Guanidinium-Based Ionic Covalent Organic Framework for Rapid and

Subscriber access provided by Gothenburg University Library

Remediation and Control Technologies

Guanidinium-Based Ionic Covalent Organic Framework (iCOF) for Rapid and Selective Removal of Toxic Cr(VI) Oxoanions from Water Santa Jansone-Popova, Anthonin Moinel, Jennifer A. Schott, Shannon M. Mahurin, Ilja Popovs, Gabriel M. Veith, and Bruce A. Moyer Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.8b04215 • Publication Date (Web): 16 Oct 2018 Downloaded from http://pubs.acs.org on October 17, 2018

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

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

Page 1 of 18

Environmental Science & Technology

1

Guanidinium-Based Ionic Covalent Organic

2

Framework (iCOF) for Rapid and Selective

3

Removal of Toxic Cr(VI) Oxoanions from Water

4

Santa Jansone-Popova,* Anthonin Moinel,† Jennifer A. Schott, Shannon M. Mahurin, Ilja

5

Popovs, Gabriel M. Veith,§ Bruce A. Moyer

6

Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831,

7

United Sates.

8

KEYWORDS: ionic covalent organic frameworks, guanidinium, chromium(VI), ion exchange

9

ABSTRACT: Ionic covalent organic frameworks is an emerging class of functional materials in

10

which the included ionic interfaces induce strong and attractive interactions with ionic species of

11

opposite charge. In this work, the strong and selective binding forces between the confined

12

diiminoguanidinium groups in the framework and tetrahedral oxoanions have led to unparalleled

13

effectiveness in the removal of toxic chromium(VI) pollutant from aqueous solutions. The new

14

functional framework can uptake from 90 to 200 mg/g of chromium(VI), dependent on pH of

15

solution, and is capable of lowering chromium(VI) concertation in water from 1 ppm to 10 ppb

16

within minutes (an order of magnitude below the current US Environmental Protection Agency

17

maximum contaminant level of 100 ppb); demonstrating superior properties among known ion

18

exchange materials and natural sorbents. ACS Paragon Plus Environment

1


19

Page 2 of 18

INTRODUCTION

20

Covalent organic frameworks (COFs) are crystalline porous polymers in which the organic units

21

are chemically crosslinked to produce ordered structures with defined pores. These materials have

22

received extensive attention due to their applications in a variety of fields ranging from gas

23

adsorption and gas storage, to catalysis and nanofiltration.[1] Ionic covalent organic frameworks

24

(iCOFs) is an emerging class of functional materials that have the combined properties of COFs

25

and ion exchange resins. These materials are made either by pre-installing the ionic groups into

26

the organic building blocks prior to polymerization or by post-functionalizing the covalent organic

27

framework itself with ionogenic groups. Although, there are only a handful of examples in the

28

literature,[2] iCOFs are emerging as materials with unique properties, capable of absorbing toxic

29

anions and dyes from aqueous solutions with high capacity and selectivity.[2e-g]

30

Demand is increasing for functional materials that can achieve fast and efficient removal of toxic

31

species from the groundwater. Chromium(VI) in particular is one of the major water pollutants

32

and at concentrations greater than 100 ppb in drinking water is likely to cause severe damage to

33

living organisms due to its carcinogenic and mutagenic properties and strong oxidizing power.[3]

34

A variety of processes, such as chemical precipitation via reduction, ion exchange, sorption, and

35

filtration have been explored towards removal of Cr(VI) from drinking water.[4] However, the

36

drawbacks associated with these processes include high cost, slow kinetics, incomplete removal

37

of toxic metal, and the lack of selectivity in real systems. Based on the ability of guanidinium

38

groups to bind strongly with a variety of oxoanions,[5] we hypothesized that the incorporation of

39

this functional group into a porous organic framework would result in a functional material capable

40

of selective separation of oxoanions. Herein, we report the synthesis of a novel iCOF and its ability

41

to remove toxic Cr(VI) ions rapidly from aqueous streams with unparalleled selectivity and uptake

ACS Paragon Plus Environment

2

Page 3 of 18


42

capacity that ranges from 90 to 200 mg/g based on the pH of medium. Moreover, these design

43

principles potentially could be extended to materials capable of removing other toxic species such

44

as perchlorate, selenate, arsenate from the groundwater as well.

