QUT Digital Repository: http://eprints.qut.edu.au/

Frost, Ray L. and Liu, Rui and Martens, Wayde N. and Yuan, Yong (2008) Synthesis, characterization of mono, di and tri alkyl surfactant intercalated Wyoming montmorillonite for the removal of phenol from aqueous systems. Journal of Colloid and Interface Science 327(2):pp. 287-294.

© Copyright 2008 Elsevier

1

Synthesis, characterisation of Mono, Di and Trialkyl Surfactant Intercalated Wyoming 1

Montmorillonite for the removal of phenol from aqueous systems 2

3

Rui Liu 1,2, Ray L. Frost1•, Wayde N. Martens 1 and Yong Yuan 1,3 4

5 1 Inorganic Materials Research Program, School of Physical and Chemical Sciences, 6

Queensland University of Technology, GPO Box 2434, Brisbane Queensland 4001, Australia. 7

8 2 Changchun Institute of Technology, Changchun Jilin 130021, China. 9

10 3 Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China. 11

12

13 Abstract 14

15

Organoclays were synthesised by the ion exchange of cationic surfactants containing single, 16

double and triple alkyl chains for sodium ions in an aqueous suspension of Wyoming Na-17

montmorillonite. The characterization of organoclays with and without adsorbed phenol was 18

determined by X-ray diffraction, TEM and thermal analysis. Differences in the surfaces and 19

in the interlayer of the mono, di and tri alkyl chain organoclays resulted in differences in the 20

adsorption efficiency for phenol with tri > di > mono >> Na-Mt. The results prove that 21

organoclays can be effective for the removal of phenol from an aqueous solution and this 22

removal is a function of the surfactant molecule and its concentration. In general, the higher 23

the concentration as measured by the CEC value and the greater the number of alkyl chains in 24

the surfactant molecule, the greater the percentage of the phenol that is removed. 25

26

27

Key words: montmorillonite, organoclay, high resolution thermogravimetric analysis, X-ray 28

diffraction, transmission electron microscopy. 29

30

• Author to whom correspondence should be addressed (r.frost@qut.edu.au)

2

Introduction 31

32

Smectites are widely used in a wide range of applications as a result of their high 33

cation exchange capacity, swelling capacity, high surface areas and consequential strong 34

adsorption capacities [1-5]. Among the swelling clays, the most common dioctahedral 35

smectite is montmorillonite, which has two siloxane tetrahedral sheets sandwiching an 36

aluminium octahedral sheet. Due to an isomorphic substitution within the layers (for example, 37

Al3+ replaced by Mg2+ or Fe2+ in the octahedral sheet; Si4+ replaced by Al3+ in the tetrahedral 38

sheet), the clay layer is negatively charged, which is counterbalanced by the exchangeable 39

cations such as Na+, Ca2+ in the interlayer. The hydration of inorganic cations on the exchange 40

sites causes the clay mineral surfaces to be hydrophilic. Thus natural clays are ineffective 41

sorbents for organic compounds [6-8]. However such a difficulty can be overcome by ion 42

exchange of the inorganic cations with organic cations. Modifying montmorillonite surface 43

with surfactants converts the hydrophilic silicate surface to an organophilic surface [9]. 44

45

Organo-montmorillonites are synthesized by intercalating cationic surfactants such as 46

quaternary ammonium compounds into the interlayer space through ion exchange [10-12]. 47

When using long-chain alkyl ammonium cations, hydrophobic partition medium within the 48

clay interlayer can form and function analogously to a bulk organic phase [3, 13-15]. The 49

interlayer height of clay before modification is relatively small and the intergallery 50

environment is hydrophilic. Intercalation of cationic surfactant not only changes the surface 51

properties from hydrophilic to hydrophobic, but also greatly increases the basal spacing of the 52

layers. Such surface property changes effect the applications of the organoclay. 53

