Opposite Wettability Research Articles

Bioinspired 1D Anisotropic Double-Spiral Metal Wires for Efficient Fog Harvesting.

Innovative design strategies of fog harvesting devices (FHDs) demonstrate promising remedy for water crisis in arid areas. 1D FHDs ensure unimpeded wind circulation and can be manufactured more cost-effectively for extensive regions. Inspired by cactus thorns, desert beetles, and spider silk, two metal organic frameworks (MOFs) functionalized Cu wires with opposite wettability are double-twisted by a mechanical twisting machine, forming 1D double-spiral Cu wires with alternating superhydrophobic/superhydrophilic dual-MOF patterns. The biomimic integration design, namely conical microneedle, stripe-patterned contrasting wettability, and double-spiral geometry, allows for efficient fog water collection due to a collaborative process. Based on such multi-cooperation theory, the optimal fog collection efficiency of dual-MOF functionalized double-spiral Cu wires can reach 0.293 ± 0.013 g cm-2 min-1 by investigating the effect of the composition, the diameter ratio and twisting wavelength λ of the two constituent wires. The double-spiral metal wires with discrepant wettability not only propose a facile and cost-effective method for fog harvesting, but also share new physical insight to inspire novel design concepts for efficient fog collection devices, benefitting the fight against the global water crisis.

Janus Spherical Robot With Multiple Wettabilities for Droplet/ Bubble Manipulation

AbstractThe flexible manipulation and directional transport of fluids, including droplets and bubbles, are foundational to numerous applications. Fluid manipulation based on external field stimulation and fixed structures has a wide range of applications in both natural and artificial materials, such as water collection, water electrolysis, droplet energy collection, medical diagnosis, etc. However, droplets and bubbles exhibit opposite wettability, and the inherent opposition between hydrophilicity and hydrophobicity presents a significant challenge in developing a manipulation system capable of manipulating both droplets and bubbles. Here, inspired by multiple natural organisms, a magnetic‐actuated Janus spherical robot with switchable wettability as the driving core of droplets or bubbles, and a solid‐like slippery surface as the manipulation platform is proposed, which achieves the dual programmable manipulation of droplets and bubbles. Furthermore, the Janus robot can achieve the transition from superhydrophobic to superhydrophilic within 8 min under UV light. It is noteworthy that the Janus robot demonstrates superior capabilities in the transport speed and carrier volume of liquid droplets (bubbles), which can reach 18 (13) cm s−1 and 800 (500) µL, respectively. This strategy provides a novel and reliable method for the automated manipulation of droplets and bubbles and broadens their applications.

Mixed superoleophilic/superoleophobic hard granular media for coalescence of oil-in-water-emulsion

To enhance the coalescence separation efficiency of oil/water emulsions, the coalescence mechanism of oil droplets between two media of opposite wettability was investigated. A coalescent-bed comprising a mix of superhydrophobic and superoleophilic quartz sand, along with superhydrophilic and underwater superoleophobic quartz sand, was constructed in a coalescer. Single-factor and response surface experiments were used to study the effects of oleophilic/oleophobic sand mixing ratio, apparent velocity, initial oil concentration, bed thickness, sand particle size on coalescence-separation performance, and to determine the optimal experimental conditions. Employing the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, the agglomeration mechanism of oil droplets within the mixed particle bed was analyzed based on interfacial energy dynamics. Results indicate that the mixing ratio of the two sands significantly influences coalescence separation performance. An optimal oleophilic/oleophobic sand mixing ratio of 1:1 yielded a mass factor of 0.69 kPa−1, showcasing superior coalescence separation efficiency and an optimal balance of separation efficiency and pressure drop. Under the optimal conditions of apparent velocity of 2.7 m/h, initial oil concentration of 471.9 mg/L, bed thickness of 12.6 cm and mixed sand particle size of 0.5 mm, the oil/water separation efficiency reached 98.08 % ± 0.87 %, with effluent oil droplet size being 2.5 to 3 times larger than at the inlet. Analysis of the oil droplet coalescence mechanism revealed a synergistic effect between the two quartz sands, enhancing oil removal performance. The strong affinity of oil to the superhydrophobic and superoleophilic sand surface increases oil droplet wetting and coalescence efficiency, while the water attraction on the superhydrophilic and underwater superoleophobic sand surface forms a stable water film, improving the flux of the continuous water phase and reducing pressure drop across the bed. This study demonstrates that combining quartz sands of opposite wettability not only overcomes the limitations of single-wettability surfaces in coalescing oil removal but also achieves high efficiency and low energy consumption in oil removal.

