The heart of the new work is graphitic carbon nitride, usually abbreviated g-C₃N₄, a metal-free polymeric semiconductor that has attracted intense interest since researchers discovered that simple organic precursors such as urea or melamine can be cooked into it by heating. The material is cheap, chemically robust, and absorbs enough visible light to run photocatalytic reactions under sunlight-like illumination. When photons strike the catalyst, electrons are promoted from the valence band to the conduction band, leaving positively charged holes behind. Both the electrons and the holes can, in principle, drive chemical reactions that shred organic pollutants. The catch is that pristine g-C₃N₄ is a poor conductor, and its light-excited electrons and holes recombine with each other far too quickly, releasing energy as heat before they can do useful chemistry. That recombination problem has long been the bottleneck keeping carbon nitride photocatalysts out of real-world water treatment.

The Chinese team, led by Zemin Zhu and Guodong Zheng, with Tiechui Yuan providing the concept and funding support, attacked the problem with a two-pronged strategy: doping and homojunction formation. First, they prepared two subtly different versions of carbon nitride. One, labeled CN, was made from urea. The other, labeled BCN, was derived from melamine and doped with boron atoms through a two-step calcination process. Boron is a clever choice of dopant because its electronic structure differs from that of carbon and nitrogen in the carbon nitride lattice. Substituting boron into the framework narrows the material’s band gap, which means less energy is needed to kick an electron into the conduction band. The practical consequence is a red-shifted light absorption edge: the doped material harvests a wider slice of the visible spectrum than its undoped counterpart, capturing photons that would otherwise go to waste.

Second, the researchers combined the two carbon nitride variants into a single composite, creating what materials scientists call a homojunction. Unlike a heterojunction, which joins two chemically different semiconductors, a homojunction interfaces two materials of the same chemical family but with slightly different electronic structures. Because the two sides are chemically compatible, they form intimate, well-matched interfaces without the lattice strain and recombination centers that can plague mismatched heterojunctions. The band alignment between CN and BCN gives photoexcited electrons and holes a built-in energetic incentive to separate, with one partner material preferentially hosting electrons and the other hosting holes. Separated charges live longer, travel further, and are far more likely to reach the catalyst surface and participate in pollutant-degrading reactions rather than simply annihilating each other.

The electrochemical measurements reported in the study confirm that the design works as intended. The CN/BCN homojunction exhibits low electrochemical impedance, meaning charges move through it with little resistance, and an optimal photocurrent response, a direct sign that light is being converted into separated, mobile charge carriers rather than being lost to recombination. The composite also shows an appropriate capability for capturing charge carriers, further extending the lifetime of the reactive electrons and holes. Each of these properties, on its own, would represent a modest improvement; together they compound into a catalyst that is substantially more photoactive than either of its parent materials.

The performance numbers are striking. When the CN/BCN catalyst was combined with potassium persulfate, a common and inexpensive oxidizing salt, and illuminated with visible light, tetracycline removal reached 98.6 percent within 60 minutes. The corresponding kinetic rate constant was 0.0748 per minute, a measure of how quickly the degradation reaction proceeds. Persulfate chemistry is central here. Persulfate ions are themselves fairly sluggish oxidants, but when they accept electrons from photoexcited catalysts they can be cleaved into sulfate radicals, extremely aggressive species that attack organic molecules indiscriminately. A photocatalyst that efficiently supplies electrons to persulfate therefore acts as an amplifier, converting a mild bulk oxidant into a torrent of destructive radicals right at the pollutant’s doorstep.

Using a combination of radical scavenging experiments, the team identified which reactive species actually do the work of degrading tetracycline in their system. Four culprits emerged: sulfate radicals (SO₄•⁻), hydroxyl radicals (•OH), superoxide radicals (•O₂⁻), and the photogenerated holes themselves. Interestingly, their relative contributions were not what a casual reading of persulfate chemistry might suggest. The ordering, from least to most important, was sulfate radical, then hydroxyl radical, then superoxide radical, with photogenerated holes contributing the most. That result underscores a key insight of the study: in a well-designed photocatalytic persulfate system, the direct oxidative power of the holes left behind in the catalyst’s valence band can rival or exceed the contribution of the radicals generated indirectly. It also suggests that strategies maximizing hole availability, such as the charge-separation engineered into the homojunction, pay double dividends.