54

The objective of this research is to use organoclays to adsorb phenol from an aqueous 55

solution. In this research phenol is used as a test molecule to see if the organoclay is effective 56

in removing the phenol from water and compare the adsorption effect of the three different 57

surfactants intercalated organoclays. This study seeks to show the changes in surface 58

properties of the organoclay with and without the adsorption of phenol. 59

60

Materials and Methods 61

Phenol is a common component of contaminated soils, groundwater or leachate [16], and 62

the presence of phenol compounds in the natural environmental has been of great concern 63

3

owing to its toxicity and reactivity. The solubility, density and log Kow of phenol are 9.3, 1.06, 64

and 1.46 g100mL-1, respectively [3]. 65

66

Materials Used 67

The montmorillonite used in this study was supplied by the Clay Minerals Society as 68

source clay SWy-2-Na-montmorillonite (Wyoming). The clay originates from Newcastle 69

formation in Cretaceous Era, County of Crook, State of Wyoming, USA. The chemical 70

composition of the montmorillonite is: SiO2 62.9%, Al2O3 19.6%, Fe2O3 3.35%, MgO 3.05%, 71

CaO 1.68%, Na2O 1.53%. The formula of the montmorillonite is (Ca0.12Na0.32 K0.05)[Al3.01 72

Fe(III)0.41 Mn0.01 Mg0.54Ti0.02][Si7.98 Al0.02]O20(OH)4. The less than 2 µm fraction was 73

separated by dispersing the raw SWy-2 (100 g) in water (3.5 l) with the aid of a shear stirrer 74

operating at 24000 rpm (Ultraturax). This suspension was centrifuged at 1500 rpm for 1 min 75

and the fine clay fraction decanted. This step was repeated a further two times to ensure the 76

removal of the quartz fraction. This fine clay fraction was dried with the aid of a rotary 77

evaporator ( mbar, Ca. 80°C) until a thick paste was formed which was further dried two days 78

in an oven at 110°C. The phenol, sodium chloride, hydrochloric acid and surfactants 79

(DDOAB, HDTMAB, MTOAB) used were of analytical grade chemical reagents. 80

The clay was then used without further purification. The cation exchange capacity (CEC) is 81

76.4 meg/100g (according to the specification of its producer). The phenol and surfactants 82

(DDOAB, HDTMAB, MTOAB) used were of analytical grade chemical reagents. The 83

surfactants used for this study were dimethyldioctadecylammonium bromide (DDOAB) 84

[CH3(CH2)17]2NBr(CH3)2, hexadecyltrimethylammonium bromide (HDTMAB) 85

[CH3(CH2)15]NBr(CH3)3, methyltrioctadecylammonium bromide (MTOAB) 86

[CH3(CH2)17]3NBr(CH3). 87

88

Synthesis of Organoclay 89

90

The Na-montmorillonite (Na-Mt) and surfactant modified montmorillonites were prepared 91

as described by Zhou et al. [17-21]. The SWy-2-Na-montmorillonite (denoted as SWy-2-92

MMT) was first dispersed in deionized water and stirred at 600rpm for 3h in a container open 93

to the atmosphere. The suspension was washed several times with deionized water until 94

bromide ion free and dried at 110ºC. Such treated montmorillonite is designated as Na-Mt. 95

1.5g of Na-Mt was added an aqueous solution of the cationic surfactant at the required 96

concentration and the mixtures were stirred slightly to avoid foaming at 80ºC for 150min. The 97

4

ratio of water to Na-Mt is ~20. The suspension was subsequently washed with distilled water 98

4 times. The moist solid material was dried at 60 °C and then ground with a mortar and pestle. 99

The cation exchange capacity (CEC) of the montmorillonite is 76.4 meg/100g. This number 100

represents a measure of the loading of the clay with the cationic surfactant. Thus 1.0 CEC 101

means that 76.4 meq of cationic surfactant has been intercalated into the montmorillonite. In 102

this way we can achieve a range of concentrations in terms of the CEC value from 0.5 CEC 103

through to 2.5 CEC. The obtained cationic surfactant exchanged montmorillonites were 104

labelled as 0.5 CEC-S, 0.7 CEC-S, 1.0 CEC-S, 1.5 CEC-S, 2.5CEC-S; 0.5 CEC-D, 0.7 CEC-105

