Oil Contact Angle Research Articles

Ti3C2/Ni2P/triphenyl phosphite as antioxidative microwave absorbers with excellent photothermal property

Microwave absorbers with the high-efficiency photothermal conversion performance are currently lacking but significantly desired as they can provide a sufficient heat energy besides the absorption property. Herein, Ti3C2/Ni2P/triphenyl phosphite (TPOP-Ti3C2/Ni2P) composite was synthesized by an ingenious one-pot solution-phase reaction and proved to be a superior antioxidative microwave absorbent with excellent photothermal properties. Ni2P can effectively optimize the impedance match of Ti3C2 MXene and consequently improve its microwave absorption (MA) performance. Results show that the minimum reflection loss value of TPOP-Ti3C2/Ni2P is −57.87 dB at 10.88 GHz, the maximum effective absorption bandwidth is 5.04 GHz, and the thickness is merely 1.8 mm. Notably, TPOP on the MXene surface can serve simultaneously as an antioxidative stabilizer and a capping agent to improve its hydrophobicity and chemical stability. The average water contact angle of TPOP-Ti3C2/Ni2P is prompted to 96.59°, while the average oil contact angle is 26.02°. Moreover, compared with the pure Ti3C2, TPOP-Ti3C2/Ni2P has an obvious antioxidant stability in aqueous solution. Additionally, Ni2P nanoparticles exhibit a dipole resonance mode under illumination conditions, which enhances the surface absorption capability of visible light. The surface temperature of the natural rubber film after introducing TPOP-Ti3C2/Ni2P increased rapidly under simulated light, showing a high photothermal conversion ability. Furthermore, the MA performance of the composite film remains basically unchanged, whether is repeatedly bent or exposed under a harsh sun. This study provides a new strategy for manufacturing MA materials with efficient photothermal properties for the possible application to design wearable devices that can combine electromagnetic protection and self-generated heat.

Multifunctional PVDF Membrane Coated with ZnO-Ag Nanocomposites for Wastewater Treatment and Fouling Mitigation: Factorial and Mechanism Analyses

In this study, a multifunctional poly(vinylidene fluoride) (PVDF) membrane was developed through chemical binding with ZnO-Ag nanocomposites to increase wastewater treatment efficiency. The unique characteristics of ZnO-Ag nanocomposites endowed the membrane with high surface hydrophilicity, organic/bio fouling resistance, and photocatalytic antibacterial activity. The significantly decreased water contact angle and increased under-water oil contact angle suggested improved surface hydrophilicity and organic fouling resistance. Through factorial analysis, it was found that the antibacterial activity of the multifunctional membrane could be significantly improved under visible light condition and with ZnO-Ag nanocomposites which obtained under higher Ag concentration and sintering temperature. The increase of Ag composition of ZnO-Ag nanocomposites on modified membrane surface significantly improved the membrane antibacterial activity but had little effect on membrane hydrophilicity. In addition, the photocatalytic antibacterial activity of ZnO-Ag nanocomposites could further improve the membrane biofouling resistance through simple exposure to visible light. The effects of different Ag chemical states on the performances of ZnO-Ag nanocomposites and the corresponding modified membranes were studied, and the relevant mechanism of antibacterial activity under both dark and light conditions was discussed. Filtration experiments with secondary wastewater effluent as feed solution indicated that the developed membrane exhibited one order of magnitude larger permeate flux compared to the pristine PVDF membrane, while maintaining comparable bacteria rejection rates during the filtration process.

Synthesis, Characterization and Statistical Optimization of Hydrophobic/Oleophilic Polystyrene Coated ZnO-Cotton Composite as Vegetable Oil Adsorbent

