有效油-水分离的水-响应膜Hygro-responsive membranes for effective oil–water separation.docx

Hygro-responsive membranes for effective oil-water separation 有效油水别离的水响应膜Kota, A. K. et al. Nat. Commun. 3:1025 doi: 10.1038/2027 (2012).There is a critical need for new energy-efficient solutions to separate oil-water mixtures, especially those stabilized by surfactants. Traditional membrane-based separation technologies are energy-intensive and limited, either by fouling or by the inability of a single membrane to separate all types of oil-water mixtures. Here we report membranes with hygro-responsive surfaces, which are both superhydrophilic and superoleophobic, in air and under water. Our membranes can separate, for the first time, a range of different oil-water mixtures in a single-unit operation, with >99.9% separation efficiency, by using the difference in capillary forces acting on the two phases. Our separation methodology is solely gravity-driven and consequently is expected to be highly energy-efficient. We anticipate that our separation methodology will have numerous applications, including the clean-up of oil spills, wastewater treatment, fuel purification and the separation of commercially relevant emulsions.迫切需要新的别离油-水混合物的节能解决方案，尤其由外表活性剂稳定的混合物。传 统膜-基别离技术是能源一密集型，且受到污染或单一膜无法别离所有类型油一水混合物的 限制。这里报告了空气和水下超亲水和超疏油外表的水-响应外表膜。首次采用作用于两相 互的毛细管力差，我们的膜可在一个单元操作中别离一系列不同的油水混合物，别离效率> 99.9%o别离方法完全为重力驱动，因此，预计会非常节能。预计我们的别离方法将有许 很多应用，包括石油泄漏清理、废水处理、燃料净化和相关商业乳化的别离。Recent events including the Deepwater Horizon oil spill in the Gulf of Mexico have highlighted the difficulty of effective oil-water separation. Efficient, cost-effective processes for oil-water separation, especially in the presence of dispersants (or surfactants), are greatly desired 1. Surfactant-stabilized mixtures of oil and water are classified?, in terms of the diameter (d) of the dispersed phase, as free oil and water if d > 150(im9 a dispersion if 20(im < d < 150or an emulsion if d < 20 pim. Conventional gravity separators and skimming techniques are incapable of separating emulsions2. Membrane-based technologies are attractive for demulsification (the conversion of an emulsion to a free oil-water mixture) because they are relatively energy-efficient, cost-effective, and are applicable across a wide range of industrial=2R%21 cos(，)breakthrough- j "2(R/D)sin ).Here 712 is the interfacial tension between the wetting phase and the non-wetting phase, and 0 is the contact angle of the non-wetting phase on the solid surface, both of which are completely immersed in the wetting phase.这里Y12是润湿相和非润湿相之间的界面张力，。是固体外表上的非-润湿相接触角， 二者都完全浸没在润湿相中。