Modification of the Surfaces of Polymer Films Irradiated by Heavy Ions and Nucleopore Nanofilters by XeF2 Vapors

The effect of xenon difluoride (XeF₂) vapors on the surface properties of the polymer films irradiated by heavy ions and of the nucleopore nanofilters produced from these films is studied. The procedure for modifying nucleopore membranes made of poly(ethylene terephthalate) and polyimide in XeF₂ vapors is developed. The hydrophilicity, electrosurface properties, and selectivity of modified membranes are investigated. It is shown that the water contact angle on the membrane surface decreases as a result of modification, and the extent of its change depends on the duration and temperature of membrane treatment. Electrokinetic measurements did not reveal any changes in the surface charge during the modification of the membranes prepared from poly(ethylene terephthalate), but their ion selectivity increased twofold. It is shown that the hydrodynamic diameter of the pores of modified membranes reversibly decreases with an increase in transmembrane pressure. The dislosed effects are explained by the presence of an elastoplastic gel-layer on the surfaces of the membrane and its pores. The gel-layer accumulates considerable surface and bulk charges and is characterized by the high hydraulic resistance hindering the convective ion transport.     

Preparation and characterization of metallic membrane using wire arc spraying

Metallic membranes can be prepared by various techniques. This work introduces a novel method for the preparation of metallic membranes using wire arc spraying. The formed metallic membranes were characterized by metallographic techniques such as microscopy image analysis. The distance between gun and the substrate surface, which is called spray distance or gun distance, was selected as the variable of metal spraying. The effects of gun distance on coating properties and membrane performance were investigated. The metallographic and performance data showed that the range of 35–40 cm is the optimum gun distance for spraying. Ion rejection capability of the prepared membrane was tested using saline water as the feed. Moreover the filtration capability of the prepared membranes for blue indigo dye particles was investigated. Energy dispersive X-ray (EDX) analysis and SEM technique were used for the investigation of filtration mechanism. The results indicate that the prepared stainless steel membrane is able to efficiently remove particles from water.     

Synthesis of lanthanum oxide doped photocatalytic nano titanium oxide through aqueous sol–gel method for titania multifunctional ultrafiltration membrane

An all aqueous sol gel route has been demonstrated for the synthesis of titania multifunctional ultrafiltration membrane on porous alumina substrate. Doping with lanthana was used to increase the thermal stability of anatase phase. This resulted in a nanoporous membrane with considerable percentage of anatase phase even after consolidation at 800°C. The highly homogeneous membranes with a thickness of ~4–5 μm could be observed in SEM. The presence of anatase phase ensured higher photoactivity for the doped membrane compared to the undoped one. The performance of the membrane was tested based on molecular weight cut off and a very high (>90%) filtration efficiency was observed on Bovine Serum Albumin of molecular weight 66 kD. Rejection of 11 nm sized particles points to the uniform nanoporous nature of these highly efficient membranes.     

The effect of diffusion on nanoaerosol filtration through porous materials with allowance for desorption processes

The effects of the finite residence time of aerosol particles in the bound state and their detachment due to thermal fluctuations on the filtration efficiency of porous and fibrous materials have been investigated with allowance for longitudinal diffusion in a flow. It has been shown that the desorption of particles affects the filtration efficiency even at times shorter than residence time τ_d of the particles in the bound state, while, at t ? τ_d, filtration stops. Allowance for the diffusion of aerosol particles in the flow leads to a decrease in the filtration efficiency as compared with the calculations performed without taking into account the longitudinal diffusion.     

Electrospun Polyacrylonitrile Nanofibrous Membranes for Point-of-Use Water and Air Cleaning

Novel electrospun polyacrylonitrile (PAN) nanofibrous membranes were prepared by using heat-press lamination under various conditions. The air permeability and the burst-pressure tests were run to select the membranes for point-of-use air and water cleaning. Membrane characterization was performed by using scanning electron microscopy, contact angle, and average pore size measurements. Selected membranes were used for both air dust filtration and cross-flow water filtration tests. Air dust filter results indicated that electrospun PAN nanofibrous membranes showed very high air-dust filtration efficiency of more than 99.99 % in between PM_0.3 and PM_2.5, whereas cross-flow filtration test showed very high water permeability over 600 L/(m²hbar) after 6 h of operation. Combining their excellent efficiency and water permeability, these membranes offer an ideal solution to filter both air and water pollutants.     

