The effect of temperature on hydrocarbon adsorption by diphenyldichlorosilane coated zeolite and its application in permeable reactive barriers in cold regions

Cold Regions Science and Technology 145 (2018) 169–176

Contents lists available at ScienceDirect

Cold Regions Science and Technology journal homepage: www.elsevier.com/locate/coldregions

The effect of temperature on hydrocarbon adsorption by diphenyldichlorosilane coated zeolite and its application in permeable reactive barriers in cold regions

MARK

Junchao Ma, Geoffrey W. Stevens, Kathryn A. Mumford⁎ Particulate Fluids Processing Centre, Department of Chemical and Biomolecular Engineering, The University of Melbourne, VIC 3010, Australia

A R T I C L E I N F O

A B S T R A C T

Keywords: Permeable reactive barriers Toluene adsorption DPDSCI coated zeolite Adsorption isotherms

Zeolite was modified and characterized for its potential application in permeable reactive barriers tasked with fuel removal. Characterization was accomplished to compare the material structure before and after the modification process. Batch sorption tests were performed to detect hydrocarbon capture performance, and regeneration experiments were conducted to determine longevity. Adsorption isotherms and thermodynamics were studied to determine the mechanism of hydrocarbon capture. Diphenyldichlorosilane (DPDSCI), a unique reactive chlorosilane with two phenyl groups, was selected to coat the zeolite. The surface characterization results revealed that the modification was successful and the inner structure of zeolite maintained its porosity. Hydrocarbon adsorption tests presented good toluene adsorption performance even under cold temperatures. Regeneration experiments indicated this modified zeolite could be used multiple times without a significant reduction in adsorption efficiency. The Langmuir adsorption isotherm fitted toluene adsorption well and the process occurred spontaneously. Based on this performance, this modified zeolite was found suitable for future application for groundwater remediation in cold regions.

1. Introduction Worldwide there are many reports of serious groundwater pollution resulting from accidental spills or improper disposal, including in cold regions (Bargagli, 2008). In attempts to clean-up groundwater and restore contaminated sites to near pristine conditions, scientists started to develop technologies such as the pump-and-treat method in the 1980's (Thiruvenkatachari et al., 2008). In the last decade, permeable reactive barriers (PRBs), filled with reactive materials to intercept and decontaminate groundwater plumes have become one of the most promising remediation technologies (Obiri-Nyarko et al., 2014). Compared to traditional pump-and-treat systems, PRBs generally have a longer serve life and lower operational cost (Bortone et al., 2013a). In Antarctica, similar practices were also conducted to treat petroleum-contaminated and heavy-metal-laden sites (Mumford et al., 2013) and at this stage, the major areas of research to improve PRB performance include improving the longevity of the reactive materials used in these systems and their adsorption capacity towards various contaminants (Bortone et al., 2013b; Erto et al., 2014; Santonastaso et al., 2015; Snape et al., 2001). Materials that rely solely on chemical or physical processes have a limited operational life as once the materials are saturated, they will

⁎

no longer perform as required (Obiri-Nyarko et al., 2014). The combination of bioremediation and physicochemical adsorption is a more promising and viable method (Freidman et al., 2016). As long as microbes are present and stimulated, the system will operate (Thiruvenkatachari et al., 2008). Previous tests have demonstrated that indigenous microorganisms present in soil and water can migrate and thrive, on and between adsorbent materials in PRBs and degrade the hydrocarbons as they migrate through the system (De Jesus et al., 2015). To enhance the bioremediation process, improving the reactive materials in PRBs is essential (Scherer et al., 2000). Among the available options, modified zeolites may present better characteristics than granular activated carbon (GAC) despite of its high adsorption capacity (Bortone et al., 2013b; Erto et al., 2017). Contaminants are not bonded as tightly onto modified zeolite surfaces, and so are more easily utilised by the microbes present (Mumford et al., 2015; Zhang et al., 1991). Zeolites have a rigid three dimensional structure of aluminosilicate and a highly microporous surface and a net negative charge that is balanced by electrostatically held cations (Torabian et al., 2010). Thanks to its unique structural characteristics and surface components, natural zeolite is usually used to capture target cations through ion exchange, with

Corresponding author. E-mail addresses: [email protected] (J. Ma), [email protected] (G.W. Stevens), [email protected] (K.A. Mumford).

http://dx.doi.org/10.1016/j.coldregions.2017.10.020 Received 19 December 2016; Received in revised form 23 October 2017; Accepted 25 October 2017 0165-232X/ © 2017 Elsevier B.V. All rights reserved.