Interfacial Cooperative Assembly of Surfactants and Opposite Wettability Nanoparticles Stabilizes Water-in-Oil Emulsions at High Temperature.

Pickering emulsions have promising applications in the development of unconventional oil and gas resources. However, the high-temperature environment of the reservoir is not conducive to the stabilization of Pickering emulsions. In addition, the preparation of Pickering emulsions under low-energy emulsification and low-concentration emulsifier conditions is a difficult challenge. Here, we report a high-temperature resistant water-in-paraffin oil Pickering emulsion, which is synergistically stabilized by polyglycerol ester (PGE) and nanoparticles with opposite wettability (lipophilic silica and hydrophilic alumina). This emulsion can be prepared under mild stirring (500 rpm) conditions and can be stable at 140 °C for at least 30 days. The synergistic effects of surfactant, silicon nanoparticles (MSNPs) with different wettability, and alumina nanoparticles (AONPs) on the stability of both emulsions and water-oil interfacial membranes were investigated through bottle experiments, cryogenic scanning electron microscopy (cryo-SEM), optical microscopy, fluorescence microscopy, etc. The results showed that both hydrophobic MSNPs and hydrophilic AONPs are adsorbed together at the water-oil interface to stabilize the W/O emulsion, which can be prepared by 500 rpm stirring. The stability of emulsions strongly depends on the wettability of MSNPs, and the MSNP with moderate hydrophobicity (for example, aqueous phase contact angle of 136°) makes the emulsion exhibit the highest stability against aggregation and settling at elevated temperatures. The emulsion stabilization mechanism was revealed in terms of the adsorption capacity of the surfactant by MSNPs, the adsorption morphology and desorption energy of nanoparticles at the water-oil interface adsorption layer, and emulsion rheology. These findings demonstrate a novel and simple strategy to prepare Pickering W/O emulsions with high-temperature stability at low shear strength.

Harnessing microscopically opposite wettability in Janus nanofiber film for solar steam generation and photodegradation

Amphiphilic Janus nanofibers film composed of microscopically assembled hydrophilic and hydrophobic nanofibers is fabricated as a base film for the solar steam generator possessing functions of solar steam generation and photodegradation. The amphiphilic Janus nanofibers film integrates many advantageous properties including water pumping, thermal resisting, self floating, salt resisting, and high stability, which make it an excellent base film for solar steam generators. The mixture comprising carbon nanotubes, black TiO2 nanoparticles and poly(dopamine) is synthesized as a dual-functional photothermal layer on the solar steam generator for realizing photothermal conversion and photocatalysis. The fabricated solar steam generator can achieve a superior water evaporation rate (2.491 kg m−2 h−1, 1 sun) and synchronously degrade organic pollutants. Furthermore, it is delighted to find that the water evaporation rate can be boosted while treating organic-contaminated water. The synergistic property of solar steam generation and photodegradation offers an inspiration in the fields of wastewater elimination and clean water generation.