45

MATERIALS AND METHODS

46

General. The 1H NMR spectra were recorded on an AvanceIII-400 MHz NMR spectrometer

47

(Bruker Company) equipped with a 5 mm PABBO probe. The

48

experiments were recorder on an AvanceIII-400 MHz NMR spectrometer equipped with a 3.2 mm

49

HXY probe. Sample was spun at 5 kHz. Elemental analyses were performed under contract by

50

Atlantic Microlab, Inc. of Norcross, GA. ICP-OES analyses were performed at ORNL on iCAP

51

700 Series ICP Spectrometer. EPA 218.6 analyses were performed under contract by ALS

52

Environmental, OH. Commercially available compounds were purchased from Aldrich Chemical

53

Co., Acros Organics, Alfa Aesar or TCI America and were used without further purification.

54

Solution pH was measured using MColorHastTM pH-indicator strips (non-bleeding).

55

Synthesis: BT-DGCl was synthesized via condensation reaction between benzene-1,3,5-

56

triscarbaldehyde (12.4 mmol, 2.00 g) and diaminoguanidine hydrochloride (18.6 mmol, 2.32 g) in

57

a 500-mL thick wall pressure vessel with Teflon screw-cap using 38 mL of water and 124 mL of

58

1,4-dioxane as the solvent mixture. The reaction mixture was heated at 120 0C for 24 hours, then

59

allowed to cool to room temperature. The formed precipitate was filtered, washed thoroughly with

60

DI water, MeOH, and acetone, then dried under vacuum at 70 0C for 12 hours. The product was

61

obtained as fluffy, orange powder (3.59 g, 97% yield). The formed ionic framework was analyzed

62

by 13C cp and cppi MAS NMR, FTIR, EA, BET, TGA, and PXRD (see Supporting Information

63

for additional details).

13

C cp and cppi/MAS NMR


3


Page 4 of 18

64

General procedure for uptake of Cr(VI) oxoanions by BT-DGCl: 50 mg of BT-DGCl were

65

contacted with 10 mL of 20 mM solution of Na2CrO4 in water by end-over-end rotation in

66

individual 15 mL centrifuge tubes using a rotating wheel in an air box set at 25.0 °C ± 0.5 °C with

67

60 RPM speed. Contacts were performed in triplicate using specified contact time. Following

68

contacting, the triplicate samples were subjected to centrifugation at 4000 RPM for five minutes.

69

Each aqueous solution was then filtered through a 0.45 um Nylon filter, an aliquot was taken and

70

diluted 20 times for inductively coupled plasma optical emission spectrometry (ICP-OES)

71

analysis. The areas found under the observed Cr peak was used for determining its concentration.

72

Uptake capacity (mmol/g) was calculated using the following formula: ((C0-Ce)*V)/(M*m), where

73

C0 - initial element concertation in aqueous solution (mg/L); Ce - element concentration in aqueous

74

solution after contact with polymer (mg/L); V - volume of aqueous solution (L); M - atomic mass

75

of the element; m - mass of the polymer used (g). Uptake capacity (qe, mg/g) was calculated using

76

the following formula: ((C0-Ce)*V)/m.

77

RESULTS AND DISCUSSION

78

Encouraged by the ability of a simple diiminoguanidinium molecule 3 to bind with chromate

79

anion (CrO42-) in solution, as evident from the change in chemical shifts of the proton signals in

80

NMR spectrum highlighted in Figure 1b,[6] we decided to explore the efficiency of solid-state

81

material that encompasses same binding functionality in selective removal of Cr(VI) and other

82

oxoanions from aqueous environment. The novel iCOF (BT-DGCl) was synthesized

83

solvothermally in one step via the polycondensation reaction of benzene-1,3,5-triscarbaldehyde

84

(BT, 4), trigonal building block, and diaminoguanidinium (DG) chloride 1, linear strut, in water-

