The research, led by P. R. Rajimol of the CSIR-National Institute for Interdisciplinary Science and Technology in Trivandrum, began with marigold (Tagetes erecta) floral waste gathered from the Attukal Bhagavathy Temple in Kerala. Marigolds are rich in phytochemicals, including flavonoids such as quercetin and quercetagetin, carotenoids like lutein and zeaxanthin, and a variety of phenolic compounds. Rather than simply using a crude extract, the team pursued an activity-guided approach: they first identified which solvent extraction produced the most potent corrosion inhibitor, and then isolated the single molecule responsible for that activity. This distinction matters, because earlier studies of marigold as a corrosion inhibitor had stopped at the extract level without pinpointing or deploying the active compound in a controlled-release coating system.

The extraction itself was deliberately simple and green. Roughly 750 grams of dried petals were extracted at room temperature using two solvents of very different polarity: hexane, which pulls out nonpolar compounds such as carotenoids and steroids, and a 60:40 ethanol-water mixture, which captures polar species including flavonoids and phenolic acids. After concentration under reduced pressure and freeze-drying, the hexane route yielded about 26 grams of crude extract and the hydroethanolic route about 33 grams. When the two extracts were compared head-to-head in salt water, the hydroethanolic extract clearly outperformed its hexane counterpart, protecting mild steel more effectively in immersion tests lasting 14 days and in electrochemical measurements.

Those electrochemical tests provided the mechanistic clues. In electrochemical impedance spectroscopy, bare mild steel in 3.5 weight percent sodium chloride solution could be modelled with a simple circuit of solution resistance, double-layer capacitance, and charge transfer resistance. In the presence of the hydroethanolic extract, however, an additional film resistance and capacitance appeared in the fitted circuit, indicating that active molecules were adsorbing onto the metal surface and forming a protective layer. Potentiodynamic polarization told a complementary story: the hydroethanolic extract shifted the corrosion potential in the anodic direction and suppressed the corrosion current density, behaving as an anodic-type inhibitor, while the hexane extract acted predominantly on the cathodic reaction. Peak performance for both extracts occurred around 200 parts per million; at higher concentrations, the physically adsorbed layers apparently began to desorb or peel, slightly reducing efficiency.

With the hydroethanolic extract confirmed as the more active fraction, the researchers used column chromatography, eluting with mixtures of ethyl acetate and hexane, to isolate the marker compound. At 90 percent ethyl acetate, a pale-yellow solid emerged. High-resolution mass spectrometry assigned it the molecular formula C15H10O8, and proton and carbon nuclear magnetic resonance spectra confirmed its identity as quercetagetin, a hexahydroxyflavone. The molecule is, in electrochemical terms, almost ideally suited to corrosion inhibition: it carries a dense array of hydroxyl groups and a carbonyl group whose lone pairs can form coordinate bonds with metal ions, while its two aromatic rings, a double bond, and the carbonyl provide a delocalized pi-electron system that can also accept electrons back from the metal in retro-donation. In effect, quercetagetin and the metal surface behave as a Lewis acid-base pair, and this molecular handshake blocks the oxidation reactions that drive corrosion.

Immersion tests bore this out dramatically. Mild steel coupons soaked for 15 days in saline solutions at acidic, neutral, and alkaline pH developed heavy corrosion products, pits, and cracks when no inhibitor was present. In the presence of quercetagetin, the surfaces remained smooth and essentially damage-free, and elemental analysis showed far less oxide formation. The hydroxyl and carbonyl groups, by coordinating to the metal, simply deny corrosive chloride ions access to the surface.

