Efficient and Green Fabrication of Porous Magnetic Chitosan Particles

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An efficient and green fabrication of porous magnetic chitosan particles based on high adhesive superhydrophobic polyimide fiber mat Lidong Tian, Xiaowei He, Xingfeng Lei, Mingtao Qiao, Junwei Gu, and Qiuyu Zhang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b02275 • Publication Date (Web): 21 Aug 2018 Downloaded from http://pubs.acs.org on August 25, 2018

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ACS Sustainable Chemistry & Engineering

1

An efficient and green fabrication of porous magnetic chitosan

2

particles based on high adhesive superhydrophobic polyimide fiber

3

mat

4

Lidong Tian a, Xiaowei He a, Xingfeng Lei a, Mingtao Qiao a, Junwei Gu a*, Qiuyu

5

Zhang a*

6

a

Shaanxi Key Laboratory of Macromolecular Science and Technology, School of

7

Science, Northwestern Polytechnical University, 1 Dongxiang Road, Chang’an

8

District, Xi’an, Shaanxi, 710129, P. R. China.

9

*

Corresponding authors to J.W. Gu and Q.Y. Zhang;

10

E-mail address: [email protected] (J.W. Gu) and [email protected] (Q.Y.

11

Zhang); Tel/Fax: +86 29-88431675.

12

Abstract: In this paper, an efficient and green strategy was developed to synthesize

13

porous magnetic chitosan (PMCS) particles via special superhydrophobic effect of a

14

porous fluorinated polyimide (PFPI) fiber mat with petal effect. By controlling the

15

fiber morphology and porous structures on fiber surface, the water contact angle on

16

the fiber mat reached as high as 155.3o and the adhesion to a water droplet was up to

17

236.4 μN, indicating that the PMCS droplets could be pinned on the fiber surface

18

steadily. Then, PMCS particles can be obtained after evaporation, exfoliation, lavation

19

and desiccation processes. Morphologies and porous structures of PMCS particles

20

were investigated. Cu (II) adsorption ability of PMCS particles have been

21

characterized, and the effects of different experimental conditions like adsorbent

22

dosage, pH, initial Cu (II) concentration and contact time on the adsorption capacity

23

were also examined. Field emission scanning electron microscopy (FE-SEMs) 1

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showed that PMCS particles presented a stable morphology and adjustable porous

25

structures. Adsorption isotherm was better fitted with Langmuir isotherm model and

26

the adsorption kinetic was followed the pseudo-second-order kinetic model. The

27

maximum adsorption capacity of PMCS particles was 188.68 mg/g. Even after eight

28

cycles, 85% adsorption capacity was still retained. These results suggested that the

29

obtained PMCS particles exhibited excellent Cu (II) adsorption capacity and

30

reusability. Moreover, compared with traditional methods, the mentioned fabrication

31

approach of PMCS particles was more effective, saves energy and environmentally

32

friendly.

33

Keywords: Porous PI fibers; High adhesion; magnetic chitosan; Cu (II) adsorption.

34

INTRODUCTION

35

Along with the rapid development of global economy, heavy metal pollution has

36

been one of the most urgent environmental problem. As a heavy metal ion, Cu (II) is

37

indispensable for animals, plants and humans. Trace amount of Cu (II) is beneficial

38

for the growth of plants and animals. However, problem arise once it is excess. For

39

example, Cu (II) can destroy the ecological environment and do harm to human

40

beings and other animals through inhibiting the metabolic process of organism

41

Additionally, plenty of disease such as high blood pressure, coronary heart disease

42

and arteriosclerosis can also be attributed to the excessive deposition of Cu (II) in the

43

body 4. Therefore, it is of great importance to study and develop effective technology

44

to alleviate the heavy metal pollution. Quite a few approaches, such as membrane

45

filtration

5, 6

, ion exchange

7, 8

, chemical precipitation 9, electrolysis 2


10

1-3

.

, chelating resin

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11

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removal from contaminated aqueous solution. Among these methods, adsorption is

48

regarded as one of the most economic and effective process and has been widely used

49

to eliminate different heavy metal ion in waste water. A few adsorbents with positive

50

adsorption capacity have been developed in recent years. Especially, magnetic

51

chitosan (MCS) has been considered as a promising hybrid adsorbent due to its

52

abundant amine and hydroxyl groups in chitosan chain and fast separation efficiency

53

14-20

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suspension polymerization

55

unavoidable problems of these methods limit the development of MCS. For

56

emulsification, separation of requisite emulsifier is difficult, which induces the

57

reduction in performance of the final MCS product. For inverse suspension

58

polymerization, chitosan, as a kind of hydrophilic polymer, is difficult to disperse in

59

aqueous phase, resulting in the mass aggregation of MCS particles. Large amount of

60

solvent with high toxicity is also necessary during the polymerization process. For

61

coprecipitation, the strength of the prepared MCS particles is unsatisfactory, and there

62

are also impurities existing in the shell, restricting the actual production of MCS. In

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addition, it is also hard to introduce tunable porous structures into MCS particles by

64

the methods mentioned above. Against this background, it is highly urgent and also

65

challenged to design and develop novel method to fabricate MCS.

and adsorption

12, 13

, have been extensively investigated for heavy metal ion

. Traditional methods to prepare MCS include emulsification 23-25

and co-precipitation

21, 22

, inverse

26, 27

, etc. Unfortunately, several

66

In recent years, one novel technique for synthesizing supraparticles, that is, the

67

evaporation of particle-containing aqueous droplets on the superhydrophobic or 3



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28-32

superamphiphobic surface, has attracted growing interests

69

successfully synthesized mesoporous silica supraparticles via superhydrophobic

70

meniscus templating method. Comparing with the well-known emulsion system, this

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method is simpler and much more environmental friendly. Furthermore, the prepared

72

silica supraparticles exhibited excellent dye and heavy metal adsorption performance

73

and separation efficiency. Wooh and his coworkers fabricated the spherical

74

mesoporous

75

superamphiphobic surface with strong liquid repellence. The synthetic process was

76

fast and flexible. Comparing with titania nanoparticles, the prepared supraparticles

77

were characterized to demonstrate larger surface area and more suitable packing size,

78

and hence displayed unique advantages in the photocatalytic process 29. On the whole,

79

this green and simple approach is very suitable to prepare various functional particles

80

in numerous research areas.

titania

supraparticles

from

nanoparticle

. Lee et al.

