The logic behind the indicator rests on the peculiar chemistry of anthocyanins, the water-soluble pigments that give red cabbage its deep color. Anthocyanins are molecular chameleons: their structure, and therefore their color, shifts with the acidity of their surroundings. In acidic conditions the pigment exists mainly as a flavylium cation, producing a rose-red hue. As pH rises toward neutral, the molecule equilibrates among several forms, including the quinoidal base and carbinol pseudo base. Above pH 7, deprotonation generates quinoidal structures with extended conjugation that shift absorbed light toward longer wavelengths, and under strongly alkaline conditions the pyran ring cleaves and rearranges into yellow chalcones. The team confirmed this behavior spectroscopically, measuring the total anthocyanin content of their dried cabbage powder at 18.90 milligrams of cyanidin-3-glucoside equivalents per gram of dry matter, and observing the absorption maximum of their extract drift from roughly 500 nanometers under acidic conditions to 600 nanometers as pH climbed from 3 to 12.

Red cabbage is an attractive pigment source because it is cheap, edible, and richer in anthocyanins than many alternative plants, which matters when the indicator will sit inside a food package where dye migration is a safety concern. Synthetic pH dyes can volatilize or leach into food matrices, so natural colorants have become the preferred option for intelligent packaging. But a pigment alone is not enough; it needs a physical platform that exposes it to the air inside the package while holding it in place. The Iranian team chose pectin, the plant polysaccharide best known for setting jam, as that platform. Pectin is built from alpha-1,4-linked D-galacturonic acid units, and its degree of esterification governs how it gels and holds water, allowing it to form the layered macroporous structures needed for aerogel fabrication.

Aerogels are among the lightest solid materials known, produced by replacing the liquid in a gel with gas while preserving the three-dimensional polymer network. To make theirs, the researchers dissolved apple pectin at concentrations of 10, 15, and 20 percent weight per volume, mixed in a diluted red cabbage extract, cast the solutions into molds, froze them in liquid nitrogen, and freeze-dried them at minus 80 degrees Celsius for 48 hours. The resulting indicators were extraordinarily porous: bulk densities ranged from 0.074 to 0.139 grams per cubic centimeter, with porosity between 90 and 95 percent. That internal free volume is the point. A highly porous network adsorbs and retains volatile spoilage gases efficiently, accumulating them near the embedded anthocyanins and amplifying the color response.

The formulation details turned out to matter enormously. Increasing the pectin concentration produced a denser, more cross-linked network: porosity fell, moisture absorption dropped from 16.1 percent to 7.9 percent, and the aerogels became harder, more cohesive, and less springy in texture analysis. Adding the red cabbage extract reinforced this trend, because hydrogen bonding between anthocyanin molecules and pectin chains packed the polymer network more tightly. Fourier-transform infrared spectroscopy revealed the signature of these interactions: the hydroxyl stretching band broadened and shifted to lower wavenumbers in loaded aerogels, while a band near 1623 per centimeter, assigned to the aromatic carbon-carbon skeletons of anthocyanin rings, grew in intensity, confirming that the pigment was genuinely integrated into the matrix rather than merely sitting on its surface. X-ray diffraction showed increased crystallinity in the loaded samples, consistent with closer molecular packing.

When the team exposed the loaded aerogels to ammonia vapor, a stand-in for the volatile bases that escaping from spoiling meat, the materials shifted from red to purple in a time-dependent manner. After 30 minutes of exposure, the 10 percent pectin formulation registered the largest total color difference, a delta E of 27.79, compared with 24.20 for the 15 percent version and 19.95 for the 20 percent version. The explanation is straightforward physics: the denser networks at higher pectin concentrations restricted ammonia diffusion and slowed the anthocyanins’ structural transformation. The 10 percent aerogel, with its lower polymer density, higher porosity, and greater anthocyanin accessibility relative to its pectin content, let the gas reach the pigment fastest and most completely.

