oil spill

Accepted Manuscript Title: CROSS-LINKED POLY(TETRAHYDROFURAN) AS PROMISING SORBENT FOR ORGANIC SOLVENT/OIL SPILL Author: Ilker Yati Gulsah Ozan Aydin Hayal Bulbul Sonmez PII: DOI: Reference:

S0304-3894(16)30126-1 http://dx.doi.org/doi:10.1016/j.jhazmat.2016.02.014 HAZMAT 17447

To appear in:

Journal of Hazardous Materials

Received date: Revised date: Accepted date:

24-11-2015 1-2-2016 4-2-2016

Please cite this article as: Ilker Yati, Gulsah Ozan Aydin, Hayal Bulbul Sonmez, CROSS-LINKED POLY(TETRAHYDROFURAN) AS PROMISING SORBENT FOR ORGANIC SOLVENT/OIL SPILL, Journal of Hazardous Materials http://dx.doi.org/10.1016/j.jhazmat.2016.02.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

CROSS-LINKED POLY(TETRAHYDROFURAN) AS PROMISING SORBENT FOR ORGANIC SOLVENT/OIL SPILL Ilker Yatia, Gulsah Ozan Aydina and Hayal Bulbul Sonmeza* a

Gebze Technical University, Department of Chemistry, PO. Box 141, 41400 Gebze, Kocaeli,

Turkey * Corresponding author: Hayal BULBUL SONMEZ, e-mail: [email protected] AUTHOR INFORMATION Corresponding Author: *Hayal BULBUL SONMEZ Gebze Technical University, Department of Chemistry, P. O. Box 141, 41400 Gebze, Kocaeli, Turkey. E-mail: [email protected]

Graphical abstract

1

HIGHLIGHTS    

Poly(tetrahydrofuran) based sorbents were prepared. PTHF sorbents demonstrate reusability at least for ten times. PTHF based sorbents show fast and quick absorption-desorption process. 19 g of oil can be absorbed by 1 g of PTHF-ICS based sorbent.

ABSTRACT In this study, a series of different molecular weights of poly(tetrahydrofuran) (PTHF), which is one of the most important commercial polymers around the world, was condensed with tris[3(trimethoxysilyl) propyl] isocyanurate (ICS) to generate a cross-linked 3-dimensional network in order to obtain oil sorbents having high swelling capacity. The prepared sorbents show high and fast swelling capacity in oils such as dichloromethane (DCM), tetrahydrofuran (THF), acetone, tbutyl methyl ether (MTBE), gasoline, euro diesel, and crude oil. The recovery of the absorbed oils from contaminated surfaces, especially from water, and the regeneration of the sorbents after several applications are effective. The characterization and thermal properties of the sorbents are

2

identified by Fourier transform infrared spectroscopy (FTIR), solid-state

13

C and

29

Si cross-

polarization magic angle spinning (CPMAS) nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC) and thermal gravimetric analyses (TGA), respectively. The new usage area of PTHF is emerged by the preparation of PTHF-based network structure with high oil absorption capacity and having excellent reusability as an oil absorbent for the removal of organic liquids from the spill site. KEYWORDS Poly(tetrahydrofuran); oil sorbent; high absorption; stability; reusability.

1. INTRODUCTION Due to the demand for millions of tons of petrochemical products used worldwide, soil and water pollution by chemical leakage has attracted a great deal of attention in recent years due to its harmful effect on the environment and wildlife [1-5]. Therefore, cleaning oil spillages from the spill site is an urgent and challenging duty [6-8]. Various techniques have been adopted for oil spillage restoration, for instance chemical dispersants [9, 10], skimmers and booms [11], bioremediation [12], in situ burning [13], and using sorbents [14, 15]. Using an oil sorbent has definite advantages of easy operation process, low cost and complete clean-up without producing secondary pollution [16]. Three-dimensional porous materials with hydrophobicity and oleophilicity are favorable candidates for oil absorption because of their perfect selectivity for oil and organic solvents, high absorption capacities, excellent reusability, and oil recovery in order to clean-up crude oil, fuels and toxic organic solvents [17, 18]. To date, a number of synthetic sorbents have been studied to improve the features of the oil sorbents such as TEOS- (tetraethyl orthosilicate) based sorbents [19-21], macroporous rubber gels [22], photoresponsive oil sorbers

3

[23], polydimethylsiloxane (PDMS) sponge [24], magnetic and highly reusable macroporous superhydrophobic/superoleophilic

PDMS/MWNT

nanocomposite

[25],

flexible

aerogel

composite [26], hydrophobic nanocellulose aerogels [27], hydrophobic plasma polymer coated silica particles [28], nanocomposite β-cyclodextrin-based oil sorbent [29], spongy graphene [30], polypropylene-acrylate fiber sorbent [31], nanoporous polystyrene fibers [32], carbon-nanotubebased organogels [33], amino acid based cross-linked polymer networks [34], alkoxysilane based sorbents [35-37], TEOC (tetraethylorthocarbonate)-based sorbents [38-40], crosslinked copolymers of octadecyl acrylate with acrylic acid [41], phase-selective sorbent xerogels [42], poly(ε-caprolactone) microfiber meshes [43], carbon-silica sorbent [44], polyurethane sponge modified by reduced graphene oxide [45]. Evolving new materials to clean up the chemical leakage is important in order to improve their potential for urgent cleaning and recovery processes. From this point of view, for the developing of new sorbent material some properties such as high absorption capacity and rate, good stability in water, floating over water before and after absorption of the oil and also reusability are required[46]. Poly(tetrahydrofuran) (PTHF), well known as poly(tetramethylene ether) glycol is one of the most important commercial polymers to produce thermoplastic elastomers such as polyesters and polyurethanes (Spandex) [47, 48]. PTHF imparts superior features like high flexibility, good hydrolytic stability, excellent abrasion resistance, perfect resiliency and attractive dynamic properties to its products [49]. It has been employed in a variety of applications, for instance block copolymers [50], amphiphilic conetworks [51-53] end-functional star polymers [54], and thermogels [55]. In a previous study, PEG-ICS amphiphilic gels that have high absorbency, high rate of uptake, and thermal stability up to 200 oC were synthesized using a simple process [56]. Using PEG

