Membranes For Water Desalination Research Articles

Applicability of Composite Magnetic Membranes in Separation Processes of Gaseous and Liquid Mixtures-A Review.

Recent years have shown a growing interest in the application of membranes exhibiting magnetic properties in various separation processes. The aim of this review is to provide an in-depth overview of magnetic membranes that can be successfully applied for gas separation, pervaporation, ultrafiltration, nanofiltration, adsorption, electrodialysis, and reverse osmosis. Based on the comparison of the efficiency of these separation processes using magnetic and non-magnetic membranes, it has been shown that magnetic particles used as fillers in polymer composite membranes can significantly improve the efficiency of separation of both gaseous and liquid mixtures. This observed separation enhancement is due to the variation of magnetic susceptibility of different molecules and distinct interactions with dispersed magnetic fillers. For gas separation, the most effective magnetic membrane consists of polyimide filled with MQFP-B particles, for which the separation factor (αrat O2/N2) increased by 211% when compared to the non-magnetic membrane. The same MQFP powder used as a filler in alginate membranes significantly improves water/ethanol separation via pervaporation, reaching a separation factor of 12,271.0. For other separation methods, poly(ethersulfone) nanofiltration membranes filled with ZnFe2O4@SiO2 demonstrated a more than four times increase in water flux when compared to the non-magnetic membranes for water desalination. The information gathered in this article can be used to further improve the separation efficiency of individual processes and to expand the application of magnetic membranes to other branches of industry. Furthermore, this review also highlights the need for further development and theoretical explanation of the role of magnetic forces in separation processes, as well as the potential for extending the concept of magnetic channels to other separation methods, such as pervaporation and ultrafiltration. This article provides valuable insights into the application of magnetic membranes and lays the groundwork for future research and development in this area.

Exploring the potential of MXene nanoslit for water desalination through molecular dynamics simulations

The charge features of nanoslit were deemed to exert significant influences on optimization of its desalination performance. The MXene nanoslit carries richness of charge features, thus it should possess exceptional desalination performance. However, the optimal application conditions of MXene nanoslit as a water desalination membrane has not been systematically explored. In this work, we adopted molecular dynamics (MD) methods to assess the desalination performance of Ti3C2TX nanoslits. The influence factors, including the termination group, the slit width, temperature, pressure, and thickness were discussed with the expectation of probing the optimal application conditions for MXene nanoslit membranes. Simulation results showed that MXene nanoslit possesses excellent desalination performance thanks to the charge features of the nanoslit channel. The increase of slit width, temperature, and pressure all promote the water permeance but deteriorate the ion rejection performance. Fortunately, the tradeoff between water permanence and ion rejection rate can be mediated by the termination groups. The increase of MXene layer number could effectively improve the desalination performance, taking both water flux and ion rejection performance into account. The present work might provide some valuable suggestions for the design of water desalination membranes with exceptional desalination performance by manipulating the electrostatic properties of membranes.

Molecular mechanisms of thickness-dependent water desalination in polyamide reverse-osmosis membranes

Using non-equilibrium molecular simulations, we systematically elaborate the relationships among synthesis (membrane's thickness and morphology), atomic-scale transport mechanism, and separation performance (permeability and selectivity) for 3D-printed polyamide (PA) membranes. Results indicated that water diffusion, swelling ratio, water flux, and water permeance proportionally decrease with increasing membrane thickness (4.0–32.5 nm). PA membranes with different thicknesses can achieve almost 100% salt rejection over the simulation time. Importantly, water permeability exponentially decreases with increasing thickness, and 15 nm is identified as the critical membrane thickness for efficient water transport. The discontinuous water-available space spreads all over PA membranes with thicknesses greater than 5 nm, allowing water molecules to jump by way of the temporary open-and-close pores. However, the connected water-useable space exists in PA membranes with thicknesses below 5 nm, offering the continuous channels to dominate water transport. More significantly, pore distribution is more homogeneous as the thickness increases. The applied high pressures can lead to membrane compaction during reverse osmosis and the thicker membranes show a lower compression ratio. In short, these investigations provide molecular insights for effectively designing and manufacturing PA membranes for water desalination and treatment at the molecular level.