85

dioxane mixture at 120 °C, forming strong imine linkages between the units; a strategy commonly

86

employed in the synthesis of COFs.[7] This particular combination of building blocks was chosen


4

Page 5 of 18


87

to favor the formation of 2D sheets, in which the guanidinium groups are located on the edges of

88

the hexagonal pores, ideally providing functionalized one-dimensional channels that penetrate

89

throughout the three-dimensional structure.[2d] The complete consumption of the starting materials

90

was confirmed by Fourier-transform infrared spectroscopy (FT-IR). The C=O carbonyl stretching

91

band of the aldehyde at 1680 cm-1 disappeared in the spectrum and was replaced with a new band

92

at 1600 cm-1, corresponding to newly formed imine C=N bonds (Figure SI-2, O

a)

Cl

O

H

O HB

HA N HB

H N

H N H

N

H

HA

2

HB

ethanol

N HB

4

NH H 2N

reflux, 24 hours

N N H H •HCl

O

N

1,4-dioxane, water

NH2

reflux, 24 hours

Cl

3 + Na2CrO4

N

N

BA C

c)

CP CPPI

N N

H

D

N

H

H

Cl

BT-DGCl

1 HB

HA

H

N

H

3

b)

H N

H N

H N

H N

N N H

N

Cl H

N

d) BT-DGCl

C D

A

B

BT-DGCl

3 8.5

8.0

7.5

[ppm]

160

150

140

130

[ppm]

93 94

Figure 1. a) Synthesis scheme of small molecular fragment 3 and polymer BT-DGCl; b) liquid 1H NMR spectra of

95

compound 3 and 3 with 1 equivalent of Na2CrO4 salt in MeOH-d4; c) 13C CP and CPPI MAS solid-state NMR spectra

96

of BT-DGCl spun at 5 kHz; d) TGA curve of BT-DGCl from 50 ˚C to 750 ˚C at 10 ˚C/minute in N2 atmosphere with

97

a purge rate of 20 mL/minute.

98

Supporting Information). Additionally, the aldehyde carbon peak was not detected in the 13C cross

99

polarization/magic angle spinning (CP/MAS) NMR spectrum of BT-DGCl, confirming a complete

100

conversion of starting materials into an imine bonded framework (Figure 1b). Spectral overlay of

101

the cross polarization with polarization inversion (CPPI) spectrum, in which CH0 appear positive


5


13

Page 6 of 18

102

and CH1 are null,[8] with

103

corresponds to guanidinium carbons (D); shoulder at ~149 ppm corresponds to imine carbons (C);

104

signal at ~135 ppm matches with quaternary aromatic carbons (A); and shoulder at ~130 ppm—to

105

benzene carbons (B).[9] The elemental composition of the iCOF was confirmed by elemental

106

analysis and matched well with the theoretical value for infinite polymer (Table SI-2, Supporting

107

Information). Based on the elemental composition, the overall anion exchange capacity was

108

estimated to be 4.3±0.3 mequiv per gram of dry BT-DGCl,[6] one of the highest values among anion

109

exchange resins and natural sorbents.[10,11]

C CP/MAS NMR spectrum revealed that the peak at ~152 ppm

110

Guanidinium—positively charged nitrogen analogue of urea—is known to form strong ion pairs

111

with oxoanions primarily due to electrostatic forces, as well as directional, noncovalent hydrogen

112

bonding interactions.[5] Thus, we expected the weakly bound chlorides in BT-DGCl to undergo

113

exchange with oxoanions, such as sulfate, selenate, and chromate. In order to maintain the charge

114

neutrality in the ionic framework, two chloride ions in BT-DGCl would be exchanged with one

115

divalent oxoanion, in other words, theoretical capacity of material for divalent anions would be

116

equal to only half of the total chloride content in the BT-DGCl, i.e. ~2.2±0.2 mequiv/g. In BT-

117

DGCl framework, a rapid and complete exchange of chloride ions with sulfate ions took place in

118

less than 10 minutes (Figure SI-3, Supporting Information), indicating apparent accessibility of

119

the exchange sites, despite low BET surface area (vide infra). Upon addition of BT-DGCl to

