Stabilized superhydrophobic composite membranes prepared by electrospinning for oil–water separation

In dealing with the oil–water separation process, improving the oil–water selectivity of the membrane surface and increasing the porosity within the membrane are effective means to achieve durable and efficient oil–water separation. Therefore, polystyrene/polyacrylonitrile-polyvinylidene fluoride/Polydimethylsiloxane Fe₃O₄ nanoparticles (PS/PAN-PVDF/PDMS@Fe₃O₄) composite membranes with superhydrophobicity and lipophilicity were prepared by electrospinning technique. By controlling the filling concentration of Fe₃O₄ nanoparticles, a stable superhydrophobic and lipophilic rough structure was constructed, and micro–nano multilayer rough voids existed inside the membrane. The results showed that the composite fiber membrane exhibited exceptional superhydrophobicity (156.2°), thermal stability (338°C), mechanical properties (tensile strength of 3.0 MPa, elongation of 33.9%), and oil adsorption capacity (30–100 g/g). Moreover, even under corrosive environments, this composite fiber membrane maintained its superhydrophobic properties (above 152°) and achieved high oil–water separation efficiency (above 97%). Remarkably, after 40 cycles, the composite membrane could sustain a separation flux of 5000 L m⁻² h⁻¹. Consequently, the composite fiber membrane manufactured using this strategy exhibits promising potential for applications in oil–water separation.     

Micro–nano structural engineering of filter paper surface for high selective oil–water separation

Cellulose-based lotus-leaf-like filter paper for selective separation of oil/water was prepared. Experimentally, cellulose nanofibril aerogel microspheres prepared by ultrasonic atomization method were coated on commercial filter papers to form unique “micro–nano” structured surface. By controlling both the morphology and chemistry of the surface, the papers could be either under-water superoleophobic or under-oil superhydrophobic. It was found that the filter papers could be engineered to effectively filter only oil or only water from their mixtures.     

Rapid formation of metal−monophenolic networks on polymer membranes for oil/water separation and dye adsorption

Surface deposition based on metal-phenolic networks (MPNs) has received increasing interest in recent years. The catechol structure is generally considered to be essential to the formation of MPNs. Our most recent results have demonstrated that some kinds of monophenols can form MPNs on substrate surfaces. Herein, we report a fast and effective surface-coating system based on the coordination of 3-(4-hydroxy-3-methoxyphenyl)-2-propenoic acid, a kind of monophenol, with Fe³⁺. Compared with other metal ions such as Cu²⁺ and Ni²⁺, Fe³⁺ with stronger electron acceptability can coordinate with the monophenol more strongly to form MPNs, and moreover, the deposition time significantly decreases to 40 min from generally 24 h. It is demonstrated that the deposition process is controlled by the coordination, Fe³⁺ hydrolysis, and deprotonation of the monophenol. The coatings endow substrates such as polypropylene microfiltration membrane with underwater superoleophobicity, which can be applied in oil/water separation with high separation efficiency and great long-term stability. In addition, the coated membranes are positively charged and thus are useful in selective adsorption of dyes. The present work not only provides a novel, fast, and one-step deposition method to fabricate MPNs, but also demonstrates that the fabrication efficiency of monophenol-based MPNs is comparable with that of polyphenol-based MPNs.     

Preparation of silica–alumina composite membranes for hydrogen separation by multi-step pore modifications

