Fabrication of High-Efficiency Polyvinyl Alcohol Nanofiber Membranes for Air Filtration Based on Principle of Stable Electrospinning

A mass flow matching model(MFMM)was established for studying the stable status of solution electrospinning.The study of the solution droplet status at the needle tip focused on various combinations of applied voltages and injection rates to figure out their influence on steadily fabricating polyvinyl alcohol(PVA)nanofibers prepared from PVA spinning solutions with two different mass fractions(10%and 16%).The results revealed that during the stable electrospinning,the influence resulted from the change of the injection rate approximately canceled out the impact brought by adjusting the applied voltage,leading to almost the same morphology as that of the PVA nanofibers.And the mass fraction of PVA in the spinning solution dominated the structure and the diameter distribution of the electrospun nanofibers.Under stable electrospinning conditions,the composite membrane was produced by depositing PVA nanofibers on the polyethylene terephthalate(PET)nonwoven substrate for an air filtration test.Furthermore,the prepared composite membrane exhibited a high air filtration efficiency(99.97%)and a low pressure drop(120 Pa)for 300-500 nm neutralized polystyrene latex(PSL)aerosol particles,demonstrating its potential as an alternative for a variety of commercial applications in air filtration.

Tannic acid/Fe^(3+)interlayer for preparation of high-permeability polyetherimide organic solvent nanofiltration membranes for organic solvent separation

Organic solvent nanofiltration(OSN)membranes have a great application prospect in organic solvent separation,but the development of OSN membranes is mainly restricted by trade-off between permeability and rejection rate.In this work,a TA/Fe^(3+)polymer was introduced into polyetherimide(PEI)ultrafiltration membranes crosslinked with hexamethylene diamine as the intermediate layer,and OSN membranes with high separation performance and solvent permeability were obtained through interfacial polymerization and solvent activation.The interlayer with high surface hydrophilicity and a fixed pore structure controlled the adsorption/diffusion of the amine monomer during interfacial polymerization,forming a smooth(average surface roughness<5.5 nm),ultra-thin(separation layer thickness reduced from 150 to 16 nm)and dense surface structure polyamide(PA)layer.The PA-Fe^(3+)_3-HDA/PEI membrane retained more than 94%of methyl blue(BS)in 0.1 g·L^(-1)BS ethanol solution at 0.6 MPa,and the ethanol permeation reached 28.56 L^(-1)·m^(-2)·h^(-1).The average flux recovery ratio(FRR)of PA-Fe^(3+)_(3)-HDA/PEI membrane was found to be 84%,which has better fouling resistance than PA-HDA/PEI membrane,and it was found to have better stability performance through different solvent immersion experiments and continuous operation in 0.1 g·L^(-1)BS ethanol solution.Compared with thin-film composite nanofiltration membranes,the PA-Fe^(3+)_(3)-HDA/PEI membrane can be manufactured from an economical and environment-friendly method and overcomes the trade-off between permeability and rejection rate,showing great application potential in organic solvent separation systems.

Effect of Heat Treatment on Structures and Properties of Polyurethane Blend Ultrafiltration Membranes

The polyurethane/polyacrylonitrile (PU/PAN) and polyurethane/cellulose acetate (PU/CA) blend ultra filtration membranes were prepared based on Loeb-Sourirajan phase transition method. The change of the structures and properties of the PU/PAN and PU/CA membranes with the heat treatment process was studied. The results showed: the water flux decreased and retention increased with the increase of heat treatment temperature of PU/PAN blend membrane, but the water flux of PU/CA blend membrane got the maximum with heat treatment temperature of 60℃ and decreased rapidly with the heat treatment temperature of 100 ℃. The interfacial microvoid structure and its influence on the properties of PU/PAN and PU/CA blend membranes were studied.

The effect of coupling coagulation and flocculation with membrane filtration in water treatment:A review

Water supply and sanitation demands are foreseen to face enormous challenges over the coming decades to meet the fast growing needs in a global perspective. Significant growth in the industry is predicted and membrane separation technologies have been identified as one of the possible solutions to meet future demands. Application and implementation of membrane technology is expected both in production of potable water as well as in treatment of wastewater. In potable water production membranes are substituting conventional separation technologies due to the superior performance, potential for less chemical use and sludge production, as well as the potential to fulfill hygienic barrier requirements. Membrane bio-reactor （MBR） technology is probably the membrane process which has had most success and has the best prospects for the future in wastewater treatment. Trends and developments indicate that this technology is becoming accepted and is rapidly becoming the best available technology for many wastewater treatment applications. A major drawback of MBR systems is membrane fouling. Studies have shown that fouling mitigation in MBR systems can potentially be done by coupling coagulation and flocculation to the process.