120

Na2CrO4 solution, an ion exchange process resulted in a concomitant color change of the material

121

from yellow to dark brown. As can be clearly seen from the time-dependent uptake isotherm

122

presented in Figure 2a, Cr(VI) removal by BT-DGCl requires less than 5 minutes to attain

123

equilibrium. The maximum uptake capacity of Cr(VI) was determined by keeping the amount of

124

BT-DGCl constant and changing the initial concentration of Cr(VI) in the aqueous solution. The


6

Page 7 of 18


125

results depicted in Figure 2b reveal sharp increase at low Cr(VI) concentrations, reaching the

126

maximum uptake capacity of ~120 mg/g at initial solution pH 7. The results obtained from uptake

127

capacity versus Cr(VI) concentration plot fitted well with Langmuir model (R2 > 0.999), consistent

128

with a site-wise exchange of Cr(VI) oxoanions. In accordance with previous reports, we observed

129

significantly improved Cr(VI) removal efficiency by BT-DGCl at low pH (Figure 2d), reaching

130

200 mg/g (3.8 mequiv/g). On the one hand, this observed trend can be explained by examining

100

3.0 2.0

60

1.5

40

1.0

20

0.5

0

0.0

0

15 30 45 60 75 90 105 120 Time, min

100 50

2

3

4

5

6 7 pH

8

9

10

120 80 60

3.5

y = 0.0084x + 0.0234 R² = 0.9997

2.5 2.0 1.5 1.0

20 0

4.0 3.0

40

Cr(VI) concentration, ppb

Cr(VI) uptake, mg/g

150

c)

140 100

e)

200

0

131

2.5

80

b)

Ce/qe g/L

3.5

qe, mg/g

4.0

120

0.5 0

100

200 Ce, mg/L

300

0.0

400

1000

f)

5 g/L BT-DGCl BT-DGCl

Uptake, mmol/g

d)

140

Cr(VI) uptake, mmol/g

Cr(VI) uptake, mg/g

a)

100

10

0

100

2.5

20 mM

200 Ce, mg/L 10 mM

300

400

1 mM

2.0 1.5 1.0 0.5

1

0.0 0

10

20

30 40 Time, min

50

60

Mo

S Se As oxoanion (MO42-)

Cr

132

Figure 2. a) Effect of the contact time on the Cr(VI) removal by BT-DGCl: initial pH = 7; dose 5 g/L; T = 25 ˚C;

133

CCr(VI) = 20 mM; b) Uptake isotherm of BT-DGCl; c) Linear regression using Langmuir adsorption model; d) Effect

134

of the initial pH on the Cr(VI) removal by BT-DGCl: dose 5 g/L; T = 25 ˚C; CCr(VI) = 20 mM; time =10 min; e) Effect

135

on the contact time on the Cr(VI) removal by BT-DGCr: initial pH = 7; dose 5 g/L; T = 25 ˚C; CCr(VI) = 1 ppm; f)

136

Effect of the concentration of different oxoanions (MoO42-, SO42-, SeO42-, HAsO42-) on the removal of Cr(VI)

137

oxoanions (CrO42-) by BT-DGCl: initial pH = 7; dose 5 g/L; T = 25 ˚C; CM = 20, 10, 1 mM each; time = 10 min.

138

the distribution of Cr(VI) species in solution, which is dependent on Cr(VI) concentration and the

139

pH.[12] At pH below 6.5, monovalent bichromate ion (HCrO4-) is the predominant Cr(VI) form

140

present in aqueous medium, as a consequence, the removal of monoanionic Cr(VI) species by BT-

141

DGCl at low pH correlates well with the observed higher adsorption capacities. On the other hand, ACS Paragon Plus Environment

7


Page 8 of 18

142

with increasing the pH, two processes contribute to decreasing the adsorption capacity of ionic

143

adsorbent: the major Cr(VI) species in solution at high pH values are divalent chromate ions

144

(CrO42-) and a number of surface charges in BT-DGCl decreases with increasing pH value of the

145

aqueous phase due to partial deprotonation of the guanidinium ions present in the framework

146

(calculated pKa value ~8.4)[6], leading to a diminished Cr(VI) removal capacity by BT-DGCl.

