The research, led by Deok Woo Kim, Dong Seop Choi, and Ji Bong Joo of Konkuk University’s Department of Chemical Engineering, tackles a long-standing dilemma in catalyst design. The standard method for opening up zeolites, known as desilication, involves treating the crystals with an alkaline solution such as sodium hydroxide. The alkali selectively dissolves silicon species from the framework, carving out larger pores that improve access. But the process is destructive and difficult to control. As silica dissolves, it can reprecipitate randomly as amorphous deposits on the crystal surface, blocking the very openings the treatment was meant to create. Worse, prolonged alkali exposure can collapse the zeolite framework entirely, destroying the microporosity and acid sites that give the material its catalytic power in the first place.

The Korean team’s solution was to introduce a surfactant, cetyltrimethylammonium bromide or CTAB, into the synthesis. Their procedure began by stirring ZSM-5 zeolite with a sodium hydroxide solution at room temperature, then adding a CTAB solution and transferring the mixture to a Teflon-lined autoclave for hydrothermal treatment at 130 degrees Celsius. After adjusting the pH to approximately 8 and continuing treatment for another 24 hours, the product was filtered, dried, and calcined at 550 degrees Celsius to burn away the organic template. The resulting material, designated HF_ZSM-5, was compared against a conventional alkali-treated sample, AT_ZSM-5, prepared by simply stirring ZSM-5 in a 0.5 molar sodium hydroxide solution at 80 degrees Celsius for five hours.

The characterization results reveal why the surfactant approach is so effective. X-ray diffraction confirmed that all samples retained the characteristic ZSM-5 framework, but the alkali-treated material showed markedly reduced crystallinity, evidence of structural damage from the harsh alkaline conditions. The hierarchical material, by contrast, preserved much higher crystallinity despite facing even harsher synthesis conditions. The researchers attribute this protection to CTAB micelles that electrostatically bind to the negatively charged zeolite surface, acting as a shield against excessive silica dissolution. Strikingly, the hierarchical sample also displayed new low-angle diffraction peaks near 2.3, 4.2, and 4.8 degrees, the signature of long-range ordered hexagonal mesoporous aluminosilicate resembling the well-known material MCM-41. In other words, the treatment did not merely etch holes in the crystal; it grew an entirely new ordered mesoporous phase on its surface.

Nitrogen adsorption measurements told a complementary story. Pristine ZSM-5 showed the classic type I isotherm of a purely microporous material. The alkali-treated sample shifted toward a type IV isotherm, indicating mesoporosity, and adsorbed far more nitrogen overall, yet paradoxically exhibited the lowest specific surface area of all the samples. This apparent contradiction points to severe framework damage: excessive alkali treatment had collapsed the micropore structure, destroying the internal surface area even as it created larger voids. The hierarchical zeolite, meanwhile, maintained a surface area comparable to the pristine material while simultaneously developing a clear distribution of mesopores in the 1 to 10 nanometer range. Transmission electron microscopy provided direct visual confirmation, revealing cylindrical pores arranged in hexagonal arrays on the surface of the hierarchical crystals, while the alkali-treated sample showed only cracks and disordered dissolution.

Acidity measurements using ammonia temperature-programmed desorption added another layer of insight. All treated samples lost some acid sites compared with pristine ZSM-5, an expected consequence of partial framework decomposition. Strong Brønsted acid sites, associated with the higher-temperature desorption peak near 400 degrees Celsius, declined more steeply than weak sites, suggesting that desilication converts strong sites into weaker ones, possibly as silica-free alumina surfaces that function as external acid sites. Crucially, the hierarchical material preserved its strong acid sites better than the simply alkali-treated sample, again because the CTAB micelles blocked deep penetration of alkaline species into the framework. The newly formed mesoporous aluminosilicate layer also contributed additional acid sites of its own, similar to those found in aluminum-containing MCM-41.

The catalytic payoff came in cracking tests conducted in a fixed-bed reactor at 500 degrees Celsius. The team chose 1,3,5-triisopropylbenzene, or TIPB, as a probe molecule for bulky feedstocks. At 0.95 nanometers, TIPB is far too large to enter the micropores of ZSM-5, so pristine zeolite could only crack it slowly on its limited external surface, achieving a conversion of just 40.1 percent. The alkali-treated sample performed better by opening access to exposed acid sites. But the hierarchical zeolite was the clear winner, reaching 80.8 percent conversion, exactly 2.01 times higher than the pristine material. Product selectivity reinforced the conclusion: the hierarchical catalyst showed the greatest selectivity toward benzene, the deep-cracking product, indicating that molecules were diffusing through the mesopores and undergoing extensive catalytic cracking rather than simple thermal pyrolysis.

