PEDOT, or poly(3,4-ethylenedioxythiophene), is one of the workhorses of organic electronics. It conducts well, is partially transparent, and bends without breaking, which makes it attractive for flexible devices. But PEDOT is hydrophobic, so it must be processed in polar solvents such as water, and that requires stabilizing additives. The most common partner is polystyrene sulfonate, PSS, an insulating polymer that keeps PEDOT dispersed in water and enables the commercial conductive inks used in solar cells, light-emitting diodes, batteries, and supercapacitors. The same ink also serves as the active layer in organic gas sensors, where it adsorbs specific gases or vapors and converts those interactions into an amplified electrical signal.

The Brazilian-Irish collaboration prepared conductive inks by adding precise volumes of commercial PEDOT:PSS to an aqueous graphene oxide dispersion, producing blends labeled GO:PEDOT:PSS with PEDOT concentrations ranging from 40 to 88 percent. Graphene oxide was synthesized by oxidizing graphite and exfoliating the resulting sheets in water. The team deposited thin films of each blend onto flexible acetate substrates fitted with interdigitated chromium-gold electrodes, then characterized their morphology with scanning electron microscopy and their electrical properties with four-probe measurements. The films were roughly 250 nanometers thick, and the sensors were tested at 21 degrees Celsius with 1,000 parts per million of methanol in dry air.

The electrical measurements confirmed a long-suspected optimum. The lowest resistivity appeared in the GO:PEDOT:PSS 78 percent blend, corresponding to a GO-to-PEDOT mass ratio of 5.8 times 10 to the minus 2 that previous studies had identified as ideal for conductivity and optical transmittance. Earlier work attributed this optimum to improved alignment of the thiophene groups within PEDOT and to additional doping facilitated by graphene oxide. The new study replicated an ethyleneglycol treatment that selectively removes PSS from the dried films, and the resistivity minimum persisted at the same 78 percent concentration, suggesting the optimum is a robust property of the blend rather than an artifact of processing.

When the same films were exposed to methanol vapor, the sensing optimum shifted. The highest response, approximately 18 percent, was achieved with GO:PEDOT:PSS 68 percent, not the 78 percent blend that conducted best. The flexible devices reproduced the qualitative behavior previously reported for sensors on glass substrates, with response values falling within the same order of magnitude. The researchers attribute the slight differences to the flexible nature of the acetate substrates, where surface interactions between the inks and the substrate alter film morphology, thickness, and exposed active area, all of which influence how methanol interacts with the active layer.

To explain why the conductivity and sensing optima occur at different mass ratios, the team turned to a theoretical model based on Kirchhoff’s circuit approach. They represented the blend as a 100 by 100 square lattice in which every node is labeled GO, PEDOT, or PSS, and every link between nodes carries a resistance encoding the interactions between those constituents. The equivalent resistance between two electrode sites is calculated from Kirchhoff’s matrix, which encodes the connectivity and interactions of the network. Because graphene oxide and PSS are insulators while PEDOT conducts, the network exhibits a competition of resistances. Below the optimum, there is not enough PEDOT to overcome the insulating pathways; above it, the sample approaches the conductivity of pure PEDOT. The calculated resistivity minimum landed at approximately 78 percent PEDOT, in agreement with the experimental data.

The same lattice model was extended to sensing by modifying the link resistances to represent methanol exposure, with the alcohol distributed throughout every component as in a saturated atmosphere. The calculated response reached its maximum at approximately 65 percent PEDOT, closely matching the 68 percent blend that performed best experimentally. The logic mirrors the resistivity case: although both graphene oxide and PSS interact with methanol, the active layer must conduct the signal to the external circuit, and PEDOT is the only conductive constituent. Graphene oxide increases the number of free charges available, and methanol molecules consume those polarons, raising the device resistance and enhancing the sensing signal at specific concentrations.

The study also compared commercial PEDOT:PSS inks with chemically synthesized aqueous PEDOT produced without PSS, using iron(III) chloride to polymerize the EDOT monomer in acetonitrile and water. The polymerized GO:PEDOT blends showed an average particle size of about 480 nanometers and a zeta potential of plus 45.8 millivolts, indicating a metastable state that can be stored at 4 degrees Celsius for up to four months without coagulation. Their resistivity values, approximately 0.35 and 0.45 ohm centimeters for GO:PEDOT and PEDOT respectively, remain competitive with the commercial ink. Scanning electron microscopy revealed that PEDOT and GO:PEDOT:PSS films are homogeneous, while GO:PEDOT films contain clusters of graphene oxide sheets coated by polymeric PEDOT, a morphology that limits cluster connectivity and keeps the sensing efficiency close to that of pure PEDOT despite additional doping.

Perhaps the most striking finding concerns the direction of the resistance change during methanol exposure. Commercial samples containing PSS showed an increase in resistance when exposed to methanol, while polymerized samples without PSS showed a decrease. The team attributes the increase to a swelling effect: PSS is hygroscopic, so polar solvents like methanol infiltrate the active layer, separate the polymeric chains, reduce connectivity, and consume free charges, raising resistance. In the absence of PSS, the decrease in resistance is associated with a reorganization of charges within the doped polymer, which can delocalize charge carriers and create new conduction pathways, temporarily increasing conductivity. Methanol is a reducing agent, so resistance changes in these devices are typically linked to doping or dedoping processes, and the polymerized samples appear to rely on charge redistribution rather than charge exchange.

The theoretical model reproduced both behaviors qualitatively, capturing the resistance increase in PSS-containing networks and the decrease in PSS-free ones. The researchers note that graphene oxide occupies a unique position in the network: it is a component with high electrical resistance but also features regions that can conduct electricity, creating the interplay between resistances that produces the contrasting responses. The model, simple as it is, addressed the three central questions of the study: the position of the resistivity minimum, the position of the response maximum, and the role of PSS in determining how methanol interacts with the active layer. The square lattice representation proved a powerful yet tractable method for studying such disordered systems, yielding results consistent with larger and more computationally demanding network models.

The implications reach beyond methanol. Organic gas sensors operate at room temperature, unlike inorganic counterparts that often require temperatures exceeding 100 degrees Celsius, which makes them appealing for confined spaces such as grain silos and fuel tanks where methanol accumulates as a toxic and flammable vapor. Lower operating temperatures demand less energy and reduce accident risk. The sensors in this study were characterized at 21 degrees Celsius with 0 percent humidity, since water vapor can hinder methanol detection through a swelling effect. The polymerized PEDOT inks, produced exclusively in water without stabilizers or surfactants, offer enhanced ecological appeal and reduced production costs, and the sensors made from them showed greater stability than commercial counterparts, with faster saturation times and no observable drift in the resistance curves.

By combining experimental characterization with a circuit-based model, the study provides a coherent picture of how methanol detection works in graphene oxide and conductive polymer active layers. The resistivity minimum and the response maximum arise from the same competition of resistances, but at different mass ratios because sensing requires both interaction with the vapor and conduction of the signal. PSS, the insulating polymer that enables water dispersibility, turns out to be essential for the doping effect that graphene oxide provides, amplifying the disruption of PEDOT doping caused by methanol molecules. The work demonstrates that a simple square lattice model, grounded in Kirchhoff’s laws, can quantitatively and qualitatively explain the behavior of real nanostructured sensing films, offering a theoretical foundation for designing next-generation flexible gas sensors.