28

68

dispersion

on

the

81

However, due to the poor adhesion of superhydrophobic or superamphiphobic

82

surface, droplets on the surface tend to rolling and aggregating together, indicating

83

that stable condition at ambient temperature is mandatory for the preparation of

84

simple supraparticles, which is not conducive for the large-scale production of MCS

85

particles. Because Fe3O4 nanoparticles in MCS droplet will rapidly deposit to the

86

bottom under the slow evaporation condition. One effective strategy to avoid this

87

problem is depositing MCS aqueous suspension droplets on the superhydrophobic

88

surface with strong adhesion, which is termed as “Petal Effect”. Even with heating,

89

blowing or rolling, MCS droplets could still be strongly “pinned” onto the surface, 4


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90

hence effectively avoiding the aggregation of MCS droplets and the dimensional

91

stability of MCS particles can be obtained. To the best of our knowledge,

92

electrospinning is regarded as a facile and effective strategy for the preparation of

93

petal effect surface

94

36

95

with different microstructures, all of which demonstrate strong adhesion to water

96

droplet. Our previous work has also demonstrated that the porous polyimide

97

electropsun fiber presented excellent hydrophobicity

98

morphology and porous structure of the resulting polyimide fibers, we anticipate that

99

the porous polyimide fibers are superhydrophobic with high adhesion and could be

100

, polyimide

33-37

. Several polymers, such as polyacrylonitrile 35, polyurethane

34, 37

, et al have been used to fabricate electrospun fibrous membrane

38

. By controlling the surface

used as “midget plant” for the preparation of MCS particles.

101

Herein, we developed a facile and green approach to synthesize PMCS particles

102

via special superhydrophobic effect of PFPI fibers with petal effect. Firstly, the PFPI

103

fibers were prepared by electrospinning without any post-treatment process.

104

Bead-fiber morphology and closed-pore structures on fiber surface are respectively

105

the key factor of the superhydrophobicity and high adhesion. The corresponding

106

morphology and porous structures of the as-prepared PFPI fibers were systematically

107

analyzed and characterized. In addition, the water contact angle and adhesive force of

108

select PFPI fibers were also measured and discussed. Then MCS acetic acid/aqueous

109

solution was sprayed on the PFPI fiber mats. After evaporation, exfoliation, lavation

110

and desiccation, PMCS particles can be obtained. The corresponding morphology and

111

porous structures of the as-prepared PMCS particles were analysed and characterized, 5



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and their adsorption properties for removal of Cu (II) were also investigated. Effects

113

of initial Cu (II) concentration and contact time on the adsorption capacity were

114

measured. Different isotherm and kinetic models were used to evaluate the

115

thermodynamics and kinetics of adsorption process. In addition, the reusability of

116

PMCS particles for Cu (II) was further studied.

117

EXPERIMENTAL PROCEDURES

118

Materials

119

1,

3-bis(4-aminophenoxy)

benzene

(1,3,4-APB)

and

120

4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) were received from

121

Changzhou Sunlight Medicine Raw Material Co., (China). 1, 3-bis (3-aminopropyl)

122

tetramethyldisiloxane (GAPD) was purchased from Hangzhou Si Long Materials

123

Technology Co., (China). Ethyl alcohol, Dimethylacetamide (DMAc), tetrahydrofuran

124

(THF) and acetic acid (HOAc) were received from Tianjin Fu Yu Fine Chemicals Co.,

125

(China). Ferric chloride (FeCl3·6H2O), carbamide, sodium citrate, sodium sulfate

126

(Na2SO4) and chitosan (CS) were purchased from Sinopharm Chemical Reagent Co.,

127

(China). Polyacrylamide (PAM) was obtained from Tianjin Kemiou Chemical

128

Reagent Co., (China). Product name, catalog number and formula of all the reported

129

chemicals and reagents were listed in Table S1.

130

Preparation of PFPI fiber mats with petal effect

131

Highly soluble fluorinated polyimide (FPI) powders were synthesized by 39

132

traditional two-step poly-condensation reaction according to our previous work

133

The chemical structure of synthetic molecules and the preparation process of FPI have 6


.

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134

been presented in Figure S1. Number-average molecular (Mn) and weight-average

135

molecular weight (Mw) of the synthesized PI was 22004 and 40457 g mol-1,

136

respectively, and the polydispersity index is 1.8386. Then, 10 wt%, 15 wt%, 20 wt%

137

and 25 wt% FPI powders were dissolved in THF under magnetic stirrer at 25oC for 1

138

h, respectively. After fully dissolved, 6 ml of precursor solution was added in the 10

139

ml syringe and 25 kV voltage was applied to the nozzles. The electrospinning

140

temperature was about 25oC and the relative humidity ranged from 10% to 70%. In

141

order to obtain the uniform PFPI fiber mat, pushing rate of needle and movement

142

speed of syringe was fixed at 2 ml h−1 and 100 cm min−1, respectively. The nanofibers

143

were collected by a rolling collector (rotation rate of 100 cpm), which was fully

144

covered by aluminum foil. And the collecting distance was 25 cm. Note that the

145

electrospinning time was fixed at 4 min per time to acquire thin fiber mat. The

146

relationship between electrospun time and fiber thickness showed a similarly linear

147

increasing trend and the thickness of fiber mat was about 90 um at 4 min, which was

148

enough to hold the droplets and could guarantee the droplets only touch fiber mat

149

steadily (Figure S2). After electrospun, all aluminum foils loaded PFPI nanofibers

150

were placed in vacuum at 100oC for 24 h to remove residual THF. The samples of 10

151

wt%, 15 wt%, 20 wt% and 25 wt% PFPI fibers were named as PFPI-10, PFPI-15,

152

PFPI-20 and PFPI-25, respectively. Notably, morphologies and porous structures of

153

PFPI fibers were stable after treatment in vacuum oven (100oC) because of the

154

excellent thermal stability of synthesized PI (Figure S3).

155

Preparation of PMCS particles 7



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156

Chitosan (CS) was dissolved into HOAc aqueous solution (0.5 g/ml, w/v), under

157

drastic magnetic stirrer at 25oC for 1 h. Fe3O4 nanoparticles were dispersed into

158

aqueous solution (0.4 g/ml, w/v) under ultrasonic for 30 min. Noteworthy, Fe3O4

159

nanoparticles were prepared following the previously reported work with

160

hydrothermal method

161

presented in Figure S4. After that, 20 ml CS/HOAc aqueous solution and 10 ml Fe3O4

162

aqueous solution were mixed under mechanical stirring (1200 rpm) to form the

163

homogeneous solution. 0.1 g, 0.3 g, 0.5 g, 0.7 g sodium sulfate was then added into

164

the mixed solution, respectively, and stirring was continued for 1 h to obtain the

165

aqueous suspension of Fe3O4/CS (MCS) particles. The addition of sodium sulfate

166

decreased solubility of CS, resulting in its rapid precipitation into particles

167

fully dispersed, the suspension solution was placed in atomizer and sprayed on the

168

PFPI fiber mats. All PFPI fiber mats with stable MCS droplets were placed in vacuum

169

oven at 140oC for 10 min to remove HOAc and water. Then, the MCS particles were

170

stripped and collected by dissolving PFPI fiber mats with THF and washed by

171

deionized water/ethanol for several times alternately to remove sodium sulfate and

172

residual THF. The samples of MCS particles with 0.1 g, 0.3 g, 0.5 g, 0.7 g sodium

173

sulfate was named as PMCS-1, PMCS-2, PMCS-3 and PMCS-4, respectively. The

174

fabrication of superhydrophobic PFPI fiber mats and PMCS hemispheres were

175

presented in Figure 1.

