrum (MS) (Figures S3-S6, seeing ESI). Moreover, the cycle

235

stability of Ag3PO4 polypod structures have been investigated (Figure 10). After three cycles under

236

indoor weak light irradiation, Ag3PO4 polypods nearly maintain activity within 36 h (Figure 10a).

237

Under visible light irradiation, however, the degradation ratios of RhB by Ag3PO4 polypods are

238

63% and 34% for the second and third cycles, respectively (Figure 10b). XRD patterns (Figure 10c)

239

show that after three cycles, only fairly small amounts of Ag metal have produced under weak light ACS Paragon Plus Environment 10


Page 12 of 28

240

irradiation; while more Ag3PO4 have decomposed into Ag under visible light. Also we observed

241

with SEM that under visible light irradiation, the polypods have broken into fractures (Figure 10d);

242

while the polypods are still maintained (not showing). Summarily, Ag3PO4 polypods show a higher

243

cycling stability under natural weak light irradiation than under visible light irradiation.

244

It is important that Ag3PO4 photocatalyst is discovered with good photocatalytic activity under

245

indoor natural weak sunlight. Compared with conventional photocatalysis, the degradation reaction

246

is carried out under indoor natural weak sunlight that does not needs extra optical system. It is a

247

green and energy-saving technology to utilize Ag3PO4 as catalyst for the degradation of

248

environmental pollutants driven by indoor natural weak light-driven, not depending on artificial

249

light source. It could be expected that Ag3PO4 polypod structures can be conveniently applied in

250

indoor air cleaning under weak light irradiation.

251

The Ag3PO4 polypod structures are discovered with an efficient degradation activity under

252

indoor weak light without needing an extra, complicate artificial optical condenser system. The

253

efficient Ag3PO4 polypods could be promising to be conveniently applied in indoor air cleaning.

254

255

Acknowledgements

256

This work is financially supported by National Science Foundation of China (21377060,

257

21103049), the Project Funded by the Science and Technology Infrastructure Program of Jiangsu

258

(BM201380277, 2013139), Jiangsu Science Foundation of China (BK2012862), Six Talent Climax

259

Foundation of Jiangsu (20100292), Jiangsu Province of Academic Scientific Research

260

Industrialization Projects (JHB2012-10, JH10-17), the Key Project of Environmental Protection

261

Program of Jiangsu (2013016, 2012028), A Project Funded by the Priority Academic Program ACS Paragon Plus Environment 11

Page 13 of 28


262

Development of Jiangsu Higher Education Institutions (PAPD) sponsored by SRF for ROCS, SEM

263

(2013S002) and “333” Outstanding Youth Scientist Foundation of Jiangsu (2011015).

264

Electronic Supporting Information (ESI)

265

This supporting material is available free of charge via the internet at http://www.acs.org

266

267

References

268

(1) Fujishima, H.; Honda, K. Electrochemical photolysis of water at a semiconductor electrode.

269

Nature 1972, 238, 37-39.

270

(2) Bi, Y. P.; Hu, H. Y.; Ouyang, S.; Jiao, Z. B.; Lu, G. X.; Ye, J. H. Selective growth of Ag3PO4

271

submicro-cubes on Ag nanowires to fabricate necklace-like heterostructures for photocatalytic

272

applications. J. Mater. Chem. 2012, 22, 14847-14850.

273 274

(3) Son, J. S.; Yu, J.; Kwon, S.; Lee, J.; Joo, J.; Hyeon, T. Colloidal synthesis of ultrathin two-dimensional semiconductor nanocrystals. Adv. Mater. 2011, 23, 3214-3219.

275

(4) Yi, Z. G.; Ye, J. H.; Kikugawa, N.; Kako, T.; Ouyang, S. X.; Williams, H. S.; Yang, H.; Cao, J.

276

Y.; Luo, W. J.; Li, Z. S.; Liu, Y.; Withers, R. L. An orthophosphate semiconductor with

277

photooxidation properties under visible-light irradiation. Nat. Mater. 2010, 9, 559-564.