Experimental study of a standalone membrane water desalination unit fully powered by solar energy

In this study, a fully solar-driven water desalination system is designed, fabricated, and tested. The proposed system is designed for remote, isolated areas with limited electricity and freshwater access. For commercial PVDF membranes, the performance of the MD unit is evaluated at various feed temperatures, flow rates, and salt concentrations. In addition, the effect of MD cell design was examined to determine the effect of the obstacles on the feed channel. Increasing the temperature by 20 degrees from 55 to 75 °C enhances productivity by 165 % from 6.2 to 16.4 kg/m2.h. At different operating conditions, the new design of the MD cell with cylindrical obstacles attained higher flux productivity compared to the conventional MD cell design. The maximum attained freshwater output flux was around 15 kg/m2.h at a feed inlet temperature of 65 °C and feed mass flowrate of 66 kg/h for the MD cell with cylindrical obstacles. In the presence of obstacles, a reduction in the specific energy consumption (SEC) by 35–15 % is associated with an increase in the gain output ratio (GOR) by 50–20 % compared to the case of no obstacles. Observations indicate that a small PV module with an area of 0.377 m2 is sufficient to operate the membrane unit for contentious 15 h. Collectively, using solar MD units collectively has the potential to be used for decentralized desalination of water.

Highly permeable polyamide-holey graphene oxide composite membrane prepared by pressure spray interface polymerization for desalination

The rise of reverse osmosis membranes (RO) has attracted significant attention, which is pivotal to addressing the water shortage. Superior permeability and high selectivity are extremely critical criteria for RO membranes. Therefore, in this study, we reported a novel strategy: pressure spray interface polymerization (PSIP) to prepare ultrathin RO composite membranes. In the approach, besides the developed novel technique, highly permeable holey graphene oxide (HGO) containing nanopores was also used to refine the size of the transport nanochannels during the reaction of m-phenylenediamine (MPD) and the trimethyl chloride (TMC). Meanwhile, the electrostatic interaction between the HGO and MPD provided a solid guarantee for good dispersion in the composite membrane. The resultant pressure spray interface polymerization-highly permeable holey graphene oxide (PSIP-HGO) composite membrane displayed high salt rejection and water permeance, which showed high water permeance of 4.0 Lm−2h−1bar−1 and Na2SO4 rejection of 95% in a concentration of 2000 ppm under 5 bar. Moreover, the PSIP-HGO membrane showed outstanding long-term stability and high chemical stability. Therefore, our work may provide a feasible pathway for designing advanced RO membranes for water desalination.

Energy and economic performance assessment of a solar-assisted regenerative vacuum membrane desalination system

Vacuum membrane water desalination is a promising technology for freshwater production with the advantages of low conduction heat loss and mass transfer resistance, compared to other membrane technologies. Such systems can be driven by solar thermal collectors for green water production, yet there is a lack of dynamic system simulations in the literature to comprehensively assess the energy and economic system performance and evaluate the impact of brine recirculation as a method of regeneration, especially under hot desert climates where solar resources are abundant, but freshwater resources are scarce (e.g., the northern coast of Egypt, considered as the case study here). In this study, a dynamic system simulation model is developed in TRNSYS, where a new “Type” is introduced for the vacuum membrane module. Initial sizing of the system with ∼20 % solar fraction resulted in annual average gained output ratio and specific thermal energy consumption of 2.51 and 133.5 kWh/m3, respectively, with levelized cost of water and payback period of 14.7 USD/m3 and 1.53 years, respectively. By increasing the solar collectors’ area from 8 to 16 m2, the levelized cost of water increased by 14.54 %. The storage volume was highly influential on the solar fraction, which increased by 101.39 % as the volume increased from 0.3 to 0.7 m3. Increasing the membrane area from 0.3 to 0.5 m2 increased the gained output ratio by 76.75 % while decreasing the levelized cost of water by 14.79 %. Internal heat regeneration through brine recirculation enhanced the system performance at lower recirculation ratios. Without recirculation, the levelized cost of water increased by 117.41 % and the system met the daily distillate water demand for only 90 days of the year.

