Plant-Derived Coating Unlocks MXene’s Potential for Cleaning Drug-Laden Wastewater

A team of researchers at Khalifa University of Science and Technology in Abu Dhabi has reported a new class of hybrid membranes that could make hospital wastewater far safer before it ever reaches a treatment plant. Writing in the journal Advanced Composites and Hybrid Materials, Zainab Alansari, Lobna Nassar, Mahendra Kumar, Aya Aboukhater, Shadi W. Hasan and colleagues describe tight ultrafiltration membranes built from sulfonated poly(ether sulfone), or SPES, reinforced with a two-dimensional material called Ti₃C₂Tₓ MXene that has been chemically modified with gallic acid, a naturally occurring polyphenol found in gallnuts, tea leaves and many other plant sources. The seemingly simple act of wrapping the MXene in this plant-derived molecule turned out to be the key to solving two long-standing problems that have kept MXene out of practical water-treatment membranes: it degrades in water, and it does not bond well to polymers.

MXenes are a family of two-dimensional materials made of layers of transition-metal carbides or nitrides, discovered relatively recently but already celebrated for their extraordinary surface area, electrical conductivity and tunable surface chemistry. Ti₃C₂Tₓ, the most studied member of the family, consists of stacked sheets of titanium carbide whose surfaces carry a mixture of terminal groups, denoted Tₓ, typically combinations of oxygen, hydroxyl and fluorine. Those surface groups make the material hydrophilic and give it a strong negative charge in water, both attractive qualities for membrane science. In principle, adding MXene nanosheets into a polymer membrane should create faster water channels, better selectivity and improved antifouling behavior, because water molecules glide along the charged, oxygen-rich surfaces far more readily than they pass through the dense polymer itself.

In practice, however, MXene has a fatal weakness in aqueous environments. The same surface chemistry that makes it hydrophilic also makes it vulnerable to oxidation: over time, water and dissolved oxygen attack the titanium carbide lattice, converting the conductive nanosheets into inert titanium dioxide and destroying the ordered layered structure that gives MXene its useful properties. A membrane that loses its MXene filler within weeks of operation would deliver none of the promised performance gains. The second obstacle is compatibility. Bare MXene nanosheets tend to aggregate and interact weakly with the surrounding polymer matrix, so instead of forming a continuous, well-bonded network they cluster into defects and voids that can actually worsen a membrane’s selectivity and mechanical integrity. These twin limitations, the authors note, have restricted MXene’s application in polymeric membranes for wastewater treatment.

The Khalifa University team’s solution was to functionalize the MXene with gallic acid before embedding it in the polymer. Gallic acid, a small molecule built around a benzene ring bearing three hydroxyl groups and one carboxylic acid group, belongs to the broad family of plant polyphenols. Its multiple oxygen-containing functional groups can interact strongly with the hydroxyl and oxygen termini already present on the MXene surface, effectively capping the nanosheets with an organic layer. That layer serves several purposes at once. It shields the underlying titanium carbide lattice from oxidative attack, dramatically improving the material’s oxidation stability in water. It improves the dispersion of the functionalized MXene, known as gMX, preventing the nanosheets from clumping together. And it creates a chemically compatible bridge between the inorganic nanosheet and the sulfonated polymer, improving the interfacial affinity between gMX and SPES so that the two phases bond as a coherent hybrid rather than separating into weakly connected domains.

Those interfacial interactions, the researchers found, ripple through every aspect of the resulting membrane. The way gMX disperses within the SPES matrix influences the membrane’s morphology, its pore-size distribution, its average pore size, its hydrophilicity and even its surface charge characteristics. In other words, by tuning the chemistry at the nanoscale interface between filler and polymer, the team gained control over the membrane’s structure and behavior at the macroscale. The polymer itself, sulfonated poly(ether sulfone), is a robust engineering plastic whose sulfonic acid groups confer hydrophilicity and negative surface charge, making it a sensible host for a charged, water-loving nanofiller. When the two components are well matched, the nanosheets act as reinforcing plates and water channels rather than as flaws.

The performance numbers reported for the optimized membrane are striking. At an optimal gMX loading of 2 weight percent, the membrane designated gMX2 achieved a pure-water flux of 16.4 liters per square meter per hour per bar, a 4.3-fold enhancement over the pristine SPES membrane. That means that, under the same driving pressure and through the same effective area, the hybrid membrane passes more than four times as much water as the unmodified polymer. In membrane engineering, flux is the currency of productivity: higher flux at a given pressure translates directly into smaller plants, lower pumping energy and cheaper treated water. Achieving a fourfold improvement by adding just two percent of a functionalized nanofiller illustrates how powerfully interfacial chemistry can amplify transport, since well-dispersed MXene sheets create continuous, hydrophilic pathways that draw water through the membrane far faster than the polymer alone allows.