147

Nonetheless, the exchange capacity of Cr(VI) as CrO42- in BT-DGCl remains high (>90 mg/g) even

148

at the initial pH values of aqueous solution as high as 10. Overall, the new framework (BT-DGCl)

149

outperforms all of the anion exchange sorbents reported to date due to its unique ability to

150

selectively uptake Cr(VI) species at neutral pH values very rapidly, whereas the majority of

151

previously-developed materials operate efficiently at low pH values and/or require long contact

152

times to achieve efficient (practical) uptake capacities (Table SI-1).

153

Rapid decontamination of water from toxic metal ions was achieved by treating aqueous solution

154

containing elevated concentration of Cr(VI) with BT-DGCl. After contacting the BT-DGCl with

155

chromate-laced water for only 1 minute, the Cr(VI) concentration decreased from the initial 1 ppm

156

to 10 ppb level—a hundred fold reduction (Figure 2e), which is an order of magnitude below the

157

current US Environmental Protection Agency (EPA) maximum contaminant level for total

158

chromium concentration of 100 ppb.[13]

159

The BT-DGCl shows an affinity towards Cr(VI) oxoanions even in the presence of competing

160

oxoanions. When the total oxoanion concentration in aqueous solution exceeds the total exchange

161

capacity of the sorbent (blue and green bars in Figure 2f), the sorbent affinity towards the

162

oxoanions follows the order: Cr(VI)>>Mo(VI)>As(V)>Se(VI)>S(VI). It is worth noting that at a

163

very low combined oxoanion concentration, when the concentration of oxoanions is significantly

164

lower than the exchange capacity of sorbent, the BT-DGCl indiscriminately and quantitatively


8

Page 9 of 18


165

removes all five oxoanions from the aqueous solution (red bars, Figure 2f). Additionally, we tested

166

the ability of excess BT-DGCl to selectively remove Cr(VI) species from a contaminated drinking

167

water sample that contained naturally-occurring concentrations of NO3- (50 ppm) and SO42- (250

168

ppm) ions, but elevated concentration of CrO42- (112 ppm). All but nitrate ions were quantitatively

169

removed by BT-DGCl (Table SI-3, Supporting Information). The above results suggest that the

170

new BT-DGCl possesses an extraordinary affinity and selectivity towards tetrahedral oxoanions.

171

We believe that the hydration energies[14] in conjunction with the basicity of an anion[6] play an

172

integral role in the observed selectivity.

173

Surprisingly, the Brunauer-Emmett-Teller (BET) surface area measured for activated BT-DGCl

174

sample appeared to be only ~3 m2/g, which is significantly lower than the previously reported

175

values for analogous iCOFs (surface area ~200-300 m2/g).[2d,6] Such a low surface area could be

176

explained by taking into consideration the poor directional control of diaminoguanidinium groups

177

used in BT-DGCl synthesis, resulting in a disordered structure and smaller-sized pores. Despite

178

this, the performance of BT-DGCl in the removal of Cr(VI) from aqueous streams is remarkable.

179

Rapid access by oxoanions to the exchangeable sites in the framework suggests the presence of

180

hydrated interconnected pores. As implied, BT-DGCl rapidly absorbs water when exposed to moist

181

air at 100 % relative humidity (Figure SI-4, Supporting Information). The maximum water uptake

182

was measured to be 25% by weight, which corresponds to approximately 3 additional water

183

molecules per ionic site. Most of the water from hydrated BT-DGCl can be removed by drying the

184

sample at 70 ˚C under vacuum. Thermogravimetric analysis (TGA), performed on vacuum-dried

185

sample of BT-DGCl, demonstrated that this material is thermally stable up to 250 ˚C under nitrogen

186

(Figure 1c), the initial drop in weight corresponds to water loss that is residing within the

187

framework. In addition, the powder X-ray diffraction (PXRD) analysis revealed low crystallinity


