Janus Membranes with Charged Carbon Nanotube Coatings for Deemulsification and Separation of Oil-in-Water Emulsions

Abstract

Oil/water separation, especially for those surfactant-stabilized oil-in-water (O/W) emulsions, is required to protect our ecological environment from destruction. Janus membranes with a function of deemulsification appear as a kind of efficient materials for the separation of O/W emulsions because of a precise adjustment of the surface nature for the hydrophilic and hydrophobic layers. However, existing strategies of membrane preparation suffer from complicated multisteps, leading to uncontrolled thickness of the hydrophilic deemulsification layer. Herein, we present a facile and tunable method to prepare a series of Janus membranes consisting of negatively or positively charged carbon nanotubes (CNTs) and hydrophobic microfiltration membranes by vacuum filtration. The thickness of the hydrophilic CNT coating is thus well-controlled by engineering the amount of CNTs deposited on the substrate membrane. The prepared Janus membranes are effective for the separation of both heavy oil and light oil from O/W emulsions through deemulsification owing to the charge-screening effect. It is very interesting that those membranes displaying a combination of water contact angle and underwater oil contact angle both above 90° have a unique oil delivery behavior and thus high separation performance of oil from O/W emulsions. Such Janus membranes can retrieve 89% of oil in 40 min from the 1,2-dichloroethane/water emulsions with the droplet size of 19 μm. This easy-to-prepare and easy-to-tune strategy provides feasibilities for practical applications of Janus membranes to the deemulsification and separation of O/W emulsions.

Asymmetric Surface Engineering for Janus Membranes

“…The Janus membranes are obtained after peeling off them from the substrates. Such technique is also employed to directly deposit hydrophilic carbon nanotubes, [ 40,41 ] hydrophobic Au nanorod, [ 42 ] or hydrophobic W 18 O 49 mesocrystals [ 43 ] on an oppositely wettable membrane to construct the Janus membrane. Commonly, these Janus membranes feature a clear boundary between the hydrophilic and hydrophobic layer but a relatively weak interfacial bonding due to the incompatibility between two layers.…”

“…The sequential electrospinning or vacuum filtration strategy provides a facile route to control the thickness of each layer which is strongly related to the concentration of electrospinning solution [ 24,31,32 ] or the content of nanomaterial in suspensions during the vacuum filtration deposition. [ 38–40 ] In the single‐side spraying, the thickness of modified layer (i.e., modification depth) is able to be regulated by tuning the diffusion ability of the spraying fog drops which is dependent on the concentration of the spray solution and the spraying parameters. It has been verified that the modification depth is increased with prolonging the spray time, shortening the spray distance, or reducing the spray speed.…”

“…Accordingly, the combination of thick lyophilic layer and thin lyophobic layer is able to achieve a rapid one‐way delivery of liquid. Such particular gating property has endowed Janus membranes with competitive advantages in the applications of liquid manipulation, including oil collection, [ 29,40,49,53,106,107 ] oil−water separation, [ 34,37–39,44,46,54,59,65,69,100,108 ] fog harvesting, [ 16,20,32,78,82,85,88 ] and biofluid management. [ 22,23,25,35,36,60 ]…”

Recent advance of two-dimensional carbon-based films and their polymer functionalized membranes for oil/water separation

“…(d) The schematic illustration of the chemical interaction force between PGS and GO, and its separation for oil/water emulsion [74] 聚合技术的优势, 本课题组 [79] 将具有疏水性PS接枝到 CNTs薄膜的一侧, 随后将膜翻转, 将具有亲水性的聚 甲基丙烯酸N,N-二甲基氨基乙酯(PDMAEME)接枝到 [82] . 为了解决这个 问题, 徐志康课题组 [83] 将氨基化(带有正电荷)或者羧基 . 利用刺 激响应性高分子的智能响应性和碳基薄膜材料的微纳 米结构及易于修饰的特点, 靳健课题组 [84]…”

pH‐Responsive Poly(dimethylsiloxane) Copolymer Decorated Magnetic Nanoparticles for Remotely Controlled Oil‐in‐Water Nanoemulsion Separation

“…The development of interface science provides an opportunity to solve the problem. To date, two different types of surfaces, superhydrophobic/superoleophilic and underwater superoleophobic surfaces, have been successfully developed by combination of appropriate chemical composition and a hierarchical rough structure, and employed in oil/water separation on the basis of their selective oil/water wettability . For example, Jiang and co‐workers reported a novel metal meshes with superhydrophilicity and underwater ultralow adhesive superoleophobicity for oil/water separation .…”