Cotton being easily available, low cost and highly porous natural material is excellent candidate as adsorbent base. However, its super hydrophilicity hinders its applications as oleophilic adsorbent. In the present study, pristine cotton was impregnated with ZnO and stearic acid to provide it with rough surface and hydrophobic properties followed by dip coating of polystyrene for further enhancement of its oil adsorption capacity. The surface morphology of polystyrene coated ZnO impregnated non-woven cotton (PS@ZnO-NWCotton) and polystyrene coated ZnO impregnated woven cotton (PS@ZnO-WCotton) showed increased surface area, roughness and pores as compared to pristine cotton. FTIR spectra confirmed conjugation of polystyrene and ZnO with cotton. Different thermal degradation behavior of pristine cotton and PS@ZnO-NWCotton further confirmed the presence of ZnO and polystyrene onto cotton. PS@ZnO-WCotton exhibited lotus-effect high hydrophobicity with a water contact angle of 145and#177;2o and super oleophilicity with an oil contact angle of 0o. Oil adsorption capacities of synthesized composites were found to have an inverse relationship with viscosity of adsorbate oil which could be due to easy mobility of lighter oils. Oil adsorption capacity of PS@ZnO-NWCotton for coconut oil was maximized by optimizing temperature, duration and oil/water ratio using central composite design (CCD). Good agreement was found between predicted values obtained by the model and the experimental values (R2 = 0.8904) for adsorption of coconut oil by PS@ZnO-NWCotton. Under the optimum conditions, the PS@ZnO-NWCotton adsorbed more than 12 times of its weight with acceptable reusability till third cycle

Composite membranes of polyacrylonitrile cross-linked with cellulose nanocrystals for emulsion separation and regeneration

• Composite nanofiber membranes were synthesized by crosslinking PAN and CNC. • PAN hydrolysis contributes to the durability of the membrane. • H-bonding networks enable membrane operation stability in aqueous media. • The membrane can be reused and shows excellent emulsion separation performance. As a result of fatigue and damage, the durability of separation membranes remains a major challenge for long-term use in the separation of multiphase systems, such as oily water and emulsions. Here, we synthesize electrospun membranes based on hydrolyzed polyacrylonitrile reinforced with cellulose nanocrystals (CNC). The nanofibers form highly porous systems that are held together by crosslinking, allowing fast mass transport while achieving high tensile strength and elongation at break. The membranes exhibit shape retention upon immersion in complex fluids. An underwater oil contact angle of 141° enables efficient emulsion separation (98.2% separation at a flux as high as 1293 L·m -2 ·h -1 for hexane-in-water emulsions) and reliable operation for at least 20 filtration cycles. A similar performance is achieved in the separation of emulsions based on toluene, petroleum ether, diesel, and vegetable oils. Overall, the designed composite membranes endow stable three-dimensional structures, excellent durability, and separation performance.

A compressible porous superhydrophobic material constructed by a multi-template high internal phase emulsion method for oil-water separation.

Superhydrophobic porous materials exhibit remarkable stability and exceptional efficacy in combating marine oil spills and containing oily water discharges. This work employed the multi-template high internal phase emulsion method to fabricate a multi-template porous superhydrophobic foam (MTPSF). The materials were characterized through SEM, IR spectroscopy, contact angle measurement, and an electronic universal testing machine. Moreover, the materials' oil-water separation capability, reusability, and compressibility were thoroughly evaluated. The obtained results demonstrate that the material displays a water contact angle of 143° and an oil contact angle of approximately 0°, thus exhibiting superhydrophobic and superoleophilic properties. Consequently, it effectively facilitates the separation of oil slicks and heavy oil underwater. Furthermore, the MTPSF conforms to the second kinetic and Webber-Morris models concerning the oil absorption process. MTPSF exhibits an outstanding oil absorption capacity, ranging from 39.40 to 102.32 g g-1, while showcasing reliable reusability, high recovery efficiency, and excellent compressibility of up to 55%. The above exceptional attributes render the MTPSF highly suitable for oil-water separation applications.

Chemically selective raising and rolling of oil-droplets underwater: an equipment-free chemical sensing method.

A dual chemically reactive multilayer coating is rationally subjected to mono- and dual-functionalization through a 1,4-conjugate addition reaction at ambient conditions to depict the raising of the oil contact angle and rolling of a beaded oil-droplet underwater, respectively, only in the presence of targeted toxic chemicals (e.g. nitrite ion and hydrazine). Rational switching of the hydrophobic aromatic moiety into a hydrophilic moiety in the modified multilayer coatings via selected modified Griess reaction and Schiff base reaction contributed to the desired change in underwater oil-wettability and oil-adhesion. Eventually, this approach allowed equipment-free and naked-eye chemical sensing with high selectivity and sensitivity.

