Membranes For Water Desalination Research Articles

Eco-Friendly Superhydrophobic Modification of Low-Cost Multi-Layer Composite Mullite Base Tubular Ceramic Membrane for Water Desalination

This study aimed to investigate and develop a cost-effective and superhydrophobic ceramic membrane for direct contact membrane distillation (DCMD) applications. Two types of mullite-based composite membranes were prepared via extrusion and sintering techniques. To create a small and narrow pore diameter distribution on the membrane surface, the dip-coating technique with 1 µm alumina was employed. The hexadecyltrimethoxysilane eco-friendly grafting agent was adopted to modify low-cost multilayer mullite-based composite membranes, transforming them from hydrophilic to superhydrophobic. The prepared membranes were characterized via field emission scanning electron microscopy (FESEM), energy-dispersive spectrometry (EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray diffraction (XRD), liquid entire pressure (LEP), contact angle, atomic force microscopy (AFM), porosity, and membrane permeability. The results of the prepared membranes validate the appropriateness of the material for membrane distillation applications. The optimized membrane, with a contact angle of 160° and LEP = 1.5 bar, was tested under DCMD using a 3.5 wt.% sodium chloride (NaCl) synthetic solution and Persian Gulf seawater as a feed. Based on the acquired results, an average permeate flux of 3.15 kg/(m2·h) and salt rejection (R%) of 99.62% were found for the 3.5 wt.% NaCl solution. Moreover, seawater desalination showed an average permeate flux of 2.37 kg/(m2·h) and salt rejection of 99.81% for a 20-h test without any pore wetting. Membrane distillation with a hydrophobic membrane decreased the turbidity of seawater by 93.13%.

Fast Water Desalination with a Graphene-MoS2 Nanoporous Heterostructure.

Energy-efficient water desalination is the key to tackle the challenges with drought and water scarcity that affect 1.2 billion people. The material and type of membrane in reverse osmosis water desalination are the key factors in their efficiency. In this work, we explored the potential of a graphene-MoS2 heterostructure membrane for water desalination, focusing on bilayer membranes and their advantages over monolayer counterparts. Through extensive molecular dynamics simulation and statistical analysis, the bilayer MoS2-graphene was investigated and compared to the monolayer of graphene and MoS2. By optimizing the heterostructure membrane, improved water flux was achieved while maintaining a high ion rejection rate. Furthermore, the study delves into the physical mechanisms underlying the superior performance of heterostructure nanopores, comparing them with circular bilayer and monolayer pores. Factors investigated include water structure, hydration shell near the membrane surface, water density, energy barrier using the potential of mean force, and porosity within the nanopore. Our findings contribute to the understanding of heterostructure membranes and their potential in enhancing the water desalination efficiency, providing valuable insights for future membrane design and optimization.

Sucrose-derived carbon membranes for sustainable water desalination

Sucrose-derived carbon membranes for sustainable water desalination

Porous rGO/networked cellulose composite membranes: Towards enhanced nanofiltration performance of rGO-based membranes

Graphene-based materials have been widely used for the fabrication of superior separation membranes for water treatment and purification. In particular, reduced graphene oxide (rGO), which has better water stability than graphene oxide (GO), has been demonstrated to be a good building block. However, rGO laminates are characterized by narrow interlayer spacing leading to dense packing and consequently lower flux limiting their direct utilization for membrane development. In this study, we report the fabrication of networked cellulose (NC)/porous rGO composite membranes with enhanced separation performance. We observed a synergistic effect due to the incorporation of NC and the presence of nano-pores on the rGO sheets. Firstly, in addition to the enhanced hydrophilicity and mechanical stability, the presence of NC with networked fibers reduced the horizontal transport resistance within the interlayer channels due to the formation of voids and wrinkles. Secondly, in-plane pores created by H2O2 oxidation of GO effectively contributed to additional transport channels providing shortened transport length for water molecules. Results showed that composite membranes maintained stable long-term performance with a pure water permeance up to 25.1 ± 2.2 Lm−2h−1bar−1 and salt rejection of 70.2 %, 63.08 %, 17.13 % and 25.62 %, for Na2SO4, MgSO4, MgCl2 and NaCl respectively. Unlike many previously reported rGO membranes that rely on ultra-thin selective layers, this work demonstrates an effective strategy for fabricating superior rGO membranes for water treatment and desalination.