9


Page 10 of 18

188

of BT-DGCl, the major broad peak at 2θ = 27˚ being consistent with vertical stacking of 2D sheets

189

(Figure SI-5, Supporting Information). This could be due to the presence of repulsive interactions

190

between the positively charged guanidinium groups, combined with the necessity to accommodate

191

chloride counterions. Similar behavior has been previously reported by Banerjee and coworkers

192

for a related material.[2d]

193

In order to gain a deeper understanding of the oxidation state of chromium present in the near-

194

surface regions of chromate-loaded BT-DG, X-ray photoelectron spectroscopy (XPS) analysis

195

was performed. The Cr 2p3/2 XPS data for BT-DGCr and BaCrVIO4 standard are plotted in Figure

196

3. The data obtained for BT-DGCr exhibits a mixture of high binding energy (~578.5 eV) and

197

lower binding energy (~576.6 eV) feature that corresponds to Cr(VI) and Cr(III), respectively. The

198

relative fraction of Cr(III) in the framework increase in more basic pH solution mixtures.

199

Normalized Intensity

1

BT-DG-Cr (pH4) BT-DG (pH Cr 4) BT-DG-Cr (pH7) BT-DG (pH Cr 7) BaCrO BaCrO4 4

0.8 0.6 0.4 0.2 0

582

580

578 576 Binding Energy (eV)

574

572

200

Figure 3. XPS spectra of BT-DGCr, prepared at initial pH = 4 and 7, and control substrate, BaCrO4.

201

This may indicate that the drying of the sample needed to perform the XPS measurements may

202

change the reduction potential of the local environment of BT-DGCr since Cr(III) compounds (i.e.,

203

Cr2O3 and Cr(OH)3) are not water soluble.[15] As expected, the analysis of the sodium chromate

204

solution at pH 7, prior to the exposure to BT-DGCl, indicated a presence of only Cr(VI) species.[6]

205

While we observed a nearly quantitative (>95%) stripping of chromium species from BT-DGCr

206

using aqueous base (Figure SI-6, Supporting Information), the resulting neutral material (BT-DG)


10

Page 11 of 18


207

retained slightly greenish, which is indicative of Cr(III) species and likely represents the remaining

208

; Marinas, B. J., Development and Performance

273

Characteization of a Polyimine Covalent Organic Framework Thin-Film Composite Nanofiltration

274

Membrane. Environ. Sci. Technol. 2017, 51 (24), 14352–14359.

275

[2] a) Du, Y.; Yang, H.; Whiteley, J. M.; Wan, S.; Jin, Y.; Lee, S.-H.; Zhang, W., Ionic Covalent

276

Organic Frameworks with Spiroborate Linkage. Angewandte Chemie International Edition 2016,

277

55 (5), 1737–1741; b) Dong, B.; Wang, L.; Zhao, S.; Ge, R.; Song, X.; Wang, Y.; Gao, Y.,

278

Immobilization of ionic liquids to covalent organic frameworks for catalyzing the formylation of

279

amines with CO2 and phenylsilane. Chemical Communications 2016, 52 (44), 7082–7085; c) Ma,

280

H.; Liu, B.; Li, B.; Zhang, L.; Li, Y.-G.; Tan, H.-Q.; Zang, H.-Y.; Zhu, G., Cationic Covalent

281

Organic Frameworks: A Simple Platform of Anionic Exchange for Porosity Tuning and Proton

282

Conduction. Journal of the American Chemical Society 2016, 138 (18), 5897–5903; d) Mitra, S.;

283

Kandambeth, S.; Biswal, B. P.; Khayum M, A.; Choudhury, C. K.; Mehta, M.; Kaur, G.; Banerjee,

284

S.; Prabhune, A.; Verma, S.; Roy, S.; Kharul, U. K.; Banerjee, R., Self-Exfoliated Guanidinium-

285

Based Ionic Covalent Organic Nanosheets (iCONs). Journal of the American Chemical Society

286

2016, 138 (8), 2823–2828; e) Su, Y.; Wang, Y.; Li, X.; Li, X.; Wang, R., Imidazolium-Based

287

Porous Organic Polymers: Anion Exchange-Driven Capture and Luminescent Probe of Cr2O72–.