Facile fabrication of ceramic-polymeric nanocomposite membrane with special surface wettability using amino decorated NH2-SiO2@SiC nanopowder for production of clean water from oily wastewater

Given the huge market potential of treating oily wastewater, a ceramic membrane with special surface wettability was fabricated by covalently decorating amino-functionalized silicon carbide (NH2-SiO2@SiC) as an active layer on alumina support. The NH2-SiO2@SiC was synthesized by growing a layer of silicon dioxide (SiO2) on silicon carbide (SiC) leading to silicon dioxide loaded silicon carbide (SiO2@SiC). Then amino (-NH2) functionalization of SiO2@SiC was carried out through 3-triethoxysilylpropylamine (APTES) yielding NH2-SiO2@SiC. The NH2-SiO2@SiC was covalently deposited as active layer on alumina support through interfacial polymerization with terephthaloyl chloride (TPC) leading to SiO2@SiC/polyamide nanocomposite decorated on alumina (SiO2@SiC/PA@Al2O3) ceramic membrane. The SiO2@SiC/PA@Al2O3 ceramic membrane was thoroughly characterized by several membrane characterization techniques including water and oil contact angles, SEM (scanning electron microscopy), elemental mapping, EDX analysis (energy dispersive x-ray) and ATR-FTIR (Attenuated Total Reflectance Fourier Transform Infrared spectroscopy). The SiO2@SiC/PA@Al2O3 ceramic membrane was applied for sepraration of surfactant stabalized oil-in-water (O/W) emulsion feed. The effect of increasing O/W emulsion concentration (33.75–250 ppm) was studied by varying the amount of oil in the emulsion. The ceramic membrane was able to maintain a separation efficiency of > 98 % with permeate flux of 270 L/m2.h at a transmembrane pressure of 2 bar. The long-term filtration tests revealed that SiO2@SiC/PA@Al2O3 ceramic membrane retained its separation efficiency at > 98 % for 420 min when 125 ppm O/W emulsion was used as feed. The SiO2@SiC/PA@Al2O3 ceramic membrane showed a potential of treating a high concentration (250 ppm) surfactant stabalized O/W emulsion.

Effect of W/O pre-emulsion prepared with different emulsifiers on the physicochemical properties of soy protein isolate-based emulsion films

The effects of incorporating a water-in-oil pre-emulsion based on different emulsifiers with similar hydrophilic-lipophilic balances on the physicochemical properties of soy protein isolate-based emulsion films were investigated. Confocal laser scanning microscopy images indicated that the oil droplet size in the polyglycerol polyricinoleate and lecithin pre-emulsions was larger than that in the glycerol monostearate, span, and sucrose ester pre-emulsions. By contrast, the oil droplet size in the film-forming emulsions had opposite orders. After drying, the polyglycerol polyricinoleate and lecithin emulsion films contained small and evenly distributed oil droplets and demonstrated a small difference of upper and lower surfaces in oil concentration and contact angle. The water vapor permeability of emulsion films prepared by polyglycerol polyricinoleate and lecithin pre-emulsion was 2.35 × 10−10 g m−1 s−1 Pa−1 and 2.32 × 10−10 g m−1 s−1 Pa−1, respectively, lower than that of other emulsion films. The control emulsion films had the highest tensile strength of 7.43 MPa, whereas polyglycerol polyricinoleate emulsion films had the lowest tensile strength of 4.87 MPa. Furthermore, the polyglycerol polyricinoleate emulsion films had the lowest glass transition temperature among the prepared emulsion films. This study concluded that the properties of film-forming emulsions could be affected by pre-emulsions based on different emulsifiers, resulting in different physicochemical properties of the emulsion films.

