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Article

Facile synthesis of polypod-like Ag3PO4 particles and its applicationin pollutant degradation under natural indoor weak light irradiation

Fei Teng, Zailun Liu, and An ZhangEnviron. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b00735 • Publication Date (Web): 25 Mar 2015

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Environmental Science & Technology

1

Facile Synthesis of Polypod-like Ag3PO4 Particles and Its Application in 1

Pollutant Degradation under Natural Indoor Weak Light Irradiation 2

3

FEI TENG,* ZAILUN LIU, AN ZHANG 4

Jiangsu Engineering and Technology Research Center of Environmental Cleaning Materials 5

(ECM), Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control 6

(AEMPC), Jiangsu Joint Laboratory of Atmospheric Pollution Control (APC), Collaborative 7

Innovation Center of Atmospheric Environment and Equipment Technology (AEET), School of 8

Environmental Science and Engineering, Nanjing University of Information Science & Technology9

，219 Ningliu Road, Nanjing 210044, China; Email: tfwd@ 163.com (F. Teng); Phone/Fax: 10

+86-25-58731090 11

12

Abstract 13

Today, it is still a big challenge for Ag3PO4 to be applied in practices mainly due to the low 14

stability resistant to light irradiation, although it is an efficient photocatalyst. Herein, Ag3PO4 15

polypods are prepared by a facile precipitation method, and we have also investigated the 16

degradation reaction of pollutants driven under indoor weak light. It is amazing that under indoor 17

weak light irradiation, rhodamine B (RhB) can be completely degraded by Ag3PO4 polypods after 18

36 h, but only 18% of RhB by N-doped TiO2 after 120 h; and that under indoor weak light 19

irradiation, the degradation rate (0.08099 h-1

) of RhB by the polypods are 46 times higher than that 20

(0.00173 h-1

) of N-doped TiO2. The high activity of Ag3PO4 polypods are mainly attributed to the 21

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three-dimensional branched nanostructure and high-energy {110} facets exposed. Surprisingly, 22

after three cycles, Ag3PO4 polypods show a higher stability under indoor weak light than under 23

visible light irradiation, while Ag3PO4 have been decomposed into Ag under visible light 24

irradiation. 25

Keywords: Nanostructures; Polypod; Crystal growth; Ag3PO4 26

27

Introduction 28

Semiconductor photocatalysis is one of the most promising ways to solve current energy and 29

environment problems (1-3). From energy-saving and environmental protection viewpoint, it is still 30

a big challenge for photocatalysis to utilize indoor natural weak light to cleaning indoor 31

environmental pollution, without needing an extra artificial optical condenser system. Up to now, 32

nevertheless, there is still short of efficient photocatalysts to meet this requirement. Recently, silver 33

orthophosphate (Ag3PO4) photocatalyst has attracted considerable interest, which has been 34

demonstrated to be an highly active photocatalyst for the degradation of organic pollutants and the 35

oxidation of water under visible light irradiation (4,5). Strikingly, Ag3PO4 photocatalyst is reported 36

to have a high quantum efficiency of 90% at the wavelengths longer than 420 nm (6). Thus, Ag3PO4 37

could be expected to be a promising catalyst driven by indoor natural weak light-driven for the 38

cleaning of environmental pollutants, but not dependent on artificial light source. 39

To date, many efforts have been devoted to improving their photoelectric and photocatalytic 40

properties, e.g., semiconductor coupling (6-9) and polymer composites (10). It is well known that 41

the photocatalytic and photo-electric properties of photocatalysts are greatly affected by the 42

morphology and the active facets exposed (5,11-16). For example, Ye et al. (5) have synthesized 43

Ag3PO4 rhombic dodecahedrons and cubes, and they have demonstrated that the rhombic 44