D, 1.0CEC-D, 1.5 CEC-D, 2.5 CEC-D; 0.5 CEC-T, 0.7CEC-T, 1.0 CEC-T, 1.5 CEC-T, 2.5 106

CEC-T. The symbols S, D, and T signify HDTMAB, DDOAB and MTOAB (please see 107

Figures). 108

109

The density of phenol is 1.07 g/cm3 and its solubility is 8.3 g/100cm3 at 20°C. A Phenol 110

solution of 4000 mg/litre was prepared. 0.2g of organoclay was combined with 30cm3 of this 111

phenol solution in Erlenmeyer flasks and shaken for 6 hours at 25 oC at 190rpm. The 112

organoclay with adsorbed phenol was separated from the aqueous phenol solution by 113

centrifugation at 3500rpm for 20mins. The phenol concentration remaining in the aqueous 114

phase was measured by spectrophotometric techniques using a UV-260 spectrophotometer 115

operating at 270nm, the detection limits being 0.05mg/L. The amount of phenol removed 116

using the organoclays was calculated by the following equation: R=(C0-Ct)/C0×100%, R is the 117

phenol removal as a percentage, C0 is the initial concentration, Ct is the equilibrium 118

concentration. The loss of the phenol by both photochemical decomposition and 119

volatilization were found to be negligible during adsorption. 120

121

Characterization methods 122

123

X-ray diffraction 124

125

The Na-Mt and organoclays were pressed in stainless steel sample holders. X-ray 126

diffraction patterns were recorded using CuKα radiation (λ = 1.5418Ǻ) on a Philips 127

PANalytical X’ Pert PRO diffractometer operating at 40 kV and 40 mA with 0.25° divergence 128

slit, 0.5° anti-scattter slit, between 1.5 and 20° (2θ) at a step size of 0.0167°. For XRD at low 129

angle section, it was between 1 and 5° (2θ) at a step size of 0.0167° with variable divergence 130

slit and 0.125° anti-scatter slit. 131

5

132

Transmission electron microscopy 133

134

All samples were dispersed in absolute ethanol solution and oscillated in a supersonic 135

facility for 2-3 minutes, then dropped onto a copper mesh with micro-grid. Transmission 136

electron microscopy (TEM) images were attained by using a Philips CM 200 operated at 160 137

kV. The interlayer spacing of organoclays can be measured directly from the high resolution 138

TEM images. 139

140

Thermogravimetric analysis 141

142

Thermogravimetric analyses of the surfactant modified montmorillonite hybrids were 143

obtained using a TA Instruments Inc. Q500 high-resolution TGA operating at ramp 5 °C /min 144

with resolution 6.0 °C from room temperature to 1000 °C in a high-purity flowing nitrogen 145

atmosphere (60 cm3/min). Approximately 50 mg of finely ground sample was heated in an 146

open platinum crucible. 147

148

Results and Discussion 149

150

X-ray diffraction 151

One method of studying organoclays is the use of powder X-ray diffraction. XRD 152

enables the spacing and the increase in d spacing to be studied as the clay in this case 153

montmorillonite is expanded with the cationic surfactant. Any changes that occur through the 154

adsorption of an organic compound such as in this case phenol may also be observed. The 155

XRD patterns of sodium exchanged montmorillonite and the cationic HDTMAB surfactant 156

exchanged organo-clay are reported in Figure 1a. The sodium exchanged montmorillonite has 157

a d-spacing of 1.24 nm which when ion exchanged with HDTMAB to the 0.5 CEC level 158

shows an expansion of 1.47nm. Upon reaching the 0.7 CEC level two d(001) spacings of 1.41 159

and 1.73 nm are observed. The expansions at the 1.0, 1.5 and 2.5 CEC levels result in the 160

expansion of the organoclay to 1.78, 1.84 and 1.91nm. A low intense peak signifying an 161

expansion 2.75nm is also observed. Such a result indicates that the surfactant molecule has at 162

least two different molecular arrangements in the montmorillonite interlayer. 163

