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This blog post is a placeholder for collecting links to interesting research papers, background reading, etc. - on the topic of graphene filters for saltwater desalination.
Suggested Background Reading:
- https://en.wikipedia.org/wiki/Potential_applications_of_graphene
- Graphene and water treatment: introduction and market status
"Scientists at Monash University have developed a graphene-based filter that can desalinate ocean water instantly using minimal energy."
"The filter is just a few atoms thick, made from graphene oxide with nanoscopic pores that allow water molecules through while blocking salt and other impurities. Unlike traditional desalination, which uses energy-intensive reverse osmosis, this filter works passively under low pressure—making it ideal for remote or disaster-stricken regions."
"Its efficiency could help solve water scarcity for millions. Tests show it can purify seawater faster and more effectively than any existing system, without relying on heavy infrastructure"
New Monash-designed water filter removes stubborn ‘forever chemicals’
"The research team designed a beta-cyclodextrin (βCD) modified graphene oxide (GO-βCD) membrane with nanoscale channels that selectively retain PFAS while allowing water to pass through."
"In tests, the Monash membrane significantly outperformed traditional polyamide membranes, which typically remove only about 35 per cent of short-chain PFAS. The team also confirmed that the membrane creates an energetic barrier that prevents PFAS movement, effectively blocking contamination."
"Study first author and Monash PhD candidate, Eubert Mahofa, highlighted the significance of this breakthrough in PFAS filtration: 'PFAS are difficult to manage because they dissolve easily in water and can spread far from their original source, making contamination challenging to contain and remediate. Removing small PFAS molecules from water has been a major hurdle for existing filters,'"
Paper:
"Removal of per- and polyfluoroalkyl substances (PFAS) from water has become a research topic of interest in recent times. However, it is very challenging to remove short-chain (<C8) PFAS from water sources using traditional means, especially in mixtures. Herein, a β-cyclodextrin (βCD)-modified graphene oxide (GO-βCD) membrane is designed with asymmetrically sized nanochannels that exhibit strong affinitive binding interactions with PFAS. PFAS transport is significantly hindered within the GO-βCD lamella due to interactions with the strategically embedded βCD sites and complementary molecular dynamics simulations reveal that short-chain PFAS exhibit ∼20% stronger binding affinity to βCD compared to that of alternative structures of cyclodextrins. The GO-βCD membrane demonstrates remarkable simultaneous retention of over 90% from a mixture of perfluorobutanoic acid (PFBA), perfluoropentanoic acid (PFPeA), perfluorohexanoic acid (PFHxA), and perfluorooctanoic acid (PFOA) while achieving a permeance of 21.7 ± 2 L m–2 h–1 bar–1 and upconcentrating the feed by ∼300%. The performance of GO-βCD was compared to that of polyamide membranes, which exhibit a significant decline in capacity to retain short-chain PFAS (∼35% for PFBA). In combining permeation experiments and molecular dynamics simulations with the transition state theory model, it was demonstrated that the energy barrier for transport of PFAS is greater within the GO-βCD laminar architecture compared to that of GO-αCD and pristine GO. These modified membranes have strategically embedded sites capable of hindering PFAS transport and provide an approach for removing broad-spectrum PFAS under realistic conditions, over long-term operation (24 h), and at concentrations relevant to surface and ground waters."
Other Suggested Papers:
"Solar desalination is a widely employed system that harnesses solar energy to produce drinking water. The key advantages of solar stills include that the generation of freshwater is a renewable energy-based, eco-friendly, and cost-effective process. This sustainable approach addresses the critical need for clean water while minimizing ecological impact and offering economic benefits. In the solar still system, the configuration of the absorber plays a crucial role, as an ineffective absorber can lead to lower thermal performance and reduced water productivity. This investigation focuses on an absorber design that incorporates a tube container containing Phase Change Material (PCM) of paraffin wax. The encapsulation of PCM within the still enhances heat transfer and provides heat energy, especially during radiation fluctuations. Moreover, the thermal properties of the PCM were improved by introducing graphene oxide nanoparticles dispersed within. Three different concentrations of graphene oxide (0.3 wt%, 0.6 wt%, and 0.9 wt%) were investigated. It was explored that paraffin with 0.9 wt% graphene oxide nanoparticle demonstrates superior thermal performance compared to paraffin alone. Significantly, at a concentration of 0.9 wt%, the paraffin/graphene oxide nanoparticles showed increased water productivity, temperature, and still thermal efficiency by around 33.9%, 41.2%, and 68.7%, respectively."
Emerging membrane technologies for sustainable water treatment: a review on recent advance
"The growing scarcity of freshwater resources, coupled with industrial pollution, necessitates the development of efficient and sustainable water treatment technologies. Membrane-based desalination and heavy metal removal processes are at the forefront of these technologies, providing efficient and reliable solutions to meet the growing demand for clean water. This study provides a comprehensive review on recent advancements in desalination technologies, focusing on emerging materials that have significantly influenced desalination and heavy metal removal performances. A meticulous screening of recent review papers on both along with experimental studies published within the last year is provided, thereby offering an updated perspective on the ongoing experiments dedicated to water treatment using membranes. Notably, this review considers various membrane types, including nanocomposites, biomimetic, thin-film composites, hybrids, and membranes associated with forward osmosis. Results indicate that nanocomposite membranes, thin-film composite membranes, and forward osmosis membranes are widely used for desalination and heavy metal removal compared to hybrid and biomimetic membranes. This widespread utilization can be attributed to their well-established fabrication techniques, robust mechanical properties, high removal%, and better scalability for industrial applications. In contrast, while hybrid and biomimetic membranes are promising, they are still under development and facing challenges pertaining to material synthesis, cost, and integration into existing systems."
