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Synthesis of hybrid ion exchanger for rhodamine B dye removal: Equilibrium, kinetic and thermodynamic studies Saruchi Sharma, Vaneet Kumar, Balbir Singh Balbir Singh Kaith, and Rajeev Jindal Jindal Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01690 • Publication Date (Web): 19 Sep 2016 Downloaded from http://pubs.acs.org on September 19, 2016

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Industrial & Engineering Chemistry Research

1

Synthesis of hybrid ion exchanger for rhodamine B dye removal: Equilibrium, kinetic and

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thermodynamic studies

3

Saruchi*1, 3, Vaneet Kumar2, B S Kaith3 and Rajeev Jindal3

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Corresponding author:

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Dr Saruchi

6

1

7

SSS National Institute of Bio-Energy, Kapurthala, Punjab, India’

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E-mail: [email protected]

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Phone: +919023991540

Biochemical Conversion Devision

10 11

2

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E-mail: [email protected]

Dr Vaneet Kumar, CT Group of Institutions, Jalandhar, India

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3

15

Punjab, India

Department of Chemistry, Dr B R Ambedkar National Institute of Technology, Jalandhar,

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*SS Supporting Information

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ABSTRACT:

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A systematic method was employed to synthesize organic-inorganic based hybrid ion-exchanger

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for the removal of rhodamine B dye from aqueous solution. Ion exchange capacity of the hybrid

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ion exchanger was found to be 2.4 meq/g. The morphology, chemical structure and elemental

22

analysis of the synthesized hybrid ion exchanger were investigated by SEM, FTIR and EDS

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ACS Paragon Plus Environment


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analytical techniques. Effects of different reaction parameters like contact time, temperature and

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pH were also investigated. The adsorption kinetics of rhodamine B molecules onto synthesized

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hybrid ion exchanger were studied and compared using psudo-first-order and pseudo-second-

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order and found that pseudo-second-order best reprented the adsorption process. The Weber-

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Morris intraparticle diffusion result showed that intra-particle diffusion is not the rate limiting

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step. The adsorption isotherm model Langmuir, Freundlich, Dubinin-Radushkevich, Tempkin

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and Redlich-Peterson isotherms were studied and found that the Langmuir is the best-fitting

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models for the experimental. An increase in temperature resulted in a decrease in rhodamine B

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dye removal, suggesting that the adsorption process was exothermic. Maximum dye removal was

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found to be 98.3 %. The kinetics of adsorption followed a pseudo-second order rate equation.

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KEYWORDS: Hybrid ion exchanger, Distribution behavior and rhodamine B

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1. INTRODUCTION

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One of the major contaminates of water is dye pollutant, which comes from textile, paper

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and leather industries1,2. Discharging waste water from these industries can contaminate surface

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as well as ground water. This causes serious damage to the aquatic flora and fauna as these dyes

40

may be toxic and mutagenic in nature3-5. Most common method used to treat waste water

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includes adsorption, filtration, biodegradation, photo degradation, reverse osmosis, coagulation,

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chemical treatment and ion-exchanger. Ion-exchanger is one of the best methods to remove these

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dyes from waste water6-8.

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The interest in organic-inorganic hybrid ion exchange materials has increased considerably in the

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last few decades because of their stability at high temperature and high ion exchange capacity.

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These are found to be more suitable than natural or commercial ion exchanger because of the

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selectivity for certain ions or groups. Stability can be utilized in ion exchange process for the

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treatment of waste water 9-11. Dowex HCR-S a synthetic resin is used to remove different heavy

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metal such as cadmium (Cd2+), nickel (Ni2+) and zinc (Zn2+) from aqueous solutions and found

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that adsorption rate increased with increase in the initial concentration of metal ions, stirring

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speed and temperature. Adsorption kinetics through different isotherm models like Langmuir,

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Freundlich, Temkin, Elovich, Khan, Sips, Toth, Radke-Praunstrzki, Koble-Corrigan were also

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studied12-14. Hydrous oxides were the most commonly used exchangers, but they lacked chemical

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stability. Organic-inorganic ion exchangers based on tetravalent metals has been considerably

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studied in the recent years because of their selectivity and intercalation properties. Zirconium

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based ion exchangers have been used because of their excellent ion-exchange behavior.