Fabrication of nanoporous multilayer graphene nanoplatelets membrane for water desalination

In recent years, graphene-based membranes are extensively explored for desalination process to fulfil the pure water scarcity. Still, there is a noticeable gap in the research on a technique that simultaneously deposits a membrane and also generates pores in the flake of membrane. In this work, we demonstrated a one-step and scalable protocol i.e. a conventional atmospheric plasma spraying (APS) to fabricate a graphene nanoplatelets (GNP) membrane for water desalination application. Various characterization tools: FE-SEM, Raman, and TEM etc. utilized to evaluate the deposition of GNPs flakes and induced sub-nanometer pores in the large area GNP membrane. Plasma-sprayed GNP membrane showed impressive desalination performance in terms of water flux, salt rejection, and permeability around ~67 Lm−2 h−1, ~99 %, and ~ 115 Lm−2h−1bar−1 respectively at 0.6 bar of transmembrane pressure (TMP). This performance of the GNP membrane was attributed to the critical role of graphene in terms of its structures, including induced pores within graphene sheets and its functions. Our deposited GNP membrane is cost-effective and showed the applicability of conventional plasma spraying in the design of nanomaterials-based membranes for various water purification protocols.

Production and characterization of graphene oxide/polymer support composite membranes for water desalination and purification

Filtration membranes play a critical role in ensuring access to clean drinking water by effectively removing contaminants and sea water desalination. Novel materials are being explored to meet the filtration membranes requirements of reduced energy consumption, high permeability, high selectivity, and affordability. Graphene nanomaterials have emerged as a highly promising option due to their exceptional properties. Due to their extraordinarily high surface area, chemical stability, mechanical durability, atomic thickness, and reactivity towards diverse water pollutants, graphene nanomaterials offer outstanding efficiency as membranes for water desalination and purification. In this study, we propose the fabrication of membranes using graphene oxide (GO) supported by commercially available porous polymeric membranes such as polytetrafluoroethylene (PTFE). Composite membranes are formed by depositing graphene oxide dispersions with different concentrations onto the support membranes through vacuum-assisted filtration. The structure and morphology of the resulting graphene oxide membranes were characterized using scanning electron microscopy (SEM-FEG), Raman spectroscopy, x-ray diffraction (XRD), and UV‐VIS spectroscopy. To assess their performance, the GO membranes were subjected to filtration tests using salted water and conductivity measurement of permeate. These measurements allow the evaluation of their efficiency in removing salts. The obtained results demonstrate the potential of the fabricated membranes for water desalination.

Highly efficient mica-incorporated graphene oxide-based membranes for water purification and desalination.

Graphene oxide (GO) has become the most attractive material for membrane technology owing to its potential application as a nanofiller in water treatment, purification, and desalination. In this study, we incorporated mica as a cross-linking reagent to increase the interlayer spacing and stability of GO sheets and fabricated a mica/GO (MGO) membrane for the first time. The MGO membrane (260 ± 10 nm) exhibits 100% rejection for biomolecules such as tannic acid (TA) and bovine serum albumin (BSA) and >99% rejection for multiple probe molecules, such as methylene blue, methyl orange, congo red, and rhodamine B. The high rejection of membranes can be attributed to the surface interaction of mica with GO nanosheets through covalent interaction, which enhances the stability and separation efficiency of the membranes for probe ions and molecules. This ultrathin MGO membrane also exhibits much better water permeability at 870 ± 5 L m-2 h-1 bar-1, which is 10-100 times greater than that reported for pure GO and GO-based composite membranes. Additionally, the membrane shows high rejection for salt ions (70%). Furthermore, the stability of the MGO membranes was evaluated under various conditions, and the membranes demonstrated remarkable stability for up to 60 days in a neutral environment.

Highly Efficient Arginine Intercalated Graphene Oxide Composite Membranes for Water Desalination.

Graphene oxide-based composite membranes have received enormous attention for highly efficient water desalination. Herein, we prepare arginine/graphene oxide (Arg/GO) composite membranes by surface functionalizing GO nanosheets with arginine amino acid. Arginine has a unique combination of hydroxyl and amino functional groups that cross-link GO nanosheets through hydrogen bonding and electrostatic interactions. The as-prepared Arg@GO composite membranes with different thicknesses are used to separate the salt and dye molecules. The 900-nm-thick Arg@GO composite membrane shows high rejection of 98% for NaCl and 99.8% for MgCl2, Ni(NO3)2, and Pb(NO3)2 with good water permeance. Such a membrane also shows a high separation efficiency (100%) for methylene blue, rhodamine B, and Evans blue dyes. At the same time, the ultrathin Arg@GO composite membrane (220 ± 10 nm) exhibits high water permeance of up to 2100 ± 10 L m-2 h-1 bar-1. Furthermore, the 900-nm-thick Arg@GO composite membrane is stable in an aqueous environment for 40 days with significantly less swelling. Therefore, these membranes can be utilized in future desalination and separation applications.

