The heart of the system is a ternary heterojunction combining bismuth oxynitride (Bi5O7NO3), titanium dioxide, and graphite, abbreviated TGBN. The researchers immobilized this composite onto honeycomb cordierite supports and slotted the resulting filters into a portable air purifier prototype. By varying the weight ratio of bismuth oxynitride relative to the titanium dioxide–graphite backbone, they produced a series labeled TGBN-x, where x denotes the BN/TG weight percentage. The optimized formulation, TGBN-10, emerged as the standout performer in a 23-liter closed-loop chamber designed to mimic indoor air environments.

Under dry conditions and illuminated by a modest 1-watt UV-LED, the TGBN-10 filter achieved complete removal of 5 parts per million formaldehyde within just six minutes. That speed matters: formaldehyde near-ambient concentrations are precisely the regime relevant to homes, offices, and schools, where chronic exposure is linked to respiratory irritation and carcinogenic risk. Doubling the catalyst loading from 0.05 to 0.1 grams boosted the chamber’s clean air delivery rate from 8.3 to 16.0 liters per minute, a direct measure of how much purified air the device can supply per unit time. These numbers place the system firmly in the territory of practical deployment rather than laboratory curiosity.

What makes the ternary design superior to simpler alternatives is its charge-carrier dynamics. When photons strike a semiconductor photocatalyst, they generate electron-hole pairs that must be separated and funneled to surface reaction sites before they recombine and waste their energy as heat. Single-component titanium dioxide suffers from rapid recombination. Binary composites improve matters but still leak charge. The TGBN-10 architecture, according to photoelectrochemical measurements, electron paramagnetic resonance spectroscopy, and X-ray photoelectron spectroscopy, exhibits an S-scheme-like charge separation mechanism. In this configuration, the two semiconductors with staggered band positions transfer electrons in a way that preserves the most energetic carriers on each side, maximizing redox power. Graphite, the third component, likely acts as a conductive interfacial mediator, shuttling charges between the two semiconductors and providing additional pathways for separation.

The S-scheme interpretation is supported by spectroscopic fingerprints of the reactive oxygen species generated at the catalyst surface. Hydroxyl radicals, superoxide anions, and other oxidants produced by the separated charges are the actual chemical scissors that slice aldehyde molecules apart. Without efficient charge separation, these radicals never form in sufficient quantity, and the catalyst stalls. The ternary design keeps the charges flowing, and the performance gap is measurable: TGBN-10 delivered a specific clean air delivery rate 1.70 times higher than the binary titanium dioxide–graphite composite under identical conditions, and an 8.93-fold higher specific clean air delivery rate at 5 ppm formaldehyde than at 100 ppm.

That concentration dependence is one of the study’s most practically significant findings. At 100 ppm formaldehyde, a level closer to industrial emission scenarios than to typical indoor air, the specific clean air delivery rate dropped considerably. When the inlet gas shifted from a multi-component mixture to a single-component system at the same total concentration, the specific clean air delivery rate jumped 2.64-fold, from 7 to 18.51 liters per minute per gram. This tells us that competitive adsorption among different aldehydes and the accumulation of oxygenated intermediates on the catalyst surface are real bottlenecks under realistic conditions, not just theoretical concerns. Any photocatalytic air purification technology intended for actual buildings must contend with this complexity.

The chain-length effect adds another layer of nuance. In a multi-component mixture with a total concentration of 100 ppm, the peak photocatalytic oxidation reached 91 percent for formaldehyde, but only 23.2 percent for propionaldehyde, 60.7 percent for valeraldehyde, and a mere 5.8 percent for acetaldehyde. The pattern is not monotonic with chain length, which suggests that a combination of adsorption affinity, molecular size, and intermediate stability governs each molecule’s fate. In situ diffuse reflectance infrared Fourier transform spectroscopy revealed the mechanistic details: formaldehyde is activated through hydroxyl-mediated pathways, forming dioxymethylene and formate intermediates before mineralization. Carboxylate species accumulated on the surface in an order that increased from valerate to acetate, hinting that shorter-chain intermediates bind more persistently and may poison active sites more effectively.

Despite this accumulation, the catalyst proved remarkably resilient. Over five consecutive photocatalytic oxidation cycles, TGBN-10 sustained high activity with minimal loss. The team attributed this durability to reversible carbonaceous fouling rather than permanent structural degradation. When the filter was exposed to UV light in clean air, it underwent photo-regeneration, burning off the accumulated carbon deposits and restoring its original performance. This self-cleaning behavior is a critical advantage over conventional adsorption filters, which saturate and require replacement. A photocatalytic filter that can periodically reset itself could dramatically extend service life and reduce operating costs.

The deep mineralization metric is equally important. It is one thing to remove an aldehyde from the gas phase; it is another to convert it fully into carbon dioxide and water rather than leaving behind partially oxidized fragments that may themselves be harmful. Across all four aldehydes in the mixture, the overall carbon dioxide yield reached 95.9 percent, confirming that the TGBN-10 system drives a deep oxidation pathway rather than merely transferring pollutants from air to catalyst surface. This is the gold standard for photocatalytic air treatment, and achieving it under multi-component, humidified conditions is a significant technical accomplishment.

Looking ahead, the researchers suggest that TGBN-10 could serve as a functional, noble-metal-free photocatalyst for aldehyde-type volatile organic compound abatement under representative industrial and indoor-air conditions. The absence of precious metals keeps material costs low, and the honeycomb cordierite support provides the mechanical stability and low pressure drop needed for integration into commercial air purifier devices. As regulatory pressure on indoor air quality intensifies worldwide, and as consumers grow more aware of the health consequences of chronic aldehyde exposure, technologies like this one bridge the gap between laboratory photocatalysis and the air we actually breathe. The chain-length-dependent structure-activity relationships uncovered here also provide a design roadmap: future photocatalyst formulations can be tuned not just for generic VOC destruction but for the specific molecular mixtures that dominate real indoor environments.