Preparation and application of low-cost fibers for efficient adsorption of oil from coal pyrolysis wastewater and establishment of quantitative equation for calculating oil contact angle under water

The removal of oil from coal pyrolysis wastewater persists to be a challenging problem. Thus, this study proposes a new scheme that integrates the adsorption of oil using fibers and subsequent centrifugation or elution to achieve efficient oil–water separation. Based on their stable chemical property, PP and were selected as the substrates for drawing the fibers. In addition, PVDF and PTFE were explored to modify the wettability of PP and PE. The performances of as-prepared fibers were tested for removing oil from wastewater in both batch and continuous modes. Among all the fibers, the PVDF-modified PP fibers exhibited the best performance. For PP-based fibers with 5 wt% PVDF, the saturated oil-removal efficiency reached 92.24 % in case of the simulated wastewater and 81.10 % for the actual wastewater. Given that the oil content in coal pyrolysis wastewater was ~2000 ppm, the residual oil content in the outlet water would be ~380 ppm, which satisfies the requirement of the subsequent treatment process. Furthermore, the PVDF-modified PP fibers exhibited excellent reusability and stability to defy various environmental corrosions. The separation of oil and water based on the adsorption by fibers offers promising prospect to remove oil from coal pyrolysis wastewater. In addition, we derived a formula to calculate the oil contact angle under water based on Young's equation using several measurable parameters. As the calculation results were consistent with real scenarios, this derived formula can provide quantitative guidance for material modification in coal wastewater treatment.

Fabrication of eco‐friendly superhydrophobic and superoleophilic PHB‐SiO2 bionanofiber membrane for gravity‐driven oil/water separation

AbstractIn this study, eco‐friendly superhydrophobic (SH) and superoleophilic (SO) poly (3‐hydroxybuthyrate) (PHB)‐SiO2 bio‐nanofiber membrane has been successfully fabricated for oil–water separation. Firstly, silica nanoparticles (SiNPs) have been synthesized via green laser ablation technique. It was placed into PHB matrix in different contents by controlling the time of ablation and then PHB‐SiO2 nanofibrous mats were obtained on commercial stainless‐steel mesh with various mesh sizes by electrospinning method. The surface morphology and chemical structure of all obtained samples have been characterized by FT‐IR, FE‐SEM and HR‐TEM techniques. It has been observed that SiNPs obtained within 30 min ablation time, with an average size distribution between 10 nm and 200 nm with spherical shape have been uniformly anchored on PHB nanofibers. PHB‐SiO2 fibrous membrane has shown superhydrophobicity with maximum water contact angle of 160.23° and superoleophilicity with oil contact angle (OCA) of being nearly 0° in air. Later, SH and SO membranes were directly employed for oil water separation without using any chemical reagent or additional force, and maximum efficiency of separation higher than 99% has been measured. These results has indicated that environmental friendly PHB‐SiO2 bio‐nanofiber membrane offers high potential for using in gravity‐driven oil–water separation.

Synthesis of inorganic/organic raspberry-like composite particles for superhydrophobic and superlipophilic coatings

A facile synthetic route to composite particles with raspberry-like structure was reported, and further led to superhydrophobic and superlipophilic surface by the usage of these composite particles. In this approach, the poly(styrene-co-3-methacryloxypropyl trimethoxysilane) (P(St-MPS)) particles were fabricated by one-step dispersion polymerization. Then, the P(St-MPS)@SiO2 composite particles with raspberry-like structure were obtained by hydrolysis of tetraethoxysilane (TEOS) with (P(St-MPS)) particles under alkaline conditions. The morphology of the (P(St-MPS))@SiO2 composite particles could be controlled by adjusting the ratio of the initial reactants 3-methacryloxypropyl trimethoxysilane (MPS) and styrene (St). A possible mechanism of the morphology changes was also discussed, the reactive siloxane groups of the (P(St-MPS)) particles induce the growth of silica generated by the hydrolysis of tetraethoxysilane (TEOS) on its surface to form raspberry-like structure. In addition, the water contact angle (WCA) of the coating was 152° ± 2°, and the oil contact angle (OCA) of the coating was close to 0°, which demonstrated a superhydrophobic and superlipophilic properties by a rational surface modification of this P(St-MPS)@SiO2 composite particles with raspberry-like structure. Hydrophobic properties could be adjusted by varying the surface morphology of the P(St-MPS)@SiO2 composite particles. The coatings could be used in applications such as self-cleaning and oil-water separation and whole process was carried out under mild conditions and did not involve complex steps.