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Heteropolyacid salts based on titanium, thorium and zirconium have been reported in the

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literature as ion exchange materials. Ion exchangers prepared through these materials have better

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properties like stability and high ion exchange capacity as compared to the simple salts of

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metals15-17.

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Rhodamine B belongs to the class of xanthene dyes and is highly soluble in water. If

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swallowed it is harmful to human beings and animals. It causes irritation to skin, eyes and

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respiratory tract. It is a chronic neurotoxin and is carcinogenic to humans and animals. Because

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of such harmful effect of this dye researchers all over the world are concerned for the removal of

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the dye from the industrial waste water before it discharges into the environment18,19.

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The present work deals with the synthesis of Gum tragacanth-zirconium (IV)

67

tungstoiodophosphate based organic-inorganic hybrid ion exchanger. Literature survey revealed

68

that three-component based ion exchangers (i.e.) zirconium (IV) iodooxalate, zirconium (IV)

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phosphosilicate, zirconium (IV) phosphoburate, zirconium (IV) tungstophosphate and zirconium

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(IV) iodophosphate have been studied for their ion exchange behavior and analytical

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applications. However zirconium (IV) tungstoiodophosphate and Gum tragacanth based ion

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exchanger was not synthesized earlier. Synthesized Gum tragacanth-zirconium (IV)

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tungstoiodophosphate based ion exchanger has high ion exchange capacity as well as higher

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chemical and thermal stability. A comparison of synthesized adsorbent with the existing

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adsorbent for the removal of rhodamine B is given in Table S120-25. The present work is also

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concerned with the characterization of Gum tragacanth-zirconium (IV) tungstoiodophosphate

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based ion exchanger and their evaluation for the removal of rhodamine B dye.

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2. EXPERIMENTAL

79 80

2.1. Materials and analytical methods

81 82

Gum tragacanth (SD Fine Chemical Pvt. Ltd.), acrylic acid, glutaraldehyde, ascorbic

83

acid, potassium persulphate (Merck), Zirconium (IV) oxychloride (ZrOCl2.8H2O), sodium

84

tungstate, potassium iodate, orthophosphoric acid (Qualigens).

85 86

2.2. Synthesis of hybrid ion exchanger

87

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A mixture of 0.1 M ZrOCl2.8H2O solution, 0.5 M sodium tungstate, potassium iodate and

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1M orthophosphoric acid in known volume ratios with intermittent shaking was prepared and pH

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was maintained at 1.0. 5 mL of the resulting mixture was taken in a reaction flask. It was

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followed by the addition of Gum tragacanth (1.0 g), ascorbic acid-potassium persulphate were

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added with continuous stirring followed by the addition of glutaraldehyde (0.5305 ×10-3 mol L-)

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and acrylic acid with thoroughly stirring to attain the homogeneity. Resulting mixture was kept

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in hot air oven at temperature of 50°C for about 2 hours26,27. After cooling to room temperature it

95

was washed with acetone and was dried in the hot air oven at 60 oC. After that it was kept in the

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solution of 1M HNO3 to convert the product into the H+ form for about 24 hours and again dried.

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The resulting ion exchanger was then crushed to get the particle of mesh size around 50-60. Ion

98

exchanger in different volume ratio of the mixture (Table S2) was prepared to get the ion

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exchanger having higher IEC value 28.

100

2.3. Studies of Physico-Chemical Properties of Ion-Exchanger

101 102

2.3.1. Ion-Exchange Capacity (IEC)

103

The ion exchange capacity of the synthesized ion exchanger was determined by the

104

column process. 0.5g of the ion exchanger (H+ form) was packed in a glass column and washed

105

with demineralized water maintaining the flow rate 20 drops per minute, to remove any excess of

106

acid that remained on the particles until it becomes acid free and it was confirmed using pH

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paper. After that 100 mL of 1M solution of KCl was passed through the column maintaining the

108

flow rate 20 drops per minute. The effluent was collected and titrated against the standard NaOH

109

solution to determine the total H+ ions released. The ion exchange capacity of the synthesized

110

hybrid ion exchangers was calculated using the equation given below29: 5



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111 112 113

IEC

=

Volume of titrant used x volume of effluent released x NaOH Concentration KCl or NaCl concentration

114 115

2.3.2. Effect of Temperature on IEC of synthesized Ion Exchanger

116

Thermo gravimetric analysis of the synthesized hybrid ion exchanger was performed at a

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heating rate of 10°C min–1. The effect of heating on the ion-exchange capacity of the material

118

was also examined. The synthesized hybrid ion exchanger was heated at different temperatures

119

for 1 h in a muffle furnace and the ion-exchange capacity for K+ was evaluated by the column

120

process as described in Section 2.3.1 after cooling it to room temperature30.