When pressure Pappiied < Pbreakthrough is applied, only the wetting phase permeates through the membrane. We use CFS in this work because it combines both demulsification and separation into a single-unit operation, it provides a very high-quality permeate and it is inherently self-repairing34. For a CFS-based system to work effectively, it is necessary that the wetting phase contact the membrane. There are several techniques to achieve this goal: gravity-driven (if the wetting phase has a higher density than the non-wetting phase), electrostatic (if the wetting phase is a polar liquid)36, forced convection3,6,7, etc. In this work, we demonstrate a proof-of-concept prototype that solely utilizes gravity to engender separation of various oilwater mixtures.当Pappiied < Pbreakthrough时，只有润湿相通过膜渗透。由于将破乳和别离结合到一个单一 的单元操作中，提供了非常高质量的渗透，且本质上为自-修复，在这项工作中我们使用 CFSo为了 CFS-基系统有效工作，润湿相必须与膜接触。有几种实现这一目标的技术：重 力-驱动(如果润湿相密度高于非润湿相)、静电(如果润湿相是极性液体)、强制对流等.在 这项工作中，验证了概念验证原型，主持利用重力，实现各种油-水混合物别离。Separation of oil-in-water emulsions.水包油乳化的别离Figure 3a,b shows solely gravity-driven CFS of a hexadecane-in-water emulsion (50 vol% hexadecane; Methods) stabilized using SDS (hydrophilic-lipophilic balance, HLB = 40). The hexadecane droplet size distribution (see Supplementary Fig. S4 and Supplementary Discussion) indicates that the greatest number fraction of droplet diameters is in the range of 10-20 |im. The separation apparatus consists of a mesh 400 (2D = 37.5 |im)9 dip-coated with a 20 wt% fluorodecyl POSS + x-PEGDA blend and sandwiched between two vertical glass tubes. We used the superhydrophilic and oleophobic meshes here as they are available in a range of different pore sizes, allowing us to systematically vary the membrane porosity. Our superhydrophilic and superoleophobic fabrics show a similar performance. The emulsion is added to the upper tube（Fig. 3a）. Once water in the emulsion contacts the membrane, the surface starts to reconfigure. Within minutes, the water-rich permeate passes through the membrane while the hexadecane-rich retentate is retained above the membrane （Fig. 3b）. Membrane oleophobicity under water is critical for the separation of hexadecane-in-water emulsions （Fig. 3a, inset）. Optical image analysis indicates that the membrane removes virtually all hexadecane droplets exceeding 40 gm in diameter （see Supplementary Fig. S5 and Supplementary Discussion）. Thermogravimetric analyses （TGA; Fig. 3c）, transmittance and density measurements （see Supplementary Fig. S6 and Supplementary Discussion） indicate that the permeate contains -0.1 wt% hexadecane, whereas the retentate contains 0.1 wt% water. Additional experiments showed that we can similarly separate, with > 99% efficiency, hexadecane-in-water emulsions containing 10 vol% and 30 vol% hexadecane. We also conducted experiments with hexadecane-in-water emulsions containing salt （sodium chloride）. As with the non-saline emulsions, we could separate saline emulsions with > 99% efficiency.图3a、b显示SDS （亲水-亲油平衡，HLB=40）稳定的水包十六烷油乳化（50 vol% 十六烷；方法）的只是中重力-驱动CFS。十六烷液滴尺寸分布（见补充图S4和补充讨论） 说明，液滴直径的最大数量分数在1020plm范围。别离装置由20 wt%氟癸基POSS + x-PEGDA混合物浸渍-涂层网400 （2D = 37.5 Rm）组成，夹在两个垂直玻璃管之间。由于一 系列不同的孔径可用，使我们能够系统地改变膜的孔隙率，我们这里使用超亲水和疏油网。 我们的超亲水和超疏油织物表现出类似的性能。乳化加入上方管中（图3a）。一旦乳化中 的水与膜接触，外表就会开始重构。在几分钟内，富含水渗透液通过膜，而富含十六烷的 保存液保存在膜上方（图3b）o膜的水下疏油性对于水包十六烷乳化的别离至关重要（图 3a,插图）。光学图像分析说明，膜几乎去除了所有直径超过40 gm的十六烷液滴（见补 充图S5和补充讨论）。