The next challenge was longevity. A free inhibitor dissolved in a coating would be consumed quickly and leach away, so the team loaded quercetagetin, and the whole hydroethanolic extract, into mesoporous silica nanoparticles synthesized by a template method using cetyltrimethylammonium bromide and tetraethyl orthosilicate. These nanocontainers are extraordinary sponges: nitrogen adsorption measurements showed a surface area of 729.67 square meters per gram and a pore volume of 0.68 cubic centimeters per gram. After loading the inhibitor at a 2:1 inhibitor-to-container weight ratio, the surface area dropped to 88.80 square meters per gram and pore volume to 0.12 cubic centimeters per gram, clear evidence that the organic molecules had filled the pores. Infrared spectroscopy confirmed that loading occurred by physisorption, with no chemical bonds formed or broken, so the inhibitor retains its full activity. Transmission and scanning electron microscopy showed spherical, slightly polydisperse particles whose surfaces became smoother and denser after loading, and thermogravimetric analysis revealed a bonus: the nanocomposite-filled epoxy was substantially more thermally stable than pristine epoxy, with the temperatures of 5 percent and 10 percent weight loss rising by 77 and 68 degrees Celsius respectively.

The coatings themselves were made by dispersing the loaded nanocontainers in a bisphenol A epoxy resin with a polyamine hardener, then dip-coating polished mild steel and aluminium-6061 panels and curing them at room temperature followed by a post-cure at 80 degrees Celsius. The average coating thickness was a modest 34 micrometers. Electrochemical testing in 3.5 percent sodium chloride revealed a clear optimum. For the whole extract, a 2 weight percent loading raised the charge transfer resistance of mild steel from 1,128 to 21,300 ohm square centimeters and cut the corrosion current density from 12.53 to 0.066 microamperes per square centimeter, an inhibition efficiency of 99.47 percent. The isolated quercetagetin did even better: at 3 weight percent, resistance climbed to 31,240 ohm square centimeters, corrosion current density fell to 0.0060 microamperes per square centimeter, and the corrosion potential shifted from minus 0.698 to minus 0.274 volts, yielding an inhibition efficiency of 99.95 percent relative to bare steel. Beyond that concentration, nanoparticles began to agglomerate, creating porous pathways that let electrolyte penetrate, so more was not better. The quercetagetin coating was also notably stable and non-hygroscopic, unlike the extract-loaded version at its highest loading. On aluminium-6061, the 3 percent quercetagetin coating raised resistance from 3,634 to 77,050 ohm square centimeters and delivered 99.67 percent inhibition by polarization measurements.

Perhaps the most remarkable results came from the coating’s responsive behavior. Because mesoporous silica releases its payload faster in acidic conditions, and because quercetagetin’s hydroxyl groups form more soluble anionic structures in alkaline media, the coating releases its inhibitor precisely where and when corrosion threatens, whether the environment is acidic, neutral, or basic. When the researchers scratched a coated aluminium panel with a razor blade and immersed it in salt water, scanning electron microscopy showed healing beginning within 3 hours and completing within 48 hours, with no corrosion products or leakage at the scratch site. Released quercetagetin fills the void, coordinates to the exposed metal, and hydrogen-bonds with the surrounding polymer, sealing the wound much as biological tissue repairs itself. The coating also proved self-sanitizing. In zone-of-inhibition tests, it produced a 3.0-centimeter inhibition zone against the gram-negative bacterium Escherichia coli and a 2.3-centimeter zone against the gram-positive Staphylococcus aureus, and quantitative testing under the AATCC-100 protocol showed 92 percent and 81 percent reductions in bacterial colonies respectively after one hour of contact. The stronger effect against gram-negative bacteria likely reflects differences in cell wall structure and their interaction with the flavonoid.

The significance of the work extends beyond the impressive numbers. Corrosion consumes an estimated 3.4 percent of global GDP each year, and the traditional inhibitors used to fight it, particularly hexavalent chromium compounds and heavy-metal complexes, are toxic, persistent, and carcinogenic, prompting tightening regulation under frameworks such as REACH. By converting temple flower waste, a documented source of water pollution, into a high-performance green inhibitor, the CSIR team addresses two environmental problems at once in a genuine waste-to-wealth strategy. The combination of passive barrier protection from the epoxy matrix and active, pH-triggered inhibition from the nanocontainers points toward a new generation of smart coatings for marine structures, healthcare surfaces, and industrial equipment, where a single layer of paint derived from discarded petals can resist rust, mend its own damage, and keep microbes at bay.