Graphene foam membranes with tunable pore size for next-generation reverse osmosis water desalination.

The development of carbon-based reverse osmosis membranes for water desalination is hindered by challenges in achieving a high pore density and controlling the pore size. We use molecular dynamics simulations to demonstrate that graphene foam membranes with a high pore density provide the possibility to tune the pore size by applying mechanical strain. As the pore size is found to be effectively reduced by a structural transformation under strain, graphene foam membranes are able to combine perfect salt rejection with unprecedented water permeability.

Synthesis and characterization of PES/PSF/PEG by immersion precipitation for Mediterranean seawater desalination by FO membrane

AbstractIn the present study, a simple, inexpensive, nontoxic, and environmentally friendly polyethylene glycol (PEG) polymer was used to enhance the hydrophilicity of the forward osmosis (FO) membrane using various PEG concentrations as a pore forming agent in the casting solution of polyethersulfone/polysulfone (PES/PSF) blend membranes. A nonwoven PES/PSF FO blend membrane was fabricated via the immersion precipitation phase inversion technique. The membrane dope solution was cast on polyethylene terephthalate (PET) nonwoven fabric. The results revealed that PEG is a pore forming agent and that adding PEG promotes membrane hydrophilicity. The membrane with 1 wt% PEG (PEG1) had about 27% lower contact angle than the pristine blend membrane. The PEG1 membrane has less tortuosity (which reduces from 3.4–2.73), resulting in a smaller structure parameter (S value) of 277 μm, due to the presence of open pores on the bottom surface structure, which results in diminished ICP. Using 1 M NaCl as the draw solution and distilled water as the feed solution, the PEG1 membrane exhibited higher water flux (136 L m−2 h−1) and lower reverse salt flux (1.94 g m−2 h−1). Also, the selectivity of the membrane, specific reverse salt flux, (Js/Jw) showed lower values (0.014 g/L). Actually, the PEG1 membrane has a 34.6% higher water flux than the commercial nonwoven‐cellulose triacetate (NW‐CTA) membrane. By means of varied concentrations of NaCl salt solution (0.6, 1, 1.5, and 2 M), the membrane with 1 wt% PEG showed improved FO separation performance with permeate water fluxes of 108, 136, 142, and 163 L m−2 h−1. In this work, we extend a promising gate for designing fast water flux PES/PSF/PEG FO blend membranes for water desalination.

Preparation of thermally stable 3-glycidyloxypropyl-POSS-derived polysilsesquioxane RO membranes for water desalination

Reverse osmosis (RO) membranes with polysilsesquioxane (PSQ) framework having high NaCl rejection and favorable resistance to heat and chlorine were prepared by the copolymerization of 3-glycidyloxypropyl-POSS (GPOSS) and bis[3-(triethoxysilyl)propyl]amine (BTESPA). It was found that NaCl rejection and liquid permeability were significantly improved by the introduction of GPOSS-derived units to the BTESPA-based membranes, yielding NaCl rejection of approximately 99% and liquid permeability of 5.5 × 10−13 m/s·Pa. These PSQ RO membranes with GPOSS-derived units also demonstrated excellent resistance to heat treatment of up to 100 °C and favorable resistance to chlorine in that no obvious RO performance change was observed after exposure to NaOCl aqueous solution (1000 ppm) for 10 h.

Aqueous Two-Phase Interfacial Assembly of COF Membranes for Water Desalination

HighlightsAll-aqueous phase approach to membrane fabrication is invented for the first time.Interfacial tension of water-water interface has pronounced effect on the evolution of membrane structures.Covalent organic framework membranes through aqueous two-phase interfacial assembly exhibit high water desalination performances.