Preparation of a superhydrophilic and superoleophobic sponge for continuous oil/water and oil/oil separation

Oily wastewater produced from various industries and oil spills has posed serious threats to the environment and human health. Promisingly, superwetting materials emerge as great candidates for efficient oil/water separation. In this work, a superhydrophilic-superoleophobic melamine sponge was prepared using a facile immersion method. Methyltrimethoxysilane (MTMS) was used as a binder, which combined fluorosurfactant (FS-50) and TiO2 onto the sponge surface. The coated sponge displayed a water contact angle of 0° and an oil contact angle of 154.5°. Accordingly, it exhibited absorption capacities of above 86 g/g for water and under 1 g/g for oils. Based on its selective permeability and 3D porous structures, the coated sponge could continuously separate various immiscible oil/water mixtures and oil-in-water emulsions with separation efficiencies larger than 99.4 % and 98.7 %, respectively. Notably, the superhydrophilic-superoleophobic sponge was extended to present opposite wettability towards polar and nonpolar liquids. Consequently, it achieved continuous separation of immiscible oil/oil mixtures, with separation efficiency over 99.1 %. Additionally, the coated sponge displayed excellent reusability, great mechanical stability against compression and abrasion, and stable separation performance for various harsh oil/water mixtures. The study presented a promising separation candidate for future applications in oily wastewater treatment and other liquid/liquid separation fields.

Electrospinning janus membranes for on‐demand oil/water collection and emulsion separation

AbstractOily water pollution has become one of the most serious water environment issue in worldwide. Membrane that can effectively and efficiently remove different oil pollutions from the complex water environment is still urgently needed. Herein, a Janus membrane with opposite wettability that can separate heavy oil–water and light oil–water mixtures on demand was prepared by using a simple sequential electrospinning and chemical crosslinking method. The membrane could remove oil or water under gravity with a high oil/water flux and excellent separation efficiency. Moreover, the membrane could separate different kinds of oil‐in‐water emulsions under gravity with a high flux of 1184 L m−2 h−1 and a tiny flux loss of 4.4% after a 10‐cycle separation. Owing to its excellent anti‐pollution properties the flux recovery rate of the membrane was still higher than 80% after 150 min of emulsion separation. Additionally, the membrane also displayed the ability to transport liquid unidirectionally, giving whom the capabilities to collect oil underwater or water underoil. This research provides a novel and simple method for producing membranes for a variety of separation applications.

Fabrication of a Janus Copper Mesh by SiO2 Spraying for Unidirectional Water Transportation and Oil/Water Separation.

Massive discharge of oily wastewater and frequent occurrence of offshore oil spills have posed an enormous threat to the socioeconomic and ecological environments. Janus membranes with asymmetric wettability properties have great potential for oil/water separation applications and have attracted widespread attention. However, existing Janus membranes still suffer from complex and costly manufacturing processes, low permeability, and poor recyclability. Herein, a novel and facile strategy was proposed to fabricate a Janus copper mesh with opposite wettability for unidirectional water transport and efficient oil/water separation. The hydrophilic side of the Janus copper mesh was prepared by coating it with Cu(OH)2 nanoneedles via a chemical oxidation method. The hydrophobic side was fabricated by coating it with hydrophobic SiO2 nanoparticles via a facile spraying method. The as-prepared Janus copper mesh showed asymmetric surface wettability, which can achieve unidirectional water transport and efficient oil/water separation with excellent recyclability, exhibiting great application potential for droplet manipulation and wastewater purification.

Janus Membranes with Asymmetric Superwettability for High-Performance and Long-Term On-Demand Oil/Water Emulsion Separation.

Current single-function superwettable materials are typically designed for either oil removal or water removal and are constrained by oil density, limiting their widespread applications. Janus membranes with opposite wettability on their two surfaces have recently emerged and present attractive opportunities for on-demand oil/water emulsion separation. Here, a combination strategy is introduced to prepare a Janus membrane with asymmetric superwettability for switchable oil/water emulsion separation. A mussel-inspired asymmetric interface introduction cooperating with the sequence-confined surface modification not only brings about an asymmetric superwettability Janus interface but also guarantees an outstanding stable interface and remarkable chemical stability surfaces. Specifically, the superhydrophilic surface with underwater superoleophobicity can separate surfactant-stabilized oil-in-water emulsions. Conversely, other surface displays opposite superhydrophobicity and superoleophilicity to treat surfactant-stabilized water-in-oil emulsions. Significantly, this superwettable Janus membrane presents superior long-term on-demand oil/water emulsion separation without obvious flux decline and high recovery ability because of its superwettability and superior stability. Furthermore, the asymmetric superwettability enhances the interfacial floatability at air-water interfaces, enabling the design of advanced interfacial materials. The as-prepared superwettable Janus membrane has established a cooperated separation system, overcoming the monotony of conventional superwettable membranes and expanding the application of these specialized membranes to oily wastewater treatment.