In the present paper, a silica–alumina composite membrane for hydrogen separation was prepared within an α-alumina support by the multi-step pore modification. The α-alumina support has an asymmetric structure composed of a thin dense skin layer and a thick coarse layer and the average pore size of its skin layer is 80 nm. The composite membrane layer was formed in the vicinity of the interphase between the two layers of the support by two consecutive steps; namely, in situ silica sol–gel reaction and soaking and vapor deposition. In order to enhance the hydrogen selectivity, palladium (Pd) particles were impregnated in the final step utilizing Pd-acetate as a Pd precursor. Although both silica and Pd induced the surface diffusion, Pd was more effective for selective hydrogen adsorption than silica. This multi-step method produced a porous membrane with moderate hydrogen selectivity and satisfactory hydrogen permeance at high temperature and at high transmembrane pressure. The separation factor of hydrogen relative to nitrogen was maintained at about 10 even when the transmembrane pressure was as high as 110 kPa, and the hydrogen permeance was still much higher than that of non-porous polymeric membranes. In addition, the microstructural distributions of Si and Pd within the intermediate membrane layer were examined by a scanning electron microscopy (SEM) and an energy dispersive X-ray analysis (EDX)     

Preparation of superhydrophobic materials for oil/water separation and oil absorption using PMHS–TEOS-derived xerogel and polystyrene

Fabrication of suerhydrophobic materials towards oil/water separation and oil absorption has been receiving great attention nowadays, due to the significant increase of industrial oily wastewater and frequent accident of oil spill. In most previous studies, the usage of expensive precursors restricted the wide applications of prepared superhydrophobic materials. In this work, superhydrophobic filter paper, fabric and polyester sponges were fabricated by dip-coating the mixed solution of polystyrene and xerogels, which were prepared with tetraethoxysilane and polymethylhydrosiloxane, based on previous work. The as-fabricated fabric can effectively separate oil and water mixtures and possesses excellent reusability; more significantly, the materials maintained its good hydrophobic and excellent oil/water separation capacity even after ten cycles. Interestingly enough, the stability was provided, as a result, the fabric still exhibited superhydrophobic after 100 abrasion times and showed high repellency towards many liquids with different pH values. Additionally, the coated polyester sponges can quickly absorb various oil and organic liquid, which will offer a practical application for the treatment of seawater or oily wastewater. By contrast, this experiment process is simple and avoided using costly fluoro-chemicals or complicated fabrication process.     

Chitosan/N-methylol nylon 6 blend membranes for the pervaporation separation of ethanol–water mixtures

Blend membranes of chitosan and N-methylol nylon 6 were prepared by solution blending. Their pervaporation performances for the separation of ethanol–water mixtures were investigated in terms of acid (H₂SO₄) post-treatment, feed concentration, blend ratio and temperature. The pervaporation performance of the blend membranes was significantly improved by ionizing with H₂SO₄. The blend ratio of chitosan and N-methylol nylon 6 plays a different role at feed solutions of low and high water content. At a feed solution having low water content, an increase in chitosan content caused a decrease in permeability and an increase in separation factor. At a feed solution having high water content, the permeability increases with an increase in chitosan content, while the separation factor shows a maximum value around 60 wt% chitosan. It is proposed that extra permeation channels generated from the phase separation boundary between ionized chitosan and N-methylol nylon 6 account for the abnormal temperature dependence of pervaporation performance of the blend membranes.     

Characteristics of sodium alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures

Alginate membranes for the pervaporation dehydration of ethanol–water and isopropanol–water mixtures were prepared and tested. The sodium alginate membrane was water soluble and mechanically weak but it showed promising performance for the pervaporation dehydration. To control the water solubility the sodium alginate membrane was crosslinked ionically using various divalent and trivalent ions. Among them the alginate membrane crosslinked with Ca²⁺ ion showed the highest pervaporation performance in terms of the flux and separation factors.     

