New S-Scheme Photocatalyst Degrades Livestock Odors With Remarkable Efficiency

Anyone who has driven past an industrial pig or dairy farm knows the smell can arrive long before the barns come into view. Behind that odor are a family of stubborn organic molecules, chief among them indole, a nitrogen-containing compound that livestock and poultry operations release into wastewater in quantities large enough to become an urgent environmental problem. Conventional treatment approaches struggle with it, and chemical oxidants add cost and secondary pollution. Now a team of researchers in China and Macao reports a photocatalyst that tears indole apart using nothing more than visible light, and they have backed their performance claims with some of the most demanding time-resolved characterization techniques available to materials science.

The material, described in the journal Advanced Composites and Hybrid Materials, is a composite the authors call LFN/CN: perovskite-type lanthanum ferrite doped with equal amounts of iron and nickel, LaFe0.5Ni0.5O3, grown together with graphitic carbon nitride, a widely studied polymeric semiconductor. The pairing is deliberate. Graphitic carbon nitride absorbs visible light but suffers from rapid recombination of the electrons and holes that light excites, while the perovskite oxide brings strong light absorption and catalytic sites of its own. By welding the two into what is known as an S-scheme heterojunction, the team created an interface where the two semiconductors’ band structures interlock in a way that keeps the most reactive charges alive and lets the useless ones cancel each other out.

The numbers are striking. Under visible-light irradiation, and crucially without any added oxidant, the optimally formulated composite, containing 15 percent of the perovskite by weight and designated 15LFN/CN, degraded indole with a rate constant of 5.99 × 10−2 per minute. That is 78.8 times faster than the pristine perovskite alone and 5.24 times faster than graphitic carbon nitride alone. Even more compelling for real-world use, the catalyst kept working across an acidity range from pH 3 to pH 11, delivering removal rates between 97.79 and 100 percent in the alkaline conditions typical of actual livestock effluent. It shrugged off interfering ions, coexisting organic matter, and even natural sunlight, conditions that routinely poison or blind less robust photocatalysts.

The breadth of the cleanup matters as much as the speed. The same catalyst dismantled 3-methylindole, the even more pungent compound responsible for much of fecal odor, along with estrogens and antibiotics, achieving removal rates of 96.28 to 100 percent for that suite of pollutants. When the researchers moved from synthetic solutions to three samples of real dairy farm wastewater, the composite still removed more than 90 percent of the indole present. Liquid chromatography–mass spectrometry traced the degradation pathway of indole into intermediate products, and a toxicity assessment of those intermediates suggested the treatment does not simply trade one hazard for another, an essential check for any technology destined for agricultural settings.

What elevates the study beyond another entry in the photocatalyst catalogue is its forensic approach to the charge-transfer mechanism. S-scheme heterojunctions have been proposed for years, but proving which way electrons actually flow across an interface is notoriously difficult, and many reported S-scheme systems rest on indirect evidence. The team attacked the question with three independent, spatiotemporally resolved techniques, building what they describe as direct and multidimensional experimental proof of the S-scheme pathway in their 15LFN/CN composite.

The first technique was in-situ irradiated X-ray photoelectron spectroscopy, in which the material’s core-level binding energies are measured while the sample is being illuminated. If electrons migrate from one component to the other under light, their chemical environments shift and the XPS peaks move accordingly. Observing those shifts in 15LFN/CN revealed the direction of electron migration across the interface, allowing the researchers to reconstruct the internal electric field and confirm that the junction behaves as an S-scheme rather than the more common type-II arrangement, which sacrifices oxidation power for charge separation.

The second line of evidence came from Kelvin probe force microscopy, which maps surface potential with nanoscale resolution. Scanning the composite surface in darkness and then under illumination, the team recorded a surface potential variation of 169.34 millivolts, the highest among the samples they compared. That large light-induced potential shift is the signature of abundant charges accumulating at the surface rather than recombining in the bulk, exactly what an effective S-scheme junction should produce.

The third and most technically ambitious measurement was femtosecond transient absorption spectroscopy, fs-TAS, which fires an ultrafast pump pulse to excite the material and then tracks the absorption of the excited charges with femtosecond resolution. The spectra resolved an interfacial electron-transfer lifetime of 164.39 picoseconds, capturing the moment charges leap from one semiconductor to the other, and an extended charge-recombination lifetime of 5.59 nanoseconds. In photocatalysis, longer recombination lifetimes mean more time for electrons and holes to reach the surface and drive reactions such as the generation of superoxide radicals that oxidize indole. Together, the three measurements form a coherent, mutually reinforcing picture of an S-scheme junction doing precisely what theory predicts.

The practical implications reach well beyond one molecule. Odor emissions from livestock and poultry farms are a growing public nuisance and a genuine environmental health concern as animal agriculture intensifies, and the malodorous compounds involved, from indoles to sulfides and amines, are chemically diverse. A catalyst that functions without chemical oxidants, tolerates the wide pH swings and complex ionic matrix of real wastewater, works under natural sunlight, and simultaneously attacks estrogens and antibiotics addresses several of agriculture’s water-quality headaches in a single treatment step. Because the process is driven by light, it also avoids the reagent costs and sludge generation associated with advanced oxidation processes that rely on hydrogen peroxide, ozone, or persulfate.

The authors, led by co-first authors Pu Yang and Kerong Fu of the Agro-Environmental Protection Institute of China’s Ministry of Agriculture and Rural Affairs, together with corresponding author Feng Wang, suggest that their findings establish a reliable methodology for validating S-scheme mechanisms in general, not just for this one material. The combination of in-situ irradiation XPS, Kelvin probe force microscopy, and femtosecond transient absorption spectroscopy offers other groups a template for proving, rather than merely asserting, how charge flows through their own heterojunctions. If that methodology spreads, it could sharpen the design of the next generation of solar-driven water-treatment catalysts. For now, the immediate takeaway is vivid enough: a perovskite and a polymer semiconductor, joined at the right interface, can turn barnyard stench into sunlight and chemistry, at rates nearly eighty times faster than either material alone.

Subject of Research: S-scheme LaFe0.5Ni0.5O3/g-C3N4 photocatalysts for visible-light deodorization of livestock wastewater

Article Title: Construction of LaFe0.5Ni0.5O3/g-C3N4 S-scheme heterojunction for dramatically enhanced photocarrier separation toward efficient photocatalytic deodorization of livestock wastewater: Based on in-situ irradiation XPS and fs-TAS analysis techniques

Article References: Construction of LaFe0.5Ni0.5O3/g-C3N4 S-scheme heterojunction for dramatically enhanced photocarrier separation toward efficient photocatalytic deodorization of livestock wastewater: Based on in-situ irradiation XPS and fs-TAS analysis techniques. (n.d.). https://doi.org/10.1007/s42114-026-02074-1

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02074-1

Keywords: S-scheme heterojunction, photocatalysis, indole degradation, livestock wastewater, LaFe0.5Ni0.5O3, graphitic carbon nitride, in-situ irradiation XPS, femtosecond transient absorption spectroscopy, Kelvin probe force microscopy, electron transfer, odor removal, pollution degradation