Subject of Research: Materials Science

Article Title: Mechanisms of methanol detection in graphene oxide and conductive polymer active layers for gas sensing devices

Article References: das Neves, M. F. F., Mukim, S., Ferreira, M. S., & Roman, L. S. (2024). Mechanisms of methanol detection in graphene oxide and conductive polymer active layers for gas sensing devices. Frontiers in Carbon, 3, Article 1352122. https://doi.org/10.3389/frcrb.2024.1352122

Image Credits: AI Generated

DOI: 10.3389/frcrb.2024.1352122

Keywords: graphene oxide, PEDOT:PSS, methanol sensor, gas sensing, flexible electronics, conductive polymers, Kirchhoff model, organic electronics, Mechanisms, methanol, detection, graphene

The team’s target material was Formlabs High Temperature resin, a photopolymer the manufacturer says reaches a heat-deflection temperature of up to 238 degrees Celsius after post-curing, comfortably above the operating range of methanol-water distillation. All specimens and columns were printed on an Original Prusa SL1S Speed masked stereolithography system with a 405 nm UV LED array, chosen for its open-material platform that allowed direct user control over the two most fundamental printing variables: per-layer exposure time and layer thickness. The researchers printed hollow tube specimens with 12 mm outer diameter and 15 mm height, wall thicknesses between 0.5 and 3.0 mm, as the main test geometry because thin-walled features are exactly what printed distillation internals demand.

The core insight driving the work is that the final material performance of an SLA part is not determined by the resin formulation alone. Commercial SLA resins are built on multifunctional acrylate or methacrylate monomers and oligomers that form crosslinked networks during photopolymerisation, but as the resin transforms from liquid to rubbery and then glassy network, the curing reaction becomes increasingly mobility-limited. Complete conversion of all reactive groups is therefore never achieved in highly crosslinked SLA parts, leaving residual monomers, oligomers, additives, and photoinitiator-derived fragments trapped inside the printed network. When methanol — a small, polar solvent that interacts strongly with acrylate networks — enters the part, it swells the polymer and simultaneously facilitates the extraction of those residual low-molecular-weight species into the contacting liquid, a diffusion-controlled process that can compromise mechanical integrity and thermomechanical properties at elevated temperatures.

Gravimetric methanol uptake served as the main quantitative indicator throughout the study, measured with an analytical balance readable to 0.0001 g following the principles of ISO 175, ISO 62, and ASTM D570 with modifications for hot methanol exposure. Specimens were placed in sealed glass vessels on heating plates, removed at defined intervals from 15 minutes to 28 days, blotted with lint-free tissue, and weighed within 60 seconds to minimise evaporative losses. Most accelerated tests ran in pure methanol at 75 degrees Celsius, while selected tests and the column-level compatibility experiment used a 50:50 mol% methanol-water mixture at temperatures up to 120 degrees Celsius to represent the realistic distillation environment. The researchers acknowledge that leaching of residual species was not analytically quantified, deferring targeted leachate identification and mechanical characterisation to future work, but they argue that solvent uptake dominates the measured mass change and correlates with leaching behaviour reported in the literature.

The printing-parameter study revealed that per-layer exposure time directly controls methanol resistance. After 6 hours in methanol, specimens printed at 8 seconds exposure reached 2.267 wt% uptake, while those printed at 12 seconds reached 1.960 wt% — a reduction of 0.307 wt% attributable to improved layer curing, stronger interlayer bonding, and a lower amount of residual reactive material. Layer thickness played a smaller but measurable role: after 28 days at room temperature, specimens printed at 0.100 mm layer thickness reached 4.46 wt% uptake compared with 4.01 wt% for 0.025 mm specimens, suggesting thicker layers introduce more pronounced interlayer regions where local bonding is less complete. Wall thickness, meanwhile, governed the time-dependent uptake behaviour — thinner walls gained mass rapidly in the first hours of exposure, while thicker walls delayed the process and extended the useful operating window before large dimensional changes occurred.

Post-processing proved even more decisive than printing parameters. Among the variables tested, UV post-cure duration ranked first in the parameter hierarchy, with the difference between 1 hour and 2 hours of UV curing at 80 degrees Celsius producing up to a 2.30 wt% reduction in methanol uptake. Raising the UV post-cure temperature from 60 to 80 degrees Celsius was more effective than simply extending cure duration at 60 degrees Celsius, because the higher temperature gives the polymer network greater molecular mobility, allowing additional curing of restricted reactive groups to proceed more effectively. Thermal post-curing at 160 degrees Celsius for 3 hours — below the resin’s heat-deflection temperature but high enough to promote additional network stabilisation — produced a consistent mass loss of approximately 0.44 to 0.47 wt%, attributed mainly to removal of residual volatile or low-molecular-weight species rather than structural degradation.

Perhaps the most surprising finding concerned support-removal timing, a step usually treated as routine handling. Specimens cured with supports still attached and removed only after post-curing showed higher methanol uptake than specimens whose supports were removed after washing and before UV curing. At 5 hours of exposure, the largest difference occurred for 1.0 mm wall specimens, where delayed support removal increased uptake by approximately 1.94 wt%. The most likely explanation is local surface damage at support contact points: once the part is fully cured, the resin is stiffer and more brittle, so removing supports can leave small cracks, fractured regions, or roughened surfaces that provide easier entry points for methanol. For very thin 0.5 mm walls, both conditions showed high uptake because the whole wall saturates rapidly, masking the support effect.

The washing protocol, by contrast, had a negligible influence once sufficient isopropyl alcohol contact had been achieved. Three IPA-based protocols — 10 minutes soaking followed by 20 minutes washing, 10 minutes soaking followed by 10 minutes washing, and 10 minutes washing followed by 10 minutes thermal drying — differed by less than 0.05 wt% in methanol uptake, well within the practical uncertainty of the gravimetric method. The researchers conclude that a minimum of 10 minutes fresh IPA contact is sufficient for HT resin parts of the type studied, though they note that manual IPA flushing through internal channels remains essential for column prototypes where uncured resin can remain trapped in enclosed regions.

With the optimised process chain — IPA washing for at least 10 minutes, support removal before UV curing, UV post-curing at 80 degrees Celsius for 2 to 3 hours, and thermal post-curing at 160 degrees Celsius for 3 hours — the team applied their findings to a full SLA-printed distillation column containing gyroid-type internal features designed to increase vapour-liquid contact area. During methanol-water reflux at temperatures up to 120 degrees Celsius, the printed column retained its shape and macroscopic integrity. After 24 hours of operation, the column gained 2.1 wt%; after 72 hours under the same conditions, the mass gain reached 5.72 wt%. No visible deformation, cracking, fracture, flooding, or leaking was observed after the 72-hour test, though the researchers stress that the reported mass gain includes both solvent uptake and leaching of residual species, and the result should be interpreted strictly as short-term survival without visible failure.

The long-term exposure data also carried an encouraging practical message for real distillation operation. Some experiments included heating periods followed by room-temperature soaking and later reheating to represent start-up and shut-down cycles. Once specimens had already gained mass during the initial methanol exposure, cooling and reheating caused only small additional changes in measured mass, suggesting most of the rapid uptake occurs during the first exposure period. Comparing the two exposure conditions, pure methanol at 75 degrees Celsius reached approximately 42% higher uptake than the 50:50 mol% methanol-water mixture after 28 days, showing that exposure severity is determined not by temperature alone but by solvent composition and duration — and that pure methanol can serve as the more conservative screening condition for methanol-water distillation prototypes. The authors are careful to position SLA photopolymers not as permanent replacements for glass or metal distillation equipment, but as a route to screening chemically exposed process equipment before designs are transferred to more durable materials. The trends observed for HT resin may be relevant to similar acrylate or methacrylate SLA resins, but the numerical values should not be transferred directly to other resin chemistries — each system will require its own process window when exposed to hot polar solvents.