164

6

The expansion of montmorillonite with DDTOAB is shown in Figure 1b. As 165

compared with the exchange of a single carbon chain cationic surfactant, the use of a double 166

chain cationic surfactant results in two expansions at each of the CEC levels. For the 0.5 CEC 167

level two expansions are observed at 1.21 and 2.43nm. At the 0.7nm level the expansions of 168

1.43 and 2.62nm and at the 1.0 CEC level 1.21 and 2.76nm. The observation of two 169

expansions shows that two structural arrangements of the DDTOAB surfactant molecule in 170

the clay interlayer exist. For the 1.5CEC organoclay two expansions at 1.88 and 3.49nm are 171

observed. For the 2.5 CEC organoclay the two expansions at 1.99 and 3.97nm are found. 172

173

Expansion of the montmorillonite with the triple chain organoclay is displayed in 174

Figure 1c. As for the triple chain organoclay several expansions of the montmorillonite are 175

observed at even low CEC levels. For the 0.5CEC d-spacings are observed at 1.74, 1.80 and 176

3.50nm are observed. It is interesting when comparing with the single and double cationic 177

surfactants that the large expansion of 3.50nm is observed even at very low CEC levels. 178

Similar values are observed for the 0.7CEC organoclay. For the 1.0CEC organoclay three 179

expansions of 1.76, 1.95 and 3.57 nm are observed and for the 1.5CEC organoclay expansions 180

of 1.79, 1.95 and 3.69 nm are found. For the 2.5CEC organoclay two expansions of 1.95 and 181

3.95nm are observed. 182

183

Transmission electron microscopy 184

185

The results of the X-ray diffraction can be complimented by the TEM images which 186

should show basal spacings similar to that of X-ray diffraction. One fundamental difference 187

exists. The d-spacings from XRD are an average of many basal spacings and are actually an 188

average of all basal spacings. With TEM, one particular basal spacing is observed and the 189

interlayer distance determined. The TEM images of the 1CEC-S and 2.5CEC-S; 1CEC-D and 190

2.5CEC-D; 1CEC-T and 1CEC-T with and without phenol are shown in Figures 2a, 2b and 2c 191

respectively. 192

193

The basal spacing of the 1.0 CEC-S organoclay is 1.78 nm. This value compares well 194

with the result of the XRD where 1.78 nm was also observed. The basal spacing increases to 195

1.90 nm for the 2.5CEC-S, which is in good agreement with the value from XRD of 1.90 nm. 196

Upon adsorption of phenol the basal spacings for the 1.0CEC-S and for the 2.5CEC-S as 197

measured by TEM remains the same. The adsorption of phenol does not appear to have 198

7

increased the interlayer spacing significantly. Some observations of the TEM images can be 199

made: a) firstly the layers are not linear but are bent; b) the interlayer spacing distance is 200

constant for a particular organoclay. In other organoclays [17, 19, 20, 22], several interlayer 201

spacings have been observed in the TEM images for the same organoclay. 202

203

In the TEM images for 1.0CEC-D, a basal spacing of 2.70 nm is observed which 204

increases to 2.73 nm upon adsorption of phenol. The value, for comparison, from XRD was 205

2.76 nm. For the 2.5CEC-D organoclay, the spacing was 1.99 nm which increased slightly to 206

2.00 nm upon adsorption of the phenol. If the phenol adsorbed on top of the surfactant 207

molecule, an increase of 0.35 nm, the calculated width of the phenol molecule would be 208

expected. This suggests that the phenol is ‘fitting’ in between the surfactant molecules. 209

210

A similar set of values are obtained for the organoclay synthesised with a surfactant 211

molecule with three long alkyl chains. The basal spacing from TEM is 1.94 nm for the 212