Durability and real-world robustness are where many promising photocatalysts stumble, and the researchers addressed both concerns directly. Over five consecutive cycling tests, the CN/BCN system retained a tetracycline removal efficiency above 90 percent, indicating that the catalyst does not rapidly deactivate, foul, or lose its boron dopant under working conditions. Equally important, the team examined how the system performs in the presence of common coexisting anions, the dissolved salts such as chloride, nitrate, and carbonate species that are ubiquitous in natural waters and wastewater. These anions exerted only minor effects on photocatalytic performance, a significant finding because many advanced oxidation processes are notoriously sensitive to water chemistry, with scavenging by background ions sharply curtailing pollutant destruction in anything other than ultrapure laboratory water.

The broader significance of the work lies in its elegance and economy. Both the urea-derived and melamine-derived carbon nitrides are made from inexpensive commodity chemicals, and the two-step calcination strategy is a straightforward thermal process rather than an exotic synthesis requiring rare metals or complicated precursors. The entire catalytic system is metal-free, which avoids the leaching of toxic metal ions that complicates many other advanced oxidation catalysts. Because the homojunction is built from two members of the same material family, the approach is also conceptually transferable: the same logic of pairing a doped and an undoped carbon nitride, or two differently doped variants, could be applied to degrade other persistent organic pollutants, from dyes to pesticides to pharmaceutical compounds beyond tetracycline.

Challenges remain before such systems treat actual wastewater at scale, including reactor engineering, catalyst recovery, and performance under variable sunlight. But the study offers a clear demonstration that careful electronic-structure engineering, boron doping to widen light harvesting and a homojunction to keep charges separated, can transform a famously limited photocatalyst into a high-performance pollutant destroyer. As antibiotic resistance accelerates into a global health emergency, technologies that can inexpensively and reliably eliminate antibiotic residues from water are urgently needed. This boron-doped carbon nitride homojunction, coupled with persulfate and plain visible light, is a compelling step in that direction.

Subject of Research: Boron-doped graphitic carbon nitride homojunction photocatalysis for persulfate-activated tetracycline degradation

Article Title: Promoting tetracycline degradation in persulfate-based photocatalytic advanced oxidation processes by construction of B-doped g-C₃N₄/g-C₃N₄ homojunction

Article References: Zhu, Z., Zheng, G., Zhou, Y., Chen, L., Wu, Q., & Yuan, T. (2026). Promoting tetracycline degradation in persulfate-based photocatalytic advanced oxidation processes by construction of B-doped g-C₃N₄/g-C₃N₄ homojunction. Journal of Nanoparticle Research, 28(10), Article 261. https://doi.org/10.1007/s11051-026-06782-z

Image Credits: AI Generated

DOI: 10.1007/s11051-026-06782-z

Keywords: graphitic carbon nitride, photocatalysis, boron doping, homojunction, persulfate activation, sulfate radicals, tetracycline, antibiotic pollution, water treatment, advanced oxidation processes, charge carrier separation, visible light

The material itself is a study in green chemistry. The researchers cleaned and dried sweet flag plants, ground the biomass through a 100-mesh sieve, and pyrolyzed it in a limited-oxygen environment inside a muffle furnace, ramping the temperature to 600 degrees Celsius at 5 degrees per minute and holding it there for 90 minutes. To introduce the dopants, they soaked the powdered biomass in solutions of manganese chloride and urea, sonicated the mixture, stirred it for 24 hours, and then repeated the calcination step. By varying the relative amounts of biochar precursor, urea, and manganese salt, the team produced a family of catalysts with different doping ratios, ultimately identifying a 1:1:1 ratio of biochar to nitrogen to manganese as the optimum. The approach recycles waste biomass, sequesters carbon, and avoids the energy-hungry activation methods, such as ultraviolet lamps, heating, or electrochemical cells, that many persulfate systems demand.

Characterization revealed why the co-doped material works so well. Scanning electron microscopy showed that the original biochar has a rough, sheet-like surface, and that manganese and nitrogen modification roughens it further, decorating the layered carbon with stacked spherical Mn-N nanoparticles that multiply the available active sites. Energy-dispersive X-ray spectroscopy confirmed the presence of carbon, oxygen, manganese, and nitrogen, with manganese accounting for a remarkable 35.35 percent of the sample mass. X-ray diffraction identified manganese oxides in multiple oxidation states, including MnO2, MnO, and Mn3O4, while Fourier-transform infrared spectroscopy detected characteristic Mn-O bonds and C-NH-C linkages, confirming that both dopants were chemically incorporated rather than merely deposited on the surface.