Subject of Research: Photocatalytic oxidation of multi-component aldehydes using an S-scheme ternary bismuth oxynitride/titanium dioxide/graphite heterojunction for indoor air purification

Article Title: Chain-length-dependent structure–activity relationships in the deep oxidation of multi-component aldehydes over an S-scheme ternary bismuth oxynitride/titanium dioxide/graphite heterojunction photocatalyst

Article References: Lu, Y., Younis, S. A., & Kim, K.-H. (2026). Chain-length-dependent structure–activity relationships in the deep oxidation of multi-component aldehydes over an S-scheme ternary bismuth oxynitride/titanium dioxide/graphite heterojunction photocatalyst. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02110-0

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02110-0

Keywords: photocatalysis, bismuth oxynitride, titanium dioxide, graphite, S-scheme heterojunction, formaldehyde, aldehydes, volatile organic compounds, air purification, clean air delivery rate, in situ DRIFTS, charge separation

The central insight of the new work is that the three most desirable properties of an air filter need not live in the same solid material. Conventional fibrous filters, including the melt-blown polypropylene media used in respirators and the dense glass-fibre mats inside HEPA units, capture particles mechanically or electrostatically on solid surfaces. Every captured particle stays put, gradually blocking the pores, raising the pressure drop across the filter and eventually forcing a costly replacement. The CILF instead delegates capture to a dynamic liquid lining that is continuously replenished, so that trapped contaminants are swept away rather than accumulated.

The researchers organise the capture process into three stages that operate in sequence. In the first stage, long-range electrostatic attraction draws airborne particles toward the filter from a distance, exploiting electric charges to overcome the fundamental weakness of purely mechanical filtration, in which only particles that happen to collide with a fibre are removed. In the second stage, particles arriving at the liquid interface are captured rapidly at the surface, where capillary and electrostatic forces combine to pull them across the boundary between air and liquid. In the third stage, the liquid bulk itself acts as a high-capacity sink, absorbing and storing the collected particles deep within its volume.

This division of labour is what gives the filter its durability. Because the liquid lining is refillable and continuously renewed, particles that would otherwise clog a solid filter are instead dissolved or suspended in the liquid phase and carried off. The team reports that the filter maintained high performance throughout 3,500 hours of continuous operation, a figure that dwarfs the service intervals typical of high-efficiency solid filters, which often degrade noticeably within weeks of intensive use. The self-cleaning behaviour of the moving liquid lining means the filter does not progressively blind itself, and the pressure drop across it remains stable rather than climbing over time.

The design builds on a growing body of work on liquid-based filtration. In 2022, a team reported in Nature a continuous air purification approach based on aqueous interface filtration and absorption, demonstrating that liquids could serve as active capture media rather than passive wetting agents. Related efforts have explored liquid-gating mechanisms with tunable multiphase selectivity and antifouling behaviour, first described in Nature in 2015, as well as biomimetic systems inspired by the human circulatory and respiratory systems. The new contribution of the CILF is to combine the liquid approach with charge-induced capture, adding the long-range electrostatic attraction that pure liquid-interface systems lack while retaining their resistance to clogging.

The physics of the interfacial capture stage draws on well-studied phenomena. Particles sitting at liquid interfaces experience capillary forces that can bind them strongly to the boundary, and electric fields can induce attractive interactions between like-charged particles at such interfaces, an effect documented experimentally more than two decades ago. By engineering the charge state of the liquid lining, the researchers harness these forces deliberately: particles approaching the interface are pulled in and then drawn into the bulk liquid, where the vast absorption capacity of the liquid phase stores them far from the airstream. Supplementary videos accompanying the paper show charge-induced adsorption on solid surfaces, bulk-phase absorption in the liquid, and the dynamic liquid lining performing its self-cleaning function.

To demonstrate that the laboratory performance translates into practical air cleaning, the team built a full-scale air cleaner prototype incorporating the CILF. In a thirty-cubic-metre test chamber, the prototype achieved a clean-air delivery rate of 377 cubic metres per hour, a measure of how much purified air a device can supply and one of the key metrics used to compare commercial air purifiers. The tests were conducted under industry standard conditions, providing a benchmark that allows direct comparison with existing filtration technologies rather than relying solely on laboratory-scale measurements.

Perhaps the most striking aspect of the work is the breadth of applications the researchers demonstrate. The team implemented the filters across a range of real-world settings, from personal protective masks to air purification systems compatible with microgravity environments. The microgravity application is particularly notable: conventional filters rely on gravity-assisted settling and replaceable cartridges that generate waste, both of which are problematic on spacecraft, where every kilogram of consumables must be launched at great expense. A filter whose capture medium is a refillable liquid, and whose performance does not depend on gravity, offers an intriguing option for long-duration missions. At the other end of the scale, a liquid-lined filter in a face mask could in principle maintain high efficiency without the breathing resistance that builds up as solid mask filters load with particles.

The energy and sustainability implications are significant. Because the filter maintains a low and stable pressure drop, the fans driving air through it consume less power than they would against a progressively clogging medium, and the refillable liquid lining replaces the steady stream of discarded filter cartridges that conventional high-efficiency systems generate. Prior analyses of air filtration have highlighted both the monetary cost of replacing high-efficiency filters and the environmental burden of disposing of them, and low-cost do-it-yourself air cleaners popularised during the COVID-19 pandemic underscored the demand for affordable, durable alternatives. A filter that combines HEPA-level efficiency with long service life and simple maintenance addresses precisely the gap that has kept such alternatives from matching professional equipment.