The real test came with actual chicken. The researchers sealed 40-gram skinless chicken samples in oriented polypropylene containers, attached the aerogel labels to the inner upper surface without direct meat contact, and stored everything at 4 degrees Celsius for 12 days, measuring pH, total volatile basic nitrogen, lipid oxidation, bacterial counts, and sensory qualities along the way. The meat started fresh, with 3.76 log colony-forming units per gram of total viable count, a pH of 5.25, and TVB-N of 9.6 milligrams of nitrogen per 100 grams. By day 8, those values had reached 7.01 log CFU per gram, 6.577, and 25.61 milligrams per 100 grams respectively, crossing the accepted spoilage thresholds for raw chicken fillets, while odor scores from trained panelists collapsed to the minimum of the hedonic scale.

The labels told the same story in color. The 10 percent pectin indicator transitioned from purple on day 0 to purplish-blue by day 6, marking semi-fresh meat, and turned green during days 8 through 12, signaling advanced spoilage. The 15 and 20 percent formulations lagged, turning purplish-blue on day 8 and green only during days 10 through 12. Critically, the team went beyond visual impressions and ran statistical analyses to determine whether the measured color change could serve as an objective spoilage metric. After controlling for storage time, only the 10 percent pectin aerogel showed significant partial correlations between its delta E values and the key spoilage indicators, total viable count and TVB-N, as well as sensory attributes including color, texture, and overall acceptability. Receiver operating characteristic analysis then established delta E cut-off values of 25.8, 16.9, and 11.1 for the 10, 15, and 20 percent formulations against the microbiological and chemical spoilage thresholds.

Those numbers carry practical weight. A delta E above 5 is generally considered the threshold at which a color change becomes visible to the naked eye, so a cut-off of 25.8 for the best formulation means the label’s color shift is not subtle; it is unmistakable. Because the indicator works passively, responding to the ammonia and other alkaline nitrogenous compounds that protein-degrading bacteria release into the package headspace, it requires no electronics, no reader device, and no cold-chain data infrastructure. A consumer, an inspector, or a warehouse camera could in principle read it. The researchers note that the anthocyanin-to-pectin ratio directly controls both the magnitude of the color response and the delta E threshold at which spoilage is flagged, which suggests the technology can be tuned for different foods and spoilage chemistries.

The study also contributes a useful design principle for the broader field of halochromic food sensors: the support matrix is not a passive carrier but an active determinant of sensitivity. Three-dimensional porous networks enhance sensing performance, but only up to the point where the matrix remains open enough for gases to diffuse. Too much polymer, and the indicator goes blind; too little, and the structure may lack the mechanical integrity to survive handling. The pectin aerogels’ combination of low density, high porosity, and anthocyanin-stabilized mechanical strength appears to hit a workable balance, and the fact that every component, from the cabbage pigment to the fruit-derived polysaccharide, is food-safe removes the migration concerns that have limited synthetic dye indicators. Whether such labels can be manufactured at scale, and whether their response holds up under the temperature fluctuations of real supply chains, remain questions for future work, but the demonstration that a simple, edible aerogel can quantitatively track chicken spoilage in real time marks a concrete step toward packaging that speaks for the food it protects.

Subject of Research: Pectin aerogel colorimetric indicators with red cabbage anthocyanins for real-time monitoring of chicken meat freshness

Article Title: Evaluation of intelligent aerogel indicators composed of red cabbage extract and pectin for monitoring chicken meat freshness

Article References: Shirkhani, H., Emamifar, A., & Davati, N. (2026). Evaluation of intelligent aerogel indicators composed of red cabbage extract and pectin for monitoring chicken meat freshness. Food Chemistry: X, Article 104615. https://doi.org/10.1016/j.fochx.2026.104615

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104615

Keywords: intelligent packaging, aerogel, anthocyanins, red cabbage extract, pectin, chicken meat freshness, colorimetric indicator, food spoilage, TVB-N, total viable count, freeze-drying, halochromic sensor