Beyond Symmetry: Exploring Asymmetric Electrospun Nanofiber Membranes for Liquid Separation

AbstractComposite membranes with asymmetric traits have gained attention in liquid separation, featuring gradient chemical and physical attributes that align or oppose mass transfer direction. Chemically asymmetric configurations harness internal driving forces to heighten separation efficiency, rendering them an appealing option for heightened separation efficiency and fouling prevention. Concurrently, the internal hierarchical structure differences within composite membranes—such as fiber‐based structural adjustments and the gradient density of functional layers—yield the dual benefits of effective liquid repelling and heightened transport efficiency. Unlike conventional phase‐change methods, electrospinning technology possesses advantages in constructing and governing composite fibrous membrane materials with asymmetric chemistry and hierarchical structures, driven by its adaptable stacking methodologies. Notably, the inherent pore structure of electrospun nanofibrous membranes emerges as a proven solution for minimizing transport resistance. In recent times, interest has surged in electrospun nanofibrous membranes endowed with internal asymmetric properties. However, the spotlight has predominantly graced Janus membranes, spotlighting opposite wettability on different sides, leaving other facets of asymmetric membrane enhancement somewhat underexplored. This comprehensive work unveils recent strides in design, fabrication, facilitated transport mechanisms, and real‐world liquid separation applications, all under the aegis of electrospun nanofiber membranes, each endowed with distinct asymmetric properties.

Fabrication of Superhydrophobic Porous Brass by Chemical Dealloying for Efficient Emulsion Separation.

By taking advantage of typical dealloying and subsequent aging methods, a novel homogeneous porous brass with a micro/nano hierarchical structure was prepared without any chemical modification. The treatment of commercial brass with hot concentrated HCl solution caused preferential etching of Zn from Cu62Zn38 alloy foil, leaving a microporous skeleton with an average tortuous channel size of 1.6 μm for liquid transfer. After storage in the atmosphere for 7 days, the wettability of the dealloyed brass changed from superhydrophilic to superhydrophobic with a contact angle > 156° and sliding angle < 7°. The aging treatment enhanced the hydrophobicity of the brass by the formation of Cu2O on the surface. By virtue of the opposite wettability to water and oil, the aged brass separated surfactant-stabilized water-in-oil emulsions with separation efficiency of over 99.4% and permeate flux of about 851 L·m-2·h-1 even after recycling for 60 times. After 10 times of tape peeling or sandpaper abrasion, the aged brass maintained its superhydrophobicity, indicating its excellent mechanical stability. Moreover, the aged brass still retained its superhydrophobicity after exposure to high temperatures or corrosive solutions, displaying high resistance to extreme environments. The reason may be that the bicontinuous porous structure throughout the whole foil endows stable mechanical properties to tolerate extreme environments. This method should have a promising future in expanding the applications of alloys.