Flux alone is meaningless, however, if the membrane cannot hold back contaminants. In separate single-solute tests, the optimized gMX2 membrane achieved greater than 95 percent rejection of selected dyes and pharmaceuticals under synthetic feed conditions. This is the defining characteristic of a tight ultrafiltration membrane: unlike conventional ultrafiltration, which passes most dissolved molecules and removes only suspended solids and large macromolecules, tight UF sits at the boundary between ultrafiltration and nanofiltration, with pores small enough and surface chemistry tuned enough to intercept small organic molecules such as dyes and active pharmaceutical ingredients. The combination of narrowed, well-distributed pores and a negatively charged, hydrophilic surface allows the membrane to reject these solutes through a combination of size exclusion and electrostatic repulsion while still maintaining the high flux that distinguishes ultrafiltration from denser, more energy-hungry nanofiltration and reverse osmosis membranes.

The most demanding test came when the researchers filtered real hospital wastewater spiked with pharmaceuticals, using a crossflow configuration in which the feed water sweeps continuously across the membrane surface for 24 hours. Crossflow operation is the industrially relevant mode, and fouling, the gradual buildup of rejected contaminants and organic matter on the membrane surface, is the perennial enemy that degrades performance over time. During the 24-hour run, the permeate flux of gMX2 settled at 11 liters per square meter per hour per bar, a decline from its clean-water value but a level the authors describe as reflecting improved flux stability and antifouling performance compared with a membrane containing unfunctionalized MXene, designated MX2. The hydrophilic, gallic-acid-modified surface resists the adhesion of foulants, so contaminants are more easily swept away by the crossflow rather than cementing themselves onto the membrane.

Removal of the pharmaceuticals themselves was more nuanced. In the hospital wastewater filtration, gMX2 achieved removal efficiencies of 77 percent for amitriptyline, an antidepressant abbreviated AMT, and 54 percent for ciprofloxacin, a widely used antibiotic abbreviated CIP, compared with the MX2 membrane. The difference between the two compounds is instructive: pharmaceuticals differ in molecular size, charge and affinity for the membrane surface, so no single membrane rejects all of them equally. Ciprofloxacin, in particular, can carry a positive or neutral charge depending on pH, which weakens electrostatic repulsion from the negatively charged membrane and allows more of it to pass. The authors position these results not as a complete solution but as support for gMX-SPES membranes as a pretreatment option, a first barrier that substantially reduces pharmaceutical loads in hospital wastewater before the stream reaches downstream treatment stages that can finish the job.

The broader significance of the work lies in its demonstration that a cheap, plant-derived molecule can rescue an otherwise fragile nanomaterial. Gallic acid is abundant, inexpensive and benign, and functionalizing MXene with it requires no exotic chemistry, which matters enormously if the membranes are ever to be manufactured at scale for real treatment plants. Hospital effluents are among the most concentrated point sources of pharmaceuticals in the urban water cycle, releasing antibiotics, antidepressants and other active compounds that drive antimicrobial resistance and disrupt aquatic ecosystems even at trace concentrations. A membrane that combines high flux, tight rejection, fouling resistance and stable operation in genuinely dirty water addresses the exact combination of properties that treatment engineers need. By solving the oxidation and compatibility problems that have held MXene back, the Abu Dhabi team has moved this promising two-dimensional material a meaningful step closer to working in the real world, one gallic-acid-wrapped nanosheet at a time.

Subject of Research: Gallic acid-functionalized Ti₃C₂Tₓ MXene/SPES hybrid tight ultrafiltration membranes for pharmaceutical removal from hospital wastewater

Article Title: Gallic acid functionalized Ti₃C₂Tₓ MXene/SPES hybrid tight ultrafiltration membranes with improved interfacial stability for wastewater treatment

Article References: Alansari, Z., Nassar, L., Kumar, M., Aboukhater, A., & Hasan, S. W. (2026). Gallic acid functionalized Ti₃C₂Tₓ MXene/SPES hybrid tight ultrafiltration membranes with improved interfacial stability for wastewater treatment. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02097-8

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02097-8

Keywords: MXene, gallic acid, sulfonated poly(ether sulfone), tight ultrafiltration, hybrid membranes, wastewater treatment, pharmaceutical removal, antifouling, oxidation stability, membrane flux, hospital wastewater, Khalifa University