Bio-inspired durable, superhydrophobic magnetic particles for oil/water separation
Graphical abstract
Introduction
In the last years, superhydrophobic materials have drawn more and more attention in many areas due to their amazing properties. As well known, lotus leaf is a typical kind of superhydrophobic material in nature, which can clean away dusts easily when water droplets roll down from the surface. This self-cleaning property of lotus leaves is ascribed to the surface micro structures (micro papillae with nano protrusions) and surface chemical composition (plant wax) [1], [2], [3]. It is necessary to obtain proper roughness and low surface energy for the preparation of superhydrophobic materials. Many different methods have been utilized for the purpose, including layer-by-layer (LBL) self-assembly, chemical etching, gelation technique, phase separation and electrospinning, etc. [4], [5], [6], [7], [8], [9]. However, these approaches exist lots of disadvantages such as relatively complex fabrication procedures, weak stability in harsh environment and low adaptability. Thus, there is a lasting demand for superhydrophobic materials with good stability, simple fabrication process and high adaptability.
Moreover, superhydrophobic materials have been found important application in the field of oil/water separation. Over the past decades, water pollution caused by oil spillage and chemical leakage have been threatening the marine life and the ecosystem seriously. Oil spill cleanup is a grand worldwide challenge currently [10], [11], [12]. It has been well revealed that the introduction of superhydrophobicity to solid can effectively absorb oil from water. For example, Gu et al. fabricated Janus hybrid membranes through grafting polystyrene (PS) and poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA) from different sides of CNT membranes. This membranes can selectively absorb some organic solvents from water [13]. Li et al. constructed a series of hierarchical rough surfaces via layer-by-layer self-assembly using different sized SiO2 nanoparticles. The surfaces after the treatment of low surface energy material showed superhydrophobicity. In addition, some of the surfaces could separate oil/water with an efficiency of above 99% and have good durability [14]. An equally interesting area is the bio-imitation of the adhesive proteins of marine organisms. Inspired by bioadhesion, Messersmith’s group addressed that dopamine was a structure mimic of the mussel adhesive proteins, which could polymerize and deposit on almost all kinds of surfaces [15]. Moreover, the resultant polydopamine (PDA) could act as a platform for secondary reactions which endowed it with wide applications, including surface wettability alternation [16].
Herein, this article presents a facile method to superhydrophobic and superoleophilic microparticles with good durability. Under the nature inspiration, PDA/Fe3O4 microparticles were prepared by the help of the metal binding ability of the catechols presented in the PDA, in order to mimic the hierarchical structure of lotus leaf. After modification, the PDA/Fe3O4 micro particles preserved high water repellency. Due to the presence of the Fe3O4 nanoparticles, the modified PDA/Fe3O4 microparticles not only could be used in oil/water separation, but also oil transportation driven by magnetic force. Superhydrophobic sponge were prepared by introduction of the microparticles to a sponge and high absorption capability of the achieved sponge was revealed. Moreover, the sponge could separate oil from water by a gravity-driven process. These findings offer a simple and versatile strategy to prepare superhydrophobic magnetic particles which could engage in oil/water separation in various paths.
Section snippets
Materials
Dopamine hydrochloride was purchased from Sigma–Aldrich. Tris(hydroxymethyl)aminomethane (Tris) (99.9%) and 1H,1H,2H,2H-perfluorodecanethiol were purchased from Aladdin. FeCl3⋅6H2O, FeCl2⋅4H2O, NH3⋅H2O (25%), n-hexane, ethyl acetate, petroleum, chloroform and hydrochloric acid (37%) were purchased from Sinopharm Chemical Reagent. PU sponges and plant oil were obtained locally. All of the reagents were used as purchased without more purification.
Preparation of superhydrophobic PDA/Fe3O4 particles
Synthesis of PDA/Fe3O4 particles: Dopamine
Result and discussion
The PDA particles with diameter about 500 nm were prepared by the oxidation and self-polymerization of dopamine from a 2.0 mg/mL dopamine solution (Fig. 1a). PDA can be used as a versatile platform for secondary reactions and act as a reducing agent because there are many quinone−hydroquinone-types in its chains [17], [18], [19]. It can effectively prevent the oxidation of FeCl2. The Fe3O4 nanoparticles were generated when ammonia was added into the mixed solution of FeCl2, FeCl3 and PDA
Conclusions
In conclusion, we used mussel inspired chemistry to prepare fluorinated PDA/Fe3O4 microparticles via a facile and mild process. The microparticles had water CA of 153.7 ± 1.6° and oil CA measured at about 0°. In other words, the fluorinated PDA/Fe3O4 particles had superhydrophobic and superoleophilic ability, which could find applications in oil/water separation. Aging test results showed that the microparticles were of good durability. Compared to reported literatures, which mostly focused on
Acknowledgments
This work was supported by NSFC (Nos. 51303010 and 51425201), Specialized Research Fund for the Doctoral Program of Higher Education (20130006120019), the Fundamental Research Funds for the Central Universities (No. FRF-TP-14-014A2) and the National Basic Research Program of China (973 Program, No. 2015CB654603).
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