📄 chemistry

Assessment of Metal-Organic Framework Incorporated Thin Film Nanocomposite Membrane in Real Seawater Desalination Via Pressure Assisted Osmosis

This study demonstrates that incorporating 0.05 wt% hydrophilic aluminium fumarate metal–organic framework (MOF) into thin film nanocomposite membranes significantly enhances water permeability and salt rejection, achieving a stabilized flux of 9.35 Lm⁻²h⁻¹ for efficient real seawater desalination via pressure-assisted osmosis.

Original authors: Rajesha Kumar Alambi, Mansour Ahmed, Garudachari Bhadrachari, Mansour Al-Rughaib, Jibu P. Thomas

Published 2026-09-23

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Rajesha Kumar Alambi, Mansour Ahmed, Garudachari Bhadrachari, Mansour Al-Rughaib, Jibu P. Thomas

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Fresh water is a precious resource, and turning the ocean's saltiness into drinkable liquid is one of humanity's most persistent engineering challenges. For decades, scientists have relied on a method called reverse osmosis, which forces seawater through a fine filter using immense pressure to squeeze out the salt. While effective, this process demands a great deal of energy. A newer, gentler approach known as forward osmosis uses the natural pull of a salty solution to draw water through a membrane, requiring far less energy but often producing water too slowly for large-scale use. To bridge this gap, researchers have developed a hybrid technique called pressure-assisted osmosis. This method combines the natural pull of osmosis with a small, gentle push of hydraulic pressure, aiming to speed up the flow of fresh water without the massive energy costs of traditional methods. The success of this technique, however, depends entirely on the quality of the membrane used; it must be strong enough to handle pressure, yet porous enough to let water rush through while keeping salt behind.

In a recent study, researchers at the Kuwait Institute for Scientific Research set out to build a better membrane for this specific purpose. They focused on creating a thin film nanocomposite membrane, a sophisticated material that acts as a selective barrier. To improve its performance, they embedded tiny, porous crystals known as metal-organic frameworks into the membrane's surface. Specifically, they used a type of crystal made from aluminum and fumaric acid, a material chosen for its ability to attract water molecules and its stability in salty environments. The team fabricated these membranes by layering a porous support fabric with a thin polyamide skin, a process where the aluminum crystals were mixed in to create new pathways for water to travel. They then tested these new membranes using real seawater collected from the coast, pushing it against a highly concentrated salt solution under varying levels of gentle pressure to see how much water could be recovered and how well the salt was blocked.

The results of the study were encouraging. The researchers found that adding the aluminum crystals significantly changed the membrane's behavior. The new membranes became much more hydrophilic, meaning they had a stronger natural affinity for water, which allowed water to pass through more easily. When tested with real seawater, the membrane containing a small amount of the aluminum crystals—specifically 0.05 percent by weight—performed better than the standard control membranes. It achieved a stable flow rate of 9.35 liters per square meter per hour while maintaining a salt rejection rate of 98.9±1.1%. This means that for every unit of water that passed through, almost all of the salt was left behind. Crucially, the membrane also demonstrated a low tendency to let salt leak backward into the fresh water, a common problem in osmotic processes that reduces efficiency.

Beyond just moving water, the study confirmed that these new membranes were physically robust enough for the job. The aluminum crystals helped reinforce the structure, making the membrane stronger and more resistant to the pressure applied during the test. The researchers observed that the crystals created a rougher, more textured surface, which increased the area available for water to interact with the membrane. This structural change, combined with the material's natural ability to attract water, helped reduce a phenomenon called internal concentration polarization, where salt builds up inside the membrane and slows down the flow. By keeping the salt from clogging the internal pathways, the membrane maintained a steady performance even as the experiment progressed.

The team also explored how different levels of pressure affected the outcome. They found that applying a moderate amount of pressure, between zero and two bar, significantly boosted the water flow. At higher pressures, the water moved faster, but the salt concentration in the feed water also rose more quickly as the draw solution became diluted. The membrane with the optimal amount of aluminum crystals managed to balance these factors effectively, offering a high flow rate without sacrificing the quality of the fresh water produced. The study suggests that this specific type of aluminum-based framework is a promising candidate for next-generation desalination systems, particularly in regions with high salinity seawater where efficiency and durability are paramount.

While the study focused on laboratory-scale tests with real seawater, the findings point toward a tangible improvement in how we might approach water scarcity. The research did not claim to have solved the global water crisis, but it did demonstrate a clear, measurable step forward in membrane technology. By proving that these specific crystals could enhance both the speed and the strength of the membrane, the researchers provided a concrete example of how nanomaterials can be tailored to solve practical engineering problems. The work highlights that the future of desalination may not lie in building bigger machines, but in refining the microscopic architecture of the filters that separate salt from water.

Technical Summary: Assessment of Metal-Organic Framework Incorporated Thin Film Nanocomposite Membrane in Real Seawater Desalination Via Pressure Assisted Osmosis

Problem Statement
Traditional Forward Osmosis (FO) membrane systems face intrinsic limitations, including low water productivity caused by severe internal concentration polarization (ICP) and a gradual decline in effective osmotic driving force. While FO offers advantages such as low fouling propensity and low hydraulic energy consumption, its practical application for seawater desalination is hindered by low permeate flux, particularly with high-salinity feed waters. Pressure-Assisted Osmosis (PAO) has emerged as a promising hybrid approach that combines the osmotic driving power of FO with moderate hydraulic pressure (typically <5 bar) applied to the feed side. This configuration aims to enhance net water transport and recovery without the extreme energy costs associated with Reverse Osmosis (RO). However, the successful deployment of PAO requires membranes that possess high water permeability, strong salt rejection, low reverse salt flux (RSF), and sufficient mechanical stability to withstand simultaneous osmotic and hydraulic loads. Current Thin Film Composite (TFC) membranes often suffer from the permeability–selectivity trade-off, where increasing water flux compromises salt rejection, and dense polyamide structures resist mass transfer. Furthermore, there is a scarcity of research evaluating Metal-Organic Framework (MOF)-incorporated membranes under real seawater PAO conditions, as most studies are limited to laboratory-scale tests with synthetic feeds.