4

polymers to build an excellent sorbent increased the solvent uptake capacities of the sorbents due to more elastic and longer chains which rebound to extend the pores of the sorbents and the elasticity. The promising results obtained from the PEG-ICS sorbents encouraged us to work on it further in order to improve the properties of the sorbents. For this purpose, we used the required worldwide commercial polymer PTHF, which is similar to the PEG structure but has superior hydrophobicity to PEG polymers in this application. To the best of our knowledge, there is no report on the use of hydrophobic PTHF as an oil sorbent. The present study describes the synthesis of PTHF-based sorbents via the condensation of PTHFs with different molecular weights and ICS, which has a larger bridging group with flexible propyl chains as a cross-linker. The synthesis of PTHF-based sorbents was carried out in solvent-free medium at relatively high temperature without using any catalyst or activator. The cleanup effect of the sorbents was examined by testing the absorption capacity of the sorbents in various organic liquids such as crude oil, gasoline, euro diesel, toluene, dichloromethane, tetrahydrofuran, MTBE and acetone. The swelling capacity of the sorbents was also investigated using water-organic liquid mixtures. In this study, the high swelling capacity and reusable, highly hydrophobic sorbents were prepared using PTHF which has high flexibility and hydrophobic features. By the preparation of PTHF-ICS cross-linked polymers, we demonstrated not only the high capacity and reusability of oil sorbents, but also a different usage for the PTHF polymers as a promising oil sorbent instead of commercial ones. 2. MATERIALS AND METHODS All the chemicals, used devices for the characterization of the sorbents, and the detailed synthesis procedure of the sorbents are mentioned in the Appendix A. Supplementary data.

5

2.1 Methods 2.1.1 Soluble Fractions (SFs) Before starting the swelling tests, the elimination of the SFs which are the unreacted macromonomers, cross-linkers or oligomers in the 3-dimensional structure of the sorbents is required for the reliable and accurate swelling tests. Dichloromethane (DCM) was chosen for the removal of SFs because it doesn’t affect the structure of the sorbents but solves the SFs. To execute this, a weight quantity of sorbent was immersed in DCM that refreshed every 24 h for 72 hours. The swollen sorbent was dried at room temperature to a constant weight after the extraction ended up. Equation 1 shows the way of the calculation of extracted SFs from the synthesized sorbents: %

100

(1)

where Wo and W are the weights of the sorbents before and after extraction, respectively. 2.1.2 Absorption studies Synthesized sorbents were ready to apply swelling tests after the elimination of the unwanted SFs. Different organic liquids were used in absorption studies and the swelling tests were performed using the following methods: Stainless steel mesh (5×2.5 cm) were used in absorption studies to detect the swelling properties of the sorbents. The mesh were dipped into the solvent and blotted gently with absorbent paper by tapping the bottom of the mesh and weighed. Afterwards, a known weight of dry sorbent was put inside the mesh and submerged into the solvent at room temperature. After the sorbents reached swelling equilibrium, the mesh was taken away from the solvent and weighed in a stoppered weighing bottle right after tapping the

6

bottom of the mesh with absorbent paper. The absorption percentage (S%) of the sorbents was computed by the equation 2 [57]. %

|

100

(2)

where Ws and Wp are the weights of the swelled and dry sorbents, individually. The swelling capacity of the synthesized sorbents was recorded by averaging at least four measurements for each solvent. For the crude oil absorption measurements, each sorbent sample was made ready for the next absorption cycle by extracting the crude oil from the sorbent using DCM and dried at room temperature after the first absorption cycle. 2.1.3 Absorption kinetics Kinetic studies were performed to understand the swelling process of the generated sorbents. To achieve this, the kinetic measurements were operated by the same approach detailed above using DCM as organic solvent. Unlike swelling test, the kinetic measurements were performed at shorter time intervals like 5, 10 and 60 minutes. All the obtained experimental information was further examined to illustrate the swelling attitude of the sorbents using the kinetic models [58]. Equation 3 exhibits the swelling rate for the first-order kinetics:



(3)

where Qt and Qmax are the swelling percentage of the sorbent at time t, and the percentage of the swollen sorbent at equilibrium. Integration of equation 3 presents: ln

(4)

7

if the plotting of ln

vs. t gives a straight line, the absorption process

follows the first order kinetics. For the second-order kinetics the swelling degree is depicted in equation 5: (5) Integration of equation 5 presents: (6)



If the plotting ⁄

versus time t generates a straight line, absorption process follows second-

order kinetics. 2.1.4 Desorption kinetics Desorption kinetics were performed to understand the solvent retention of the sorbents. To accomplish this, the sorbents were allowed to swell in DCM which is the most absorbable volatile solvent for the synthesized sorbents. After the sorbents reached maximum capacity, DCM retention of the sorbents was settled by weighing the swollen sorbent as a function of time in air at room condition without using any desorption method such as vacuum, extraction or heating. The whole synthesized PTHF-ICS based sorbents can desorb the absorbed volatile DCM by itself without using any exterior force at room condition. 2.1.5 The separation of water–organic solvent mixture For the direct removal of organic solvents from a water surface, 20 mL of crude oil or toluene and 30 mL of water were used to form the oil and water suspension. The mesh filled with 0.2 g of sorbent was placed on the surface of the organic solvent/water mixture and swelling was