121 122

2.3.3. pH Titration of Hybrid Ion Exchanger

123

pH titration was performed by the batch process using the method of Topp and Pepper31.

124

0.5g of the synthesized ion exchanger was placed in each of the several 250 mL conical flasks

125

followed by equimolar solution of alkali metal chlorides (KCl, NaCl) and their hydroxides

126

(KOH, NaOH) in different volume ratios, the final volume was maintained up to 50 mL to

127

maintain the ionic strength constant. The pH of each solution was measured and plotted against

128

milliequivalents of OH ions31,32.

129 130

2.3.4. Chemical stability

131 132

Effect of different chemical solutions on IEC was studied. The extent of dissolution of

133

the material in different mineral acids and organic acid was studied. 0.5g of synthesized ion 6


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exchanger was equilibrated with 25 mL of the different solutions like 1M HCl, 2M HCl, 1M

135

HNO3 and 2M HNO3 for twenty four hours at room temperature. The remaining amount of

136

material was filtered and washed by water. After removal of excess acid or base, it was dried in

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hot air oven at 50oC. The IEC of remaining material was determined by column method as

138

described in Section 2.3.1.

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2.3.5. Distribution Studies of synthesized Ion exchanger

140 141

Distribution studies were carried out for three metal ions by batch process. The metal ion

142

solutions were treated with the known amount of the exchanger separately. 6 hours shaking of

143

solutions was done to maintain equilibrium using a shaker. Then solutions were kept as such for

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a definite interval of time at room temperature. A definite volume of the solution was taken into

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conical flask using a pipette and titrated against EDTA solution. The metal ion solutions without

146

exchanger were also titrated against EDTA solution. The distribution coefficient (Kd) values for

147

synthesized hybrid ion exchanger for metal ions was calculated using the following equation32,33

148

=

( − ) ( )

149 150 151

Where, I and F are initial and final metal ion concentration, respectively. V is the volume of

152

solution and W is the weight of the ion exchanger

153

154

2.4. Dye Removal Studies 7



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Removal of rhodamine B dye was studied through batch experiment. The concentration

156

of the rhodamine B dye was varied from 10-100 ppm. A known weight of the synthesized

157

sample was taken in the 100 mL of dye solution having known concentration. Effect of

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physiological pH, dye concentration, temperature and synthesized sample dosage on dye removal

159

was studied. The amount of dye removed from per unit mass of the synthesized sample (qt) was

160

calculated using the equation given below32,33:

=

− ()

161

Where, Co and Ct are the concentration of dye at the initial stage and after time t, V is the volume

162

of the dye solution; M is the mass of the synthesized material.

% =

( − ) ()

163

Where, Co and Ce are the initial and equilibrium concentration of dye; %R is the percentage

164

removal of dye.

165

3. RESULTS AND DISCUSSION

166 167

3.1. Ion Exchange Capacity (IEC)

168

The ion-exchange capacity of the synthesized ion exchanger at different volume ratio of

169

the mixture was calculated and the maximum ion-exchange capacity was found to be 2.4 meq/g

170

at the volume ratio of 1:1:3:1. IEC of different volume ratio are given in Table S3. The

171

synthesized ion exchanger was optimized with respect to ion exchange capacity and the

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maximum ion exchange capacity occurred at the volume ratio of 1:1:3:1. Further all the reactions

173

were carried out using this volume ratio.