The Charge of the Pores of Poly(ethylene terephthalate) Nucleopore Membranes

The electrosurface properties of nucleopore membranes are studied by the streaming potential and EPR spectroscopy methods. Large differences between the values of surface charge of pores obtained by these methods are disclosed. This effect can be explained by the presence of the developed gel-layer on the pore surface.     

SEM研究PET核孔膜的光接枝聚合

以PET核孔膜为基材 ,二苯甲酮为引发剂 ,采用光接枝方法实现了丙烯酸和丙烯酰胺在核孔膜上的接枝 ,用扫描电镜 (SEM)直接观察了接枝前后膜的表面形貌 ,考察了不同因素对于接枝位置和接枝效果的影响 .发现膜材料本身特性和接枝反应条件对接枝位置和接枝效果有较大影响 .通过光接枝能够实现膜孔的封盖、缩小、填堵等不同的效果 .采用正侧涂布法反应 ,标准直孔 ,特别是小孔径膜 (0 4 μm) ,不利于孔内的接枝 ,接枝主要在膜的表面 ,从而产生孔封盖效应 .双锥形的非标准直孔 ,由于孔壁的受光性好 ,容易发生孔壁上的接枝从而被填充 .大孔径的膜 (5 μm) ,需要加入交联剂才能在孔壁上形成厚的接枝层 .提出了一种新的反应方法 背侧吸附法 ,反应液依靠毛细作用由膜的底部吸入膜孔 ,膜的向光侧表面不存在反应液 ,接枝只发生在膜孔内 ,从而得到很好的填孔效果 .     

Histograms of the size distribution of kraft lignin particles in aqueous solutions at various pH values

The size distribution of kraft lignin particles in aqueous solutions in a wide pH range (9.5−2.0) was studied by filtration through track membranes.     

Efficiency of inertial deposition of aerosol particles in fibrous filters with regard to particle rebounds from fibers

The inertial deposition of submicron aerosol nanoparticles onto fibers during gas filtration through fine-fiber filters is considered. It is shown that there is critical filtration velocity U* below which the energy loss upon collisions has no influence on the filtration efficiency. Above this critical velocity, the filtration efficiency depends on the mechanism of the inelastic energy loss and can be noticeably lower than the result of its estimation with no allowance for the particle rebound. For a rather dense fibrous medium, when not all particles that have rebounded from a fiber have time to attain the flow velocity before the next collision with another fiber, the filtration efficiency depends on the velocity distribution of the rebounding particles. It is shown that, in this case, the filtration efficiency must increase with the packing density of a filter.     

光接枝法制备新型pH开关核孔膜

用表面光接枝方法制备了具有pH开关特性的丙烯酸接枝PET核孔膜 .XPS、SEM和AFM的表征结果证明 ,接枝膜具有非对称结构 ,丙烯酸接枝层主要在膜的向光侧表面 ,膜背侧和膜孔内没有变化 .膜孔周围的接枝链在湿态下沉入膜孔 ,接枝层对膜孔顶部产生封盖 .接枝链的体积随环境pH值的不同而变化 ,从而控制接枝膜的滤过特性 .在低接枝程度时 ,接枝链体积变化对膜孔径的影响小 ,不具有pH开关特性 ,但是接枝提高了膜的亲水性 ,通量得到提高 ;接枝程度达到一定程度时 (如 0 5 %) ,膜孔径受接枝链体积变化的影响显著 ,接枝膜表现出pH开关效应 .在pH大于 5时 ,接枝膜通量恒定 ,基本不受溶液pH值影响 .当pH值小于 4时 ,膜通量随溶液酸性的增加迅速升高 .接枝膜的开关幅度JpH =2 JpH =6 8,随接枝程度的增加而增加 .膜的通量和开关幅度可以通过接枝程度来调节     

Factors affecting membrane fouling reduction by surface modification and backpulsing