176

Batch Cu (II) adsorption test of PMCS particles

177

40

, and the morphology of prepared Fe3O4 nanoparticles was

41

. After

Cu (II) adsorption capacities of PMCS-1, PMCS-2, PMCS-3 and PMCS-4 were 8


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178

evaluated by batch adsorption experiments, respectively. A series of conical flasks

179

(100 mL) containing 30 mg PMCS sample and 50 mL Cu (II) solution were stirred at

180

25oC for 24 h. The initial and final concentration of Cu (II) were analyzed with an

181

atomic adsorption spectrophotometer (YCA-1000, Japan). The solution pH was

182

conducted at 5.0 and the amount of adsorption (q) was defined as the following

183

equation:

q = (C − C )

184

(1)

185

where Co and Ce were the initial and equilibrium concentration of Cu (II) (mg/L),

186

respectively, q (mg/g) was the amount of Cu (II) adsorption, V (L) and M (g)

187

represented the volume of solution and the weight of adsorbent, respectively.

188

Characterization

189

Molecular weights and polydispersity indices of synthesized FPI were measured

190

by gel permeation chromatography (GPC, Waters 2414, USA). The morphologies of

191

PMCS and Fe3O4 were viewed by field emission scanning electron microscopy

192

(FE-SEM, Zeiss Ultra 55, Germany). Prior to measurement, the samples were coated

193

with a thin layer of gold. The electric current is 10 mA, the spraying time is 200 s and

194

the thickness of gold layer is 10 nm. Water contact angle (CA) of PFPI fiber mat were

195

investigated using a contact-angle system (JC2000D1, Powereach, China). The

196

surface adhesive force of PFPI fibers were measured by a highly sensitive dynamic

197

contact angle detector (DCAT21, Dataphysics, Germany). Atomic Force Microscope

198

(AFM, Bruker, Germany) was used to investigate the surface morphologies of PFPI

199

fibers. The specific surface area (SSA) of PMCS was calculated from nitrogen 9



Page 10 of 46

200

physisorption (Tristar 3020, Mecromeritics, USA). Pore size distribution, average

201

pore

202

Barrett-Joyner-Halenda method. All PMCS samples were degassed under high

203

vacuum for 24 h at 60oC prior to analysis. The magnetic properties of Fe3O4 and

204

PMCS were examined by vibrating sample magnetometer (VSM, LakeShore 7307,

205

USA). X-ray diffraction (XRD, Shimadzu XRD-7000, Japan) was used to

206

characterize the phase structures of Fe3O4 and PMCS. The FTIR spectra of samples

207

were recorded using a Fourier transform infrared spectrometer (TENSOR27,

208

Germany). The Cu (ΙΙ) adsorption property of samples were analyzed with an atomic

209

adsorption spectrophotometer (YCA-1000, Japan) and the adsorption value was

210

calculated on the basis of mass balance.

211

RESULTS AND DISCUSSION

212

Fabrication of superhydrophobic PFPI fiber mats

width

and

total

pore

volume

of

PMCS

were

measured

by

the

213

FE-SEM and CA images of synthetic FPI are shown in Figure 2a. The surface of

214

FPI film is smooth, and the CA is 83.8°, higher than that of common PI film (CA =

215

67°). This can be attributed to the introduction of a low free energy group, CF3, into

216

the PI backbone during the polymerization 37. It has been proved that a surface with a

217

bead–string structure is more favorable to achieve superhydrophobicity

218

this theory, electrospun FPI fibers with different structures were fabricated by

219

adjusting the concentration of precursor solution. Figures 2b, 2c, 2d, and 2e show the

220

morphologies of PFPI-10, PFPI-15, PFPI-20, and PFPI-25, respectively. Clearly with

221

increasing concentration from 10% to 25%, the morphology of FPI mat changed from 10


42

. Based on

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222

particle to fiber. For PFPI-10 and PFPI-15, a large amount of particles and slight

223

fibers was observed in the mat; this can be attributed to the low concentration of FPI

224

precursor solution (Figures 2b and 2c). Poor adhesion stress obtained from a low

225

concentration was not enough to resist the strong electric field force, and the

226

electrospun jet was broken to form particles under the action of surface tension

227

Unlike PFPI-10 and PFPI-15, typical spindle bead–fiber structures without any large

228

size particles were observed in PFPI-20; this can be ascribed to the competition

229

between stretching force from electric field and fiber surface tension (Figure 2d).

230

When the concentration increased to 25%, the electrospun jet was completely

231

stretched, and pure fiber structures without any beads and particles were observed in

232

the mat (Figure 2e). The corresponding CAs of PFPI-10, PFPI-15, PFPI-20, and

233

PFPI-25 are 125.7°, 139.2°, 153.6°, and 143.5°, respectively (Figure 2f). Compared

234

with the FPI film, all the PFPI fibers have excellent hydrophobicity. Nevertheless,

235

only PFPI-20 exhibited typical superhydrophobicity. This can be attributed to a larger

236

surface roughness owing to the spindle bead–fiber structure. This result is consistent

237

with the previous report mentioned above

238

“midget plant” for preparing PMCS particles.

239

High adhesion of superhydrophobic PFPI fiber mats

43, 44

.

42

, indicating that PFPI-20 is a suitable

240

To avoid the mass aggregation of MCS droplets during the preparation, a high

241

adhesion of as-prepared PFPI fiber mat to water droplet is indispensable. Figure S5

242

shows that water droplets dyed with azaleine were stable on PFPI-20 fiber mat even

243

when the mat was rotated 90° or turned upside down, exhibiting strong adhesion 11



244

between the mat and water droplet. This is mainly dominated by the chemical

245

composition and geometrical structure. Some hydrophilic groups in PI backbone

246

increased the interaction with water, contributing to a part of the adhesion. In addition,

247

as shown in Figure 2d, spindle beads and fibers simultaneously existed in the fiber

248

mat, such a hierarchical structure significantly affected the solid/liquid adhesion. On

249

one hand, a large roughness resulted in a dry contact between the water droplet and

250

pore structure in fiber mat. On the other hand, some relatively smooth fibers were

251

wetted because of the presence of hydrophilic groups in the PI backbone.

