Superwetting and photocatalytic Ag2O/TiO2@CuC2O4 nanocomposite-coated mesh membranes for oil/water separation and soluble dye removal

A novel oily wastewater treatment strategy of simultaneously removing insoluble oily compounds and soluble organic pollutants is highly desirable. Herein, a hierarchical Ag₂O/TiO₂ heterojunction-loaded CuC₂O₄ nanosheet-decorated copper mesh (Ag₂O/TiO₂@CuC₂O₄ CM) was rationally designed by a combination of chemical etching and solvothermal deposition methods to implement the strategy. The Ag₂O/TiO₂@CuC₂O₄ CM with hierarchical nanostructures derived from hydrophilic CuC₂O₄ nanosheets and belt-like Ag₂O/TiO₂ heterojunction was proven to exhibit superior superhydrophilicity, underwater superoleophobicity, and photocatalytic ability, which greatly improved the antipollution ability of the substrate mesh. The as-fabricated mesh with a reasonable mesh number can efficiently separate oil/water mixtures with an ultra-high flux (～70 kL m^?2 h^?1) and surfactant-stabilized oil-in-water emulsions with an ultra-low residue oil content in filtrate (<60 mg L^?1). More importantly, the loaded heterojunction on the CM showed a high photodegradation efficiency of about 94.1% toward soluble methylene blue and self-cleaning ability to regenerate oil-contaminated mesh within 60 min under visible light irradiation by photo-Fenton-like reaction. Besides, the favorable salt resistance, acid and alkali resistance, and stability of the CM for long-term use were also observed. Thus, this study provides a new way for the treatment of complex oily wastewater.     

Chemical cleaning of oil contaminated polyethylene hollow fiber microfiltration membranes

The primary aim of this paper was to develop a more effective and economical procedure for cleaning polyethylene hollow fiber microfiltration membranes that have been used for removing oil from contaminated seawater. Alkaline cleaning showed higher recovery of operating cycle time but lower permeate flux recovery than acid cleaning. The combination of both alkaline and acid cleaning agents gave the best operating cycle time and flux recoveries (e.g. 96% and 94%, respectively). As the cleaning agent soaking time was reduced, the actual operating cycle time was reduced. However, the ratio of operating time/chemical cleaning time increased as the soaking time was reduced. The soaking time was recommended to be as short as possible (8–10 h) in the design of small capacity plants and 30 h or higher in case of large capacity plants. SEM analysis showed that in case of alkaline cleaning, most of the pores remained covered with a foulant layer, resulting in low flux recovery. The SEM results of acid cleaned membranes showed more complete removal of the foulant layer from the pores resulting in better flux recovery. Surface analysis of membranes cleaned with combined acid/base agents showed the best results. A membrane surface similar to the original one was obtained. The long-term objective is to increase the understanding of membrane fouling phenomena, preventive means and membrane cleaning processes as it applies to the clean-up and desalination of oil contaminated seawater.     

Single gas permeation through compositionally different zeolite NaA membranes: Observations on the intercrystalline porosity in an unconventional,semicrystalline layer

The successful application of zeolite A membranes in the industrial market has thus far been restricted to the pervaporative dehydration of solvent streams in the pharmaceutical and engineering industries. Their application in gas separation processes remains elusive, largely due to the existence of uncontrollable, intercrystalline diffusion pathways in the boundary regions of neighbouring crystals.     

In situ evaluation of defect size distribution for supported zeolite membranes

The permporometry measurements are performed with respect to a series of zeolite membranes with different defect sizes, which can be further applied for in situ measurement of the defect size distribution in zeolite membranes. Gas permeation experiments are conducted for CO₂/N₂ gas mixture to test the separation performance of the studied zeolite membranes. By taking into account the “t-layer” on defect walls, a mathematical model and the corresponding procedure are developed so that the defect size distribution in zeolite membranes can be calculated by using the results of permporometry measurements. The defect size distribution and the maximal defect size show a good correlation with the separation performance of CO₂/N₂ gas mixture for zeolite membranes. It is demonstrated that the separation performance of zeolite membranes is mainly determined by large defects. It has been shown that the permporometry-based methodology proposed in this contribution is an effective way for the quality evaluation of zeolite membranes.     

