Calcium Sulfate Hemihydrate Nanowires: One Robust Material in

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Calcium Sulfate Hemihydrate Nanowires: One Robust Material in Separation of Water from Water-in-Oil Emulsion Guangming Jiang, Wenyang Fu, Yuzheng Wang, Xiaoying Liu, Yu Xin Zhang, Fan Dong, Zhiyong Zhang, Xianming Zhang, Yuming Huang, Sen Zhang, and Xiaoshu Lv Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.7b02901 • Publication Date (Web): 28 Aug 2017 Downloaded from http://pubs.acs.org on August 28, 2017

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Environmental Science & Technology

1

Calcium Sulfate Hemihydrate Nanowires: One

2

Robust Material in Separation of Water from

3

Water-in-Oil Emulsion

4

Guangming Jiang,1,* Wenyang Fu,1 Yuzheng Wang,1 Xiaoying Liu,3 Yuxin Zhang,3 Fan Dong,1

5

Zhiyong Zhang,2 Xianming Zhang,1 Yuming Huang,4,* Sen Zhang,2 Xiaoshu Lv1,*

6

1

Engineering Research Center for Waste Oil Recovery Technology and Equipment, Ministry of Education, Chongqing Technology and Business University, Chongqing 400067, China

7 8

2

Department of Chemistry, University of Virginia, Charlottesville, Virginia, 22904, United States

9 10

3

College of Materials Science and Engineering, Chongqing University, Chongqing 400044, China

11 12

4

The Key Laboratory of Eco-environments in Three Gorges Reservoir Region, Ministry of

13

Education, College of Chemistry and Chemical Engineering, Southwest University, Chongqing

14

400715, China

15 16

∗

To whom correspondence should be addressed.

E-mail: [email protected]; [email protected]; [email protected]

1

ACS Paragon Plus Environment


17

Abstract

18

Here we report a facile and cost-effective wet-chemical approach to the synthesis of

19

calcium sulfate hemihydrate nanowires (HH NWs, CaSO4.0.5H2O), and their robust

20

performance in immobilizing water molecules to the crystal lattice of CaSO4 and then

21

separating them from a surfactant-stabilized water-in-oil emulsion (mean droplet size

22

of around 1.2 µm). Every gram of HH NWs are capable of treating 20 mL emulsion

23

(water content: 10.00 mg mL-1) with a separation efficiency of 99.23% at room

24

temperature, and this efficiency can be further improved by tuning the surface charge

25

density of HH. Along with the water immobilization, HH NWs are converted to large

26

cubic-like calcium sulfate dihydrate microparticles (DH, CaSO4.2H2O, mean size: 50

27

µm), and the accompanied size increment enables efficient collection of the solid

28

phase from oil. DH microparticles can be regenerated into HH NWs, which retain the

29

high performance of the original NWs. Such a unique renewable feature improves the

30

economics of our method and simultaneously prevents the secondary pollution.

31

Further economic evaluation finds that purification of every cubic meters of emulsion

32

(water content: 10.00 mg mL-1) will cost about $ 34.18 for HH NWs, much lower than

33

$ 490.78 for the previously reported HH NPs, and $ 11,052.05-23,420.32 Fe3O4

34

NP-based adsorbents, respectively. With the high efficiency, easy collection, low cost

35

and renewable feature, HH NWs show highly promising applications in the field of oil

36

purification and recycle.

37

2


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Graphical Abstract

39 40

3



41

INTRODUCTION

42

The ever-increasing consumption of petroleum/synthetic oil products (such as

43

lubricating oil, transformer oil and etc.) have led to the generation of million tons of

44

wasted oil every year (the wasted oil refers to the one that has lost the function due to

45

the inclusion of impurities and the change in composition).[1] The management and

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disposal of them have therefore become a critical issue for governments due to the

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relevant environmental concerns, such as the oil-induced water and soil pollution.[2]

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Oil regeneration via a stepwise purification and refining strategy is one promising

49

solution, which can also contribute to saving petroleum resources.[3-4] The purification

50

process is intended to remove the undesired impurities in oil, including water,

51

particles, polymers and ions.[5] Among them, water droplets are usually stabilized by

52

surfactants, emulsified in oil phase, and have a mean size less than ten micrometers,

53

making them very difficult to get removed.