1.0CEC-T organoclay and 1.96 nm for 2.5CEC-T organoclay. In the XRD patterns of the 213

1.0CEC-T organoclay multiple spacings were observed, one of which was 1.95 nm which 214

corresponds to the value estimated from the TEM images. Upon adsorption of phenol, the 215

interlayer spacings from the TEM images increase to 1.96 and 1.97 nm respectively. The 216

increase is less than the size of the phenol molecule. The results of the TEM images are in 217

harmony with the results from the XRD. 218

219

Differential thermogravimetric analysis 220

221

One method of studying the thermal stability of organoclays and the adsorbed organic 222

molecules on the surface is to use thermogravimetric analysis. Such a technique shows the 223

temperature of decomposition of the organoclays and the temperature of desorption and/or 224

combustion of the phenol. The differential thermogravimetric analyses of the single, double 225

and triple chain organoclays with adsorbed phenol are displayed in Figures 3a, 3c and 3d 226

respectively. Figure 3b displays the DTG analysis of phenol. 227

228

The DTG pattern of the montmorillonite shows two peaks at 335 and 654°C, attributed 229

to the dehydration and dehydroxylation of the montmorillonite. The high temperature of 230

dehydration is noted. This indicates how strongly bound the water molecules are in the clay 231

interlayer. The DTG curves for the single chain organoclays with adsorbed phenol are shown 232

8

in Figure 3a. For comparison the DTG of pure phenol is displayed in Figure 3b. For the 233

0.5CEC organoclay two low temperature peaks at 80 and 124°C are observed and attributed 234

to dehydration of the organoclay. Two higher temperature mass losses are observed at 402 235

and 587°C. The broad DTG peak at 587°C is attributed to the dehydroxylation of the 236

montmorillonite. It is noted that effect of the cationic surfactant is to lower this 237

dehydroxylation temperature from 654°C to 587°C. The mass loss steps at 357 and 402°C are 238

assigned to the combustion of the adsorbed phenol and surfactant. For the 0.7CEC 239

organoclay, low temperature mass losses are also observed but the amount of water lost is less 240

than for the 0.5CEC organoclay. This is because there is less water present as the sodium 241

ions are replaced by the cationic surfactant. Mass loss steps are observed at 297, 347, 407 and 242

574°C. The first mass loss is assigned to the sublimation of the organoclay, the desorption of 243

the phenol and the combustion of the surfactant. The mass loss step at 574°C is due to the 244

dehydroxylation of the organoclay. It is noted that there is a steady decrease in this 245

dehydroxylation temperature as the CEC is increased. It is proposed that the surfactant 246

penetrates the ditrigonal cavity of the montmorillonite and interacts with the OH groups of the 247

montmorillonite. This interaction provides a mechanism for the loss of the OH groups. For 248

the thermal analysis of the 1.0CEC organoclay, definitive mass losses are observed at 297, 249

407 and 560°C. These decomposition steps are assigned to the desorption of phenol, the 250

combustion of the surfactant and the dehydroxylation of the montmorillonite. For the 1.5CEC 251

organoclay an additional mass loss is observed at 243°C. The DTG pattern for the 2.5CEC 252

appears different. A large mass loss at 238°C is observed. Two mass losses at 573 and 653°C 253

are observed and are attributed to the dehydroxylation of the organoclay and the 254

dehydroxylation of the montmorillonite without surfactant. 255

256

The thermal analysis patterns for the double chain organoclay montmorillonite with 257

adsorbed phenol are shown in Figure 3c. The DTG patterns for the sodium exchanged 258

montmorillonite with adsorbed phenol shows two mass loss steps at 335 and 654°C. The 259

mass loss at 335°C is ascribed to the combustion/desorption of phenol. The mass loss step at 260