The biodegradable polymer at the heart of the work is poly(butylene adipate-co-terephthalate), or PBAT, a flexible compostable plastic familiar from shopping bags and food packaging films. PBAT is cheap, tough and breaks down in the environment, which makes it an attractive candidate for a carrier scaffold that encapsulates a phase-change material. Yet, as the authors note, PBAT has been substantially underexplored in this role, largely because making it porous is surprisingly difficult. The two standard routes each carry a serious flaw. Phase inversion, in which a polymer solution is cast and the solvent is exchanged away, relies on toxic organic solvents that sit awkwardly with any claim to sustainability. Carbon dioxide foaming, meanwhile, tends to produce predominantly closed-cell pores, tiny sealed bubbles that a molten phase-change material cannot easily enter or be retained within.

The Chinese team’s solution borrows its logic from one of the oldest techniques in materials processing: hot-pressing. Instead of dissolving PBAT or blowing it into foam, they used a graphene oxide aerogel as both a dispersion medium and a carrier for PBAT powder particles. Graphene oxide, the oxidized flake form of graphene, naturally assembles into lightweight three-dimensional networks when dispersed in water and frozen or gelated. Into this porous carbon scaffold the researchers introduced PBAT powder, allowing the particles to distribute uniformly and aggregate throughout the aerogel interior to form a macroscopically stable PBAT/GO composite aerogel. The key trick came next: isothermal heating. Held at a temperature that softened but did not destroy the polymer, adjacent PBAT particles began to melt at their contact points and fuse together, a process the authors describe as melt-bridging, effectively welding the powder into a continuous porous skeleton in situ.

What makes the resulting pore architecture clever is that it is formed by two cooperating mechanisms. The three-dimensional graphene oxide network provides the macroscopic template, while the physical space occupied by ice crystals during the freezing step carves out additional channels. When the ice sublimes or melts away, it leaves behind an interconnected, open-pore structure, precisely the kind of plumbing that a liquid phase-change material needs. The graphene oxide is simultaneously reduced to reduced graphene oxide during the thermal treatment, yielding the final PBAT/rGO porous composites, labeled PG-x, where x denotes the compositional series. No toxic solvent is involved at any stage, and the process avoids the closed-cell trap that has limited foamed PBAT carriers.

With the scaffold in hand, the researchers loaded it with polyethylene glycol, or PEG, a workhorse organic phase-change material that stores and releases large amounts of latent heat near room temperature. Loading was accomplished by vacuum impregnation, in which the porous composite is evacuated and then flooded with molten PEG so that capillary forces draw the liquid deep into every interconnected channel. The resulting shape-stable composites, designated PGP-x, held an average actual PEG loading ratio that peaked at 70.04 weight percent, an impressively high fraction for a polymer-based support. At that loading the composite delivered a phase-change enthalpy of 110.37 joules per gram, meaning that each gram of material absorbs or releases more than a hundred joules of heat as PEG melts and solidifies.

Shape stability, the property that gives these composites their name, is where the numbers become genuinely striking. The researchers subjected the PGP-x samples to 100 consecutive thermal cycles of melting and freezing, a torture test that would quickly expose any weak scaffold. After 100 cycles, the leakage rate remained below 2 weight percent, indicating that the welded PBAT/rGO network, together with capillary confinement and possible interfacial interactions between PEG and the reduced graphene oxide walls, keeps the molten wax-like PEG locked in place. For applications such as building envelopes, solar thermal collectors, battery thermal management and waste-heat recovery, where a leaking composite would stain, corrode or short-circuit surrounding components, that kind of cycling durability is the difference between a laboratory curiosity and a deployable technology.

