Membranes For Water Desalination Research Articles

Thin-film nanocomposite nanofiltration membrane with enhanced desalination and antifouling performance via incorporating L-aspartic acid functionalized graphene quantum dots

To fabricate thin-film nanocomposite (TFN) nanofiltration (NF) membrane with enhanced desalination and antifouling performance, L-aspartic acid functionalized graphene quantum dots (AGQDs), integrating the advantages of L-aspartic acid and graphene quantum dots (GQDs), were successfully synthesized and incorporated into the polyamide (PA) selective layer via interfacial polymerization (IP) method. The fabricated TFN membranes with various AGQDs contents were systematically characterized by the microstructures, surface properties, desalination, and antifouling performance. The optimal AGQDs concentration in the aqueous solution reaches 3000 ppm, the resultant TFN-3 membrane exhibits an outstanding water permeance of 18.5 LMH/bar, 60.9% higher than the TFC-blank membrane. Meanwhile, the TFN-3 membrane possesses a higher Na2SO4 rejection than that of the TFC-blank membrane (98.4% vs 95.7%). Additionally, the TFN-3 membrane shows superior antifouling performance over the TFC-blank membrane in the presence of either the negatively charged foulant (BSA) or the positively charged foulant (lysozyme). An appropriate amount of AGQDs added into aqueous solution favors the formation of a smooth, thin, hydrophilic, and electrically neutral selective layer. As a result, the overall separation performance of the TFN-3 membrane, especially the desalination and antifouling performance, are significantly enhanced with the help of AGQDs. Therefore, the incorporation of amino acid-functionalized GQDs into the PA selective layer presents a novel strategy to produce a high-performance NF membrane for water desalination.

Large area continuous multilayer graphene membrane for water desalination

This manuscript reports the preparation of a large area (84 cm2) desalination membrane based on multilayers (11 nm thickness) of B,N-codoped defective graphene. The process consists of coating a porous ceramic α-Al2O3 support (100 nm pore size) with a continuous nanometric (50 nm) chitosan film containing adsorbed (NH4)3BO3. Subsequent pyrolysis in the presence of hydrogen converts chitosan into multilayer defective B,N-codoped graphene. The partial removal of B and N dopant atoms by H2 during the pyrolysis causes the generation of subnanometric pores due to atom vacancy, as determined by control experiments in the absence of this gas. A NaCl and KCl removal efficiency from brackish water higher than 95% for a permeate flux of 24.3 L m−2 h−1 at 10 bars were achieved.

Hydrophilic Coating Layer by Layer on Polyethersulfone Membranes for Desalination

Water Desalination is becoming an issue for saving the required potable and drinking water due to shrinkage of pure water. Thus, this work deals with antifouling membrane preparation using poly meric compounds of Polyethersulfone/ Polyvinylalcohol (PES/PVA) with nanomaterials to produce antifouling membrane for water desalination. The PES membrane has prepared by phase inversion process followed by different coating ways. The coating with PVA provided the highest hydrophilic surface. The characterization of prepared membranes was carried out using various analysis methods such as scanning electron microscopy (SEM), mechanical properties, porosity and contact angle. The pore size distribution of prepared membranes was determined using the Brunauer-Emmett-Teller (BET) method. The result showed that the best membrane performance was membrane which has a coating with PVA layer, where rejection reached to 99 %, 95% and 88% as a function of concentration 500, 1500, and 3000 ppm respectively, while the permeate flux reached to 48.4 L/m2.h, 32.3 L/m2.h and 21.5 L/m2.h as a function of concentration 500, 1500, and 3000 ppm respectively.

Self-passivated nanoporous phosphorene as a membrane for water desalination

Using molecular dynamics simulations, we investigated the mechanism of water transport and ions movement across nanoporous phosphorene for water desalination performance. Phosphorene nanopore areas ranged from 4 Å2 to 41 Å2. The self-passivated phosphorene nanopores showed 100% ability to reject salt ions (Na+ and Cl−) for all pore areas even at higher pressures. Water flux through narrow pores exhibits a slow increase while sharper increase and linear dependence is observed for wider pores i.e. D16 and D18. The increase in water flux is attributed to broadened cross-sectional area and dense water layering in the vicinity of pores. The desalination performance is strongly influenced by structure of nanopore such as size, shape; water-membrane interaction and applied pressure. Further, oxygen density maps reveal the hydrophilic nature of phosphorene nanopores hence, it effects the water flux. Our results also indicate that during the entire simulation, pore atoms of the membrane retained their atomic arrangement implying the stability of phosphorene as a membrane. Findings of this work establish molecular insight into phosphorene desalination performance, which helps in systematic design of water treatment plants.

Membrane and Electrochemical Processes for Water Desalination: A Short Perspective and the Role of Nanotechnology.