Transport properties of alkanes through ceramic thin zeolite MFI membranes

Polycrystalline randomly oriented defect free zeolite layers on porous α-Al₂O₃ supports are prepared with a thickness of less than 5 μm by in situ crystallisation of silicalite-1. The flux of alkanes is a function of the sorption and intracrystalline diffusion. In mixtures of strongly and weakly adsorbing gases and a high loadings of the strongly adsorbing molecule in the zeolite poze, the flux of the weakly adsorbing molecule is suppressed by the sorption and the mobility of the strongly adsorbing molecule resulting in pore-blocking effects. The separation of these mixtures is mainly based on the sorption and completely different from the permselectivity. At low loadings of the strongly adsorbing molecules the separation is based on the sorption and the diffusion and is the same as the permselectivity. Separation factors for the isomers of butane (n-butane/isobutane) and hexane (hexane/2,2-dimethylbutane) are respectively high (10) and very high (> 2000) at 200°C. These high separation factors are a strong evidence that the membrane shows selectivity by size-exclusion and that transport in pores larger than the zeolite MFI pores (possible defects, etc) can be neglected.     

Removal of pollutants from indoor air using zeolite membranes

MFI-type zeolite membranes prepared by liquid phase hydrothermal synthesis on tubular commercial supports were used to remove model pollutants n-hexane, formaldehyde and benzene present at very low concentration levels (2–230 ppmv) in indoor air. The influence of several operating parameters was studied both in batch and continuous separation experiments. Depending on the operation conditions, permeation fluxes of the organic compound up to 3300, 130 and 30 mg/(m² h) and organic/air separation factors of 250, 6.3 and 38 were achieved for n-hexane, formaldehyde and benzene, respectively.     

Microwave synthesis of zeolite membranes: A review

Significant progress has been achieved in the last years on microwave synthesis of zeolite membranes. In many cases, microwave synthesis has proven to remarkably reduce the synthesis time. In addition, microwave synthesis could also result in different membrane morphology, orientation, composition, and thus the different permeation characteristics as compared with those synthesized by conventional heating. This review attempts to summarize the obtained progress in microwave synthesis of zeolite membranes. Some topics are discussed, including: (1) case study of microwave synthesis of zeolite membranes, e.g. LTA, MFI, AFI, and other types of zeolite membranes; (2) differences between conventional and microwave synthesis; (3) formation mechanism and the so called “specific microwave effect” in the case of microwave synthesis of zeolite membranes; (4) scaling-up of zeolite membrane production by employing microwave heating. The latter three topics are mainly focused on LTA type zeolite membranes. Concluding remarks and future perspective are also suggested in the end.     

Copper-exchanged LTA zeolite membranes with enhanced water flux for ethanol dehydration

Phase-pure and well-intergrown Cu-LTA membranes are developed through copper ions exchange of sodium ions in Na-LTA framework. For pervaporation of 90.0 wt% ethanol/10.0 wt% water mixtures, the Cu-LTA membrane shows much higher water flux than Na-LTA membranes due to the enhancement of the pore size after ions exchange.     

Whey protein fouling of large pore-size ceramic microfiltration membranes at small cross-flow velocity

Microfiltration of whey protein solutions by tubular ceramic membranes, under constant cross-flow and trans-membrane pressure, with periodic backwashing, is investigated using a fully instrumented pilot unit. Relatively large nominal membrane pore size (0.8 μm) insures very high protein transmission, which is desirable in applications such as microbial load reduction. In the first of a sequence of three filtration-backwashing cycles, irreversible and reversible fouling are identified, over the tested pressure range of 5–17.5 psi. Early in the first cycle, especially at the higher pressures, a pore constriction/blocking mechanism appears to be responsible for the irreversible fouling. In the other two cycles only the reversible fouling is significant, possibly due to some kind of protein layer formation on the membrane surface. The permeate flux level tends to increase by increasing trans-membrane pressure up to a near-optimum value of 10 psi, beyond which pressure has a negative effect. This interesting trend is attributed to the interplay of cross-flow velocity, which tends to reduce fouling by promoting re-suspension and breakage of colloidal protein agglomerates, with the trans-membrane pressure (and related flux) which leads to protein layer formation on the membrane and may impose compressive stresses, thereby increasing its resistance to permeation.     

清液体系中T型分子筛膜的高重复性合成与渗透汽化性能

以自制微米级分子筛为晶种,在清液体系中成功合成出高性能的T型分子筛膜,考察了硅铝比、水硅比、碱度及合成温度与时间等条件对膜的生长和渗透汽化性能的影响.结果表明,在摩尔组成为1SiO₂:0.015Al₂O₃:0.41(Na₂O+K₂O):30H₂O的清液体系中,于423K晶化6h的条件下可较快地形成一层厚度为5μm的连续致密纯相T型分子筛膜,较大缩短了膜合成时间且提高了膜致密性.在优化条件下所合成的膜具有优良的分离性能和高重复性.348K时,在10wt%水-90wt%异丙醇混合物体系中膜的渗透通量和分离因子分别高达4.20kg/(m²·h)和7800.     