278

(5) Bi, Y. P.; Ouyang, S. X.; Umezawa, N.; Cao, J. Y.; Ye, J. H. Facet effect of single-crystalline

279

Ag3PO4 sub-microcrystals on photocatalytic properties. J. Am. Chem. Soc. 2011, 133,

280

6490-6492.



Page 14 of 28

281

(6) Bi, Y.; Ouyang, S.; Cao, J.; Ye, J. Facile synthesis of rhombic dodecahedral AgX/Ag3PO4 (X =

282

Cl, Br, I) heterocrystals with enhanced photocatalytic properties and stabilities. Phys. Chem.

283

Chem. Phys. 2011, 13, 10071-10075.

284

(7) Zhang, L.; Zhang, H.; Huang, H.; Liu, Y.; Kang, Z. Ag3PO4/SnO2 semiconductor

285

nanocomposites with enhanced photocatalytic activity and stability. New J. Chem. 2012, 36,

286

1041-1044.

287

(8) Yao, W. F.; Zhang, B.; Huang, C. P.; Ma, C.; Song, X. L.; Xu, Q. J. Synthesis and

288

characterization of high efficiency and stable Ag3PO4/TiO2 visible light photocatalyst for the

289

degradation of methylene blue and rhodamine B solutions. J. Mater. Chem. 2012, 22,

290

4050–4055

291

(9) Li, G. P.; Mao, L. Magnetically separable Fe3O4–Ag3PO4 sub-micrometre composite: facile

292

synthesis, high visible light-driven photocatalytic efficiency, and good recyclability. RSC Adv.

293

2012, 2, 5108-5011.

294

(10) Zhang, H.; Huang, H.; Ming, H.; Li, H.; Zhang, L.; Liu, Y.; Kang, Z. Carbon quantum

295

dots/Ag3PO4 complex photocatalysts with enhanced photocatalytic activity and stability under

296

visible light. J. Mater. Chem. 2012, 22, 10501-10506.

297

(11) Dinh, C. T.; Nguyen, T. D.; Kleitz, F.; Do, T.-O. Large-scale synthesis of uniform silver

298

orthophosphate colloidal nanocrystals exhibiting high visible light photocatalytic activity.

299

ChemComm. 2011, 47, 7797-7799.

300

(12) Liang, Q. H.; Ma, W. J.; Shi, Y.; Li, Z.; Yang, X. M. Hierarchical Ag3PO4 porous microcubes

301

with enhanced photocatalytic properties synthesized with the assistance of trisodium citrate.

302

CrystEngComm. 2012, 14, 2966-2973. ACS Paragon Plus Environment 13

Page 15 of 28


303

(13) Wang, H.; He, L.; Wang, L. H.; Hu, P. F.; Guo, L.; Han, X. D.; Li, J. H. Facile synthesis of

304

Ag3PO4 tetrapod microcrystals with an increased percentage of exposed {110} facets and

305

highly efficient photocatalytic properties. CrystEngComm. 2012, 14, 8342-8344.

306

(14) Jiao, Z. B.; Zhang, Y.; Yu, H. C.; Lu, G. X.; Ye, J. H.; Bi, Y. P. Concave trisoctahedral Ag3PO4

307

microcrystals with high-index facets and enhanced photocatalytic properties. Chem. Commun.

308

2013, 49, 636-638.

309

(15) Wang, H.; Bai, Y. S.; Yang, J. T.; Lang, X. F.; Li, J. H.; Guo L. A facile way to rejuvenate

310

Ag3PO4 as a recyclable highly efficient photocatalyst. Chem. Eur. J. 2012, 18, 5524-5529.

311

(16) Wang, J.; Teng, F.; Chen, M. D.; Xu, J. J.; Song, Y. Q.; Zhou X. L. Facile synthesis of novel

312

Ag3PO4 tetrapods and the {110} facets-dominated photocatalytic activity. CrystEngComm.

313

2013, 15, 39-42.