174

3.2. Fourier transform infrared spectroscopy (FT-IR)

175

IR spectrum of synthesized ion exchanger showed broad peaks at 3398 cm-1 (O-H

176

stretching of carbohydrates), 2928 cm-1 (-CH stretching), 1039 cm-1 (-C-O stretching region as

177

complex bands resulting from C-O and C-O-C stretching vibrations), one peak at 1377cm-1 due

178

to CH, CH2 and OH in plane bending in carbohydrates and peak at668 cm-1 (pyranose ring)

179

(Figure 1a ). New peaks at 2927 cm-1 (C-H stretching of CH3, CH2) and 1724 cm-1 (C=O

180

stretching of COOH) were observed which suggested that these functional groups may interact

181

with the rhodamine B dye (Figure 1b).

182

3.3. Energy-dispersive spectroscopy (EDS)

183

In order to have the conducting impact, the samples were gold plated and the scanning

184

was synchronized with microscopic beam so as to maintain the small size over a large distance

185

relative to the specimen. The EDS of the Gum tragacanth clearly indicates that the constituents

186

of Gum tragacanth are carbon and hydrogen only (Figure S 1a). EDS spectra of the synthesized

187

ion exchanger clearly showed that in the synthesized ion exchanger zirconium (Zr), tunguston

188

(W) and phosphorous (P) are present (Figure S 1b).

189

3.4. Scanning Electron Microscopy (SEM)

190

In order to have the conducting impact, the samples were gold plated and the scanning was

191

synchronized with microscopic beam so as to maintain the small size over a large distance

192

relative to the specimen. A three dimensional appearance with high resolution was obtained in

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193

synthesized ion exchanger. SEM images clearly exhibited the differences in the surface

194

morphology of the Gum tragacanth (see Figure S2a) and synthesized ion exchanger (Figure

195

S2b). Smaller granules and folded structure were observed in case of synthesized organo

196

inorganic hybrid ion exchangers. The surface morphology of the synthesized ion exchanger

197

showed many folded structure inside it and this provide a large surface area to interact with the

198

rhodamine B dye and it is quite clear from the Figs. (Figure S2b and S2c) that there is no change

199

in the surface morphology after treating the synthesized ion exchanger with rhodamine B dye.

200

Thus, it can be concluded that no distinct change occurred in the surface morphology before and

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after dye treatment.

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3.5. X-ray diffraction

204

Gum tragacanth was found to be less crystalline in comparison to synthesized ion

205

exchanger with least coherence value. It has been observed that anisotropy decreases with

206

increase in coherence length. In case of synthesized ion exchanger (Figure 2b) maximum

207

intensity peak correspond to 2θ=20.1485o (L= 0.12426 Å) which is higher than that of Gum

208

tragacanth (L= 0.0816 Å) (Figure 2a) indicating that the synthesized ion exchanger are more

209

crystalline.

210

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3.6. Evaluation of Various Properties of Ion-Exchanger

212

3.6.1. Effect of Temperature on Ion Exchange Capacity

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213

The ion exchange capacity of synthesized ion exchangers was found to be affected by

214

drying temperature. As the drying temperature increases ion-exchange capacity decreases. The

215

results are given in Table S4. It is quite clear from the results that ion exchange capacity of the

216

synthesized ion exchangers decreases with increase in temperature which may be due to the

217

reason that at high temperature physical denaturation of network at both molecular and

218

macroscopic levels takes place.

219

220

3.6.2. pH Titrations

221

pH titration curve of synthesized ion exchanger was shown in Figure S3. Initially the pH

222

of the ion- exchanger is low (~2.9) in each case but with the increase in KCl/KOH and

223

NaCl/NaOH the pH increases. It appears to be strong cation exchanger as indicated by a low pH

224

(~2.9) of the solution when no OH- ion was added. As the volume of NaOH added to the system

225

is increased, more OH- ions are consumed suggesting in the increase of the rate of ion exchange

226

in basic medium due to the removal of H+ ions from the external solution (Figure S3). The

227

experiments were carried-out in triplicate to maintain the accuracy as well as the reproducibility

228

of the data.

229

3.6.3. Chemical Stability

230

The effect of various chemicals of different molarity on ion exchange capacity of the

231

synthesized ion exchanger was studied and it was found that weight of ion exchanger sample

232

decrease when dipped in 2M HCl, 2M HNO3,1M HCl, and 1M HNO3. The effect of ion

233

exchange capacity of synthesized ion exchanger in different mineral acids is presented in Table 1

11



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234

and Increase in ion exchange capacity may be due to disintegration of the ion-exchanger under

235

acidic conditions as the weight loss was observed 34.