Not every physical change was an improvement. Brunauer-Emmett-Teller measurements showed that the specific surface area of the biochar collapsed from 117.534 square meters per gram in the pristine material to just 7.232 square meters per gram after doping, a consequence of nitrogen species and manganese particles partially filling the micropores and mesopores. Nitrogen adsorption-desorption isotherms, showing combined type I and type IV behavior with H4 hysteresis loops, indicated that both micropores smaller than 2 nanometers and mesopores between 2 and 50 nanometers coexist in the material. The trade-off proved worthwhile: although adsorption performance declined, the doping introduced a wealth of catalytically active sites and structural defects, including pyridine nitrogen, graphitic nitrogen, and manganese oxide species, that more than compensated by dramatically accelerating persulfate activation.

X-ray photoelectron spectroscopy provided the most detailed picture of the catalytic machinery. The nitrogen 1s spectra revealed pyridine N, pyrrole N, and graphite N at binding energies of 398.10, 399.29, and 400.20 electronvolts, with pyridine nitrogen dominating at 52.58 percent before reaction. Manganese appeared as Mn(II), Mn(III), and Mn(IV), and the valence distribution shifted as the reaction proceeded: the fractions of Mn(II) and Mn(III) fell from 44.31 and 30.75 percent to 39.75 and 23.72 percent, while Mn(IV) rose to 36.52 percent. This valence climb is the fingerprint of electron transfer, in which the lower-valence manganese ions donate electrons to persulfate, cleaving its O-O bond and generating sulfate radicals as the metal centers oxidize toward higher states.

Performance testing under optimized conditions, 2 millimolar peroxydisulfate, 1.0 gram per liter of catalyst, and 20 milligrams per liter of tetracycline at pH 7, delivered a removal rate of 93.76 percent in 120 minutes, with a pseudo-first-order rate constant of 0.0199 per minute. The comparisons were telling. Peroxydisulfate alone did essentially nothing, plain biochar adsorbed 48.52 percent of the antibiotic, and singly doped catalysts paired with persulfate managed 68.00 percent for manganese-only and 60.65 percent for nitrogen-only materials. The co-doped system outperformed a comparable delta-MnO2/biochar persulfate system reported previously, which achieved 85.5 percent removal, and it did so through simple catalyst addition rather than the energy-intensive three-dimensional electrochemical activation used in some rival designs.

The team systematically probed the operational window. Increasing the peroxydisulfate concentration from 0.5 to 2 millimolar raised removal from 72.82 to 93.76 percent, but further additions plateaued because excess oxidant self-quenches the very sulfate radicals it generates. Raising the catalyst dose from 0.3 to 1.0 grams per liter improved degradation, though pushing to 2.0 grams per liter brought no further gain, likely because superfluous doped species compete with pollutants for radicals. Degradation efficiency exceeded 93 percent at low initial tetracycline concentrations and declined gradually as pollutant loading rose. Encouragingly, the system proved remarkably pH-tolerant, holding removal near 93 percent across the range from pH 3 to 9, with only strongly alkaline conditions at pH 11 dropping performance to 74.89 percent, a flexibility that matters for real wastewater streams of variable composition.

Electron paramagnetic resonance spectroscopy and radical quenching experiments untangled the chemistry driving the degradation. The EPR spectra captured three reactive species: sulfate radicals, hydroxyl radicals, and singlet oxygen, the latter a non-radical oxidant generated at structural defects and carbonyl groups on the nitrogen-doped carbon. Kinetic calculations from quenching tests using methanol, tert-butanol, L-histidine, and p-benzoquinone assigned contribution rates of 73.7 percent for superoxide radicals, 51.5 percent for singlet oxygen, 39.2 percent for hydroxyl radicals, and 13.4 percent for sulfate radicals, revealing that the non-radical and superoxide pathways, long underappreciated in persulfate chemistry, actually dominate. Liquid chromatography-mass spectrometry identified twelve intermediates and allowed the researchers to propose three degradation routes involving deamination, demethylation, dehydroxylation, ring cleavage, and ring opening of the tetracycline skeleton.

Durability and practicality rounded out the assessment. Across three consecutive reuse cycles the catalyst degraded 93.8, 86.0, and 80.3 percent of the antibiotic, retaining more than 80 percent of its initial activity, with the gradual decline attributed to leaching of manganese active centers, a known challenge for metal-carbon composites. In a proof-of-concept flow experiment, catalyst-loaded polyurethane sponges packed into a reaction column fed by a peristaltic pump removed 83.1 percent of tetracycline initially and stabilized around 69 percent after adsorption saturation. Computational toxicity prediction with the TEST software suggested that acute toxicity, measured as LC50 values against fathead minnow and the water flea Daphnia magna, generally decreased as tetracycline was converted into smaller intermediates, although the authors caution that these are model predictions rather than bioassays and that some fragments retain significant toxicity.