In the past few decades, membrane-based processes have become mainstream in water desalination because of their relatively high water flux, salt rejection, and reasonable operating cost over thermal-based desalination processes. The energy consumption of the membrane process has been continuously lowered (from >10 kWh m−3 to ~3 kWh m−3) over the past decades but remains higher than the theoretical minimum value (~0.8 kWh m−3) for seawater desalination. Thus, the high energy consumption of membrane processes has led to the development of alternative processes, such as the electrochemical, that use relatively less energy. Decades of research have revealed that the low energy consumption of the electrochemical process is closely coupled with a relatively low extent of desalination. Recent studies indicate that electrochemical process must overcome efficiency rather than energy consumption hurdles. This short perspective aims to provide platforms to compare the energy efficiency of the representative membrane and electrochemical processes based on the working principle of each process. Future water desalination methods and the potential role of nanotechnology as an efficient tool to overcome current limitations are also discussed.

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.

Porous Graphene for Sea Water Desalination Considering the Effects of Fluorine/nitrogen Modification: A Molecular Dynamic Study

Sea water desalination becomes more and more important as the consumption of fresh water. Forward osmosis (FO) is a novel technology for sea water or brackish water desalination, where a most important device, semi-permeable membrane, are required low resistance, high selection and inexpensive. In this study, based on molecular dynamic simulations, we explored the performance of porous graphene as the semi-permeable membrane for sea water desalination. Fluorine (F) and nitrogen (N) are adopted to optimize the property of graphene pore. We found that although pure pore have highest water flux (indicating lower resistance), N modified pore has the best selection due to the high electronegativity of N atoms. The about 60 L/cm2/h water flux and 100% solute rejection ratio confirm the graphene with N modified pores is good candidate as a semi-permeable membrane for sea water desalination.

Poly(phenyl sulfone) hollow fiber forward osmosis membrane for saline water desalination

Different PPSU nanofiltration (NF) fibers were used for the first time as a potential fiber for saline water desalination by forward osmosis (FO). The characteristics of fibers, such as their surface structure, cross-sectional structure, and thickness were measured using a SEM and an AFM, with fiber porosity also measured. The effects of the PPSU amount and operating conditions on the performance of water transport were investigated. The structural parameter (S = 467–601) displayed small values for three PPSU fibers due to their high porosity and because the fiber was less thick, which corresponded well to their performance. The prepared PPSU fiber tested under the FO process displayed high water fluxes utilizing 3.0 M NaCl as the draw solution. High salt rejection for all PPSU FO fibers was obtained, and the salt reverse fluxes were preserved below 7.30, 6.58, and 3.89 gMH for PPSU 25, 29, and 30 wt.%, respectively. Increasing the PPSU amounts led to decreasing the specific reverse salt flux. The PPSU NF hollow fibers prepared in this work are eligible FO membranes for water desalination.

Enhanced chlorine‐resistant and low biofouling reverse osmosis polyimide‐graphene oxide thin film nanocomposite membranes for water desalination

AbstractThe effect of graphene oxide (GO) loading (0.03, 0.06, 0.09, 0.12, and 0.30 wt%) in the aqueous phase on the performance of reverse osmosis (RO) polyimide (PI) thin film composite (TFC) membrane was investigated. TFC and thin film nanocomposite (TFN) membranes were produced through interfacial polymerization and the imide linkage was confirmed by attenuated total reflection Fourier transform infrared spectroscopy. The spongy‐like structure with vertical fingers of RO PI‐GO TFN membranes was explored by top‐surface and cross‐sectional field emission scanning electron microscope (FE‐SEM). The roughness of the membranes was determined. All PI‐GO TFN membranes exhibited enhanced desalination performance in comparison with PI membranes. Samples with 0.06 wt% GO performed the best with a water flux of 31.80 L/m2/h, salt rejection of 98.8%, and very good antibiofouling properties. This hydrophilic membrane displayed significantly enhanced chlorine‐resistance with water flux of 36.3 L/m2/h and salt rejection of 98.5%. This work provides a promising start for designing rapid water permeation PI‐GO TFN membranes in water desalination.

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.

Vertically aligned carbon nanotube membrane: synthesis, characterization and application in salt water desalination

Previous studies have used molecular dynamics simulation to assess the feasibility of applying vertically aligned carbon nanotube membranes (VA-CNT) for salt water desalination. The presented report experimentally determined the potential of salt water desalination by employing VA-CNT membranes. The VA-CNT membranes were synthesized through the template-assisted pyrolysis of polybenzimidazole-Kapton inside the pores of anodized aluminum oxide (AAO) and characterized by several techniques. The permeability, salt rejection, and biofouling tendency of VA-CNT membranes were measured in various operating conditions; the results were compared with the performance of a commercial reverse osmosis (RO) membrane (BW30). The VA-CNT membrane permeability was about twofold higher than the permeability of the RO membrane. Furthermore, the VA-CNT membranes had higher stability against biofouling phenomena; they also showed antibacterial activity so that about 70% of the adsorbed cells on the VA-CNT membranes were killed by CNTs tips that were vertically aligned on the membrane surface. The rejection efficiency of the VA-CNT membrane was comparable to that of the commercial RO membrane. Finally, the chlorine stability studies showed that high hypochlorite exposure (48000 ppm.h) did not significantly fail the flux and rejection of the VA-CNT membranes, confirming their chemical stability. This study shows the high capability of the VA-CNT membrane in the water treatment process.