Graphene-Based Membranes for Water Desalination: A Literature Review and Content Analysis.

Graphene-based membranes have unique nanochannels and can offer advantageous properties for the water desalination process. Although tremendous efforts have been devoted to heightening membrane performance and broadening their application, there is still lack of a systematic literature review on the development and future directions of graphene-based membranes for desalination. In this mini-review, literature published between 2011 and 2022 were analyzed by using the bibliometric method. We found that the major contributors to these publications and the highest citations were from China and the USA. Nearly 80% of author keywords in this analysis were used less than twice, showing the broad interest and great dispersion in this field. The recent advances, remaining gaps, and strategies for future research, were discussed. The development of new multifunctional nanocomposite materials, heat-driven/solar-driven seawater desalination, and large-scale industrial applications, will be important research directions in the future. This literature analysis summarized the recent development of the graphene-based membranes for desalination application, and will be useful for researchers in gaining new insights into this field.

Electrolyte adsorption in graphene and hexagonal boron nitride nanochannels

Understanding the dynamics of confined electrolytes through graphene-based channels is essential in multiple fields of science including: (a) developing novel artificial membranes for drug delivery, DNA sequencing and water desalination and (b) developing quantum nanoelectronic devices. In this work, All-Atom molecular dynamics simulations are used to study the adsorption of confined NaCl electrolyte solutions in graphene (GR), hexagonal boron nitride (hBN) and combined GR-hBN-GR nano-channels over a wide range of electrolyte concentrations c∈(0.1,2) M. The behavior of electrolytes confined between these surfaces is analyzed by evaluating the ionic density profiles, Potential of Mean Force (PMF), net charge density and integrated charge. Although neither graphene nor hBN has net electric charge, we observed significant changes in the ionic structure including the enhanced accumulation of sodium and the depletion in chloride density close to the hBN interfaces at low salt concentration. However, increasing the salt concentration leads to accumulation of chloride close to hBN surfaces. Two different types of hBN-GR junctions are considered in this study: a) shuffle (zigzag bonds) and (b) glide (parallel bonds). High adsorption of sodium and chloride ions near shuffle GR-hBN-GR surfaces is observed due to electrostatic attraction forces between the sodium and nitrogen atoms and between chloride and boron atoms at hBN–graphene junctions across zigzag bonds. This study reveals that GR-hBN-GR with shuffle interface is highly advantageous in adsorbing sodium and chloride ions than graphene and hBN alone. To the best of our knowledge, this is the first study that elucidates the interaction between monovalent electrolytes and GR-hBN-GR heterostructures in a confined medium.

Formation of Hydrophobic and Superhydrophobic Coatings on Track-Etched Membrane Surfaces to Create Composite Membranes for Water Desalination

Formation of Hydrophobic and Superhydrophobic Coatings on Track-Etched Membrane Surfaces to Create Composite Membranes for Water Desalination

Molecular insights into the structure-property relationships of 3D printed polyamide reverse-osmosis membrane for desalination

3D-printing is an emerging method for manufacturing polyamide (PA) reserve osmosis (RO) membranes for water treatment and desalination, which can precisely control membrane structural properties, such as thickness, roughness, and resolution. However, the synthesis-structure (i.e., degree of cross-linking (DC), m-phenylenediamine/trimesoyl chloride (MPD/TMC) ratio, and membrane thickness) to property (permeability and water-salt selectivity) relationships for these membranes has not been well understood. At the same time, a microscopic understanding of the physical mechanism of water and salt transport is needed to guide the design of high-performance 3D-printed membranes and improve the printing efficiency. Thus, the atomic-scale transport features and energetics of water and salt ions are studied at high pressure for the 3D-printed PA RO membranes with the different DCs and MPD/TMC ratios through non-equilibrium molecular dynamics (NEMD) simulations. Factoring in membrane structure properties, rejection ratio of salt ions and pressure-dependent water flux, 3D-printed PA membranes having an MPD/TMC ratio of 3.0:2.0 and a DC between 80%∼90% attains ideal performance: high water flux, high rejection of salt ions, and excellent structural integrity. Mechanistically, water permeability for highly cross-linked PA RO membranes depends on the temporary on-and-off channels that allow water molecules to jump from one cavity to another at high pressure. In addition, higher pressures cause rapid compaction of PA membranes’ free volume and membrane thickness. Membrane failure at high pressure is determined by the DC and MPD/TMC ratios-dependent compressive yield strength. In short, these findings provide physical insights for optimizing existing PA membranes and designing next-generation desalination membranes at the molecular level.

