Membranes For Water Purification Research Articles

Graphene Oxide/Polyamide-Based Nanofiltration Membranes for Water Purification

A novel electric field-assisted strategy to fabricate graphene oxide (GO)-functionalized nanofiltration (NF) membranes was reported. The resulting polyamide (PA) NF membranes were formed by interfacial polymerization (IP) of trimesoyl chloride (TMC) in an organic phase and piperazine as well as GO with a concentration between 0.1 and 0.5 in the water phase under an electric field using a polysulfone (PSF) ultrafiltration membrane as a substrate. Due to the electric field-induced repulsion in GO during polymerization, the resulting GO/PA nanofiltration membranes showed a Turing-like structure in the composite functional layer as well as higher hydrophilicity. As a result, a substantially improved water flux was observed, and TFC-G0.3-DC even showed a water permeability of 28.5 L·m–2·h–1·bar–1, which is ∼30% higher than that of its analogue TFC-G0.3 without an electric field. Additionally, the TFC-G0.3-DC NF membrane also demonstrated high rejection rates for Na2SO4 (97.6%) and MgSO4 (97.3%) at 4 bar but relatively low NaCl rejection (25.1%), which suggests that it has the potential to separate divalent and monovalent ions. More importantly, GO-PA composite nanofiltration membranes also exhibited excellent antifouling properties with HA and BSA flux recovery rates reaching more than 95%. The simultaneously enhanced water flux, high divalent/monovalent ion selectivity, and improved antifouling property by the electric field are promising advances that may impact applications of NF membranes in water purification.

CoWO4-x -Based Photothermal Membranes for Solar-Driven Water Evaporation and Eutrophic Lake Water Purification.

Solar-driven water evaporation has been proven to be a promising and efficient method for the energy crisis and clean water shortage issues. Herein, we strategically design and fabricate a novel nonstoichiometric CoWO4–x-deposited foam nickel (NF) membrane (CoWO4–x@NF) that possesses all the desirable optical, thermal, and wetting properties for efficient water evaporation and purification. The broadband absorption of CoWO4–x nanoparticles (NPs) obtained by hydrogen reduction contributes to light-to-heat conversion, while NF with a three-dimensional porous structure can support CoWO4–x NPs and ensure the rapid flow of water molecules during the water evaporation process. We systematically explore and compare the outdoor water evaporation performance of the pure water group, NF group, and CoWO4–x@NF group, and the results show that CoWO4–x@NF performs well under natural sunlight irradiation (water evaporation: 2.91 kg m–2). Significantly, under solar irradiation, the remarkable reduction of Cyanophyta and Euglenophyta in lake water is achieved in the CoWO4–x@NF membrane-administered group, and these two algae are the main factors for eutrophication of the lake water. Our work highlights the great potentials of the CoWO4–x@NF membrane as a device for realizing outdoor solar energy-driven water evaporation and proposes a new strategy for purifying the eutrophication of the lake water.

Solvent Resistant Polyimide Nanofiltration Membranes for Water Purification and Wastewater Management

Solvent Resistant Polyimide Nanofiltration Membranes for Water Purification and Wastewater Management

Artificial Water Channels: Towards Biomimetic Membranes for Desalination.

Natural Aquaporin (AQP) channels are efficient water translocating proteins, rejecting ions. Inspired by this masterpiece of nature, Artificial Water Channels (AWCs) with controlled functional structures, can be potentially used to mimic the AQPs to a certain extent, offering flexible avenues toward biomimetic membranes for water purification. The objective of this paper is to trace the historical development and significant advancements of current reported AWCs. Meanwhile, we attempt to reveal important structural insights and supramolecular self-assembly principles governing the selective water transport mechanisms, toward innovative AWC-based biomimetic membranes for desalination.

High flux and adsorption based non-functionalized hexagonal boron nitride lamellar membrane for ultrafast water purification

