Universal Janus Filters for the Rapid Separation of Oil from Emulsions Stabilized by Ionic or Nonionic Surfactants

The first use of atomic layer deposition (ALD) to produce Janus membranes is reported, with an example system consisting of a compositional gradient ranging from hydrophilic Al2O3 on one face to hydrophobic poly(propylene) on the opposite face. Alternating pulses of trimethyl aluminum and water vapor lead to the growth of covalently bonded Al2O3 conforming to the membrane pore surfaces. Precise control of ALD parameters significantly affects the surface wetting of the modified membrane face and the depth of Al2O3 infiltration into the porosity. This depth control derives from slow precursor diffusion through the 200 nm membrane pores compared to much faster ALD surface reactions. For a given precursor exposure and purge time, increasing the number of ALD cycles decreases the water contact angle at the modified surface from hydrophobic to hydrophilic, until the water droplet is completely imbibed by the membrane. To demonstrate the utility of these Janus membranes, a hydrophilic/superaerophobic Janus treatment is shown to greatly reduce the size of air bubbles generated through the membrane, enabling faster mixing. This technique represents the first application of vapor‐deposited covalently bonded metal oxides to form Janus membranes. Further opportunities are afforded by the ability to laterally pattern Al2O3 across the membrane surface via physical masking.

Section: Introductionmentioning

confidence: 99%

Janus Membranes via Diffusion‐Controlled Atomic Layer Deposition

Waldman

Yang

Mandia

et al. 2018

“…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 ]…”

Section: Asymmetric Surface Engineering Of Janus Membranes For Targetmentioning

confidence: 99%

“…[ 76 ] Either mussel‐inspired depositing, [ 53 ] electrospinning, [ 29 ] or electrospraying [ 76 ] has been demonstrated as thickness‐controllable methods for the preparation of Janus membranes, which ensures the expected combination of a thin oleophobic layer and a thick oleophilic layer for oil collection (Figure 3b). Furthermore, the introduction of deemulsification agents through grafting polyelectrolyte, [ 98,106,107 ] depositing charged carbon nanotube, [ 40 ] or polydopamine‐polyelectrolyte [ 49 ] onto the oleophobic surface endows the Janus membrane with a deemulsification function (Figure 3c). Such Janus membranes are able to separate surfactant‐stabilized oil‐in‐water emulsions which is regarded as a tough task in the field of oil−water separation.…”

Section: Asymmetric Surface Engineering Of Janus Membranes For Targetmentioning

confidence: 99%

Asymmetric Surface Engineering for Janus Membranes

Yang

2020

Emerging Janus membranes, named after the ancient Roman god with two faces to better survey both the past and the future, are appealing materials to tackle this challenge. They possess opposing chemicophysical properties on two sides for achieving a breakthrough in their performances. [12] The opposite surface properties usually include asymmetric wettability and charge but not limited to them. [13] Janus membranes with asymmetric wettable surfaces have received most of the attention in diverse research fields for a wide variety of applications because of their distinctive mass (e.g., liquid or gas) transport behaviors in two-phase or multiphase systems. Such unique fluid transportation relies on the cooperative effect arisen from the asymmetric wettability in the direction of membrane thickness. [14] Therefore, how to create and regulate asymmetry is a core task in the preparation of Janus membranes.Surface engineering, a process for modifying the surface of a material, provides a powerful toolbox to enhance and optimize the performance of the material, especially for porous membranes with large internal surface area. A myriad of modification methods including surface coating, grafting, and self-assembling have been developed to regulate membrane surface properties which are usually uniform in the spatial distribution. As distinguished from ordinary surface treatments, asymmetric surface engineering aims to accurately control the uneven distribution of surface properties or functionalities in the direction of membrane thickness, being an effective means for the preparation of Janus membranes.Benefiting from the asymmetric surface engineering, the researches on Janus membranes have mushroomed in recent years. Hundreds of literatures have explored the possibilities for Janus membranes to substitute traditional ones for achieving enhanced performances in the mass transfer between two phases, including water−oil, water−gas, and oil−gas systems. Some researchers have reviewed the research progresses on Janus membranes from different perspectives. Our previous review has discussed the definition and fabrication of Janus membranes and summarized their applications in the field of environmental science. [13] Another two reviews, presented by Zhao et al. [14] and Zhou et al., [15] have described the distinctive unidirectional fluid transport phenomenon of Janus membranes and their functional applications. Besides, a recent review has detailed the potential of Janus configuration in terms of enhancing energy efficiency in membrane processes. [12] However, the vital role of asymmetric surface engineering in the construction of asymmetric configurations, the modulation of surface properties, and the implementation of ultimate applications has not been addressed. Herein, Janus membranes show great promise toward various applications and are undergoing a fast-paced development in materials science. The asymmetric surface engineering on surface wettability, layer thickness, and pore structure enables Janus membranes with super...