Superwetting Ti3C2TX MXene membranes intercalated with sodium alginate for oil/water separation

Oily wastewater seriously endangers human health. Ti3C2Tx MXene has attracted extensive attention as a building block for separating membranes because of its unique two-dimensional structure and excellent hydrophilicity. In this study, we constructed a superwetting Ti3C2Tx MXene membrane intercalated with sodium alginate. The hydrophilic sodium alginate not only enlarged the nanochannel of the MXene membrane but also decorated the membrane surface and endowed the membrane with excellent surface superwetting properties. The underwater oil contact angle (OCA) was about 151°, indicating an extremely low adhesion between oil and membrane surface. The membrane could also separate a series of oil-water emulsions with high separation efficiency and flux. Due to its excellent underwater superoleophobicity, the membrane demonstrated outstanding antifouling property. Excellent separation performance was maintained even after separation cycles. This work provides insights into the rational use of MXene-based membranes design and demonstrates its potential in the field of membrane separation.

Reversed micelles with well-amphiphobic properties from main-chain type semifluorinated alternating copolymer

Amphiphobic coatings are of great interest in academic and industrial areas. In this work, amphiphobic coating surfaces from fluorinated reversed micelles, which synthesized via a polymerization-induced self-assembly (PISA) strategy, were fabricated just by simple spin coating. Through this strategy, the low surface energy properties of fluorine-containing components can be used simply and efficiently, and a certain degree of roughness can be obtained at the same time. The influence of the reaction solvent and polymerization conditions on the wettability of the reversed micelles were investigated to determine the optimal experimental parameters that maximized the amphiphobicity of the surfaces. The water contact angles of spin-coated reversed micelles coatings could reach to 151.9° with the lowest sliding angle (5.0°) and oil contact angle for oleic acid up to 131.6° among all samples. The facile, easy to control, and efficient method can provide new insights into fabricating amphiphobic surfaces, and can open up a new way for the basic research and practical application of amphiphobic surfaces on a large scale.

Coral stone-inspired superwetting membranes with anti-fouling and self-cleaning properties for highly efficient oil–water separation

Nowadays, the use of separation membranes to deal with oil–water emulsions has gained popularity. However, oil fouling of membrane surfaces during the separation of oil–water emulsion is still a significant challenge. In this study, inspired by the biological coral stone structure, the gel layer was firmly attached to the surface of membrane using a simple co-blending and cross-linking strategy. A super-wetting membrane (PVDF/CD-SA) with a coral stone structure was obtained. The PVDF/CD-SA membrane had a high permeate flux that was 4.2 times higher than that of the original membrane and a high separation efficiency of about 99.2 % for the separation of oil–water emulsion. Furthermore, the membrane had outstanding chemical stability. The fluxes of several different oil-in-water emulsions significantly improved, and the separation efficiencies were as high as 98 %. Moreover, the separation efficiencies and contact angles of the membrane remained unchanged after numerous cycles of use. The membrane exhibited excellent superhydrophilicity in air (instantaneous water wetting in air) and superoleophobicity under water (underwater oil contact angle > 156°). Most importantly, the oil was able to automatically detach from the surface of membrane, resulting in self-cleaning performance. Therefore, this PVDF/CD-SA membrane eliminated the problem of oil adhesion, exhibiting excellent potential for practical applications in oil–water separation.

Bionic engineering-induced formation of hierarchical structured minerals with superwetting surfaces for oil-water separation

Harnessing the living organisms to fabricate the biomimetic materials with hierarchical ordered structures via biomineralization process shows great potential in oil-water separation. Herein, we exploited a bacteria-assisted mineralization strategy with environmental friendliness to realize the growth of the CaCO3 minerals with hierarchical micro/nanostructures on the stainless steel meshes (SSMs). The biomimetic CaCO3 minerals coated-SSMs (CaCO3-SSMs) owned superhydrophilicity and underwater superoleophobicity with water contact angles of nearly 0° and underwater oil contact angles of up to 161°. The CaCO3-SSMs showed excellent oil-water separation performance with ultrahigh permeation flux (1.55 × 105 L m−2 h−1) and high separation efficiency (≥98.5%), while concurrently demonstrating high chemical and mechanical stability. Furthermore, the CaCO3-SSMs possessed ultralow oil-adhesion force in water, endowing them with outstanding anti-oil fouling property. We expect that the bionic engineering-induced formation of the minerals with hierarchical structures could help for the development of next generation superwetting materials.