236

3.7. Distribution Studies

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237

The distribution studies showed high Kd values for Pb2+ and hence ion exchanger was

238

found to be highly selective for Pb2+. The selectivity of Pb2+ may be due to reason that the size of

239

this cation just match with the size of the cavity in the respective exchanger matrix. This cation

240

forms stronger M-O bond hence is preferred over the other cations which don’t have appropriate

241

size. The study revealed that the material, in DMW showed high preference in the following

242

order: Pb2+> Cu2+> K+>, so the exchanger is lead selective. Reported ion exchanger zirconium

243

(IV) tungstoiodophosphate also shows a very high selectivity towards Pb2+ ions over the other

244

ions35. The results for distribution studies are summarized in Table 2.

245

3.8. Dye removal from aqueous solution

246

The efficiency of synthesized sample was evaluated for the dye removal from aqueous

247

solution. Various parameters like dye concentration, synthesized sample doses, pH and

248

temperature were optimized in order to get the maximum dye removal from aqueous solution.

249

Schematic presentation of adsorption mechanism of rhodamine B dye on synthesized hybrid ion

250

exchanger (Gt-Zr) is given in scheme 1.

251

252

253

254 12


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255

256

COO-

Rh B 257

Repulsion force by electrostatic force

258 N+ 259 Electrostatic interaction 260

261

-------------------------------------------------------------Gt-Zr based adsorbent

262

263

Scheme 1: Schematic presentation of adsorption of rhodamine B on synthesized Gt-Zr

264

based adsorbent.

265

3.8.1. Effect of synthesized sample dosage on dye removal

266

The effect of sample dosage on removal of rhodamine B dye was studied in the range of

267

1-5 g/L. The dye removal using different dosage of synthesized sample is presented in Fig. 6. It

268

is quite clear from the results that percentage dye removal was increased with increase in the

269

dosage level. The maximum dye removal (98.3%) was observed with 5g/L of the sample dose. It

270

was due to the fact that in the presence of higher dose of the adsorbent leads to increase in

271

surface area for the adsorption of dye and thus increases the removal of rhodamine B from the

272

solution or in simple words this can also be explained that larger dosage size provides large

273

active sites for the removal of dye (Figure S4) 36,37.

13



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274

3.8.2. Effect of pH

275

The effect of solution pH on dye removal was also investigated in the present study. Dye

276

removal from synthesized ion exchanger is highly affected by the solution pH. When the solution

277

pH was less than pKa2 (7.7) the dye removal was found to be 89%. Above the pKa2 at pH 10 the

278

dye removal was decreased sharply and was found to be 18% only38. In acidic condition i.e. at

279

pH 4, the dye removal was found to be 78%. This showed that pH has great influence on the dye

280

removal from synthesized ion exchanger. The pHpzc is the point of zero discharge, which is

281

defined as the point where the net charge of the adsorbent surface is zero. pHzac of the

282

synthesized ion exchanger occurred at pH 9. pH was monitored using a paper pH strip. All the

283

experiments were carried out for this study was in triplicate.

284

285

3.8.3. Effect of dye concentration

286

Effect of initial dye concentration on percentage dye removal was also investigated by

287

varying the dye concentration from 10-80 ppm. The results obtained showed that percentage dye

288

removal was found maximum (98%) using 10 ppm dye (Figure 3)39.

289

3.8.4. Thermodynamics Parameters

290

Temperature dependency of adsorption process were obtained using different thermodynamic

291

parameters like Gibbs function change (∆G0), standard enthalpy change (∆H0) and standard

292

entropy change (∆S0).

293

Thermodynamic constant can be calculated using the equation given below:

294

14


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∆ ∆ = − + () 295

The value of ∆H0 and ∆S0 were obtained from the slope and intercept of the linear plot of

296

vs 1/T (Figure 4) and the results are given in Table 3. The value of Kd was obtained at different

297

temperature from dye adsorption at different concentration. It is quite clear from the results that

298

dye removal was gradually decreased with increase in temperature which indicated exothermic

299

nature of dye removal. The positive value of ∆G0 at all the temperature indicated that dye

300

removal process is not spontaneous. The value of ∆G0 decreases with decrease in temperature

301

indicated that dye removal was higher at low temperature. The negative value of ∆H0 confirmed

302

that dye removal process is exothermic in nature.