Challenges remain before charge-induced liquid-lined filters appear in homes, hospitals and spacecraft. The nature and management of the working liquid, its consumption rate, the electrical power needed to sustain the charge-induced capture, and the behaviour of the system across extremes of temperature and humidity are all questions that the broader deployment of the technology will need to answer, and the paper’s supplementary materials, including extensive notes and tables, suggest the authors have begun mapping this terrain in detail. Still, the headline numbers are difficult to ignore: 99.6 percent single-pass efficiency at a face velocity of one metre per second, 3,500 hours of continuous high performance, and a clean-air delivery rate of 377 cubic metres per hour in a full-scale prototype. If the approach scales as the authors suggest, the familiar ritual of replacing clogged filters may one day give way to simply topping up a liquid reservoir, and the trade-off that has defined air purification for decades may finally be resolved in favour of clean air that is simultaneously efficient, durable and affordable.

Subject of Research: A charge-induced liquid-lined filter for high-efficiency, durable and low-maintenance air purification

Article Title: Highly efficient air purification by a charge-induced liquid-lined filter

Article References: Zhang, J., Li, M., Chen, S., Guo, Z., Yang, B., Li, L., Zhou, X., Zhang, J., Ye, C., Liu, J., Yao, W., Zhang, Y., & Hou, X. (2026). Highly efficient air purification by a charge-induced liquid-lined filter. Nature Sustainability. https://doi.org/10.1038/s41893-026-01920-w

Image Credits: AI Generated

DOI: 10.1038/s41893-026-01920-w

Keywords: air purification, liquid-lined filter, electrostatic capture, particulate matter, Nature Sustainability, filter durability, clean-air delivery rate, interfacial science, self-cleaning, microgravity, sustainable technology, fluidics

A new study published in Advanced Composites and Hybrid Materials by Lu Liu, Hubdar Ali Maitlo, Younes Ahmadi, Omnia A. A. El-Shamy, and Ki-Hyun Kim of Hanyang University and their collaborators reports a strikingly simple lever for boosting that efficiency: the physical size of copper oxide nanocubes. The team fabricated cuprous oxide, Cu2O, in three precisely controlled cube edge lengths of 30, 55, and 315 nanometers, then combined each with titanium dioxide, TiO2, at a fixed loading of one weight percent. The resulting composites, labeled CT-30, CT-55, and CT-315 according to cube size, were tested for the photodegradation of benzene, toluene, and xylene. The smallest cubes won decisively, and the reason traces back to a subtle electronic property that few synthetic strategies have targeted so directly: the position of the Fermi level.

The Fermi level is the electrochemical yardstick of a semiconductor, defining the energy at which electron occupancy transitions from filled to empty states. Its position relative to the conduction and valence bands determines how electrons and holes behave when two dissimilar semiconductors are brought into contact. When Cu2O meets TiO2, electrons flow across the interface until their Fermi levels equilibrate, bending the bands and establishing a built-in electric field. In an S-scheme heterojunction, so named because the charge transfer pathway resembles the letter S in energy band diagrams, this field performs a remarkable sorting trick. It drives the recombination of the lower-energy carriers, the conduction band electrons of TiO2 and the valence band holes of Cu2O, while preserving the high-energy electrons in the Cu2O conduction band and the high-energy holes in the TiO2 valence band. The result is a photocatalyst that keeps its most potent oxidizing and reducing species alive instead of squandering them.

What the Korean-led team demonstrated is that the strength of this sorting mechanism depends on how large the Cu2O crystals are. Using detailed electronic characterization, including Kelvin probe force microscopy performed with a Park NX10 instrument, they showed that smaller Cu2O nanocubes possess a more negative conduction band position. That shift enlarges the Fermi-level offset, denoted ΔEF, between Cu2O and TiO2. A larger offset means a stronger interfacial electric field when the two materials equilibrate, and a stronger field means more efficient separation and longer survival of the high-energy charge carriers. In effect, shrinking the cube from 315 nanometers to 30 nanometers rewires the internal electronics of the junction without changing its chemical composition at all.

The performance consequences were dramatic. With the same one weight percent Cu2O loading, the CT-30 composite achieved oxidation efficiencies of 84.3 percent for benzene, 98.2 percent for toluene, and 94.1 percent for xylene. These figures substantially outperformed pure TiO2, pure Cu2O, and the large-cube CT-315 composite, isolating cube size as the decisive variable. For toluene, the flagship substrate in the study, the CT-30 catalyst delivered an apparent quantum yield of 3.2 percent and a reaction rate of 6.04 micromoles per gram per hour. Quantum yield, the fraction of incident photons that translate into chemical transformations, is a demanding metric in photocatalysis, and any improvement in it signals genuinely better carrier utilization rather than merely more light absorption.

The chemistry underlying these numbers follows a well-charted radical cascade. The electrons retained in the Cu2O conduction band sit at a potential of approximately minus 0.79 volts versus the normal hydrogen electrode, negative enough to reduce dissolved oxygen molecules into superoxide radicals. These superoxide species, in turn, participate in reactions that generate hydroxyl radicals, the most aggressive oxidants in aqueous and interfacial chemistry. Together, the radical suite attacks the aromatic rings of BTX molecules and progressively cleaves them, achieving full mineralization to carbon dioxide and water rather than stopping at partially oxidized intermediates that can themselves be toxic. The study’s emphasis on mineralization matters, because incomplete degradation products are a persistent pitfall in photocatalytic air treatment.