Preparation and properties of CNTs-Cu hybrids/epoxy superhydrophobic and anticorrosive coatings

In this work, hydrophobized copper powders combined siloxane-modified carbon nanotubes (SHMWCNTs) to obtain intertwined hybrids of carbon nanotubes and copper (CNTs-Cu hybrids), and superhydrophobic CNTs-Cu hybrids/epoxy coatings were prepared on the surface of AH36 carbon steel by drop coating. The surface morphology and wettability of coatings were changed by adjusting the ratios of SHMWCNTs to hydrophobized copper powders. The obtained coating can show a water contact angle of 167.2°, a water sliding angle of 2.9°, a plant oil contact angle of 134.3°, and self-cleaning properties. The coating maintains superhydrophobicity after 300 tape-peeling times, exhibiting excellent mechanical durability. The fouled area percentages of chlorella on the coating and a pure epoxy resin were 0.23(±0.07)% and 12.18(±1.22)%, respectively, displaying anti-biofouling resistances. The coating has excellent corrosion resistance, and its corrosion current density reached 9.55 × 10-8 A/cm2.

An efficient and simple strategy for fabricating a polypyrrole decorated ceramic-polymeric porous membrane for purification of a variety of oily wastewater streams

A ceramic-polymeric membrane was fabricated through in-situ oxidative polymerization of pyrrole (Py) on alumina (Al2O3) ceramic ultrafiltration support. The establishment of polypyrrole (PPy) active layer on the ceramic support led to a new PPy coated ceramic-polymeric membrane. Various salient features such as surface wettability, surface morphology, composition and functional goups of PPy coated ceramic-polymeric membrane were determined by various characterization techniques water contact angle (WCA), scanning electron microscopy (SEM), energy dispersive x-ray (EDX) analysis and attenuated total reflectance fourier transform infrared (ATR-FTIR). The PPy coated ceramic-polymeric membrane showed superhydrophilic nature owing to its under water oil contact angle of ≥160° (superoleophobic). Thanks to stable deposition of PPy active layer on ceramic support, the membrane retained a separation efficiency of >99% for O/W emulsions at varied transmembrane pressures ranging from 0.5 bar to 2 bar with a feed concentration of 125 ppm of oil in water. Moreover, the PPy coated ceramic-polymeric membrane exhibited an ideal behaviour to the applied transmembrane pressure with a linear increase from 380 LMH to 2112 LMH in permeate flux as the pressure increased from 0.5 bar to 2 bar. As the concentration of oil was raised from 50 ppm to 250 ppm, the separation efficeincy separation remained at >99%. From among the different types of oils (Motor oil, Diesel oil and Crude oil) to mimic the oily waste water streams, the permeate flux was found to be highest in case of motor oil with a value reaching to 1690 LMH at 1 bar. The stability test revealed that the PPy coated ceramic-polymeric membrane was able to separate >99% of 125 ppm O/W surfactant stabilized emulsion for a period of 420 min.

Fluorosilane-Modified Antireflash Sodium Bicarbonate Fire Extinguishing Agent with Advanced Hydrophobic and Oleophobic Properties