654°C is attributed to the dehydroxylation of the montmorillonite. It is interesting to study 261

the temperature of the dehydroxylation step as the CEC is increased from Na-Mt, 0.5, 0.7, 1.0 262

and 1.5 CEC and the temperature changes from 654°C, to 585, 570, 559 and 550°C. The 263

dehydroxylation temperature decreases as the CEC value increases. This effect of the change 264

of dehydroxylation temperature with increased surfactant concentration proves that an 265

interaction between the surfactant molecule and the hydroxyl units of the montmorillonite has 266

9

occurred. For the 0.5CEC-D two DTG mass loss steps are observed at 347 and 401 °C which 267

are assigned to the combustion of firstly phenol and secondly the surfactant. For the 0.7CEC 268

these temperatures decrease to 341 and 396 °C. A further decrease in mass loss temperature 269

is observed for the 1.0CEC. The temperatures of 312 and 349 °C are found. Although the 270

DTG pattern is more complex for the 1.5CEC organoclay DTG curve, the mass loss 271

temperatures of 256 and 354 °C are observed. This complexity in the DTG curves is further 272

observed in the 2.5CEC organoclay. The first DTG step is observed at 204 °C and is assigned 273

to the sublimation of the phenol from the organoclay. The second at 275 °C, third at 300 °C 274

and fourth DTG step at 390 °C are assigned to the combustion of the phenol and the 275

surfactant. 276

277

Each of the DTG patterns for the three surfactant modified organoclays is different. 278

The CEC-T series reported in Figure 3d is different from that of the CEC-D series. For the 0.5 279

CEC-T with adsorbed phenol, three mass loss steps are observed at 190, 333 and 387 °C as 280

well as the dehydroxylation mass loss step. These three steps are attributed to: (a) the 281

desorption and sublimation of phenol; (b) the combustion of phenol; (c) the combustion of the 282

surfactant. The DTG pattern for the 0.7CEC-T appears different and is not considered further. 283

The pattern for the 1.0CEC-T is similar to that of the 0.5CEC-T DTG pattern. Three mass 284

loss steps are observed at 191, 325 and 385°C. A similar set of temperatures is observed for 285

the 1.5CEC-T organoclay. The values for the 2.5CEC-T organoclay are 188, 342 and 388 °C. 286

It is not unexpected to see an increase in the peak at 188 °C attributed to the sublimation of 287

phenol. The amount of phenol adsorbed is greatest for the (a) higher CEC value and (b) 288

highest for the triple chain surfactant intercalated montmorillonite. 289

290

Efficiency of adsorption of the organoclays 291

292

The percentage removal of phenol by the three organoclays as a function of CEC 293

concentration is shown in Figure 4. The Na-Mt only removes phenol to a 14% level, but 294

organoclay can greatly improve the remove rate of phenol. It is showed in Figure 10 that: 295

a) The synthesizing organoclays are the effective minerals of removal of phenol from 296

water. 297

b) The percentage of organoclays removal of phenol is function of CEC concentration. 298

It is quite clear that the percentage removal of phenol increases as the CEC value 299

rises. 300

10

c) There is much difference in the percentage removal with mono, di, and trialkyl 301

surfactant intercalated Wyoming montmorillonite. 302

d) The organoclay synthesised with a triple chain is more effective at removing 303

phenol than double which is more effective than the surfactant based upon a single 304

chain. 305

306

307

308

Conclusions 309

310

Sodium exchanged Wyoming montmorillonite was used as the base clay for the 311

synthesis of organoclays with mono, di and tri alkyl chain surfactants 312

[hexadecyltrimethylammonium bromide (HDTMAB), dimethyldioctadecylammonium 313

bromide (DDOAB), ethyltrioctadecylammonium bromide (MTOAB)]. As a valuable 314

material for adsorption, these exchanged organoclays have environmental applications in 315

water treatment for removal of organic pollutants such as phenol. These new materials were 316

characterized using the techniques of XRD, TEM and TG-DTG. It is noted that these 317

techniques all focus on the characterization of dry material which may not necessarily be the 318

same as a suspension of the organoclay in an aqueous solution of phenol. Nevertheless 319

techniques for the characterization of such aqueous suspensions are not available. 320