"This study explores the strategic synthesis of sulfonated polyethersulfone (SPES) with tunable sulfonation degrees to engineer selective interfacial layers (SLs) for thin-film composite (TFC) forward osmosis (FO) membranes. To overcome the persistent trade-off between water permeability and salt rejection in conventional TFC membranes, this work introduces an interlayer engineering strategy utilizing zeolitic imidazolate framework-8 nanoparticles (ZIF-8 NPs). Unlike traditional approaches that focus solely on membrane surface modification, the integration of ZIF-8 as a nanostructured interlayer addresses interfacial defects and enhances solute screening by leveraging its molecular sieving capabilities and hydrophilicity through the Janus membrane effect. SPES-based membranes exhibited a notable enhancement for water flux from 15.23 to 32.12 L/m2 h compared to neat polyethersulfone (PES) SLs. Simultaneously, the salt rejection effectively reached 93.9% for SPES/ZIF-8/PA(#2). XRD and FTIR analyses confirmed the crystallinity and chemical integrity of ZIF-8 NPs, while FESEM revealed their uniform dispersion across the SL surface. Notably, the sulfonation process not only enhanced surface porosity but also created a chemically reactive interface for ZIF-8 anchoring, a dual-functionality rarely achieved in prior studies. The findings offer a scalable framework for designing high-performance TFC membranes with hierarchically engineered interfaces, paving the way for next-generation desalination and resource recovery systems."
"The accumulation of dense crystal layers on solar evaporators compromises performances by reducing light absorption efficiency and obstructing water transport channels, ultimately diminishing evaporation rate. To mitigate this issue, spatially separated crystallization sites can be engineered on the evaporator surface to disrupt salt adhesion and prevent dense layers formation. In this study, we developed a 3D column-shaped wood evaporator (KAC-DW) by coating delignified wood (DW) with KOH-activated carbon (KAC). The KAC coating creates microstructured surface featuring abundant protrusions (~144 mm−2, each 20 μm in height), which effectively inhibit salt crystal adhesion. Under 1 kW m−2 solar radiation with a 15 wt% NaCl solution, the KAC-DW evaporator achieved an impressive water evaporation rate of 8.18 kg m−2 h−1 over 96 h (0 m s−1 wind speed)—more than double the performance of uncoated DW (3.91 kg m−2 h−1). This enhancement stems from two key mechanisms: (1) the KAC protrusions prevent dense crystal layer formation, preserving open surface channels for evaporation, and (2) they promote the growth of loose salt crystals, thereby expanding the effective evaporation area and further boosting the evaporation rate."
"Global population growth and climate change are causing freshwater scarcity, which necessitates creative solutions like solar-driven desalination. This technology's widespread adoption is hampered by cost and efficiency issues. Intrinsic photothermal conversion efficiency has gotten less attention than light trapping and thermal management, which have been the main focuses of efforts to increase photo-to-vapor efficiencies. Here, a commercial padding and vapor polymerization method are used to develop scalable nylon fabrics that act as solar absorbers. This is achieved by anchoring iron catalysts with hydrolyzed perfluorooctyltriethoxysilane chains, which cause confined polymerization of pyrrole to generate polypyrrole. By narrowing the bandgap and generating bioinspired light-trapping nanostructures, this technique achieves a superior intrinsic photothermal conversion efficiency of 84.6%, which is 4.94 times higher than that of unconfined polymerization. These fabrics are used to create a Janus evaporator, which operates steadily in prolonged seawater testing and shows an evaporation rate of 3.84 kg m−2 h−1. The low manufacturing cost of ≈28 RMB m−2 emphasizes its scalability and economic potential. This work offers insights into the design of high-performance, scalable, and cost-effective solar absorbers by prioritizing increases in light absorption and intrinsic photothermal conversion efficiencies for developing solar desalination technology."
"Usually, reinforcement is introduced into the membrane matrix to solve the problem of hollow fiber membranes with poor mechanical properties. Herein, the fiber bundle reinforced PES hollow fiber loose NF membranes with GO doping were fabricated by the skin-core fiber spinning technology and concentric circle method in order to overcome the easily collapsible hollow fiber membrane at medium and high-pressure operation. The reinforced structure and content of GO exhibited noticeable effects on the structure and properties of membranes. On the one hand, the fiber bundle constructed the excellent mechanical properties of the membrane (185 MPa) for enhancing the lateral pressure resistance, which was beneficial for long-term stability. On the other hand, the high permeation flux and efficient dye desalination property were obtained due to the doping of GO. For example, the permeation flux of the obtained PPG-3 membrane was up to 115.6 L m−2 h−1 with the rejection of Congo red (99.8%) and MgCl2 (only 4.0%). Consequently, the GO-doping and fiber bundle reinforced way could be considered as a synergistic effect to prepare the high permeation flux and long-term operation stability of the hollow fiber loose NF membranes, which will be suitable for dye desalination in textile wastewater treatment."