The graphene component contributes more than mechanical containment. Graphene oxide and its reduced form are strong broadband absorbers of solar radiation, converting absorbed photons into heat with high efficiency. Because the reduced graphene oxide sheets line the pore walls throughout the composite, sunlight penetrating the material is captured close to where the PEG is stored, so the photothermal conversion performance of the PGP-x composites was significantly enhanced relative to the neat phase-change material. In practical terms, this means the composites can be charged directly by sunlight: place them in the sun and the graphene framework heats up, melts the PEG, and the latent heat is banked for later release. This light-driven charging pathway opens the door to passive solar energy storage in walls, windows, textiles and off-grid devices without any pumps, heat exchangers or electrical input.

The choice of a biodegradable carrier deserves emphasis in an era when the materials community is scrutinizing the end-of-life footprint of every new composite. Most shape-stable phase-change composites reported to date rely on non-degradable supports such as expanded graphite, metal foams, polyurethane foams or MXene-polymer hybrids. A PBAT-based scaffold, by contrast, can in principle compost along with the polymer matrix once the storage material is recovered, aligning the composite with circular-economy principles. The authors argue that their solvent-free, hot-pressing-inspired preparation method offers novel insights for latent heat energy storage research precisely because it sidesteps the environmental liabilities of phase inversion while solving the pore-connectivity problem of CO2 foaming. The approach is also conceptually portable: any thermoplastic powder that melt-bridges under isothermal heating could, in principle, be welded inside a graphene oxide or other aerogel template by the same route.

There are, of course, questions that follow any such laboratory demonstration. The reported enthalpy of 110.37 joules per gram, while respectable, is below that of pure PEG, since the non-melting scaffold dilutes the active material, and further engineering would be needed to push energy density toward the levels demanded by grid-scale storage. Long-term behavior beyond 100 cycles, mechanical robustness under compression, and the cost of graphene oxide at scale all remain open engineering challenges. The work was supported by the National Natural Science Foundation of China and startup funding from the Guizhou Institute of Technology, and the authors report no conflicts of interest. Still, the demonstration that a humble compostable plastic can be thermally welded into a high-performance, sunlight-charging heat reservoir, using water, ice and heat as the only processing agents, is the kind of elegant simplification that tends to reshape a field.

If the broader promise holds, the implications extend well beyond thermal storage. The same in situ thermal welding strategy could produce open-porous PBAT structures for filtration membranes, oil-spill remediation monoliths, tissue engineering scaffolds and electromagnetic shielding foams, all areas where PBAT composites are already being explored but where solvent-free, interconnected porosity has been hard to achieve. For the energy transition, meanwhile, the study adds a compelling entry to the growing catalog of carbon-based porous supports for form-stable phase-change materials, one distinguished by its biodegradability and by the sheer simplicity of its fabrication. A plastic bag polymer, a graphene oxide aerogel and a hot plate may sound like an unlikely recipe for the future of heat storage, but the numbers, 70 percent loading, 110 joules per gram, and less than 2 percent leakage over a hundred melt-freeze cycles, make a persuasive case that sometimes the greenest route is also the simplest one.

Subject of Research: Biodegradable PBAT/reduced graphene oxide porous scaffolds for shape-stable composite phase-change thermal energy storage materials

Article Title: In situ thermal welding for constructing PBAT/rGO porous structures for shape-stable composite phase-change materials

Article References: Zhang, Y., Luo, D., Zhang, X., & Deng, Y. (2026). In situ thermal welding for constructing PBAT/rGO porous structures for shape-stable composite phase-change materials. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13861-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13861-y

Keywords: phase-change materials, PBAT, graphene oxide, thermal energy storage, polyethylene glycol, biodegradable polymers, aerogel, porous materials, photothermal conversion, shape-stable composites, thermal welding, latent heat

The biological prototype is Melanophila acuminata, the fire-chaser beetle, whose thoracic pit organs house infrared sensilla capable of detecting the thermal glow of distant burning forests. Using scanning electron microscopy, the team mapped the ultrastructure of these natural photodetectors and found a densely packed array of synaptic-like protrusions separated by gaps, each covered in nanoscale wrinkles and dotted with nanopores. The gaps provide paths for repeated reflection and scattering of incoming radiation, the micrometer-scale protrusions act as resonant structures, the nanoscale wrinkles resonate with far-infrared waves, and the nanopores push the impedance of the sensillum closer to that of air, so that radiation enters rather than bounces off. The sensilla detect infrared rather than microwave radiation, but the researchers recognized that the underlying wave-management principles were transferable.

