Flower-Shaped Bismuth Catalyst Turns Chlorite Into a Powerful Water Purifier

Bisphenol A, better known as BPA, has become one of the most stubborn contaminants in the world’s water supplies. The compound, which is widely used in plastics and epoxy resins, belongs to a family of chemicals known as endocrine disrupting chemicals, or EDCs, because they can interfere with hormonal systems even at very low concentrations. Conventional treatment plants were never designed to strip these molecules out of wastewater, and their persistence in rivers, lakes, and even drinking water sources has raised growing concern among environmental scientists and public health authorities alike. Now, a team of researchers at Huizhou University in China, working with a colleague at Shenzhen Polytechnic University, has reported a photocatalytic system that can destroy BPA in water with remarkable speed and efficiency, and their findings have been published in the journal Catalysis Letters.

The heart of the new technology is a carefully engineered composite photocatalyst made of two bismuth-based semiconductors: bismuth oxybromide, BiOBr, and bismuth oxycarbonate, Bi2O2CO3. The researchers synthesized a series of these composites, which they labeled xyDBi according to the ratio of the two components, and shaped them into flower-like microstructures assembled from two-dimensional nanosheets. Crucially, the synthesis was tuned so that the (001) crystal facet is the predominantly exposed plane of the material. Facet engineering of this kind matters because different crystal faces have different atomic arrangements, surface energies, and electronic properties, and exposing the right facet can dramatically improve how a photocatalyst absorbs light, adsorbs molecules, and shuttles charge carriers to its surface where reactions take place.

What makes the composite truly special, however, is not just its shape but the way the two semiconductors interact at their junction. When BiOBr and Bi2O2CO3 are brought into intimate contact, their mismatched energy bands create a robust internal electric field at the interface. Through comprehensive materials characterization and theoretical calculations, the team showed that this field drives an S-scheme charge transfer mechanism, in which the photogenerated electrons and holes with lower reactivity recombine with each other across the junction, preserving the strongly oxidizing and reducing carriers on opposite sides. This spatial separation of charges is the holy grail of photocatalysis: it prevents the energy of absorbed sunlight from being wasted as heat while keeping the most powerful oxidants and reductants available to attack pollutants.

The second ingredient in the system is chlorite, a chlorine-oxygen anion that has recently attracted attention as an unconventional oxidant for advanced oxidation processes. On its own, chlorite is relatively inert, but when it is activated on the right catalytic surface it can generate chlorine dioxide, a selective and potent oxidizing species that is already familiar to water treatment engineers as a disinfectant. The Chinese team’s insight was to combine chlorite activation with visible-light photocatalysis in a single integrated process, so that the same illuminated catalyst that harvests sunlight also unlocks the oxidizing potential stored in the chlorite ions. The result is a dual-engine system in which light-driven chemistry and chemical activation reinforce one another.

A key question was where, exactly, chlorite ions bind and react on the catalyst surface. To answer it, the researchers turned to density functional theory calculations and in situ diffuse reflectance infrared Fourier transform spectroscopy, a technique that allows scientists to watch molecules adsorb and react on a surface in real time under reaction conditions. Both approaches pointed to the same answer: oxygen vacancies, the tiny defects where oxygen atoms are missing from the crystal lattice, act as Brønsted acid sites that facilitate the adsorption of chlorite ions. In other words, the defects are not passive imperfections but active players, anchoring the oxidant precisely where it needs to be to react with photogenerated carriers. This defect-mediated activation pathway adds a new dimension to the design of photocatalysts for water treatment.

Once adsorbed, the chlorite is converted into chlorine dioxide through two distinct pathways, the team found. In one route, the oxygen vacancies themselves drive the activation of chlorite ions into chlorine dioxide. In the other, hydroxyl radicals, the ferociously reactive species generated when photogenerated holes oxidize water or surface hydroxyl groups, attack chlorite and convert it into the same product. Chlorine dioxide was identified as the primary reactive species responsible for degrading BPA, which is notable because chlorine dioxide tends to attack pollutants through selective one-electron oxidation reactions rather than the indiscriminate, non-selective chemistry of hydroxyl radicals. That selectivity can be an advantage, since it reduces the waste of oxidizing power on harmless background constituents of the water and limits the formation of problematic disinfection byproducts.