252

Notably, the adhesion could be adjusted by changing the morphology of a single

253

fiber surface. PFPI-20 fibers with different surface morphologies were fabricated

254

under 10–70% RH, and the corresponding FE-SEM and AFM images are shown in

255

Figures 3a-3d. Clearly, PFPI-20 exhibited a smooth surface under 10% RH (Figure

256

3a). However, with increasing RH, the surface morphologies of PFPI-20 changed

257

from smooth to wrinkled and porous structures (Figures 3b-3d). Especially for

258

PFPI-20-70% RH, a large amount of pores are present on the fiber surface (Figure

259

3d). During this process, water vapor was used as a template for the preparation of

260

pore structure because of its good compatibility with THF. The adhesion curves of

261

PFPI-20 under different RHs are shown in Figure 3e. PFPI-20-70% RH exhibited a

262

maximal adhesion of 236.4 μN, ∼2.5 times higher than that of PFPI-20-10% RH

263

(90.5 μN), indicating that the porous structure on fiber surface played a key role in

264

increasing the adhesion. The pores on single fiber surface could seal air into the

265

solid/liquid interface 37, 45. When the droplet left the surface, the sealed air generated a 12


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266

negative pressure to resist the external force, further strengthening the adhesion of

267

fiber mat to water droplet. The surface characterizations of PFPI-20 under different

268

RHs are shown in Table S2. Figure 3f shows the adhesion test of PFPI-20-70% RH,

269

and the corresponding movie is provided in Supporting Information. When the water

270

droplet left the fiber surface, apparent deformation was observed because of strong

271

adhesion, indicating successful fabrication of a high-adhesion superhydrophobic

272

surface by electrospinning technique.

273

Morphologies and pore structures of PMCS particles

274

The schematic illustration in Figure 4a shows the formation of PMCS particles on

275

PFPI-20-70% RH fiber mat from the MCS droplets. Initially, the MCS droplet

276

retained a spherical shape on the fiber mat. Water and HOAc in the droplet rapidly

277

evaporated below 140 °C, and MCS was simultaneously assembled into particles by

278

capillary force. When water and HOAc were completely evaporated, rigid MCS

279

particles were obtained. Notably, the entire processing time was only 10 min,

280

indicating a rapid preparation rate. In contrast to the supraparticles obtained from a

281

superamphiphobic or superhydrophobic surface with a low adhesion 28, 29, the shape of

282

MCS particles prepared in this study were not spherical but hemispherical. This is

283

probably because of the high adhesion of PFPI fiber mat. When an MCS droplet was

284

pinned on a PFPI fiber mat, a contact line was observed at the interface. During the

285

evaporation, the contact line was stable because of the high adhesion between the

286

drop and PFPI fiber mat. Therefore, after the evaporation, hemispherical MCS

287

agglomerates were obtained (Figure S6). Then, the hemispherical MCS agglomerates 13



288

were stripped and collected by dissolving the PFPI fiber mats with THF and

289

alternately washed with deionized water/ethanol for several times to prepare PMCS

290

particles with the removal of sodium sulfate and residual THF.

291

The FE-SEM images of PMCS-1, PMCS-2, PMCS-3, and PMCS-4 at different

292

magnifications are shown in Figures 4b–4m. Numerous particles were hemispherical,

293

this can be ascribed to the high adhesion of superhydrophobic PFPI fiber mats.

294

Besides, a part of the particles was irregular, and the size was inhomogeneous

295

(Figures 4b, 4e, 4h, and 4k). This is mainly because of various influencing factors

296

during the spraying 46. Figures 4c, 4f, 4i, and 4l show the surface morphologies of

297

PMCS particles. Clearly, all the PMCS samples exhibited intact and rigid surfaces,

298

beneficial for the separation and reuse of PMCS particles. Moreover, notably sodium

299

sulfate as porogen played an important role in the formation of porous structures.

300

With increasing addition of sodium sulfate, distinct porous structures were observed

301

in PMCS particles (Figures 4d, 4g, 4j, and 4m). The pore structures increased the

302

specific surface area (SSA) of PMCS, beneficial for the adsorption of Cu (II).

303

Especially, interconnected open-pore structures were observed in PMCS-4 (Figure

304

4m), exhibiting a more positive effect on the adsorption of Cu(II). A Cu(II) solution

305

rapidly diffused into PMCS-4 because of such through-hole structures, resulting in a

306

higher adsorption efficiency.

307

The SSA and pore structures of PMCS samples were further characterized by

308

Brunauer–Emmett–Teller (BET) and Barrett–Joyner–Halenda (BJH) methods. Figure

309

5a shows the nitrogen adsorption–desorption isotherms of PMCS-1, PMCS-2, 14


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310

PMCS-3, and PMCS-4, respectively. PMCS-4 exhibited a maximal nitrogen

311

adsorption capacity of 167.16 cm3g−1, ∼9 times higher than that of PMCS-1 (19.61

312

cm3 g−1), indicating that more pore structures existed in PMCS-4. According to the

313

International Union and Applied Chemistry (IUPAC) classification 47, the isotherms of

314

all the PMCS samples with distinct hysteresis loops can be assigned as type II,

315

characteristic of mesopores (2–50 nm) and macropores (>50 nm). In addition, the

316

SSA and total pore volume of PMCS-4 were 61.37 m2 g−1 and 0.24 cm3 g−1,

317

respectively, ∼4 and 6 times higher than those of PMCS-1 (16.74 m2 g−1 and 0.04 cm3

318

g−1). The detailed nitrogen physisorption characterization of PMCS samples is shown

319

in Table 1. The pore distributions of PMCS samples are shown in Figure 5b.

320

Typically polydispersed porous structures of PMCS were observed in the range of 9–

321

120 nm, and two peaks appeared at 28 nm and 113 nm. This is consistent with the

322

nitrogen adsorption–desorption isotherms (type II) as well as the FE-SEM results

323

shown in Figures 4d, 4g, 4j and 4m.