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dodecahedrons with the active {110} facets exposed have a much higher activity than the cubes 45

with the exposed {100} facets for the degradation of rhodamine B (RhB). Moreover, they have 46

reported that Ag3PO4 concave trisoctahedrons with the high-index facets exposed have the 47

improved photocatalytic activity (14). Besides, Wang et al. (15) have reported that Ag3PO4 crystals 48

with the exposed {111} facets have the improved photocatalytic properties. Recently, our groups 49

have also reported that the Ag3PO4 tetrapods with the high-energy {110} facets exposed have a 50

higher photocatalytic activity than the irregular one (16). To the best of our knowledge, 51

nevertheless, only the limited micro/nanostructures have been reported for Ag3PO4 so far (5,11-16). 52

It still remains a big challenge to acquire Ag3PO4 with the other novel micro/nanostructures to 53

further improve its photocatalytic activity. The present question is that whether we can obtain the 54

other new nanostructures for Ag3PO4. Numerous studies (17) on Cu2O could provide us with the 55

positive answer, because both Ag3PO4 and Cu2O have the same bulk centre cubic (bcc) structures. 56

It is well known that various Cu2O micro/nanostructures have been achieved by the chemical 57

methods (17), for example, cubes, octahedrons, dodecahedrons, polyhedrons, nanowires, 58

nanocages, multipods, hierarchical and hollow structures, and so on. Recently, we have reported the 59

synthesis of the non-overlapped Ag3PO4 tetrapods (NOT), which are acquired under hydrothermal 60

conditions (16). The preparation is time-consuming and energy intensive. Therefore, we hold that it 61

is feasible to achieve novel Ag3PO4 nanostructures with greatly improved performances through an 62

innovative approach. On the other hand, it is still a big challenge for Ag3PO4 to be applied in 63

practices mainly due to the low stability resistant to light irradiation, although it is a highly efficient 64

photocatalyst. 65

Herein, the samples are synthesized by a simple precipitation reaction in a mixture containing 66

both tetrahydrofuran (THF) and water (W). Furthermore, we have mainly investigated the photo 67

degradation properties under indoor under weak light and visible light irradiation. It could be 68

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expected that a green and energy-saving cleaning approach could be developed using Ag3PO4 for 69

the cleaning of environmental pollutants under indoor natural weak light. 70

Experimental Section 71

Chemicals. All the chemicals are purchased from Shanghai Chemical Company, are of analytical 72

grade and used without further purification. The samples are synthesized by a simple precipitation 73

reaction, in which a mixture containing both tetrahydrofuran (THF) and water (W) is employed as 74

the solvent, phosphoric acid is used as the phosphorus source, and hexamethylenetetramine (HMT) 75

is added to adjust the pH value of the system. 76

Threefold-overlapped tetrapods (TOTs). Typically, 32 mL of deionized water was placed in a 77

breaker, and 8 mL THF was then added. 0.318 g Ag3NO4 was added into the mixed solvent above 78

under stirring. Then, 41 µL of 85 Wt.% H3PO4 was added drop wise to the solution above. Finally, 79

0.197 g of hexamethylenetetramine (HMT) was introduced into the above solution. The whole 80

process was carried out at room temperature under stirring. The color of the reaction mixture 81

changed from silvery white to golden yellow after injection of the HMT. After stirring for 5 min, 82

the yellow precipitation was collected, washed with deionized water for several times, and dried at 83

room temperature. 84

Three-dimensional towers (TDTs) and highly-branched tetrapods (HBTs). The same 85

procedures as above were taken, but the THF/W volumetric ratios were changed to 0:1 and 0.13:1 86

while the solvent volumes were kept same (40 mL) for TDT and HBT, respectively. 87

Non-overlapped tetrapods (NOTs). NOTs sample is synthesized as our previously reported 88

(16). Typically, 3 mmol of 85 Wt.% H3PO4 was dissolved in 80 mL of deionized water and 2.5 89

mmol of AgNO3 was added under stirring. Then, 37.5 mmol of urea were put into above solution. 90

The resulting precursor was transferred into a Teflon-lined stainless steel autoclave and maintained 91