The poor antireflash performance of NaHCO3 dry powder fire extinguishing agent in class B fire is the key problem that restricts its application in large oil fires. In this work, the NaHCO3 was surface modified by sol–gel method to introduce functional fluorosilane structure (named FSi-NaHCO3) and enhance the hydrophobic and oleophobic properties. The water contact angle (WCA) and oil contact angle (OCA) of FSi-NaHCO35 are 147.0° and 144.2°, respectively, which means that FSi-NaHCO35 has advanced hydrophobic and oleophobic properties. The hydrophobic and oleophobic ratio of FSi-NaHCO35 are 92.35% and 91.59%, respectively. Furthermore, FSi-NaHCO35 dry powder fire extinguishing agent can extinguish aviation kerosene and n-heptane oil pool fires in 0.15 and 0.18 s, respectively, which is shorter than that of NaHCO3 dry powder fire extinguishing agent. After the secondary ignition, using FSi-NaHCO35 as dry powder fire extinguishing agent, the fire temperature of the aviation kerosene oil is significantly lower, and the full reburning time of the aviation kerosene oil fire is significantly longer than that of NaHCO3 dry powder fire extinguishing agent, which means FSi-NaHCO35 obviously has antireflash performance in an aviation kerosene oil pool fire.

Insights into the interaction between lowsal-alkali formulation: Debunking the effect of alkali and lowsal-alkali formulation on the wettability alteration of the quartz substrate

The role of salts in altering the interfacial tension (IFT) and wettability of the rock towards oil recovery is evident through low salinity (lowsal) water flooding. On the other hand, alkali flooding is a well-established method of chemical enhanced oil recovery, which works by reducing the IFT of liquid–liquid system, alters the wettability of rock, and emulsifies the oil–water. Despite having sound knowledge on the applicability of alkali in EOR, the synergistic effect between salts and alkali towards the oil recovery still needs more investigation. In this work, the interaction of salts such as (NaCl and CaCl2) and alkali (NaOH, Na2CO3) on the IFT and wettability of the quartz substrate is investigated. To understand the effect of individual components of crude oil on the IFT and wettability, two different model oils, an aliphatic hydrocarbon (decane), and also actual crude oil from oilfield are employed. It is observed that the lowsal (NaCl)-alkali (NaOH, Na2CO3) formulation effectively reduces the IFT of basic model oil–water and aliphatic-water system than the individual effect of alkali and salts. The lowsal (NaCl)-alkali formulation completely swept the hydrocarbon from the quartz substrate by imparting Marangoni force. Thereby a complete removal of the crude oil droplet from the quartz surface is visually reported for the first time using lowsal (NaCl)-alkali system. These results are further validated by a new approach of Petri dish based static experimental technique which confirms the saponification reaction between acidic and the basic components in the crude oil. Further, the attraction of anionic surfactant (sodium stearate) by cations (Na+) in the NaCl is also validated. We also conclusively show that the increase in contact angle of crude oil and acidic model oil in wettability experiments is primarily due to neutralization reaction and it is not an indicator of oil-wet.

Underwater superoleophobic GO-PEI-SiO2-Hal quaternary sphere-rod nacre-inspired mesh by LBL self-assembly for high-efficiency oil-water separation

The easy preparation of robust superwetting materials for oily wastewater disposal still remains a challenge. Inspired by the self-cleaning and mechanical properties of natural nacre underwater, herein, we have successfully developed sphere-rod quaternary artificial nacre-inspired meshes (named GO-PEI-SiO2-Hal) via interfacial self-assembly using 2D graphene oxide nanosheets, hyperbranched polyethyleneimine, SiO2 nanospheres, and hollow halloysite nanotubes (Hal) as the building blocks. The nacre-like “brick-and-mortar” layered microstructure was successfully formed and tightly coated to the mesh, showing excellent mechanical properties with Young's modulus up to 19.7 ± 2.6 GPa. Compared to the ternary structures, the quaternary sphere-rod morphology improved the surface roughness, and these four organic/inorganic building blocks are all hydrophilic, which together resulted in the superhydrophilic and underwater superoleophobic characteristics. The effects of building block concentration, dipping number, and mesh size on wettability and oil-water separation performance were studied in detail. The optimal (GO-PEI-SiO2-Hal-1)15@Fe300 mesh showed an underwater oil contact angle of 159o for 1,2-dichloroethane, low oil adhesion, and excellent separation efficiency up to 99.8% at an ultrahigh flux up to 195,038 L m−2 h−1. This nacre-like mesh exhibited excellent salt tolerance, acid-alkali resistance, recycling ability, and mechanical properties for practical oily wastewater treatment.