Micro-/nano architectures in MOF membrane accelerate oil-water separation

image: (a, b) SEM images and (c) of AFM image ZIF-8-coated mesh membrane; (d) The photograph of several oil droplets on the ZIF-8-coated mesh membrane. view more 

Credit: ©Science China Press

Oil pollutions have been generated by the petroleum, steel, and textile industries and the frequent oil spills during oil transportation and have been becoming critical global environmental and economic. Oil-water separation is a very significant research topic for the basic scientific research in academia and industry.

Traditional oil-water separation technologies include centrifugation, filtration, dissolved air flotation, oil skinners and adsorption, etc. Such technologies are low efficiency and consume a lot of energy during complex separation processes.

Membrane separation is a very promising and economical approach to tackle energy and environmental challenges and has rapidly developed in the past decades. Enlightened by the antiwetting behavior of the oil droplet on the lower side of lotus leaves or the fish scale in water, underwater superoleophobic materials have been rapidly developed in recent years.

Nevertheless, some organic polymer membranes lose oil-water separation capacity at high temperature or exposure to various organic solvent and most of inorganic membranes need complex preparation process.

In order to solve above problems, Ming Xue and co-workers from Jilin University, China, recently, introduced micro/nanostructure into MOF membrane to improve the water/oil separation efficiency. This work is published in Science China Materials.

"We successfully constructed a ZIF-8-coated mesh membrane with excellent oil-water separation performance by simply immersing mesh in precursor solution under room temperature and atmospheric pressure", Prof. Xue introduced, "the membrane shows underwater superoleophobic properties, which is attributed to the micro and nanostructure on the surface of the ZIF-8-coated membrane."

Prof. Xue explained "the water phase imbibes into the micro and nano hierarchical structure of membrane surface, forming a barrier layer, which allows the water phase to pass through the membrane by its gravity quickly, and rejects the oil phase. This is the separation mechanism."

This MOF membrane exhibits excellent separation efficiency over 99.99% for various oil-water mixtures with the residual oil content in the collected water less than 4 ppm. It also shows a remarkable water flux as high as 102000 L/m2h and higher oil intrusion pressure of 6400 Pa. For the stability, Xue said "this membrane displays outstanding stability towards high temperature (200°C) and various organic solvents (tetrahydrofuran (THF), N, N'-dimethylformamide (DMF), N-methyl-2-pyrrolidone (NMP), dichloromethane (DCM) and n-hexane) immersion."

"More importantly," he added, "based on its facile fabrication method and the readily available and cheap materials, this kind of MOF membrane can be easily enlarged, and able to treat a large amount of oil-water mixture."

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This research was funded by the National Natural Science Foundation of China (21571076, 21390394, 21571079, 61701543), "111" project (B07016), the Ministry of Science and Technology of SINOPEC (A381) and Open Projects of State Key Laboratory of Safety and Control for Chemicals (SKL-038).

See the article: Mingqiu Song, Yuxin Zhao , Shanjun Mu , Chunming Jiang , Zhan, Li, Pingping Yang, Qianrong Fang, Ming Xue*, Shilun Qiu. "A stable ZIF-8-coated mesh membrane with micro-/nano architectures produced by a facile fabrication method for high-efficiency oil-water separation" Sci. China Mater. 2018, doi: 10.1007/s40843-018-9345-3 http://engine.scichina.com/doi/10.1007/s40843-018-9345-3