Performance investigation of Fe_3O_4 blended poly(vinylidene fluoride) membrane on filtration and benzyl alcohol oxidation:Evaluation of sufficiency for catalytic reactors

Fe_3O_4-PVDF membranes were prepared by blending of magnetic Fe_3O_4 powders with polyvinylidene fluoride to investigate whether those were usable or not in catalytic membrane reactors. Filtration performances and catalytic activity of membranes in microwave conditions were measured in separate processes. Composite Fe_3O_4-PVDF membranes were characterized by TG-DTA, FTIR, XRD, SEM and contact angle techniques.Disappearing of α-phases at PVDF was observed with increasing amount of additives from XRD diffraction patterns. Decomposition of polymer fastened due to catalytic effect of Fe_3O_4. Finger-like structures and large number of small pores were observed at the SEM images. Those provided effective transportation of substrate among the active sites of catalyst. At the experiments conducted in batch reactor, 51%, 77%, 66% and 63% benzyl alcohol conversion were recorded for 2%, 4%, 6% and 8% Fe_3O_4-PVDF composite pieces respectively. Catalyst were separated magnetically and reused several times. On the other hand Fe_3O_4 blended PVDF membranes provided improved flux and BSA rejection compared with performance of bare PVDF membrane; 41.6% BSA rejection was obtained with 4% Fe_3O_4-PVDF whereas it was only 6.7% for PVDF. Fe_3O_4-PVDF composites performed high activity for the benzyl alcohol oxidation in batch reactor and also better filtration at filtration cell. These results promise to obtain practical and low cost membrane material for catalytic reactors usable in microwave support to get fast results.

Evaluation of media for simultaneous enumeration of total coliform and Escherichia coli in drinking water supplies by membrane filtration techniques

This study evaluated three different dehydrated media for simultaneous detection and enumeration of total coliform （TC） and Escherichia coil in drinking water samples with a standard membrane filtration procedure. The experiment indicated that the differential coliform agar （DCA） medium was the most effective among the tested media in enumerating TC and E. coil, without the need for extensive accompanying confirmation tests. The results for DCA medium were highly reproducible for both TC and E. coil with standard deviation of 6.0 and 6.1, respectively. A high agreement （82%） was found between DCA and m-Endo media on 152 drinking water samples in terms of TC positive. The DCA medium also reduced concealment of background bacteria.

Zeolite powder addition to improve the performance of submerged gravitation-filtration membrane bioreactor

In this study, the effect of zeolite powder addition on submerged membrane bioreactor （SMBR） on membrane permeability, and the removals for COD, NH3-N, TN were investigated. Through the parallel operation of control and test systems, it was found that the zeolite powder addition could alleviate the ultra-filtration membrane fouling and enhance the membrane permeability. On the basis of experimental investigations, a concept of ＂protection coating layer＂ was proposed to illustrate the phenomenon of UF membrane fouling. In addition, the removal for COD in test system was more stable, a little higher compared to the control system. Due to the combination of nitrification and ion exchange, a more excellent removal for NH3-N in test system was obtained regardless of influent NH3-N loading rate. It was also found that a mean 25% higher TN removal took place in the test system, and ion exchange and simultaneous nitrification and de-nitrification were analyzed to be main factors. During the stable operation period, the SOURs of test zeolite powder added sludge and control activated sludge were measured to be 75 mgO2/（gMLVSS, h） and 24 mgO2/（gMLVSS, h） respectively, it meant that the zeolite powder addition could enhance the microorganism activity significantly.

Model Study on a Submerged Catalysis/Membrane Filtration System for Phenol Hydroxylation Catalyzed by TS-1

This research is focused on the development of a simple design model of the submerged catalysis/membrane filtration(catalysis/MF)system for phenol hydroxylation over TS-1 based on the material balance of the phenol under steady state and the reported kinetic studies.Based on the developed model,the theoretical phenol conversions at steady state could be calculated using the kinetic parameters obtained from the previous batch experiments.The theoretical conversions are in good agreement with the experimental data obtained in the submerged catalysis/MF system within relative error of±5%.The model can be used to determine the optimal experimental conditions to carry out the phenol hydroxylation over TS-1 in the submerged catalysis/MF system.