Subject of Research: Green multifunctional epoxy nanocomposite coatings from marigold floral waste for anticorrosive, antimicrobial, and self-healing metal protection

Article Title: Multifunctional epoxy nanocomposite coatings with anticorrosive, antimicrobial, and self-healing characteristics derived from floral biomass

Article References: Rajimol, P. R., Samuel, A. S., Ulaeto, S. B., & Rajan, T. P. D. (2026). Multifunctional epoxy nanocomposite coatings with anticorrosive, antimicrobial, and self-healing characteristics derived from floral biomass. Discover Electrochemistry, 3(1), Article 49. https://doi.org/10.1007/s44373-026-00122-5

Image Credits: AI Generated

DOI: 10.1007/s44373-026-00122-5

Keywords: corrosion inhibition, quercetagetin, marigold floral waste, mesoporous silica nanoparticles, epoxy nanocomposite, self-healing coating, antimicrobial coating, green chemistry, mild steel, aluminium alloy, electrochemical impedance spectroscopy, waste valorisation

The research team, led by Snigdha Homroy and Rajni Chopra at the National Institute of Food Technology Entrepreneurship and Management in Kundli, Haryana, collected discarded Tagetes erecta flowers from a local temple within six to eight hours of generation and processed them within a day to minimise the loss of volatile phytochemicals. The flowers, which had a moisture content of approximately 88 percent, were gently crushed rather than milled to preserve the delicate glandular trichomes that house the oil-bearing volatiles. From this waste stream, the researchers extracted marigold essential oil using four different approaches: conventional hydro-distillation, ultrasound-assisted hydro-distillation, freeze-thaw-assisted hydro-distillation and solvent-free microwave extraction.

The choice of extraction route proved decisive. Hydro-distillation in a Clevenger-type apparatus for four hours yielded 0.0164 grams of oil per 100 grams of fresh flowers. When the flowers were first pre-treated with ultrasound at 500 watts and 20 kilohertz, acoustic cavitation, the violent formation and collapse of microscopic bubbles, tore open cell structures and improved solvent penetration, raising the yield by roughly 25 percent. A freeze-thaw pre-treatment, in which flowers were cycled between minus 80 degrees Celsius and room temperature three times, boosted the yield by about 17 percent, because ice crystals physically rupture cell walls and membranes during freezing, enlarging the porous network available to the extracting water.

Solvent-free microwave extraction, by contrast, performed poorly in this matrix, delivering a yield 85.3 percent lower than conventional hydro-distillation. The authors attribute this to the absence of added water and the limited intrinsic free moisture of the flowers, which restricted internal heating and volatilisation of the essential oil. The result is a useful reminder that green extraction technologies are not universally interchangeable: microwave methods that excel with aromatic herbs, as previous work on rosemary showed, can falter with high-moisture, fibrous floral waste. The relatively low absolute yields across all methods also reflect the use of whole flowers, which mix oil-rich tissues with fibrous, low-oil material, and the reporting of yields on a fresh-weight basis.

Chemical profiling by headspace gas chromatography-mass spectrometry identified 41 phytochemical constituents across the oils, with a profile rich in compounds prized for antioxidant, antimicrobial and anti-inflammatory activity. Nootkatone, limonene, tagetone, piperitone, ocimene, beta-caryophyllene and isoeugenol dominated, although their proportions shifted with the extraction method. Ultrasound-assisted hydro-distillation produced the highest overall content of key volatiles, enriching oxygenated sesquiterpenes and ketones such as nootkatone, which reached 11.15 percent, while freeze-thaw treatment similarly favoured sesquiterpenes. Microwave extraction skewed toward lighter hydrocarbons and phenolics, including isopentane and isoeugenol, which contribute aroma but are less relevant to oxidative protection.