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at 80 oC for 24 h. After cooling to room temperature, the yellow precipitation was collected, washed 92

with deionized water several times, and dried overnight at 60 oC. 93

Bulk Ag3PO4. Bulk Ag3PO4 was synthesized as previously reported. Specifically, the 94

appropriate amounts of Na2HPO4 and AgNO3 powders were thoroughly ground until the initial 95

white changed to yellow. The sample is obtained by washing and drying as same above. 96

N-doped TiO2 (NTs). Nitrogen doping was conducted as described previously (18). Typically, 97

0.5 g of Degauss P25 TiO2 powders was suspended in ethanol (5 mL). Then, urea (1 g) dissolved in 98

a mixture solvent of both 2.5 mL ethanol and 0.5 mL H2O was added into the suspension above. 99

The mixture was stirred and heated to completely evaporate the solvent, followed by calcination at 100

400 oC for 4 h in air. 101

Characterization. The crystal structures of the samples were determined by X-ray powder 102

polycrystalline diffractometer (Rigaku D/max-2550VB), using graphite monochromatized CuKα 103

radiation (λ= 0.154 nm), operating at 40 kV and 50 mA. The XRD patterns were scanned in the 104

range of 20-80o (2θ) at a scanning rate of 5

o min

-1. The samples were characterized on a scanning 105

electron microscope (SEM, Hitachi SU-1510) with an acceleration voltage of 15 keV. The samples 106

were coated with 5-nm-thick gold layer before observations. The texture properties of the samples 107

were measured by nitrogen sorption isotherms. The surface areas the samples were calculated by 108

the Brunauer-Emmett-Teller (BET) method. UV-Vis diffuse reflectance spectra (UV-DRS) of the 109

samples were obtained using a UV-vis spectrophotometer (UV-2550, Shimadzu, Japan). 110

Photocatalytic degradation reaction. Photocatalytic activities of the samples were evaluated 111

by photocatalytic decomposition of rhodamine B (RhB). Typically, the suitable amounts of powders 112

were put into a solution of RhB (100 mL, 10 mg L-1

), which was irradiated with a 300W Xe arc 113

lamp equipped with an ultraviolet cut off filter to provide visible light (λ ≥ 420 nm). Because the 114

BET areas of HBTs, TDTs, TOTs, NOTs and NTs are 4.9, 3.2, 3.3, 3.1, 32.2 m2 g

-1, 64 mg of 115

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HBTs, 97 mg of TDTs, 94 mg of TOTs, 100 mg of NOTs and 96 mg of NTs are used in the 116

degradation, respectively. According to reference (19), the aim is to keep their surface areas same. 117

The degradation reactions are also carried out under indoor weak light irradiation, while keeping the 118

other conditions constant. 119

Results and Discussion 120

Effect of THF/W volumetric ratio. Figure 1 shows the typical scanning electron microscopy 121

(SEM) images of the samples prepared at different THF/W volumetric ratios. When the volume 122

ratio of THF/W is increased, the morphology of Ag3PO4 changes from three-dimensional towers 123

(TDTs) to highly-branched tetrapods (HBTs), threefold-overlapped tetrapods (TOTs), irregular 124

Ag3PO4. At 0:1, Three-dimensional towers (TDT) form, whose bifurcated angle between the shaft 125

and secondary branch is about 109o28' (Figure 1a). A few of fractured HBT are found in TDT 126

sample. At 0.13:1, the formed HBT sample has four stretched shafts, which further grow through 127

the secondary branching growth (Figure 1b). From the SEM images, we can observe that the four 128

shafts of HBT stretch along four [111] directions (16) and they have further branched through a 129

secondary growth process. Figure 1c shows the uniform TOTs formed at 0.25:1, whose bifurcated 130

angles are also 109°28′. Nevertheless, these TOTs are distinct from the previously reported 131

unoverlapped tetrapods (13,15,16). The threefold-overlapped branches are parallel to one another 132

and their twelve arms are 5-8 µm × 500 nm. The twelve branches are about 5-8 µm in length and 133