Crucially, the team emphasizes that the strategy is one of functional translation rather than geometric copying. The beetle’s architecture operates in the infrared regime, whereas the synthetic material targets microwaves in the 2 to 18 GHz band. The designers therefore mapped each biological feature onto a corresponding synthetic element: the cavities and interspaces of the sensillum became a three-dimensional porous carbon framework that lowers the effective permittivity and improves impedance matching with free space; the synaptic protrusions became rough, interconnected carbon struts decorated with cerium dioxide and MXene nanosheets; and the nanoscale wrinkles and pores became abundant heterointerfaces, oxygen vacancies, and surface terminations that act as polarization and loss centers. The result is a hierarchical structure that preserves the beetle’s strategy of multiscale impedance regulation and interfacial energy dissipation while rescaling the characteristic dimensions to microwave physics.

Before fabricating anything, the team validated the concept computationally. They modeled the aerogel as an irregular Voronoi polyhedral framework, a geometry chosen both for its resemblance to the biological template and because structural irregularity favors absorption. Density functional theory calculations on the two chosen nanomaterials, cerium dioxide and Ti3C2Tx MXene, revealed strong electronic coupling at their junction. Differential charge density analysis showed electrons accumulating on the cerium dioxide side and depleting on the MXene side, creating a built-in electric field and prominent interfacial dipoles. Work function calculations quantified the driving force: 6.030 eV for the cerium dioxide surface versus 5.394 eV for Ti3C2OF, the stoichiometry derived from quantitative elemental analysis of the actual synthesized MXene. Electrons therefore flow from MXene to cerium dioxide until the Fermi levels align, strengthening Maxwell-Wagner interfacial polarization, a key dielectric loss mechanism under an alternating electromagnetic field.

The electronic structure calculations added further support. The density of states near the Fermi level is dominated by titanium 3d orbitals, indicating that the heterostructure retains good intrinsic conductivity channeled through the MXene layers, which enables energy dissipation via conduction losses. Significant orbital hybridization among Ce 4f, Ti 3d, O 2p, and F 2p states above the Fermi level creates unoccupied hybridized states into which incident radiation can excite electrons, opening an additional channel for energy dissipation. COMSOL electromagnetic simulations of the materialized unit cell, combined with transmission line theory and the ABCD matrix method, predicted reflection loss below −10 dB, corresponding to more than 90 percent absorption, across nearly the entire 2 to 18 GHz range.

To realize the design experimentally, the researchers used melamine foam as a sacrificial template because its skeletal structure and pore dimensions closely mimic the theoretically optimized Voronoi-like architecture. The foam was impregnated with a dispersion of cerium dioxide and MXene nanosheets, freeze-dried, and then heat-treated under argon at 350 and 800 degrees Celsius, which carbonizes the template and burns it away as a sacrificial scaffold. The resulting aerogels have densities between 0.018 and 0.117 grams per cubic centimeter and shrink only 5.60 to 13.07 percent during formation. X-ray diffraction confirmed cubic cerium dioxide and the characteristic (002) reflection of MXene, Raman spectroscopy identified the component phases and the graphitic carbon framework, and X-ray photoelectron spectroscopy revealed the coexistence of Ce3+ and Ce4+ states, a signature of high oxygen-vacancy concentration in the ceria lattice.