324

Characterization of PMCS particles

325

Figure 6a shows the XRD patterns of Fe3O4 and PMCS-4. The diffraction peaks

326

of Fe3O4 appeared at 2θ of 30.1°, 35.5°, 43°, 53.4°, 57°, and 62.6°, corresponding to

327

indices (220), (311), (400), (422), (511), and (400). According to the JCPDF file (PDF

328

No. 65-3107), these diffraction peaks indicate the cubic spinel structure of Fe3O4. For

329

PMCS-4, the diffraction peaks were very similar to those of Fe3O4, indicating that the

330

crystal structure of Fe3O4 did not change during the synthesis. Furthermore, the small

331

peak at 20° in PMCS-4 indicates the presence of amorphous chitosan. Figure 6b 15



332

shows the FTIR patterns of chitosan, Fe3O4, and PMCS-4. The peak at 3435 cm−1 can

333

be assigned to the stretching vibration of N–H bond. The peak at 2890 cm−1

334

corresponds to the stretching vibration of C–H bond. Besides, the peak at 1389 cm−1

335

can be attributed to the C–O stretching of primary alcoholic group in chitosan, and the

336

peak at 1083 cm−1 can be assigned to the C–OH bond stretching. For Fe3O4 spectra,

337

the peak at 584 cm−1 corresponds to Fe–O bond. Clearly, the adsorption peaks of

338

PMCS-4 are very similar to those of chitosan and Fe3O4, indicating that the

339

fabrication of PMCS did not damage the functional groups of chitosan. According to

340

the XRD and FTIR analysis results, it can be concluded that Fe3O4 with an intact

341

crystal structure was successfully introduced into chitosan.

342

The magnetic properties of Fe3O4 and PMCS-4 were analyzed by VSM

343

measurements at room temperature, and the results are shown in Figure 6c. An

344

“S”-shaped magnetic hysteresis loop of the samples indicates the superparamagnetic

345

behavior

346

and 33.6 emu/g, respectively. The low saturation magnetization of PMCS-4 compared

347

with Fe3O4 can be attributed to the encapsulation of Fe3O4 nanoparticles by

348

diamagnetic chitosan 16. However, the magnetism of PMCS-4 was sufficient enough

349

for the magnetic separation of treated water using an external magnetic field, and the

350

sedimentation rate was within 30 s, leading to efficient recycling and reuse (Figure 6c

351

inset).

352

Cu (II) adsorption property of PMCS particles

353

Effects of adsorbent dosage and pH on Cu (II) adsorption

48, 49

. The saturation magnetization of Fe3O4 and PMCS-4 was ∼92.7 emu/g

16


Page 16 of 46

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


354

Figure 7a shows the removal efficiencies of PMCS samples at different adsorbent

355

dosages (1–150 mg). Each sample was dispersed in 30 mL of Cu(II) aqueous solution

356

(100 mg/L) for 12 h at pH 5. The removal efficiencies of all the PMCS samples

357

significantly increased with increasing dosage and reached equilibrium. This is

358

because the increased adsorbent dosage provided more active sites for the adsorption

359

of Cu(II), increasing the removal efficiency. In addition, when the removal efficiency

360

reached equilibrium, PMCS-4 exhibited the minimum dosage (29.4 mg), ∼5 times

361

lower than PMCS-1 (148.6 mg). Such efficient Cu(II) adsorption property can be

362

attributed to the large amount of porous structures present in PMCS-4, providing

363

more adsorption sites for Cu(II).

364

Figure 7b shows the effect of pH on the Cu(II) adsorption of PMCS samples, and

365

the pH was selected in the range 2–6. The adsorption capacities of all the PMCS

366

samples increased with increasing pH from 2 to 5. The maximum capacities were

367

achieved at pH 5, and the corresponding capacities of PMCS-1, PMCS-2, PMCS-3,

368

and PMCS-4 were 33.1 mg/g, 62.6 mg/g, 75.3 mg/g, and 83.4 mg/g, respectively.

369

Generally, the amine groups of PMCS samples are highly protonated at a low pH,

370

inducing electrostatic repulsion of Cu(II). Besides, when the pH increased from 5 to 6,

371

the adsorption capacities of PMCS samples exhibited a slight decrease. This can be

372

attributed to hydrolysis in this pH interval 50.

373

Effect of initial concentration of Cu (II) and adsorption isotherms

374

The adsorption capacities of PMCS particles were evaluated at different initial

375

Cu(II) concentrations (Ce) ranging from 10 mg/L to 200 mg/L under a fixed 17



Page 18 of 46

376

adsorption time (24 h) and solution pH (5.0) (Figure 7c). Obviously, the adsorption

377

capacity exhibited an increasing trend with increasing Ce. For PMCS-4, the saturation

378

point was 200 mg/L, two times higher than PMCS-1 (100 mg/L). Besides, PMCS-4

379

showed a maximal Cu(II) adsorption capacity at the saturation point (123.46 mg/g),

380

about three times higher than that of PMCS-1 (43.21 mg/g). The remarkable

381

adsorption capacity of PMCS-4 can be attributed to the higher SSA and larger amount

382

of pore structures in the particles.

383

For further interpretation of the adsorption data, Langmuir and Freundlich

384

adsorption isotherm models were used to analyze the equilibrium adsorption of PMCS

385

samples. The Langmuir isotherm model can be expressed as follows:

386

= +

(2)

387

where Ce (mg/L) is the equilibrium concentration, qe (mg/g) is the adsorption capacity

388

at equilibrium, qm is the maximum adsorption capacity (mg/g), and B (L/mg) is a

389

constant related to the heat of adsorption.

390 391 392

Freundlich isotherm is an empirical equation used to describe a heterogeneous surface and nonuniform distribution of adsorption heat: lnq = lnK +

(3)

393

where Kf is Freundlich constant and n is the heterogeneity factor.

394

The parameters calculated from the adsorption isotherm models are shown in Table 2,

395

and the adsorption isotherms of PMCS samples are shown in Figure S7. Obviously,

396

for PMCS-4, the curve of Langmuir model (R2 = 0.9989) provided a much better fit to

397

the experimental data than that of Freundlich model (R2 = 0.9861), indicating that the 18


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398

process was monolayer adsorption. The maximum adsorption capacity (qm) calculated

399

using the Langmuir model was 188.68 mg/g, about four times than PMCS-1 (45.66

400

mg/g), indicating that PMCS-4 had more active sites and a better adsorption capacity.

401

Besides, the qm of PMCS-4 in this study was much higher than that of other similar

402

adsorbents reported previously, as shown in Table 3. The values of Freundlich

403

constant (n) for PMCS-1, PMCS-2, PMCS-3, and PMCS-4 were 5.3991, 2.8878,

404

1.8159, and 1.4778, respectively, indicating that the adsorption systems are favorable

405

51

406

Effect of contact time and adsorption kinetics

.