The study, published open access on 29 September 2026 and supported by China’s National Key Research and Development Program, arrives amid growing alarm over antibiotic residues in the environment and the resistance crisis they accelerate. Its significance lies less in any single number than in the demonstration that a cheap, plant-derived carbon, doped with two abundant elements and paired with a common oxidant, can rival far more elaborate treatment trains without external energy input. The authors are candid that the flow-through results and cycling stability represent early-stage proof of concept rather than an engineered solution, and that manganese leaching and residual toxic intermediates must be addressed. Even so, the work charts a credible path from laboratory beaker toward continuous water treatment, and it adds sweet flag, a wetland plant once prized in traditional medicine, to the growing roster of biomass feedstocks being reborn as environmental catalysts.

Subject of Research: Mn/N co-doped biochar-activated persulfate degradation of tetracycline in water

Article Title: Mn/N co-doped biochar-activated persulfate degradation of tetracycline in water

Article References: Cui, H., Li, L., Jia, Y., Xu, N., Wang, Z., Liu, Z., Zhang, J., Zhang, C., Gong, W., Feng, W., Shan, Y., & Xue, H. (2026). Mn/N co-doped biochar-activated persulfate degradation of tetracycline in water. Journal of Saudi Chemical Society, 30(5), Article 74. https://doi.org/10.1007/s44442-026-00113-6

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00113-6

Keywords: biochar, persulfate activation, tetracycline, advanced oxidation processes, manganese doping, nitrogen doping, Acorus calamus, antibiotic pollution, water treatment, singlet oxygen, sulfate radicals, catalyst reusability

The technology belongs to a family of treatments known as advanced oxidation processes, which rely on highly reactive chemical species to break down organic contaminants that conventional treatment plants cannot fully remove. In this study, the oxidant of choice was peroxydisulfate, a stable and inexpensive persulfate salt that, in its ordinary state, is too sluggish to attack most pollutants. The trick is activation: persuading the peroxydisulfate molecule to split apart and generate reactive species capable of shredding complex organic structures such as the sulfonamide backbone of sulfamethoxazole. Iron-based activators have long been favored for this job because iron is abundant, cheap, and environmentally benign compared with alternatives like cobalt.

Nanoscale zero-valent iron, or nZVI, is essentially iron metal ground down to particles tens of nanometers across. At that scale, iron is ferociously reactive, donating electrons that can cleave the peroxydisulfate molecule and set the oxidation cascade in motion. But nZVI has a notorious flaw: the nanoparticles clump together, or agglomerate, driven by magnetic forces and high surface energy. When they aggregate, much of their reactive surface becomes buried inside the clusters, inaccessible to the oxidant and the pollutant alike. The particles also corrode and passivate quickly, further eroding their catalytic punch over time.

The research team, led by Honglei Fan of the North University of China in Taiyuan, together with colleagues from Shihezi University and Southwest University, tackled the agglomeration problem by growing the iron nanoparticles directly on sheets of reduced graphene oxide, a conductive, high-surface-area carbon material derived from graphite. Using an in situ liquid-phase reduction method, they formed the composite so that the iron particles nucleate and anchor on the graphene scaffold rather than on each other. Characterization of the resulting material showed that the graphene support did exactly what the designers hoped: it improved the dispersion of the iron nanoparticles and increased both the specific surface area and the pore volume of the composite, exposing far more active sites to the surrounding water.

The performance gains were dramatic. Under the optimized reaction conditions, the rGO/nZVI/PDS system achieved greater than 98 percent removal of sulfamethoxazole within 10 minutes. The apparent rate constant of the degradation was 5.6 times higher than that of a system using nanoscale zero-valent iron alone with peroxydisulfate, and 13.2 times higher than peroxydisulfate on its own. Those multipliers matter, because in water treatment the difference between a reaction that finishes in minutes and one that takes an hour or more determines whether a technology is a laboratory curiosity or a practical engineering option.

Perhaps the most intriguing part of the study is what the researchers found when they probed the underlying chemistry. In the textbook picture of persulfate activation, the oxidant splits into sulfate radicals and, secondarily, hydroxyl radicals—aggressive, short-lived species that indiscriminately oxidize organic molecules in solution. But when the team ran quenching experiments, using selective scavenger chemicals to neutralize specific reactive species, and confirmed their results with electron paramagnetic resonance spectroscopy, a different story emerged. Freely diffusing sulfate radicals and hydroxyl radicals were not the predominant species driving sulfamethoxazole degradation under the tested conditions. Instead, the evidence pointed to singlet oxygen, a milder but selective excited state of molecular oxygen, as the key player.