Subject of Research: Materials Science

Article Title: Process-chain optimisation of SLA-printed high-temperature resin for short-term methanol compatibility in distillation prototypes

Article References: Kumari, N., Jayavelu, V., & Klahn, C. (2026). Process-chain optimisation of SLA-printed high-temperature resin for short-term methanol compatibility in distillation prototypes. Results in Engineering, 32, Article 113491. https://doi.org/10.1016/j.rineng.2026.113491

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113491

Keywords: 3D printing, stereolithography, distillation, methanol, photopolymer, additive manufacturing, chemical engineering, post-processing, Process-chain, optimisation, SLA-printed, high-temperature

The core of the innovation is a photon–phonon co-driven strategy, abbreviated PPCC by the team. Conventional photocatalysis uses light alone to drive chemical reactions, while thermocatalysis relies purely on heat. Each approach has inherent limits. Photocatalysis suffers from a quantum efficiency ceiling, because a single photon can only do so much work, and thermocatalysis often forces a trade-off between yield and selectivity. Methanol conversion to hydrogen and formaldehyde is particularly demanding: it is an endothermic process that doubles the gas-phase volume, and it proceeds through two sequential dehydrogenation steps, each with a different activation energy. No single energy input can efficiently satisfy both. By coupling 365-nanometre ultraviolet light from an LED with moderate heating at 150 degrees Celsius in a continuous-flow reactor, the Tsinghua team matched each elementary step with the energy source best suited to it, photons for the hardest activation step and phonons, the lattice vibrations that carry thermal energy, for the rest.

The catalyst itself is a masterclass in atomic-scale engineering. Platinum single atoms were anchored to a mixed anatase-rutile titanium dioxide support and surrounded by lithium, forming what the evidence suggests are PtLi2 clusters. The optimal formulation, containing roughly 0.3 weight percent platinum and 0.2 weight percent nominal lithium input, delivered a hydrogen production rate of 4.36 moles per gram of catalyst per hour at 150 degrees Celsius, a figure 30.3 times higher than unmodified TiO2 and roughly an order of magnitude above the best low-temperature thermal catalytic benchmarks. The apparent turnover frequency reached a record 275,000 per hour. Even more striking is the overall quantum yield of 184 percent, a value exceeding 100 percent because thermal energy contributes additional driving force beyond the incident photons alone. In the dark, the same catalyst at the same temperature managed only 0.11 moles per gram per hour, confirming that light is the primary driver and heat the essential promoter.

Crucially, the carbon does not end up as carbon dioxide. Instead, the dominant carbon-containing product is formaldehyde, produced with 94 percent selectivity at a synthesis rate of 3.5 moles per gram per hour. In batch experiments, the team accumulated a concentrated formaldehyde solution of 21.2 weight percent after just 140 minutes, a strength approaching commercial grades used in medicine and in the manufacture of industrial resins and plastics. Formaldehyde is currently made by oxidizing methanol over silver catalysts at around 600 degrees Celsius or iron-based catalysts at around 350 degrees, a process that consumes more than 30 percent of global methanol output. Co-generating hydrogen and formaldehyde from a single mild-temperature process therefore offers two saleable products with net-zero carbon emissions and complete atomic utilization of the methanol feedstock.

Lithium turned out to be the quiet hero of the story, performing no fewer than five distinct jobs. First, it retards the recombination of photogenerated charge carriers in the catalyst bulk, extending the lifetime of the reactive electrons and holes. Second, it facilitates electron transfer from the TiO2 bulk to the platinum reaction sites, with density functional theory calculations showing that the intrinsic electron transfer energy becomes more favourable as lithium is added, and that lithium lowers the quantum tunnelling barrier for directional electron injection. Third, it weakens the binding of hydrogen atoms on the platinum surface; computed adsorption free energies shift from a strongly binding minus 0.32 electronvolts on platinum nanoparticles to a nearly ideal minus 0.04 electronvolts on the Pt1Li2 site, easing hydrogen desorption and avoiding catalyst poisoning. Fourth, it maximizes the fraction of platinum present as Pt2+ rather than metallic Pt0, which the team’s poisoning experiments identified as the true active sites. Fifth, and perhaps most importantly, it stabilizes those single atoms against aggregation.

That stabilizing role was demonstrated with unusual rigour. X-ray photoelectron spectroscopy showed that in a lithium-free Pt–TiO2 catalyst the Pt2+ fraction collapsed from 70 percent to 29 percent within one hour of reaction, while in the lithium-modified material it barely moved, from 100 percent to 96 percent. Extended X-ray absorption fine structure revealed growing platinum-platinum coordination in the unmodified catalyst, a signature of clustering, but no such change in the lithium version. Identical-location electron microscopy, in which the very same catalyst particles were imaged before and after one hour under realistic reaction conditions, directly visualized new platinum nanoparticles forming and existing particles growing on Pt–TiO2, while the lithium-stabilized sample remained atomically dispersed. The practical consequence was dramatic: the catalyst ran stably for 19 days under a simulated solar cycle of eight hours illumination and sixteen hours darkness, maintaining hydrogen output and formaldehyde selectivity above 94 percent throughout.

The mechanistic picture that emerges from transient absorption spectroscopy, isotope labelling, in situ electron paramagnetic resonance and infrared measurements is an elegant division of labour between light and heat. Photons excite charge carriers in TiO2, which couple to the lattice to form polarons; thermal phonons then help these polarons hop to the surface rather than remaining trapped. On the surface, water adsorbs more strongly than methanol, so photogenerated holes preferentially oxidize water to hydroxyl radicals. These radicals, rather than the holes themselves, attack methanol, abstracting a hydrogen atom to form the hydroxymethyl radical, a step calculated to cost only 0.37 electronvolts compared with roughly 0.83 electronvolts for direct hole-driven cleavage. Kinetic isotope experiments confirmed that carbon-hydrogen bond cleavage in methanol is the rate-determining step, and it is precisely this demanding step that the energetic photogenerated carriers are positioned to drive. The subsequent dehydrogenation of the hydroxymethyl intermediate to formaldehyde, by contrast, is a nearly barrierless thermal transformation that phonons alone can push forward.

The team also showed the concept scales in a practical sense: connecting two flow reactors in series boosted hydrogen production by 1.7 times, and the system tolerated variations in light intensity, pressure, flow rate and catalyst loading that were systematically optimized. The 40 percent methanol feed concentration proved optimal, with control experiments showing that any carbon dioxide formed arises secondarily from formaldehyde reforming with water rather than from direct over-oxidation. Isotope labelling with deuterated methanol confirmed that hydrogen atoms from the methyl group of methanol end up in the hydrogen gas, while hydroxyl hydrogens exchange with water, consistent with the proposed cascade.

Beyond the headline numbers, the significance of this work lies in its conceptual generality. Photon–phonon co-driven catalysis offers a framework for any transformation hobbled by an activity-selectivity trade-off, by assigning each elementary step to the energy input that matches its activation barrier. The authors argue that future progress will depend on reactor engineering tailored to dual energy fields, explicitly managing photon transport and heat flow to balance the energy budget. If those engineering challenges can be met, a methanol economy in which the liquid fuel doubles as a hydrogen battery and a chemical feedstock, releasing no carbon dioxide in the process, moves a decisive step closer to industrial reality.