热重分析（TGA；图3c）、透射率和密度测量（见补充图S6和 补充讨论）说明渗透液含0.1 wt%十六烷，而保存液含0.1 wt%水。其他实验说明， 我们可同样以>99%的效率别离含有10 vol%和30 vol%十六烷的水包十六烷乳化。我 们也进行了对含盐（氯化钠）的水包十六烷乳化实验。与非盐水乳化一样，我们可以以> 99%的效率别离盐水乳化。Figure 3 Batch separation of oil-in-water and water-in-oil emulsions, (a) Separationapparatus with a 50:50 v:v hexadecane-in-water emulsion above the membrane. Inset,hexadecane droplet on a surface spin-coated with a 20 wt% fluorodecyl POSS + x-PEGDAblend, submerged in water containing dissolved SDS(1 mg m(b) Water-rich permeatepasses through the membrane whereas hexadecane-rich retentate is retained, (c) TGA datafor the permeates and the retentates. HD, hexadecane, (d) Apparatus with a 30:70 v:v water-in-hexadecane emulsion above the membrane. Inset, hexadecane droplet on a surfacespin coated with a 20 wt% fluorodecyl POSS + x-PEGDA blend, submerged in watercontaining dissolved PSs80 (1 mg ml-1), (e) Water-rich permeate passes through themembrane whereas hexadecane-rich retentate is retained. Water is dyed blue andhexadecane is dyed red. Sscale bars, 2 cm.水包油和油包水乳化的序批别离。(a)膜上50:50 v:v水包十六烷乳化的别离装置。插图，20 wt%氟癸基POSS + x-PEGDA混合物旋转涂层外表上浸没在含溶解的SDS (1 mgmr1)水中十六烷液滴。(b)富含水的渗透液通过膜，而富含十六烷的保存液保存下来。液通过膜，而富含十六烷的保存液保存下来。(c)渗透液和保存液的TGA数据。HD.十六烷。(d)膜上装有30:70 v:v十六烷包水乳化的装置。插图，20 wt%氟癸基POSS + x-PEGDA混合物旋转.涂层外表上浸没在含溶解PS 80 (1 mg ml水中的十六烷液滴。(e)富含是的渗透液通过膜，而富含十六烷的保存液保存下来。水被染成蓝色，十六烷染成红色。比例尺，2 cmoSeparation of water-in-oil emulsions.油包水乳化别离Figure 3d,e shows the solely gravity-driven CFS of a water-in-oil emulsion (30 vol% water; Methods) stabilized using Polysorbate80 (PS80; HLB = 15). The apparatus is the same as that used for the separation of oil-in-water emulsions. The emulsion is added to the upper tube (Fig. 3d). Once water droplets within the emulsion contact the membrane, the surface starts to reconfigure. Before the breakthrough of the water-rich permeate, hexadecane is retained above the membrane because of membrane oleophobicity in air. After surface reconfiguration, the water-rich permeate passes through the membrane while the hexadecane-rich retentate is retained above the membrane (Fig. 3e). During the permeation of the water-rich permeate, the hexadecane-rich retentate is retained above the membrane because of membrane oleophobicity under water. Membrane oleophobicity, both in air and under water, is critical for separating water-in-hexadecane emulsions. TGA (Fig. 3c), transmittance and density measurements (see Supplementary Fig. S6 and Supplementary Discussion) indicate that the permeate contains 0.1 wt% hexadecane, whereas the retentate contains 0.1 wt% water. Additional experiments showed that we can similarly separate, with > 99% efficiency, water-in-hexadecane emulsions containing 10 vol% and 20 vol% water. Further, we can also similarly separate span80 (HLB = 4.3) stabilized water-in-hexadecane emulsions containing 10, 20 and 30 vol% water, with > 99% efficiency. Our analysis also indicates that after separation, the surfactant fractionates intoboth the water-rich and the hexadecane-rich phases, depending upon its relative solubility in each phase (see Supplementary Fig. S7 and Supplementary Discussion).