Low-Temperature Chemical Trick Grows Tough Water-Repelling Nanostructures for Desalination

Fresh water scarcity is one of the defining challenges of the twenty-first century, and one of the most promising technologies to combat it has long been plagued by a frustratingly fragile Achilles heel: membranes that cannot survive contact with the very liquids they are meant to reject. Now, a research team led by scientists at Universiti Teknologi Malaysia’s Advanced Membrane Technology Research Centre (AMTEC) has unveiled a low-temperature manufacturing strategy that could finally push omniphobic membranes out of the laboratory and into industrial desalination plants. Writing in the Journal of Materials Science, Rendy Muhamad Iqbal, Zhong Sheng Tai, Mohd Hafiz Dzarfan Othman and their colleagues describe a simple electroless deposition technique that grows tough, re-entrant zinc oxide nanostructures directly on polymer hollow fiber membranes, producing a surface that shrugs off water, oils, and organic contaminants alike.

Membrane distillation is a deceptively elegant process. Instead of pushing salt water through tiny pores at high pressure, as in reverse osmosis, membrane distillation exploits a temperature difference across a hydrophobic, microporous membrane. Water vapor evaporates from the warm feed stream, travels through the air-filled pores, and condenses on the cooler permeate side, leaving salts, metals, and most dissolved impurities behind. Because the driving force is vapor pressure rather than hydraulic pressure, the method can concentrate extremely saline brines, treat produced water from oilfields, and even recover valuable resources from waste streams. Its one great vulnerability, however, lies in the word hydrophobic. Standard hydrophobic membranes resist pure water, but real-world feeds are full of surfactants, oils, alcohols, and low-surface-tension organics that can sneak into the pores, flooding the membrane and destroying the air-water interface on which the whole process depends.

The field’s answer has been the omniphobic membrane, a surface engineered to repel essentially all liquids, not just water. The trick to true omniphobicity lies in geometry as much as chemistry. Surfaces decorated with re-entrant structures, overhanging profiles that curve inward like the walls of a mushroom or a springtail’s skin texture, can trap a stable layer of air beneath low-surface-tension liquids, because the liquid cannot make contact angle progress on the undercut geometry even when its surface tension is low. Researchers have fabricated such surfaces using fluorinated silanes, sprayed nanoparticles, and hydrothermally grown nanorods. But each approach carries a cost: nanoparticles are only weakly glued to the substrate and shear away in turbulent feed flows, hydrothermal synthesis typically demands high temperatures and multiple steps, and complex layer-by-layer recipes resist scale-up beyond small membrane coupons.

The Malaysian team’s contribution is to sidestep all three problems at once with a single, scalable chemistry. Electroless deposition, a process borrowed from metallurgy and recently demonstrated on fabrics and eggshell membranes, uses a catalytic seed layer to drive crystal growth from an aqueous solution without any external electrical power. In their scheme, the polyvinylidene fluoride (PVDF) hollow fiber membranes are first sensitized with a catalyst, then immersed in a zinc salt solution where zinc oxide nucleates and grows directly on the fiber surface. Crucially, the entire process operates below 90 degrees Celsius and at ambient pressure, conditions mild enough that the polymer substrate never softens, warps, or degrades, and mild enough that continuous, roll-to-roll-style fabrication of long membrane modules becomes genuinely plausible.

The elegance of the method lies in its tunability. By simply varying the concentration of the zinc precursor, the researchers grew two distinct families of nanostructures. Dilute solutions of 0.05 molar produced rod-like protrusions, while richer solutions at 0.1 and 0.2 molar shifted the growth toward prism-type architectures. Because the crystals form in situ, anchored at their roots by the catalytic interface rather than merely sitting atop the polymer, the resulting structures resist detachment far better than dip-coated nanoparticles, which the same group had previously shown to be vulnerable to adhesion loss. That structural integration matters enormously in membrane distillation, where feed sparging, crossflow shear, and chemical fouling constantly batter the surface.