54

To realize water/oil separation, various techniques, such as magnetic separation,

55

oil skimming, electroflotation and selective adsorption, have been developed,[6-7]

56

which, however, are limited to separate layered water/oil mixtures[8-9] and oil-in-water

57

emulsions.[10-11] Their performance toward wasted oil (kind of a surfactant-stabilized

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water-in-oil emulsion) is still unsatisfactory due to the nano/micro size of droplet, the

59

large viscosity of oil phase and the high stability of emulsion.[12-13] Recently, filtration

60

techniques, which separate water and oil via selective penetration through one filter

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with superhydrophobic/superoleophilic or superhydrophilic/superoleophobic surfaces,

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have attracted increased research interests.[14,15,16] Till now, various smart membrane, 4


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sponge and mesh-based filters have been developed.[17,18,19,20,21] When armed with

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unique pore structure and surface wettability, these filters can efficiently separate

65

water-in-oil emulsions.[22,23,24,25] However during practical applications, the filtration

66

techniques are still challenged by the issues associated with the filter fouling,

67

processing capacity and flux.[26,27] For example in Zhang’s work[28], the maximum

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flux for the surfactant-stabilized water-in-oil emulsion is reported to be only 1000 L

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m-2 h-1 (oil phase: isooctane; viscosity: 0.53 mPa s-1; droplet size: 5-20 µm), and this

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flux will be further reduced when the droplet size drops to nanoscale, and a more

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viscous oil is used. Very recently, our group reported a novel immobilization-

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separation approach, which can facilely remove 95.87% of water from a

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surfactant-stabilized water-in-oil emulsion (water content: 10.00 mg L-1).[29] In this

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process, EDTA-capped calcium sulfate hemihydrate nanoparticles (HH NPs,

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CaSO4.0.5H2O) were dropped into the emulsion, which can adsorb the water droplets

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and immobilize them into the crystal lattice of HH. The solidified water was then

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separated along with the removal of the solid phase. Compared with the developed

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adsorption separation and filtration technology, [10-11] this immobilization-separation

79

approach could fix the water molecules more firmly and remove them without the

80

concern of desorption, and can also continuously separate the emulsion without the

81

concern of the fouling and processing capacity. However for real use, there is still

82

room for improvement in the separation efficiency as well as the cost and yield for

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HH synthesis.

84

Herein, we report a more facile large-scale synthesis of well-defined HH 5



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nanowires (NWs) for efficient water separation from a surfactant-stabilized water-in

86

-transformer oil emulsion at room temperature. Different from the previously reported

87

HH NPs synthesis using (NH4)2SO4 and CaCl2 as precursors,[30] HH NWs were

88

prepared from the conversion of gypsum (one earth-abundant mineral, calcium sulfate

89

dihydrate, CaSO4.2H2O, DH) in a Mg2+-containing glycerol solution at 95 °C:[31-32] CaSO4·2H2O (DH) →CaSO4·0.5H2O (HH) +1.5H2O

90

1)

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With such a simple reaction condition, we were able to produce 10 g of HH NWs in

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one batch, which was around 23 times more than that of the HH NPs (0.44 g)[30]. The

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separation experiments show that every gram of HH NWs are capable of treating 20

94

mL emulsion (water content: 10.00 mg mL-1) with a separation efficiency of 99.23%

95

at room temperature. This efficiency can be further improved by tuning the surface

96

charge density of HH (characterized by Zeta potential). After the water

97

immobilization, HH NWs convert into large cubic-like DH microparticles (mean size:

98

50 µm), and the accompanied size increment feature is critical to the efficient

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collection of the solid phase from oil. DH could be regenerated into HH NWs with a

100

comparable separating performance to the original NWs. Such a unique renewable

101

feature improves the economics of our method and also prevents the secondary

102

pollution. The economic evaluation finds that the purification of every cubic meter of

103

emulsion (water content of 10.00 mg mL-1) will cost about $ 34.18 for HH NWs,

104

much lower than $ 490.78 for HH NPs, and $ 11,052.05-23,420.32 Fe3O4 NP-based

105

adsorbents, respectively.

106

EXPERIMENTAL SECTION 6


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Materials. Analytical reagent grade DH, MgCl2•6H2O, Na2EDTA, hexane, ethanol

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and glycerol were all purchased from Sinopharm Chemical Reagent Co., Ltd,

109

Shanghai, China. The surfactant Span80 was obtained from Alfa Aesar. All chemicals

110

were used without further purification.

111

Synthesis of HH NWs. A typical synthetic approach for HH NWs was as follows: 1.5

112

g of MgCl2•6H2O was first dissolved in 5 mL of water, which was added into 100 mL

113

glycerol and heated to 95 °C under magnetic stirring (Mg2+ concentration: 12 mM).