8

monitored as a function of time. The absorption capacity in the solvent mixture was calculated using Equation 2. For the photographs of the capture of toluene from the water surface, 2 mL of organic solvents was poured into 10 mL of water. The PTHF sorbent was then held so that it touched the toluene until the absorbents were swollen. 2.1.6 Stability in oil and water As explained in the swelling test, a known amount of the sorbent was immersed in toluene, gasoline and water to examine any possible capacity loss for 1, 7, 14, 21, 28 … 63 days. 2.1.7 Reusability To study reusability of sorbents, absorption and desorption process of polymers was followed by the weighing method in DCM as described above. The first absorption-desorption cycle was performed as the following method: A known weight dry sorbent was put in DCM and allowed to reach equilibrium swelling rate for 5 hours. After 5 hours, the swollen sorbent was permitted to desorb the all absorbed DCM for 2 hours at room conditions. The complete desorption of DCM by the sorbent was checked by comparing the dry mass of the sorbent after desorption and initial weight of the dry sorbent. These cycles were repeated ten times. 3. RESULTS AND DISCUSSION 3.1 Synthesis process of the sorbents A number of hydrophobic PTHF macromonomers (PTHF 250, PTHF 650, PTHF 1000, PTHF 1400, PTHF 2000, and PTHF 2900) were condensed with ICS at 160 oC under argon atmosphere in a solvent-free medium to produce PTHF-based sorbents. By using the different molecular

9

weights of PTHF macromonomers, the changes of the absorption capacity and also thermal properties of the sorbents were monitored. Also, low molecular weight 1,4-butanediol was reacted with ICS by the same synthesis procedure defined above as a model polymer. The reason to synthesize 1,4 butanediol-ICS is to display the swelling peculiarity resulting from the use of the small molecule instead of macromonomers. Scheme 1 shows the summarizing of the condensation reactions between monomers and cross-linkers. The verification of the sorbent structures was performed by FTIR, NMR, TGA, and DSC. FTIR spectra of generated sorbents in Figure S1 (Supporting Information) show a broad characteristic ─OH absorption peak between 3200 and 3600 cm-1, which originates from the hydroxyl groups of PTHF macromonomers and 1,4-butanediol monomer which were the unreacted parts of the sorbent chains. The peaks between 2700 and 2900 cm-1 indicate the vibrations of aliphatic ─CH2 carbons that come from the macromonomers and ICS. The strong peaks at 1685 cm-1 indicate the carbonyl groups of the cyanurate ring of the cross-linker. The bending vibrations of aliphatic ─CH bonds were observed at 1360 and 1460 cm-1; the strong stretching vibrations of ─Si─O─C─ bond existed at 1090 cm-1. The solid-state 13C CPMAS NMR spectra of sorbents are represented in Figure S2 (Supporting Information). The resonance at 169.0 ppm for polymers and around 130.0 ppm for the rest of the sorbents proves the presence of ─C=O carbons which originate from the ICS. The signal of the carbonyl group for PTHF 2000-ICS and PTHF 2900-ICS was not detectable because of the bulkiness of the sorbent and the usage of very little cross-linker according to stoichiometric proportions. The signal at 56.0 ppm is based on the carbon atoms appearing at both sides of the oxygen atom (─CH2─O─CH2─) on the PTHF chains. While the ─Si─O─C─ carbons take place at 46.0 ppm, the aliphatic carbons on PTHF chains come up at 11.0 ppm for all synthesized

10

sorbents. The resonances shown in Figure S2 confirm that the expected structure of the sorbents was completed. The solid state

29

Si CPMAS NMR spectra of sorbents represented in Figure S3 (Supporting

Information) demonstrate that the Si atoms were incorporated into the sorbent structure successfully by the peaks of CH2─Si─O at -60.0 and -68.0 ppm that come from different chemical environments.

TGA and DSC techniques were used to evaluate the thermal properties of obtained sorbents. Figure S4 and Figure S5 (Supporting Information) exhibit the TGA thermograms and DSC curves of the synthesized sorbents, respectively. All of the synthesized PTHF-ICS sorbents exhibit excellent thermal stability up to 250 oC as shown by the TGA thermograms in Figure S4. The cross-linking density in the sorbent structure makes the construction of the 3D-network more thorough when the cross-linking density reaches higher levels. This circumstance occurred in the synthesized sorbent series. The cross-linking density of the sorbents decreases at higher molecular weights, and the thermal stability of the sorbents decreases when the molecular weights of the PTHF macromonomers in the sorbent synthesis increase due to the lower crosslinking density. According to TGA thermograms, while the structure of 1,4-ICS displays the heaviest cross-linking density, the PTHF 2900-ICS demonstrated lower cross-linking density among the generated sorbents. The real silicon content of the synthesized sorbents at 900 °C was in the following order which also shows the cross-linking tendency of the polymers: PTHF 2900-ICS (4.28%) < PTHF 2000ICS (5.45%) < PTHF 1400-ICS (8.16%) < PTHF 1000-ICS (9.94%) < PTHF 650-ICS (14.4%) <

11

PTHF 250-ICS (24.36%) < 1,4-ICS (35.42%). The more cross-linked structure had more silicon content because of the higher incorporation of the cross-linkers in the polymer structure.

DSC curves of the synthesized sorbents are represented in Figure S5 and the reveal that the molecular weights of the PTHF, or in another words the length of the macromonomers, affect the thermal behavior of the sorbents. The sorbents have crystalline melting points between 13oC and 46oC originating from the different molecular weights of PTHF polymers, due to the incorporation of the PTHF macromolecules in the sorbent structure. The crystalline melting points of the sorbents increased from PTHF 1000-ICS to PTHF 2900-ICS analogous with the incorporated PTHF polymers into the network structure. The crystallinity can no longer be observed by DSC in the lower molecular weights of the sorbents (PTHF 250-ICS and PTHF 650ICS) due to the denser cross-linking nature of the sorbents which inhibits the chain stacking. 3.2 Absorption and desorption properties of the sorbents Seven PTHF-based sorbents were synthesized for the cleanup of organic liquids from the spill site in the scope of this study. Different molecular weights of PTHFs (PTHF 250, PTHF 650, PTHF 1000, PTHF 1400, PTHF 2000, and PTHF 2900) were used to generate hydrophobic sorbents by cross-linking with ICS. In addition, 1,4-butanediol was condensed with ICS to get a model sorbent that included a low molecular weight of monomer instead of a large macromonomer in order to compare the diversity of the absorption properties. Absorption properties of the sorbents were confirmed using several organic liquids, such as DCM, THF, toluene, MTBE, acetone, gasoline, diesel, and crude oil. Before the swelling tests, soluble fractions (SFs) that were unreacted monomer or oligomers must be eliminated from the network structure to achieve accurate swelling measurements without the contrary effect of SFs. Disposal