Environment friendly hydrothermal synthesis of carbon–Co_3O_4 nanorods composite as an efficient catalyst for oxygen evolution reaction

The design of cost-effective, highly active catalysts for hydrogen energy production is a vital element in the societal pursuit of sustainable energy. Water electrolysis is one of the most convenient processes to produce high purity hydrogen. Cobalt-based catalysts are well-known electrocatalysts for oxygen evolution reaction(OER). In this article, all these merits indicate that the present cobalt nanocomposite is a promising electrocatalyst for OER. C–Co_3O_4-nanorods catalyst with nanorod structure was synthesized by hydrothermal treatment of CoCl_2·6H_2O/dextrose/urea mixture at 180 °C for 18 h and then calcined at400 °C for 3.5 h. The role of dextrose percentage in solution to achieve the uniform coating of carbon on the surface of Co_3O_4-nanorods has been demonstrated. The prepared materials were characterized by X-ray diffraction(XRD), X-ray photoelectron spectrum(XPS), field emission scanning electron microscopy(FE-SEM), high-resolution transmission electron microscopy(HR-TEM), and Brunauer–Emmett–Teller instrument(BET). Due to its unique morphology, the C–Co_3O_4-nanorods catalyst exhibited better activity than Co_3O_4-microplates catalyst for OER in 1 M KOH aqueous solution. The results showed a highly efficient, scalable, and low-cost method for developing highly active and stable OER electrocatalysts in alkaline solution.     

Structural and mechanical characterizations of microporous silica–boron membranes for gas separation

This paper presents structural and mechanical characterizations of microporous silica membranes for gas separation. The membrane separative layer is made of microporous silica–B₂O₃ produced via a sol–gel process. This layer of about 200 nm of thickness is deposited on the internal surface of a tubular asymmetric γ-alumina/α-alumina support. FTIR and Raman analyses indicate the presence of the boron in the silica net and the above methods in conjunction with ¹¹B MAS NMR analyses of the samples indicate that boron is located mainly in the tetrahedral framework position. Such membranes present interesting gas separation properties at temperatures up to 500 °C and transmembrane pressures lower than 8 bar. He permeance values close to 10⁻¹⁰ kmol m⁻² s⁻¹ Pa⁻¹ are obtained, associated with ideal selectivity α(He/CO₂) which can reach 55. Mechanical properties of separative silica-modified layers are measured by nanoindentation and the coefficient of thermal expansion is obtained from pure material.     

Microextraction in packed syringe by using a three-dimensional carbon nanotube/carbon nanofiber–graphene nanostructure coupled to dispersive liquid-liquid microextraction for the determination of phthalate esters in water samples

Microchimica Acta - Microextraction in packed syringe (MEPS) was combined with dispersive liquid-liquid microextraction (DLLME) for the extraction of phthalate esters (PEs) from water samples prior...     

Effect of γ-irradiation on the growth of ZnO nanorod films for photocatalytic disinfection of contaminated water

The growth of ZnO nanorods on a flat substrate containing γ-irradiated seeds and their ability to photocatalytically eliminate bacteria in water were studied. The seed layer was obtained, by the spray pyrolysis technique, from zinc acetate solutions γ-irradiated within the range from 0 to 100 kGy. Subsequently, to grow the rods, the seeds were immersed in a basic solution of zinc nitrate maintained at 90 °C. The rate of crystal growth on the seed layer during the thermal bath treatment was kept constant. The resulting materials were characterized morphologically by scanning electron and atomic force microscopies; X-ray diffraction was used to study their morphology and structure and ultraviolet-visible spectroscopy to determine their absorbance. The obtained seed films were morphologically dependent on the radiation dose and this was correlated with the ZnO nanorod films which presented a texture in the (002) direction perpendicular to the substrate. The rods have a hexagonal mean cross section between 20 and 140 nm. Using these rods, the photocatalytic degradation of Escherichia coli bacteria in water was studied; a positive influence of the crystalline texture on the degradation rate was observed.     