321

The d(001) spacings XRD patterns are a function of the CEC value and the number of 322

alkyl chains in the surfactant. The interlayer spacings of organoclays increase with the CEC 323

value. Low CEC level has a less expansion of interlayer spacings than that of the higher level 324

concentration organoclay. The TEM images further prove that the basal spacings increased 325

with intercalating mono, di and trialkyl surfactant in the Wyoming montmorillonite. The 326

values of basal spacings of organoclays are in harmony with the results of from the XRD. 327

The organoclays were characterized by thermal analysis using their DTG patterns. The effect 328

of increasing CEC value resulted in the decrease of the organoclay dehydroxylation 329

temperature. It is proposed that this decrease indicates the interaction of the surfactant 330

molecules with the inner hydroxyl of the montmorillonite. 331

332

The results proved that the effective removal of phenol from an aqueous medium is a 333

function of the surfactant molecule and its concentration. In general, the greater the CEC 334

11

value and the greater the number of alkyl chains in the surfactant molecule, the greater the 335

percentage of the phenol that is removed. 336

337

Acknowledgements 338

339

This work was funded by Chinese Academy of Sciences (Grant No. Kzcx2-yw-112) 340

and Natural Science Foundation of Guangdong Province (Grant No. 030471 and 05103410). 341

The Inorganic Materials Research Program, Queensland University of Technology, is 342

gratefully acknowledged for infra-structural support. 343

12

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385

386

387

388

14

List of Figures 389

390

Figure 1a X-ray diffraction patterns of montmorillonite , montmorillonite with absorbed 391

phenol and organo-montmorillonite modified by HDTMAB at 0.5, 0.7. 1.0. 1.5 and 392

2.5 CEC with adsorbed phenol. 393

394

Figure 1b X-ray diffraction patterns of montmorillonite, montmorillonite with absorbed 395

phenol and organo-montmorillonite modified by DDOAB at 0.5, 0.7. 1.0. 1.5 and 396

2.5 CEC. 397

with adsorbed phenol. 398

399

Figure 1c X-ray diffraction patterns of montmorillonite, montmorillonite with absorbed 400

phenol and organo-montmorillonite modified by MTOAB at 0.5, 0.7. 1.0. 1.5 and 401

2.5 CEC. 402

with adsorbed phenol. 403

404

Fig. 2a TEM micrographs of 1CEC-S, 1CEC-S+Phenol, 2.5CEC-S, 2.5CEC-S+Phenol 405

406

Fig. 2b TEM micrographs of 1CEC-D, 1CEC-D+Phenol, 2.5CEC-D, 2.5CEC-D+Phenol 407

408

Fig. 2c TEM micrographs of 1CEC-T, 1CEC-T+Phenol, 2.5CEC-T, 2.5CEC-T+Phenol 409

410

Figure 3a DTG patterns of Na-montmorillonite and montmorillonite modified by 411

HDTMAB at 0.5, 0.7. 1.0. 1.5 and 2.5 CEC with absorbed phenol. 412

413

Figure 3b Thermogravimetric analysis of phenol. 414

415

Figure 3c DTG patterns of Na-montmorillonite and montmorillonite modified by DDOAB 416

HDTMAB at 0.5, 0.7. 1.0. 1.5 and 2.5 CEC with absorbed phenol. 417

418

.Figure 3d DTG patterns of Na-montmorillonite and montmorillonite modified by MTOAB 419

HDTMAB at 0.5, 0.7. 1.0. 1.5 and 2.5 CEC with absorbed phenol. 420

421

Figure 4 Removal percentage of phenol by modified montmorillonite organoclay as a 422

15

function of surfactant and surfactant loading. 423

16

424

2 7 12 17 22 27

Degrees 2 Theta

Cou

nts/

sec.