407

Contact time is very important for the adsorption process because it reflects the

408

adsorption kinetics of adsorbent. Figure 7d shows the effect of contact time on the

409

adsorption capacities of PMCS samples. In the first 10 min, the adsorption capacities

410

of all the PMCS samples sharply increased and reached half of those at equilibrium

411

times, exhibiting a fast adsorption rate. This can be attributed to strong chelating

412

interactions between chitosan and Cu(II) 23. Then, the adsorption rates slowed down,

413

and the adsorption amount of PMCS-1, PMCS-2, PMCS-3, and PMCS-4 reached

414

saturation at 100 min, 150 min, 250 min, and 300 min, respectively. Pore structures

415

influenced the equilibrium time of PMCS samples. For PMCS-4, more pore structures

416

increased the amount of adsorption site, prolonging the contact time between chitosan

417

and Cu(II). Even so, compared with similar adsorbents 23, 50, PMCS-4 still exhibited a

418

rapid adsorption time, very competitive for practical applications.

419

To further investigate the controlling mechanism of adsorption process, 19



Page 20 of 46

420

pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were used

421

to analyze the obtained adsorption/contact time data of PMCS samples. The

422

pseudo-first-order equation can be expressed as follows: log(q − q ) = log(q ) −

423

(4)

424

where t is the adsorption time; qe and qt (mg/g) are the adsorption capacities of PMCS

425

samples at equilibrium time and t time, respectively. K1 is the adsorption rate constant

426

(min−1) of pseudo-first-order kinetic model for adsorption. C is a constant with a fixed

427

value of 2.303.

428

The pseudo-second-order equation can be expressed as follows:

429 430 431

!

=

" "

+

(5)

where K2 (g/(mg min)) is the adsorption rate constant of pseudo-second-order model. The intraparticle diffusion model can be expressed as follows: q = K # t/& + M

432

(6)

433

where K3 (mg g−1 min1/2) is the intraparticle diffusion rate constant and M is the

434

intercept.

435

The parameters calculated from the three adsorption kinetic models are shown in

436

Table 4, and the relevant fitting curves of PMCS-4 and other PMCS samples are

437

shown in Figure S8. For all the PMCS samples, the correlation coefficient (R2) of

438

pseudo-second-order model was higher than that for the pseudo-first-order and

439

intraparticle diffusion models. In addition, the adsorption capacities (qe) of all the

440

PMCS samples obtained from the pseudo-second-order model were much closer to

441

the experimental data (qexp), indicating that the pseudo-second-order model can 20


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442

describe the adsorption process and the overall process is controlled by chemisorption

443

56

444

Reusability

.

445

The adsorption capacities of PMCS samples for eight cycles for Cu(II) are shown

446

in Figure 8. After the first four cycles, the adsorption capacities of PMCS-1, PMCS-2,

447

PMCS-3, and PMCS-4 decreased by only 4.6%, 3.8%, 2.3%, and 2.5% of the initial

448

value, exhibiting a stable adsorption property. The adsorption capacities of all the

449

PMCS samples continuously decreased in the following cycles. This can be attributed

450

to the loss of adsorbent during the washing steps after each adsorption–desorption

451

cycle. However, even after eight cycles, all the samples still maintained more than 70%

452

adsorption efficiency. Particularly for PMCS-4, the decrease in adsorption efficiency

453

was only 14.7% of the initial value, and the adsorption capacity was 105.88 mg/g,

454

indicating excellent reusability. This outstanding adsorption efficiency can be

455

attributed to the stable overall structure and more adsorption sites in the porous

456

structures of PMCS-4. It is reasonable to conclude that PMCS-4 has excellent Cu(II)

457

adsorption property, consistent with the requirements for treating Cu(II) pollution and

458

potential applications in heavy metal adsorption and separation.

459

CONCLUSIONS

460

In conclusion, a PFPI fiber mat with high-adhesion superhydrophobicity was

461

fabricated via a simple electrospinning method. The spindle bead–fiber structure of

462

PFPI fiber mat performed a key role in providing superhydrophobicity. Besides, with

463

increasing RH from 10% to 70%, the surface morphologies of PFPI fibers changed 21



464

from smooth to wrinkled and porous structures. A much higher adhesion was obtained

465

for PFPI-20-70% RH (236.4 μN), ∼2.5 times higher than PFPI-20-10% RH (90.5

466

μN). Then, PFPI-20-70% RH was used as a reactant for the formation of PMCS

467

particles. In this preparation process, sodium sulfate as a porogen played an important

468

role in the formation of pore structures. PMCS-4 exhibited the highest SSA (61.37 m2

469

g−1), about four times higher than PMCS-1 (16.74 m2 g−1). The saturation

470

magnetization of PMCS-4 was 33.6 emu/g, and the sedimentation rate was within 30 s,

471

indicating an excellent separation efficiency. Besides, all the PMCS samples showed a

472

higher adsorption capacity and fast kinetics for Cu(II). The adsorption isotherms

473

followed the Langmuir adsorption model, and the adsorption processes better fitted to

474

the pseudo-second-order kinetic model. The maximum adsorption capacity of

475

PMCS-4 (188.68 mg/g) was obtained with 200 mg/L of the initial Cu(II)

476

concentration at pH 5.0, about four times than that of PMCS-1 (45.66 mg/g). Even

477

after eight cycles, the decreasing adsorption capacity did not exceed 15% of the initial

478

value, indicating outstanding reusability. Compared with other similar adsorbents,

479

PMCS-4 exhibited efficient adsorption performance and have potential applications in

480

the removal of Cu(II) from a contaminated aqueous solution. Importantly, compared

481

with the traditional preparation methods, the mentioned approach is more effective,

482

saves energy, and environmentally friendly, exhibiting wide application prospects in

483

the field of environmental governance.

484

ASSOCIATED CONTENT

485

Supporting Information 22


Page 22 of 46

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486

FE-SEM images of prepared Fe3O4 nanoparticles with different magnifications;

487

Schematic illustrations of the evaporation of droplet on different surface; Langmuir

488

adsorption isotherms and Pseudo-first-order models of PMCS samples (PDF file).

489

Dynamic adhesion test of PFPI sample (MPG).

490

Corresponding Author

491

*

Junwei Gu: [email protected]

492

*

Qiuyu Zhang: [email protected]

493

Notes

494

The authors declare no competing financial interest.

495

ACKNOWLEDGEMENTS

496

The authors are grateful for the support and funding from the Foundation of

497

Shanxi Province Science and Technology Co-ordination Innovative Engineering

498

Project (No. 2016KTCQ01-92); Foundation of National Natural Science Foundation

499

of China (No. 51433008); Fundamental Research Funds for the Central Universities

500

(No. 3102017jc01001). We would like to thank the Analytical & Testing Center of

501

Northwestern Polytechnical University for the AFM test. We also thank Pro. Jingxia

502

Guo from Technical Institute of Physics and Chemistry (CAS) for the adhesion test.

503

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Y. Novel reusable porous polyimide fibers for hot-oil adsorption. J. Hazard.