Janus membranes with opposite wettability prompting the synchronous synthesis and separation of hydrophobic ionic liquids

Traditional production of ionic liquids (ILs) includes isolated processes of synthesis followed by extraction purification with organic solvents. A remained challenge is to produce these green solvents by a simultaneous synthesis and separation procedure disusing volatile organic solvents. Herein, we describe a framework for the synchronous synthesis and separation of hydrophobic ILs based on an environmentally benign membrane reactor system. A Janus hollow fiber membrane reactor (JHFMR) with a thin and charged inner surface (IL-phobic) and an IL-philic outer surface is prepared by mussel-inspired co-deposition technique. The hydrophilic lumen surface supplies a reaction zone for anion metathesis. The inner surface charge destabilizes the emulsified target ILs dispersed in water. The deemulsified ILs actively pass through the JHFMR from IL-phobic side to IL-philic side driven by the gradient of surface energy. Multiple JHFMRs are ultimately assembled to prepare a JHFMR module for achieving a continuous and large-scale production of hydrophobic ILs in a cross-flow mode. The final ILs yield under a low reactant concentration (l.0 mol/L) is enhanced to reach 96% after 30 h by doubling the packing density of module. The residual water content in IL products is below 1.0 wt%. Other ion impurity is negligible (Li+ < 10 ppm, and Br- is below the detectable limit). Such enormously low impurity level is attributable to the synchronous separation of ILs once they are synthesized within the JHFMR module. Moreover, the module maintains a stable performance after repeated cycles. The proposed all-in-one strategy has a potential for continuous preparation of hydrophobic ILs at a large scale, with high yield and low impurity under “greener” operating conditions, e.g., at room temperature and avoidance of using volatile organic solvents.

Janus resorcinol-formaldehyde-based membrane with opposite wettability for efficient separation of oil and water emulsion

A resorcinol-formaldehyde (RF)-based Janus membrane was fabricated by casting graphene oxide (GO)-dispersed RF solution on Janus-B side and Cu salt-RF solution on the opposite Janus-A side of an activated carbon fibre (ACF) substrate, and then subjecting the composite material to chemical vapor deposition to form a web of carbon nanofiber (CNF) on the Janus-A side. CNF imparted the super-hydrophobic (water contact angle WCA ∼151°) and super-oleophilic (oil contact angle OCA ∼0°) characteristics, while GO-RF imparted the hydrophilic (WCA 30°) and olephobic (OCA ∼121°) characteristics to the membrane. The microfiltration tests were carried out under different conditions of oil and water feed concentrations (0–15% v/v) and operating pressure (1–3 bar). The super-hydrophobic side showed 99.75% water rejection efficiency and the initial permeate flux of 1020 Lm−2h−1 for a 5% (v/v) water-in-oil (W/O) emulsion, while the hydrophilic side showed 99.96% oil rejection efficiency and the initial permeate flux of 380 Lm−2h−1 for 5% (v/v) oil-in-water (O/W) emulsion. The material showed good chemical stability in acidic, basic and corrosive media as well as an excellent repeatability under the repeated alternate cycles of pure diesel/water and emulsion post- simple ethanol wash. Considering that the method of fabrication is simple, fast, and scalable, the comparative performance data clearly pitch CNF-RF/ACF/GO-RF ahead of the other membranes discussed in the literature for oil-water emulsion.

3D Janus structure MXene/cellulose nanofibers/luffa aerogels with superb mechanical strength and high-efficiency desalination for solar-driven interfacial evaporation

Interfacial solar steam generation (ISSG) is considered to be an attractive technique to address the water shortage. However, developing a sustainable thermal management, salt rejection, and excellent mechanical strength ISSG device for long-term stability desalination is still a challenge. Herein, a biomass ISSG device with superb mechanical properties was prepared by introducing a luffa sponge as the skeleton and constructing the MXene/cellulose nanofibers (CNFs) aerogels via freeze-drying. The Janus MXene-decorated CNFs/luffa (JMCL) aerogels integrated the multifunction of fast water transport, good thermal management, and efficient photothermal conversion in a single module, to achieve high-efficiency desalination. 3D Janus structure endowed the JMCL aerogel with opposite wettability, which is feasible to construct the localized photothermal generation and self-floating. The mechanical strength of JMCL aerogels is 437 times that of MXene/CNFs aerogels. The JMCL aerogels delivered a water evaporation rate of 1.40 kg m-2h−1 and an efficiency of 91.20% under 1 sun illumination. The excellent salt resistance during 24 h working and long-term solar vapor generation of up to 28 days were achieved. The multifunctional JMCL aerogels with 3D Janus structure offer new insights for developing good durability and eco-friendly biopolymer-based steam generators.