Several factors affecting microfiltration membrane fouling and cleaning, including backpulsing, crossflushing, backwashing, particle size, membrane surface chemistry, and ionic strength, were investigated with suspensions of latex beads. Approximately two-fold permeate volume enhancements over 1 h of filtration were obtained by using water or gas backpulsing, and 50% enhancement was obtained with crossflushing, for filtration of 1.0 μm diameter carboxylate modified latex (CML) particles using unmodified polypropylene (PP) membranes of 0.3 μm nominal pore diameter. When 0.2 μm diameter CML particles or mixtures of 1.0 and 0.2 μm CML particles were used, however, the average flux decreased 60% compared with using 1.0 μm CML particles for experiments with or without backpulsing.PP membranes were rendered hydrophilic with neutral or positively on negatively charged surfaces by grafting monomers of poly(ethylene glycol 200) monomethacrylate (PEG200MA), dimethyl aminoethyl methacrylate (DMAEMA), or acrylic acid (AA), respectively, to the base PP membranes. Filtration experiments show that fouling is not strongly dependent on membrane surface chemistry for filtration of 1.0 μm CML particles without backpulsing. With backpulsing, however, a 10% increase and a 20% decrease of permeate volumes collected in 1 h were observed when the CML particles and the membranes had like charges and opposite charges, respectively, compared to the permeate collected with the unmodified membrane. Using the PP membranes modified with AA, permeate volumes with backpulsing decreased 30 and 40% when NaCl concentrations of 0.01 and 0.1 M, respectively, were added to the feed. However, the permeate volumes did not vary significantly with changing ionic strength for filtration without backpulsing.     

Tunable filtration media employing alternating current electrokinetics

Separation of colloidal particles from aqueous media by barrier filtration is typically dictated by sieving mechanisms. Here, we demonstrate that colloid filtration by porous membranes can be considerably augmented by suitably superimposing an alternating current (AC) electric field on the membrane. The combined steric-dielectrophoretic filtration can result in very high rejection of the particles compared to solely steric rejection.     

Pore blocking mechanisms during early stages of membrane fouling by colloids

A method based on a simple linear regression fitting was proposed and used to determine the type, the chronological sequence, and the relative importance of individual fouling mechanisms in experiments on the dead-end filtration of colloidal suspensions with membranes ranging from loose ultrafiltration (UF) to nanofiltration (NF) to non-porous reverse osmosis (RO). For all membranes, flux decline was consistent with one or more pore blocking mechanisms during the earlier stages and with the cake filtration mechanism during the later stages of filtration. For ultrafiltration membranes, pore blocking was identified as the largest contributor to the observed flux decline. The chronological sequence of blocking mechanisms was interpreted to depend on the size distribution and surface density of membrane pores. For salt-rejecting membranes, the flux decline during the earlier stages of filtration was attributed to either intermediate blocking of relatively more permeable areas of the membrane skin, or to the cake filtration in its early transient stages, or a combination of these two mechanisms. The findings emphasize the practical importance of the clear identification of, and differentiation between mechanisms of pore blocking and cake formation as determining the potential for the irreversible fouling of membranes and the efficiency of membrane cleaning.     

Improvement of pore geometry and performances of poly(ethylene terephthalate) track membranes by a protective layer method using plasma-induced graft polymerization of 1H,1H,2H-perfluoro-1-octene monomer

The process of geometrical modification of pores in poly(ethylene terephthalate) track-etched membranes (TM) by use of plasma deposition of a fluorine-containing polymer protective layer on one membrane surface and alkali etching of the other surface has been studied in order to produce membranes with improved performance characteristics. Samples of membranes with conical pores have been obtained which have better filtration efficiency compared with initial TM with cylindric pores. Plasma polymerization of 1H,1H,2H-perfluoro-1-octene at the membrane surface was used to produce the protective layer resistant to alkali solutions. The occurrence of plasma modification and changing of pore geometry have been verified by X-ray photoelectron spectroscopy and scanning electron microscopy studies. The filtration efficiency and selectivity of the modified membranes have been studied.     

Microporous silica membranes deposited on porous supports by filtration

Water based particulate silica sols have been coated onto Anodisc® filters by filtration. The membranes prepared by this technique are more uniform than those formed by slip-casting. The average diameter of the silica particles used in these studies is 6 nm. Unsupported silica membranes formed from these sols have a microporous structure. The adhesion between silica and the alumina support is influenced by the sol pH. Coating thickness can be controlled by the concentration and volume of the sol filtered. Polyvinyl alcohol (PVA) was used to improve adhesion and to prevent cracking during drying. When the PVA/SiO₂ ratio by weight is less than 20%, the membranes retain their microporosity after firing. The membranes prepared by this filtration method have their pore size in Knudsen diffusion range.     