1.24nm

1.46nm

1.73nm

1.47nm

1.41nm

1.78nm

1.91nm

1.84nm

SWy-Mt

Na-Mt+Phenol

0.5CEC-S+Phenol

0.7CEC-S+Phenol

1.0CEC-S+ Phenol

1.5CEC-S+Phenol

2.5CEC-S + Phenol

2.75nm

1.36nm

425 426

427

Fig. 1a 428

429

17

430

431

2 7 12 17 22 27

Degrees 2 Theta

Cou

nts/

sec.

1.24nm

1.46nm

1.21nm2.43nm

2.62nm1.43nm

1.15nm

1.21nm2.76nm

1.19nm1.88nm

3.49nm

1.33nm

1.99nm

3.97nm

SWy-Mt

Na-Mt + Phenol

0.5CEC-D + Phenol

0.7CEC-D + Phenol

1.0CEC-D + Phenol

1.5CEC-D + Phenol

2.5CEC-D + Phenol1.22nm

432 Fig. 1b 433

434

435

436

437

438

439

440

441

442

443

444

18

2 7 12 17 22 27

Degrees 2 Theta

Cou

nts/

sec.

Na-Mt + Phenol

0.5CEC-T + Phenol

0.7CEC-T + Phenol

1.0 CEC-T + Phenol

1.5CEC-T + Phenol

2.5CEC-T + Phenol

1.24nm

1.95nm

1.79nm

1.76nm

1.80nm

1.46nm

1.95nm

1.74nm

3.95nm

3.69nm

3.57nm

3.52nm

3.50nm

1.80nm

SWy-Mt

1.95nm

1.32nm1.11nm

1.18nm

1.17nm

1.18nm

1.18nm1.32nm

1.31nm

1.44nm

1.42nm

445 446

447

448

Fig. 1c 449

450

19

451

452 453

454

Fig. 2a TEM micrographs of 1CEC-S, 1CEC-S+Phenol, 2.5CEC-S, 2.5CEC-S+Phenol 455

456

457

20

458

459

460

461

462

463 464

465

Fig. 2b TEM micrographs of 1CEC-D, 1CEC-D+Phenol, 2.5CEC-D, 2.5CEC-D+Phenol 466

467

21

468

469

470

471 472

473

Fig. 2c TEM micrographs of 1CEC-T, 1CEC-T+Phenol, 2.5CEC-T, 2.5CEC-474

T+Phenol 475

476

477

22

478

50 250 450 650 850

Temperature /°C

Der

ivat

ive

mas

s %

2.5CEC-S+Phenol

1.5CEC-S+Phenol

1.0CEC-S+Phenol

0.7CEC-S+Phenol

0.5CEC-S+PhenolNa-Mt+Phenol

238°C

243°C 293° 406°C

297°C 407°C

407°C

402°C

573°

335°C 654°C

587°C

574°C

560°C

556°C

653°C

80°C124°C

297°C

347°C

357°C

479 480

481

Figure 3a 482

483

23

484 485

Figure 3b486

24

50 250 450 650 850

Temperature /°C

Der

ivat

ive

mas

s %

Na-Mt+Phenol

0.5 CEC-D+Phenol

0.7CEC-D+Phenol

1.0 CEC-D+Phenol

1.5 CEC-D+Phenol

2.5 CEC-D+Phenol

390°C300°C

204°C 256°C354°C

312°C349°C

341°C 396°C

347°C401°C

654°C335°C

585°C

570°C

559°

550°C

275°C

487 Fig. 3c488

25

489

50 250 450 650 850

Temperature /°C

Der

ivat

ive

mas

s %

Na-Mt+Phenol

0.5CEC-T+Phenol

0.7CEC-T+Phenol

1CEC-T+Phenol

1.5CEC-T+Phenol

2.5CEC-T+Phenol

190°C

333°C387°C

365°C

191°C

325°C385°C

190°C

337°C

389°C188°C

342°C388°C

335°C654°C

490 491

492

Fig. 3d 493

494

26

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5 3CEC concentration

Rem

oval

(%)

▲MTOAB

■HDTMAB

♦DDOAB

495 Fig. 4 496

497