288

ACS Applied Materials & Interfaces 2016, 8 (29), 18904–18911; f) Li, Z.; Li, H.; Guan, X.; Tang,

289

J.; Yusran, Y.; Li, Z.; Xue, M.; Fang, Q.; Yan, Y.; Valtchev, V.; Qiu, S., Three-Dimensional Ionic

290

Covalent Organic Frameworks for Rapid, Reversible, and Selective Ion Exchange. Journal of the

291

American Chemical Society 2017, 139 (49), 17771–17774; g) Huang, N.; Wang, P.; Addicoat, M.

292

A.; Heine, T.; Jiang, D., Ionic Covalent Organic Frameworks: Design of a Charged Interface


14

Page 15 of 18


293

Aligned on 1D Channel Walls and Its Unusual Electrostatic Functions. Angewandte Chemie

294

International Edition 2017, 56 (18), 4982–4986.

295

[3] a) Towill, L. E.; Shriner, C. R.; Drury, J. S.; Hammons, A. S.; Holleman, J. W., Reviews of the

296

Environmental Effects of Pollutants: III. Chromium, National Technical Information Service

297

Springfield, Virginia 1977; b) U.S. Department of Health and Human Services, Toxicological

298

Profile for Chromium, Agency for Toxic Substances and Disease Registry 2012; c) Shadreck, M.;

299

Mugadza, T., Chromium, an essential nutrient and pollutant: A review. African Journal of Pure

300

and Applied Chemistry 2013, 7, 310–317.

301

[4] a) Dabrowski, A.; Hubicki, Z.; Podkościelny, P.; Robens, E., Selective removal of the heavy

302

metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere 2004,

303

56 (2), 91–106; b) Hawley, E. L.; Deeb, R. A.; Kavanaugh, M. C.; Jacobs R.G, J., Treatment

304

Technologies for Cromium(VI), CRC Press LLC 2004, 273; c) McGuire, M. J.; Blute, N. K.; Qin,

305

G.; Kavounas, P.; Froelich, D.; Fong, L., Hexavalent Chromium Removal Using Anion Exchange

306

and Reduction With Coagulation and Filtration, AwwaRF and City of Glendale Water and Power

307

2007.

308

[5] a) Blondeau, P.; Segura, M.; Perez-Fernandez, R.; de Mendoza, J., Molecular recognition of

309

oxoanions based on guanidinium receptors. Chemical Society Reviews 2007, 36 (2), 198–210; b)

310

Custelcean, R.; Williams, N. J.; Seipp, C. A.; Ivanov, A. S.; Bryantsev, V. S., Aqueous Sulfate

311

Separation by Sequestration of [(SO4)2(H2O)4]4− Clusters within Highly Insoluble Imine-Linked

312

Bis-Guanidinium Crystals. Chemistry – A European Journal 2016, 22 (6), 1997–2003; c) Haj-

313

Zaroubi, M.; Schmidtchen, F. P., Probing Binding-Mode Diversity in Guanidinium–Oxoanion

314

Host–Guest Systems. ChemPhysChem 2005, 6 (6), 1181–1186; d) Schmidtchen, F. P.; Berger, M.,

315

Artificial Organic Host Molecules for Anions. Chemical Reviews 1997, 97 (5), 1609–1646; e)


15


Page 16 of 18

316

Seipp, C. A.; Williams, N. J.; Bryantsev, V. S.; Moyer, B. A., Simple guanidinium motif for the

317

selective binding and extraction of sulfate. Separation Science and Technology 2017, 53 (12,

318

1864–1873.

319

[6] See Supporting Information for additional details.

320

[7] Segura, J. L.; Mancheno, M. J.; Zamora, F., Covalent organic frameworks based on Schiff-

321

base chemistry: synthesis, properties and potential applications. Chemical Society Reviews 2016,

322

45 (20), 5635–5671.

323

[8] Wu, X. L.; Zilm, K. W., Complete Spectral Editing in CPMAS NMR. Journal of Magnetic

324

Resonance, Series A 1993, 102 (2), 205–213.