114

10 g of DH powder was then added into the solution. The mixture was kept at 95 °C

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for 2.0 h to achieve the complete phase transition from DH to HH. After the reaction,

116

the hot slurry was filtered, washed with boiling water, and rinsed with ethanol. The

117

collected solid was dried at 60 °C to remove any absorbed water or ethanol. To tune

118

the surface charge density of HH NWs, more MgCl2.6H2O or controlled amount of

119

Na2EDTA were added into the solution right after the 2.0 hour’s reaction, to avoid

120

their effects on the shape of HH NWs during synthesis (See the morphologies of HH

121

NWs synthesized under 12 and 96 mM MgCl2, respectively, in Figure S1).

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Preparation of Water-in-oil Emulsions and Water Separation. The surfactant-

123

stabilized water-in-transformer oil emulsion was prepared following a reported

124

work[33]. 2.0 g of water were mixed with 200 mL transformer oil with the assistance of

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0.2 g of Span80 (surfactant). The mixture was then intensively stirred for 3 h and

126

sonicated for another 3.0 h (sonication power: 700W; frequency: 40 kHZ; temperature

127

25-30 oC) to form a stable milky emulsion (See Figure S2). The surfactant-stabilized

128

emulsion is stable over two weeks without any observable precipitation or 7



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de-emulsification.

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To examine the separation efficiency, a certain amount of dried HH NWs was

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mixed with 20 mL of the surfactant-stabilized water-in-oil emulsion in a 25 mL vial.

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The suspension was then magnetically stirred for 30 min and then kept still to allow

133

the solid phase settling down to the bottom. The transparent oil could be obtained by

134

centrifugation at 3000 rpm for 2.0 minutes. The separated solid phase was washed by

135

hexane to remove the adsorbed oil and dried at 60 oC for regeneration or further

136

characterization.

137

Characterization. The crystal phase in solid samples was investigated by

138

thermogravimetry/differential scanning calorimetry analysis (TG/DSC, NET- ZSCH

139

STA 409 Luxx) and powder X-ray diffraction analysis (XRD, D/Max-2550 pc). TG

140

analysis was also used to determine the crystal water content in solid sample. For

141

TG/DSC analysis, 20 mg of the dried sample was sealed in an Al2O3 crucible with a

142

lid and scanned at 10 °C min-1 under N2 flow. The XRD analysis was performed with

143

CuKα radiation at a scanning rate of 5 ° min-1 in 2θ range of 10 - 60°. Particle

144

morphology

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HITACHES-570, Hitachi) and transmission electron microscopy (TEM, JEOL,

146

JEM-2010). The particle size distribution of the solid sample was measured by a laser

147

particle size analyzer (Mastersizer 2000), and the droplet size in emulsions was

148

measured by dynamic light scattering (DLS) (Malvern Zetasizer Nano ZS90). The

149

Brunauer–Emmett–Teller (BET) specific surface area of the sample was determined

150

using nitrogen adsorption/desorption apparatus (ASAP 2020) with all samples

was examined

by the

scanning

electron

8


microscopy

(SEM,

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151

degassed at 80 oC for 12 h prior to measurements. The water content (mg mL-1) in

152

emulsion before and after the water separation was determined by Carr’s moisture

153

titrator (899 coulometer + 860 KF Thermoprep., Metrohm, Herisau, Swiss) and

154

multielement oil analyzer (MOA II plus,MOA Instrumentation, Inc. Levittown, USA),

155

respectively. The separation efficiency (SE) is calculated by

156

ܵ‫= ܧ‬

஼బ ି஼೟ ஼బ

× 100%

2)

157

Where C0 and Ct are the initial and final water content in emulsion, respectively.

158

RESULTS AND DISCUSSION

159

Synthesis and Characterizations of HH NWs. HH NWs were prepared in a hot

160

glycerol solution with gypsum (DH, CaSO4.2H2O) as the precursor and Mg2+ as the

161

shape mediator. The volume ratio of glycerol to water and the reaction temperature

162

were set to be 10 and 95 oC, respectively, to provide the thermodynamic driving force

163

for the phase transition of DH to HH,[30-31] while the presence of Mg2+ contributes to

164

the formation of NWs.[34] Figure 1a gives a typical SEM image of the as-synthesized

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HH, which presents a uniform NW structure with an average length of around 20 - 30

166

µm. The TEM image in Figure 1b shows the NWs are of an average diameter of 100

167

nm, thus their length/width ratio can reach 200-300. Compared with the previous

168

reported HH NPs (in the shape of ellipsoid, 600 nm by 300 nm),[29] the present HH

169

NWs obviously show a much larger surface area. The N2 adsorption–desorption

170

isotherms confirm that HH NWs have a nearly four times larger BET specific surface

171

area (4.535 cm2 g-1) than HH NPs (1.351 cm2 g-1, See Figure S3). Since the water

172

immobilization into the crystal lattice is an interface-based reaction, a larger surface 9



173

area should be beneficial to achieve a higher separation kinetics and efficiency.