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

Table 1 Previous research on modified natural zeolite and synthesized zeolite. Base material

Modification material

Target

Capacity Linear Kd (L/kg)

Clinoptilolite

Synthetic zeolite

Diphenyldichlorosilane (DPDSCI)

Toluene Xylene Naphthalene

Octadecyltrichlorosilane (C18)

Naphthalene Xylene

17.30 9.70

Hexadecyltrimethylammonium (HDTMA)

Benzene Phenol Aniline Nitrobenzene Chlorophenol

79.21 43.25

n-Cetylpyridinium bromide (CPB)

Benzene Phenol

103.4 47.41

Benzyltetradecyl ammonium chloride (BDTDA)

Langmuir qm (mg/g)

Freundlich Kf (mg1 – n g− 1 Ln) 0.02 0.05 0.15

Calculated capacity (using Langmuir isotherm qm) (μmol/g)

Reference

5.16 8.90 22.32

(Huttenloch et al., 2001)

(Northcott et al., 2010a) 16.61 11.35

212.95 120.74

12.71

0.39 0.17 0.13 1.25 0.06

98.86

(Ghiaci et al., 2004) (Ersoy and Celik, 2004) (Kuleyin, 2007)

23.07 11.88

0.36 0.22

295.77 126.38

(Ghiaci et al., 2004)

Phenol Chlorophenol

1.30 6.41

0.05 0.77

13.81 49.86

(Kuleyin, 2007)

Stearyldimethyl benzyl ammonium chloride (SDBAC)

Atrazine Lindane Diazinone

0.43 0.99 1.35

2.00 3.40 4.40

(Lemic et al., 2006)

Octadecyldimethyl benzyl ammonium (ODMBA)

Ochratoxin A

3.41

8.45

Fumonisin B1

7.35

10.18

(Daković et al., 2003) (Daković et al., 2007)

Octylmethyldichlorosilane

Toluene

215.60

2340

(Song et al., 2005)

Hexadecyltrimethylammonium (HDTMA)

Benzene Toluene Phenol

48.53 48.66 29.02

7.74 9.33 7.42

0.40 0.39 0.15

99.26 101.43 78.96

(Ghiaci et al., 2004)

n-Cetylpyridinium bromide (CPB)

Benzene Toluene Phenol

82.46 80.51 34.23

14.95 16.44 9.425

0.39 0.48 0.14

191.67 178.70 100.27

(Ghiaci et al., 2004)

Hexadecyltrimethylammonium bromide (CTAB)

TPH

92.30%

(Saremnia et al., 2016)

(Huttenloch et al., 2001). This treatment provides a stable chemical linkage between organosilane and the substrate instead of the weaker electrostatic interactions of cationic surfactants, which greatly reduces the loss of hydrophobic coating during its use (Northcott et al., 2010a). Previous research has shown that octadecyltrichlorosilane modified natural zeolite possesses high capacity in removing dissolved o-xylene and naphthalene from water (Northcott et al., 2010a) and the octylmethyldichlorosilane coated synthetic zeolite possesses a similar toluene adsorption capacity to GAC (Arora et al., 2011; Song et al., 2005). In addition to the use of zeolites as base materials, there are studies regarding the grafting of chlorosilane onto GAC to enhance 2,4-dichlorophenol removal, by improving its hydrophobicity in permeable reactive barriers (Yang et al., 2010). Though chlorosilane is less likely to be leached off from the surface of the substrate, one of the most significant challenges is finding the most efficient organosilane to enhance sorption (Huttenloch et al., 2001). In previous work, chlorosilane with phenyl headgroups have been shown to have better affinity for aromatic compounds compared with others (Huttenloch et al., 2001), and therefore can be viewed as potential coating material to enhance hydrocarbon capture. The basic silanization process (Huttenloch et al., 2001) for surface modification on zeolite is shown in Fig. 1. In the presence of pyridine and elevated temperatures, the chlorine on silicon compounds has a high affinity to the hydrogen of hydroxyl groups on zeolite surface. This

no applications in anions and organics adsorption (Mahabadi et al., 2007; Widiastuti et al., 2008). Research has focused on the development of modified zeolites with higher hydrocarbon adsorption capacities compared to natural zeolite (Wang and Peng, 2010). One of the most frequent methods is the use of cationic surfactants that are bound to the external zeolite surface via electrostatic forces. Examples include hexadecyltrimethylammonium bromide (HDTMA) or cetylpyridinium bromide (CPB) (Wang and Peng, 2010). This treatment reduces or reverses the charge of zeolite and thus leads to anions or non-polar organics being captured on the surfactant coating (Wang and Peng, 2010). This process has been extensively investigated and presented good outcomes compared with natural zeolite in removing soluble hydrocarbons from groundwater with a summary of the results presented in Table 1 (Bowman, 2003; Ghiaci et al., 2004; Kuleyin, 2007; Li et al., 2000; Michael Ranck et al., 2005). Despite this promising performance, cationic surfactants like HDTMA or CPB still face many challenges, such as the loss of the surface coating and the disintegration of the zeolite particle itself (Michael Ranck et al., 2005). Therefore, alternative techniques are needed. Here chlorosilane is selected as it can be covalently bound to the surface of zeolite thereby improving the material stability while still enhancing its adsorption capacity. Chlorosilane is a reactive chemical compound with up to three nonpolar aliphatic or aromatic functional groups which can be covalently grafted to the silanol groups on a mineral adsorbent surface 170

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

Fig. 1. Reaction process for the surface modification with organosilane on zeolite.