Smart Janus fabrics for one-way sweat sampling and skin-friendly colorimetric detection

Functionalized textiles with biofluid management capability have attracted tremendous attention in recent years due to their significant roles in health monitoring and dehydration prevention. Here we propose a one-way colorimetric sweat sampling and sensing system based on a Janus fabric using interfacial modification techniques. The opposite wettability of Janus fabric enables sweat to be quickly moved from the skin surface to the hydrophilic side and colorimetric patches. The unidirectional sweat-wicking performance of Janus fabric not only facilitates adequate sweat sampling but also inhibits the backflow of hydrated colorimetric regent from the assay patch toward the skin, eliminating potential epidermal contaminations. On this basis, visual and portable detection of sweat biomarkers including chloride, pH, and urea is also achieved. The results show that the true concentrations of chloride, pH, and urea in sweat are ∼10 mM, ∼7.2, and ∼10 mM, respectively. The detection limits of chloride and urea are 1.06 mM and 3.05 mM. This work bridges the gap between sweat sampling and a friendly epidermal microenvironment, providing a promising way for multifunctional textiles.

In-situ growth of robust and superhydrophilic nano-skin on electrospun Janus nanofibrous membrane for oil/water emulsions separation

It is difficult for composite fibrous membranes to achieve up to 99.5% separation efficiency for oil/water emulsions under cycling separation. Herein, a simple method is developed to in-situ grow surperhydrophilic nanocoating on a single electrospun polyvinylidene fluoride (PVDF) fiber surface for fabricating asymmetric wettable Janus PVDF fibrous membranes. Particularly, polysaccharide fluids with zwitterionic polymer chains are generated from the nanofiber subsurface in an inside-out way during the electrospinning process, forming the robust superhydrophilic nanocoating (<5°) under a synergistic effect of both the electric field force and self-migration feature of N-carboxymethyl chitosan fluids (CMCfs). Benefiting from opposite wettability of the PVDF Janus membrane, the results show that the as-prepared Janus membranes with asymmetrical wettability exhibit excellent separation efficiency (S/E) (>99.5 %), a high flux (up to 4325 L m−2 h−1 bar−1), antibacterial activity (>99%) and antifoul properties. Moreover, the obtained Janus membranes own surprising flux cycling stability and retained 99.5% separation efficiency after 12 cycles without any treatment, indicating that the multi-arm polysaccharide fluids acted as the water channel in such membrane and accelerated the flow of water molecules. The Janus PVDF composite membranes have potential applications for oily wastewater treatment and water purification in the future.

Intelligent device composed of two membranes with opposite wettability for identification and purification of both water and oil phases from oil-in-water and water-in-oil emulsions

Oil/water separation based on superwettable materials has been a fast-growing field due to the economical, energy-efficient separation process but superior separation efficiency. Nevertheless, the separation of complicated oil/water systems that may contain oil-in-water and water-in-oil emulsions in one batch, which actually is of great importance for true applications, has not been explored. Herein, we created an intelligent device composed of two porous membranes with opposite superwettability, e.g., one of them displays superhydrophobicity/superoleophilicity, whereas the other shows superhydrophilicity/underwater superoleophobicity. Highly efficient separation and purification of both water and oil phases from complicated oil/water systems can be achieved by the integration of two membranes with opposite superwettability in one single device. The oil-in-water and water-in-oil emulsions can be automatically identified and purified by the right membrane due to their suitable wettability, which avoid the failure of the separation for unknown type of emulsion. Consequently, clean water and oil can be obtained only through a single operational unit using such a separation device. This work paves the way toward true industrial applications related to oil/water separation in which the type or composition of the oil/water systems may change from time to time.