12

of SFs in the sorbents was executed in the following process: a known weight of dry sorbent was put into DCM, is a harmless solvent to the network structure, which was allowed to dissolve the unwanted SFs in the sorbents for 72 hours at room temperature. After the extraction was completed, the swollen sorbents were dried under room conditions to a constant weight. The calculated percentages of the prepared sorbents were found to be 9.5% for 1,4-ICS, 23.4% for PTHF 250-ICS, 33.7% for PTHF 650-ICS, 29.5% for PTHF 1000-ICS, 42.5% for PTHF 1400ICS, 38.7% for PTHF 2000-ICS and 34.5% for PTHF 2900-ICS. SFs increase when the molecular weight of diols increases from 1,4-ICS to PTHF 2900-ICS.This is because, the functional groups of the monomers have difficulties to find each other when the distance are too long between the cross-linking points. Besides, cross-linking density of the sorbents on the high molecular weight sorbents (e.g. PTHF 2900-ICS, PTHF 2000-ICS, etc.) get lower than the low molecular weight sorbents (e.g. 1,4-ICS, PTHF 250-ICS, etc.) due to decrease in cross-linker density. Oil absorption studies of the PTHF-based sorbents were carried out using the various organic solvents (DCM, polar aprotic, Ɛ=9.1; THF, polar aprotic, Ɛ=7.5; acetone, polar aprotic, Ɛ=20.7; MTBE, polar aprotic, Ɛ=2.6; toluene, nonpolar aprotic, Ɛ=2.4) and fuels such as gasoline, diesel, and crude oil after the removal of SFs from the synthesized sorbents. Swelling measurements were taken at room temperature in a closed system, and the results were recorded by averaging at least four measurements for each synthesized sorbent to be sure of obtaining the correct swelling values. Swelling percentages of the synthesized PTHF-based sorbents are shown in Figure 1. While all the obtained sorbents exhibit quite a high swelling capability, they stay stable in these liquids without dissolving. In Figure 1, it is clear that the PTHF 2900-ICS has the highest sorption capacity and the PTHF 250-ICS has the lowest sorption capacity in DCM by the value

13

of 1800 and 213%, respectively. The model sorbent, 1,4-butanediol-ICS, showed very low sorption (125%, in DCM) as we expected. First, using small molecules in the sorbent synthesis resulted in a more cross-linked structure. So for this denser cross-linking causing barriers for the solvent diffusion, swelling values were found to be less than the sorbent synthesized from the macromonomers. Second, the swelling behavior of the sorbents was affected by the molecular weight of the PTHF moieties in the sorbent structure. As seen from the swelling graphic in Figure 1, the absorption percentage of the sorbents increased by the increment of the molecular weights of the PTHF units. Longer PTHF chains expand the distance between cross-linking points. Therefore, the gaps inside the sorbent structure become larger and ready to hold more liquids into the network. Also, the elasticity of the PTHF macromonomer provides more space to diffuse organic liquids into the sorbent network by broadening the sorbent walls. In our previous study, we synthesized high capacity PEG based gels with ICS. Because of the amphiphilic nature of the gels, they have high swelling ratios both in polar and nonpolar solvents [56]. In this paper, we used more hydrophobic macromonomers (PTHF) than PEG molecules in order to increase the hydrophobic character of the sorbents to reach higher swelling capacities in organic solvents. In this respect, we succeeded in generating higher swelling capacity sorbents by PTHF-ICS compared to PEG-ICS based sorbents. The highest capacity was found in PEG based gels at 1000% in DCM, whereas using more hydrophobic polyether we reached the maximum capacity in DCM at around 1800%. As we expected, inserting more hydrophobicity in the polymer structure resulted in more organic solvents/oil affinity and swelling capacities increased to 1.8 fold without interaction with water. All these results suggest that using hydrophobic material to start with resulted in more hydrophobic networks and the chain length of the PTHF also affects the solvent interaction of the sorbents.

14

Solvent diffusion into the sorbent network affects the swelling rates of the sorbents. According to swelling degrees of the synthesized sorbents, crude oil and diesel were absorbed less by the obtained sorbents than the other organic liquids due to their high viscosity features. Gasoline, which consists of various ingredients, primarily short chain hydrocarbons, is more volatile than diesel and crude oil and was absorbed by the prepared sorbents to higher degrees (518%, for PTHF 2900-ICS) than the diesel and crude oil. The promising absorption values of the synthesized PTHF-ICS based sorbents are compared in Table S1 in the supporting information. These competitive results showed that the new PTHFICS based sorbents have great potential to be applied as organic solvent/oil absorptive materials. Photographs of equal weight sample of PTHF 2900-ICS sorbent that swollen in different oils/solvents are provided as Figure 2. As seen from the pictures that after absorbing of each oil/solvent, the size of sorbent become much larger than their original dry size. This is also show the high absorptive future of the PTHF sorbents visually. 3.3 The separation of water–organic solvent mixture For environmental issues, the efficiency of the sorption from a water surface is another important parameter. Separation of organic solvent from a water surface is indicated in Figure 3 as an example. The pictures show toluene (dyed using methyl red) sorption over water by PTHF 2900ICS which is the highest capacity sorbent prepared in this study. As seen in Figure 3, the sorbent absorbed toluene very quickly, within 5 minutes. The separation of toluene and water was achieved easily by a simple filtration process. The usage of PTHF-ICS based sorbents on separation of toluene over water is very fast and effective. Additionally, as seen from the graph, it has an excellent ability for removal of toluene from water; the oil absorption capacities of the

15

gel did not change in the aqueous medium. This result also demonstrated the effectiveness of the sorbents in that the swelling capacity of the sorbent is not affected by the environment whether water is present or not—the absorbing capacity of the PTHF sorbent is constant. Another important point of this experiment was that before and after absorbing solvent, the PTHF sorbent was floating on the water surface. This is also another important parameter for the practical application.

