Magnetic Nanotube Catalyst Makes Pyridines and Triazines in Water Within an Hour

Chemists have long chased a simple goal: build the complex nitrogen-rich molecules that modern medicine and electronics depend on, without the toxic solvents, harsh heat and wasteful processes that traditionally come with them. A research team now reports a solution that reads almost like a recipe for green chemistry. Writing in the Journal of the Saudi Chemical Society, they describe a new magnetic nanocatalyst that assembles valuable heterocyclic compounds in water, in as little as one hour, with yields reaching 99 percent, and then can be pulled straight out of the reaction mixture with a magnet and reused again and again.

The catalyst, known as Fe₃O₄/MWCNTs–Melamine/TCT–CuI, is a carefully layered hybrid material in which each component plays a distinct role. Multi-walled carbon nanotubes form the backbone, prized for their enormous surface area and excellent electrical conductivity. Decorated onto these tubes are iron oxide nanoparticles, which lend the entire structure its magnetic personality and allow the catalyst to be separated from reaction mixtures with an external magnet rather than by tedious filtration. Wrapped around the tubes is a nitrogen-rich ligand framework, formed by linking melamine with 2,4,6-trichloro-1,3,5-triazine, and finally copper(I) iodide is immobilized within that framework to supply the active catalytic centers.

The synthesis proceeds in three deliberate stages. Carboxylated nanotubes are first magnetized with iron oxide, then treated with thionyl chloride to convert the surface carboxylic acid groups into highly reactive acid chlorides. Meanwhile, melamine and trichlorotriazine are coupled to build a polymeric, nitrogen-dense network that is grafted covalently onto the activated nanotubes in toluene. In the final step, copper(I) iodide is stirred into the composite in dimethylformamide, where the copper ions nestle into the nitrogen-rich cavities of the melamine–triazine framework, held firmly in place by multiple coordination bonds. The result is a stable, reusable hybrid nanocatalyst that resists the aggregation and metal leaching that plague many conventional systems.

Characterization of the material was exhaustive, and the evidence is strikingly consistent across a battery of techniques. Fourier-transform infrared spectroscopy traced each chemical transformation, from the appearance of iron–oxygen stretches after magnetization to the intense carbon–nitrogen signals confirming the grafted organic framework. X-ray photoelectron spectroscopy located the copper in its +1 oxidation state, with characteristic Cu 2p peaks at 932.6 and 952.4 electron volts and, crucially, no shake-up satellite peaks that would signal unwanted Cu(II). X-ray diffraction confirmed the coexistence of the graphite carbon peak, the cubic spinel reflections of magnetite and the signatures of copper iodide in a single integrated material.

Microscopy told an equally persuasive story. Scanning electron microscopy revealed the once-smooth nanotube surfaces densely coated with nanoparticles and a thick organic layer, while transmission electron microscopy showed the tubular skeleton intact after every modification step, with iron oxide and copper centers uniformly immobilized on the outer walls. Particle-size analysis gave an average diameter of about 54 nanometers, a narrow distribution that signals well-controlled functionalization and maximal accessible surface. Energy-dispersive X-ray analysis confirmed all expected elements, including 8.03 percent nitrogen from the ligand layer and 4.25 percent copper, while ICP-OES quantified the copper loading at 1.57 × 10⁻³ moles per gram.

Porosity and magnetism, the twin workhorses of any good heterogeneous catalyst, were also verified. BET analysis showed a specific surface area of 86.4 square meters per gram with a mesoporous structure of 9.8-nanometer average pores, features that ease reactant diffusion and expose abundant active sites. Vibrating sample magnetometry demonstrated superparamagnetic behavior: the catalyst snaps to attention in a magnetic field but sheds its magnetism the moment the field is removed, preventing clumping in solution. Although grafting the non-magnetic organic framework reduced saturation magnetization from 62.7 to 39.3 electromagnetic units per gram, that residual pull remains more than enough for rapid recovery with a simple hand magnet.