The second half of the study tested whether this waste-derived oil could defend perilla seed oil, a cold-pressed, omega-3-rich oil whose high polyunsaturated fatty acid content makes it exceptionally vulnerable to rancidity. The researchers fortified the oil with marigold essential oil at 500, 1000 and 1500 parts per million and compared the results against 200 parts per million of tert-butylhydroquinone, or TBHQ, the synthetic antioxidant benchmark, and an untreated control. Samples were then subjected to a 20-day Schaal oven test at 60 degrees Celsius, an accelerated storage protocol that compresses months of ambient shelf-life degradation into weeks by speeding the same radical chain reactions that occur in normal storage.

Across every measure, the 1500 ppm marigold treatment performed impressively. Rancimat analysis showed a statistically significant, concentration-dependent extension of the induction period, indicating delayed oxidation onset. Viscosity, which climbs as oxidation generates polymeric degradation products, rose only to 37.1 centipoise in the marigold-fortified oil, compared with 40.3 centipoise in the untreated control. The untreated oil’s peroxide value, a gauge of primary oxidation, soared to 28.63 milliequivalents of oxygen per kilogram by day 20, whereas the marigold-supplemented oil held at 10.03 and TBHQ at 9.71. Acid value, p-anisidine value and conjugated triene content, which track hydrolysis and secondary aldehyde and ketone formation, followed the same pattern, with the highest marigold dose approaching TBHQ performance throughout.

Antioxidant capacity assays reinforced the picture. Untreated perilla oil lost radical-scavenging capacity rapidly, with DPPH inhibition falling from 84.42 to 74.35 percent and ABTS inhibition from 80.15 to 66.40 percent over the storage period. The 1500 ppm marigold sample, by contrast, retained 83.86 percent DPPH and 72.94 percent ABTS inhibition after 20 days, losses of less than seven percent, comparable to TBHQ-treated oil. The oil also preserved its golden carotenoid pigments better, retaining a yellow Lovibond value of 12.2 against 9.1 for the control. Hierarchical cluster analysis of all stability parameters grouped the control and 500 ppm samples together as low-stability outliers while placing the 1500 ppm marigold oil in the same high-stability cluster as TBHQ, a statistical confirmation that the floral waste extract can match a regulated synthetic preservative at its maximum permitted concentration.

The protective mechanism stems from the oil’s constellation of bioactive volatiles, which scavenge free radicals, chelate pro-oxidant metals and interrupt lipid peroxidation chain reactions, with synergy among compounds such as beta-caryophyllene, nootkatone and isoeugenol likely amplifying the effect. The study’s significance extends beyond food chemistry. It couples two sustainability goals at once: diverting a vast, culturally generated waste stream from landfill and offering food manufacturers a clean-label alternative to synthetic antioxidants such as BHA, BHT and TBHQ, whose potential carcinogenic, genotoxic and endocrine-disrupting effects have drawn increasing scrutiny in animal and mechanistic studies. The authors note that future work should clarify the underlying preservation mechanisms and extend testing to other oxidation-sensitive oils such as flaxseed and chia. If those trials succeed, the garlands left behind at temples across India could become a genuine industrial resource, turning ritual offerings into shelf life for the world’s healthiest cooking oils.

Subject of Research: Extraction of essential oil from marigold floral waste and its use as a natural antioxidant to stabilise polyunsaturated fatty acid-rich perilla seed oil.

Article Title: Valorisation of marigold floral waste for essential oil extraction and its application in stabilisation of PUFA rich perilla seed oil

Article References: Homroy, S., Madan, H., Sharma, S., Chopra, R., & Kumari, R. (2026). Valorisation of marigold floral waste for essential oil extraction and its application in stabilisation of PUFA rich perilla seed oil. Discover Green Chemistry, 1(1), Article 16. https://doi.org/10.1007/s44509-026-00015-1

Image Credits: AI Generated

DOI: 10.1007/s44509-026-00015-1

Keywords: marigold floral waste, Tagetes erecta, essential oil, hydro-distillation, ultrasound-assisted extraction, solvent-free microwave extraction, perilla seed oil, natural antioxidants, oxidative stability, TBHQ, omega-3, waste valorisation