Smart Cotton Fabric with CO2-Responsive Wettability for Controlled Oil/Water Separation
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Stimuli-responsive materials with switchable wettability have promising practical applications in oil/water separation. A novel CO2-responsive cotton fabric for controlled oil/water separation was fabricated based on mussel-inspired reaction and polymerized with 2-(dimethylamino)ethyl methacrylate (DMAEMA). As expected, the modified fabric exhibited switchable hydrophilicity and hydrophobicity after CO2/N2 alternation, and it could be used for gravity-driven CO2-controlled oil/water separation. Water was selectively penetrated through the fabric and separated from oil after treating by CO2. A reversed wettability could be generated through simply treated with N2. It is expected that the as-prepared fabrics could be applied in smart oil/water separation due to the attractive properties of CO2-switchable system.
KeywordsBioinspired fabric Fiber CO2-responsiv Oil/water separation
Effective separation of oil/water mixtures is regarded as a potential solution to resolve environmental pollution for oil spillages, industrial discharge of oils/organic solvents, and environmental protection [1, 2, 3, 4, 5]. In recent years, the oil/water separation materials with special surface wettability have been widely studied, and there are many approaches have been developed to construct the special materials, including adsorption, biological treatment, gravity separation membrane filtration, centrifugation, and ultrasonic separation [6, 7, 8]. However, these methods are limited in practical applications due to their low efficiency, complicated instrument setup, second pollutants, and high energy usage. Moreover, these materials do not possess the switchable wettability between hydrophobicity and hydrophilicity, and they could not separate different types of oil/water mixtures.
To overcome the limitation, novel materials with switchable surface wettability in response to external stimuli have been designed, such as thermal treatment , pH , light irradiation , and magnetism , etc. However, there are some critical issues in practical applications. It still remains a challenge for developing novel stimuli-responsive membranes that can be triggered by environmentally friendly and cost-effective stimulus. Fortunately, gas stimulus has provided a great opportunity for the development of smart materials and systems since they could be added and removed easily in a large volume operation for industrial applications. CO2-responsive polymers have been investigated in the past few years due to the “green” feature, including hybrid nanoparticles , breathing microgels , latexes , and hydrogels . Such stimuli-responsive features are attributed to the reversible reactions of CO2 with such functional groups as guanidines, amines and amidines in aqueous solution, which regulate hydrophobicity/polarity properties [17, 18, 19]. For example, Yuan et al.  synthesized PMMA-co-PDEAEMA copolymers by radical copolymerization reactions and prepared nanostructured electrospun polymer membranes with their surface wettability switchable by CO2/N2 alternation. Zhao et al.  prepared a “smart” graphene oxide (GO) based nanofiltration membrane through electrostatic and π–π interaction-driven complexation with poly(N, N-diethylaminoethyl methacrylate) bearing a pyrene end group (Py-PDEAEMA). However, applications of these materials for oil/water separation are limited with low mechanical strength, since once being mechanically destroyed they lose their behavior. So, design of separation material with CO2-responsive polymer will remain to be investigated.
Actually, oil/water separation is an interfacial phenomenon, and the surface wettability is an important factor for the separation material, which could be regulated by incorporating the surface chemical composition of functional monomers or components for substance [2, 22, 23]. So, design of separation material with high mechanical strength and stability against liquid flow and exhibit higher filtration efficiencies is a critical issue. Inspired by the strong adhesive protein in mussels, dopamine has gained a great interest as a surface modification agent in a wide range of applications, which can strongly adhere to any organic or inorganic surfaces including metals, metal oxides, alumina, silica, mica, ceramics and polymers [24, 25]. Therefore, the environmentally friendly mussel-inspired reaction paves the way for their application in oil/water separation . Cotton is a kind of favorable natural plant fiber material with various excellent properties of flexibility, biodegradability, low cost and density and high mechanical stability [27, 28]. So, the fabrication of CO2-responsive cotton fabric for controlled oil/water separation could find potential applications in the oil/water separation.