The performance figures are where the chemistry gets genuinely viral-worthy. In the model reaction, the one-pot condensation of benzaldehyde, acetophenone and ammonium acetate to form 2,4,6-triphenylpyridine, the team systematically screened catalyst loadings and solvents. With 6 mol percent of the nanocatalyst in water at reflux, the product arrived in 99 percent yield within one hour. Ethanol, acetonitrile, DMF, THF, toluene, DMSO, ionic liquids, glycerol, polyethylene glycol and even a choline chloride–urea deep eutectic solvent all trailed behind. Control experiments were unambiguous: no catalyst, no product; copper iodide alone yielded just 12 percent; and every partial version of the catalyst failed. Only the fully integrated system works, a textbook demonstration of synergy between the magnetic core, carbon nanotube support, nitrogen ligand and copper centers.

The substrate scope proved broad and forgiving. Fifteen triarylpyridines and fifteen triaryl-1,3,5-triazines were synthesized, with yields ranging from 87 to 99 percent across electron-rich, electron-poor, halogenated and heteroaromatic substrates, including pyridine-, furan- and thiophene-containing partners. Methyl and methoxy substituents boosted reactivity, while nitro and halogen groups only modestly dented yields, and the retained halogens leave useful handles for later cross-coupling. The proposed mechanism is a condensation–addition–cyclization–oxidation sequence in which the copper centers act as Lewis acids, activating carbonyl groups and steering polar intermediates toward aromatic pyridine and triazine rings, with water stabilizing the charged species along the way.

Recyclability is the headline the industry will read most closely. Over nine consecutive cycles, yields fell only marginally, from about 99 percent to 89 percent for the pyridine and from 99 to 88 percent for the triazine. After nine runs, the catalyst still showed a saturation magnetization of 36.1 emu/g, intact nanotube morphology, unchanged X-ray diffraction patterns and untouched infrared signatures. ICP-OES revealed copper content dropped only from 1.57 to 1.54 × 10⁻³ mol/g, while a hot filtration test indicated the active species remains predominantly bound to the solid, with any transiently leached copper efficiently recaptured in a release-and-catch equilibrium. Against previously reported catalysts, which typically demand 4 to 20 hours, toxic solvents, harsh oxidants and recyclability of at most six cycles, the new system is faster, greener, higher-yielding and more durable.

Because 2,4,6-triarylpyridines carry documented antimicrobial, anti-inflammatory, antiviral and anticancer activities, and triaryltriazines serve as electron-transport materials in OLEDs, organic photovoltaics and flame-retardant polymers, a one-hour, water-based, magnetically recyclable route to both classes is more than a laboratory curiosity. It is a template for how designed hybrid nanomaterials can make the building blocks of pharmaceuticals and advanced electronics cleaner, cheaper and, quite literally, easier to pull out of the pot.

Subject of Research: Design of a magnetically recoverable Fe₃O₄/MWCNTs–Melamine/TCT–CuI heterogeneous nanocatalyst for green one-pot synthesis of triarylpyridines and triaryltriazines in water

Article Title: Fe₃O₄/MWCNTs–Melamine/TCT–CuI: an advanced heterogeneous catalyst for sustainable synthesis of highly substituted pyridines and triazines

Article References: Al-Assi, G., Eldalawy, R., Ali, A. M., Shukla, M. B., Rekha, M. M., Sasikumar, Y., Chopra, L., Aldulaimi, A., & Mohammadi, R. (2026). Fe₃O₄/MWCNTs–Melamine/TCT–CuI: an advanced heterogeneous catalyst for sustainable synthesis of highly substituted pyridines and triazines. Journal of Saudi Chemical Society, 30(4), Article 52. https://doi.org/10.1007/s44442-026-00104-7

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00104-7

Keywords: Fe₃O₄/MWCNTs–Melamine/TCT–CuI, heterogeneous catalysis, triarylpyridines, triaryltriazines, magnetic nanocatalyst, carbon nanotubes, green chemistry, multicomponent reaction, water solvent, copper(I) iodide, catalyst recyclability, nitrogen heterocycles