Omniphobic Hollow Fiber Membranes for Water Recovery and Desalination

Despite remarkable progress in developing wetting-resistant membranes for the desalination of challenging water resources through membrane distillation, practical approaches that allow for the fabr...

Hexagonal boron nitride with nanoslits as a membrane for water desalination: A molecular dynamics investigation

In this work, we investigate how nanoporous hexagonal boron nitride (hBN) membrane can achieve efficient water/ion separation using molecular dynamics simulations. In particular, it is interesting to figure out the transport mechanisms through slit-like orifices with different edge patterns, namely armchair, B-edged, and N-edged. It is observed that the water and ion conduction rates are sensitive to the edge patterns, which is attributed to the intriguing electrostatic interactions between hBN and solution particles. The armchair nanoslits barely discriminate ion from water molecules, whereas the nanoslits edged with zigzag patterns collaboratively impede ion permeation and allow fast water conduction. Our simulations not only support that hBN is a promising candidate for the development of permeable membrane for water desalination but also highlight the importance of nanoslit edge pattern. Together, this work will be helpful for the design of permeable membrane in the future.

Fabrication of High-Performance Thin-Film Composite Nanofiltration Membrane by Dynamic Calcium-Carboxyl Intra-Bridging during Post-Treatment.

Widespread applications of nanofiltration (NF) and reverse osmosis (RO)-based processes for water purification and desalination call for high-performance thin-film composite (TFC) membranes. In this work, a novel and facile modification method was proposed to fabricate high-performance thin-film composite nanofiltration membrane by introducing Ca2+ in the heat post-treatment. The introduction of Ca2+ induced in situ Ca2+-carboxyl intra-bridging, leading to the embedment of Ca2+ in the polyamide (PA) layer. This post modification enhanced the hydrophilicity and surface charge of NF membranes compared to the pristine membrane. More interestingly, the modified membrane had more nodules and exhibited rougher morphology. Such changes brought by the addition of Ca2+ enabled the significant increase of water permeability (increasing from 17.9 L·m−2·h−1·bar−1 to 29.8 L·m−2·h−1·bar−1) while maintaining a high selectivity (Na2SO4 rejection rate of 98.0%). Furthermore, the intra-bridging between calcium and carboxyl imparted the NF membranes with evident antifouling properties, exhibiting milder permeability decline of 4.2% (compared to 16.7% of NF-control) during filtration of sodium alginate solution. The results highlight the potential of using Ca2+-carboxyl intra-bridging post-treatment to fabricate high-performance TFC membranes for water purification and desalination.

Nanofiltration membranes prepared from pristine and functionalised multiwall carbon nanotubes/biopolymer composites for water treatment applications

A filtration method was used to prepare buckypaper (BP) membranes for water desalination. The samples are made from a biopolymer (chitosan) containing functionalized multiwall carbon nanotubes (MWCNTs) with –NH2 and −COOH moieties. Comprehensive characteristics of all BP membranes were systematically investigated. This included optimisation of sonication time, electrical and mechanical properties (ranging from 7 ± 1 to 69 ± 1 S/cm and tensile strengths between 17 ± 2 and 60 ± 2 MPa, respectively), contact angle (36 ± 3° to 105°±2°), morphology, surface area (ranging from 12 ± 2 m2/g to 112 ± 4 m2/g), surface charge, water permeability (from 0.5 ± 0.1 to 6.5 ± 0.2 L/m2 h bar), and salt rejection. The results indicate that the properties of the BP membrane have been significantly affected as the top layer by the type of multi-walled carbon nanotubes. With MWCNTs−COOH / chitosan BP membranes, the highest permeability towards water was achieved while the MWCNTs-NH2/chitosan membranes provided the best performance in salt rejection by properly balancing amine groups on the top layer, which could be separate monovalent and multivalent cations from salt solutions. Moreover, for monovalent cations (e.g. Na+) BP membranes (MWCNTs/chitosan and MWCNTs-NH2/chitosan) with sufficiently balanced amine groups on the top layer are shown to be much bigger rejection than for higher-valent cations (e.g. Mg2+).