Why should crystal size shift the conduction band in the first place? The answer lies in quantum confinement and surface chemistry effects that become pronounced at the nanoscale. As semiconductor crystallites shrink below certain dimensions, their electronic structure changes: band gaps widen, band edges shift, and the density of surface states grows relative to the bulk. For Cu2O cubes in the tens of nanometers, the conduction band edge moves to more negative potentials, which is precisely the direction that strengthens the Fermi-level offset with TiO2. The 315-nanometer cubes, by contrast, behave much more like bulk material, with a conduction band closer to the bulk value and a correspondingly weaker interfacial field. The study thus converts a fundamental size effect into an engineering dial.

The broader significance of this work lies in its design principle. Heterojunction photocatalysts have been built for decades by pairing semiconductors and hoping their band alignments cooperate. This study shows that even with a fixed material pairing and fixed loading, the interfacial electronic structure, and therefore the catalytic outcome, can be tuned by morphology alone. Size-mediated Fermi level engineering, as the authors describe it, adds a controllable parameter that does not require new chemistries, exotic dopants, or rare cocatalysts. Because Cu2O is inexpensive, abundant, and synthesizable with well-defined cube morphologies, the strategy is compatible with scale-up ambitions, and the fixed one weight percent loading keeps material costs minimal.

There remain the usual caveats between laboratory performance and real-world deployment. BTX degradation was measured under controlled conditions, and practical air purifiers must contend with fluctuating humidity, competing pollutants, variable light intensity, and long-term catalyst stability. Cu2O is also known to be susceptible to photocorrosion, a challenge that heterojunction engineering partially mitigates by rapidly draining high-energy holes away from the Cu2O phase, but durability over thousands of operating hours will need explicit verification. Still, the study’s central message stands on firm quantitative ground: the Fermi level is not a fixed property to be accepted but a design variable to be positioned. For a field racing to turn sunlight and air into clean air, that insight may prove as valuable as any single efficiency number. The work was supported by the National Research Foundation of Korea and related Korean government programs, and the article is open access for readers who wish to examine the full dataset.

Subject of Research: Size-dependent Fermi level engineering in Cu2O/TiO2 S-scheme photocatalysts for VOC degradation

Article Title: Nanocube-size-dependent Fermi level positioning in Cu2O/TiO2 S-scheme heterojunctions for optimized VOC photodegradation

Article References: Liu, L., Maitlo, H. A., Ahmadi, Y., El-Shamy, O. A. A., & Kim, K.-H. (2026). Nanocube-size-dependent Fermi level positioning in Cu2O/TiO2 S-scheme heterojunctions for optimized VOC photodegradation. Advanced Composites and Hybrid Materials. https://doi.org/10.1007/s42114-026-02045-6

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02045-6

Keywords: photocatalysis, Cu2O, TiO2, S-scheme heterojunction, Fermi level, nanocubes, VOC degradation, benzene, toluene, xylene, superoxide radicals, air purification

The choice of host material is no accident. Graphitic carbon nitride is a metal-free, two-dimensional polymer-like semiconductor that has become one of the most studied photocatalysts of the past decade thanks to its chemical robustness and earth-abundant composition. Yet it suffers from a well-known weakness: it absorbs only the blue portion of visible light, and ultraviolet light, which many wider-bandgap semiconductors rely on, accounts for less than five percent of the energy reaching Earth from the sun. Coupling g-C3N4 with a partner semiconductor that harvests longer wavelengths is therefore essential if solar energy is to be used efficiently. CsPbI3 is an ideal candidate because, among the all-inorganic cesium lead halide perovskites, it possesses the narrowest band gap, allowing absorption to stretch from the visible deep into the near-infrared region.

Working with CsPbI3 is not without difficulty. The compound is notoriously unstable in polar and humid environments because the cesium ion is slightly too small to fully stabilize the lead-iodide octahedral lattice, which triggers structural distortion and phase degradation. Moreover, perovskite nanostructures are typically synthesized in hydrophobic solvents that coat their surfaces with long-chain organic ligands such as oleic acid and oleylamine. These ligands are useful for controlling growth but act as insulating barriers that block intimate contact and charge transfer at a heterojunction. The research team, led by Xiao Zhang and San Ping Jiang, overcame both obstacles with a two-step fabrication strategy: a mechano-chemical pre-treatment that partially strips the ligands and promotes hydrogen-bonding between the perovskite and the nitrogen-rich nanosheet surface, followed by a solvothermal treatment at 150 degrees Celsius that locks the two components into a robust, face-to-face architecture.

The structural characterization reveals just how intimate that contact is. Transmission electron microscopy shows cubic CsPbI3 nanocrystals, averaging roughly 18 nanometers, anchored uniformly across the g-C3N4 sheets without agglomeration, with lattice fringes at 0.61 nanometers confirming the cubic (100) plane. The nanowire composites tell a different story: wires of approximately 3.8 nanometers in diameter become partially embedded within the nanosheets rather than sitting loosely on top, forming the kind of continuous, ordered interface that engineers of solar materials dream about. X-ray diffraction confirms the cubic perovskite phase in both composites alongside the characteristic (002) reflection of g-C3N4 at 27.5 degrees, while elemental mapping verifies the even distribution of cesium, lead, and iodine across the hybrid structures.