• Highly ordered h-BN lamellar membrane was fabricated without functionalization. • Acidic solution increased dyes retention (>90%) and permeances of several folds. • Maximum solutes adsorption capacity was in between 120 and 328 mg/g. • Both cake filtration and intermediate blocking govern the membrane fouling. • Good recycling ability (90% of dye removal after four consecutive cycles test). Water pollution has prejudicial effects on human health and ecosystems. An advanced membrane technology, which uses less energy for pollutants removal from water, is strongly desired for improving cost efficiency. This study demonstrates a high-flux enabled non-functionalized hexagonal boron nitride (h-BN) lamellar membrane, which retains pollutants through adsorption mediated filtration system–a phenomenon that is not yet studied. The membrane is found to be pH responsive, and acidic solution increases anionic methyl orange (MO) and direct red-80 (DR-80) dyes retention up to ≥90%. It also improves permeance fluxes by ~15 and 61-folds for MO and DR-80, respectively, as compared with the previous studies. Next, the membrane qualifies to be a good adsorbent for pollutants removal. The maximum adsorption capacities of this h-BN membrane for bisphenol A, MO and DR-80 are 125.7, 120.8, and 328.2 mg g −1 , respectively. Furthermore, the anti-fouling performance of the membrane has been studied. The membrane exhibits normal fouling tendency, but could be recovered to 80% after washing. The membrane is very stable, and no swelling is observed even in extremely high acidic and basic conditions. The membrane could be regenerated with ethanol treatment and retained dye removal efficiency (around 90%) after four consecutive cycles test.

Recent Progress in Qantum Dots Containing Thin Film Composite Membrane for Water Purification

Recent Progress in Qantum Dots Containing Thin Film Composite Membrane for Water Purification

Fracture behaviour of pristine and defective form of water submerged h-BN nanosheets

Hexagonal boron nitride (h-BN) nanosheets are emerging as potential candidates to replace polymeric membrane for water purification. Synthesizing the membrane size of immaculate h-BN is a fictitious concept. So far, no articles have reported on the fracture behaviour of pristine and defective h-BN nanosheets in a water-submerged state. In this article, classical mechanics-based simulations were employed to study the effect of the hydrogen functionalization of sp-hybridized crack edge atoms and spatial distribution of Stone–Thrower–Wales (STW) and dislocation defects on the fracture properties of water-submerged h-BN nanosheets. Classical mechanics-based simulations were carried out with the help of hybrid-type interatomic potential in which reactive force field and transferable intermolecular potentials were used for arresting the atomistic interaction in h-BN and water, respectively, while for interfacial interactions, Lennard–Jones potential was employed. Enhancement in the values of fracture toughness of h-BN was investigated in the prescence of water molecules compared to in a dry state. It was deduced from the results that passivation, as well as the spatial distribution of STW defects, have a deteriorating effect on the values of fracture toughness of h-BN in the dry state, but water molecules help in nullifying a negative affect. Compared to the spatial distribution of dislocations, the STW type of defects have a more pronounced effect on the values of fracture toughness of h-BN water-submerged state. It can be predicted from the simulations that these improved fracture toughness values in a water-submerged state will help in developing these nanosheets as an effective desalination membrane in water purification.

Fabrication of Bentonite-Silica Sand/Suspended Waste Palm Leaf Composite Membrane for Water Purification.

In this study, a method for fabricating tubular ceramic membranes via extrusion using economical and locally available bentonite–silica sand and waste palm leaves was developed as a tool for conducting the necessary task of purifying water polluted with oil and suspended solid materials produced via various industrial processes. The developed tubular ceramic membranes were found to be highly efficient at separating the pollutants from water. The properties of the fabricated membrane were evaluated via mechanical testing, pore size distribution analysis, and contact angle measurements. The water contact angle of the fabricated membrane was determined to be 55.5°, which indicates that the membrane surface is hydrophilic, and the average pore size was found to be 66 nm. The membrane was found to demonstrate excellent corrosion resistance under acidic as well as basic conditions, with weight losses of less than 1% in each case. The membrane surface was found to be negatively charged and it could strongly repulse the negatively charged fine bentonite particles and oil droplets suspended in the water, thereby enabling facile purification through backwashing. The obtained ceramic membranes with desirable hydrophilic properties can thus serve as good candidates for use in ultrafiltration processes.

Recovery of nanosized silica and lignin from sugarcane bagasse waste and their engineering in fabrication of composite membrane for water purification.

Environmental benign catalytic process was developed for the valorisation of sugarcane bagasse into functional nanomaterials. Bagasse saccharification was carried out with an acid catalyst (H2SO4 0.5%, wt/wt) to separate sugars after pre-treatment of biomass with ethanol. Subsequently, a combination of peroxide and base (0.5% H2O2, wt/wt and 1% NaOH, wt/wt) was stacked to concurrently synthesise SiO2 (35nm with 5.65% yield) and lignin (20nm with 10.15% yield) from bagasse slurry. In the final step, precipitation using catalyst was completed to separate highly pure functional materials in powdered form. Zeta potential (ζ) of the synthesised materials was found to be - 35.6mV for SiO2 and - 13.1mV for lignin. Obtained silica and lignin nanomaterials were used in the fabrication of strong as well as flexible functional membrane for purification of solute particles and gases. The adsorption/desorption curve of the developed functional membrane showed type II isotherm with a H3 hysteresis loop. The observed Brunauer-Emmett-Teller surface area of the membrane was 400.3m2/g. The pore size and pore volume as recorded by Barrett-Joyner-Halenda method was 25.5nm and 0.624cm3/g, respectively. Hence, the developed simple and sustainable process could be highly suitable for filtration of contaminated water and air purification.