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and thermally stable copolyimides modified with trifluoromethyl and siloxane. J.

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of one-dimensional Fe3O4@P(MAA-DVB)–Pd(0) magnetic nanochains and

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application for rapid degradation of organic dyes. RSC Adv. 2016, 6,

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(41) Areas, J. L.; Reddy, L. H.; Couvreur, P. Fe3O4/chitosan nanocomposite for magnetic drug targeting to cancer. J. Mater. Chem. 2012, 22, 7622-7632.

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microsphere/nanofiber composite film prepared by electrhydrodynamics. Angew.

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Chem. Int. Edit. 2004, 116, 4438-4441.

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(43) Lin, J. Y.; Ding, B.; Yu, J. Y.; Hsieh, Y. Direct fabrication of highly nanoporous polystyrene fibers via electrospinning. ACS Appl. Mater. Inter. 2010, 2, 521-528. 29



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process relationship of electrospun bioabsorbable nanofiber membranes. Polymer

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2002, 43, 4403-4412.

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(45) Richard, D.; Clanet, C.; Quere. D. Surface phenomena: Contact time of a bouncing drop. Nature 2002, 417, 811.

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Uptake of Pb (II) and Cd (II) on chitosan microsphere surface successively

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grafted by methyl acrylate and diethylenetriamine. ACS Appl. Mater. Inter. 2017,

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9, 11144-11155.

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(47) Kim, C.; Jeong, Y. I.; Ngoc, B. T. N.; Yang, K. S.; Kojima, M.; Kim, Y. A.; Endo,

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M.; Lee, J. W. Synthesis and characterization of porous carbon nanofibers with

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hollow cores through the thermal treatment of electrospun copolymeric nanofiber

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webs. Small 2007, 3, 91–95.

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Chu, L. Y. A novel smart microsphere with magnetic core and ion−recognizable

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shell for Pb2+ adsorption and separation. ACS Appl. Mater. Inter. 2014, 6,

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9530−9542.

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(49) Duan, B.; Liu, F.; He, M.; Zhang, L. N.; Ag-Fe3O4 nanocomposites@chitin

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microspheres constructed by in situ one−pot synthesis for rapid hydrogenation

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catalysis. Green Chem. 2014, 16, 2835−2845.

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Magnetic cellulose–chitosan hydrogels prepared from ionic liquids as reusable 30


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adsorbent for removal of heavy metal ions. Chem. Commun. 2012, 48,

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(52) Cai, Y. L.; Zheng, L. C.; Fang, Z. Q. Selective adsorption of Cu (II) from an

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aqueous solution by ion imprinted magnetic chitosan microspheres prepared from

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steel pickling waste liquor. RSC Adv. 2015, 5, 97435-97445.

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Heavy metals removal by EDTA-functionalized chitosan graphene oxide

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nanocomposites. RSC Adv. 2017, 7, 9764-9771.

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competitive adsorption of Pb (II) and Cu (II) using tetraethylenepentamine

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modified chitosan/CoFe2O4 particles. J. Hazard. Mater. 2017, 326, 211-220.

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Removal of Cu (II) and fulvic acid by graphene oxide nanosheets decorated with

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Fe3O4 nanoparticles. ACS Appl. Mater. Inter. 2012, 4, 4991-5000.

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680

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681

2010, 177, 962-970.

682

31



683

Figures and Tables

684

Figure 1. Diagram illustrating the fabrication of high adhesive superhydrophobic

685

PFPI fiber mat and PMCS particles.

686

Figure 2. FE-SEM and CA images of FPI film and PFPI fibers with different

687

concentration: (a) FPI film; (b)PFPI-10; (c) PFPI-15; (d) PFPI-20; (e) PFPI-25; (f)

688

The corresponding CA values of FPI film and PFPI fibers.

689

Figure 3 (a) FE-SEM and AFM images of PFPI-20 fiber under different RH: (a) 10%;

690

(b) 30%; (c) 50%; (d) 70%; (e) Adhesion curves of PFPI-20 fiber mat under different

691

RH; (f) Adhesion test of PFPI-20 fiber mat under 70% RH.

692

Figure 4 MCS particles formation process and FE-SEM images of PMCS samples

693

with different magnifications. (a) Schematic illustration of the formation of MCS

694

particles; (b-d) FE-SEM images of PMCS-1 with different magnifications; (e-g)

695

FE-SEM images of PMCS-2 with different magnifications; (h-j) FE-SEM images of

696

PMCS-3 with different magnifications; (k-m) FE-SEM images of PMCS-4 with

697

different magnifications; Images of each group above were in turn taken at

698

magnifications of 2 k, 5 k and 30 k, respectively.

699

Figure 5 (a) Nitrogen adsorption-desorption isotherms of PMCS samples. (b) Pore

700

size distribution curves of PMCS samples calculated by the BJH method. (Nitrogen

701

physisorption characterization of PMCS samples shown in Table 1).

702

Figure 6 (a) XRD patterns of Fe3O4 and PMCS-4; (b) FTIR spectra of chitosan, Fe3O4

703

and PMCS-4; (c) Magnetization curves of Fe3O4 and PMCS-4 at room temperature

704

and magnetically separation of PMCS-4 from solution (inset). 32


Page 32 of 46

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


705

Figure 7 (a) Effect of adsorbent dosage on removal efficiencies of PMCS samples

706

(conditions: pH=5, contact time=12 h, initial Cu (II) concentration=100 mg/L,

707

temperature=303 K); (b) Effect of pH on adsorption capacities of PMCS samples

708

(conditions: adsorbent dosage=30 mg, contact time=12 h, initial Cu (II)

709

concentration=100 mg/L, temperature=303 K); (c) Effect of initial Cu (II)

710

concentration on adsorption capacities of PMCS samples (conditions: pH=5,

711

adsorbent dosage=30 mg, contact time=12 h, temperature=303 K); (d) Effect of

712

contact time on adsorption capacities of PMCS samples (conditions: pH=5, adsorbent

713

dosage=30 mg, initial Cu (II) concentration=200 mg/L, temperature=303 K).

714

Figure 8 Cu (II) adsorption capacities of PMCS samples versus eight cycles.

715

Table 1 Nitrogen physisorption characterization of PMCS samples

716

Table 2 Adsorption parameters of Langmuir and Freundlich adsorption isotherm

717

models of PMCS samples

718

Table 3 Comparison of the maximum Cu (II) adsorption capacity with other

719

adsorbents

720

Table 4 Adsorption rate constants of pseudo-first-order, pseudo-second-order and

721

intraparticle diffusion models of PMCS samples

722

The table of contents (TOC) graphic of this manuscript

723

33



724 725

Figure 1 Diagram illustrating the fabrication of high adhesive superhydrophobic PFPI

726

fiber mat and PMCS particles.