Subject of Research: Photon–phonon co-driven catalytic conversion of methanol to hydrogen and formaldehyde using lithium-modified platinum single atoms on titanium dioxide

Article Title: Green synthesis of hydrogen and formaldehyde from methanol with enhanced quantum efficiency

Article References: Zhao, J., Xiong, L., Zheng, Y., Nie, Q., Yu, Z., Guo, J., Li, X., Liu, Q., Sun, X., Zheng, X., Wang, Z., Selloni, A., Gong, X., Huang, W., & Tang, J. (2026). Green synthesis of hydrogen and formaldehyde from methanol with enhanced quantum efficiency. Nature Sustainability. https://doi.org/10.1038/s41893-026-01959-9

Image Credits: AI Generated

DOI: 10.1038/s41893-026-01959-9

Keywords: hydrogen production, methanol, formaldehyde, single-atom catalysis, photocatalysis, photon–phonon co-driven catalysis, platinum catalyst, titanium dioxide, lithium modification, quantum yield, green chemistry, Nature Sustainability

Researchers from Zhejiang University set out to systematically test how this so-called fermented fruit state shapes both the flavor quality of kiwi wine and the accumulation of methanol, the primary hazardous byproduct in fruit wines. Methanol in fruit wine originates almost entirely from the enzymatic breakdown of pectin, the gelling polysaccharide that gives fruit its structure. Pectin methylesterase, or PME, cleaves methyl ester groups from pectin molecules, releasing methanol in the process. At sub-toxic concentrations methanol already degrades flavor purity, and at elevated levels it poses serious health risks, including blindness and death. Because kiwifruit is unusually rich in pectin, particularly in its peel and pulp tissues, the question of how much solid fruit material to include during fermentation is not merely a matter of taste. It is a safety question.

The team, led by Jiahui Shao and Huan Cheng, worked with three commercial cultivars representing the three main flesh-color backgrounds of the genus Actinidia: Hongyang, a red-fleshed variety; Jinyan, yellow-fleshed; and Xuxiang, green-fleshed. All fruit was harvested from Cangxi County in Sichuan Province and sorted to a uniform firmness of 3 to 5 newtons using a texture analyzer. Each cultivar was then fermented under four conditions: peeled juice fermentation, peel-involved juice fermentation, peeled pulp maceration, and peel-involved pulp maceration. That produced a twelve-treatment factorial experiment, with three independent fermentation replicates for each combination. All treatments received identical pectinase pretreatment, potassium metabisulfite, sucrose adjustment to 23 degrees Brix, and inoculation with Saccharomyces cerevisiae at 23 degrees Celsius for eight days, ensuring that any differences could be attributed to the fruit state rather than fermentation efficiency.

The analytical arsenal deployed on the resulting wines was formidable. Headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry identified 130 volatile compounds across all samples, including 39 alcohols, 42 esters, 13 acids, 5 aldehydes, 6 ketones, and 6 terpenes. Odor activity value analysis, which divides a compound’s concentration by its sensory perception threshold, pinpointed 12 aroma-active compounds with values above 1.0. Isoamyl acetate emerged as the single dominant contributor to the fruity character of the wines, while 3-methyl-1-butanol, with odor activity values ranging from 11.45 to 45.36, drove the alcoholic and cheese-like notes. Electronic nose and electronic tongue instruments provided complementary fingerprinting, and a trained fifteen-member sensory panel rated each wine on a nine-point intensity scale after a month of training.

The flavor results told a clear story. Pulp maceration generally increased the proportion of esters, the class of compounds responsible for fruity and floral aromas, with pulp-fermented wines reaching ester proportions of 20.13 to 56.37 percent compared with 13.46 to 52.23 percent in juice-fermented wines. Ethyl caprylate, a compound associated with fruity sweetness, was notably more abundant in pulp treatments. Pulp fermentation also raised total phenolic content, which ranged from 2657 to 5053 milligrams of gallic acid equivalents per liter in pulp wines versus 2053 to 4384 in juice wines, along with total flavonoids. But these gains came at a cost. The electronic tongue and sensory panel both detected elevated bitterness and sourness in the maceration wines, particularly in the green-fleshed Xuxiang samples, which consistently showed the highest phenolic and flavonoid levels. Phenolics interact with bitter taste receptors and bind salivary proteins, producing astringency, so richer is not always better.

Peel contact produced more cultivar-dependent effects. In juice fermentation, peel involvement slightly raised phenolic content, consistent with the well-known enrichment of polyphenols in fruit skins. In pulp maceration, however, peeled samples sometimes showed higher measurable phenolics than their peel-involved counterparts, likely because oxidative enzymes released during maceration polymerized the phenolics or bound them to proteins and polysaccharides, rendering them undetectable by the assay. Flavonoids, by contrast, were enhanced by peel presence in both fermentation systems. The hierarchical clustering of odor activity values showed a clean separation between peeled and peel-involved treatments across all cultivars, confirming that peel contact fundamentally reshapes the aroma profile rather than simply amplifying it.

The methanol data revealed the darker side of the trade-off. Methanol concentrations were lowest in peeled juice fermentation and rose with both peel involvement and pulp maceration in most cases. Across cultivars, Hongyang wines showed the lowest levels, from 96.57 to 156.33 milligrams per liter, while Jinyan wines were highest at 142.71 to 215.03 milligrams per liter, and Xuxiang fell in between. All values remained below the benchmarks set by the International Organisation of Vine and Wine, which caps methanol at 400 milligrams per liter for red wines and 250 for white and rosé wines, but the Jinyan peel-involved pulp maceration treatment came uncomfortably close to the 250 milligram threshold. The mechanistic explanation lies in the pectin chemistry: water-soluble pectin consumption and total pectin degradation were both greatest in the peel-involved pulp treatments, providing more substrate for PME-mediated demethylation.

Correlation and regression analyses sharpened the picture further. Apparent PME activity at the fermentation endpoint correlated moderately but significantly with methanol content, with a Pearson coefficient of 0.55 across 36 samples, and partial least squares regression identified total pectin consumption and PME activity as the most important predictors, with PME earning a variable importance in projection score of 1.18. Polygalacturonase and pectin lyase, the two enzymes that cleave the pectin backbone, showed only weak and non-significant direct associations with methanol, suggesting their role is indirect: they dismantle cell walls and expose pectin substrates, which PME then demethylates. Intriguingly, pectin lyase activity was negatively correlated with water-soluble pectin consumption, the strongest association in the entire correlation matrix at r equals minus 0.71, possibly because the enzyme releases soluble fragments from insoluble cell wall pectin, replenishing rather than depleting that pool.

To reconcile the competing objectives of aroma enrichment and methanol control, the researchers applied an entropy-weighted TOPSIS analysis, integrating total odor activity, sensory fruity and floral intensity, bitterness, and methanol concentration into a single score. The result was striking: the red-fleshed Hongyang wine fermented with both peel and pulp achieved the highest composite score of 0.6836, combining a fruity profile with comparatively low methanol. For Jinyan, peeled treatments ranked highest, and juice fermentation may be preferable when methanol reduction is the priority. For Xuxiang, the bitterness associated with maceration suggests that sensory balance should guide the decision. The overarching lesson is that there is no universal recipe. The optimal fermented fruit state depends on the cultivar, and winemakers seeking to capture the full aromatic potential of kiwifruit must weigh the enzymatic consequences of every gram of peel and pulp they leave in the tank. Future work, the authors note, should track pectin fractions, enzyme activities, and methanol dynamically throughout fermentation, and disentangle the contributions of endogenous fruit enzymes from the commercial pectinase added during pretreatment.