174 175

Figure 1. SEM image (a), TEM image and SEAD pattern (b), XRD pattern (c) and

176

TG/DSC pattern (d) of the as-synthesized HH NWs.

177

The SEAD pattern of the NWs in Figure 1b inset exhibits numbers of spots with

178

random orientation as well as several inconspicuous diffraction rings, which suggest a

179

polycrystalline nature of these NWs. The XRD pattern of the sample in Figure 1c

180

confirms the formation of a pure HH phase (PDF#041-0244) with the characteristic

181

diffraction peaks at 2θ=14.70°, 25.62°,29.69°, 31.89°, 42.25° and 49.36°, for HH

182

(110), (013), (004), (-411), (503) and (-415), respectively. The TG pattern in Figure

183

1d shows a weight loss of 6.25 wt% when HH is heated to 200 oC, which is assigned

184

to the escape of the crystal water. It is noted that this value is consistent with the

185

crystal water content of 6.22 wt% in the pure HH phase. The DSC pattern (the inset in

186

Figure 1d) presents one typical hemihydrate crystal water removal profile of HH, 10


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187

with the weight loss initiating with an endothermic reaction with the peak temperature

188

of 149.2 °C, following by an exothermic reaction with the peak of 180.1 °C.[35-36] All

189

these confirm the NWs to be the phase of HH.

190

Water Separation from the Water-in-Oil Emulsion. The separation experiment

191

proceeds by dropping HH NWs in the form of dried powders into the water-in-oil

192

emulsion (0.2 g H2O in 20 mL transformer oil), which was then intensively stirred for

193

30 mins at room temperature to drive the immobilization of water into crystal lattice

194

of HH. The dosage of HH is set to be 1.07 g, which allows the whole immobilization

195

of the water molecules according to the following Equation:

196

CaSO4·0.5H2O(HH) +1.5H2O→CaSO4·2H2O(DH)

197

As shown in Figure 2a, the system right after the stirring appears to be homogeneous,

198

with little difference from the original emulsion (Figure S2). After sitting for 30 min,

199

a clear interface is formed as the solids gradually settle down toward the bottom under

200

gravity force, leaving the transparent oil phase on top layer (Figure 2b). After settling

201

for 120 min, most of the solid was precipitated at the bottom of the vial (Figure 2c),

202

indicating the solids are easily separated from the oil phase, avoiding the secondary

203

pollution caused by nanostructures. A transparent liquid is facilely achieved by simply

204

removing the solid precipitates with a mild centrifugation (Figure 2d). Figure 2e and

205

2f compare the optical microscope images of the emulsion before and after the water

206

separation, where the bright spot denotes the water droplet. It is clear that a large

207

amount of the water droplets with a mean size of 1.2 µm (See the size distribution

208

curve in Figure S4) exist in the original emulsion, and the number drops dramatically 11


3)


209

after the separation, suggesting most of the water has been removed. The SEM

210

examination of the collected solid phase (Figure 2g) shows that the HH NWs have

211

transformed into cubic-like microparticles with an average size of 50 µm (See the

212

particle size distribution profile in Figure S5). The XRD pattern in Figure 2h

213

indicates these microparticles are mainly composed of DH with a small proportion of

214

HH left in them, indicating an effective water immobilization in HH NWs. It should

215

be noted that the particle size increment along with the water immobilization process

216

is important to ensure the efficient removal of the solids from the viscous oil and

217

avoid the risk of particle pollution to oil.

218

219

Figure 2. (a-d) Digital images of the whole separation process; (e-f) Optical

220

microscope image of the water-in-oil emulsion before and after water separation; (g) 12


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SEM image of the collected solid phase after water separation; (h) Comparison in

222

XRD patterns of the as-synthesized HH NWs and the collected solid phase.