Theoretical Study on Dynamic Filtration with the Membrane in Simple Harmonic Motion

A simple harmonic motion is proposed to make the membrane nove in a simple harmonic way so as to enhance the membrane filtration, and minimize the membrane fouling and concentration polarization. The velocity distribution and pressure distribution are deduced from the Navier-Stokes equation on the basis of a laminar flow when the membrane rotates at the speed of A sin(αt). And then the shear stress, shear force, moment of force on the membrane surface and power consumed by viscous force are calculated. The velocity distribution demonstrates that the phase of membrane velocity does not synchronize with that of shear stress. The simple harmonic motion can result in self-cleaning, optimize energy utilization, provide the velocity field with instability, and make the feed fluid fluctuation. It also results in higher shear stress on the membrane surface than the constant motion when they consume the same quantitative energy.

Simulation of Structural Characteristics and Depth Filtration Elements in Interconnected Nanofibrous Membrane Based on Adaptive Image Analysis

Due to their unique structural features, electrospun membranes have gained considerable attention for use in applications where quality of depth filtration is a dominant performance factor. To elucidate the depth filtration phenomena it is important to quantify the intrinsic structural properties independent from the dynamics of transport media. Several methods have been proposed for structural characterization of such membranes. However, these methods do not meet the requirement for the quantification of intrinsic structural properties in depth filtration. This may be due to the complex influence of transport media dynamics and structural elements in the depth filtration process. In addition, the different morphological architectures of electrospun membranes present obstacles to precise quantification. This paper seeks to quantify the structural characteristics of electrospun membranes by introducing a robust image analysis technique and exploiting it to evaluate the permeation-filtration mechanism. To this end, a nanostructured fibrous network was simulated as an ideal membrane using adaptive local criteria in the image analysis. The reliability of the proposed approach was validated with measurements and comparison of structural characteristics in different morphological conditions. The results were found to be well compatible with empirical observations of perfect membrane structures. This approach, based on optimization of electrospinning parameters, may pave the way for producing optimal membrane structures for boosting the performance of electrospun membranes in end-use applications.

Purification of bioethanol fermentation broth using hydrophilic PVA crosslinked PVDF-GO/TiO_(2) membrane

The presence of impurities in the bioethanol fermentation broth should be removed to mitigate any possible ineffective refining processes as well as to enhance bioethanol production. In this study, a prefiltration process was carried out for separating fermentation yeast cells and residual substrates using a microfiltration membrane. Hydrophilic polyvinylidene fluoride-graphene oxide/titanium dioxide(PVDF-GO/TiO_(2)) membrane with polyvinyl alcohol(PVA) surface-coating modification was fabricated and characterized. Membrane modification attempts have succeeded in increasing the hydrophilicity as indicated by contact angle decline from 72.10° to 34.83° and affinity towards water leading to higher water permeability. The performance evaluation showed that 90.77% of unwanted by-products(yeast cells and residual substrate) can be removed. This high rejection is also followed by a high and stable flux performance at 40.20 L·m^(-2)·h^(-1) where the flux was increased by 13 times compared to that of the neat membrane. The PVA-coated PVDF-GO/TiO2showed the best anti-biofouling performance with a flux recovery ratio after 5 days incubation(FRR5d) of 93.55%. This membrane material has excellent prospects in future membrane development for either in-situ application or as a pre-filtration in the fermentation process to separate living cells and residual substrates before being further processed in the refining processes.

Recent Progress of Fabrication,Characterization,and Applications of Anodic Aluminum Oxide(AAO)Membrane:A Review

The progress of membrane technology with the development of membranes with controlled parameters led to porous membranes.These membranes can be formed using different methods and have numerous applications in science and technology.Anodization of aluminum in this aspect is an electro-synthetic process that changes the surface of the metal through oxidation to deliver an anodic oxide layer.This process results in a self-coordinated,exceptional cluster of round and hollow formed pores with controllable pore widths,periodicity,and thickness.Categorization in barrier type and porous type films,and different methods for the preparation of membranes,have been discussed.After the initial introduction,the paper proceeds with a brief overview of anodizing process.That engages anodic aluminum oxide(AAO)layers to be used as formats in various nanotechnology applications without the necessity for expensive lithographical systems.This review article surveys the current status of the investigation on AAO membranes.A comprehensive analysis is performed on AAO membranes in applications;filtration,sensors,drug delivery,template-assisted growth of various nanostructures.Their multiple usages in nanotechnology have also been discussed to gather nanomaterials and devices or unite theminto specific applications,such as nano-electronic gadgets,channel layers,and clinical platforms tissue designing.From this review,the fact that the specified enhancement of properties of AAO can be done by varying geometric parameters of AAO has been highlighted.No review paper focused on a detailed discussion of multiple applications of AAO with prospects and challenges.Also,it is a challenge for the research community to compare results reported in the literature.This paper provides tables for easy comparison of reported applications with membrane parameters.This review paper represents the formation,properties,applications with objective consideration of the prospects and challenges of AAO applications.The prospects may appeal to researchers to promote the development of unique membranes with functionalization and controlled geometric parameters and check the feasibility of the AAO membranes in nanotechnology and devices.

