A new photocatalyst that combines sunlight and a common water-treatment oxidant can rapidly strip dangerous organic matter from water, offering a promising tool for safer drinking water and cleaner natural waterways.
Cleaning up hidden hazards in water
Fulvic acid, a major component of natural organic matter, gives many rivers and reservoirs their yellow-brown color and can react with chlorine during disinfection to form carcinogenic byproducts in tap water. These disinfection byproducts, including trihalomethanes and haloacetic acids, pose long-term risks to human health and complicate water treatment in both cities and rural areas. Removing fulvic acid and similar "refractory" organics efficiently and at scale has been a long-standing challenge for engineers and utilities.
A sunlight driven catalyst
Researchers have now developed a recyclable photocatalyst, made from bismuth oxychloride and a two dimensional material called MXene, that harnesses visible light to supercharge a widely used oxidant known as peroxymonosulfate. In tests, this BiOCl MXene composite removed 98.43 percent of fulvic acid from water in just 30 minutes under visible light, with a reaction rate more than three times faster than that of conventional BiOCl alone. The team reports that the catalyst retains over 80 percent of its removal efficiency after five reuse cycles, highlighting strong durability for repeated operation.
People often think of water pollution as something you can see, like plastic or algae, but some of the most harmful compounds are invisible and extremely difficult to break down. Our material uses ordinary light and a common oxidant to dismantle these complex molecules quickly, which is very attractive for real world water treatment."
Chenglong Sun, lead author, Qingdao Agricultural University
How the technology works
The composite forms a Schottky junction, a special interface where metallic MXene and semiconducting BiOCl work together to separate and shuttle photogenerated charges much more efficiently than either material alone. When illuminated, electrons move into the MXene while holes remain in BiOCl, minimizing recombination and making more reactive species available to attack pollutants. The incorporation of MXene also expands the catalysts surface area from 9.17 to 41.73 square meters per gram, providing many more active sites for reactions to occur.
By activating peroxymonosulfate, the system generates a cocktail of powerful oxidants, notably holes and superoxide radicals, which were identified as the dominant species driving degradation. Advanced spectroscopic analyses showed that the process rapidly destroys the aromatic structures and chromophores that make fulvic acid stable and light absorbing, with specific ultraviolet absorbance values and fluorescence signals plummeting within the first few minutes of reaction. Measurements of total organic carbon confirmed that nearly half of the carbon in fulvic acid was mineralized to carbon dioxide and small non fluorescent molecules within 30 minutes.
Robust in real water and for many pollutants
Beyond ideal laboratory conditions, the photocatalyst performed strongly across a wide pH range from 3 to 9 and maintained high removal efficiencies even as fulvic acid concentration increased from 20 to 100 milligrams per liter. Common ions found in natural and treated waters, such as chloride, sulfate and nitrate, caused only modest interference at realistic levels, and the system preserved more than 80 percent removal efficiency when low concentrations of these anions were present. In tap water and lake water, which contain natural organic matter and various dissolved salts, the catalyst still removed over 70 percent of fulvic acid within 30 minutes.
The researchers also demonstrated that the same system can tackle a broad spectrum of organic pollutants beyond fulvic acid. Under visible light and peroxymonosulfate, the composite achieved removal rates as high as 99.99 percent for the antibiotic doxycycline, above 98 percent for dyes such as methylene blue and rhodamine B, and up to 94.71 percent for phenolic contaminants like nonylphenol. This versatility suggests that the material could be deployed for treating diverse industrial wastewaters and emerging contaminants that resist conventional treatment.
Toward safer and more sustainable treatment
Senior author Guangshan Zhang emphasizes that the work links fundamental materials design with practical environmental needs. "The key is that we did not just chase higher reaction rates," Zhang said. "We focused on stability, resistance to real water conditions, and clear mechanistic understanding, so that this concept can be scaled and adapted in advanced oxidation units for real treatment plants."
The team envisions that BiOCl MXene based reactors could be integrated into existing advanced oxidation processes to polish drinking water, safeguard small rural systems, or remediate heavily polluted surface waters. Because the catalyst works under visible light and uses a controllable oxidant already familiar to the water industry, it may offer a practical route to reduce hidden carcinogenic risks while lowering energy demand and chemical footprints.
Sun, C., et al. (2026). Synergistic photocatalysis of BiOCl/MXene activates peroxymonosulfate for enhanced fulvic acid degradation: performance and mechanism insights. Agricultural Ecology and Environment. doi: 10.48130/aee-0025-0014. https://www.maxapress.com/article/doi/10.48130/aee-0025-0014