Mixed-matrix membrane adsorbers for protein separation

The separation of two similarly sized proteins, bovine serum albumin (BSA) and bovine hemoglobin (Hb) was carried out using a new type of ion-exchange mixed-matrix adsorber membranes. The adsorber membranes were prepared by incorporation of various types of Lewatit ion-exchange resins into an ethylene-vinyl alcohol copolymer porous structure. The obtained heterogeneous matrices, composed of solid particles surrounded by the polymeric film, display high static and dynamic protein adsorption capacities. The effect of operational parameters such as filtration flow-rate, pH, and ionic strength on the protein separation performances was investigated for cation- as well as anion-exchange adsorber membranes. An average separation factor was calculated by numerical integration of the protein concentration in the permeate curve during the filtration run. High average separation factor values were obtained for BSA-Hb separation at physiological ionic strength with a filtration flow-rate up to 20 1/h per m2, until the protein breakthrough point at 10% of the feed concentration.     

Filtration of nanoaerosols through porous materials with allowance for desorption processes

The effects of finite residence time of aerosol particles in a bound state and their detachment due to thermal fluctuations on the filtration efficiency of porous and fibrous filters have been studied. It has been shown that, when desorption processes are taken into account, nanoparticle filtration efficiency decreases with time already at times that are short compared with the residence time of particles in the bound state.     

Nanoaerosol Filtration with Fine-Fiber Polydisperse Filters

The self-consistent theory of nanoaerosol filtration has been considered at small Peclet numbers. It has been shown that, at Pe < 1, it is necessary to consider the deposition of particles simultaneously on thePe < entire ensemble of fibers. Only at can the filtration efficiency be found from the collection efficiencies calculated separately for each fiber. The self-consistent theory has been used to estimate the efficiencies of filtration with polydisperse fibrous filters. The penetrations of particles through filters with different variances of the functions of fiber length distribution over fiber radii have been compared at a constant packing density or a constant total length of all fibers. It has been shown that, at a constant packing density, a rise in the variance leads to a decrease in the filtration efficiency, while, at a constant total fiber length, the efficiency is almost independent of the width of the distribution function.     

Particle-loaded hollow-fiber membrane adsorbers for lysozyme separation

The separation of lysozyme (LZ), a valuable enzyme naturally present in chicken egg white, was carried out using a new type of ion exchange hollow-fiber membranes. Functionalities were incorporated into the polymeric membranes by dispersing ion-exchange resins (IERs) in a microporous structure formed by phase inversion. The obtained hollow-fibers were composed of ion-exchange particles surrounded by a polymeric matrix and possessed both high static and dynamic adsorption capacities of more than 60 mg/ml membrane. The hollow-fiber membrane adsorbers were connected in series with different numbers of fibers thereby increasing the effective thickness and the protein residence time within the module. By choosing appropriate operation conditions, the membranes adsorbed solely LZ from fresh chicken egg white (eventually also the minor component avidin), whereas the adsorption of ovalbumin, ovotransferrin, and other low isoelectric point proteins was negligible. An average separation factor for LZ of about 150 was calculated by numerical integration of the protein concentrations in the elution curve during the filtration run. The effect of the filtration flow rate, protein concentration and ionic strength on the membrane's performance was investigated to determine the optimum operation parameters.     

Some Aspects of Magnetic Filtration Theory for Removal of Fine Particles from Aqueous Suspensions

The magnetic filtration theory was evaluated to intensify the filtration of industrial fluids by magnetic filters. Effects of filtration velocity and external magnetic field intensity on filter performance were investigated and the dependence of the logarithmic efficiency coefficient on filtration velocity was questioned. It was concluded that change in the magnetic susceptibility of the dispersion particles, caused by external magnetic field, and change in the flow rate properties of the liquid alongside the filter pores are the most essential factors to be considered in the design, development, and modeling of magnetic filtration systems in various industrial areas.