500 nm in diameter. At too higher THF/W ratios (0.5:1, 1:1 and 1:0), however, the irregular samples 134

are obtained (Figure S1, seeing electronic supporting information (ESI)). It is clear that the THF/W 135

ratio plays a key role in the growth of Ag3PO4. 136

Figure 2A shows X-ray diffraction (XRD) patterns of the samples prepared at THF/W =0/1, 137

0.13/1 and 0.25/1. All diffraction peaks can be well indexed to the bcc Ag3PO4 (JCPDS No. 138

06-0505) and no impurities phases are found, confirming the formation of phase-pure Ag3PO4. 139

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Furthermore, we have calculated the intensity ratios of (222)/(110) and (222)/(200) peaks of TDTs 140

(Figure 2B). The peak intensity ratios of (222)/(110) and (222)/(200) are 2.86 and 2.83, 141

respectively; whereas 1.43 and 1.47 for the bulk one (Figure S2, seeing ESI). The results mean that 142

{111} crystal facets may preferentially grow. We have tried to perform the high-resolution 143

transmission electron microscopy to determine its growth direction. However, our attempt is 144

unsuccessful because the Ag3PO4 crystals are too large and unstable under irradiation with 145

high-energy electrons. Nevertheless, several researchers have demonstrated that the branches of 146

Ag3PO4 tetrapods grow preferentially along the [111] direction (13,15,16). Herein, we could only 147

assume that the crystals grow preferentially along the [111] direction. Moreover, Yu et al. have 148

revealed the correlation of the ZnO tetrapods with the growth orientation (20). 149

Effects of pH value and reaction temperature. First, the HMT-dependent experiments have been 150

performed to understand the role of HMT, while keeping the THF/W volumetric ratio at 0.25:1 at 151

30 oC. It is obviously observed from Figure 3 that H3PO4 has four existing forms at different pH 152

values. Under strong acidic conditions, we hold that at pH values low than 0.21, phosphorous 153

source mainly exists as the molecular form of H3PO4. Thus, Ag3PO4 can not form without adding 154

HMT. We have found that with increasing the HMT amount, the pH value of the system increases 155

from 0.21 to 4.82 due to the hydrolysis of HMT (Table S1 of ESI). As a result, Ag3PO4 can form 156

only in a certain molar ratio range of HMT/Ag(I) (Figure 4). At 0.5:1 (HMT/Ag(I)), TOTs form, on 157

which a few nanoparticles attaches (Figure 4A). Although TOTs can also form at 0.75:1, almost no 158

any nanoparticles attach on their surfaces (Figure 4B). At 1:1, the pitted tetrahedrons form (Figure 159

4C); and at 1.25:1 and 1.5:1, the formed samples are poly-armed Ag3PO4 (Figure 4D). It is clear 160

that the HMT amount added has also a great influence on the morphology of Ag3PO4. 161

On base of the results above, we hold that it is the pH value that has changed the existing form 162

and distribution of phosphate ions, namely, more PO43-

ions exist at high pH values (21). Hence the 163

nucleation and growth rates of Ag3PO4 greatly increase with the HMT amount added. As a result, 164

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the branching growth of Ag3PO4 becomes pronounced, leading to the formation of poly-armed 165

sample. 166

Moreover, the temperature-dependent experiments are also performed (Figure 5). The results 167

show that the non-overlapped Ag3PO4 tetrapods (NOT) form at 15 and 20 oC, which have the wide 168

leaves (Figure 5(A,B)). At 30 and 45 oC, the threefold-overlapped Ag3PO4 tetrapods (TOTs) form 169