图3d、e显示了采用聚山梨醇酯80 (PS80； HLB = 15)稳定的油包水乳化(30 vol% 水；方法)的只是重力驱动CFSo装置与用于别离水包油乳化的相同。乳化加入上方管中 (图3d)。一旦乳化中的水滴接触到膜，外表就开始重构。在富含水的渗透液突破之前， 由于膜在空气中的疏油性，十六烷保存在膜上方。外表重构后，富含水的渗透液通过膜， 而富含十六烷的保存液保存在膜上方(图3e)o在富含水的渗透液渗透过程中，富含十六 烷保存液由于膜在水中的疏油性而保存在膜上方。空气和水下膜的疏油性对于别离十六烷 包水乳化至关重要。TGA (图3c)、透射率和密度测量(见补充图S6和补充讨论)说明渗 透液含0.1 wt%十六烷，而保存液含0.1 wt%水。其他实验说明，我们同样可以99%的 效率别离含10 vol%和20 vol%水的十六烷包水乳化。另外，我们也可同样别离含10、 20和30 vol%水的span80(HLB =4.3)稳定的十六烷包水乳化，效率99%。我们的分 析也说明，别离后，外表活性剂分馈到富水相和富十六烷相分储，取决于其在每个相中的 相对溶解度(见补充图S7和补充讨论)。Separation of free oil and water.游离油和水的别离Figure 4a-c show the solely gravity- driven CFS of free rapeseed oil and water using a mesh 100 (2D = 138 |im) coated with a 20 wt% fluorodecyl POSS + x-PEGDA blend. Water is added to the upper tube (Fig. 4a) immediately followed by rapeseed oil (Fig. 4b). The corresponding insets in Fig. 4a,b show a drop of water placed on a spin-coated surface of 20 wt% fluorodecyl POSS + x-PEGDA, and a drop of rapeseed oil immediately placed on top of the drop of water, respectively. Upon surface reconfiguration, water permeates through the membrane, while rapeseed oil is retained above the membrane (Fig. 4c). On a spin-coated 20 wt% fluorodecyl POSS + x-PEGDA surface, previously wet by water, a drop of rapeseed oil displays a contact angle of 0Oii,adv = 45° (Fig. 4c, inset (ii). Thus, for rapeseed oil on the membrane, the robustness factor A*oii = 3.2. Consequently, rapeseed oil is retained above the membrane. A video illustrating the nearly complete separation of free oil and water is provided as Supplementary Movie 2. As illustrated in the video, water permeates through the membrane at Atwater = 1.25. The experimentally measured flux of water through the membrane (mesh 100; 2D =138 pim), Qwater - 43,200 1 m -2 h- This is significantly lower than the flux of the water (i-l mPa s), Qwater = 509,000 1 m -2 h- l, predicted using the Hagen-Poiseuille relation37. This isbecause the number of pores through which water is flowing at any given time （so-called "active pores9） in CFS can be significantly lower （1 - 10%） than the actual number of pores35. Comparing the measured and the predicted fluxes, we estimate that 8.5% of the total pores are active during the separation of free oil and water.图4ac显示采用20 wt%氟癸基POSS + x-PEGDA混合物涂层的网100 （2D =138 pim）的游离菜籽油和水的只是重力驱动的CFSo水加入上方管（图4a）,之后立即加入菜 籽油（图4b）o图4a、b中的相应插图分别显示放置在20 wt%氟癸基POSS + x-PEGDA 旋转-涂层外表上的一滴水，以及立即放置在水滴顶部的一滴菜籽油。在外表重构后，水通 过膜渗透，而菜籽油保存在膜上方（图4c）o在现有水润湿的20 wt%氟癸基POSS + x-PEGDA旋转-涂层外表，一滴菜籽油显示接触角。ii,adv = 45。（图4c,插图（ii）。因此， 对于膜上的菜籽油，坚固性因子A*°n = 3.2。因此，菜籽油保存在膜上方。作为补充电影2,提供说明游离油和 水几乎完全别离的 视频。如视频中所示, 水在A*water 1.25 处渗透通过膜。实验 测量的水通过膜的通量（网100； 2D=138m） Qwater 43,200 1 m-2 h-1 o这明显低于采用 Hagen-Poiseuille 关系预测的水通量（四1 mPa s）Qwater= 509,000 1 m - 2 h - 1。这是由于 CFS 过程中任何给定时间水流过的孔隙数量（所谓“有效孔隙”）可能比实际孔数量低得多（110%）。比照测量和预测的通量，我们估计总孔隙的8.5%在游离油和水别离过程中 有效。