Subject of Research: Effects of peel presence and pulp maceration on flavor quality and methanol accumulation in kiwifruit wine fermentation across three flesh-colored cultivars

Article Title: Fermented fruit state shapes flavor quality and methanol accumulation in kiwi wine: A comparative study of three flesh-colored kiwifruit cultivars

Article References: Shao, J., Huang, S., Lou, Y., Chen, S., Ye, X., & Cheng, H. (2026). Fermented fruit state shapes flavor quality and methanol accumulation in kiwi wine: A comparative study of three flesh-colored kiwifruit cultivars. Food Chemistry: X, Article 104583. https://doi.org/10.1016/j.fochx.2026.104583

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104583

Keywords: kiwifruit wine, methanol, pectin, pectin methylesterase, fermentation, flavor chemistry, aroma compounds, pulp maceration, peel contact, phenolics, cultivar comparison, food safety

The chemical heart of the discovery lies in a structural feature of lignin called the methoxy group, written chemically as –OCH₃. These groups decorate the lignin framework in enormous numbers and are the key to how the polymer stores carbon. In the decay pathways known until now, microorganisms and their enzymes typically liberate only the methyl portion of these groups, leaving the oxygen behind. The Heidelberg team demonstrated something different: reactive iron-oxygen species attack the lignin and cleave the entire methoxy group as a single unit, a process the researchers call demethoxylation. Because the group departs intact, it emerges directly as methanol, which is subsequently oxidized to formaldehyde under natural conditions. This mechanistic distinction matters, because it explains how two small, highly mobile carbon compounds can be generated from woody plant matter without any biological catalyst participating in the reaction.

What makes the result especially striking is how mild the conditions are. Dr. Jonas Hädeler, who carried out the laboratory experiments in the biogeochemistry research group led by Prof. Dr. Frank Keppler, explains that the reaction proceeds at ambient temperature and normal pressure in water, and only intensifies as temperatures rise. Until now, chemists knew how to strip methoxy groups from lignin only in industrial settings, using temperatures above 285 degrees Celsius, elevated pressures and a hydrogen atmosphere. Nature, it turns out, achieves the same transformation with nothing more elaborate than iron, reactive oxygen and moisture. Reactive oxygen species are oxygen-containing molecules with very high chemical reactivity, and they can form in soils particularly under changing environmental conditions, for example when soils alternate between wet and dry states. This means the ingredients for the reaction are already present in many landscapes, waiting for the right conditions to bring them together.

The researchers did not rely on indirect inference to establish the mechanism. They followed the reaction pathway directly using isotope-marked molecules, in which individual atoms are replaced by heavier variants that can be tracked through the reaction. These experiments confirmed that the methoxy group is cleaved as a unit and thereby forms the methanol, in clear contrast to processes in which only methyl groups are removed. Quantum chemical calculations performed in the working group of Prof. Dr. Peter Comba at Heidelberg University’s Institute of Inorganic Chemistry provided independent theoretical support. As Prof. Comba explains, the calculations indicate the lowest energy barrier for cleavage of the whole methoxy group, which in chemical terms is the most favorable of the reactive pathways investigated, and that prediction matches the experimental observations exactly. The agreement between isotope tracing and computational chemistry gives the mechanistic picture unusual solidity for a study of environmental chemistry.

Perhaps the most consequential step was moving from purified lignin to real soil. In experiments with sterilized soil samples, the Heidelberg team showed that the process occurs under natural conditions: methanol and then formaldehyde formed through wetting alone, without the addition of iron or reactive oxygen species. The soil’s own iron minerals and oxidants were sufficient. Methanol formation also continued through several wetting-drying cycles, suggesting that the reaction can operate repeatedly whenever rain or snowmelt re-wets soil that has dried out. As a control, the researchers deliberately removed the methoxy groups from the organic material in advance, and methanol formation stopped, confirming that those groups are indeed the source. These experiments establish that the abiotic pathway is not a laboratory artifact but a genuine soil process, driven by nothing more exotic than water arriving in an iron-rich, lignin-rich environment.

The comparison with biologically active soils reveals where this chemistry fits into the larger ecological picture. In untreated soils teeming with microorganisms, the team found considerably less methanol, because soil microbes rapidly consume the compound as it forms. Dr. Hädeler describes the compound as primarily functioning as an intermediate product linking abiotic chemistry and microbial metabolism. In other words, the chemical reaction generates a small carbon molecule that microbes would otherwise have to obtain through more laborious enzymatic routes. This positions the iron-driven demethoxylation as a potential feeder reaction at the boundary between the geochemical and biological halves of the carbon cycle, supplying reduced carbon from structural plant polymers directly into the soil food web. The formaldehyde produced alongside it is likewise a substrate that microorganisms can metabolize, extending the same linkage one oxidation step further.

Prof. Keppler admits that the result surprised the team: it was not expected that methanol and formaldehyde could be released entirely chemically from lignin-rich organic materials. The surprise has practical consequences, because both compounds are trace gases with atmospheric significance. When they enter the air, they influence photochemical reactions there and thus atmospheric chemistry, affecting oxidation processes in the lowest layer of the atmosphere. The temperature experiments add a climatic dimension: formation of the two compounds increases with rising temperatures. The photo accompanying the release, taken on Kauai Island in Hawaii, illustrates the interplay of iron oxide-rich soils, water, vegetation and higher temperatures, conditions that may generally favor the abiotic formation of methanol and formaldehyde described in the study. As Keppler notes, what this means in the climate context is something further field studies will have to clarify.

The work also opens a technological window. Lignin accumulates in vast quantities as a by-product of the paper industry, and finding low-energy ways to convert it into valuable small molecules is a long-standing goal of green chemistry. The Heidelberg reaction, which requires only ambient temperature, normal pressure and water, offers a template for how lignin might be depolymerized under far gentler conditions than the high-temperature, high-pressure, hydrogen-rich processes used industrially today. The researchers suggest that the current findings might be interesting in the near future for using lignin as a by-product of the paper industry, potentially turning a waste stream into a source of methanol and formaldehyde or the chemistry built upon them. Any such application would still need to overcome questions of yield and scalability, but the demonstration that the cleavage is the energetically favored pathway is an encouraging starting point.

Scientifically, the study reframes how a major carbon reservoir is cycled. Lignin’s resistance to degradation is a cornerstone of carbon storage in soils and sediments, and every additional decay route identified changes estimates of how long plant carbon persists and how quickly it returns to the atmosphere or to microbial biomass. An abiotic, moisture-triggered, temperature-sensitive pathway implies that lignin turnover may respond directly to environmental drivers such as rainfall patterns and warming, independently of the microbial communities usually credited with decomposition. The research was funded by the German Research Foundation and by the Max Planck School Matter to Life, sponsored by the Federal Ministry of Research, Technology and Space and the Max Planck Society, and involved the Institute of Earth Sciences, the Institute of Inorganic Chemistry, the Heidelberg Center for the Environment and the Interdisciplinary Center for Scientific Computing of Heidelberg University. Future field studies, the team says, will determine how much of the methanol and formaldehyde fluxing out of soils worldwide traces back to this hidden iron-driven chemistry.

Subject of Research: Abiotic iron-induced demethoxylation of lignin in soils as a natural source of methanol and formaldehyde

Article Title: Without bacteria or chemicals: How methanol and formaldehyde form abiotically in nature

Article References: Without bacteria or chemicals: How methanol and formaldehyde form abiotically in nature. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: lignin, methanol, formaldehyde, iron minerals, reactive oxygen species, soil chemistry, abiotic degradation, carbon cycle, biogeochemistry, atmospheric chemistry, methoxy groups, Heidelberg University

The research, led by A. Yeghikyan and colleagues at the Byurakan Astrophysical Observatory in Armenia, focuses on a subtle but crucial energy source: the internal ultraviolet field generated when cosmic rays collide with molecular hydrogen. This mechanism, first described by Prasad and Tarafdar in 1983, has long been recognized as the only meaningful source of ultraviolet photons deep inside dense molecular clouds, where external starlight cannot penetrate. Cosmic rays strip electrons from gas molecules as they pass through, and those secondary electrons, carrying energies of roughly 30 to 50 electron volts, excite hydrogen molecules, which then release ultraviolet photons as they relax. That faint luminescence, invisible to telescopes but pervasive throughout the cloud interior, becomes the engine of astrochemistry.