Spectroscopic measurements then demonstrate why these interfaces matter. Photoluminescence, the light a semiconductor emits when excited electrons recombine with holes, is dramatically quenched in both composites, a signature of efficient charge separation. The average fluorescence lifetime of the nanocrystal composite lengthens from about 15 to nearly 27 nanoseconds, indicating that an interfacial built-in electric field is suppressing wasteful radiative recombination. Transient photocurrent measurements reinforce the point: the nanowire composite generates the highest photocurrent density of all samples, reflecting the ability of one-dimensional structures to shuttle carriers directionally along their long axis. X-ray photoelectron spectroscopy adds further evidence, with the nitrogen, cesium, lead, and iodine core-level peaks all shifting upon coupling, a fingerprint of electronic interaction and interfacial electron redistribution between the two semiconductors.

The band alignment explains the underlying physics. Tauc analysis of diffuse reflectance data yields band gaps of 2.78 electronvolts for g-C3N4 and 1.95 electronvolts for the CsPbI3 nanowires, while Mott-Schottky measurements place the flat-band potential of the nanowires at a more negative value than that of the nanosheets. When the two semiconductors touch, electrons spontaneously flow from the higher-Fermi-level perovskite into the carbon nitride until equilibrium is reached, creating a depletion region and an internal electric field across the junction. Electrochemical impedance spectroscopy shows that both composites have smaller semicircle radii than their parent materials, confirming lower charge-transfer resistance. Together, these measurements establish an S-scheme charge transport mechanism, in which excited electrons in the conduction band of g-C3N4 recombine with holes in the valence band of CsPbI3, preserving the most strongly reducing electrons and the most strongly oxidizing holes for chemistry.

That mechanism pays off spectacularly in carbon dioxide reduction. Under visible light, the nanowire composite produces carbon monoxide at a rate of 4.6 micromoles per gram per hour, outperforming the nanocrystal version at 3.6 and far exceeding bare g-C3N4. Remarkably, carbon monoxide is the only detectable product, corresponding to 100 percent selectivity, a feat attributed to the well-matched redox potentials of the preserved carriers. Because the two-electron pathway from carbon dioxide to carbon monoxide is both thermodynamically and kinetically favorable, and because separating mixed gas products is a costly downstream burden, this level of selectivity is highly valuable for both mechanistic studies and practical deployment. Radical scavenging experiments with ascorbic acid and isopropanol show that superoxide radicals play the decisive role, indicating that photogenerated electrons activate dissolved oxygen to form reactive intermediates that assist the reduction chemistry.

Stability and safety, the perennial Achilles heels of lead-halide perovskites, also fare well. After ten consecutive carbon dioxide reduction cycles, the nanowire and nanocrystal composites retain 91 and 94 percent of their initial activity respectively, and the X-ray diffraction pattern of the cycled nanowire sample remains unchanged. Lead ion leakage into solution after testing measures a mere 0.31 nanomolar, kept low by the small perovskite loading and by the residual hydrophobic ligands that suppress dissolution. For a class of materials often dismissed as too fragile and too toxic for real-world catalysis, these numbers represent a meaningful step toward credibility.

The air-purification results are equally compelling, and here the morphology story flips. The nanocrystal composite removes 69.5 percent of nitric oxide at a realistic concentration of 600 parts per billion, compared with 59.2 percent for the nanowire version and just 23.9 percent for pristine g-C3N4. More importantly, the fraction of nitric oxide converted into nitrogen dioxide, a toxic byproduct that contributes to acid rain, drops from 14.2 percent for bare carbon nitride to only 5.0 percent for the nanocrystal system. The S-scheme pathway generates an abundance of superoxide radicals, which oxidize nitric oxide first to nitrogen dioxide and then further to nitrate, effectively preventing the dangerous intermediate from accumulating. Hydroxyl radicals, generated through a chain involving hydrogen peroxide formed on the water-adsorbing carbon nitride surface, drive the final conversion to stable nitrous and nitric acids. The nanocrystal catalyst also retained its full activity over five successive reaction cycles.

The deeper lesson of this work lies in quantum confinement and defect engineering. The 3.8-nanometer-diameter nanowires possess a wider band gap of about 1.95 electronvolts, while the larger 18-nanometer nanocrystals sit at roughly 1.68 electronvolts, absorbing more effectively in the red. The nanocrystals also exhibit well-defined facets and far fewer surface defects than the defect-rich nanowires, whose vacancies and dangling bonds can trap carriers and diminish oxidative power. By simply choosing which morphology to grow, the researchers can dial the same chemical system toward reduction chemistry or oxidation chemistry, a strategy they describe as morphology-governed redox tuning. As the world searches for technologies that simultaneously address the carbon problem and the air-quality crisis, this study suggests that some of the most powerful answers may come not from new compounds, but from reshaping the ones we already have.

Subject of Research: Morphology-dependent CsPbI3/g-C3N4 S-scheme heterostructures for photocatalytic CO2 reduction and NO removal

Article Title: Perovskite CsPbI3 Nanocrystal and Nanowire Incorporated G‐C3N4 Nanosheets for CO2 Reduction and NO Removal

Article References: Zhang, X., & Jiang, S. P. (2026). Perovskite CsPbI 3 Nanocrystal and Nanowire Incorporated G‐C 3 N 4 Nanosheets for CO 2 Reduction and NO Removal. Advanced Science, Article e78119. https://doi.org/10.1002/advs.78119

Image Credits: AI Generated

DOI: 10.1002/advs.78119

Keywords: photocatalysis, CsPbI3 perovskite, graphitic carbon nitride, CO2 reduction, NO removal, S-scheme heterojunction, nanowires, nanocrystals, quantum confinement, charge separation, solar fuels, air purification

The research team, led by Min Seok Kwon and corresponding author No-Kuk Park of Yeungnam University, together with colleagues from the Institute of Clean Technology and Inwoo Eco Corporation, set out to understand precisely why manganese-oxide catalysts lose their appetite for ozone and then to compare two fundamentally different regeneration strategies. Their choice of material was deliberate. Manganese dioxide sits among the most effective and inexpensive catalysts for splitting ozone into ordinary oxygen at ambient conditions, which makes it attractive for small-scale VOC treatment systems where energy budgets are tight and elaborate heating equipment is impractical. Yet manganese oxides carry a well-known weakness: they are highly susceptible to moisture, and their performance decays steadily during prolonged use.