Nanocomposite fuel cell membranes based on Nafion and acid functionalized zeolite beta nanocrystals

We have prepared nanocomposite proton exchange membranes (PEMs) based on Nafion with sulfonic acid functionalized zeolite beta (AFB) as an additive. 2.5 and 5 wt% AFB composite membranes possess proton conductivity/methanol permeability (selectivity) ratios as much as 93% higher than commercial Nafion 117 at 21 °C, and 63% higher at 80 °C. These 2.5 and 5 wt% AFB composite membranes also outperform commercial Nafion 117 in direct methanol fuel cell performance evaluations. The composite membranes are characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, four-electrode impedance for proton conductivity, two-compartment permeation for methanol crossover, and direct methanol fuel cell performance.     

Preparation of emulsion‐templated fluorinated polymers and their application in oil/water separation

A series of emulsion‐templated fluorinated polymers (polyHIPEs) were first synthesized with introducing 2‐(perfluorohexyl)ethyl methacrylate (PEM) to the external phase of water‐in‐styrene high internal phase emulsion (HIPE) templates. The morphology (i.e., void size and its distribution) of these porous materials could be tuned simply by changing PEM and/or surfactant amount. The synergistic effect between the surface chemistry and surface architecture allowed the polyHIPEs to possess hydrophobicity with a water contact angle of 151°. The superhydrophobicity and oleophilicity of the polyHIPEs, together with their highly open porous structure, make the material a very competitive candidate as a filtration material for oil/water separation in practice with the efficiency of separating dichloromethane from the oil/water mixture of 95%. Such oil/water separating capacity was maintained after 10 cycles of filtration of oil/water, indicating the cyclic usage of the polyHIPE is feasible. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1508–1515     

Nano/subnano-tuning of porous ceramic membranes for molecular separation

In sol–gel processing, porous ceramic membranes can be prepared by sol-coating porous substrates and drying for gelling, followed by a firing process. Ceramic membranes prepared by sol–gel processing can be categorized into amorphous materials such as silica, and crystalline materials such as alumina and titania. Amorphous silica networks, which can be prepared by the polymeric sol route, have ultra-microporous pores that allow small molecules such as helium and hydrogen to permeate. On the other hand, crystalline materials, which are mostly prepared by the colloidal sol route, have nano-sized pores in the range of one to several nanometers. In this article, sol–gel derived SiO₂ and TiO₂ membranes with controlled pore sizes in the range of sub-nano to nanometers will be reviewed with respect to membrane preparation and to their application in the separation of the gas and liquid phases. Ceramic membranes with high performance can be obtained by precise control of membrane structures (pore size, pore size distribution, thickness, pore shape, etc.) and membrane materials (SiO₂, TiO₂, composite oxide, hybrid materials, etc.). Nano/subnano-tuning of porous ceramic membranes is quite important for the improvement of membrane permeability and selectivity.     

Preparation and catalytic activity of titanium silicalite-1 zeolite membrane with TPABr as template

The preparation of the supported titanium silicalite-1 (TS-1) zeolite membrane with inexpensive tetrapropylammonium bromide (TPABr)/weak base synthesis system was studied by three methods, and the catalytic activity of the obtained TS-1 zeolite membrane was evaluated with the oxidation of 2-propanol (IPA) under pervaporation condition. It was found that TS-1 zeolite membrane could be successfully prepared with “seeding” or “seeding in situ” method, but could not be achieved with “in situ” method. Adding a little amount of promoter ions of PO₄³⁻ into the synthesis gel was of benefit to the catalytic activity of the prepared TS-1 zeolite membrane, but had no obvious effect on the membrane layer formation on the mullite porous support. For “seeding” method, the membrane prepared with the synthesis gel having molar composition of SiO₂:0.1TPABr:0.9Et₂NH:0.03TiO₂:80H₂O:0.06H₃PO₄ at 150 °C for 48 h showed the highest oxidation conversion of IPA of 72% accompanied by a flux of 0.35 kg/m² h. Further more, much higher IPA oxidation conversion of 76% accompanied by a flux of 0.65 kg/m² h was obtained for the TS-1 zeolite membrane prepared with the same synthesis gel by “seeding in situ” method at 150 °C for 72 h.     