To quantify how much of this ultraviolet energy is actually absorbed by acetylene, formaldehyde, and methanol, the team modeled two distinct physical scenarios for the nebulae. In the first, the nebula is treated as a static molecular cloud with a hydrogen density of about one thousand molecules per cubic centimeter—a relatively diffuse environment typical of quiescent star-forming gas. In the second, the nebula undergoes gravitational collapse, following the classical self-similar solution for an isothermal sphere, with densities climbing from ten thousand to a staggering one billion molecules per cubic centimeter as material falls inward over scales ranging from ten billion kilometers down to a hundred million kilometers from the center.

The ultraviolet field itself was parametrized using recent calculations by Padovani and collaborators, published in 2024, which describe the ultraviolet luminescence of molecular hydrogen induced by cosmic rays with unprecedented detail. To validate these analytical prescriptions, the team ran independent simulations with the CLOUDY photoionization code, version C25, one of the most widely used tools for modeling the transfer of radiation through astrophysical gas. The agreement between the analytical parametrization and the numerical validation gave the researchers confidence that their dose estimates rest on a solid physical foundation.

The results are striking. Integrated over a timescale of one million years—a reasonable interval for the early evolution of such objects—the absorbed ultraviolet dose reaches approximately one thousand electron volts per molecule in the static cloud scenario. In the collapsing core, where densities rise dramatically and secondary electrons dominate the energy deposition at the smallest radii, the dose exceeds ten thousand electron volts per molecule. Those figures are several orders of magnitude above the single-electron reaction threshold required for glycine formation, as identified in laboratory experiments where ices of carbon dioxide, methane, and ammonia were bombarded with electrons in the 0 to 70 electron volt range and yielded the simplest amino acid.

This comparison to laboratory work is central to the study’s significance. For decades, experimenters have irradiated interstellar ice analogues with ultraviolet photons and energetic particles, producing amino acids and other complex organic molecules in the process. The question has always been whether natural astrophysical environments can deliver comparable doses over realistic timescales. The new calculations show that in the densest regions of collapsing Parsamian nebulae, the answer is yes: the cosmic-ray-induced ultraviolet field falls squarely within the energetically permissive regime identified in laboratory ice-irradiation studies, meaning that the same photochemistry and radiation chemistry observed in the lab can plausibly operate in these objects.

Among the possible chemical outcomes, one stands out for its biological resonance. The team highlights the formation of isoprene precursors through the polymerization of acetylene. Isoprene, a five-carbon molecule with the formula C5H8, is the fundamental building block of terpenes, the largest class of natural products on Earth, and its skeletal structure appears in molecules ranging from cholesterol to rubber. The idea that acetylene, exposed to sufficient ultraviolet dose in a cold nebula, could polymerize toward isoprene-like structures connects these distant star-forming environments to the organic inventory that may have seeded the early solar system.

But the chemistry does not follow a single path. The researchers identify the abundance ratio of acetylene to methanol as the key diagnostic that separates two competing chemical futures. When acetylene dominates, ultraviolet processing drives the prebiotic pathway toward isoprene precursors. When methanol is more abundant, the energy instead feeds the carbonaceous pathway, building polycyclic aromatic hydrocarbons—the robust, ring-shaped molecules that constitute a significant fraction of cosmic carbon. Measuring this ratio in Parsamian 13 and Parsamian 21 would therefore reveal which chemical branch each nebula is pursuing, and the study concludes that both objects currently sit within the regime favorable to complex prebiotic chemistry.

Parsamian cometary nebulae themselves are curious objects. They were catalogued by Elma Parsamian in 1965 from surveys of the Palomar Observatory sky maps, and their comet-like appearance—bright heads with long, reflective tails—has made them favorite targets for studies of dust scattering and young stellar objects. Parsamian 21, in particular, has been identified with an edge-on FU Orionis disc, a young star undergoing a dramatic accretion outburst, while polarimetric observations of Parsamian 13 have mapped the magnetic-field-aligned dust grains surrounding its central source. The new work adds a chemical dimension to this observational heritage, arguing that these visually striking nebulae are also energetic chemical reactors.

The broader implications reach into one of astrobiology’s deepest questions: where and how did the organic molecules that life requires first form? If cosmic rays, an unavoidable feature of every galaxy, can drive dense cloud interiors to ultraviolet doses capable of forging amino acids and isoprene precursors, then prebiotic chemistry may be a generic consequence of star formation rather than a rare accident. Every collapsing molecular core, bathed in its own faint hydrogen luminescence, would carry an inherent capacity for molecular complexity. The molecules forged in these dark nurseries could then be incorporated into the ices of comets and asteroids, delivering them to nascent planets. For Parsamian 13 and Parsamian 21, the message of the new calculations is clear: beneath their quiet, dusty exteriors, the energy needed to build the chemistry of life is already flowing.

Subject of Research: Ultraviolet dose rates from cosmic-ray-induced hydrogen excitation driving prebiotic chemistry in Parsamian cometary nebulae

Article Title: UV dose rates in Parsamian cometary nebulae: cosmic-ray-induced energetic processing of C2H2, H2CO, and CH3OH

Article References: Yeghikyan, A., Rah, M., Darbinyan, L., Alizadeh, M., Shamyar, S., & Khachatryan, S. (2026). UV dose rates in Parsamian cometary nebulae: cosmic-ray-induced energetic processing of C2H2, H2CO, and CH3OH. Astrophysics and Space Science, 371(9), Article 104. https://doi.org/10.1007/s10509-026-04636-7

Image Credits: AI Generated

DOI: 10.1007/s10509-026-04636-7

Keywords: astrochemistry, cosmic rays, ultraviolet radiation, Parsamian nebulae, molecular clouds, prebiotic molecules, Prasad–Tarafdar mechanism, acetylene, methanol, formaldehyde, isoprene, star formation

The material at the heart of the study is niobium pentoxide, or Nb2O5, a semiconductor widely produced in Brazil, which holds most of the world’s niobium reserves. Niobium oxide has long attracted attention as a photocatalyst because of its unusual surface chemistry: it hosts both Brønsted and Lewis acid sites that can chemisorb CO2, forming an unstable carboxyl intermediate that light-driven electrons can then reduce into fuels and oxygenated chemicals. Under aqueous conditions, Brønsted acid sites become dominant, anchoring CO2 through its carbon atom and enabling the cascade of reduction steps that ultimately yield products such as methanol, a potential liquid fuel, and acetic acid, an industrial feedstock.

But acidity alone is not the whole story. The team began by synthesizing a highly reactive form of Nb2O5 using the oxidant peroxide method, dissolving a niobium oxalate precursor in water and hydrogen peroxide, heating the mixture to form a gel, and then drying and gently calcining the solid at just 150 degrees Celsius. This mild treatment preserves a disordered, defect-rich structure bristling with reactive peroxo groups, which give the material its characteristic yellow color and high initial activity. The researchers then dispersed the powder in phosphoric acid solutions at concentrations of 0.1, 0.5 and 1.0 mol per liter for 48 hours, washing and drying the resulting phosphatized catalysts, labeled Nb-0.1, Nb-0.5 and Nb-1.0 according to the acid concentration used.

