MOF-Infused Hydrogel Captures Up to 98% of Microplastics from Laundry Wastewater

Every wash cycle releases thousands of microscopic plastic fibers into the drain, and from there they slip through most treatment plants and into rivers, lakes, and oceans. Now a team of researchers at the University of Technology Sydney, working with colleagues in Vietnam, has engineered a sponge-like filter material that can strip nearly all of these particles out of real laundry wastewater. The material, described in Environmental Science and Pollution Research, combines two of materials science’s most promising tools: metal–organic frameworks, or MOFs, and hydrogels. In tests, their best composite removed up to 97 percent of polyethylene terephthalate (PET) and 98 percent of polyethylene (PE) microplastics, and it kept working after being reused six times.

The scale of the problem the team set out to tackle is enormous. Microplastics, defined as plastic particles smaller than 5 millimeters, were first named by researchers in 2004, though most particles in the environment are actually under 500 micrometers. They come from at least 14 different polymers and appear as fibers, fragments, and films. Laundry effluent is one of the richest sources, since synthetic fabrics shed fibers with every wash; other major contributors include plastic recycling wastewater, landfill leachate, and sewage sludge. Because microplastics carry chemicals from manufacturing and can also adsorb pollutants from surrounding water, their ingestion threatens wildlife and human health through combined physical and chemical toxicity. Yet the field remains exploratory, with few standards, methods, or policies governing detection, removal, and discharge.

Among available treatment options, adsorption has drawn growing attention because it is operationally simple, energy-efficient, and effective against a wide range of contaminants. MOFs, a class of crystalline materials built from metal ions connected by organic linkers, are natural candidates for the job. Their exceptional porosity and vast internal surface areas give them strong selectivity toward pollutants. In water, most microplastics acquire negative surface charges, so MOFs containing positively charged ions can capture them through strong electrostatic attraction. But earlier MOF-based removal studies have been disappointing, achieving removal efficiencies of only around 32.6 percent in one case and 76.5 percent in another. A 2025 review of more than 65 studies concluded that the field needs better synthesis efficiency, scalable applications, and environmental assessment.

The core obstacle is physical form. Pristine MOF powders exist as fine, discrete particles that lack structural stability and are difficult to deploy in continuous water treatment systems. Loose powder would clog columns, wash away, or resist handling entirely. The Sydney-led team’s solution was to embed the MOF inside a hydrogel, a three-dimensional polymer network that is porous, water-permeable, and mechanically robust. By combining the high surface activity of MOFs with the structural integrity and processability of a polymeric scaffold, the composite turns a laboratory curiosity into something that can sit at the bottom of a filtration column and treat wastewater continuously.

The fabrication process itself is deliberately simple. The researchers first synthesized two batches of a zeolitic imidazolate framework called ZIF-8 by mixing zinc nitrate with the organic linker 2-methylimidazole at different concentrations, using a conventional solvothermal method. X-ray diffraction analysis showed that the first batch, ZIF-8.1, had sharper diffraction peaks and a narrower full width at half maximum than its counterpart, indicating roughly 44 percent higher peak intensity and superior crystallinity. Nitrogen adsorption measurements confirmed classic microporous behavior, with a steep uptake at very low relative pressures and no hysteresis loop, and a surface area of about 496 square meters per gram. ZIF-8.1 was therefore selected for incorporation into the hydrogel.

To build the composite, the team dispersed 6 milligrams of ZIF-8 in water by ultrasonication, then added poly(ethylene glycol) diacrylate, a photoinitiator, and a solution of polyvinyl alcohol. The mixture was cast into a mold and exposed to ultraviolet light for 10 minutes to trigger photopolymerization, then frozen overnight and chemically cross-linked with glutaraldehyde. After rinsing and freeze-drying, the result was a disc-shaped hydrogel filter studded with ZIF-8 nanocrystals. Infrared spectroscopy confirmed the successful integration, showing new peaks corresponding to ZIF-8’s imidazole ring vibrations alongside the hydrogel’s own carbonyl and ether signals. Scanning electron microscopy revealed small crystalline particles distributed across the hydrogel skeleton without disrupting its intrinsic pore structure.