results in the combination of H+ and Cl− of the two compounds and as such the formation of a stable SieOeSieC bond, leading to chlorosilane covalently grafted to the zeolite surface. The more hydroxyl groups on the zeolite surface, the more organosilane molecules with phenyl groups that may be attached, leading to a better adsorption capacity towards organic contaminants. Besides maintaining high adsorption capacity, regeneration is another important issue for the longevity of PRBs (Obiri-Nyarko et al., 2014). In large scale tests, air sparging is commonly applied to remove adsorbed hydrocarbon from the sorbents (Michael Ranck et al., 2005; Soto et al., 2011), and previous researchers (Northcott et al., 2010a) have shown that water or organic solvent can be used to regenerate the materials in batch tests and that regenerated modified zeolite can be reused for hydrocarbon sorption at least 3 times. Normally the organic solvent selected for regeneration is methanol (Northcott et al., 2010a), as it is the simplest alcohol and most hydrocarbons may be dissolved in it. However as this material is to be used for environmental remediation purposes, it is important to minimise waste, therefore, it is worthwhile undertaking regeneration tests in water as well. In this study, diphenyldichlorosilane (DPDSCI) modification was selected based on the results of previous work (Huttenloch et al., 2001). Beside the general surface characterization and normal temperature adsorption tests, low temperature adsorption tests and regeneration experiments were also performed to determine the capacity and longevity in the cold conditions. Furthermore, different isotherms and thermodynamics of adsorption were calculated to analyse the specific adsorption process of DPDSCI modified zeolite.

ensured that the reaction was conducted in an anhydrous condition, preventing the hydrolysis of chlorosilane. Following this, the modified material was filtered and washed with acetone and distilled water and dried at 105 °C. 2.3. Surface characterization The modified and unamended zeolite were analysed using the following techniques: Fourier transform-infrared spectroscopy (FT-IR) was used to determine the reactive functional groups on the surface of modified zeolite and the unamended material. This work was conducted using a Frontier™ (Perkin Elmer Inc., USA). Thermogravimetric analysis (TGA) measurements were performed using a TGA/SDTA851e (Mettler Toledo) to determine the change in mass with temperature. This was used to interpret the physical and chemical properties of the unamended zeolite and surface modified zeolite. In this evaluation, the starting temperature was 25 °C and samples were heated in an oxygen atmosphere to 900 °C with a heating rate of 10 °C/min. 2.4. Reagents for sorption tests

2. Materials and methods

Except where otherwise stated, the chemicals used in adsorption test are all received without further purification. All solutions were made with MilliQ water. Toluene (Ajax) was selected to evaluate the hydrocarbon sorption properties of the materials because it was a typical aromatic hydrocarbon with a relatively high water solubility of 515 mg L− 1.

2.1. Raw materials

2.5. Analysis of toluene in solution

The raw zeolite material used was natural clinoptilolite zeolite (Castle Mountain Zeolite, Quirindi, N.S.W., Australia). It was sieved with an 8 × 16 US mesh sieve (2.36–0.85 mm) and measured to have a BET surface area of 18.01 m2/g (Freidman et al., 2016). Energy Dispersive Spectroscopy (EDS) Microanalysis of raw zeolite indicated that it had the following composition (% atomic weight): O-66.99; Al-6.99; Si-24.85; Fe-0.16; Na-0.8; K-0.11; Ca-0.21; N-0.00; Mg-0.02; S-0.00; P0.01 (Freidman et al., 2016). The chlorosilane used in this experiment was diphenyldichlorosilane (Sigma-Aldrich, purity 97%). Pyridine (Ajax, purity 99%) was added as organic solvent and a buffer for the produced hydrochloric acid in this reaction.

High performance liquid chromatography (HPLC) (LC-20A prominence, Shimadzu) was used to measure concentrations of toluene in solution before and after adsorption equilibrium with surface modified and unamended zeolite was reached. This analysis was performed using a C18 column (Agilent, 3.5 μm size, 4.6 × 75 mm) under the following conditions: an acetonitrile (Ajax) and water mixture with a ratio of 60:40 v/v at a flow rate of 0.8 mL/min as the mobile phase; sample injection volume 50 μL, isocratic elution mode, 10 min run time. Detection was performed at a wavelength of 220 nm and 254 nm. The autosampler was conditioned at 10 °C to avoid sample evaporation, and the column temperature was 30 °C. Toluene concentration was evaluated against standards prepared over the range between 20 and 100 mg/L, toluene peak retention time is observed at 3.3–3.4 min.

2.2. Surface modification 2.6. Batch equilibrium tests Before surface modification, raw zeolite was washed with 20 (w/w) % hydrochloric acid in a batch for 24 h to remove impurities and then washed by distilled water until the effluent reached pH 5. The resulting material was dried at 105 °C for 24 h. Ten grams of dried zeolite was weighed and placed into a twonecked flask with 40 mL pyridine and 92 mmol diphenyldichlorosilane (DPDSCI). The mixed solution was heated under nitrogen atmosphere at 80 °C for 48 h in a temperature controlled heating bath. This design

Batch equilibrium experiments were conducted using the same mass of adsorbent (300 mg of unamended zeolite and DPDSCI-zeolite) with varying concentrations of toluene in solution (10–100 mg/L). 40 mL of toluene solution was added into each vial and capped with a Teflon lined septa cap. A blank was also used for each concentration of toluene solution to ensure the initial concentration was accurately known and to check for evaporative losses of toluene. All vials were shaken for 24 h 171

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

3.3. Linear isotherms

at 120 rpm at known temperatures (20 °C and 4 °C) in a shaking incubator (TLM-590, Thermoline Scientific). Preliminary results, not shown here, confirmed that 24 h was sufficient for equilibrium to be achieved by both zeolite materials at temperate and low temperature conditions (Hornig et al., 2008; Li et al., 2000; Li et al., 1998). After shaking, 4 mL solution was taken from each vial and the concentration was determined by HPLC. Each test was conducted in duplicate.