To build their catalyst, the researchers employed a potassium permanganate-assisted precipitation route. Aqueous manganese nitrate was combined with potassium permanganate in a 3:2 molar ratio at 80 degrees Celsius, a slow addition that drove oxidation and precipitation of manganese oxide from solution. After roughly 24 hours of aging, the precipitate was filtered, washed three times with deionized water to strip away residual nitrate and unreacted permanganate, dried at 110 degrees Celsius overnight, and pulverized. The powder was then shaped by extrusion with methyl cellulose and colloidal silica binders into cylindrical pellets a few millimeters across, later ground and sieved to particles between 300 and 800 micrometers for testing. X-ray fluorescence confirmed a product dominated by manganese oxide, roughly 93.2 weight percent MnO with about 4.6 percent SiO2 carried in from the binder. Crucially, because the synthesis avoided high-temperature calcination, the resulting catalyst remained only partially crystalline, a structure rich in lattice defects and oxygen vacancies that previous work has linked to exceptional ozone-decomposition activity.

The deactivation experiments told a vivid story. When about one gram of the catalyst was loaded into a tubular reactor and fed roughly 15 ppmv of ozone in air at room temperature and atmospheric pressure, the outlet ozone concentration plummeted to zero. Complete decomposition held for approximately 40 minutes before ozone began to creep back into the effluent, ultimately stabilizing near 8 ppmv, equivalent to about 50 percent conversion. This classic breakthrough curve is the fingerprint of a catalyst whose active sites are being progressively occupied. The mechanism behind ozone destruction on manganese oxide proceeds in three steps: ozone adsorbs onto the surface and splits off an adsorbed atomic oxygen species, a second ozone molecule reacts with that atomic oxygen to form two adsorbed molecular oxygen species, and finally those molecular species desorb as gaseous oxygen, freeing the site for another cycle. At low ozone concentrations, that third step, desorption, becomes the bottleneck. When desorption lags, oxygen intermediates pile up on the surface like cars in a parking garage with no exit, sealing off the very sites the reaction depends on.

Temperature-dependence experiments reinforced this interpretation. When the team gradually heated a deactivated catalyst, ozone removal climbed from partial conversion at 30 degrees Celsius to essentially complete destruction at 40 degrees Celsius, with no ozone detectable at the outlet above that point. Thermal energy, in other words, helps the trapped oxygen intermediates escape, temporarily re-exposing active sites. But definitive evidence came from X-ray photoelectron spectroscopy, or XPS, which probes the chemical state of the outermost atomic layers. On the fresh catalyst, the oxygen 1s spectrum was dominated by a lattice oxygen peak near 529.9 electronvolts. On the deactivated sample, a feature near 532 electronvolts, corresponding to surface-adsorbed oxygen species, swelled to encompass roughly 72 percent of the total spectral envelope. The poison was not some exotic contaminant; it was the reaction’s own intermediate, hoarded on the surface until the catalyst choked on its product.

With the deactivation mechanism established, the team tested the conventional remedy: thermal treatment. Deactivated catalyst samples were heated in an electric furnace at 100 to 600 degrees Celsius in 100-degree intervals for four hours each, at a controlled ramp of 5 degrees per minute, and then re-examined by X-ray diffraction and re-run in the ozone reactor. Between 100 and 500 degrees Celsius, the XRD patterns remained broad and weak, the signature of amorphous or partially crystalline phases studded with defects and vacancies, including traces of tunnel-structured epsilon-MnO2 that readily hosts oxygen vacancies. But above 600 degrees Celsius the picture changed dramatically: sharp diffraction peaks of alpha-Mn2O3 appeared, marking crystallization into a stable cubic phase with few vacancies and a high desorption energy for oxygen. In effect, the intense heat welded the catalyst into a form that no longer wanted to work.

The activity measurements tracked this structural narrative precisely. The fresh catalyst had a breakthrough time of about 40 minutes; samples treated at 100, 200, 300, 400, 500, and 600 degrees Celsius held out for approximately 8, 15, 23, 26, 22, and 3 minutes respectively. Expressed as recovery of initial activity, treatments at 100 and 200 degrees Celsius managed only about 20 and 37.5 percent, while the 300-to-500-degree-Celsius window consistently delivered around 57.5 percent. Beyond that, performance collapsed: catalysts treated at 500 and 600 degrees Celsius allowed steady-state outlet ozone concentrations of 9.5 and 11 ppmv, far above the roughly 8 ppmv seen after milder treatments. XPS confirmed that thermal treatment did strip away much of the adsorbed oxygen responsible for poisoning, but the accompanying loss of lattice defects at high temperatures meant that even a clean surface had fewer places to work. Thermal regeneration, the study showed, is a compromise: hot enough to free the surface, but not so hot as to crystallize the active phase.

The more surprising result came from the alternative strategy. Instead of heating the catalyst to hundreds of degrees, the researchers flowed a dilute mixture of 10 percent hydrogen in nitrogen over the spent catalyst at just 40 and 60 degrees Celsius. Embedded thermocouples revealed the chemistry happening in real time: the catalyst bed temperature fluctuated by up to 0.15 degrees Celsius at 40 degrees and within a 0.65-degree band at 60 degrees, transient swings produced when adsorbed oxygen species oxidized the incoming hydrogen to water in small local exotherms. Those gentle temperature excursions are direct evidence that the adsorbed oxygen, the poison itself, was being selectively consumed. After hydrogen exposure at 40 degrees Celsius, the catalyst regained about 25 percent of its initial activity; at 60 degrees Celsius, recovery reached approximately 55 percent, achieved with a fraction of the energy demanded by thermal treatment.