Singlet oxygen belongs to the growing catalog of so-called non-radical or surface-mediated oxidation pathways in advanced oxidation chemistry. Unlike free radicals, which are quenched almost instantly by the background matrix of natural waters—chloride, bicarbonate, and natural organic matter all act as radical sinks—singlet oxygen and related surface-bound processes tend to be far more tolerant of complex water chemistries. That resilience is a major practical advantage, because real wastewater is never as clean as laboratory reagent water. A treatment that depends on free radicals can lose most of its efficiency the moment it encounters a realistic water matrix, whereas a singlet-oxygen-dominated process can keep working.

The authors attribute the enhanced performance of the rGO/nZVI composite to several converging factors. The improved dispersion of iron-containing sites means more of the metal is available to interact with peroxydisulfate. The increased accessibility of the composite surface, a direct consequence of the graphene scaffold’s high area and open pore structure, allows both the oxidant and the pollutant to reach those sites efficiently. In addition, the researchers suggest that the conductive graphene network may alter interfacial electron-transfer processes during peroxydisulfate activation, facilitating the movement of electrons from the iron core to the oxidant and steering the reaction network toward singlet oxygen generation rather than radical fragmentation. Graphene’s role as an electron highway between catalytic sites and adsorbed molecules is a recurring theme in carbon-supported catalyst research, and this study adds another data point to that picture.

The broader context makes the result timely. Sulfamethoxazole is one of the most frequently detected pharmaceuticals in surface waters and wastewater treatment effluents worldwide, and its persistence raises concerns beyond simple toxicity. Residual antibiotics in the environment exert selection pressure on bacteria, accelerating the spread of antibiotic resistance genes—one of the most serious public health threats identified by global health agencies. Conventional activated sludge treatment removes only a fraction of the drug, and biodegradation of sulfamethoxazole is slow and incomplete. That gap between what treatment plants deliver and what the environment needs has fueled an intense search for fast, robust polishing technologies, and persulfate-based advanced oxidation has emerged as a leading candidate because of its low cost, chemical stability, and ease of transport and storage compared with alternatives such as ozone or hydrogen peroxide under certain conditions.

Iron-carbon composites of various kinds have been explored for this purpose before, including biochar-supported iron, iron-carbon materials derived from industrial wastes, and graphene oxide-supported sulfidated zero-valent iron. What distinguishes the new work is the combination of extreme speed, the clear mechanistic evidence for a singlet oxygen pathway, and the straightforward in situ synthesis route, which grows the composite in a single liquid-phase step rather than requiring multi-stage high-temperature processing. Simplicity of manufacture is often the deciding factor in whether a promising catalyst ever leaves the laboratory, and a one-pot aqueous synthesis is about as simple as nanomaterial preparation gets.

Challenges remain before the technology can be scaled. The study reports performance under controlled laboratory conditions, and real-world application will require testing across a wider range of water matrices, pH values, and competing contaminants. The long-term stability and reusability of the composite, the fate of the iron as it corrodes, and the cost of reduced graphene oxide at industrial scale all need to be addressed. The authors also note that the datasets generated in the study are available from the corresponding author on reasonable request, inviting further scrutiny and replication. The work was supported by the Fundamental Research Program of Shanxi Province of China and the National Natural Science Foundation of China.

Even with those caveats, the study offers a compelling demonstration of how rational materials design can transform a familiar chemistry. By giving unruly iron nanoparticles a graphene scaffold to stand on, the researchers unlocked a degradation rate that outpaces conventional iron activation by more than a factor of five and revealed a selective, matrix-tolerant oxidation pathway in the process. As water utilities grapple with a steady stream of emerging contaminants, composite activators like rGO/nZVI may well become a standard tool in the effort to strip antibiotics—and the resistance risks they carry—out of the water we all share.

Subject of Research: Activation of peroxydisulfate by reduced graphene oxide-supported nanoscale zero-valent iron for rapid degradation of the antibiotic sulfamethoxazole in water

Article Title: Enhanced peroxydisulfate activation by rGO/nZVI composites for efficient sulfamethoxazole degradation

Article References: Fan, H., Sun, Z., Xuan, K., Liu, Y., Zhou, S., & Huang, J. (2026). Enhanced peroxydisulfate activation by rGO/nZVI composites for efficient sulfamethoxazole degradation. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38202-z

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38202-z

Keywords: rGO/nZVI, peroxydisulfate activation, sulfamethoxazole, singlet oxygen, advanced oxidation processes, nanoscale zero-valent iron, reduced graphene oxide, water treatment, antibiotic degradation, sulfate radical, non-radical pathway, emerging contaminants