Although both Langmuir and Freundlich isotherms are commonly applied to observe the behaviour of many sorption systems, linear isotherms are more often used to describe hydrocarbon sorption, especially at narrow concentration ranges and low concentration levels (Northcott et al., 2010a). This isotherm implies that sorption is not dependent on the initial hydrocarbon concentration of the aqueous solutions. The linear sorption behaviour may be described by the following equation:

2.7. Regeneration tests A regeneration test was conducted to detect whether the material could be used multiple times without significant decrease in hydrocarbon adsorption ability. Used materials were collected, mixed, separated into three groups and either washed by hot water, methanol or acetone respectively for 6 h. Following washing, the excess solvent was removed by drying in a vacuum oven at 60 °C for 24 h. The material collected after single adsorption test and then conducted first washing cycle was termed 1st regenerated. After conducting the adsorption test on 1st regenerated sample, the material collected again and repeated same washing cycle was called 2nd regenerated. The 1st and 2nd regenerated sample and fresh sample (500 mg) were used in the toluene adsorption tests, with 100 mg/L toluene solution and under 20 °C for 24 h. The sorption results were compared among fresh, 1st regenerated and 2nd regenerated samples.

Cm = K d ∙Cs

In this form, Cm and Cs have similar meanings to the Freundlich adsorption equations, while the Kd (L/g) is the distribution coefficient. 3.4. Adsorption thermodynamics The Gibbs free energy function shows how the equilibrium constant is related to temperature. The standard Gibbs free energy can be calculated from the standard enthalpy change and standard entropy change.

ΔG 0 = ΔH 0 − T ΔS 0

where ΔG (kJ/mol) is the Gibbs free energy for a specific temperature and pressure. ΔH0 (kJ/mol) is the standard enthalpy change and ΔS0 (kJ/mol) is the entropy change. At equilibrium, K is related to the standard free energy change via Eq. (7):

Modelling of the adsorption experiments was conducted using the Langmuir, Freundlich and linear isotherms. These isotherms are most commonly used in batch experiments to describe a system of solute molecules adsorbed onto material surface (Arora et al., 2011).

ΔG 0 = −RT ln K

The Langmuir model is more likely to be relevant for monolayer and homogeneous surface adsorption processes. The specific equation is represented as (Chatterjee et al., 2010; Chern and Chien, 2002; Northcott et al., 2010b):

ln K = −

4.1. Thermogravimetric analysis The results of the thermogravimetric analysis for the modified and unamended zeolite are presented in Fig. 2. This figure shows the weight loss curves (TG) and the corresponding differential curves (DTG) of the materials, which indicates the endothermic and exothermic reactions during the heating of the samples to 900 °C. As shown, the curves of modified zeolite are different to that of raw zeolite with different mass change steps and peak temperatures. The change in untreated zeolite as best shown on the DTG Natural Zeolite curve, which at between 25 and 200 °C water is evaporating (Bish and Stucki, 1989), while this dehydration process does not significantly occur in modified zeolite as there is only a slight weight loss and no apparent DTG peak until temperature rises to 200 °C or more. From 200 to 800 °C, the modified zeolite begins to lose weight (8–9%) due to the volatilization of phenyl groups on surface (Huttenloch et al., 2001). In DTG curves, it is clearly shown that there are two significant steps happened during these endothermic and exothermic reactions (at 260 °C and 560 °C) due to the breaking of covalent bonds between the organosilane and zeolite surface (Huttenloch et al., 2001). These two peaks may be explained by two different bonding arrangements of DPDSCI with the zeolite surface during modification process: double bonds to two adjacent surface silanol groups; single bond to surface silanol group or to an organosilanol group after two successive synthetic processes (Ogawa et al., 1998). The double bonds require more energy to break, and so this occurs at the

(2)

Freundlich type isotherm has been used to describe many adsorption systems, and has been found applicable whether the surface is homogeneous or not (Hornig et al., 2008). The equation may be represented as follows: (3)

It may be linearized to give the following:

log Cm = log Kf + n·log Cs

(8)

4. Results and discussion

3.2. Freundlich adsorption equations

Cm = Kf ·Csn

ΔH 0 ∆S 0 + RT R

(1)

where Ce is the concentration of contaminants in solution at equilibrium (μmol/L), qe is the adsorption capacity at equilibrium (μmol/g). qmax, the Langmuir constant, is related to the maximum adsorption capacity (μmol/g) of the adsorbent and Kl is a constant, similar to equilibrium constant (L/μmol). The Langmuir equation can be re-arranged as follows:

Ce C 1 = e + qe qmax qmax Kl

(7)

where K is the equilibrium adsorption coefficient and T is the absolute temperature in Kelvin. R represents the molar gas constant, which is 8.314 J/(mol K). The enthalpy change (ΔH0) can thus be obtained from the variation of K with temperature by combination of Eqs. (6) and (7).