Analytical reagent grade dopamine hydrochloride, methacryloyl chloride, sodium metabisulfite (SBS), ammonium persulfate (APS), Ethylene dimethacrylate (EGDMA), and 2-(dimethylamino)ethyl methacrylate (DMAEMA) were purchased from Aladdin Industrial Inc., Shanghai, China. Analytical reagent grade methanol, ethanol, dimethylformamide (DMF), borax (Na2B4O7∙10H2O), ethyl acetate (EtOAc), anhydrous magnesium sulfate (MgSO4), sodium carbonate (Na2CO3), and hydrochloric acid (HCl) were obtained from Sinopharm Chemical Reagent Co., Ltd, China and used as received without further purification. Deionized water was used in all preparations. Fabrics were commercially available cotton fabric.
Modification of Fabric with DMA
The dopamine methacrylamide (DMA) was synthesized based on the previously reported work . The cotton fabric used as substrate was cut into about 5 cm × 5 cm pieces, and they were cleaned with ethanol and deionized water by ultrasonication. Then, a piece of clean fabric was immersed in a 1 mg/mL DMA aqueous solution for 24 h at ambient temperature in the dark. Finally, the modified cotton fabric was taken out and washed with anhydrous ethanol and deionized water to remove the residuals, and then dried at 60 °C for 12 h to obtain DMA modified fabrics.
Preparation of p(DMA-DMAEMA)-Grafted Fabric
DMAEMA was grafted on fabric surface modified with DMA through free radical polymerization reaction according to Fig. 1a. The DMA modified fabrics were placed in a 3-neck flask with a Teflon-coated stirrer with a constant stirring rate of 150 rpm. SBS (0.03 g) and APS (0.08 g) were dissolved in 10 mL of water and methanol (1: 1), and the solutions were mixed homogenously, followed by the addition of EGDMA (100 μL) and DMAEMA (2 g). In the polymerization process, the mixture was placed in a water bath at 38 °C to initiate the polymerization. The fabrics were taken out after 1 h, and washed with methanol. Finally, the polymer-grafted fabrics were further dried at 60 °C for 12 h.
The chemical structures were investigated by a Nicolet 170SX Fourier transform infrared spectroscopy (FTIR, USA). Thermo gravimetric analyses were performed in TG/DTA6300 equipment (TG, Japan). SEM images were obtained on an EM-30 scanning electron microscope (SEM, Korea). Contact angles were measured by an OCA50 machine (Data-Physics, Germany) at ambient temperature. The average value of five measurements performed at different positions on the same sample was adopted as the contact angle. The abrasion durability was performed according to the GB/T 3920–2008 standard, and the specific steps were followed the same procedure reported in our previous work . All the photos were taken using a Canon camera.
Results and Discussion
FTIR Spectroscopy Analysis
Analysis of SEM Morphology
Thermal Analysis of Fabrics
Thermal characteristic data
T20 % (°C)a
Polymerized with DMAEMA
CO2-Responsive Performances and Mechanism Analysis
Durability of Abrasion and Tensile Properties
Mechanical properties of the cotton fabric before and after modifying
Tensile strength (N)
10.26 ± 0.49
401.35 ± 19.23
10.21 ± 0.52
411.58 ± 22.26
6.83 ± 0.56
486.79 ± 26.19
CO2/N2-Responsive Performance and Separation of Oil/Water
In summary, a novel CO2-responsive cotton fabric for controlled oil/water separation was fabricated, based on mussel-inspired reaction. The fabric was synthesized by free radical polymerization process with DMAEMA. The modified fabric exhibited switchable hydrophilicity and hydrophobicity upon CO2/N2 alternation. During the process of separation, using CO2 as driving force, no external force was used except their own weight. The separation efficiency was > 90% on average with various types of oils used in the oil/water mixtures. Therefore, this modified fabric shows a great potential to be applied in oil/water separation.
The authors gratefully acknowledge the financial support of the National Natural Science Foundation of China (Grant no. 51703130), Zhejiang Provincial Natural Science Foundation of China (Grant no. LY18E080018), Shaoxing Public Welfare Project (Grant no. 2017B70042), and the International Science and Technology Cooperation Project of Shaoxing University (Grant no. 2019LGGH1004).
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
Supplementary material 1 (MP4 6978 kb)
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