Optimisation of direct contact membrane distillation to enhance brackish water desalination and study polyvinylidene fluoride (PVDF) membrane performance

This study explores the optimisation of operational parameters in direct contact membrane distillation (DCMD) for brackish water desalination using polyvinylidene fluoride (PVDF) membranes. Central composite design (CCD) identified optimal conditions, and quadratic regression models demonstrated a strong correlation (R2 values: 0.98 for salt rejection, 0.99 for permeate flux) between operational factors and membrane performance. Artificial neural network (ANN) models surpassed Response Surface Methodology (RSM) in predictability for permeate flux and salt rejection. Multi-objective Genetic Algorithm (MOGA) optimisation yielded a pareto optimal solution, revealing two sets of conditions: one maximising permeate flux (21.40 L/m2 h) with 44.75 LPH feed flowrate and the other achieving 100 % salt rejection with 52.48 LPH feed flowrate. Optimising DCMD for flexible water desalination, this study positions it as a promising, sustainable technique, providing practical large-scale implementation guidance. Addressing limitations is key to widespread adoption as a cost-effective freshwater production method.

Development of a high flux Janus PVDF membrane for oily saline water desalination by membrane distillation via PDA-TEOS-APTES surface modification

Membrane distillation (MD) is a promising approach for water desalination. However, in practice, this process is hindered by poor water flux and severe membrane fouling. In this study, a series of Janus membranes were designed for the desalination of oily saline water via direct contact membrane distillation (DCMD). Janus membranes were fabricated by a simple and facile method, direct deposition of dopamine (DA), tetraethylorthosilicate (TEOS), and aminopropyltriethoxysilane (APTES) on one side of the polyvinylidene fluoride (PVDF) membrane, which was modified by hydrophobic SiO2 nanoparticles. In brief, one side of the optimum Janus membrane was strongly hydrophobic (WCA: 149.7 ± 1°) while another side exhibited in air hydrophilicity (WA: 36.3 ± 1.2°) and underwater superoleophobicity. Additionally, the optimum Janus membrane experienced a remarkable enhancement in water flux, reaching an impressive value of 52.6 kg/m2h, (69.2 % increment compared to the pristine PVDF). Notably, the optimal Janus membrane demonstrated long-term stability and significant resistance toward oil fouling during the DCMD desalination of oily saline water while preserving its rejection and high vapor flux. The applied strategies may offer a fresh perspective on membrane design with efficient performance for MD by a facile method.

Charged nanoporous phosphorene as a water desalination membrane: insights from molecular dynamics

Phosphorene, due to its remarkable properties such as self-passivation, stability, and anti-fouling, makes it a promising material for desalination membranes. Practically, these membranes acquire charges and affect the salt rejection and water flux. In this article, water desalination performance through positively charged (PC), negatively charged (NC), and charged but overall neutral (CN) single-layer nanoporous phosphorene (NPP) membrane of nanopore size ∼41 Å2 is investigated using pressure-driven molecular dynamics simulations. It is observed that the electrostatic interactions due to the distribution of charge around the nanopore edges strongly affect the desalination performance rather than steric hindrance. Overall, with an equivalent magnitude of total applied charge, the water flux through the CN membrane is more than PC and NC membranes. A membrane best suited for desalination performance among the charged NPP membranes is a CN membrane due to its high flux and adequate salt rejection, though it allows the passage of both ions. Comparatively, a PC or NC membrane has lower flux and allows the course of their counter ions respectively. To construe this observation salt ion density maps and molar concentration profiles are further examined. The degree of localization of counter ions around the nanopore edge increases with the increased total applied charge. While no such localization is observed for the CN membranes. PC and NC membranes provide more energetic barriers to co-ions due to strong coulombic repulsions and molecular layering of the adsorbed water, which hinder their transport. This study suggests the design of charged phosphorene membranes to maximize water transport while still maintaining the salt rejection potential.