314 315 316 317 318 319

(17) Sun, S. D.; Song, X. P.; Kong. C. C.; Yang, Z. M. Selective-etching growth of urchin-like Cu2O architectures. CrystEngComm. 2011, 13, 6616-6620. (18) Mitoraj, D.; Kisch, H. The nature of nitrogen-modified titanium dioxide photocatalysts active in visible light. Angew. Chem., Int. Ed. 2008, 47, 9975-9978. (19) Xu, L.; Jiang, L.-P.; Zhu, J.-J. Sonochemical synthesis and photocatalysis of porous Cu2O nanospheres with controllable structures. Nanotechnol. 2009, 20, 045605-045610.

320

(20) Yu, W. D.; Li, X. M.; Gao, X.D. Catalytic synthesis and structural characteristics of

321

high-quality tetrapod-like ZnO nanocrystals by a modified vapor transport process. Cryst.

322

Growth & Des. 2005, 5, 151-155.

323 324

(21) M.Z. Cai, Y.P. Hang, Q. Yu, Anal. Chem. South China University of Technology, Beijing, Chem. Ind. Press, 2009. ACS Paragon Plus Environment 14


325 326 327 328

Page 16 of 28

(22) L. M. Liz-Marzan, Increasing complexity while maintaining a high degree of symmetry in nanocrystal growth, Angew. Chem. Int. Ed. 2015, 54, 3860-3861 (23) Li, G. ; Zhang, D. ; Yu, J. A new visible-light photocatalyst: CdS quantum dots embedded mesoporous TiO2. Environ. Sci. Technol. 2009, 43, 7079-7085.


Page 17 of 28


329

Title list of Figures and Tables

330

FIGURE 1 Scanning electron microscopy (SEM) macrographs of the samples

331

synthesized at different volumetric ratios of tetrahydrofuran (THF) to water (W): (a)

332

0:1, Three-dimensional towers (TDT); (b) 0.13:1, Highly-branched tetrapods (HBT);

333

(c) 0.25:1, Threefold-overlapped tetrapods (TOT); Scale bar = 5 µm; Reaction

334

temperature: 30 oC; Hexamethylenetetramine (HMT)/Ag(I) = 0.75 (molar ratio); the

335

arrow direction is along [111]

336

FIGURE 2 (A) X-ray diffraction (XRD) patterns of the samples and (B) Intensity

337

ratios of (222)/(110) and (222)/(200) peaks of (a) TDT and (b) bulk Ag3PO4

338

FIGURE 3 Distribution diagram of various existing forms of H3PO4 at different pH

339

values (the dotted line marked by arrow, indicating the pH value for our system)

340

FIGURE 4 SEM images of the samples synthesized at different molar ratios of

341

HMT/Ag(I): (A) 0.5:1; (B) 0.75:1; (C) 1:1 and 1.25:1; (D) 1.5:1. Reaction

342

temperature: 30 oC; THF/W = 0.25:1

343

FIGURE 5 SEM images of the samples synthesized at different reaction

344

temperatures: (A) 15 oC; (B) 20 oC; (C) 30 oC; (D) 45 oC. HMT/Ag(I) = 0.75/1;

345

THF/W = 0.25/1

346

FIGURE 6 The degradation curves (A) and apparent reaction kinetic constants (B)

347

of the samples for the degradation of rhodamine B under visible light irradiation (λ >

348

420 nm): HBT (64 mg); TDT (97 mg); TOT (94 mg); Non-overlapped tetrapods

349

(NOT, 100 mg) and N-doped TiO2 (NT, 9.6 mg)

16



350

FIGURE 7 The absorption spectra of RhB at different irradiation times

351

FIGURE 8 UV-vis diffuse reflectance spectra (UV-DRS) of the Ag3PO4 samples

352

FIGURE 9 Degradation and reaction kinetic curves of rhodamine B over Ag3PO4

353

polypod structures and N-doped TiO2 under indoor weak light

354

FIGURE 10 Cycle stability of Ag3PO4 polypod structures: (a) under indoor natural

355

dim light; (b) under visible light irradiations; (c) XRD patterns; (d) SEM images

356

after reaction under visible light irradiation

17


Page 18 of 28

Page 19 of 28


357 358 359

FIGURE 1

360 361 362 9µm

363 364 365

(a)

(c)

(b)

366 367

18



Page 20 of 28

368 369 FIGURE 2

210

320 321

400 411 420 421 332

(a)

310

222

211 200

110

Intensity (a.u.)