Graphene-Coated PVDF Membranes: Effects of Multi-Scale Rough Structure on Membrane Distillation Performance.

Graphene-coated membranes for membrane distillation have been fabricated by using a wet-filtration approach. Graphene nanoplatelets have been deposited onto PVDF membrane surfaces. Morphology and physicochemical properties have been explored to evaluate the changes in the surface topography and related effects on the membrane performance in water desalination. The membranes have been tested in membrane distillation plants by using mixtures of sodium chloride and humic acid. The multi-scale rough structure of the surface has been envisaged to amplify the wetting and fouling resistance of the graphene-coated membranes so that a better flux and full salt rejection have been achieved in comparison with pristine PVDF. Total salt rejection and an increase of 77% in flux have been observed for coated membrane with optimized graphene content when worked with NaCl 0.6 M (DCMD, ΔT ≈ 24 °C) over a test period of 6 h. The experimental findings suggest these novel graphene-coated membranes as promising materials to develop functional membranes for high-performing water desalination.

A Novel BiOCl Based Nanocomposite Membrane for Water Desalination.

In this study, BiOCl based nanocomposites were used as photocatalytic membranes for a simulated study on water desalination in reverse osmosis membrane systems. Through molecular dynamic simulation, the molecular structure of BiOCl, BiOCl/Ag2S and BiOCl/Bi2O3 heterojunctions were designed and their electronic properties, mechanical properties, and membrane performance for water desalination were evaluated for the first time. The molecular structure was created, and a geometry optimization task was used to optimize it. Material Studio 2019 CASTEP was used for simulation of the electronic and mechanical properties and water desalination was performed by ReaxFF software under pressures between 0 and 250 MPa. The novel BiOCl based nanocomposites showed improved electronic and mechanical properties and, most importantly, improvements in salt rejection and water permeability as compared to well-known materials such as graphene and MoS2. BiOCl and BiOCl/Ag2S had a bandgap around two, which is the ideal bandgap for semiconductor photocatalysts. A salt rejection of 98% was achieved under an applied pressure of 10 MPa. Salt rejection was higher for BiOCl/Bi2O3, while water permeability was higher for BiOCl/Ag2S. The monolayer BiOCl was unstable under pressures higher than 50 MPa, but the mechanical stability of BiOCl/Ag2S increased twofold and increased fourfold for BiOCl/Bi2O3, which is even higher than MoS2. However, between the three nanocomposites, BiOCl/Ag2S was found to be the most ideal photocatalytic nanocomposite membrane.

Thin-film nanocomposite forward osmosis membrane for water desalination: synthesis, characterization and performance improvement