Electrochemical filtration for drinking water purification:A review on membrane materials,mechanisms and roles

Electrochemical filtration can not only enrich low concentrations of pollutants but also produce reactive oxygen species to interact with toxic pollutants with the assistance of a power supply,making it an effective strategy for drinking water purification.In addition,the application of electrochemical filtration facilitates the reduction of pretreatment procedures and the use of chemicals,which has outstanding potential for maximizing process simplicity and reducing operating costs,enabling the production of safe drinking water in smaller installations.In recent years,the research on electrochemical filtration has gradually increased,but there has been a lack of attention on its application in the removal of low concentrations of pollutants from low conductivity water.In this review,membrane substrates and electrocatalysts used to improve the performance of electrochemical membranes are briefly summarized.Meanwhile,the application prospects of emerging single-atom catalysts in electrochemical filtration are also presented.Thereafter,several electrochemical advanced oxidation processes coupled with membrane filtration are described,and the related working mechanisms and their advantages and shortcomings used in drinking water purification are illustrated.Finally,the roles of electrochemical filtration in drinking water purification are presented,and the main problems and future perspectives of electrochemical filtration in the removal of low concentration pollutants are discussed.

Ba^(2+)/Ca^(2+)co-crosslinked alginate hydrogel filtration membrane with high strength,high flux and stability for dye/salt separation

Alginate is a natural polysaccharide polymer.Hydrogel filtration membranes prepared from alginate show excellent fouling resistance and controllable separation performance,but poor mechanical properties limit the use of algae hydrogels.In this study,Ba^(2+)/Ca^(2+)co-crosslinked alginate(Ba/CaAlg)hydrogel membrane was prepared by cross-linking sodium alginate with a blend aqueous solution of barium ions and calcium ions,and the membrane was applied to the separation of dyes/salts from dyeing wastewater.Compared with the CaAlg membrane,the Ba/CaAlg hydrogel membrane exhibited more stable structure,and the mechanical properties and salt tolerance of the membrane were significantly improved.The flux of Ba/CaAlg membrane for methyl blue/sodium chloride mixed solution reached 43.5 L m^(−2) h^(−1),which was significantly higher than that of CaAlg membrane.Besides,the Ba/CaAlg membrane showed higher dye rejection(>99.6%)and lower salt rejection(<8.2%).The structure of Ba/CaAlg membrane was preliminarily simulated by molecular dynamics,and the pore size and distribution of the membrane were calculated.The Ba/CaAlg membrane has a broad application prospect in dyes/salts separation.

Changes of Resistance During Polyelectrolyte-enhanced Stirred Batch Ultrafiltration

The permeation flux or the resistance in the ultrafiltration process is mainly limited by osmotic pressure, and it may originate from various kinds of polymer interactions. However, the real origin of permeation resistance hasn’t been clarified yet in the light of polymer solution nature. The removal of nitrate contamination by polyelectrolytes was carried out with stirred batch ultrafiltration. The polyelectrolyte concentrations both in permeate and retentate were analyzed with total organic carbon analyzer and permeate mass was acquired by electronic balance connected with computer. The total resistance was calculated and interpreted based on the osmotic pressures in three concentration regimes. In the dilute region, the resistance was proportional to polymer concentration; in the semidilute region, the resistance depended on polymer concentration in the parabolic relationship; in the highly concentrated solution regime, the osmotic pressure factor (OPF) would dominate the total resistance; and the deviation from OPF control could come from the electrostatic repulsion between the tightly compacted and charged polyelectrolyte particles at extremely concentrated solution regime. It was first found that dilute and semidilute concentration regions can be easily detected by plotting the log-log curves of the polymer concentration versus the ratio of the total resistance to polymer concentration. The new concept OPF was defined and did work well at highly concentrated regime.