Fast absorption rate is an important parameter for an excellent sorbent especially for practical applications. Absorption kinetic tests of the synthesized sorbents were undertaken to realize the saturation time by measuring in a short time intervals (5, 10, 30 minutes) using DCM which is the best absorbable solvent for these PTHF-ICS based sorbents. As seen in Figure 4, the sorbents very quickly reached close to their maximum swelling within 5 minutes. With the molecular weight of the PTHF macromonomers inside the sorbent structure, saturation time of the sorbent (here it is PTHF 2900-ICS) extended to nearly 60 minutes because of the bulkiness of the network structure.

The experimental data set of kinetic studies was further analyzed using pseudo kinetic parameters due to the good understanding of the absorption process. The straight lines obtained on the plot of t/Qt versus time (t) from Equation 6 confirm that the absorption process follows second-order kinetics (Figure 5). The intercept of the linear plots gives the k2 values and are depicted in Table 1 with the other experimental data (R2, Qmax). The correlation coefficient values (R2) are higher than 0.99 for all the synthesized sorbents and theoretical Qmax values are in close agreement with the experimental values.

16

Desorption of the absorbed dichloromethane from the synthesized networks is depicted in Figure 6; this was achieved in the open air at room conditions without any necessity of exterior force such as vacuum or heating. According to the graph in Figure 6, the desorption rate of the absorbed dichloromethane was quite fast. The desorption process continued more rapidly when we used a lower molecular weight of PTHFs (PTHF 250-ICS, PTHF 650-ICS) in the sorbent synthesis than the higher molecular weight of PTHFs (PTHF 1000-ICS, PTHF 1400-ICS, PTHF 2000-ICS, PTHF 2900-ICS). All the obtained sorbents released absorbed dichloromethane without using vacuum or heating within 40 minutes which is a considerably shorter time for a reusable sorbent. 3.4 Reusability of the synthesized sorbents

The reusability in oil sorption capacity of hydrophobic PTHF 2900-ICS sorbent for DCM after ten sorption and desorption cycles is calculated according to Equation 2 for PTHF 2900-ICS as a representative example. A known weight of dry PTHF 2900-ICS sorbent was immersed in DCM to reach equilibrium swelling state for 5 hours using the platform shaker to increase the sorbentsolvent interaction. After 5 hours (all the prepared sorbents can reach its maximum absorption level under 2 hours), the swollen sorbent was allowed to desorb absorbed DCM without using exterior forces such as vacuum or heating at room conditions for 2 hours. After the complete desorption of absorbed DCM (all the prepared sorbents can completely desorb DCM under 1 hour) after 2 hours, the sorbent sample was used for the next absorption-desorption cycle. The relevant result showed that the absorption capacity was almost unchanged even over ten cycles and this sorbent can be used several times without any change in the sorption capacity (Figure 7).

17

3.5 Stability in oils and water As a potential oil sorbent, these materials also have outstanding capability of stability in oils, which is extremely important for the proposed application. In Figure 8, the swelling of the PTHF 2000-ICS in toluene, gasoline and water was demonstrated for 63 days. For this measurement, sample polymers were put in the previously-mentioned solvents and after certain times they were removed, the solvent absorption capacity was measured then they were returned to the same solvent. Synthesized PTHF sorbents are very stable against long-term immersion in various oils and also in water. After interaction with the solvent for more than two months, neither the polymer’s solvent absorption capacity nor the polymer structure changed. Another evidence for the stability of the polymers is that there was no weight loss in this test for each sample. Besides these results, to show there were no structural changes, details of the FTIR. The swelling capacity of the sorbent did not change for 63 days except for a small change in swelling rate. Water absorbency of the sorbent is mostly 40% which should be considered as the wetting factor of the sorbent more than swelling. In this context, the sorbent can be used for the removal of organic solvents such as toluene and gasoline from a water surface without being affected for at least 63 days. This long-term stability of the synthesized sorbents together with all swelling values and kinetic measurements is the evidence that these PTHF-based sorbents have potential application as a commercial material for the cleaning of water from oils and organic solvents without losing their swelling capacity. The structure of PTHF 2000-ICS was checked out by FTIR spectra of the sorbent to establish if there was any distortion on the structure of the sorbent after usage over the times studied that was carried out in toluene, gasoline, and water. As seen in Figure S6 (Supporting Information),

18

all of the FTIR spectra of PTHF 2000-ICS demonstrated that there was no structural defect on the sorbent network before and after the usage time study. The usability of the sorbent is extremely effective even after two months without capacity loss. 4. CONCLUSIONS

Finally, elastic and hydrophobic PTHF macromolecules have been successfully condensed with ICS in a solvent-free medium without using any catalyst or activator, to obtain high capacity and reusable sorbents. PTHF sorbents can absorb more than 19 g of oil per 1 g of sorbent. While the prepared PTHF-ICS-based sorbents show fast and high capacity absorbencies, they can be reused for at least for two months without capacity loss. Using PTHFs which are important commercial, low cost, and widely-used polymer in both research and commercial synthetic materials, to prepare high swelling capacity, low density and reusable sorbents is important to propose a different usage area for PTHF macromolecules. These new kind of sorbents can be a good candidate for the removing of oil/organic solvents from the environment.

Author Contributions The manuscript was written through contributions of all authors. ACKNOWLEDGMENT We thank the Turkish Petroleum Refineries Co. for supplying of crude oil samples. Supplementary Data. Experimental details, FTIR,

13

C and

29

Si CPMAS NMR spectra, TGA,

and DSC thermograms.