Those oxygen vacancies matter enormously for performance. The presence of Ce3+ introduces additional electronic energy levels and local charge imbalance, generating defect dipoles that relax under an alternating electromagnetic field and convert wave energy into heat. The minor titanium dioxide phase detected in the spectra further enhances interfacial polarization at newly formed heterogeneous boundaries. When the aerogels were vacuum-impregnated with epoxy resin for testing, dielectric measurements showed that increasing nanomaterial loading raised the complex permittivity substantially, while the permeability remained essentially unchanged because the primary components are non-magnetic. Cole-Cole analysis revealed four distinct Debye relaxation processes in the optimal samples, and impedance spectroscopy showed low charge-transfer resistance at high frequencies, consistent with the highly conductive MXene and carbon networks.

The absorption measurements validated every element of the design. The CMX5 sample achieved a minimum reflection loss of −63.10 dB at 3.1 mm thickness and 13.58 GHz, with an effective bandwidth of 6.46 GHz, and reached its maximum bandwidth of 7.82 GHz at 4.0 mm thickness. The CMX3 sample performed even more impressively in bandwidth terms: at 3.9 mm it covered 9.43 GHz, spanning 6.70 to 16.13 GHz, surpassing all previously reported carbon-based absorbers while using an ultralow 3.74 weight percent loading. By simply adjusting thickness, the material can be tuned to cover 100 percent of the X-band and up to 84.5 percent of the Ku-band, or 73 percent of the C-band, because polarization relaxation processes dominate at low and mid frequencies. Radar cross-section simulations confirmed that coated objects would be substantially harder for radar to detect.

The team also demonstrated practical relevance beyond the laboratory bench. When a resin patch of the material was placed over a chip inside a communication device, the measured radiation intensity dropped from 110 volts per meter on the bare chip to roughly 10 to 40 volts per meter, a striking reduction in electromagnetic pollution at the component level. The aerogels additionally proved mechanically resilient, retaining elasticity after compression and supporting a 100-gram load with minimal deformation, thermally insulating, with a cubic centimeter sample keeping its top surface below 50 degrees Celsius on a hot plate at 100 to 200 degrees Celsius, and fire-resistant, with the framework remaining largely intact after direct ablation. Filling the aerogel with epoxy even raised the resin’s thermal conductivity and glass transition temperature, because the continuous carbon network provides pathways for phonon transport and mechanically interlocks with the polymer chains.

The broader significance of the work lies in demonstrating that a biological sensory organ tuned to infrared radiation can be rationally translated into a metamaterial for an entirely different part of the electromagnetic spectrum. Rather than copying the beetle’s geometry, the researchers extracted its design logic, hierarchical impedance grading, radiation trapping through multiple scattering, extended propagation pathways, and interfacial energy conversion, and re-implemented it with cerium dioxide nanoparticles, MXene nanosheets, and a porous carbon scaffold. The synergy between dielectric loss in ceria, conductive and interfacial losses in MXene, and defect dipoles from oxygen vacancies produces complementary attenuation mechanisms that no single component could deliver. With broadband coverage, high absorption efficiency, ultralow density, and minimal filler content combined in one material, the beetle-inspired aerogel points toward next-generation electromagnetic interference shielding, stealth coatings, and protection for the ever-denser wireless electronics of modern life.

Subject of Research: Bio-inspired CeO2/MXene hierarchical aerogels for broadband microwave absorption

Article Title: Modified MXene Aerogel With Broadband Microwave Absorption Inspired by Melanophila Acuminata Beetle

Article References: Liu, Z., Xu, D., Liu, Z., Song, H., Zhang, Q., Zhou, J., & Wen, X. (2026). Modified MXene Aerogel With Broadband Microwave Absorption Inspired by Melanophila Acuminata Beetle. Advanced Science, 13(55), Article e76496. https://doi.org/10.1002/advs.76496

Image Credits: AI Generated

DOI: 10.1002/advs.76496

Keywords: MXene, aerogel, biomimetics, Melanophila acuminata, microwave absorption, electromagnetic interference, CeO2, carbon foam, impedance matching, stealth technology, dielectric loss, DFT calculations