Bioinspired humic acid-based membranes for water desalination: Mechanistic insights from molecular simulations

Bioinspired membranes have received considerable interest for separation, but their design is challenging because of lack in fundamental understanding of separation mechanism involved. Herein, we explore renewable humic acid (HA)-based bioinspired membranes for water desalination via molecular simulations. Different HA membranes (monomeric, Y- and star-crosslinked) with microscopic “ridge-and-valley” patterned pore structures are constructed. With the existence of intermolecular hydrogen bonds, the HA membranes possess good mechanical strength with Young's moduli ranging from 0.44 to 1.64 GPa. Water desalination performance of the HA membranes is comprehensively examined in 12 salt solutions with different cations (Mg2+, Ca2+, Li+, Na+, K+ and NH4+) and anions (CO32−, SO42−, F−, OH−, Cl− and NO3−), respectively. Water and ion in the HA membranes are revealed to follow a dynamical “hopping-transport” mechanism. The HA membranes exhibit superior desalination performance, comparable to commercial reverse osmosis membranes and graphene oxide membranes. Interestingly, water flux in the monomeric HA membrane is enhanced by tailoring the membrane structure from monomeric to crosslinked architecture. Upon varying cation or anion in a salt solution, salt rejection drops when ion hydration level decreases. From bottom-up, the simulations provide mechanistic insights into water desalination and would facilitate the development of new membranes for high-performance water desalination.

A mini-review on MoS2 membrane for water desalination: Recent development and challenges

Abstract This review provides comprehensive studies of molybdenum disulfide (MoS2) for water desalination. The most recent molecular dynamics simulation and experimental work on the design, fabrication, ion rejection, and water flux of MoS2 were summarized. Since MoS2 has excellent properties such as physicochemical, mechanical, and biological properties compared to other 2D materials such as graphene-based nanomaterial, it is necessary to have a critical study on MoS2-based membranes. Hence, a critical review of MoS2-based membranes has been found essential for us to investigate and evaluate the findings in this field and objectively assess the current state-of-the-art in water desalination. The advantages of desalination technology and the primary approaches that have been used up until now are first outlined in this study, deeply emphasizing membrane technology. The primary mechanism of salt rejection in membrane technology is explained. Then, the types of MoS2-based membranes for water desalination are reviewed based on the different published works while critically reviewing the performance of each type of MoS2-based membranes.

Preparation and characterization of nanocomposite Forward Osmosis Membranes for water desalination.

Preparation and characterization of nanocomposite Forward Osmosis Membranes for water desalination.

In situ modification of ultrafiltration membranes with eco-friendly pyrogallol/taurine to enhance antifouling performance

Fouling is a long-standing problem in water treatment membranes because it substantially deteriorates process efficiency. Here, we present a facile strategy for the in situ modification of polyethersulfone (PES) ultrafiltration (UF) membranes with eco-friendly antifouling materials (i.e., pyrogallol and taurine) to enhance their fouling resistance. When the PES dope solution was immersed into the nonsolvent containing pyrogallol and taurine, the phase separation and surface modification of the PES phase occurred simultaneously. Surface modification with taurine was mediated by pyrogallol, which reacted with taurine to form pyrogallol–taurine complexes. Amphiphilic pyrogallol–taurine complexes were effectively bound to the phase-transitioning PES, resulting in their uniform, dense, and robust deposition throughout the external and internal pore surfaces of the membrane without changing its pore structure. Consequently, the in situ-modified PES membrane exhibited remarkably higher surface hydrophilicity and a more negative charge than pristine PES. Importantly, the proposed in situ modification strategy significantly improved the protein anti-adhesive and antifouling properties of the pristine membrane and enhanced its permeance performance, which cannot be achieved by ex situ modification. Our study provides a facile antifouling strategy that can be applied to various membranes for water purification and desalination and extensively describes the underlying modification mechanism.

Water flow rate quantification through an experimental CNT membrane: A molecular dynamics simulation approach

The comprehension of water flow rate within carbon nanostructures holds great importance in both theoretical understanding and engineering design of microscale and nanoscale devices. This study presents a comprehensive numerical model for analyzing the water flow rate in Carbon Nanotube (CNT) membranes. The outcomes of this model have particular relevance in predicting the performance and designing CNT membranes for water desalination, which offer the potential for remarkably rapid transport. By investigating the characteristics of the CNT membrane, various geometric properties that influence the overall flow rate are quantified. Apart from the diameter and length, attention is also given to non-ideal factors associated with the deformation of CNTs from their original structures. Specifically, the impact of eccentricity and bending on the flow rate through CNTs is examined, revealing limited but noteworthy effects. Additionally, a simplified model is developed to characterize the membrane using statistical data pertaining to CNT synthesis. The results of the total water flow rate demonstrate that the existing numerical model closely aligns with the reported experimental values.