Polyethylenimine Grafted Chitosan Nanofiber Membrane as Adsorbent for Selective Elimination of Anionic Dyes

In order to improve the adsorption capacity of chitosan to organic dyes, the amino rich functionalized chitosan electrospun nanofibers membrane was prepared. In the process of high efficiency synthesis, PGMA and PEI were grafted on the surface of CS NFMs in turn. By means of XRD, ATR-FTIR and XPS, the successful introduction of amino group into CS was confirmed. The selective adsorption capacity of CS-PGMA-PEI NFMs for anionic dyes was studied. The adsorption kinetics analysis shows that the adsorption process of CS-PGMA-PEI NFMs is mainly pseudo second-order model. Its adsorption isotherms can be described by the Langmuir model and it conforms to monolayer adsorption. The maximum adsorption capacity of Congo red calculated by Langmuir model is 657.47 mg/g. CS-PGMA-PEI NFMs has selective adsorption capacity for Congo red/methylene blue mixture. CS-PGMA-PEI NFMs also showed good circulation stability. This study provides a method for the synthesis of water purification membrane.

Synergistic multiple active species for catalytic self-cleaning membrane degradation of persistent pollutants by activating peroxymonosulfate

Recently, the development of dual functional catalytic membrane for the synergistic degradation and filtration of persistent pollutants has attracted considerable attention in environmental remediation. Herein, novel CoFe alloy and CoFe2O4 nanoparticles encapsulated in N-doped microtube composites (CoFe-NMTs) were firstly fabricated through in-situ pyrolysis of simple-source Prussian blue analogues (PBA). As expected, this unique structure not only inhibited the nanoparticles agglomeration, but also provided a “highway” that accelerated the Co3+/Co2+ and Fe3+/Fe2+ redox cycles. Therefore, CoFe-NMT-800 (0.1 g/L, pyrolyzed at 800 °C) achieved over 90% tetracycline (TC, 30 mg/L, 0.1821 min−1) removal after 30 min at a wide pH (2.55–9.55) by coupling with peroxymonosulfate (PMS, 0.3 g/L), which dramatically outperformed the majority of the reported catalysts (such as Co3O4, CoFe alloy, CoFe2O4 and N-doped carbon nanotubes, etc.). Additionally, CoFe-NMTs-800 also exhibited excellent catalytic activity in the existence of inorganic anions (Cl−, HCO3− and H2PO4−) and natural organic matters (humic acid (HA)). Subsequently, CoFe-NMTs-800 was immobilized into polyvinylidene fluoride (PVDF) membrane as catalytic self-cleaning membrane via applying phase-inversion technology. It was found that CoFe-NMTs-800/PVDF membrane not only maintained high removal efficiency for TC degradation (over 90%) in TC/HA coexistence system, but also effectively eliminated the adverse effect of membrane fouling. Besides, the fabricated membrane also showed desirable reusability and neglectable metal leaching (0.003 mg/L Fe and 0.015 mg/L) with almost constant flux after five cycles. The quenching experiments and electron paramagnetic resonance (EPR) results clearly indicated that sulfate radicals (SO4−), hydroxyl radicals (OH and singlet oxygen (1O2) were responsible for TC degradation and SO4− was a major contributor. Significantly, this work was very meaningful to construct novel catalytic self-cleaning membrane for water purification.

Morphology, physical, and mechanical properties of potentially applicable coelectrospun polysulfone/chitosan‐polyvinylalcohol fibrous membranes in water purification

AbstractPolysulfone (PSU) is a widely used polymer in water purification membranes. However, its hydrophobicity hinders its practical application. Herein, the wettability of PSU has been improved by producing a coelectrospun fibrous composite membrane using a hydrophilic component, chitosan‐polyvinyl alcohol (CS‐PVA). First, different proportions of PVA and CS solutions were mixed and electrospun to prepare CS‐PVA blend fibers. Scanning electron microscope (SEM) observations revealed that CS‐PVA blend fibers with maximum CS content can be obtained in 30:70 CS:PVA weight ratio. The optimum CS‐PVA solution was subsequently used alongside PSU solution and were fed into two distinct syringes, which were then electrospun simultaneously at a constant voltage and distance of 15 kV and 15 cm, respectively. Different composite compositions of PSU/CS‐PVA were achieved using different feeding rates for each solution. Based on SEM images, the prepared composite fibers were beadless. The ultimate strength of the composite mats decreased by increasing the amount of CS‐PVA due to the significant difference in the fiber diameter of each component and the resulting stress concentration. However, the thermal stability of composite membranes remained almost the same as pure PSU fibers. Moreover, samples with higher CS‐PVA content showed better wettability and higher water flux.