(A)

220

370

(b) (c)

20

30

40 50 60 2Theta (Degree)

70

80

371

3.0

Intensity ratio

2.5

(B)

TDT Bulk 2.86

2.83

2.0 1.5 1.0

1.47

1.43

0.5 0.0 (222)/(110)

(222)/(200)

372


Page 21 of 28


373 374

FIGURE 3

375 376 377 378 379 380 381 382 383 384 385 386



Page 22 of 28

387 388

FIGURE 4

389 390 391 392

5 µm

393 394 395 396

20 µm

(A)

3 µm

(B)

397 398 399

10 µm

5 µm

400 401 402 403

20 µm

(C)

30 µm

404 405 406


(D)

Page 23 of 28


407 408

FIGURE 5

409 410

A

B

C

D

411 412 413 414 415 416 417 418 419 420 421 422



Page 24 of 28

423 FIGURE 6

1.0

5

0.8

4

0.6

ln(C0/C)

C/C0

424

HBT TDT TOT NOT NT

0.4 0.2

3

-1

HBT: ka=1.1335 min

2

TDT: ka=0.6936 min

-1

TOT: ka=0.4008 min

-1 -1

NOT: ka=0.2199 min

1

-1

NT: ka=0.0078 min

0.0 0

2

4

6 8 10 (A) t (min)

12

14

0

16

0

4

425 426


8

12 16 (B) t (min)

20

24

Page 25 of 28


427 428

FIGURE 7

TDT Absorbance

Absorbance

HBT

0min 1min 2min 3min

300

400

500

600

700

0 min 2 min 3 min 4 min

300

800

400

500

600

700

800

700

800

700

800

Light length /nm

Length / nm

429

NOT Absorbance

Absorbance

TOT

0 2min 4min 6min 10min

300

400

500

600

700

0 2min 4min 6min 10min 15min

300

800

400

500

600

Light length /nm

Light length (nm)

430

Blank Absorbance

Absorbance

NT

0min 10min 15min 20min

300

400

500

600

700

0mim 20mim 40mim 60mim 80mim 300

800

400

500

600

Light length /nm

Light length (nm)

431 432



433 434

FIGURE 8

Absorbance (a.u.)

435

HBT TOT B ulk

300

400

500

600

700

W avelength (nm )

436 437


800

Page 26 of 28

Page 27 of 28


438 439

FIGURE 9

3.5

1.0 0.8 ln(C0/C)

2.5

0.6 C/C0

(b)

3.0

0.4 0.2

0

1.5 HBT:

1.0

ka=0.08099 h

-1 -1

N-TiO2: ka=0.00173 h

0.5

HBT NT

0.0 (a)

2.0

0.0

15 30 45 60 75 90 105 120

0

15 30 45 60 75 90 105 120

t /h

t /h

440 441



Page 28 of 28

442 443

FIGURE 10

444 445

1.0

1.0

1st cycle 2nd cycle 0.8

0.8

0.6

0.6

C/C0

C/C0

446

1st cycle

3rd cycle

0.4

0.4

0.2

0.2

447 448

0.0

449

0

15 30 45 60 75 90 105 120 Reaction time /h

(c)

Under indoor weak light Under visible light irradiation

0.0

(b) 0 1 2 3 4 5 6 7 8 9 10 11 12 Time /min

(d)

Intensity /a.u.

450

(a)

2nd cycle 3rd cycle

451 452

10

20

30

40

50

60

70

80

2Theta /degree

453 454

27


Photocatalytic Performances of Ag3PO4 Polypods ... - ACS Publications

Recommend Documents