Steel Slag Transformed Into Sunlight-Driven Textiles That Strip Viscous Oil From Water

Every year, the world’s steel industry churns out hundreds of millions of tonnes of slag, the stony byproduct left over after iron ore is smelted and refined. Most of it ends up stockpiled in vast heaps or relegated to low-grade road fill, a monument to the inefficiencies of heavy industry. Now, a team of researchers in China has found a way to turn this industrial waste into something remarkably sophisticated: a smart textile that uses sunlight to heat its surface and rapidly peel sticky, viscous oils away from water. The work, published in the Journal of Materials Science, describes a composite material built from three separate streams of waste — steel slag, a two-dimensional material called MXene, and discarded cotton pads — and demonstrates that the resulting fabric can separate even the most stubborn oil-water mixtures with impressive speed and durability.

The central challenge the researchers set out to solve is one that has plagued environmental engineers for years: viscous oil. Light oils such as diesel or gasoline flow readily, and conventional superwetting membranes handle them reasonably well. But heavy oils — crude oil residues, lubricants, cooking grease — cling to surfaces with a tenacity that quickly clogs pores and kills filtration rates. When such oils are cold, their high viscosity makes them behave almost like tar, and pumping them through a membrane becomes an exercise in futility. The solution explored by the team, led by Junxiang Guo of the Shougang Group Research Institute of Technology and Shan Peng of Hebei University, is to heat the oil directly on the membrane surface. Warm oil flows. The trick is generating that heat efficiently, sustainably, and without external power.

Enter the photothermal effect. Certain materials convert absorbed light into heat with remarkable efficiency, and the researchers harnessed this by synthesizing an iron-based metal-organic framework, or Fe-MOF, directly from steel slag. Metal-organic frameworks are crystalline lattices in which metal ions are connected by organic linkers into porous, sponge-like architectures. Iron is abundant in steel slag, which means the waste material itself can serve as the metal feedstock for the framework. Rather than requiring purified iron salts from a chemical supplier, the process taps the slag’s own iron content, converting a disposal liability into a functional nanomaterial. This is the kind of closed-loop chemistry that waste-valorization researchers dream about: the pollutant becomes the product.

But a Fe-MOF alone was not enough. To maximize the photothermal response, the team embedded their slag-derived framework into the layers of MXene, a family of two-dimensional titanium carbide materials known for exceptional light-to-heat conversion and electrical conductivity. MXenes are typically stacked in tight, parallel sheets, and their performance in composite devices depends heavily on how accessible those interlayer spaces are. The Fe-MOF particles, wedged between the MXene layers, pried the sheets apart, widening the interlayer spacing. According to the study, this expansion did more than create room — it formed heterojunctions at the interface between the two semiconductors, dramatically improving electron transport across the boundary. The practical consequence was a photothermal system that responds faster and reaches higher heating intensity than either component could achieve alone.

The next problem was durability. Superhydrophilic surfaces — surfaces that water wets completely, spreading into a thin film — are the foundation of underwater superoleophobic membranes. Because water spreads instantly across the surface and fills the pores, oil droplets are physically repelled when the membrane is submerged, allowing water to pass while oil is blocked. The trouble is that many superhydrophilic coatings are fragile; viscous oils and repeated washing gradually strip away the hydration layer, and the membrane loses its selectivity. The researchers addressed this with an elegant biochemical additive: glycyrrhizic acid, a naturally occurring saponin compound extracted from licorice root. The highly hydrophilic glycyrrhizic acid forms a gel-like protective layer on the textile, held in place by complex intermolecular forces, and this gel acts as a water reservoir that locks in the stable superhydrophilic state even under prolonged exposure to fouling oils.

The substrate for all this chemistry is itself recycled. The composite was deposited onto a superhydrophilic fiber cloth made from waste cotton pads, giving the material a third environmental credential. The finished textile therefore embodies a triple act of recycling: metallurgical slag becomes a functional MOF, waste cotton becomes the structural fabric, and the whole assembly is stabilized by a plant-derived molecule. The authors describe the resulting material as exhibiting superior and stable superhydrophilic and underwater superoleophobic properties, meaning that in water it repels oil almost completely while welcoming water through its pores.

Where the material truly shines is in its separation performance under illumination. When light strikes the textile, the Fe-MOF/MXene composite converts it to heat at the surface, warming viscous oil on contact and slashing its viscosity so that it can be driven off the membrane quickly rather than smearing across it. The study reports that the composite enables rapid separation of viscous oil/water mixtures as well as emulsion systems, in which oil droplets are so finely dispersed that ordinary filters fail. It also demonstrates excellent oil pollution resistance and a high cycled usage rate, meaning the textile can be used repeatedly without losing performance — a critical requirement for any material hoping to leave the laboratory. For spill response, industrial wastewater treatment, and kitchen-grease separation alike, the combination of solar-driven heating and antifouling wetting behavior addresses the two failure modes that doom most conventional membranes.

There is a bonus capability woven into the fabric: flame retardancy. A textile designed for oil handling operates in an environment where flammable vapors and ignition sources are never far away, and a material that resists burning adds a meaningful margin of safety. The study reports that the composite textile achieved flame-retardant properties, an unusual feature for a separation membrane and one that stems from the inorganic-rich composition of the slag-derived components layered onto the cotton substrate. This multifunctionality — separation, photothermal heating, antifouling stability, and fire resistance in a single recycled textile — is what distinguishes the work from the long catalogue of single-purpose oil-water separation membranes that have appeared over the past decade.

The broader significance of the research lies in its template for high-value waste utilization. Steel slag’s global utilization rate remains stubbornly low, and the authors argue that novel processing routes are urgently needed. Conventional applications — aggregate for concrete, road base, cement additive — capture little of the slag’s chemical value. By extracting iron to build a metal-organic framework, the process moves slag up the value chain from bulk filler to engineered nanomaterial. Meanwhile, the use of waste cotton pads tackles another underappreciated waste stream, and the glycyrrhizic acid stabilization shows how biomass-derived molecules can solve engineering problems that synthetic polymers have struggled with. The paper, the authors note, not only reports a new oil/water separation material but also provides a new pathway for the high-value utilization of steel slag and the recycling of waste cotton pads.

Much work remains before such textiles could be deployed at the scale of an oil spill or a refinery’s wastewater stream — scaling MOF synthesis from slag, ensuring consistent MXene production, and validating long-term outdoor durability under real sunlight are all open questions. But the demonstration is a compelling proof of concept: a material assembled almost entirely from waste, powered by sunlight, and capable of doing one of environmental engineering’s hardest jobs quickly and repeatedly. If the chemistry scales, the mountains of slag outside the world’s steel mills may one day be looked at not as waste, but as raw material waiting for its second act.

Subject of Research: Recycling steel slag into Fe-MOF/MXene photothermal superwetting textiles for viscous oil/water separation

Article Title: Resource utilization of steel slag for fabrication of Fe-MOF-based photothermal superwetting textiles with rapid viscous oil/water separation

Article References: Guo, J., Cheng, Z., Peng, S., Yin, Y., Wu, J., Gu, M., & Mei, Z. (2026). Resource utilization of steel slag for fabrication of Fe-MOF-based photothermal superwetting textiles with rapid viscous oil/water separation. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13791-9

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13791-9

Keywords: steel slag, Fe-MOF, MXene, photothermal, superwetting, oil/water separation, glycyrrhizic acid, waste valorization, flame retardant, emulsion separation, recycled cotton, metal-organic frameworks