19

REFERENCES [1] Y. Pan, W. Wang, C. Peng, K. Shi, Y. Luo, X. Ji, Novel hydrophobic polyvinyl alcoholformaldehyde foams for organic solvents absorption and effective separation, RSC Adv. 4 (2014) 660-669. [2] K.C. Payne, C.D. Jackson, C.E. Aizpurua, O.J. Rojas, M.A. Hubbe, Oil Spills Abatement: Factors Affecting Oil Uptake by Cellulosic Fibers, Environ. Sci. Technol. 46 (2012) 7725-7730. [3] R.S. Rengasamy, D. Das, C. Praba Karan, Study of oil sorption behavior of filled and structured fiber assemblies made from polypropylene, kapok and milkweed fibers, J. Hazard. Mater. 186 (2011) 526-532. [4] S. Mirshahghassemi, J.R. Lead, Oil Recovery from Water under Environmentally Relevant Conditions Using Magnetic Nanoparticles, Environ. Sci. Technol. 49 (2015) 11729-11736. [5] P. Calcagnile, D. Fragouli, I.S. Bayer, G.C. Anyfantis, L. Martiradonna, P.D. Cozzoli, R. Cingolani, A. Athanassiou, Magnetically Driven Floating Foams for the Removal of Oil Contaminants from Water, ACS Nano, 6 (2012) 5413-5419. [6] H. Sai, R. Fu, L. Xing, J. Xiang, Z. Li, F. Li, T. Zhang, Surface Modification of Bacterial Cellulose Aerogels’ Web-like Skeleton for Oil/Water Separation, ACS Appl. Mater. Inter. 7 (2015) 7373-7381. [7] A.F. Avila, V.C. Munhoz, A.M. de Oliveira, M.C.G. Santos, G.R.B.S. Lacerda, C.P. Gonçalves, Nano-based systems for oil spills control and cleanup, J. Hazard. Mater. 272 (2014) 20-27. [8] A.M.A. Pintor, A.M. Silvestre-Albero, C.I.A. Ferreira, J.P.C. Pereira, V.J.P. Vilar, C.M.S. Botelho, F. Rodríguez-Reinoso, R.A.R. Boaventura, Textural and Surface Characterization of Cork-Based Sorbents for the Removal of Oil from Water, Ind. Eng. Chem. Res. 52 (2013) 16427-16435. [9] E.B. Kujawinski, M.C. Kido Soule, D.L. Valentine, A.K. Boysen, K. Longnecker, M.C. Redmond, Fate of Dispersants Associated with the Deepwater Horizon Oil Spill, Environ. Sci. Technol. 45 (2011) 1298-1306. [10] R.S. Judson, M.T. Martin, D.M. Reif, K.A. Houck, T.B. Knudsen, D.M. Rotroff, M.H. Xia, S. Sakamuru, R.L. Huang, P. Shinn, C.P. Austin, R.J. Kavlock, D.J. Dix, Analysis of Eight Oil

20

Spill Dispersants Using Rapid, In Vitro Tests for Endocrine and Other Biological Activity, Environ. Sci. Technol. 44 (2010) 5979-5985. [11] K.R. Bitting, Evaluating a Protocol for Testing a Fire-Resistant Oil-Spill Containment Boom, Spill Sci. Technol. Bull. 5 (1999) 337-339. [12] B. Singh, A. Bhattacharya, V. Channashettar, C.P. Jeyaseelan, S. Gupta, P. Sarma, A. Mandal, B. Lal, Biodegradation of Oil Spill by Petroleum Refineries Using Consortia of Novel Bacterial Strains, Bull. Environ. Contam. Toxicol. 89 (2012) 257-262. [13] D.E. Fritz, In Situ Burning of Spilled Oil in Freshwater Inland Regions of the United States, Spill Sci. Technol. Bull. 8 (2003) 331-335. [14] S. Zhou, W. Jiang, T. Wang, Y. Lu, Highly Hydrophobic, Compressible, and Magnetic Polystyrene/Fe3O4/Graphene Aerogel Composite for Oil–Water Separation, Ind. Eng. Chem. Res. 54 (2015) 5460-5467. [15] V.H. Pham, J.H. Dickerson, Superhydrophobic Silanized Melamine Sponges as High Efficiency Oil Absorbent Materials, ACS Appl. Mater. Inter. 6 (2014) 14181-14188. [16] H. Zhu, S. Qiu, W. Jiang, D. Wu, C. Zhang, Evaluation of Electrospun Polyvinyl Chloride/Polystyrene Fibers As Sorbent Materials for Oil Spill Cleanup, Environ. Sci. Technol. 45 (2011) 4527-4531. [17] A.M. Atta, R.A.M. El-Ghazawy, R.K. Farag, A.-A.A. Abdel-Azim, Crosslinked reactive macromonomers based on polyisobutylene and octadecyl acrylate copolymers as crude oil sorbers, React. Funct. Polym. 66 (2006) 931-943. [18] C. Teas, S. Kalligeros, F. Zanikos, S. Stournas, E. Lois, G. Anastopoulos, Investigation of the effectiveness of absorbent materials in oil spills clean up, Desalination 140 (2001) 259-264. [19] K. Karadag, H.B. Sonmez, Novel poly(orthosilicate)s based on linear aliphatic diols: Synthesis, characterization, and swelling properties, J. Appl. Polym. Sci. 129 (2013) 2121-2127. [20] H.B. Sonmez, K. Karadag, G. Onaran, Synthesis and swelling properties of crosslinked poly(orthosilicate)s from cyclohexanedimethanols, J. Appl. Polym. Sci. 122 (2011) 1182-1189. [21] K. Karadag, G. Onaran, H.B. Sonmez, Synthesis of crosslinked poly(orthosilicate)s based on cyclohexanediol derivatives and their swelling properties, Polym. J. 42 (2010) 706-710. [22] I. Karakutuk, O. Okay, Macroporous rubber gels as reusable sorbents for the removal of oil from surface waters, React. Funct. Polym. 70 (2010) 585-595.