The study, published in Results in Chemistry, centers on lignin, the second most abundant natural polymer on Earth and a major fraction of empty fruit bunches. Lignin is a dense, highly cross-linked polyphenolic macromolecule with an intrinsic capacity to absorb ultraviolet and visible light and to dissipate that energy as heat, a property known as photothermal conversion. Despite these attributes, roughly 95 percent of industrial lignin is still simply burned for low-grade heat and power. The researchers argue that this underutilization stems from lignin’s structural complexity and compositional variability, which have hindered its use in high-performance materials. Their answer is a dual valorization strategy: rather than choosing between chemical modification or nanocarbon conversion, they pursue both pathways from the same extracted lignin feedstock, building a hierarchically structured, entirely biobased photothermal platform.

The first step was extraction. Empty fruit bunches from a local palm oil mill were delignified in a rotary digester using an aqueous sodium hydroxide solution at 170 degrees Celsius under 8 atmospheres of pressure, with an active alkali charge of 19.5 weight percent and a liquor-to-solid ratio of 20 to 1. Lignin was then recovered from the concentrated black liquor by acid precipitation at pH 2.0, yielding 15.13 percent of the dry biomass weight. The recovered lignin proved remarkably pure, with a total lignin content of 95.83 percent, low ash content of 2.78 percent, and modest moisture retention, confirming that the acid precipitation recovered structurally intact lignin with minimal contamination from polysaccharides or inorganic residues.

Half of this lignin was then acetylated using glacial acetic acid and acetyl chloride at a 4 to 1 volume ratio, held at 40 degrees Celsius for two hours. The chemistry is subtle but powerful. Substituting hydroxyl groups with electron-withdrawing acetyl moieties creates donor-acceptor electronic configurations within the aromatic network, extends pi-conjugation, and weakens the hydrogen-bonding networks that normally lock lignin molecules in place. Spectroscopic evidence confirmed the transformation: the broad hydroxyl stretching band at 3376 wavenumbers vanished, a strong new ester carbonyl band appeared at 1740 wavenumbers, and pyrolysis analysis detected coniferyl alcohol diacetate, a direct marker of successful esterification of guaiacyl units. Thermogravimetric analysis showed the acetylated lignin was more thermally stable, with a higher maximum degradation temperature and far less char residue at 750 degrees Celsius, just 11.8 percent versus 26.4 percent for native lignin, a trait that avoids char interference with light absorption during thermal cycling.

The other half of the lignin took a very different path. Through oxidative depolymerization in nitric acid followed by hydrothermal carbonization at 200 degrees Celsius, the macromolecular aromatic network was cleaved into nanoscale carbon fragments that reassembled into lignin-derived graphene quantum dots, dubbed PL-GQDs, with a mass yield of 8.45 percent. These zero-dimensional carbon nanostructures averaged just 5.73 nanometers in hydrodynamic diameter, with transmission electron microscopy revealing nearly spherical particles between 2 and 5 nanometers. High-resolution imaging showed well-defined lattice fringes with an interplanar spacing of about 0.23 nanometers, matching the (100) plane of graphitic carbon. X-ray diffraction confirmed partial graphitization, with the interlayer spacing shrinking from 0.42 nanometers in the precursor lignin to 0.33 nanometers in the quantum dots, evidence of compact sp2-hybridized carbon layers forming from lignin’s aromatic rings.

The two materials were then deployed in complementary architectures. The first was a flexible photothermal film composite, built by dispersing the quantum dots and acetylated lignin into a poly(vinyl alcohol) matrix. Under simulated sunlight at one sun intensity, the neat polymer film warmed by only 6.8 degrees Celsius, but the optimized film containing 50 weight percent acetylated lignin reached a temperature rise of 15.4 degrees Celsius, hitting 42.7 degrees Celsius. Placed on a thermoelectric generator module, that film produced an open-circuit voltage of about 24.3 millivolts, compared with just 2.2 millivolts for the neat polymer and a significantly lower 12.8 millivolts for a film loaded with unmodified lignin. The apparent photothermal conversion efficiency reached 23.2 percent, a figure the authors attribute to the synergy between the acetylated lignin’s enhanced photon capture and the quantum dots’ graphitic, broadband-absorbing heat-generating domains.