“…Water pollution is anticipated to grow worse with the development of society, economy, industry, and agriculture. In recent years, industrial oily sewage and frequent oil leakage pose threats to humans and environment, causing catastrophic consequences of environmental deterioration and survival crises, as well as stricter regulations concerning the treatment of oily wastewater . It has been a global challenge to deal with the water contamination, which has attracted worldwide attention in both fundamental research and application.…”

Section: Introductionmentioning

confidence: 99%

Smart Nylon Membranes with pH‐Responsive Wettability: High‐Efficiency Separation on Demand for Various Oil/Water Mixtures and Surfactant‐Stabilized Emulsions

Zhang

et al. 2018

and costly device, as well as the inability to separate efficiently various emulsions including oil-in-water and water-in-oil types.Taking all strategies into account, membrane separation technique governed by interfacial phenomena is regarded as an ideal candidate due to the advantages of method simplicity, low cost, and high efficiency. [13][14][15][16] Since the idea of taking special wettability into membrane separation technique was proposed, [13] superwetting materials have aroused considerable interest in either immiscible oil/water separation or emulsified oil/water ones. Numerous superwetting materials have been realized in terms of the synergistic effect of chemical composition and hierarchical structures on the surface in last decades. Nevertheless, the surfaces of accustomed superwetting materials have constant water wettability of superhydrophilicity or superhydrophobicity, which are classified into "water-removing" materials or "oil-removing" materials aiming to separate single type of oil/ water mixtures. [17][18][19][20] The rigid wettability for nonswitchable separation type cannot adapt to the multicomponent immiscible oil/water mixtures involved different density of oils, not to mention the disposal of oil-in-water or water-in-oil emulsions in the actual processing situation. Hence, it is expected that smart materials with tunable wettability in response to external stimuli are promising for application of multitype oil/water separation, which requires simpler separation equipment and lower energy consumption than monofunctional separation materials.Driven by the actual processing demand for oily sewage treatment, impressive progress has been made in the field of smart materials that show switchable and reversible wettability in response to external stimulus, such as electric field, [21,22] light irradiation, [23][24][25] temperature, [26,27] counterions, [28,29] pH value, [30][31][32] or multistimuli. [33,34] For instance, Kung et al. demonstrated an approach for fast and reversible control over the wettability of electrodeposited copper meshes by electrochemical manipulating of the oxidation state of the copper oxide shell phase, achieving the controllable separation of immiscible oil/water mixtures in either oil removal or water-removal mode. [21] Kwon et al. prepared dye-sensitized nanoporous TiO 2 surfaces via dip-coating method to change selectively the wettability toward contacting liquids upon visible light illumination, revealing promise of new light-driven oil-water cleanup and demulsification technology. [23] Our Water contaminated with various oils has become one of the most pervasive environmental issues. Developing an efficient and durable separation membrane is of significance but challenging due to the critical limitations of nonuniversality and discontinuity for oil/water separation. Herein, a material is presented by combining the porous nylon membrane with self-assembled thiol molecules, exhibiting tunable wettability property upon the pH variation. Such a smart membrane show...