Roughness-enhanced hydrophobic graphene oxide membrane for water desalination via membrane distillation

Novel design of hydrophobic membrane could improve the efficiency of membrane distillation (MD) technology. Owning to being easy to realize hydrophobic modification, fast radial heat transfer rate and limiting the passage of larger contaminants, hydrophobic graphene oxide (GO) membrane shows potential for MD process. In this work, we reported on a new type of nanoparticles intercalated GO membrane with hydrophobic surface for MD application fabricated by vacuum-filtration method. The introduction of nanoparticles (SiO2) by physical mixing enhanced the surface roughness of GO membrane. A subsequent grafting of long alkyl chains (hexadecyltrimethoxysilane) further increased the membrane hydrophobicity. The effects of treating temperature and nanoparticles content on the membrane nanostructures, surface hydrophobicity and desalination performance were systematically investigated. The optimized membrane annealed at 80 °C with hydrophobic surface (water contact angle: 120.8°) exhibited water flux of 13.59 kg m-2 h-1 and salt rejection of 99.99% under 60 °C for 35 g L-1 NaCl in water during vacuum MD process. Besides of the expected gradually higher water flux at elevated temperature, such excellent desalination performance remains stable by varying the salt concentration or adding model foulants such as surfactant sodium dodecyl sulfate and organic humid acid in the feed.

Why is Single-Layer MoS2 a More Energy Efficient Membrane for Water Desalination?

Water desalination technologies are extensively utilized to solve water scarcity problems in many regions of the world. Discovery and application of two-dimensional (2D) nanoporous materials provid...

POC/PIM-1 mixed-matrix membranes for water desalination: A molecular simulation study

As a new class of porous materials, porous organic cages (POCs) are dissolvable in common organic solvents and can be readily incorporated into polymers to fabricate mixed-matrix membranes (MMMs). Herein, we report a molecular simulation study on MMMs formed by a POC (PB-1A) and a polymer of intrinsic microporosity (PIM-1) for water desalination. Three MMMs with different PB-1A/PIM-1 ratios are constructed, namely MMM1 (1 cage/13 PIM-1 chains), MMM2 (1 cage/20 PIM-1 chains) and MMM3 (1 cage/28 PIM-1 chains). After swelling in water, the voids in the MMMs are observed to become larger. The swelling degrees are estimated to be 69.3%, 64.9% and 56.6% in MMM1, MMM2 and MMM3, respectively, which are greater than 20–30% in the pristine PIM-1. Due to the presence of PB-1A cage, water permeability is significantly enhanced in the MMMs, along with nearly complete salt rejection. Particularly, water permeability in MMM1 is 1.1 × 10−5 kg m/(m2·h·bar), which is one order of magnitude higher than 8.6 × 10−7 kg m/(m2·hr·bar) in the pristine PIM-1, and is also higher than those in a wide variety of reported membranes. This simulation study provides microscopic insights into the structural and dynamic properties of water and ions in the PB-1A/PIM-1 MMMs, suggests that the MMMs might be interesting candidates for water desalination.

Computational methods towards increased efficiency design of graphene membranes for gas separation and water desalination

Abstract The potential impact of climate change is widely known as having serious consequences. The themes of water desalination and gas separation are closely related to the environment and energy industry. Graphene-based membranes are promising filtration devices for the two tasks. This review aims to supply a comprehensive overview of the recent computational studies investigating the performance of graphene-based membranes used in water desalination or gas separation. With the use of computational methods, the literature covered finds evidence for key factors, such as pore shape and density, affecting the performance of the investigated membranes. The reviewed studies are expected to act as an impulse towards more computational studies and eventually actual design of graphene-based membranes for water desalination and gas separation.

Preparation and characterization of a novel green silica/PVA membrane for water desalination by pervaporation

In this study, silica was extracted from rice husk (RH) waste to develop a novel green silica/PVA hybrid membrane for improving the desalination performance by pervaporation. A thermal method with citric acid leaching was applied for the extraction of green silica under different conditions, and the best high-cost purity silica obtained was incorporated into the PVA membrane with loadings of 0%, 10% and 20%. The effect of the green silica content on the membrane characteristics, desalination performance, and pervaporation temperature was investigated. The purest silica (>97 wt%) was obtained for a 5% acid leaching solution, which was used as the filler in the PVA membrane, and at a combustion temperature of 700 °C. The green silica/PVA membrane exhibited a higher roughness and hydrophilicity and a lower crystallinity compared with pure PVA, indicating an enhancement in the permeation flux. The flux of hybrid membranes reached the maximum value of 12.3 kg m−2h−1 at 60 °C for 10% silica loading with a 3.5 wt% NaCl feed concentration. Salt rejection remained higher than 99.9% for all membranes, and the apparent activation energy showed no significant difference between experiments. The results showed that the pervaporation performance was successfully improved by incorporating the RH silica into the PVA membrane.