The second application pushed the same chemistry into a porous solar-driven lignin aerogel designed for interfacial solar steam generation. Here the textural data tell a striking story. The aerogel combining acetylated lignin with the quantum dots achieved a specific surface area of 177.5 square meters per gram and a pore volume of 0.259 cubic centimeters per gram, more than an eightfold increase over an aerogel made with native lignin. Acetylation, by reducing the density of free hydroxyl groups, weakens the hydrogen-bond-driven aggregation that otherwise densifies and collapses the gel network, while the quantum dots act as nanoscale spacers that inhibit framework shrinkage during freeze-drying. Scanning electron microscopy revealed a hierarchical architecture of interconnected macropores and intertwined nanofibers, ideal for capillary-driven water supply and rapid evaporation.

Performance followed structure. The optimized aerogel achieved a water evaporation rate of 944.7 grams per square meter per hour under one sun, corresponding to a solar steam generation efficiency of 59.2 percent, more than a 60-fold enhancement over direct water evaporation. Over six consecutive evaporation cycles the system averaged 911.3 grams per square meter per hour with a relative standard deviation of only about 3.5 percent, demonstrating excellent reproducibility. The aerogel also sustained steam generation from saline feed solutions up to 10 weight percent sodium chloride, although salt crystals accumulated on the pore walls and cut the accessible surface area sharply, signaling that anti-scaling strategies will be needed for prolonged desalination duty. The authors also note candidly that the efficiency remains moderate compared with leading biomass evaporators, because the aerogel’s thermal conductivity rises from 0.143 to 0.477 watts per meter-kelvin when wet, allowing some heat to leak into the bulk water rather than staying confined at the evaporation interface.

The mechanistic picture ties everything together. Acetylation narrows the electronic gap between lignin’s highest occupied and lowest unoccupied molecular orbitals, from 5.58 to 5.34 electronvolts in related work, facilitating electronic excitation and non-radiative relaxation, while weakened hydrogen bonding grants molecules the freedom to dissipate absorbed photon energy as vibrational heat. The quantum dots contribute additional photon-capturing graphitic domains across the visible and near-infrared spectrum. In the film, this synergy builds thermal gradients that drive thermoelectric voltage; in the aerogel, it localizes heat at the water-air interface where it is most useful. What makes the work resonate beyond the laboratory numbers is its circular economy logic: a single agricultural waste stream, normally an environmental liability, is upgraded into two complementary functional materials for solar desalination and off-grid power generation. The researchers, funded by Indonesia’s National Research and Innovation Agency, suggest the strategy could extend the value of oil palm residues across multifunctional solar-energy harvesting technologies, turning one of the tropics’ most abundant waste problems into a feedstock for the renewable energy transition.

Subject of Research: Dual valorization of oil palm empty fruit bunch lignin into acetylated lignin and graphene quantum dots for photothermal solar energy conversion

Article Title: Dual valorization of oil palm empty fruit bunches: acetyl-modified lignin and lignin-derived graphene quantum dots for sustainable photothermal conversion

Article References: Ariyanta, H. A., Utami, K. N., Prihati, S. R., Sarwana, W., Sudirman, Rois, M. F., Priatmoko, S., Annas, D., & Holilah (2026). Dual valorization of oil palm empty fruit bunches: acetyl-modified lignin and lignin-derived graphene quantum dots for sustainable photothermal conversion. Results in Chemistry, 31, Article 103897. https://doi.org/10.1016/j.rechem.2026.103897

Image Credits: AI Generated

DOI: 10.1016/j.rechem.2026.103897

Keywords: lignin, oil palm empty fruit bunches, graphene quantum dots, photothermal conversion, solar steam generation, photothermoelectric, biomass valorization, acetylation, aerogel, circular bioeconomy, desalination, renewable energy