3.1. Langmuir adsorption equations

qmax Kl Ce 1 + Kl Ce

(6)

0

3. Modelling

qe =

(5)

(4)

where Cm (μmol/g) and Cs (μmol/L) respectively represent the concentration of contaminants in material surface and solution at equilibrium. The terms Kf and n are constants for the given system. 172

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

560°C

100°C

260°C

Fig. 2. Thermoanalytical data of raw zeolite and DPDSCI-zeolite.

different. At low initial toluene concentrations, 17% of toluene can be absorbed by DPDSCI coated zeolite while less than 1% is captured by raw zeolite. This demonstrates the modification of the zeolite surface improves the adsorption ability of zeolite. Compared with the performance at 20 °C, only 8.7% of toluene is captured by modified zeolite at low initial toluene concentrations at 4 °C. This trend continues across all toluene concentration ranges, therefore it may be concluded that the adsorption is temperature dependent. Similar temperature dependence for toluene sorption onto HDTMA modified zeolite has been previously reported (Hornig et al., 2008). The fitting of Freundlich, Langmuir and Linear isotherms for toluene adsorption on DPDSCI coated zeolite at 20 °C and 4 °C are presented in Fig. 5. As shown, the linear model does not appear appropriate to fit the experimental data well at low concentrations while the Langmuir isotherm fits the data best over the whole concentration range (Table 2). This indicates that the adsorption on the DPDSCI coated zeolite is a monolayer and homogenous surface adsorption process (Kuleyin, 2007). According to the Langmuir isotherm, the maximum toluene uptake is 8.85 μmol/g at 20 °C and 6.74 μmol/g at 4 °C. The maximum capacity of this material at 20 °C is of a similar order of magnitude found in previous work (Huttenloch et al., 2001). Compared to the performance of octylmethyldichlorosilane modified synthetic zeolite (Song et al., 2005), the capacity for toluene is not as high. The reason for this may be that there are more effective hydroxyl groups on the surface of

higher temperature (Huttenloch et al., 2001). 4.2. FT-IR analysis The FI-IR spectrum of the raw zeolite and DPDSCI modified zeolite is presented in Fig. 3. As shown, significant changes to the zeolite surface occurs during modification. It has been reported previously that the characteristic peaks of zeolite are between 500 and 1200 cm− 1 and specifically, in the 830–1110 cm− 1 band which is silicon‑oxygen stretching (Northcott et al., 2010a). This can be seen for both zeolite materials presented. However, the DPDSCI coated zeolite shows more an apparent peak, indicating the modification is successful and silane has been grafted to the zeolite surface. Further evidence is in the bond range 1450–1650 cm− 1, where DPDSCI coated zeolite presents multicharacteristic peaks of benzene (Silverstein et al., 2014). In addition, the modified zeolite does not show any apparent peaks in 3003–3077 cm− 1, which suggests that there is no pyridine on the surface of zeolite (Silverstein et al., 2014). 4.3. Adsorption behaviour of sorbent material The adsorption performances of DPDSCI coated zeolite and natural zeolite at various toluene concentrations and different temperatures are shown in Fig. 4. At both 20 °C and 4 °C, the adsorption of toluene by modified zeolite follows the traditional isotherm shape. At 20 °C, the behaviour of modified and unamended zeolite is very

Benzene skeleton vibration

Silicon-oxygen stretching bond

Fig. 3. FT-IR spectra of raw zeolite and DPDSCI-zeolite.

173

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

Fig. 4. Toluene adsorption isotherms on DPDSCI-zeolite at 20 °C and 4 °C.

a

synthetic zeolite compared to a natural zeolite, which increases the chlorosilane loading on the particle, thus improving the adsorption capacity. Also, the maximum capacity of this material is less than that of cationic surfactants modified synthetic zeolite (Ghiaci et al., 2004). It is likely that the different bonding process during surface modification results in the different capacities. As chlorosilane requires specific bonding sites for attachment it is limited by available sites, whereas as the surfactant is held by electrostatic attraction there is more scope for attachment (Wang and Peng, 2010). 4.4. Adsorption thermodynamics The free energy and enthalpy change of toluene adsorption of DPDSCI coated zeolite are shown in Table 3. As the Kf in Freundlich isotherm does not have any physical meaning (Northcott et al., 2010b), it is not used in this analysis. In the Langmuir and linear isotherms, the constant K may be used to reflect the equilibrium constant (Northcott et al., 2010a; Woinarski et al., 2003), as the Langmuir isotherm fitted the data best, it was used in this analysis to examine the enthalpy and free energy. The negative number for the free energy (ΔG) in Table 3 indicates the sorption process occurs spontaneously, which is the nature of adsorption processes (Kuleyin, 2007). This process was found to be endothermic as the enthalpy change of this process is positive. This inference also fits the trend presented in Fig. 4, as with temperature increasing, the toluene uptake is increased. As the enthalpy change is around 1.5 kJ/mol, it indicates that intermolecular interactions during adsorption process would be mainly Van der Waals interactions (4–9 kJ/mol) with some hydrophobic bonding (4 kJ/mol) and charge transfer, which occurs between aromatic moieties (π-π electron stacking interactions) (Von Oepen et al., 1991). The low equilibrium enthalpy means there is a small temperature influence (Hamaker and Thompson, 1972), suggesting the adsorption capacity of this material would not be significantly affected by the cold temperature. It also shows weaker bonds (Ten Hulscher and Cornelissen, 1996), indicating the strength of toluene adsorption is not very strong and the hydrocarbon on the modified zeolite surface might be easily utilised by