Spectroscopy sealed the case for selectivity. After hydrogen reduction, the 531.6-electronvolt XPS peak assigned to adsorbed oxygen dropped sharply, falling to an area fraction of 26.31 percent at 60 degrees Celsius and 29.61 percent at 40 degrees Celsius, while the lattice oxygen and oxygen vacancy signals remained essentially untouched. The hydrogen had removed the poison without disturbing the underlying active structure, avoiding the crystallization and defect loss that plague high-temperature regeneration. Intriguingly, catalysts regenerated by hydrogen outperformed some heat-treated samples even when their residual adsorbed-oxygen levels were comparable, because the hydrogen-treated surfaces retained their defect-rich, vacancy-laden architecture. The authors also noted that the reaction rate in ozone decomposition is governed by the interplay between adsorbed atomic oxygen and ozone forming adsorbed molecular oxygen, and that hydrogen regeneration short-circuits the poisoning cycle by converting the trapped species directly to water. For an industry searching for ways to extend catalyst lifetimes in compact, low-energy air-purification systems, the message is clear: sometimes the gentlest treatment, a warm whisper of hydrogen rather than a blast of furnace heat, is precisely what a poisoned catalyst needs to breathe again.

Subject of Research: Regeneration of deactivated manganese-based ozone decomposition catalysts by thermal treatment and hydrogen reduction

Article Title: Optimization of regeneration conditions for ozone decomposition catalysts via thermal treatment and hydrogen reduction

Article References: Kwon, M. S., Jang, J. G., Kim, M., Kwon, B. C., Park, N.-K., Kong, J. S., & Kong, S. W. (2025). Optimization of regeneration conditions for ozone decomposition catalysts via thermal treatment and hydrogen reduction. Advances in Industrial and Engineering Chemistry, 1(1), Article 29. https://doi.org/10.1007/s44405-025-00030-z

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00030-z

Keywords: ozone decomposition, manganese catalyst, catalyst regeneration, hydrogen reduction, thermal treatment, XPS, adsorbed oxygen, oxygen vacancies, VOC treatment, air purification, MnO2, deactivation

The study, published in the Journal of Saudi Chemical Society, describes ZIF-8/CA composite porous carbons: materials built by combining zeolitic imidazolate framework-8, a metal-organic framework prized for its ultrahigh surface area, with cellulose acetate, the biocompatible and biodegradable polymer that already dominates commercial cigarette filter manufacturing. The research was led by Wei-li Xu, Pei-jian Sun and Cong Nie of the Key Laboratory of Tobacco Chemistry at the Zhengzhou Tobacco Research Institute of CNTC, working with colleagues from China Tobacco Shaanxi Industrial and China Tobacco Shandong Industrial. Their central insight is deceptively simple: the ratio in which the two ingredients are mixed before carbonization decides everything about how well the final carbon can grab benzene molecules from a moving gas stream.

To build the composites, the team turned to a dual emulsion-solvent evaporation method, a technique borrowed from soft-matter chemistry that is rarely applied to metal-organic framework composites. First they synthesized ZIF-8 powder by mixing zinc nitrate hexahydrate with 2-methylimidazole in water at a precisely controlled molar ratio and stirring the milky suspension for 24 hours. They then created a primary emulsion by injecting an aqueous internal phase containing ammonium bicarbonate into a solution of cellulose acetate dissolved in dichloromethane, adjusting the ZIF-8 to cellulose acetate mass ratios to 3/7, 4/6, 6/4 and 7/3. Droplets of this emulsion were dispersed into a dilute polyvinyl alcohol solution to form a secondary emulsion. As the solvent evaporated over six hours of stirring, uniform composite microspheres formed. The final and most transformative step was pyrolysis: heating the microspheres to 950 degrees Celsius at 5 degrees per minute under nitrogen and holding them there for two hours, converting the polymer-framework hybrid into porous carbon.

Why go to such lengths? The answer lies in the complementary weaknesses of existing adsorbents. Conventional activated carbon, the workhorse of volatile organic compound control, suffers from a moderate specific surface area, irregular pore structures and weak affinity for benzene at low concentrations. ZIF-8, by contrast, offers exceptional microporosity, strong pi-pi interactions with aromatic molecules and a gate-opening flexibility that accommodates bulky guests like benzene and toluene — but the raw powder is notoriously difficult to process, tends to agglomerate, and cannot easily be shaped into practical devices such as filter cartridges. Cellulose acetate solves the processability problem: its hydroxyl and acetyl groups form hydrogen bonds with ZIF-8, promoting even dispersion and mechanical stability, while its carbonization generates additional pores. What remained unknown, and what this study set out to map systematically, was how the ZIF-to-polymer mass ratio shapes the full hierarchy of pore sizes and, in turn, the benzene uptake.