To quantify how phosphatization changed the surfaces, the team measured the concentration of acidic sites through indirect potentiometric titration in alkaline suspensions, a technique that probes the Brønsted acidity of these amphoteric oxides in water. The response to phosphatization was strikingly non-linear. Acidity rose from moderate values at low phosphoric acid concentration to a peak of 0.99 plus or minus 0.07 millimoles per gram at the intermediate treatment, then fell back slightly at the highest concentration. This optimum, the researchers found, reflects a delicate balance: phosphate groups both introduce new Brønsted acid sites and clear away organic residues left over from synthesis, but too much phosphate begins to clog the very pores and sites the reaction depends on.

An extensive characterization campaign using X-ray diffraction, infrared and Raman spectroscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance, X-ray fluorescence, electron microscopy, atomic force microscopy with infrared detection and nitrogen physisorption painted a consistent picture of what phosphatization actually does. The treatment stripped residual carboxylate and carbonate species from the surface, evidenced by declining carbon content in elemental analysis and changes in the oxygen 1s photoelectron spectra, while covalently anchoring phosphate tetrahedra to the niobia framework through Nb–O–P linkages. X-ray photoelectron spectroscopy revealed phosphorus in mixed plus-five and plus-three oxidation states at 133.2 and 134.1 electronvolts, confirming the formation of a surface niobium phosphate layer rather than a separate bulk phase. Crucially, the amorphous, pseudohexagonal TT structure of the underlying oxide, built from distorted NbO6 octahedra rich in catalytically useful defects, remained intact throughout.

The textural transformation was equally dramatic. The untreated control material showed weak, Type III nitrogen adsorption isotherms, a low surface area of 13.47 square meters per gram, and pores blocked by organic debris. After phosphatization, the isotherms shifted to Type II behavior and the surface area soared more than sixfold, reaching a maximum of 82.15 square meters per gram for the intermediate sample, whose surface roughness also dropped from 154 to 65 nanometers as measured by atomic force microscopy. At the highest acid concentration, however, excess phosphate accumulation drove the surface area back down to 41.62 square meters per gram, underscoring that more is not always better.

When the catalysts were put to work, the differences became unmissable. In a quartz reactor filled with CO2-saturated water and illuminated by ultraviolet lamps at 254 nanometers, the phosphatized catalyst prepared with 0.5 mol per liter phosphoric acid delivered the standout performance. It produced acetic acid at 267 plus or minus 49 micromoles per gram per hour and methanol at 181 plus or minus 33 micromoles per gram per hour, with the two products together accounting for 99 percent of everything detected. Selectivity reached roughly 59 percent for acetic acid and 40 percent for methanol, while carbon monoxide, a common and less useful byproduct that made up about 20 percent of the control’s output, was suppressed to below 0.1 percent. Formic acid and carbon monoxide lingered only as traces of around 0.2 percent, suggesting they act as fleeting intermediates on the modified surface rather than endpoint products.

The mechanistic explanation, the researchers propose, lies in how phosphate-modified Brønsted acid sites handle the reaction intermediates. On the untreated oxide, carbon monoxide formed during reduction is released prematurely, cutting the reaction chain short and limiting yields. On the phosphatized surface, carbonate and bicarbonate species adsorb more effectively, and intermediates such as the carboxyl radical are retained long enough to undergo the additional reduction and even carbon–carbon coupling steps needed to form methanol and the two-carbon acetic acid. Control experiments, including photolysis without catalyst, irradiation under visible light, and nitrogen bubbling in place of CO2, confirmed that the product formation genuinely depended on the photocatalyst, the ultraviolet light, and the presence of carbon dioxide.

Perhaps most importantly, phosphatization solved a chronic durability problem. Peroxo groups inherited from the oxidant peroxide synthesis route are highly reactive but tend to deactivate within the first reaction cycle, and the untreated control lost essentially all activity by its second run, while continuing to emit carbon monoxide. The phosphatized catalysts, by contrast, remained functional across four consecutive four-hour reaction cycles, retaining roughly half of their initial activity even as their yellow peroxo coloration faded to white. Post-mortem analysis showed that the characteristic Raman band of the Nb–O–P bond at 872 wavenumbers and the corresponding infrared phosphate bands survived the reaction, along with carbonate signatures near 2400 to 2500 wavenumbers that pointed to active CO2 adsorption on the spent surface. Although wavelength-dispersive X-ray fluorescence recorded a partial drop in the phosphorus-to-niobium ratio after cycling, from 0.24 to 0.11, the residual phosphate layer continued to supply the Brønsted acidity and structural stability that kept the catalyst alive.

The authors caution that the acidity measured by titration must be interpreted alongside surface composition, textural accessibility and catalytic performance, and that direct confirmation of the proposed surface intermediates will require in situ or operando spectroscopic studies. They also note that the bandgap of the semiconductor, between 3.04 and 3.10 electronvolts, barely changed with treatment, meaning the performance gains came entirely from surface engineering rather than optical tuning. Even so, the message of the work is clear and potentially far-reaching: by pairing an abundant, locally produced oxide with a cheap acid treatment, the team has shown that surface acidity, when combined with accessible texture and phosphate stabilization, is a strategic design parameter for artificial photosynthesis. As the world searches for ways to recycle carbon dioxide into fuels rather than merely capture it, a modest dip in phosphoric acid may prove to be one of the most elegant tricks in the playbook.

Subject of Research: Phosphate-modified niobium pentoxide photocatalysts for the aqueous photoreduction of CO2 into methanol and acetic acid

Article Title: Influence of the Surface Acidity of Niobium Catalysts Modified with Phosphate in the Photocatalysis of CO2 for Conversion into Methanol and Acetic Acid

Article References: Oliveira, E., da Cruz, J. C., Magalhaes, W. L. E., & Ribeiro, C. (2026). Influence of the Surface Acidity of Niobium Catalysts Modified with Phosphate in the Photocatalysis of CO2 for Conversion into Methanol and Acetic Acid. Catalysis Letters, 156(10), Article 277. https://doi.org/10.1007/s10562-026-05495-1

Image Credits: AI Generated

DOI: 10.1007/s10562-026-05495-1

Keywords: CO2 photoreduction, artificial photosynthesis, niobium pentoxide, photocatalysis, surface acidity, phosphatization, methanol, acetic acid, Brønsted acid sites, niobium phosphate, sustainable fuels, carbon dioxide conversion

The core problem the researchers tackled is one that plagues nearly all conventional microbial production platforms: during growth, a substantial fraction of the carbon a cell assimilates is ultimately released as biogenic carbon dioxide. In methanol-grown organisms, this loss occurs through central metabolic reactions, most notably the decarboxylation of pyruvate to acetyl-coenzyme A, a step shared by virtually every industrial chassis in use or under development, as well as through the oxidative branch of the ribulose monophosphate cycle that methylotrophs use to assimilate formaldehyde derived from methanol. Every molecule of carbon dioxide vented in this way represents feedstock that was purchased, delivered, and then effectively thrown away, capping biomass yields and undermining the economics of industrial methylotrophic bioprocesses. Reducing carbon loss at these junctions is therefore an established priority for developing low-oxidative, carbon-efficient biocatalysts.