Microfiltration,ultrafiltration and nanofiltration as a post-treatment of biological treatment process with references to oil field produced water of Moran oilfield of Assam

The selection of an apt technology for the treatment of Oilfield Produced Water(OFPW)depends mainly on the quality of OFPW and methods of pre-and post-treatment processes.The most challenging part of the OFPW treatment process is the removal of Suspended Solid(SS),Oil&Grease(O&G)and dissolved organics.SS and O&G pose an acute problem to the membrane filtration system by fouling the membrane surface which increases operation&maintenance costs and decreases the life of the membrane.Fouling of the membrane surface is mainly attributed to the presence of low molecular weight aromatic compounds and naphthenic acids in the suspended and dissolved organic compounds.Thus,the removal of these suspended and dissolved organic compounds before membrane filtration proffers a challenge to the researchers.In this research,bioremediation process has been applied to remove the organic compounds and the performance and fouling behaviour of hollow fibre Microfiltration(MF),Ultrafiltration(UF)and Nanofiltration(NF)membranes after the bioremediation process has been analyzed in detail.The level of toxicity was determined by comparing the pollutants with the safe discharge limit for disposal into the environment set by Central Pollution Control Board(CPCB),India.The research presents its novelty by using a hydrocarbon-degrading bacteria,Pseudomonas aeruginosa for the Reduction of Organic Loads(ROL)from OFPW of Moran oil field of Upper Assam as a pre-treatment to membrane filtration.The Total Sum Corrected Area(TSCA)method through chromatographic analyses was used for this.The organic loads removal from OFPW by the TSCA method was found to be 67-100%,100%and 100%after 7,14 and 21 days of bioremediation respectively.The major parameters in feed OFPW of Moran oil field were found to be pH(7.5-9.3),Total Dissolved Solid(TDS)(1.79-4.75)ppt,O&G(1.78-2.8)ppt,Salinity(2.94-6.98)ppt,Chloride(Cl^(-))(1.6-3.86)ppt,Bicarbonate(HCO_(3)^(-))(2.89-4.03)ppt.It was observed that the ranges of pollutants removal by NF was highest such as TDS(26-86%),salinity(81-86%),turbidity(78-94%),hardness(67-75%),O&G(96-99%),Cl^(-)(80-89%)and HCO_(3)^(-)(95-97%).

Meltblown fabric vs nanofiber membrane, which is better for fabricating personal protective equipments

The coronavirus disease 2019(COVID-19)pandemic has led to a great demand on the personal protection products such as reusable masks.As a key raw material for masks,meltblown fabrics play an important role in rejection of aerosols.However,the electrostatic dominated aerosol rejection mechanism of meltblown fabrics prevents the mask from maintaining the desired protective effect after the static charge degradation.Herein,novel reusable masks with high aerosols rejection efficiency were fabricated by the introduction of spider-web bionic nanofiber membrane(nano cobweb-biomimetic membrane).The reuse stability of meltblown and nanofiber membrane mask was separately evaluated by infiltrating water,75%alcohol solution,and exposing under ultraviolet(UV)light.After the water immersion test,the filtration efficiency of meltblown mask was decreased to about 79%,while the nanofiber membrane was maintained at 99%.The same phenomenon could be observed after the 75%alcohol treatment,a high filtration efficiency of 99%was maintained in nanofiber membrane,but obvious negative effect was observed in meltblown mask,which decreased to about 50%.In addition,after long-term expose under UV light,no filtration efficiency decrease was observed in nanofiber membrane,which provide a suitable way to disinfect the potential carried virus.This work successfully achieved the daily disinfection and reuse of masks,which effectively alleviate the shortage of masks during this special period.

Membrane preconcentration of iron in seawater samples and on-site determination in spectrophotometry

A novel method for on-site determination of trace iron was developed using membrane preconcentration and spectrophotometric detection. Fe(Ⅱ)-ferrozine complex was reacted with cetyltrimethylammonium bromide (CTAB) to form a Fe(Ⅱ)-ferrozine-CTAB paired compound, which was collected on a membrane by filtration under vacuum. The membrane was immersed in 2 mL of ethanol-nitric acid and the absorbance of the solution measured for quantitative analysis. Various factors affecting the iron collection and determination were investigated. With different sample preconcentration volumes, the range of determination was broadened to 0.5-120 g/L. The detection limit of this method reached 0.19 g/L and the recoveries were between 97.2 and 109% when the concentration enrichment was about 45. The relative standard deviation (n = 7) was 1.9% for samples containing 10 g/L Fe. Twelve seawater samples were analyzed on-site using the proposed method, and two were also analyzed in inductively coupled plasma mass spectrometry. No significant difference was shown between the two methods by the Student's t-test. The method has also been used on-site for iron enrichment experiments with phytoplankton and concluded to be simple, accurate and inexpensive.