Multifunctional solar bamboo straw: Multiscale 3D membrane for self-sustained solar-thermal water desalination and purification and thermoelectric waste heat recovery and storage

Solar desalination and purification based on interfacial evaporation have great potential to alleviate global water scarcity. However, real-world interfacial evaporation suffers from several issues in clean water collection and solar-to-clean-water energy efficiency. Here, a new concept of multifunctional natural membrane interfacial evaporation (MNMIE) is demonstrated, achieving the whole cycle of energy conversion from solar energy harvesting to waste heat recovery and storage while effectively desalinating and purifying water. The 3D, multiscale membrane derived from sustainable bamboo presents a mean pore size of 150 nm and a porosity of 63.8%, comparable to the commercial membranes. The as-generated vapor from a self-sustained evaporation process is guided to permeate through the porous bamboo node into the bamboo chamber facing unfocused incident light (1 sun) and then condenses, resulting in a high water collection ratio of 81.0% and solar-to-clean water efficiency of 67.4%. Moreover, the waste heat from desalination is recovered through direct thermoelectric energy conversion and storage under unfocused solar light. The fully integrated cycle of energy conversion, storage, and utilization for clean water and electricity generation enabled by the multifunctional natural membrane is scalable, economic and represents a highly promising solution for sustainable energy cycles enabled by nanotechnology-empowered natural resources.

TETA-anchored graphene oxide enhanced polyamide thin film nanofiltration membrane for water purification; performance and antifouling properties

This work investigates the performance and structure of polyamide thin film nanocomposite (PA-TFN) membrane incorporated with triethylenetetramine-modified graphene oxide (GO-TETA). The embedment of GO-TETA nanosheets within the structure of PA-TFN membrane was evaluated at different concentrations (0.005, 0.01, 0.03 wt%; in aqueous piperazine (PIP)) through interfacial polymerization (IP). The physicochemical properties of the prepared membrane were investigated by SEM, AFM, water contact angle, and zeta potential as well as ATR-IR spectroscopy. The presence of longer chains of amino groups (in comparison with the directly linked amino ones) among the stacked GO nanosheets was assumed to increase interlayer spacing, resulting in remarkable changes in water permeance and separation behavior of modified polyamide (PA) membrane. It is seen that GO-TETA nanosheets were uniformly distributed in the matrix of PA layer. With increasing the concentration of GO-TETA, the flux of TFN membranes under 6 bar was increased from 49.8 l/m2 h (no additive) to 73.2 l/m2 h (TFN comprising 0.03 wt% GO-TETA. In addition, more loading GO-TETA resulted in a significant decrease in the average thickness of the polyamide layer from ~380 to ~150 nm. Furthermore, addition of GO-TETA improved the hydrophilicity of nanocomposite membranes, resulting in superb water flux recovery (antifouling indicator) as high as 95% after filtration of bovine serum albumin solution. Also, the retention capability of the TFN membranes towards some textile dyes increased as high as 99.6%.

Ultrathin and ultradense aligned carbon nanotube membranes for water purification with enhanced rejection performance

Carbon nanotube (CNT) membranes are promising for high-performance self-assembly membranes in water purification, and their molecular sieving performance depends on the effective pore size of the membranes. For the first time, to enhance the separation selectivity of water purification membranes, we prepared the SACNT membrane with smaller pore sizes, more compact pores with 15 nm thickness and an average 0.88 nm CNT spacing in the observed area for water purification. We found that the aligned CNT membranes exhibited salt rejection 2 times higher than that of membranes prepared by disordered CNTs. It can be explained by the sieving effect. In addition, the adsorption interactions between the CNTs and aromatic rings in dyes also contributed to the improved rejection performance, which was confirmed by the molecular dynamics simulation. Our study represents a significant exploration of enhanced properties for aligned CNT membrane fabricated by a simple method, paving the way for high-performance membrane for water purification.