727

34


Page 34 of 46

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


728 729

Figure 2 FE-SEM and CA images of FPI film and PFPI fibers with different

730

concentration: (a) FPI film; (b)PFPI-10; (c) PFPI-15; (d) PFPI-20; (e) PFPI-25; (f)

731

The corresponding CA values of FPI film and PFPI fibers.

732

35



733 734

Figure 3 (a) FE-SEM and AFM images of PFPI-20 fiber under different RH: (a) 10%;

735

(b) 30%; (c) 50%; (d) 70%; (e) Adhesion curves of PFPI-20 fiber mat under different

736

RH; (f) Adhesion test of PFPI-20 fiber mat under 70% RH.

737

36


Page 36 of 46

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


738 739

Figure 4 MCS particles formation process and FE-SEM images of PMCS samples

740

with different magnifications. (a) Schematic illustration of the formation of MCS

741

particles; (b-d) FE-SEM images of PMCS-1 with different magnifications; (e-g)

742

FE-SEM images of PMCS-2 with different magnifications; (h-j) FE-SEM images of

743

PMCS-3 with different magnifications; (k-m) FE-SEM images of PMCS-4 with

744

different magnifications; Images of each group above were in turn taken at

745

magnifications of 2 k, 5 k and 30 k, respectively.

746

37



747 748

Figure 5 (a) Nitrogen adsorption-desorption isotherms of PMCS samples. (b) Pore

749

size distribution curves of PMCS samples calculated by the BJH method. (Nitrogen

750

physisorption characterization of PMCS samples shown in Table 1).

751

38


Page 38 of 46

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


752 753

Figure 6 (a) XRD patterns of Fe3O4 and PMCS-4; (b) FTIR spectra of chitosan, Fe3O4

754

and PMCS-4; (c) Magnetization curves of Fe3O4 and PMCS-4 at room temperature

755

and magnetically separation of PMCS-4 from solution (inset).

756

39



757 758

Figure 7 (a) Effect of adsorbent dosage on removal efficiencies of PMCS samples

759

(conditions: pH=5, contact time=12 h, initial Cu (II) concentration=100 mg/L,

760

temperature=303 K); (b) Effect of pH on adsorption capacities of PMCS samples

761

(conditions: adsorbent dosage=30 mg, contact time=12 h, initial Cu (II)

762

concentration=100 mg/L, temperature=303 K); (c) Effect of initial Cu (II)

763

concentration on adsorption capacities of PMCS samples (conditions: pH=5,

764

adsorbent dosage=30 mg, contact time=12 h, temperature=303 K); (d) Effect of

765

contact time on adsorption capacities of PMCS samples (conditions: pH=5, adsorbent

766

dosage=30 mg, initial Cu (II) concentration=200 mg/L, temperature=303 K).

767

40


Page 40 of 46

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


768 769

Figure 8 Cu (II) adsorption capacities of PMCS samples versus eight cycles.

770

41



771

Page 42 of 46

Table 1 Nitrogen physisorption characterization of PMCS samples SSA [a]

TPV [b]

Vmeso [c]

Vmacro [d]

APS [e]

[m2 g-1]

[cm3 g-1]

[cm3 g-1]

[cm3 g-1]

[nm]

PMCS-1

16.74

0.04

0.03

0.01

9.77

PMCS-2

30.95

0.10

0.09

0.01

13.95

PMCS-3

42.38

0.16

0.12

0.04

14.04

PMCS-4

61.37

0.24

0.22

0.01

18.31

Sample

772

[a] Specific surface area (SSA) is calculated by the Brunauer-Emmett-Teller (BET)

773

method. [b] TPV means the total pore volume. [c] Vmeso indicates the mesopore

774

(2-50nm) volume calculated by the BJH method. [d] Vmacro indicates the macropore

775

(﹥50nm) volume calculated by the BJH method. [e] APS indicates the adsorption

776

average pore width calculated by the BET method (4V/A by BET).

777

42


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


778

Table 2 Adsorption parameters of Langmuir and Freundlich adsorption isotherm

779

models of PMCS samples Langmuir model

Freundlich model

Sample qm (mg/g)

B

R2

n

KF

R2

PMCS-1

45.66

0.1039

0.9985

5.3990

17.3137

0.9159

PMCS-2

84.75

0.0419

0.9973

2.8877

13.3191

0.9517

PMCS-3

126.58

0.0172

0.9984

1.8159

6.0177

0.9733

PMCS-4

188.68

0.0095

0.9989

1.4778

3.8857

0.9861

780 781

43



Page 44 of 46

782

Table 3 Comparison of the maximum Cu (II) adsorption capacity with other

783

adsorbents adsorbent

qm (mg g-1)

ref

Xanthate-modified magnetic chitosan

34.5

14

Magnetic chitosan

129.6

16

Nanoporous magnetic cellulose-chitosan

65.8

21

Ion-imprinted magnetic chitosan

132

23

Magnetic cellulose-chitosan hydrogel

44.7

50

Ion imprinted magnetic chitosan

109.89

52

EDTA-functionalized magnetic chitosan/grapheme oxide

207.26

53

TEPA modified chitosan/CoFe3O4

168.07

54

GO/Fe3O4

14.1

55

Magnetic chitosan

103.16

56

PMCS-4

188.68

this work

784 785

44


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


786

Table 4 Adsorption rate constants of pseudo-first-order, pseudo-second-order and

787

intraparticle diffusion models of PMCS samples

sample

qexp (mg/g)

pseudo-first-order

pseudo-second-order

intraparticle

model

model

diffusion model

qe

qe K1

R

2

(mg/g)

K2

R2

K3

R2

(mg/g)

PMCS-1

45.82

9.13

0.0085

0.6328

46.30

0.0052

0.9999

1.3706

0.6111

PMCS-2

77.12

25.90

0.0076

0.6316

79.37

0.0012

0.9987

2.8690

0.7514

PMCS-3

91.76

47.21

0.0088

0.9109

93.46

0.0009

0.9989

3.2034

0.8286

PMCS-4

124.13

54.06

0.0108

0.8700

125.01

0.0006

0.9981

4.7043

0.7921

788 789

45



790

The table of contents (TOC) graphic of this manuscript

791 792

Brief synopsis: Porous magnetic chitosan particles is synthesized via special superhydrophobic

793

surface of electrospun polyimide fiber mat with petal effect. Compared with traditional methods,

794

the mentioned fabrication approach is more effective and environmentally friendly, exhibiting

795

wide application prospects in the field of environment sustainable development.

796

46


Page 46 of 46

Efficient and Green Fabrication of Porous Magnetic Chitosan Particles

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