b

Fig. 5. Freundlich, Langmuir and Linear isotherms for toluene adsorption on DPDSCIzeolite at 20 °C (a) and 4 °C (b).

Table 2 Freundlich, Langmuir and Linear parameters for toluene adsorption on DPDSCI-zeolite at 20 °C and 4 °C. Isotherms

Parameters

20 °C

4 °C

Freundlich

nf Kf (μmol1 – n g− 1 Ln) R2 qmax (μmol/g) Kl (L/μmol) R2 Kd (L/g) Log KOC R2

0.4307 0.3289 0.9702 8.850 0.0026 0.9751 6.803 1.903 0.1934

0.4725 0.1887 0.9806 6.739 0.0025 0.9953 5.344 1.798 0.083

Langmuir

Linear

Table 3 Adsorption thermodynamics parameters for toluene adsorption on DPDSCI-zeolite under Langmuir and Linear isotherms at 20 °C and 4 °C.

174

Isotherms

Parameters

20 °C

Langmuir

ΔG (kJ/mol) ΔH (kJ/mol) ΔS (J/mol)

− 19.15

4 °C −18.04 1.206 69.45

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

References Arora, M., Snape, I., Stevens, G.W., 2011. The effect of temperature on toluene sorption by granular activated carbon and its use in permeable reactive barriers in cold regions. Cold Reg. Sci. Technol. 66 (1), 12–16. Bargagli, R., 2008. Environmental contamination in Antarctic ecosystems. Sci. Total Environ. 400 (1–3), 212–226. Bish, D.L., Stucki, J.W., 1989. Thermal analysis in clay science. In: Clay Minerals Society Workshop Lectures. Clay Minerals Society, Colorado, pp. 3. Bortone, I., Chianesea, S., Di Nardoa, A., Di, M., Natalea, A.E., Musmarraa, D., 2013a. A comparison between pump & treat technique and permeable reactive barriers for the remediation of groundwater contaminated by chlorinated organic compounds. Chem. Eng. Trans. 32, 31–36. Bortone, I., Di Nardo, A., Di Natale, M., Erto, A., Musmarra, D., Santonastaso, G.F., 2013b. Remediation of an aquifer polluted with dissolved tetrachloroethylene by an array of wells filled with activated carbon. J. Hazard. Mater. 260, 914–920. Bowman, R.S., 2003. Applications of surfactant-modified zeolites to environmental remediation. Microporous Mesoporous Mater. 61 (1–3), 43–56. Chatterjee, S., Lee, M.W., Woo, S.H., 2010. Adsorption of congo red by chitosan hydrogel beads impregnated with carbon nanotubes. Bioresour. Technol. 101 (6), 1800–1806. Chern, J.-M., Chien, Y.-W., 2002. Adsorption of nitrophenol onto activated carbon: isotherms and breakthrough curves. Water Res. 36, 647–655. Daković, A., Tomašević-Čanović, M., Rottinghaus, G., Dondur, V., Mašić, Z., 2003. Adsorption of ochratoxin A on octadecyldimethyl benzyl ammonium exchangedclinoptilolite-heulandite tuff. Colloids Surf. B: Biointerfaces 30 (1–2), 157–165. Daković, A., Tomašević-Čanović, M., Rottinghaus, G.E., Matijašević, S., Sekulić, Ž., 2007. Fumonisin B1 adsorption to octadecyldimethylbenzyl ammonium-modified clinoptilolite-rich zeolitic tuff. Microporous Mesoporous Mater. 105 (3), 285–290. De Jesus, H.E., Peixoto, R.S., Cury, J.C., Van Elsas, J.D., Rosado, A.S., 2015. Evaluation of soil bioremediation techniques in an aged diesel spill at the Antarctic Peninsula. Appl. Microbiol. Biotechnol. 99 (24), 10815–10827. Ersoy, B., Celik, M.S., 2004. Uptake of aniline and nitrobenzene from aqueous solution by organo-zeolite. Environ. Technol. 25 (3), 341–348. Erto, A., Bortone, I., Di Nardo, A., Di Natale, M., Musmarra, D., 2014. Permeable adsorptive barrier (PAB) for the remediation of groundwater simultaneously contaminated by some chlorinated organic compounds. J. Environ. Manag. 