Figure 4 Batch separation of free oil and water and four component mixtures, (a) Sseparation apparatus with water above the membrane, (b) Rapeseed oil is added above water, (c) Water permeates through the membrane whereas rapeseed oil is retained. Insets, water droplet on a surface spin-coated with a 20 wt% fluorodecyl POSS + x-PEGDA blend, rapeseed oil droplet on top of the water droplet, rapeseed oil droplet on the reconfigured surface, (d) TGA data for the permeate and the retentate. HD, hexadecane, (e) Apparatus with the four-component mixture above the membrane. Inset, larger quantity of feed in a glass vial, depicting the presence of different phases, (f) Water-rich permeate passes through the membrane whereas hexadecane-rich retentate is retained. Water is dyed blue, hexadecane and rapeseed oil are dyed red. Sscale bars, 2 cm.游离油和水以及四种成分混合物的序批别离。（a）膜上别离装置与水。（b）菜籽油加在水上。（c）水渗透通过 膜，而菜籽油保存下来。插图，20 wt%氟癸基POSS + x-PEGDA混合物旋转.如层外表 上的水滴,水滴上方的菜籽油滴，重构外表上的菜籽油滴。（d）渗透液和保存与的TGA数 据。HD.十六烷。（e）膜上装置与四种成分混合物。插图，玻璃瓶中更大量进料，描绘了不同相的存在。(f)富含水的渗透液通过膜，而富含十六烷的保存液保存下来。水染成 蓝色，十六烷和菜籽油染成红色。比例尺，2 emoSeparation of four-component mixtures. 4成分混合物的别离Figure 4e,f show the separation of a mixture containing four components: water, hexadecane, a 30:70 v:v water-in-hexadecane emulsion and a 50:50 v:v hexadecane-in-water emulsion. Again, mesh 400 dip coated with a 20 wt% fluorodecyl POSS + x-PEGDA blend separated this mixture into highly pure constituents, that is, a permeate containing 0.1 wt% hexadecane and a retentate containing 0.1 wt% water, as confirmed by TGA (Fig. 4d). To our knowledge, this is the first ever report of solely gravity-driven separation of surfactant-stabilized emulsions and their mixtures into highly pure constituents. Furthermore, the dip-coating-based membrane fabrication process is easy to scale up, and we have developed an apparatus to separate several litres of oil-water mixtures (Supplementary Movie 3). As illustrated in the video, separation occurs even if the non-wetting phase (oil) contacts the dry membrane before the wetting phase.图4e、f显示了含四种成分混合物的别离：水、十六烷、30:70 v:v十六烷包水乳化 和50:50 v:v十六烷包水乳化。20 wt%氟癸基POSS + x-PEGDA混合物浸渍涂层网400 还是将这种混合物别离成高纯度成分，即含0.1 wt%十六烷的渗透液和含0.1 wt%水的 保存液，如TGA (图4d)验证的那样。据我们所知，这是首项只是重力-驱动将外表活性 剂稳定乳化及其混合物别离为高纯度成分的包括。另外，浸渍-涂层膜制造工艺易于放大， 我们开发了一种别离几升油-水混合物的装置(补充电影3)。如视频所示，即使非-润湿相 (油)在润湿相之前接触干膜，也会发生别离。Breakthrough height.突破高度For the separation apparatus shown in Figs 3 and 4 the maximum height of the liquid column before the oil phase permeates through the membrane (hbreakthrough) can be obtained using equation (1) when the membrane is in air or equation (2) when the membrane is submerged under water. Note that Pbreakthrough = pghbreakthrough. For free oil and water separation, 0oii,adv = 45°, yiv = 35.7 mN m- 1 and hbreakthrough is predicted to be 1.3 cm (Pbreakthrough = 117 Pa) using equation (1). For the SDS-stabilized 50:50 v:v hexadecane-in-water emulsion, 0oii,adv = 120° (Fig. 3a, inset), yi2 = 4.0 mN m_