303

3.9. Dye removal Kinetics

ln Kd

304

Removal of dye using synthesized sample depends upon the chemical and physical

305

interaction of the dye and the surface of the synthesized sample. The dye removal using

306

synthesized sample was evaluated in terms of the dye removal kinetics by measuring removal of

307

dye at different time interval (qt) until equilibrium (qe) reached for a known amount of initial

308

concentration of rhodamine B dye. Pseudo-first-order, pseudo-second-order and Weber-Morris

309

intraparticle diffusion models were used for characterizing the kinetics data of dye removal40,41.

310

The linearised equation of pseudo-first-order is expressed as:

!" ( − ) = #$ −

& (') .

311

15



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312

Where qt is the amount of rhodamine B dye adsorbed on the synthesized ion exchanger

313

(mg/g) at time t, k1 is the pseudo-first-order rate constant (min-1). Linear plot of ln(qe - qt) vs t

314

was used to derive the values of pseudo-first-order parameter. Pseudo-first-order differ in two

315

ways from true order equation: the qe parameters does not represent the number of available sites

316

and the log qe parameter is not frequently equal to the intercept of the plot (logqe - logqt) vs t,

317

which propose that pseudo-first-order equation is an approximate solution to the first order rate

318

mechanism.

319

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Pseudo-second-order equation is expressed as:

320

( =

& ())

+ &

= &* / + , (-) 321

Where, qt and qe are the dye removal at time t and equilibrium, respectively. Kp is the rate

322

constant for intra particle diffusion and K2 (g mg-1 min-1) is the second order rate constant.

323

Kinetic parameters like qt, k2, kp and c were determined by directly fitting the value of qt and t in

324

the above equation.

325

The different parameters of the kinetics models were summarized in Table 4. The R2 is one of

326

the most important determinants, which showed that which experimental data best fitted the

327

model42,43. It is quite clear from the results that the value of R2 for pseudo-second-order (0.973 to

328

0.987) are higher than those obtained from the pseudo-first-order (0.961 to 0.974) (Figures 5a,b

329

and Table 4), therefore, based on the value of R2, it can be concluded that the pseudo-second-

330

order model is best fitted to the experimental data. 16


Page 17 of 41

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331

Weber-Morris intraparticle diffusion models describes the diffusion mechanism and is expressed

332

as: = & / +

333

(8)

334

Where k3 and C are the intraparticle diffusion rate constant (mg g-1 min-1/2) and intercept,

335

respectively. The linear plot of qt vs t1/2 were used to determine the parameters k3 and C. The

336

intercept C should cross the origin if the diffusion mechanism is controlled by intraparticle

337

diffusion as per the Weber-Morris model, but as shown in Figure 5c and Table 4 all the intercept

338

are non zero i.e. not crossing the origin, thus it showed that intra particle diffusion is not rate

339

limiting.

340

3.10. Adsorption Isotherms

341

The two widely used isotherms, the theoretical Langmuir and empirical Freundlich to model the

342

adsorption equilibrium data were examined.

343

Langmuir isotherm is one of the best isotherms which are applied to solid/liquid system to

344

describe the saturated monolayer adsorption. It can be represented as below36,44,45:

. =

./01 2 (3)

/2

345

Where, Ce is the concentration of dye at equilibrium. KL is the Langmuir constant (dm3/g) Qmax

346

is the monolayer capacity of the synthesized sample (mg/g). The values of constants KL and Qmax

347

were calculated from the intercept and slope of the linear plot of 1/Qe and 1/Ce (Figure 6) and the

348

results are given in Table 5.

17



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

349

The shape of the Langmuir isotherm was calculated from the dimensionless constant called

350

separation factor RL 36,46-48.

2 =

Page 18 of 41

( )

+ 2 (

351

352

Where, Ci is the initial concentration of the dye, KL is the Langmuir constant. The value of RL

353

indicates the type of isotherm. If the value of RL =1, it indicates linear isotherm, if RL = 0, it

354

indicates isotherm to be irreversible, if the value lies (0

Synthesis of Hybrid Ion Exchanger for Rhodamine ... - ACS Publications

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