223

The concentration of water in the purified oil is measured to be 0.077 mg mL-1,

224

showing a high separation efficiency of 99.23 wt%. The present HH NWs are even

225

more efficient than the previously reported HH NPs, which only show a SE of 95.87

226

wt% under the same separation conditions and dosage.[29] The crystal water content in

227

the collected solid was determined to be 20.05 wt%. Considering the HH dosage of

228

1.07 g and the initial crystal water content of 6.25 wt%, the immobilized water

229

reaches 0.185 g, and therefore the immobilization efficiency of the NWs is around

230

92.50 % (The immobilization efficiency is defined as the mass of water immobilized

231

in HH NWs over the total mass of water in the original emulsion, thus its value here

232

equals 0.185 g / 0.200 g = 92.50 %, See the calculation process in Supporting

233

Information), much higher than the HH NPs (77.58 %). The significant increase in

234

immobilization efficiency should be ascribed to the larger specific surface area and

235

the one dimension property of the NW. It should also be mentioned that the

236

immobilization efficiency (92.50 %) is a little lower than the separation efficiency

237

(99.23 %), which may arise from the adsorption behavior of the solid phase. Overall,

238

our HH NWs present an excellent performance toward the water separation from a

239

surfactant-stabilized water-in-oil emulsion.

240

Influence of the surface charge of HH. The surface charge is usually an important

241

descriptor for interface reactions. To understand the role of surface charge during

242

water separation, the surface charge on HH NWs is tuned from positive (by inclusion 13



243

of Mg2+ during synthesis) to negative (by inclusion of EDTA during synthesis), and is

244

characterized by Zeta potential. The dependence of the immobilization and separation

245

efficiency on the Zeta potential of HH NWs is presented on Figure 3a. The results

246

show that with an increase in Mg2+ dosage from 12 to 24 mM, the Zeta potential of

247

the NWs increases from 1.27 to 27.9 mV, and the corresponding immobilization and

248

separation efficiencies increase from 68.54 to 93.12 % and 77.56 to 99.51 %,

249

respectively. It is suggested that a high zeta potential will promote the immobilization

250

process, and this should be induced by the enhanced water affinity of HH NWs with a

251

higher surface charge density. When EDTA is introduced during the HH synthesis, the

252

Zeta potential of the NWs turns to be negative. With increased dosage of EDTA, the

253

Zeta potential moves to more negative, and the corresponding immobilization and

254

separation efficiencies increase to the peak of 77.56 % and 97.23 % (at 10 mM

255

EDTA). This increment further confirms that a higher surface charge density will

256

benefit the water separation. However, at an even higher concentration, the EDTA

257

molecule will over-cap the NWs and block the efficient mass transfer between water

258

droplets and HH NWs, therefore, lowering the separation efficiency.

259

260

Figure 3. (a) Dependence of the immobilization and separation efficiency on Zeta 14


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potential of the HH NWs; (b) Schematic illustration of the effect of the surface charge

262

density of HH material on water immobilization.

263

On the basis of the above results, we can conclude that the surface charge density

264

should be an important factor that determines the performance of HH NWs in

265

water/oil separation. As schemed in Figure 3b, since the water molecule is of higher

266

polarity than the oil molecule, it usually shows a stronger affinity to a material with a

267

high surface charge density. Such a feature will significantly enhance the possibility

268

of interface reactions between water droplets and the surface-charged HH NWs,

269

leading to a higher water immobilization efficiency. More importantly, it allows us to

270

optimize the separation efficiency via the surface charge engineering of the material.

271

Economic Evaluation. Economics is crucial for the commercialization of a new

272

rising process. Here, the economy of our method is evaluated by calculating the total

273

cost of the chemical and energy consumptions during HH NW synthesis, and then

274

comparing it with those of our previous HH NPs-based separation method[29] and the

275

developed Fe3O4 NP adsorption techniques.[9,11] Table S2 shows that the synthesis of

276

every ton of HH NWs cost $ 638.83, only about 6.96%, 0.14% and 0.31% of that for

277

the synthesis of every ton of HH NPs ($ 9173.40), Fe3O4 NP-based adsorbents in

278

Duan’s ($ 437,763.70) and Mirshahghassemi’s ($ 206,580.40) work, respectively.

279

Considering the similar water removal capacity, we can roughly estimate that the

280

purification of every cubic meters of emulsion (water content of 10.00 mg mL-1) will

281

take about $ 34.18 for HH NWs, much lower than $ 490.78, $ 23,420.32 and

282

$ 11,052.05 for HH NPs and Fe3O4 NP-based adsorbents in Duan’s[11] and 15



283

Mirshahghassemi’s[9] work, respectively. All these demonstrate that the HH

284

NWs-based method is much more cost-effective.