Preparation and application in oil–water separation of ZrO2/α-Al2O3 MF membrane

The composite tubular membranes were prepared by applying suspensions of zirconia particles to form separation top-layers on two different porous α-alumina supports and heating the coated supports to partly sinter the particles of top-layers. The conditions of synthesizing the ZrO₂/α-Al₂O₃ membranes were investigated systematically. The mean pore diameter of zirconia membrane was about 0.2 μm by gas bubble pressure method, and the pure water flux was about 400 and 1500 l/(m² h bar) for ZrO₂ membrane on symmetric and asymmetric Al₂O₃ support, respectively. Zirconia membrane and three different alumina membranes were applied to separate oil–water emulsion obtained from steelworks to evaluate the permeability and separation characteristics, the ZrO₂/α-Al₂O₃ MF membrane in this work was the preferred membrane.     

Advances in high carbon dioxide separation performance of poly(ethylene oxide)-based membranes

Poly(ethylene-oxide)(PEO)-based membranes have attracted much attention recently for CO2 separation because CO2 is highly soluble into PEO and shows high selectivity over other gases such as CH4 and N2.Unfortunately,those membranes are not strong enough mechanically and highly crystalline,which hinders their broader applications for separation membranes.In this review discussions are made,as much in detail as possible,on the strategies to improve gas separation performance of PEO-based membranes.Some of techniques such as synthesis of graft copolymers that contain PEO,cross-linking of polymers and blending with long chains polymers contributed significantly to improvement of membrane.Incorporation of ionic liquids/nanoparticles has also been found effective.However,surface modification of nanoparticles has been done chemically or physically to enhance their compatibility with polymer matrix.As a result of all such efforts,an excellent performance,i.e.,CO2 permeability up to 200 Barrer,CO2/N2 selectivity up to 200 and CO2/CH4 selectivity up to 70,could be achieved.Another method is to introduce functional groups into PEO-based polymers which boosted CO2 permeability up to 200 Barrer with CO2/CH4 selectivity between 40 and 50.The CO2 permeability of PEO-based membranes increases,without much change in selectivity,when the length of ethylene oxide is increased.     

Enhancing oil–water emulsion separation using improved styrene–acrylonitrile copolymer membrane: Experimental and thermodynamic study of the impact of solvent mixtures

This study investigated the fabrication of styrene–acrylonitrile copolymer (SAN) membrane using the nonsolvent-induced phase separation (NIPS) method with a combination of solvents, namely N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) and water as the nonsolvent. Since the impact of varying solvent ratios on SAN membrane performance remained unexplored, this study aimed to address this knowledge gap in the context of oil–water emulsion separation. Experimental results demonstrated that employing a solvent mixture, rather than a pure solvent, led to improved membrane performance. The primary objective of this work was to experimentally determine the optimal solvent ratio for enhancing SAN copolymer membrane performance. Additionally, the Flory–Huggins thermodynamic model was applied to investigate the possibility of predicting membrane binodal data. The thermodynamic analysis revealed a strong agreement between calculated and experimental binodal data, with an error of less than 3.8%. Notably, membranes produced with an equal solvent ratio exhibited the most hydrophilic properties, resulting in increased permeability. The permeate flux for distilled water reached 320 L/(m² h) (LMH), and water contact angle of the membrane was 22°. Furthermore, mechanical resistance increased up to 50%. These results highlight the promising potential of fabricating SAN membrane using solvent mixtures for oil–water emulsion separation.     

Ultrathin dynamic networks formed by the surfactant SPAN 65 at the air–water and oil–water interface

Some surfactants tend to form ultrathin films at the surface of water or at the interface between oil and water. A representative of these surface-active compounds is SPAN 65 (trioctadecanyl ester of sorbic acid). Induced by attractive interactions these molecules can self-associate to form temporary networks. At the planar surface we measured the two-dimensional relaxation modulus, the storage modulus, the loss modulus and the relaxation spectrum. In addition to these measurements, we have also investigated the molecular structure of these networks with “Brewster-angle-microscopy”. The results indicate that temporary cross-linking points, which have lifetimes of the order of a few seconds, tend to stabilize these films. This dynamic network formation is also interesting for numerous technical applications, and it might be used for the preparation of emulsions, foams or microcapsules. Received: 23 October 2000 Accepted: 3 November 2000     

Functionalization of cellulose via ATRP and “click” chemistry to construct hydrophobic filter paper for oil/water separation

Cellulose - Cellulosic materials show great superiority in oil/water separation owing to abundance, low cost, renewability and biodegradability. Herein, silylated cellulose graft copolymer...     