21

[23] E.U. Kulawardana, D.C. Neckers, Photoresponsive oil sorbers, J. Polym. Sci., Part A: Polym. Chem. 48 (2010) 55-62. [24] S.-J. Choi, T.-H. Kwon, H. Im, D.-I. Moon, D.J. Baek, M.-L. Seol, J.P. Duarte, Y.-K. Choi, A Polydimethylsiloxane (PDMS) Sponge for the Selective Absorption of Oil from Water, ACS Appl. Mater. Inter. 3 (2011) 4552-4556. [25] A. Turco, C. Malitesta, G. Barillaro, A. Greco, A. Maffezzoli, E. Mazzotta, A magnetic and highly reusable macroporous superhydrophobic/superoleophilic PDMS/MWNT nanocomposite for oil sorption from water, J. Mater. Chem. A 3 (2015) 17685-17696. [26] O. Karatum, S.A. Steiner, J.S. Griffin, W. Shi, D.L. Plata, Flexible, Mechanically Durable Aerogel Composites for Oil Capture and Recovery, ACS Appl. Mater. Inter. 8 (2016) 215-224. [27] J.T. Korhonen, M. Kettunen, R.H.A. Ras, O. Ikkala, Hydrophobic Nanocellulose Aerogels as Floating, Sustainable, Reusable, and Recyclable Oil Absorbents, ACS Appl. Mater. Inter. 3 (2011) 1813-1816. [28] B. Akhavan, K. Jarvis, P. Majewski, Hydrophobic Plasma Polymer Coated Silica Particles for Petroleum Hydrocarbon Removal, ACS Appl. Mater. Inter. 5 (2013) 8563-8571. [29] L. Ding, Y. Li, D. Jia, J. Deng, W. Yang, β-Cyclodextrin-based oil-absorbents: Preparation, high oil absorbency and reusability, Carbohydr. Polym. 83 (2011) 1990-1996. [30] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, F. Xu, F. Banhart, L. Sun, R.S. Ruoff, Spongy Graphene as a Highly Efficient and Recyclable Sorbent for Oils and Organic Solvents, Adv. Funct. Mater. 22 (2012) 4421-4425. [31] S. Li, J. Wei, Synthesis of novel polypropylene-acrylate fiber sorbent and evaluation of the sorption properties for organic contaminants from water surface, Desalin. Water. Treat. 46 (2012) 359-365. [32] J. Lin, Y. Shang, B. Ding, J. Yang, J. Yu, S.S. Al-Deyab, Nanoporous polystyrene fibers for oil spill cleanup, Mar. Pollut. Bull. 64 (2012) 347-352. [33] A. Pourjavadi, M. Doulabi, R. Soleyman, Novel carbon-nanotube-based organogels as candidates for oil recovery, Polym. Int. 62 (2013) 179-183. [34] S.G. Roy, U. Haldar, P. De, Remarkable Swelling Capability of Amino Acid Based CrossLinked Polymer Networks in Organic and Aqueous Medium, ACS Appl. Mater. Inter. 6 (2014) 4233-4241.

22

[35] K. Karadag, H. B. Sonmez, Sorption behavior of polymeric gels based on alkoxysilane and aliphatic diol, J Polym Res. 20 (2013) 1-8. [36] Y.H. Yin, Y.J. Yang, H.B. Xu, Hydrophobically modified hydrogels containing azoaromatic cross-links: swelling properties, degradation in vivo and application in drug delivery, Eur. Polym. J. 38 (2002) 2305-2311. [37] G. Ozan Aydin, H. B. Sonmez, Hydrophobic poly(alkoxysilane) organogels as sorbent material for oil spill cleanup, Mar. Pollut. Bull. 96 (2015) 155-164. [38] I. Yati, G.O. Aydin, H.B. Sonmez, Organic Solvent Absorbents Based on Linear Diol, Polym. Eng. Sci. 53 (2013) 2102-2108. [39] K. Karadag, G. Onaran, H.B. Sonmez, Synthesis and swelling properties of new crosslinked polyorthocarbonates, J. Appl. Polym. Sci. 121 (2011) 3300-3305. [40] H.B. Sonmez, F. Wudl, Cross-Linked Poly(orthocarbonate)s as Organic Solvent Sorbents, Macromolecules 38 (2005) 1623-1626. [41] A.M. Atta, W. Brostow, H.E. Hagg Lobland, A.-R.M. Hasan, J. Perez, Porous crosslinked copolymers of octadecyl acrylate with acrylic acid as sorbers for crude petroleum spills, Polym. Int. 62 (2013) 1225-1235. [42] P. Lee, M.A. Rogers, Phase-Selective Sorbent Xerogels as Reclamation Agents for Oil Spills, Langmuir 29 (2013) 5617-5621. [43] J.S. Hersey, S.T. Yohe, M.W. Grinstaff, Poly(ε-caprolactone) microfiber meshes for repeated oil retrieval, Environ. Sci.: Water Res. Technol. 1 (2015) 779-786. [44] D.R. Latypova, A.G. Badamshin, S.P. Kuleshov, E.O. Timashev, B.A. Kulnitskiy, Y.V. Tomilov, N.E. Nifantiev, V.A. Dokichev, New high-efficiency carbon-silica sorbent, Russ. J. Appl. Chem. 88 (2015) 1428-1433. [45] R. Tjandra, G. Lui, A. Veilleux, J. Broughton, G. Chiu, A. Yu, Introduction of an Enhanced Binding of Reduced Graphene Oxide to Polyurethane Sponge for Oil Absorption, Ind. Eng. Chem. Res. 54 (2015) 3657-3663. [46] D. Ceylan, S. Dogu, B. Karacik, S.D. Yakan, O.S. Okay, O. Okay, Evaluation of Butyl Rubber as Sorbent Material for the Removal of Oil and Polycyclic Aromatic Hydrocarbons from Seawater, Environ. Sci. Technol. 43 (2009) 3846-3852.