Osmotic water permeability of aquaporin-1 under radial tensile and compressive stimuli

With the rapid development of biological technology and membrane synthesis, water industries have inclined towards biomimetic membranes for water purification and desalination. Aquaporin (AQP) embedded synthetic membranes seem to be promising due to the AQP's high selectivity and permeability, however, the effect of inherent membranous residual stress on protein structure and water permeation has been rarely studied yet and remains unclear. Here, we studied water permeability through the tetrameric human AQP1, embedded in a POPC lipid bilayer, under lateral mechanical stimuli using all-atom molecular dynamics simulations. Four different systems were studied where different stimuli were applied to the simulation cell. By counting the permeation events, we found that radially stretching protein though opens up and widens the pore in the planar direction; it reduced the final permeability compared to control. The hydrostatic pressure stimulus system possesses the highest permeability coefficient followed by the protein compressing system. By screening the water occupancy and pore-lining residues in different systems, we found that stretching the protein increased the dynamics of the pore-lining residues which interrupts the single-file line of water molecules in the pore, hence reducing the likelihood of water molecules to pass the pore. We also observed that the constriction site is located where the two pore-lining residues of ASN76 and ILE 60 meet. Our result provides a benchmark for designing a more efficient membrane desalination system for the treatment of water worldwide.

Surface Characterization of Nano-sized Star Block Copolymers for Antifouling Coatings on Water Purification Membranes

Surface Characterization of Nano-sized Star Block Copolymers for Antifouling Coatings on Water Purification Membranes

Ferroelectric membrane for water purification with arsenic as model pollutant

Membrane filtration is widely applied, but often subject to a trade-off between permeability and selectivity, an inherent challenge in membrane processes. Charged membranes are a promising alternative to address this challenge. Here, ferroelectric BaTiO3 nanoparticles, with a spontaneous electric polarization, were assembled into the traditional polyamide nanofiltration membranes by interfacial polymerization then charged by corona poling. Importantly, charges of ferroelectric BaTiO3 nanoparticles sealed in polymers were hardly affected by ambient aqueous environment. The polarized ferroelectric membrane (TFN-mBTO-E) showed higher permeability (2.4 and 1.5 times) and favorable rejection ratio about 97% for arsenic removal, a strictly controlled contaminant, compared with common membranes and unpolarized TFN-mBTO membranes, due to strong hydrophilicity and increased surface potential derived from ferroelectric charges. Thereby, it could provide new insight into charged membrane, laying a foundation for the application of ferroelectric materials in membrane filtration.

Mussel-inspired structure evolution customizing membrane interface hydrophilization

Advanced energy-water systems demand fabrication of high-performance water purification membranes. Polymeric membranes are typically hydrophobic, not amenable to conventional surface functionalization methods. Mussel adhesive proteins have inspired numerous adhesive polymer coatings via the structure-function simulation. Nonetheless, research about maximizing membrane interface hydrophilization and relevant concept guidance are still far from enough. Here, we put forward a “split-and-adjust” concept and proof it using a simplified catechol/silane biomimetic composite coating system for boosting interface hydrophilization. As a result, the hierarchically nanostructured silicified hydrophilic membranes were fabricated. The hydrophilicity could be tailored via tuning reagent dose recipes. The as-fabricated hydrophilic membrane presented benign fouling resistance in oil-in-water emulsion filtration tests. In addition, the rinsing examination indicates the coating is well stabilized. The as-developed “split-and-adjust” concept for the composite coating system provides promising guidance to broaden and optimize the customized biomimetic interface functionalization toolbox.

The significant role of support layer solvent annealing in interfacial polymerization: The case of epoxide-based membranes

The applicability of state-of-the-art water purification membranes in harsh feed streams is limited due to their insufficient chemical robustness. Epoxide chemistry has been recently introduced to achieve pH- and chlorine-stable nanofiltration (NF). This study further investigated the influence of interfacial polymerization (IP) synthesis parameters on the resulting epoxide-based thin-film composite (TFC) membrane structure and performance. Epoxide polymerization could be initiated by N,N,N′,N′-tetramethyl-1,6-hexanediamine and NaOH. Surprisingly, neither the type of initiator, nor the initiator concentration used during IP, influenced membrane rejection of rose bengal (RB) dye (1017 g mol-1), which was constant at ~ 90%. This consistent RB rejection was primarily determined by annealing of the cross-linked polyimide support by toluene, which is the solvent used during IP. In contrast, the poly(epoxyether) top-layer determined membrane selectivity for methyl orange, a smaller dye of 327 g mol-1. The effect of solvent annealing of the membrane support by diethyl carbonate, dimethyl sulfoxide and m-xylene was also investigated and revealed that the changes induced by solvent contact are physical rather than chemical in nature. This study shows, for the first time, the substantial direct impact of the solvents used during IP to influence support properties and the resulting membrane performance. Solvent annealing can therefore be considered as a tool in membrane fabrication—during IP or as a post-treatment step—to further tune the separation performance for specific applications.