285

As seen in Figure 2g-h, HH NWs are converted into DH after immobilizing the

286

water molecules, and become a solid waste. One may thus concern about the disposal

287

of these byproducts. Since the collected solid waste is determined by XRD and SEM

288

to be composed of DH with similar particle morphology to the commercial DH

289

powders, we propose that the waste may serve as the precursor resources to regenerate

290

HH NWs. Figure 4a gives a typical SEM image of the as-synthesized NWs using the

291

collected DH as the precursor, which show nearly the same morphology and size with

292

those synthesized from the commercial DH powders. The XRD pattern in Figure 4b

293

confirms that these NWs (as indicated by 1st run) to be the HH phase. Notably, these

294

HH NWs maintain a high immobilization efficiency of 94.38 % and a high separation

295

efficiency of 99.29 %, demonstrating that the solid waste could be regenerated into

296

HH NWs and used again for water/oil separation.

297

298

Figure 4. (a) SEM image of HH NWs prepared from the collected DH; (b) XRD

299

patterns of HH NWs after different runs of separation-regeneration process. 16


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300

We further extended the runs of the separation-regeneration experiments. Figure

301

4b shows that HH NWs could keep their phase with a high purity even after five-run

302

regeneration test. Table 1 summarizes the immobilization and separation efficiencies

303

of HH NWs after different runs of separation-regeneration process, which shows that

304

the regenerated HH NWs show comparable performances to the original ones. This

305

unique renewable feature is quite appealing, which could reduce the consumption of

306

calcium sulfate resources, and more importantly, avoid the secondary pollution

307

induced by the generated solid waste.

308

Table 1. Immobilization and separation efficiency of HH NWs after different runs of

309

separation-regeneration process Number

Original

1st run

2nd run

3rd run

4th run

5th run

Immobilization efficiency

92.50

94.38

91.56

92.34

93.51

94.51

Separation efficiency

99.23

99.29

99.05

99.17

99.23

99.41

310

Environmental Application. In the presented work, we demonstrate that HH NWs

311

can immobilize the nano/micro-sized water droplets into their crystal lattice and then

312

separate them from the surfactant-stabilized emulsions simply by the removal of the

313

solid phase. To check the possibility of real application, we further examined the

314

water separation from real wasted emulsified oil. Figure 5 presents the digital images

315

of the wasted transformer oil (provided by Chongqing Science and Technology

316

Development Co.) and wasted sealing oil (provided by Chongqing ZhanjiangBaosteel

317

Iron & Steel Co., Ltd.) before and after the water removal. It is clear that both of the 17



318

transformer oil and sealing oil become much more transparent after the water

319

extraction. The corresponding water content decreases from 17.259 to 1.254 mg mL-1

320

for sealing oil, while from 15.637 to 0.152 mg mL-1 for transformer oil. The

321

separation efficiency and immobilization efficiency are determined to be 92.73 % and

322

81.23 % for sealing oil, and 99.02 % and 89.72 % for transformer oil, respectively.

323

The lower immobilization efficiency in the case of sealing oil may be attributed to the

324

larger kinematic viscosity of sealing oil (47 mm2 s-1) than that of transformer oil (9.9

325

mm2 s-1). Despite of these, HH NWs still show promising as robust materials in water

326

separation from a water-in-oil emulsion and in the field of oil purification.

327

328

Figure 5. Application of HH NWs in oil extraction from the wasted sealing oil and

329

transformer oil.

330

SUPPORTING INFORMATION: SEM images of the HH NWs; Digital image of

331

the as-synthesized emulsion; N2 adsorption-desorption isotherms of the HH NWs and

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HH NPs; Droplet size distribution in emulsion; Particle size distribution of the

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collected DH microparticles; The total cost for the synthesis of every ton of the 18


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materials. The Supporting Information is available free of charge on the ACS

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Publications websites.

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Corresponding Author:

338

*

E-mail: [email protected] (G. M. Jiang);

339

*

E-mail:[email protected] (Y. M. Huang);

340

*

E-mail: [email protected] (X. S. Lv); Tel./Fax.: 86-023-62769787

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Notes: The authors declare no competing financial interest.

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The present work is financially supported by National Natural Science Foundation of

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China (Project 51608077), China Postdoctoral Science Foundation Funded Project

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(2016M602660), and Innovative Research Team of Chongqing (CXTDG201602014).

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AUTHOR INFORMATION

ACKNOWLEDGES

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Calcium Sulfate Hemihydrate Nanowires: One Robust Material in

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