Comparing Water Transport Properties of Janus Membranes Fabricated from Copper Mesh and Foam Using a Femtosecond Laser

One of the important aspects of manipulating and controlling liquid transport is the design of membrane surfaces. Janus membranes with opposite wettability characteristics can be manufactured for efficient directional water transfer. In this work, two types of materials were used to fabricate membranes with an asymmetric wettability behavior: copper foam and copper mesh. One side of the membranes was treated by scanning with a femtosecond laser beam, as a result of which it was converted to a superhydrophilic state, while the untreated side remained hydrophobic. Both membranes demonstrated excellent properties of a water diode through which water droplets could easily pass from the hydrophobic side to the hydrophilic side, but not vice versa. This behavior was achieved by finding the optimal laser scanning speed. This type of Janus membrane has found applications in collecting water droplets from fog; therefore, the samples obtained were also tested in terms of harvesting micro-droplets. The Janus mesh-based structure has demonstrated a higher water collection efficiency (3.9 g/cm2 h) compared to the foam-based membrane (2.5 g/cm2 h). Since the fog-water conversion efficiency decreased over time (to 0.5 g/cm2 h in 2 weeks) due to the absorbance of organic pollutants, a coating of titanium oxide was applied to the laser-treated side of the Janus membranes. As a result, the effective function of the systems became distinctly long-lasting and was well maintained for at least 60 days. Moreover, the fabricated systems were protected from further degradation by simply placing them under sunlight for several hours. Our results prove to be useful in developing asymmetric hydrophobic-superhydrophilic membranes, which have potential applications in high-precision drop control and in harvesting water from arid environments.

A Gemini-Type Superwettable Separator for Consecutive Purification of Water and Oil Phases from Oil-Water Mixtures and Emulsions.

Oil pollution results from daily activities and a variety of industries have caused not only severe environmental problems but also wastage of valuable petrochemical resources. Separation based on superwettable materials holds promise; however, practical applications of a single type of superwettable materials were often limited due to their ability in treatment of complicated oil-water systems. Herein, a Gemini-type separator was created through the cooperation of two kinds of superwettable sand particles with opposite wettability, i. e., one is superhydrophobic whereas the other is superhydrophilic. Cooperatively by the two types of superwettable sand, consecutive separation and purification of both water and oil phases from complicated oil-water systems (e. g., water mixed with a lighter or denser oil, water emulsified in oil, oil emulsified in water, and/or a combination of them in one batch) could be achieved with high flux and superior efficiency just in one single operation unit.

Application of combined granular media with opposite wettability for demulsification of oily wastewater by microchannel filter

Oil-water separation with high efficiency and low energy consumption is a tremendous challenge in the green treatment of oily wastewater. In this paper, a novel filtration method with combined granular media for collaborative removal emulsified oil and suspended solids (SS) was proposed, followed by the exploration of demulsification feasibility and oil removal mechanism. The effect of the operation and structural parameters of the filter bed on oil separation performance was thoroughly investigated, and its feasibility for raw oily wastewater treatment was also explored. A remarkable demulsification performance was observed with the combined granular media filter, and a balance of separation efficiency and pressure drop in the emulsified oily wastewater filtration was also achieved subsequently. Effective oil droplet capture and coalescence were observed with a high speed camera system, and pore clogging could be avoided in combined media. The optimal parameters of the combined media filter (CMF) were concluded to be a combined media ratio of 1:1, a superficial velocity of 0.20 m min−1, and a bed porosity of 58.1%. The average oil and suspended solids concentrations in raw oily wastewater was decreased to 8.4 mg/L and 23.3 mg/L during the pilot-scale operation, which indicated that the novel filter composed of combined media had better performance in collaboratively removing oil and SS, even in the period of fluctuating influent parameters. It is believed that a novel and efficient oil removal method, especially including of emulsified oil removal was provided, which also shows great potential and value for the green treatment of industrial oily wastewater.