325

[9] Full 13C CP and CPPI MAS NMR spectra are included in the Supporting Information, Figure

326

SI-1.

327

[10] Few examples of ion exchange resins used in Cr(VI) removal: a) Sengupta, A. K.; Roy, T.;

328

Jessen, D., Modified anion-exchange resins for improved chromate selectivity and increased

329

efficiency of regeneration. Reactive Polymers, Ion Exchangers, Sorbents 1988, 9 (3), 293–299; b)

330

Balan, C.; Volf, I.; Bilba, D., Chromium (VI) removal from aqueous solutions by Purolite base

331

anion-exchange resins with gel structure. Chemical Industry & Chemical Engineering Quarterly

332

2013, 19, 615–628; c) Das, S.; Chakraborty, P.; Ghosh, R.; Paul, S.; Mondal, S.; Panja, A.; Nandi,

333

A. K., Folic Acid-Polyaniline Hybrid Hydrogel for Adsorption/Reduction of Chromium(VI) and

334

Selective Adsorption of Anionic Dye from Water. ACS Sustainable Chemistry & Engineering

335

2017, 5 (10), 9325–9337; d) Edebali, S.; Pehlivan, E., Evaluation of Amberlite IRA96 and Dowex

336

1×8 ion-exchange resins for the removal of Cr(VI) from aqueous solution. Chemical Engineering

337

Journal 2010, 161, 161–166; e) Zhao, D.; SenGupta, A. K.; Stewart, L., Selective Removal of


16

Page 17 of 18


338

Cr(VI) Oxyanions with a New Anion Exchanger. Industrial & Engineering Chemistry Research

339

1998, 37 (11), 4383–4387.

340

[11] Few examples of natural sorbents used in Cr(VI) removal: a) Venditti, F.; Cuomo, F.; Ceglie,

341

A.; Ambrosone, L.; Lopez, F., Effects of sulfate ions and slightly acidic pH conditions on Cr(VI)

342

adsorption onto silica gelatin composite. Journal of hazardous materials 2010, 173 (1-3), 552–7;

343

b) Jardine, P. M.; Fendorf, S. E.; Mayes, M. A.; Larsen, I. L.; Brooks, S. C.; Bailey, W. B., Fate

344

and Transport of Hexavalent Chromium in Undisturbed Heterogeneous Soil. Environmental

345

Science & Technology 1999, 33 (17), 2939–2944; c) Mutongo, F.; Kuipa, O.; Kuipa, P. K.,

346

Removal of Cr(VI) from Aqueous Solutions Using Powder of Potato Peelings as a Low Cost

347

Sorbent. Bioinorganic Chemistry and Applications 2014, 2014, 7.

348

[12] a) Tong, J. Y.-p.; King, E. L., A Spectrophotometric Investigation of the Equilibria Existing

349

in Acidic Solutions of Chromium(VI)1-3. Journal of the American Chemical Society 1953, 75

350

(24), 6180–6186; b) Sengupta, A. K.; Clifford, D.; Subramonian, S., Chromate ion-exchange

351

process at alkaline pH. Water Research 1986, 20 (9), 1177–1184.

352

[13]

353

https://www.epa.gov/dwstandardsregulations/chromium-drinking-water. b) R. Sutton, Chromium-

354

6 in U.S. Tap Water, Environmental Working Group, 2010. c) Chromium-6 in Drinking Water

355

Sources: Sampling Results, California Department of Public Health, Sacramento, CA, 2009.

356

[14] Smith, D. W., Ionic Hydration Enthalpies. Journal of Chemical Education 1977, 54 (9), 540–

357

542.

358

[15] Rai, D.; Sass, B. M.; Moore, D. A., Chromium(III) hydrolysis constants and solubility of

359

chromium(III) hydroxide. Inorganic Chemistry 1987, 26 (3), 345–349.

a)

United

States

Environmental

Protection

Agency

website;

360


17


361

Page 18 of 18

TABLE OF CONTENTS (TOC)

362


18

Guanidinium-Based Ionic Covalent Organic Framework for Rapid and

Recommend Documents