(Figure 5(C,D)). It seems that TOTs form from the NOTs with wide leaves. It is reasonable that the 170

wide leaves are metastable due to the high surface energy. At high temperatures, the wide leaves 171

may split and grow into the overlapped branches through the dissolution and re-crystallization 172

processes. At low temperatures, the tetrapods with wide leaves form; with increasing the 173

temperature, each wide leaf of tetrapods gradually transform into three independent branches, and 174

finally become overlapped tetrapods. 175

Generally, crystal formation is determined by the thermodynamics and kinetics of growth. Thus 176

various parameters, including intrinsic crystal structure, nature and concentration of precursor, 177

molecule adsorption, temperature, time, and the other moieties present in solution such as counter 178

ions and foreign metal ions, can greatly affect the final crystal (22). Obviously, these factors are 179

closely interdependent and cannot be considered independently. It seems that the crystals form 180

through the complicated process of dissolution – recrystallization – splitting growth. It is reasonable 181

that reaction temperature generally has a significant influence on the kinetics and thermodynamics 182

of nucleation and growth, leading to different morphologies. 183

Formation mechanism of Ag3PO4. On base of the results above, a plausible growth mechanism is 184

proposed as follows. First, THF, as an aprotic, polar solvent, can strongly solvate Ag(I) ions, 185

resulting in a slow diffusion rate of Ag(I) ion. Moreover, a large spatial obstacle will exist by the 186

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

. As a 187

result, the secondary branching growth of the shaft is refrained, as demonstrated by the fact that the 188

sub-branches of HBTs are shorter than those of TDTs (Figures 1C vs. 1A). The sub-branches of 189

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TDT can fully grow without THF. Limited by small space close to the center of a tetrapod, the 190

fully-grown sub-branches of the four shafts will intersect and squeeze one another and finally the 191

shafts snap off, leading to the formation of TDTs with long sub-branches (Figure 1A). 192

We hold that the adsorption of THF on the surface of Ag3PO4 is another important factor. Since 193

the oxygen atom of THF molecule has two pairs of unshared electrons, THF molecules are easy to 194

adsorb on Ag(I)-enriched facets of Ag3PO4 nanocrystals through the coordination of Ag(I) with the 195

oxygen of THF (5). As a result, the growth rate of Ag(I) ion-enriched facets, i.e. {110}, may be 196

reduced greatly. With further increasing the THF amount, the growth of sub-branches is inhibited 197

significantly. As a result, the uniform TOTs form at 0.25:1 (Figures 1C and 4). At too high THF/W 198

ratios (0.5:1, 1:1, 1:0), AgNO3 can not completely dissolve in the system, leading to the formation 199

of irregular particles (Figure S1, seeing ESI). To conclude, THF plays a vital role in the growth of 200

Ag3PO4, which needs extensive research in future. 201

Degradation performance of Ag3PO4 polypods under visible light irradiation The 202

photocatalytic activities of the typical samples have been investigated using the degradation of 203

rhodamine B (RhB) as the probe reaction (Figure 6). Herein, N-doped TiO2 (NT) is also prepared to 204

compare with Ag3PO4. Because the BET areas of HBTs, TDTs, TOTs, NOTs and NTs are measured 205

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, 100 206

and 9.6 mg, respectively. The aim is to keep their surface areas same according to the reference (19). 207

Moreover, we have measured the absorption spectra of RhB with irradiation time. It is obvious that 208

RhB has been destroyed, characterized by the disappearance of the maximum absorbance of RhB at 209

553 nm (Figure 7). The apparent reaction rate constants are 1.1335, 0.6936, 0.4008, 0.2199 and 210

0.0078 min-1

for HBT, TDT, TOT, NOT and NT, respectively (Figure 6B). The apparent rate 211

constants of HBT, TDT, TOT and NOT are 144.3, 87.9, 50.4 and 27.2 times higher than that of NT, 212

respectively, indicating the high photocatalytic activity of Ag3PO4 (4). For the Ag3PO4 samples, 213

their activity orders are HBT > TDT > TOT > NOT. On one hand, the percentages of the {110} 214