23

[47] Y. Ge, Z. Jia, C. Gao, L. Zhao, H. Li, Y. Zhang, Y. Zhao, SiO2-Al2O3 composite oxides with hierarchical pores as solid acid catalysts for tetrahydrofuran polymerization, Kinet. Catal. 54 (2013) 761-766. [48] J.W. Kang, Y.K. Han, Polymerization of tetrahydrofuran with new transition metal catalyst and its mechanism: (p-Methylbenzyl)-o-cyanopyridinium hexafluoroantimonate, Bull. Korean Chem. Soc. 18 (1997) 433-438. [49] M.A. Tasdelen, W. Van Camp, E. Goethals, P. Dubois, F. Du Prez, Y. Yagci, Polytetrahydrofuran/Clay Nanocomposites by In Situ Polymerization and “Click” Chemistry Processes, Macromolecules 41 (2008) 6035-6040. [50] L. Rueda-Larraz, B.F. d’Arlas, A. Tercjak, A. Ribes, I. Mondragon, A. Eceiza, Synthesis and microstructure–mechanical property relationships of segmented polyurethanes based on a PCL–PTHF–PCL block copolymer as soft segment, Eur. Polym. J. 45 (2009) 2096-2109. [51] C. Fodor, A. Domjan, B. Ivan, Unprecedented scissor effect of macromolecular crosslinkers on the glass transition temperature of poly(N-vinylimidazole), crystallinity suppression of poly(tetrahydrofuran) and molecular mobility by solid state NMR in poly(N-vinylimidazole)-lpoly(tetrahydrofuran) conetworks, Polym. Chem. 4 (2013) 3714-3724. [52] Y. Guan, X. Ding, W. Zhang, G. Wan, Y. Peng, Polytetrahydrofuran Amphiphilic Networks, 5. Synthesis and Swelling Behavior of Thermosensitive Poly(N-isopropylacrylamide)l-polytetrahydrofuran Networks, Macromol. Chem. Phys. 203 (2002) 900-908. [53] C. Pomel, C. Leborgne, H. Cheradame, D. Scherman, A. Kichler, P. Guegan, Synthesis and Evaluation of Amphiphilic Poly(tetrahydrofuran-b-ethylene oxide) Copolymers for DNA Delivery into Skeletal Muscle, Pharm. Res. 25 (2008) 2963-2971. [54] L.M. Van Renterghem, E.J. Goethals, F.E. Du Prez, Star-Shaped Poly(tetrahydrofuran) with Reactive End Groups:  Design, MALDI-TOF Study, and Solution Behavior, Macromolecules 39 (2006) 528-534. [55] X.J. Loh, H.X. Gan, H. Wang, S.J.E. Tan, K.Y. Neoh, S.S. Jean Tan, H.F. Diong, J.J. Kim, W.L. Sharon Lee, X. Fang, O. Cally, S.S. Yap, K.P. Liong, K.H. Chan, New thermogelling poly(ether carbonate urethane)s based on pluronics F127 and poly(polytetrahydrofuran carbonate), J. Appl. Polym. Sci. 131 (2014) (Special issue). [56] I. Yati, K. Karadag, H.B. Sonmez, Amphiphilic poly(ethylene glycol) gels and their swelling features, Polym. Adv. Technol. 26 (2015) 635-644.

24

[57] T. Yu, K. Wakuda, D.L. Blair, R.G. Weiss, Reversibly Cross-Linking Amino-Polysiloxanes by Simple Triatomic Molecules. Facile Methods for Tuning Thermal, Rheological, and Adhesive Properties, J. Phys. Chem. C 113 (2009) 11546-11553. [58] P. Dutta, B. Gogoi, N.N. Dass, N. Sen Sarma, Efficient organic solvent and oil sorbent copolyesters: Poly-9-octadecenylacrylate/methacrylate with 1-hexene, React. Funct. Polym. 73 (2013) 457-464.

Fig. 1. Absorption capacities of the prepared PTHF-ICS based sorbents

25

Fig. 2. Photograph of the PTHF 2900-ICS sorbent that swollen in different oils/solvents

26

Fig. 3. Toluene absorption over water surface by PTHF 2900-ICS; A) water/toluene (dyed by methyl red) system and dry PTHF 2900-ICS, B) toluene absorption by PTHF 2900-ICS after 20s, C) toluene sorption by PTHF 2900-ICS after 2 mins, D) toluene absorption by PTHF 2900-ICS after 5 mins, E) water/toluene separation by simple filtration method, F) separated water and toluene absorbed sorbent G) Absorption capacity of PTHF 2900-ICS for water, toluene and toluene/water mixture.

27

Fig. 4. Dichloromethane absorption kinetics of the synthesized PTHF-ICS based sorbents

28

Fig. 5. t/Qt versus time (t) plot for the synthesized PTHF-ICS based sorbents

29

Fig. 6. Dichloromethane retention of the synthesized PTHF-ICS based sorbents

30

Fig. 7. Reusability of the PTHF 2900-ICS for DCM

31

Fig. 8. The stability of PTHF 2000-ICS for 63 days in various oils and water

32

Scheme 1. General reactions of the synthesized PTHF-ICS sorbents

33

Table 1. Parameters for the second-order kinetic model for the synthesized sorbents

a

a

a

Sorbents

k2

R2

Qmax (%) (theoretical)

Qmax (%) (experimental)

PTHF 250-ICS

212×10-4

0.99998

217

213

PTHF 650-ICS

13.3×10-4

0.99967

500

445

PTHF 1000-ICS

2.0×10-4

0.99995

746

745

PTHF 1400-ICS

6.8×10-4

0.99982

1248

1240

PTHF 2000-ICS

4.0×10-4

0.99966

1314

1287

PTHF 2900-ICS

1.8×10-4

0.99945

1826

1800

Maximum swelling degree in dichloromethane

34