Sol–gel synthesis of porous titania fibers by electro-spinning for water purification

In this study, porous ceramic fibers were prepared by the sol–gel-assisted electro-spinning process using colloidal dispersion of complex fluids for the application of phtotocatalysts. First, polystyrene nanospheres were synthesized by dispersion polymerization as sacrificial templates for porous fibers. Then, the mixture of polyvinylpyrrolidone and the ceramic precursor with the polymeric nanospheres was prepared as the spinning solution and self-organized by electro-spinning, followed by calcination of the electrospun composite fibers. The morphologies of the porous fibers could be controlled according to the size of the templates and the amount of the ceramic precursor. The nano-structure of the pores in the fibrous materials could also be adjusted as open or closed cavities with various potential applications. As a demonstrative application, the macroporous titania fibers could be utilized as photocatalysts for the removal of organic dyes dissolved in water. A better photocatalytic activity of the macroporous fibers with 700-nm pore diameter was observed compared to the result of nonporous titania fibers due to the increased porosity. Collectively, the macroporous ceramic fibers were found to be efficient functional materials to prepare the unique nano-structured materials other than simple nonporous fibers.     

Enhanced photocatalytic activity of Ni doped TiO2 nanowire–nanoparticle hetero–structured films prepared by hydrothermal and sol–gel methods

TiO₂ nanowire-nanoparticle hetero-structured films were prepared via a sol–gel method and coated on glass substrates by dipping method for photocatalytic activity. In this study 0, 1, 3, and 5 mol% of Ni doped were studied. One-dimensional TiO₂ nanowires (NWs) were prepared by hydrothermal treatment with TiO₂ nanoparticles (NPs) which are commercially available. XRD, FESEM, DRS, and XPS were used to characterize the prepared nanowire-nanoparticle hetero-structures films. 3%Ni doped TiO₂ hetero-structured film (TNi3) had the highest photocatalytic activity on the degradation of methylene blue (MB). TNi3 films provided about 4.3 times of degradation rate compared to undoped TiO₂ (T). It revealed that TNi3 film resulted in shifting the absorption wavelength towards narrowing the energy band gap and small crystallite size. Therefore, the TNi3 film exhibited a photocatalytic activity on the degradation of MB under visible light irradiation greater than undoped film.     

Novel separation method for highly sensitive speciation of cancerostatic platinum compounds by HPLC–ICP–MS

A high-performance liquid chromatography–inductively coupled plasma mass spectrometry (HPLC–ICP–MS) method is presented for analysis of cisplatin, monoaquacisplatin, diaquacisplatin, carboplatin, and oxaliplatin in biological and environmental samples. Chromatographic separation was achieved on pentafluorophenylpropyl-functionalized silica gel. For cisplatin, carboplatin, and oxaliplatin limits of detection of 0.09, 0.10, and 0.15 g L^–1, respectively, were calculated at m/z 194, using aqueous standard solutions. (3 L injection volume). The method was utilized for model experiments studying the stability of carboplatin and oxaliplatin at different chloride concentrations simulating wastewater and surface water conditions. It was found that a high fraction of carboplatin is stable in ultrapure water and in solutions containing 1.5 mol L^–1 Cl^–, whereas oxaliplatin degradation was increased by increasing the chloride concentration. In order to support the assessment of oxaliplatin eco-toxicology, the method was tested for speciation of patient urine. The urine sample contained more than 17 different reaction products, which demonstrates the extensive biotransformation of the compound. In a second step of the study the method was successfully evaluated for monitoring cancerostatic platinum compounds in hospital waste water.