The characterization data tell a striking story of structural optimization. Scanning electron microscopy revealed spherical particles between 100 and 500 micrometers in diameter, but their internal architecture varied dramatically with composition. At the 3/7 ratio, excess cellulose acetate caused the polymer matrix to aggregate, producing a dense, nearly pore-free cross-section. Pushing ZIF-8 content too high, at 6/4 and 7/3, triggered the opposite failure: agglomerated carbon particles and larger but poorly distributed pores. The sweet spot arrived at 4/6, where the surface roughened into uniform microscale protrusions and the cross-section displayed a beautifully interconnected porous network. Nitrogen physisorption measurements confirmed the visual evidence: the 4/6 composite achieved a Brunauer-Emmett-Teller specific surface area of 1380 square meters per gram and a mesopore volume of 0.77 cubic centimeters per gram, far exceeding the 577, 657 and 796 square meters per gram recorded for the other formulations. All samples showed Type IV isotherms with H4 hysteresis, a fingerprint of mesoporosity, with mesopores concentrated near 2.5 nanometers.

Mercury intrusion porosimetry added the final piece of the hierarchical puzzle, probing pores far too large for nitrogen adsorption to detect. The dominant macropore diameter increased progressively with ZIF-8 content, a trend the researchers attribute to gas evolution — carbon dioxide and nitrogen released as the framework decomposes — which inflates and expands the pores during carbonization. This revealed an elegant division of labor: cellulose acetate carbonization builds mesopores and surface area, while ZIF-8 decomposition carves macropores. The two effects compete, and the 4/6 composition strikes the optimal balance between abundant mesoporous adsorption domains and macroporous highways for rapid molecular transport. Many high-surface-area carbons perform poorly in dynamic adsorption because blocked channels or excessive micropores strangle diffusion; this composite avoids both traps by design.

Dynamic benzene vapor adsorption tests brought the structure-property relationship into sharp focus. In breakthrough experiments with a benzene stream flowing at 100 milliliters per minute through a thermostatted column at 25 degrees Celsius, the saturation adsorption capacity traced a volcano-shaped curve across the composition series, peaking at 235.0 milligrams per gram for the 4/6 sample — well above its siblings and competitive with previously reported adsorbents. To dissect the kinetics, the team fitted the breakthrough curves with two classical fixed-bed models. The Apiratikul-Chu model reproduced the entire breakthrough curves with correlation coefficients exceeding 0.99, capturing the asymmetric tailing that arises from internal diffusion through tortuous pore networks. The 4/6 composite also displayed the highest rate constant, at 65.2 per minute, thanks to plentiful active sites and macropores that slash mass-transfer resistance. The Adams-Bohart model, applied to the initial stage of adsorption, delivered correlation coefficients above 0.97, confirming that surface adsorption and external mass transfer govern the onset of uptake.

The chemistry behind the capture is as important as the physics of the pores. Both the graphitic carbon formed from cellulose acetate and the residual framework structure of ZIF-8 are rich in delocalized pi-electrons, which form strong pi-pi stacking interactions with the aromatic ring of benzene — an affinity that physical adsorption alone cannot provide. Meanwhile, the graded pore hierarchy produces a confinement effect: micropores and mesopores physically trap benzene molecules, while interconnected channels accelerate their diffusion toward those sites. Macropores lower external diffusion resistance, mesopores and micropores dominate intraparticle diffusion, and the result is a material whose adsorption rate is as impressive as its capacity.

The most headline-grabbing result came when the material faced its intended real-world challenge: actual cigarette smoke. Using a custom-built apparatus connected to an SM-450 smoking machine operating under the ISO standard protocol — 35-milliliter puffs drawn over two seconds with 60-second intervals — the researchers loaded 10 milligrams of adsorbent into each cigarette filter and analyzed trapped benzene by gas chromatography-mass spectrometry. The ZIF-8/CA 4/6 composite removed 49.0 percent of benzene from mainstream smoke, dramatically outperforming a ZIF-8/polylactic acid control composite prepared under identical conditions, which managed only 20.7 percent. Even in the chemical chaos of real smoke, where countless gaseous components compete for adsorption sites, the hierarchical pore structure and pi-pi selectivity for aromatic compounds allowed the composite to maintain high benzene capture. The authors note that only benzene was quantified in this study, with multi-component analysis and regeneration and long-term cycling tests planned for follow-up work, and that static adsorption isotherms will be examined in future research.

Beyond the laboratory numbers, the study delivers a genuinely versatile design principle. By simply tuning a mixing ratio before a single carbonization step, researchers can dial in a micro-meso-macroporous architecture tailored to a target pollutant — a rational, adaptable strategy that could extend well beyond cigarette filters to industrial off-gas treatment, indoor air purifiers and protective respirators. The rigid carbon skeleton also promises structural stability for cyclic use. For a compound as pervasive and as dangerous as benzene, a scalable material that more than doubles the removal efficiency of a comparable commercial polymer composite represents meaningful progress — and a reminder that sometimes the biggest advances in environmental health come not from exotic new chemistry, but from getting the architecture of familiar ingredients exactly right.

Subject of Research: Hierarchical pore engineering of ZIF-8/cellulose acetate composite porous carbon for benzene vapor adsorption and cigarette smoke purification.

Article Title: Hierarchical pore structure modulation of ZIF-8/CA composite porous carbon for efficient benzene vapor adsorption

Article References: Xu, W.-L., Sun, P.-J., Sun, X.-H., Wang, Y.-P., Li, J.-L., Ge, C., Liu, Q., Zhou, J., Yang, F., Song, X.-H., & Nie, C. (2026). Hierarchical pore structure modulation of ZIF-8/CA composite porous carbon for efficient benzene vapor adsorption. Journal of Saudi Chemical Society, 30(4), Article 56. https://doi.org/10.1007/s44442-026-00098-2

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00098-2

Keywords: ZIF-8, cellulose acetate, porous carbon, benzene adsorption, volatile organic compounds, hierarchical pores, metal-organic frameworks, cigarette smoke filtration, air purification, carbonization, adsorption kinetics, breakthrough curves