Methodology
This study focuses on the fabrication and evaluation of Thin Film Nanocomposite (TFN) membranes incorporating Aluminium Fumarate (Al-Fumarate) MOF nanoparticles for PAO applications.

Membrane Fabrication: The membranes were synthesized on a polyethersulfone (PES) support layer reinforced with nonwoven fabric. The selective polyamide layer was formed via interfacial polymerization using meta-phenylenediamine (MPD) and trimesoyl chloride (TMC). Al-Fumarate MOF nanoparticles were dispersed into the MPD solution at varying concentrations (0.0125, 0.05, and 0.10 wt%) prior to polymerization to create TFN membranes (denoted M0.0125, M0.050, M0.10), alongside a control membrane (M0/M1) without MOF.
Characterization: The MOF and membranes underwent comprehensive characterization. The MOF was analyzed for crystallinity and stability in saline media using XRD and BET analysis. Membrane properties were assessed via Scanning Electron Microscopy (SEM) for morphology, Atomic Force Microscopy (AFM) for surface roughness, Attenuated Total Reflectance Infrared Spectroscopy (ATR-IR) and X-ray Photoelectron Spectroscopy (XPS) for chemical composition, contact angle measurements for hydrophilicity, and tensile testing for mechanical strength.
Performance Testing: Desalination performance was evaluated using a laboratory-scale cross-flow PAO system. The feed solution consisted of real seawater collected from a beachwell, while the draw solution was 2 M NaCl. Tests were conducted at hydraulic pressures ranging from 0 to 2 bar. Key performance metrics included water flux ( $J_v$ ), reverse salt flux ( $J_s$ ), feed side conductivity changes, draw side dilution, and the difference in conductivity ( $\Delta C$ ) across the membrane.

Key Contributions and Results
The study demonstrates that incorporating Al-Fumarate MOF into the polyamide selective layer significantly alters the membrane's physicochemical properties and desalination performance:

MOF Stability and Morphology: Al-Fumarate MOF exhibited high crystallinity and maintained its structural integrity after 72 hours of exposure to 3.5 wt% NaCl solution, as confirmed by XRD. SEM analysis revealed that moderate MOF loading (0.05 wt%) resulted in a uniform dispersion and a leaf-like or nodular surface morphology with spherical voids. Higher loading (0.1 wt%) led to particle agglomeration.
Hydrophilicity and Roughness: The incorporation of Al-Fumarate increased membrane hydrophilicity, reducing the water contact angle to 49.8° at the highest loading. AFM analysis confirmed increased surface roughness, with the M4 membrane (0.1 wt%) showing a peak roughness ( $R_a$ ) of 138 nm, attributed to the formation of nodular structures.
Mechanical Strength: The inclusion of a nonwoven fabric support was critical for mechanical robustness. The TFN membrane with 0.05 wt% MOF (M3) exhibited the highest mechanical properties, with a Young's modulus of 46.82 MPa and a tensile strength of 2.78 MPa, surpassing both the unsupported PES and the control TFC membranes.
Transport Properties: The M3 membrane (0.05 wt% MOF) achieved an optimal balance between permeability and selectivity. It demonstrated a water permeability of 3.8 ± 0.22 Lm⁻²h⁻¹bar⁻¹ and a NaCl rejection of 98.9 ± 1.1%, with a low B/A ratio of 8.9 kPa.
Real Seawater PAO Performance: In real seawater tests with 2 M NaCl draw solution, the M3 membrane showed superior performance at hydraulic pressures between 0 and 2 bar.
- Flux: The membrane achieved a stabilized flux of 9.35 Lm⁻²h⁻¹. While flux increased with pressure (peaking initially at ~20 Lm⁻²h⁻¹ at 2 bar), higher pressures accelerated draw solution dilution, leading to flux decline over time.
- Selectivity and RSF: The M3 membrane maintained lower reverse salt flux compared to higher loading membranes. At moderate pressures (1.0–1.5 bar), the membrane exhibited the most stable RSF and enhanced selectivity. The hydrophilic nature of the MOF facilitated water transport and mitigated internal concentration polarization, resulting in more efficient draw dilution and reduced feed concentration polarization.

Significance
The paper claims that the integration of hydrophilic Al-Fumarate MOF into TFN membranes addresses the critical permeability–selectivity trade-off and mechanical limitations of conventional FO/PAO membranes. The study highlights that the Al-Fumarate MOF's microporous framework boosts water transport, reduces internal concentration polarization, and improves structural stability under hydraulic loading. Specifically, the M3 membrane (0.05 wt% MOF) is identified as a superior candidate for seawater PAO desalination in high-salinity settings, offering a reliable balance of high water flux, excellent salt rejection, and low reverse salt flux. The research provides empirical evidence that MOF-incorporated membranes can withstand real-world seawater conditions and moderate hydraulic pressures, offering a pathway toward more efficient osmotic desalination technologies.

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