140, 111–119. Erto, A., Chianese, S., Lancia, A., Musmarra, D., 2017. On the mechanism of benzene and toluene adsorption in single-compound and binary systems: energetic interactions and competitive effects. Desalin. Water Treat. 86, 259–265. Freidman, B.L., Gras, S.L., Snape, I., Stevens, G.W., Mumford, K.A., 2016. The performance of ammonium exchanged zeolite for the biodegradation of petroleum hydrocarbons migrating in soil water. J. Hazard. Mater. 313, 272–282. Ghiaci, M., Abbaspur, A., Kia, R., Seyedeyn-Azad, F., 2004. Equilibrium isotherm studies for the sorption of benzene, toluene, and phenol onto organo-zeolites and as-synthesized MCM-41. Sep. Purif. Technol. 40 (3), 217–229. Hamaker, J., Thompson, J., 1972. Adsorption. In: Goring, C.A.I., Hamaker, J.W. (Eds.), Organic Chemicals in the Soil Environment. Marcel Dekker, Inc, New York, pp. 49–143. Hornig, G., Northcott, K., Snape, I., Stevens, G., 2008. Assessment of sorbent materials for treatment of hydrocarbon contaminated ground water in cold regions. Cold Reg. Sci. Technol. 53 (1), 83–91. Huttenloch, P., Roehl, K.E., Czurda, K., 2001. Sorption of nonpolar aromatic contaminants by chlorosilane surface modified natural minerals. Environ. Sci. Technol. 35, 4260–4264. Kuleyin, A., 2007. Removal of phenol and 4-chlorophenol by surfactant-modified natural zeolite. J. Hazard. Mater. 144 (1–2), 307–315. Lemic, J., Kovacevic, D., Tomasevic-Canovic, M., Kovacevic, D., Stanic, T., Pfend, R., 2006. Removal of atrazine, lindane and diazinone from water by organo-zeolites. Water Res. 40 (5), 1079–1085. Li, Z., Roy, S.J., Zou, Y., Bowman, R.S., 1998. Long-term chemical and biological stability of surfactant-modified zeolite. Environ. Sci. Technol. 32, 2628–2632. Li, Z., Burt, T., Bowman, R.S., 2000. Sorption of ionizable organic solutes by surfactantmodified zeolite. Environ. Sci. Technol. 34, 3756–3760. Mahabadi, A.A., Hajabbasi, M.A., Khademi, H., Kazemian, H., 2007. Soil cadmium stabilization using an Iranian natural zeolite. Geoderma 137 (3–4), 388–393. Michael Ranck, J., Bowman, R.S., Weeber, J.L., Katz, L.E., Sullivan, E.J., 2005. BTEX removal from produced water using surfactant-modified zeolite. J. Environ. Eng. 131 (3), 434–442. Mumford, K.A., Rayner, J.L., Snape, I., Stark, S.C., Stevens, G.W., Gore, D.B., 2013. Design, installation and preliminary testing of a permeable reactive barrier for diesel fuel remediation at Casey Station, Antarctica. Cold Reg. Sci. Technol. 96, 96–107. Mumford, K.A., Powell, S.M., Rayner, J.L., Hince, G., Snape, I., Stevens, G.W., 2015. Evaluation of a permeable reactive barrier to capture and degrade hydrocarbon contaminants. Environ. Sci. Pollut. Res. 22 (16), 12298–12308. Northcott, K.A., Bacus, J., Taya, N., Komatsu, Y., Perera, J.M., Stevens, G.W., 2010a. Synthesis and characterization of hydrophobic zeolite for the treatment of hydrocarbon contaminated ground water. J. Hazard. Mater. 183 (1–3), 434–440. Northcott, K.A., Miyakawa, K., Oshima, S., Komatsu, Y., Perera, J.M., Stevens, G.W., 2010b. The adsorption of divalent metal cations on mesoporous silicate MCM-41. Chem. Eng. J. 157 (1), 25–28. Obiri-Nyarko, F., Grajales-Mesa, S.J., Malina, G., 2014. An overview of permeable reactive barriers for in situ sustainable groundwater remediation. Chemosphere 111, 243–259. Ogawa, M., Okutomo, S., Kuroda, K., 1998. Control of interlayer microstructures of a

Fig. 6. Regeneration test for toluene uptake onto DPDSCI-zeolite.