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facets exposed are calculated to be 99%, 97%, 90% and 87% for HBT, TDT, TOT and NOT, 215

respectively. Taking their same surface areas into account, their different activities can be mainly 216

attributed to the active {110} facets exposed. Many researchers (4,5,13,14,16) have reported that the 217

surface energies of {110} and {100} facets are 1.31 and 1.12 J/m2; respectively; and further 218

demonstrated that the high-energy {110} facets have a higher photocatalytic activity than the {100} 219

and {111} facets for the degradation of RhB. On the other hand, the ultraviolet-visible diffuse 220

reflectance spectra (UV-DRS) reveal that three Ag3PO4 samples can absorb the visible light with a 221

wavelength shorter than 510 nm, which have the same absorption edge, indicating their same band 222

gap energy (Figure 8). However, the absorbencies of both polypods are about 2.5 times higher than 223

the bulk, which may favor to improve the photo activity. The high absorbencies of the former two 224

samples can be attributed to their three-dimensional microstructures, which favors for the 225

repeatedly reflections and absorptions of irradiation light (the inset of Figure 8) (17,23). 226

Degradation performance of Ag3PO4 polypods under natural indoor weak light We have 227

investigated the indoor weak light-driven degradation performances of Ag3PO4 polypod structures 228

(Figure 9). It is amazing that under indoor weak light irradiation, 100% RhB has been degraded 229

after 36 h, while only 18% can be degraded by N-doped TiO2 after 120 h (Figure 9a). The apparent 230

reaction kinetic constant (0.08099 h-1

) of Ag3PO4 polypods is 46.8 times higher than that (0.00173 231

h-1

) of N-doped TiO2 (Figure 9b). Besides, the complete mineralization of RhB dye by Ag3PO4 has 232

been confirmed by using the organic carbon (TOC) test, infrared spectroscopy (IR), UV-Vis 233

absorption spectra and mass spectrum (MS) (Figures S3-S6, seeing ESI). Moreover, the cycle 234

stability of Ag3PO4 polypod structures have been investigated (Figure 10). After three cycles under 235

indoor weak light irradiation, Ag3PO4 polypods nearly maintain activity within 36 h (Figure 10a). 236

Under visible light irradiation, however, the degradation ratios of RhB by Ag3PO4 polypods are 237

63% and 34% for the second and third cycles, respectively (Figure 10b). XRD patterns (Figure 10c) 238

show that after three cycles, only fairly small amounts of Ag metal have produced under weak light 239

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irradiation; while more Ag3PO4 have decomposed into Ag under visible light. Also we observed 240

with SEM that under visible light irradiation, the polypods have broken into fractures (Figure 10d); 241

while the polypods are still maintained (not showing). Summarily, Ag3PO4 polypods show a higher 242

cycling stability under natural weak light irradiation than under visible light irradiation. 243

It is important that Ag3PO4 photocatalyst is discovered with good photocatalytic activity under 244

indoor natural weak sunlight. Compared with conventional photocatalysis, the degradation reaction 245

is carried out under indoor natural weak sunlight that does not needs extra optical system. It is a 246

green and energy-saving technology to utilize Ag3PO4 as catalyst for the degradation of 247

environmental pollutants driven by indoor natural weak light-driven, not depending on artificial 248

light source. It could be expected that Ag3PO4 polypod structures can be conveniently applied in 249

indoor air cleaning under weak light irradiation. 250

The Ag3PO4 polypod structures are discovered with an efficient degradation activity under 251

indoor weak light without needing an extra, complicate artificial optical condenser system. The 252

efficient Ag3PO4 polypods could be promising to be conveniently applied in indoor air cleaning. 253

254

Acknowledgements 255

This work is financially supported by National Science Foundation of China (21377060, 256

21103049), the Project Funded by the Science and Technology Infrastructure Program of Jiangsu 257

(BM201380277, 2013139), Jiangsu Science Foundation of China (BK2012862), Six Talent Climax 258

Foundation of Jiangsu (20100292), Jiangsu Province of Academic Scientific Research 259

Industrialization Projects (JHB2012-10, JH10-17), the Key Project of Environmental Protection 260