Performance testing used a low-pressure filtration column with a 30-millimeter-diameter hydrogel disc, 2.5 millimeters thick, operated at a flow rate of 1.2 liters per hour. The test water was genuine laundry wastewater collected from a residential washing machine running synthetic-fiber loads, spiked with PE and PET particles to reach 100 milligrams per liter of each polymer. The raw effluent itself contained 9,000 to 11,000 microplastic particles per liter, with particles ranging from the nanometer scale up to 200 micrometers. The bare hydrogel managed only 65 percent PET and 52 percent PE removal, hampered by its negatively charged surface, which repels similarly charged plastics. Adding 3 milligrams of ZIF-8 lifted those figures to 90 and 81 percent, and at 6 milligrams the composite reached its peak of 97 percent for PET and 98 percent for PE. At 9 milligrams, however, particle aggregation clogged the pores and wastewater could no longer pass through at all, revealing a delicate balance in MOF loading.

The mechanism behind the capture is a layered one. Zeta potential measurements showed the ZIF-8 particles carry strongly positive charges of about 26.8 millivolts, while PET, PE, and PVC particles all carry negative charges between roughly minus 22 and minus 25 millivolts, setting up powerful electrostatic attraction. Infrared analysis after filtration suggested that polar PET adsorbs through hydrogen bonding and dipole–dipole interactions between its ester groups and ZIF-8’s nitrogen-rich moieties, combined with confinement in pores around 1.16 nanometers wide. Nonpolar PE, lacking such chemical handles, is retained mainly through van der Waals forces, hydrophobic interactions, and mechanical entrapment. The interpenetrating hydrogel network adds physical sieving on top of these surface interactions, meaning removal involves filtration and particle–surface attraction working together rather than adsorption alone.

Durability and cost are where the material becomes genuinely compelling. After six filtration–regeneration cycles, PET removal had fallen only slightly, from 97 percent to 96 percent, and electron microscopy showed the composite’s morphology largely preserved after washing, with the ZIF-8 nanocrystals still anchored in place. The filter operated stably for roughly four hours per cycle, and pretreatment combined with backwashing dramatically improved long-term performance: without pretreatment, water flux dropped 21.7 percent over a 300-minute run, but with pretreatment the decline was just 5.8 percent, a stark contrast to the 9 to 54 percent flux losses reported for conventional membrane systems treating microplastic-laden municipal wastewater. The hydrogel can be freeze-dried, stored at ambient conditions without special preservation, and cast in different dimensions to fit various column configurations.

The economics look promising too. Assuming a year of continuous operation at a filtration rate of 1.7 meters per hour, with each filter replaced after six four-hour cycles, the team estimated a total annual cost of approximately 3.1 Australian dollars, or about 0.3 Australian dollars per cubic meter of laundry wastewater treated, covering only chemical and energy inputs for fabrication. That figure positions the MOF-derived hydrogel as a potentially sustainable and affordable alternative to existing technologies. The authors caution that more work is needed on long-term durability, scalability, and techno-economic feasibility at industrial scale, and they propose using X-ray photoelectron spectroscopy and Raman spectroscopy to further verify the removal mechanisms, along with testing how pH, temperature, and influent concentration affect performance. But as microplastic pollution accelerates worldwide, a cheap, reusable, sunlight-cured sponge that catches nearly every plastic particle passing through it offers a rare piece of genuinely good environmental news.

Subject of Research: Development of a ZIF-8 metal–organic framework hydrogel for removing microplastics from laundry wastewater

Article Title: Synthesis of metal organic framework-based hydrogel for microplastics removal from aquatic environments

Article References: Luu, T. T., Mao, S., Truong, D. Q., Shi, Y., Duong, T. N. O., Fu, Q., Do, V. M., Vigneswaran, S., & Nguyen, T. V. (2026). Synthesis of metal organic framework-based hydrogel for microplastics removal from aquatic environments. Environmental Science and Pollution Research, 33(28), 14165-14177. https://doi.org/10.1007/s11356-026-38156-2

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38156-2

Keywords: microplastics, metal-organic frameworks, ZIF-8, hydrogel, laundry wastewater, water treatment, adsorption, filtration, PET, polyethylene, electrostatic attraction, pollution remediation