Smart dynamic hybrid membranes with self-cleaning capability

The growing freshwater scarcity has caused increased use of membrane desalination of seawater as a relatively sustainable technology that promises to provide long-term solution for the increasingly water-stressed world. However, the currently used membranes for desalination on an industrial scale are inevitably prone to fouling that results in decreased flux and necessity for periodic chemical cleaning, and incur unacceptably high energy cost while also leaving an environmental footprint with unforeseeable long-term consequences. This extant problem requires an immediate shift to smart separation approaches with self-cleaning capability for enhanced efficiency and prolonged operational lifetime. Here, we describe a conceptually innovative approach to the design of smart membranes where a dynamic functionality is added to the surface layer of otherwise static membranes by incorporating stimuli-responsive organic crystals. We demonstrate a gating effect in the resulting smart dynamic membranes, whereby mechanical instability caused by rapid mechanical response of the crystals to heating slightly above room temperature activates the membrane and effectively removes the foulants, thereby increasing the mass transfer and extending its operational lifetime. The approach proposed here sets a platform for the development of a variety of energy-efficient hybrid membranes for water desalination and other separation processes that are devoid of fouling issues and circumvents the necessity of chemical cleaning operations.

Anatase-cellulose acetate for reinforced desalination membrane with antibacterial properties

This study aimed to prepare antifouling and highly mechanical strengthening membranes for brackish and underground water desalination. It was designed from cellulose acetate (CA) loaded anatase. Anatase was prepared from tetra-iso-propylorthotitanate and carboxymethyl cellulose. Different concentrations of anatase (0.2, 0.3, 0.5, 0.6, 0.7, and 0.8)% were loaded onto CA during the inversion phase preparation of the membranes. The prepared membranes were characterized using Fourier Transform Infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM & EDX), mechanical properties, swelling ratio, porosity determination, and ion release. The analysis confirmed the formation of anatase on the surface and inside the macro-voids of the membrane. Furthermore, anatase loading improved the CA membrane’s mechanical properties and decreased its swelling and porosity rate. Also, CA-loaded anatase membranes displayed a significant antibacterial potential against Gram-positive and Gram-negative bacteria. The results showed that the salt rejection of the CA/anatase films as-prepared varies considerably with the addition of nanomaterial, rising from 46%:92% with the prepared membranes under the 10-bar operation condition and 5 g/L NaCl input concentration. It can be concluded that the prepared CA-loaded anatase membranes have high mechanical properties that are safe, economical, available, and can stop membrane biofouling.

Oscillating electric field assisted nano-incised graphene kirigami for ultrahigh-performance water desalination membrane

Benefiting from the single-atom thickness, dense honeycomb structure, nano-size pores, and adjustable selection capability, graphene kirigami (GK) is expected to be a promising candidate for the membrane of water desalination. However, due to the low bending stiffness of the GK structure, the fluctuation in incision size and the accumulation of salt ions around the incisions always limit the GK membrane from higher water desalination efficiency. In this study, we adopted an oscillating electric field to improve the water desalination efficiency of nano-incised GK via molecular dynamic (MD) simulation. The results reveal that with the oscillating electric field's assistance, the water permeability of the GK membrane achieves 1351.6 L/m2/h/bar theoretically under the condition of 100 % salt rejection, 5.9–7.1 times higher than the reported nano-porous graphene membrane and 2–5 orders of magnitude higher than the existing reverse osmosis membranes. The oscillating electric field can enhance the water desalination efficiency of the proposed GK membranes mainly by alleviating the structural fluctuation of the GK membrane and dredging the permeation pathway for water molecules. The considerable potential of the oscillating electric field-assisted GK membrane reported by this study will attract great attention in the field of water separation and purification.

Functionalized Carbon Honeycomb Membranes for Reverse Osmosis Water Desalination

AbstractReverse osmosis desalination is a common technique to obtain fresh water from saltwater. Conventional membranes suffer from a trade‐off between salt rejection and water permeability, raising a need for developing new classes of membranes. C‐based membranes with porous graphene and carbon nanotubes offer high salt rejection, water permeability, and fouling resistance. However, controlling the pore size of these membranes is challenging. Therefore, a carbon honeycomb membrane is studied using classical molecular dynamics simulations. It is reported that functionalization with −COO– groups provides 100% salt rejection with around 1000 times higher water permeability than conventional polyamide membranes. Atomic‐level understanding of the effect of the functional groups' location on salt rejection and water permeability is developed.