一种简单组装纳米沸石粒子层的方法及其二次法成膜研究

使用一种简单、新颖的纳米沸石晶体自组装方法, 以γ-氨丙基三甲氧基硅烷(AP-TMS)为偶联剂, 成功地实现了纳米A型沸石粒子在多孔不锈钢、陶瓷以及单晶硅表面的沉积组装, 获得了覆盖度高的续、均匀的沸石粒子层. 组装过程在合成釜内分为载体功能化和晶种化两步. 以该沸石粒子层为晶种二次法成膜, 形成了交织生长的连续、均匀的沸石膜, 并用含少量水的苯甲醛混合液评价了微型膜的渗透蒸发性能, 水-苯甲醛分离系数超过10 000以上. 考察了使用γ-氨丙基三甲氧基硅烷(AP-TMS)、γ-氯丙基三甲氧基硅烷(CP-TMS)和γ-巯丙基三甲氧基硅烷(SP-TMS)三种不同偶联剂时, 纳米A型沸石晶体在多孔不锈钢、陶瓷以及单晶硅表面的自组装效果. 研究发现, 使用CP-TMS作为偶联剂时, 只在不锈钢载体上形成较为连续的粒子层, 而使用SP-TMS作为偶联剂时, 在三种载体上纳米A型沸石粒子均不能沉积形成粒子层. 对偶联剂的作用和粒子组装机制进行了讨论和预测.     

Rapid crystallization and morphological adjustment of zeolite ZSM-5 in nonionic emulsions

Zeolite ZSM-5 was synthesized for the first time in a nonionic emulsion composed of polyoxyethylated alkylphenol, butanol, cyclohexane and tetraethylammonium hydroxide (TEAOH)-containing zeolite synthesis mixture. The crystallization kinetics in the emulsion was investigated and the ZSM-5 product was characterized in detail by XRD, SEM, FT-IR, TG, N₂ adsorption and CHN analysis techniques. Compared with the conventionally hydrothermal synthesis with the same structure directing agent TEAOH, the emulsion system allows rapid crystallization of ZSM-5. The ZSM-5 product exhibits unusual agglomerated structure and possesses larger specific surface area. The FT-IR, TG results plus CHN analysis show the encapsulation of a trace of emulsion components in the emulsion ZSM-5. Control experiments show the emulsion system exerts the crystallization induction and morphological adjustment effects mainly during the aging period. The effects are tentatively attributed to the confined space domains, surfactant-water interaction as well as surfactant-growing crystals interaction existing in the emulsion.     

New low-cost tubular ceramic microfiltration membrane based on natural sand for tangential urban wastewater treatment

In wastewater treatment, the development of low-cost separation methods is of significant importance. Low-cost membranes based on natural materials have become a highly active research topic in recent years. Herein, using low-cost natural Moroccan sand, new ceramic supports have been developed and characterized using different techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), differential thermal analysis (DTA), along with scanning electron microscope (SEM). Plastic paste (average particle size ≤125 µm) was blended with organic additives and water, then the obtained paste was extruded into porous tubular supports. The support had a porosity of 43%, water permeability of 1928 L/h m² bar, excellent chemical and mechanical properties and an average pore diameter in the range of 8–15 µm after firing at 950 °C/2 h. As per SEM analysis, the tubular supports had a smooth and crack-free surface. The slip casting process was used to create a microfiltration layer from the same natural sand powder (average particle size ≤63 µm) using a mixture of powder sand, water, and polyvinyl alcohol solution. The water permeability of the microfiltration membrane sintered at 950 °C/2 h was 1052 L/h m² bar, the average pore size diameter was about 0.90 µm and 82% of pores had a diameter ≤1.00 µm. The obtained microfiltration membrane was tested for the treatment of urban wastewater. The membrane showed excellent separation performance in turbidity removal and chemical oxygen demand.     

A new generation of track etched membranes for microfiltration and ultrafiltration. Part I. Preparation and characterisation

A new experimental apparatus for porous track etched membrane production has been designed, tested and installed near the core of the IEA-R1 nuclear reactor at IPEN-Sao Paulo. The thermal neutron flux close to the centre of the reactor core has been used to produce fission fragments from uranium sample which was deposited on a rod located at the centre of an evacuated aluminium chamber.     

Intercalation of xylenol orange, morin and calmagite into NaY zeolite and their application in dye/zeolite modified electrode

The intercalation of xylenol orange, morin and Calmaigite into NiaY zeolite were studied by XRD, TGA, and BET and diffuse reflectance. These dye incorporated into NaY zeolite by ion exchange in aqueous phase. Results show that xylenol orange can be intercalating better into zeolite. The dye molecules are strongly retained in the channels of zeolites. The prepared intercalated dye/zeolite, for the first time, was used as the modifier for carbon past electrode. The dye/zeolite modified carbon paste electrode was developed for the voltammetric determination of Cu(II). Copper(II) was selectively preconcentrated. Results shows the peak current intensity increased in order of calmagite > xylenol orange > morin dyes intercalated in zeolite. The results agree with complex formation of those dyes as chelating agents with Copper(II).