Janus Membrane for Simultaneous Water Purification and Power Generation
"The intricate water‐energy nexus pinpoints the necessity of simultaneously managing both resources. The effective interaction between water movement and porous materials lies at the heart of membrane processes as well as hydrovoltaic technology. Herein, an innovative water‐energy cogeneration system combining hydrovoltaic technology into membrane distillation processes is reported, leveraging hierarchically porous structures composed of polyaniline (PANI) and polydopamine (PDA)‐modified carbon nanotubes (CNTs) nanofilaments on a commercial PVDF substrate. The heat‐conductive CNTs network with the water‐rich PDA, improves thermal efficiency, enhancing water production by 17.3% compared to bare PVDF. Synergistically enhanced by efficient ion transport within the PANI network, electron accumulation along the PANI‐PDA‐CNTs direction, and the conductive nanobridge effect of CNTs, a continuous and durable power density of 2.78 µW cm⁻² is achieved in the commercially available membrane filtration process. This work provides an accessible approach to concurrently addressing water and energy challenges."
"Nanofiltration membranes with high charge density are highly attractive for selectively removing organic micropollutants and divalent anions from water environments. Here we constructed polyamide (PA) membranes with ultra-high negative charge density via a sea-squirt nanofibrillated cellulose restricted interfacial polymerization process. Sea-squirt nanofibrillated cellulose, which contains a high content of 7.0% carboxyl groups and 29.8% hydroxyl groups, effectively fettered piperazine and regulated the interfacial polymerization reaction kinetics. As a result, the optimized membrane had an ultra-high zeta potential of −148 mV at pH 7 and a charge density of −32.6 mC m ⁻² . This membrane achieved outstanding performance metrics, including a water permeance of 41.5 l m ⁻² h ⁻¹ bar ⁻¹ , exceptional SO 4 ²⁻ /Cl ⁻ selectivity of 144.5 and greatly increased water/organic micropollutant selectivity. Molecular dynamics simulations revealed a 73.1% reduction in the diffusion rate of piperazine due to competitive forces, leading to a PA surface enriched with -COOH groups. This work provides an effective strategy for tuning the PA membrane charge density to increase water purification and wastewater treatment efficiency."
"High-performance and sustainable membranes for water desalination applications are crucial to address the growing global demand for clean water. Concurrently, electrospinning has emerged as a versatile manufacturing method for fabricating nanofibrous membranes for membrane distillation. However, widespread adoption of electrospinning for processing water–insoluble polymers, such as fluoropolymers, is hindered by the reliance on hazardous organic solvents during production. Moreover, restrictions on industrial solvents are tightening as environmental regulations demand greener alternatives. This critical challenge is addressed here by demonstrating, for the first time, the fabrication of nanofibrous electrospun membranes of PVDF-HFP, poly(vinylidene fluoride)-co-hexafluoropropylene using a renewable, environment- and user-friendly solvent system containing Cyrene (dihydrolevoglucosenone), dimethyl sulfoxide, and dimethyl carbonate. The same solvent system was further used to produce nanocomposite graphene oxide (GO) and graphene nanoplatelet (GNP)-containing nanofibrous electrospun membranes. When tested for water desalination via membrane distillation, these membranes either outperformed or matched the performance of those produced with hazardous organic solvents, achieving salt rejection rates of >99.84% and long-term stability. The economic viability of the green solvent system was further validated through Monte Carlo simulations. This work demonstrates the potential to move fluoropolymer electrospinning from dimethylformamide-based systems to greener alternatives, enabling the consistent production of high-quality nanofibrous membranes. These findings pave the way for more sustainable manufacturing practices in membrane technology, specifically for water desalination via membrane distillation."
2D Materials for Potable Water Application: Basic Nanoarchitectonics and Recent Progresses
"Water polluted by toxic chemicals due to waste from chemical/pharmaceuticals and harmful microbes such as E. Coli bacteria causes several fatal diseases; and therefore, water filtration is crucial for accessing clean and safe water necessary for good health. Conventional water filtration technologies include activated carbon filters, reverse osmosis, and ultrafiltration. However, they face several challenges, including high energy consumption, fouling, limited selectivity, inefficiencies in removing certain contaminants, dimensional control of pores, and structural/chemical changes at higher thermal conditions and upon prolonged usage of water filter. Recently, the advent of 2D materials such as graphene, BN, MoS2, MXenes, and so on opens new avenues for advanced water filtration systems. This review delves into the nanoarchitectonics of 2D materials for water filtration applications. The current state of water filtration technologies is explored, the inherent challenges they face are outlines, and the unique properties and advantages of 2D materials are highlighted. Furthermore, the scope of this review is discussed, which encompasses the synthesis, characterization, and application of various 2D materials in water filtration, providing insights into future research directions and potential industrial applications."
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