Abstract The major scope of this study is the fabrication and development of a substrate and polyamide rejection layer for an efficient thin-film hydrophilic composite forward osmosis (TFC-FO) membrane. Fabrication of a thin-film nanocomposite forward osmosis membrane employing interfacial polymerization and modification of substrate characteristics using titanium dioxide (TiO2) nanoparticles as additives (TFNC-FO) are studied. Characterizations of the prepared TFC-FO and TFNC-FO membranes were determined. The morphologies of cross-section, upper and bottom surfaces for the TFC-FO and TFNC-FO membranes were studied using scanning electron microscopy (SEM). Energy-dispersive X-ray (EDX) spectroscopy was used to examine the compositions of different elements for both membranes. The hydrophilicity of the prepared TFC-FO and TFNC-FO membranes was investigated using the measurement of the contact angle test. A Fourier Transform Infrared (FT-IR) spectrophotometer was used to observe the existing functional groups of the TFC-FO and TFNC-FO membranes. The thermal stability of the membrane was evaluated via thermogravimetric analysis (TGA). The overall performance of TFC-FO membranes was evaluated with and without adding TiO2 nanoparticles through different parameters, such as membrane flux, initial feed concentration, draw solution concentrations, reverse solute fluxes, membrane permeabilities, and finally, the effect of FO membrane orientations. FO membrane performance was successfully enhanced by adding different concentrations of TiO2 nanoparticles from 0.5 to 1.5 wt%. The findings indicated that an increase in the concentration from 0.5 to 1 wt% leads to a clear increase in both the porosity and hydrophilicity of the nanocomposite substrate and consequently, an increase in the water flux. However, further increasing the concentration of TiO2 nanoparticles to more than 1 wt% affects the membrane performance.

Microscopic Insight into Water Desalination through Nanoporous Graphene: The Influence of the Dipole Moment.

Nanoporous graphene membranes with controllable pore size and chemical functionality may be one of the most desirable materials for water desalination. Herein, we investigate desalination performance of hydrogen-functionalized nanoporous graphene membranes. The charge values on hydrogen atoms (qH) and carbon atoms at the pore rim are systematically adjusted. For qH > 0, the flow rate decreases as qH increases, whereas for qH < 0, the flow rate tends to increase first and then decrease with increasing qH, yielding a peak at ∼ -0.2 e. Moreover, nanopores with large dipole moments at the rim have little effect on the salt rejection. The calculated oxygen and hydrogen density maps, the potential of mean force for water molecule and salt ion passage through the nanopores, and the coordination number unveil the mechanisms underlying water desalination in nanoporous graphene. This work may inspire the design and improvement of two-dimensional membranes for water desalination.

Graphene kirigami as an ultra-permeable water desalination membrane

In the present study, we reveal the potential of graphene kirigami (GK) as an ultra-permeable membrane for water desalination using molecular dynamics simulation. The results demonstrate that the GK membrane has superior performance in water permeance, obtaining over 103 L/m2/h/bar with 100% salt rejection. The theoretical efficiency of water permeance using GK membrane is 2.4–5.8 times higher than that of the nanoporous graphene membrane and 2–4 orders of magnitude higher than reported conventional reverse osmosis membranes. Due to the unique geometry of the kirigami structure, the GK membrane would form the adsorption channels to reduce the energy barrier during the desalination processes and guide water molecules to be filtered more effectively. Moreover, compared with the nanoporous graphene, the GK membranes do not have rigorous pore geometry restrictions for desalination and can be generated via mechanical deformation, which provides significant convenience for future applications in practical projects.

Thermal Decomposition of Hydrated Graphite Oxide: A Computational Study

We study the behavior of hydrated graphite oxide (GO) at high temperatures using thermally-accelerated molecular dynamics simulations based on ab initio density-functional theory. Our results suggest that GO, a viable candidate for water treatment and desalination membranes, is more heat resilient than currently used organic materials. The system we consider to represent important aspects of thermal processes in highly disordered GO is a hydrated GO bilayer in a vacuum. Our study provides microscopic insight into reactions involving water and functional epoxy-$\mathrm{O}$ and $\mathrm{OH}$ groups bonded to graphene layers, and also describes the swelling of the structure by water vapor pressure at elevated temperatures. We find the system withstands simulation temperatures up to approximately $2500\phantom{\rule{0.2em}{0ex}}\mathrm{K}$ before the graphitic layers start decomposing, implying the possibility of cleaning biofouling residue from a GO-based membrane by heating it in an inert-gas atmosphere.