microbes compared with GAC (Zhang et al., 1991), which is an important foundation for future bioremediation processes. 4.5. Regeneration test The results of the regeneration test for toluene capture onto DPDSCI coated zeolite are shown in Fig. 6. Three methods are applied (washed by acetone, methanol and hot water respectively) and compared with the fresh DPDSCI-zeolite. For the first regeneration, there is a significant difference (around 20%) between the adsorption observed for the fresh sample and washed samples. Among them, methanol washed samples presented the best performance. For the second regeneration, the sorption percentage of both acetone and methanol washed samples reduced further, while that of hot water washed samples kept stable. Therefore, the DPDSCI coated zeolite has the potential to be used and regenerated with a tolerable reduction in performance. Regeneration with water is also a more environmentally friendly option as compared to the other solvents trialled. 5. Conclusions According to the results from TGA and FT-IR, the chlorosilane, diphenyldichlorosilane was successfully coated on to the surface of a natural zeolite without change to the internal porous structure. Batch adsorption tests showed a good capacity in adsorbing toluene by DPDSCI coated zeolite, compared with the raw material. The adsorption study demonstrated that the Langmuir isotherm fitted the adsorption best, indicating its monolayer and homogeneous character. The thermodynamics calculation showed the sorption process was spontaneous and endothermic. Based on the enthalpy change of adsorption, the intermolecular interactions between hydrocarbon and DPDSCI coated zeolite were mainly Van der Waals interactions with some enhancement of hydrophobic bonding and π-π electron stacking interactions. The results from regeneration test also demonstrated this modified zeolite can be used several times with tolerable reduction. Therefore, this modified zeolite has the advantages of good adsorption capacity with less adsorption strength, good regenerated ability and less temperature dependency. Compared with the drawbacks of GAC, the irreversible adsorption which is hard to combine with bioremediation and unstable mechanism in the freeze-thaw cycles, this modified zeolite is more suitable as fill material for the future application in PRBs in cold regions. Acknowledgement This study was supported by the Particulate Fluids Processing Centre, a Special Research Centre of the Australia Research Council. The Australian zeolite was supplied by the Australian Antarctic Division. Thanks to University of Melbourne and Chinese Scholarship Council for scholarship support. 175

Cold Regions Science and Technology 145 (2018) 169–176

J. Ma et al.

Ten Hulscher, T.E.M., Cornelissen, G., 1996. Effect of temperature on sorption equilibrium and sorption kinetics of organic micropollutants - a review. Chemosphere 32 (4), 609–626. Thiruvenkatachari, R., Vigneswaran, S., Naidu, R., 2008. Permeable reactive barrier for groundwater remediation. J. Ind. Eng. Chem. 14 (2), 145–156. Torabian, A., Kazemian, H., Seifi, L., Bidhendi, G.N., Azimi, A.A., Ghadiri, S.K., 2010. Removal of petroleum aromatic hydrocarbons by surfactant-modified natural zeolite: the effect of surfactant. Clean 38 (1), 77–83. Von Oepen, B., Korel, W., Klein, W., 1991. Sorption of nonpolar and polar compounds to soils: processes, measurement and experience with the applicability of the modified OECD-guideline 106. Chemosphere 22, 285–304. Wang, S., Peng, Y., 2010. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem. Eng. J. 156 (1), 11–24. Widiastuti, N., Wu, H., Ang, M., Zhang, D.-k., 2008. The potential application of natural zeolite for greywater treatment. Desalination 218 (1–3), 271–280. Woinarski, A.Z., Snape, I., Stevens, G.W., Stark, S.C., 2003. The effects of cold temperature on copper ion exchange by natural zeolite for use in a permeable reactive barrier in Antarctica. Cold Reg. Sci. Technol. 37 (2), 159–168. Yang, J., Cao, L., Guo, R., Jia, J., 2010. Permeable reactive barrier of surface hydrophobic granular activated carbon coupled with elemental iron for the removal of 2,4-dichlorophenol in water. J. Hazard. Mater. 184 (1–3), 782–787. Zhang, X., Wang, Z., Gu, X., 1991. Simple combination of biodegradation and carbon adsorption—the mechanism of the biological activated carbon process. Water Res. 25 (2), 165–172.

layered silicate by surface modification with organochlorosilanes. J. Am. Chem. Soc. 120 (29), 7361–7362. Santonastaso, G.F., Bortone, I., Chianese, S., Erto, A., Di Nardo, A., Di Natale, M., Musmarra, D., 2015. Application of a discontinuous permeable adsorptive barrier for aquifer remediation. A comparison with a continuous adsorptive barrier. Desalin. Water Treat. 57 (48–49), 23372–23381. Saremnia, B., Esmaeili, A., Sohrabi, M.-R., 2016. Removal of total petroleum hydrocarbons from oil refinery waste using granulated NaA zeolite nanoparticles modified with hexadecyltrimethylammonium bromide. Can. J. Chem. 94 (2), 163–169. Scherer, M.M., Richter, S., Valentine, R.L., Alvarez, P.J.J., 2000. Chemistry and microbiology of permeable reactive barriers for in situ groundwater clean up. Crit. Rev. Microbiol. 26 (4), 221–264. Silverstein, R.M., Webster, F.X., Kiemle, D., Bryce, D.L., 2014. Spectrometric Identification of Organic Compounds, 8th edition. John Wiley & Sons Inc, New Jersey. Snape, I., Morris, C.E., Cole, C.M., 2001. The use of permeable reactive barriers to control contaminant dispersal during site remediation in Antarctica. Cold Reg. Sci. Technol. 32, 157–174. Song, W., Li, G., Grassian, V.H., Larsen, S.C., 2005. Development of improved materials for environmental applications: nanocrystalline NaY zeolites. Environ. Sci. Technol. 39 (5), 1214–1220. Soto, M.L., Moure, A., Domínguez, H., Parajó, J.C., 2011. Recovery, concentration and purification of phenolic compounds by adsorption: a review. J. Food Eng. 105 (1), 1–27.

176