The solution explored in the study exploits an enzyme known as phosphoketolase, or PKT, which cleaves the sugar phosphates fructose-6-phosphate and xylulose-5-phosphate into acetyl-phosphate plus either erythrose-4-phosphate or glyceraldehyde-3-phosphate. Acetyl-phosphate is valuable because it can be converted to acetyl-coenzyme A, the essential biosynthetic precursor, either in a single step by phosphotransacetylase or in two steps via acetate kinase and acetyl-CoA synthetase, entirely without passing through pyruvate decarboxylation. The side products, erythrose-4-phosphate and glyceraldehyde-3-phosphate, are recycled back into the ribulose monophosphate and pentose phosphate pathways. In effect, the enzyme provides a carbon-conserving detour around the cell’s biggest carbon dioxide leak. Previous work had shown that PKT-based pathways can dramatically enhance biomass yield and carbon conversion efficiency in several microbial hosts, including the methanotroph Methylotuvimicrobium buryatense 5GB1C, where overexpression of its native pktB gene substantially improved methane conversion efficiency.

Bacillus methanolicus emerged as an ideal test chassis for several reasons. It is a facultative ribulose monophosphate methylotroph that grows rapidly on methanol, doubling in roughly 1.4 hours under optimal conditions, faster than other native methylotrophs such as Methylobacterium extorquens AM1 at 3.6 hours, the yeast Pichia pastoris at 4.6 hours, and engineered Escherichia coli strains at 4.3 hours. It is also industrially interesting in its own right, capable of producing more than 50 grams per liter of glutamate under optimized conditions as well as lysine. Crucially, while B. methanolicus lacks any native phosphoketolase gene, it already encodes the downstream machinery needed to convert acetyl-phosphate to acetyl-CoA. That combination made it the perfect organism to test whether a methylotroph without native PKT genes could benefit from the carbon-conserving pathway, a question that had remained open.

To carry out the engineering, the team first built a suite of new genetic tools for the organism. They adapted an anhydrous tetracycline-inducible expression system, originally developed for Bacillus subtilis, by fusing the B. subtilis xylA promoter to the Tn10 tet operator and placing the tetR repressor under the control of a strong native B. methanolicus methanol dehydrogenase promoter. When validated with a green fluorescent protein reporter, the system proved highly tunable: fluorescence rose with increasing inducer concentration, and after induction with 0.8 micromolar anhydrous tetracycline, reporter expression climbed roughly 19-fold over five hours, from about 2,450 to about 46,000 normalized relative fluorescent units, before declining as free inducer was depleted. The researchers also characterized four native constitutive promoters of varying strengths, driving reporter expression from the tuf promoter at the highest levels, followed by pdxK, icd, and the much weaker dppE promoter, giving the community a graded palette of expression tools for this organism.

With the expression toolkit in hand, the team introduced a codon-optimized pktB gene from M. buryatense into B. methanolicus. Under inducible expression, the engineered strain produced 0.49 grams of dry cell weight per gram of methanol consumed, compared with 0.41 grams for the empty vector control, a 20 percent improvement in methanol-to-biomass yield. Constitutive expression from native promoters delivered comparable gains: the pdxK-pktB and icd-pktB strains each reached 0.52 grams of dry cell weight per gram of methanol consumed, and the tuf-pktB strain reached 0.50 grams, against a control baseline of 0.42 grams, improvements of roughly 18 to 24 percent. The pdxK-pktB strain, which showed the greatest yield enhancement without the most severe growth penalty, was selected for deeper analysis. Notably, all pktB-expressing strains displayed some growth defect relative to controls, a trade-off the researchers attribute to disruption of the carefully balanced flux through the ribulose monophosphate cycle.

Biochemical and molecular analyses confirmed the enzyme was doing its intended job. Whole-cell lysates from the pdxK-pktB strain produced 0.86 millimolar acetyl-phosphate in a hydroxamate activity assay, nearly double the 0.44 millimolar measured in the control strain, demonstrating functional PKT activity inside the thermophilic host. Reverse transcription PCR showed pktB transcripts at 13.13 times the level of the rpoB housekeeping gene during mid-log growth. Most importantly, when cultures were grown in sealed bottles and headspace gas analyzed by gas chromatography, the pktB-expressing strain released 0.44 moles of carbon dioxide per mole of methanol consumed versus 0.49 for the control, a 9 percent reduction in total biogenic carbon dioxide production, directly linking the yield gain to reduced carbon loss as hypothesized.

To eliminate the burden of maintaining plasmids, which themselves caused growth defects in control strains, the researchers deployed a recently developed temperature-sensitive chromosomal integration method, inserting the pdxK-pktB expression cassette into the chromosome by homologous recombination. The resulting integrated strain, BMGA3::pktB, grew more slowly and consumed methanol more slowly than the wild type, yet still delivered a 19 percent biomass yield enhancement, producing 0.82 grams of dry cell weight per gram of methanol consumed versus 0.69 grams for wild type. Carbon dioxide output fell 12 percent relative to wild type, from 0.49 to 0.44 moles per mole of methanol consumed. Intriguingly, pktB expression in the integrated strain was far lower than in the plasmid strain, just 0.16 times the housekeeping gene, suggesting that once enzyme expression exceeds a certain threshold, other factors such as substrate limitation, protein misfolding, or the enzyme’s thermolability may cap the achievable yield gain at around 24 percent.

The study also revealed unexpected shifts in byproduct metabolism. Whereas pktB overexpression in the enzyme’s native host M. buryatense had previously increased acetate excretion, the integrated B. methanolicus strain excreted no detectable acetate, while the wild type released roughly 3 millimolar. The authors propose two possible explanations: the slower growth rate of the engineered strain may simply reduce overflow metabolism, or carbon flux through acetyl-phosphate may be preferentially channeled toward acetyl-CoA rather than acetate. Distinguishing between these scenarios will require future metabolic flux analyses and intracellular metabolite measurements. Either way, the result hints that the engineered strain channels more carbon toward acetyl-CoA, potentially driving greater flux through the oxidative branch of a partially non-cyclic TCA cycle that fluxomic studies have shown operates at low levels during methanol growth.

Beyond the specific yield numbers, the work carries a broader lesson for metabolic engineering: the outcome of installing a carbon-conserving pathway depends not only on the enzyme’s catalytic properties but on the metabolic architecture of the host into which it is placed. This is, to the authors’ knowledge, the first report of introducing a phosphoketolase into a native methylotroph that lacks a PKT system, and the phenotypes observed differ meaningfully from those in the enzyme’s original host. The researchers suggest that adaptive laboratory evolution of the integrated strain could resolve the growth defect and optimize flux through the combined PKT-ribulose monophosphate network, while adding xylose utilization genes could boost regeneration of ribulose-5-phosphate and further support the pathway. As methanol, increasingly available from renewable electricity and captured carbon dioxide, gains traction as a feedstock, phosphoketolase-based carbon conservation stands out as a broadly applicable strategy for squeezing more product out of every carbon atom.

Subject of Research: Metabolic engineering of Bacillus methanolicus with heterologous phosphoketolase to enhance biomass yield from methanol and reduce CO2 loss

Article Title: Rewiring Carbon Metabolism in Bacillus methanolicus via Heterologous Phosphoketolase Expression Enhances Biomass Yield From Methanol and Reduces CO2 Loss

Article References: Toporek, Y. J., Humphreys, J. R., Musselwhite, T. J., Bray, M. S., Michel, K. P., Rosenbach, K. A., & Guarnieri, M. T. (2026). Rewiring Carbon Metabolism in Bacillus methanolicus via Heterologous Phosphoketolase Expression Enhances Biomass Yield From Methanol and Reduces CO 2 Loss. Microbial Biotechnology, 19(9), Article e70430. https://doi.org/10.1111/1751-7915.70430

Image Credits: AI Generated

DOI: 10.1111/1751-7915.70430

Keywords: Bacillus methanolicus, phosphoketolase, methanol, methylotroph, RuMP cycle, carbon conservation, biomass yield, CO2 reduction, metabolic engineering, synthetic biology, biomanufacturing, acetyl-CoA