Among the membranes tested, the one grown from the intermediate 0.1 molar precursor struck the most favorable balance between roughness, pore blockage, and vapor permeability. Its surface resisted wetting by multiple low-surface-tension liquids, holding contact angles above 112 degrees even for liquids that would instantly soak a conventional hydrophobic membrane. It withstood a liquid entry pressure of 5.8 bar, a measure of how hard the feed can push before liquid forces its way into the pores, while still transporting water vapor efficiently. The lesson is that more nanostructure is not always better: excessively aggressive growth raises mass transfer resistance and shrinks effective pore size, throttling the flux that makes a desalination membrane economically viable.

Performance under realistic fouling conditions is where the new membrane truly distinguished itself. The team challenged it with direct contact membrane distillation using a saline feed spiked with humic acid, a ubiquitous natural organic matter component notorious for gluing foulants to membrane surfaces and for teaming up with salts to induce catastrophic pore wetting. Over short-term tests the optimized membrane lost only 4.6 percent of its water flux, and over a full 24-hour continuous run the decline reached just 13 percent, all while rejecting nearly 100 percent of the salt. Stable salt rejection throughout the run is the key indicator: it means the pores stayed dry, the entrained air layer held, and the liquid never breached the membrane, even in the presence of wetting-prone organic matter.

The broader significance of the work is as much about manufacturing as it is about materials science. Laboratory demonstrations of omniphobic membranes are abundant, but industrial deployment demands processes that are cheap, energy-efficient, continuous, and tolerant of the polymer substrates used in commercial hollow fiber spinning. A process that runs below 90 degrees Celsius in ordinary aqueous baths at atmospheric pressure, requiring no autoclaves, no vacuum systems, and no exotic precursors, fits the bill. The authors point out that electroless deposition can in principle be applied continuously to long lengths of hollow fiber, turning membrane modification from a batch-bound bottleneck into an in-line production step. That kind of manufacturability, they argue, is what separates a promising paper from a deployable technology.

There are, of course, questions that only longer trials will answer. Twenty-four hours of stable operation is encouraging but a far cry from the months of continuous duty expected in a plant, and the long-term durability of the fluorinated surface chemistry that typically accompanies omniphobic membranes remains an industry-wide concern. Scaling effects, feed chemistries beyond humic acid, and the economics of precursor consumption all await scrutiny. Yet the core achievement stands: a re-entrant, strongly anchored, omniphobic nanostructure grown on a flexible polymer fiber under conditions gentle enough for mass production. If desalination is to reach the hypersaline brines, oilfield waters, and industrial effluents that reverse osmosis cannot touch, membranes like these, built by chemistry simple enough to be scaled, may prove to be exactly the durable, wetting-resistant workhorses the field has been searching for.

Subject of Research: Low-temperature electroless growth of ZnO re-entrant nanostructures on PVDF hollow fiber membranes for omniphobic, wetting-resistant membrane distillation desalination.

Article Title: A low-temperature electroless route for in-situ growth of ZnO re-entrant nanostructures for scalable omniphobic hollow fiber membranes in wetting-resistant membrane distillation

Article References: Iqbal, R. M., Tai, Z. S., Othman, M. H. D., Arifin, N. D. T., Shazana, N. A., Rahman, M. A., Mustapa, W. N. F. W., Kadirkhan, F., Puteh, M. H., Jaafar, J., Rahman, M. A., & Ismail, A. F. (2026). A low-temperature electroless route for in-situ growth of ZnO re-entrant nanostructures for scalable omniphobic hollow fiber membranes in wetting-resistant membrane distillation. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13735-3

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13735-3

Keywords: membrane distillation, omniphobic membrane, zinc oxide, electroless deposition, PVDF hollow fiber, re-entrant nanostructures, desalination, wetting resistance, anti-fouling, water treatment, nanomaterials, membrane fabrication