The performance numbers are striking. Under visible light irradiation, the addition of chlorite to the photocatalytic system based on the optimal composite, 11DBi, achieved 92.7 percent removal of BPA within just 25 minutes. Equally important for any technology hoping to leave the laboratory, the catalyst proved exceptionally stable across a broad range of realistic conditions. The team tested variations in initial pH, the presence of coexisting anions and cations that would normally be found in natural waters and wastewater, repeated recycling of the catalyst over multiple runs, and different water matrices. The system held up across all of them, suggesting that the material is not a fragile laboratory curiosity but a candidate robust enough to survive the messy chemistry of real-world treatment scenarios.

Beyond simply measuring how fast BPA disappeared, the researchers worked out how the molecule is actually dismantled. By identifying the intermediate products formed during degradation, they deduced that the destruction of BPA proceeds through demethylation, hydroxylation, and cleavage of the isopropylidene bridge, the central carbon structure that holds the two phenolic rings of the molecule together. Breaking that bridge effectively splits the molecule into smaller fragments that can be further oxidized toward benign end products. Understanding the degradation pathway at this level of detail matters because it allows toxicologists and engineers to assess whether the intermediates formed along the way are themselves hazardous, and to tune the process so that the treatment genuinely detoxifies the water rather than merely transforming one pollutant into another.

The broader significance of the work lies in the synergy it demonstrates between defect-rich S-scheme heterojunctions and chlorite activation. S-scheme architectures have rapidly become one of the most celebrated design principles in photocatalysis because they solve the fundamental trade-off between light absorption, charge separation, and redox power. By pairing that architecture with an oxidant that can be activated directly on defect sites, the researchers have effectively built a system in which every component has a defined role: the (001) facets and flower-like morphology maximize light harvesting and surface area, the internal electric field preserves the most energetic charge carriers, the oxygen vacancies capture and activate chlorite, and the resulting chlorine dioxide, supplemented by hydroxyl radicals, does the chemical demolition of the pollutant. It is a level of mechanistic coordination that few advanced oxidation processes can claim.

For the millions of people whose water supplies carry traces of endocrine disrupting chemicals, the study offers a glimpse of a practical route forward. The process runs on visible light, uses a bismuth-based catalyst built from relatively abundant and low-toxicity elements, and employs chlorite, a chemical already handled routinely in water treatment, as its oxidant feedstock. While scaling any photocatalytic technology from beaker to treatment plant remains a formidable engineering challenge, the combination of high degradation efficiency, broad operational stability, and a clearly mapped reaction mechanism gives this approach a credible foundation. As regulators tighten limits on EDCs and other micropollutants, integrated systems of this kind, where sunlight, defects, and a simple chlorine oxidant work in concert, may well become a standard weapon in the effort to keep hormones and their mimics out of the water we drink.

Subject of Research: Visible-light photocatalytic activation of chlorite by BiOBr/Bi2O2CO3 S-scheme heterojunctions for degrading endocrine disrupting chemicals in wastewater

Article Title: Efficient Removal of Endocrine Disrupting Chemicals by BiOBr/Bi2O2CO3 Heterojunctions with the Presence of Chlorite: Photocatalytic and Chlorite Activation Mechanisms

Article References: Wang, Y., Liu, G., Yang, J., Wang, Y., Lu, M., Liu, Z., Shen, Y., Xian, W., & Zhang, G. (2026). Efficient Removal of Endocrine Disrupting Chemicals by BiOBr/Bi2O2CO3 Heterojunctions with the Presence of Chlorite: Photocatalytic and Chlorite Activation Mechanisms. Catalysis Letters, 156(11), Article 293. https://doi.org/10.1007/s10562-026-05536-9

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05536-9

Keywords: photocatalysis, S-scheme heterojunction, chlorite activation, chlorine dioxide, bisphenol A, endocrine disrupting chemicals, oxygen vacancies, bismuth oxybromide, water treatment, advanced oxidation processes, facet engineering, density functional theory