Program of Jiangsu (2013016, 2012028), A Project Funded by the Priority Academic Program 261

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Development of Jiangsu Higher Education Institutions (PAPD) sponsored by SRF for ROCS, SEM 262

(2013S002) and “333” Outstanding Youth Scientist Foundation of Jiangsu (2011015). 263

Electronic Supporting Information (ESI) 264

This supporting material is available free of charge via the internet at http://www.acs.org 265

266

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microcrystals with high-index facets and enhanced photocatalytic properties. Chem. Commun. 307

2013, 49, 636-638. 308

(15) Wang, H.; Bai, Y. S.; Yang, J. T.; Lang, X. F.; Li, J. H.; Guo L. A facile way to rejuvenate 309

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Ag3PO4 tetrapods and the {110} facets-dominated photocatalytic activity. CrystEngComm. 312

2013, 15, 39-42. 313

(17) Sun, S. D.; Song, X. P.; Kong. C. C.; Yang, Z. M. Selective-etching growth of urchin-like 314

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(18) Mitoraj, D.; Kisch, H. The nature of nitrogen-modified titanium dioxide photocatalysts active 316

in visible light. Angew. Chem., Int. Ed. 2008, 47, 9975-9978. 317

(19) Xu, L.; Jiang, L.-P.; Zhu, J.-J. Sonochemical synthesis and photocatalysis of porous Cu2O 318

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(22) L. M. Liz-Marzan, Increasing complexity while maintaining a high degree of symmetry in 325

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mesoporous TiO2. Environ. Sci. Technol. 2009, 43, 7079-7085. 328

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16

Title list of Figures and Tables 329

FIGURE 1 Scanning electron microscopy (SEM) macrographs of the samples 330

synthesized at different volumetric ratios of tetrahydrofuran (THF) to water (W): (a) 331

0:1, Three-dimensional towers (TDT); (b) 0.13:1, Highly-branched tetrapods (HBT); 332

(c) 0.25:1, Threefold-overlapped tetrapods (TOT); Scale bar = 5 µm; Reaction 333

temperature: 30 oC; Hexamethylenetetramine (HMT)/Ag(I) = 0.75 (molar ratio); the 334

arrow direction is along [111] 335

FIGURE 2 (A) X-ray diffraction (XRD) patterns of the samples and (B) Intensity 336

ratios of (222)/(110) and (222)/(200) peaks of (a) TDT and (b) bulk Ag3PO4 337

FIGURE 3 Distribution diagram of various existing forms of H3PO4 at different pH 338

values (the dotted line marked by arrow, indicating the pH value for our system) 339

FIGURE 4 SEM images of the samples synthesized at different molar ratios of 340

HMT/Ag(I): (A) 0.5:1; (B) 0.75:1; (C) 1:1 and 1.25:1; (D) 1.5:1. Reaction 341

temperature: 30 oC; THF/W = 0.25:1 342

FIGURE 5 SEM images of the samples synthesized at different reaction 343

temperatures: (A) 15 oC; (B) 20

oC; (C) 30

oC; (D) 45

oC. HMT/Ag(I) = 0.75/1; 344

THF/W = 0.25/1 345

FIGURE 6 The degradation curves (A) and apparent reaction kinetic constants (B) 346

of the samples for the degradation of rhodamine B under visible light irradiation (λ > 347

420 nm): HBT (64 mg); TDT (97 mg); TOT (94 mg); Non-overlapped tetrapods 348

(NOT, 100 mg) and N-doped TiO2 (NT, 9.6 mg) 349

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17

FIGURE 7 The absorption spectra of RhB at different irradiation times 350

FIGURE 8 UV-vis diffuse reflectance spectra (UV-DRS) of the Ag3PO4 samples 351

FIGURE 9 Degradation and reaction kinetic curves of rhodamine B over Ag3PO4 352

polypod structures and N-doped TiO2 under indoor weak light 353

FIGURE 10 Cycle stability of Ag3PO4 polypod structures: (a) under indoor natural 354

dim light; (b) under visible light irradiations; (c) XRD patterns; (d) SEM images 355

after reaction under visible light irradiation 356

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18

357

358

FIGURE 1 359

360

361

362

363

364

365

366

367

(a) (c)

(b)

9µm

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19

368

369

FIGURE 2 370

20 30 40 50 60 70 80

(a)

(b)

Inte

nsi

ty (

a.u.)

2Theta (Degree)

110

200

210

211

22

0 31

0

22

2320

321

40

0

411

42

0421

332

(c)

(A)

371

0.0

0.5

1.0

1.5

2.0

2.5

3.0

(222)/(110)

1.471.43

2.83

(222)/(200)

Intensity ratio

TDT

Bulk

2.86

(B)

372

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20

373

FIGURE 3 374

375

376

377

378

379

380

381

382

383

384

385

386

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21

387

FIGURE 4 388

389

390

391

392

393

394

395

396

397

398

399

400

401

402

403

404

405

406

20 µµµµm (A) 3 µµµµm (B)

20 µµµµm (C) 30 µµµµm (D)

5 µµµµm

5 µµµµm

10 µµµµm

Page 22 of 28



22

407

FIGURE 5 408

409

410

411

412

413

414

415

416

417

418

419

420

421

422

C D

B A

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23

423

FIGURE 6 424

0 2 4 6 8 10 12 14 160.0

0.2

0.4

0.6

0.8

1.0

HBT

TDT

TOT

NOT

NT

C/C

0

(A) t (min)

0 4 8 12 16 20 240

1

2

3

4

5

ln(C

0/C)

(B) t (min)

HBT: ka=1.1335 min

-1

TDT: ka=0.6936 min

-1

TOT: ka=0.4008 min

-1

NOT: ka=0.2199 min

-1

NT: ka=0.0078 min

-1

425

426

Page 24 of 28



24

427

FIGURE 7 428

300 400 500 600 700 800

HBT

Absorbance

Length / nm

0min

1min

2min

3min

300 400 500 600 700 800

Absorbance

Light length /nm

0 min

2 min

3 min

4 min

TDT

429

300 400 500 600 700 800

Absorbance

Light length (nm)

0

2min

4min

6min

10min

TOT

300 400 500 600 700 800

Absorbance

Light length /nm

0

2min

4min

6min

10min

15min

NOT

430

300 400 500 600 700 800

Absorbance

Light length (nm)

0min

10min

15min

20min

NT

300 400 500 600 700 800

Absorbance

Light length /nm

0mim

20mim

40mim

60mim

80mim

Blank

431

432

Page 25 of 28



25

433

FIGURE 8 434

435

300 400 500 600 700 800

A

bso

rban

ce (

a.u.)

W avelength (nm )

H BT

TO T

B ulk

436

437

Page 26 of 28



26

438

FIGURE 9 439

0 15 30 45 60 75 90 105 120

0.0

0.2

0.4

0.6

0.8

1.0

C/C

0

t /h

HBT

NT(a)

0 15 30 45 60 75 90 105 120

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

ln(C

0/C)

t /h

HBT: ka=0.08099 h

-1

N-TiO2: k

a=0.00173 h

-1

(b)

440

441

Page 27 of 28



27

442

FIGURE 10 443

444

445

446

447

448

449

450

451

452

453

454

(d)

10 20 30 40 50 60 70 80

Intensity /a.u.

2Theta /degree

Under indoor weak light

Under visible light irradiation(c)

0 15 30 45 60 75 90 105 1200.0

0.2

0.4

0.6

0.8

1.0

C/C

0

Reaction time /h

1st cycle 2nd cycle 3rd cycle

(a)

0 1 2 3 4 5 6 7 8 9 10 11 120.0

0.2

0.4

0.6

0.8

1.0

3rd cycle2nd cycle

C/C

0Time /min

(b)

1st cycle

Page 28 of 28



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