A second test with n-dodecane, a linear hydrocarbon small enough to diffuse into ZSM-5 micropores, revealed a different but equally important advantage. Here the pristine zeolite achieved the highest conversion thanks to its abundant internal acid sites, while the alkali-treated sample fared worst because its collapsed framework had lost so much acidity. The hierarchical material landed in between, retaining enough acid sites for respectable conversion. The decisive metric, however, was coke formation. Coke, the polyaromatic carbonaceous residue that builds up when cracked hydrocarbon fragments linger and carbonize inside pores, is the chief cause of catalyst deactivation in industrial cracking. Pristine ZSM-5, despite its high conversion, produced the most coke because its strong acid sites trap intermediates within narrow micropores. The hierarchical zeolite produced the least coke of all, because its mesopore network allowed fragments to diffuse out before they could accumulate and transform into pore-blocking polyaromatics.

The implications for the petroleum industry are considerable. Fluid catalytic cracking remains the dominant route to transportation fuels worldwide, and its efficiency hinges on how well catalysts can convert the heaviest, bulkiest fractions of crude oil. The Konkuk team’s findings demonstrate that surfactant-templated recrystallization can deliver the best of both worlds: a preserved crystalline zeolite framework with its strong acid sites intact, plus an ordered network of mesopores that welcomes large molecules and sweeps coke precursors away. Compared with conventional desilication, which trades structural integrity for porosity, the hierarchical approach achieved higher conversion of bulky molecules, retained substantial activity toward smaller ones, and minimized deactivating coke deposits. As refineries face pressure to process heavier feedstocks and squeeze more value from every barrel, catalysts engineered with this kind of hierarchical pore architecture could prove transformative, turning molecular traffic jams into open highways for chemistry.

Subject of Research: Synthesis of hierarchical mesoporous zeolites for enhanced catalytic cracking of bulky hydrocarbon molecules

Article Title: Synthesis of hierarchical zeolites for enhanced catalytic cracking performance toward larger hydrocarbon molecules

Article References: Kim, D. W., Choi, D. S., & Joo, J. B. (2025). Synthesis of hierarchical zeolites for enhanced catalytic cracking performance toward larger hydrocarbon molecules. Advances in Industrial and Engineering Chemistry, 1(1), Article 30. https://doi.org/10.1007/s44405-025-00031-y

Image Credits: AI Generated

DOI: 10.1007/s44405-025-00031-y

Keywords: zeolites, hierarchical zeolites, catalytic cracking, ZSM-5, mesoporous materials, fluid catalytic cracking, desilication, CTAB surfactant, MCM-41, coke formation, acid sites, petroleum refining

The coating, dubbed Ag-Zeo by the team, begins with an unlikely raw material: metakaolin derived from halloysite clay nanotubes, a natural aluminosilicate precursor. Conventional ZSM-5 synthesis relies on organic structure-directing agents such as tetrapropylammonium hydroxide, chemicals that are expensive and environmentally unfriendly. By substituting metakaolin, Ludox silica, silver nitrate and a small amount of ZSM-5 seed crystals, the researchers avoided organic templates entirely. The polished steel coupons were cleaned, aged in the zeolite sol for 48 hours, and then crystallized in a high-pressure reactor at 175 degrees Celsius for two days, allowing zeolite crystals to nucleate and grow directly on the metal surface without any binder.

Characterization confirmed that the coating is the real thing. X-ray diffraction revealed the hallmark reflections of the MFI-type ZSM-5 framework, including the intense peak near 23 degrees two-theta, alongside weaker peaks at 38.1 and 44.8 degrees corresponding to face-centered cubic metallic silver. Nitrogen adsorption measurements showed a Type I isotherm typical of microporous materials, with an exceptionally high BET surface area of about 474 square meters per gram, a pore volume of 0.26 cubic centimeters per gram and an average pore diameter of 2.24 nanometers. Scanning and transmission electron microscopy captured the classic coffin-shaped micron-sized ZSM-5 crystals, roughly 1.21 micrometers across, deposited as a thin, homogeneous film of one to five percent by weight on the steel.

Perhaps the most important structural finding is that silver was incorporated into the zeolite framework rather than simply sprinkled on top. Diffuse reflectance ultraviolet-visible spectroscopy identified three distinct silver species: isolated Ag-plus ions absorbing near 210 nanometers, sub-nanometer silver clusters near 290 nanometers, and metallic Ag-zero nanoparticles showing a surface plasmon band at 418 nanometers. Fourier-transform infrared spectroscopy showed the preserved five-membered ring vibration at about 545 wavenumbers, while shifts in the silicon-oxygen and aluminum-oxygen stretching region between 970 and 1220 wavenumbers pointed to genuine isomorphous substitution. Energy-dispersive X-ray mapping confirmed silver at 1.03 percent by weight, uniformly distributed alongside silicon, aluminum, oxygen and sodium throughout the crystals.

On the coated implant, elemental mapping told an equally encouraging story. Signals from iron, chromium and nickel revealed the underlying alloy, while silver, silicon, oxygen and aluminum confirmed a continuous zeolite layer above it. Because the coating is thin, the electron beam still interacts with the substrate, indicating intimate contact between the two. The researchers argue that this uniform integration matters biologically: silver locked into the framework leaches slowly and evenly, avoiding the concentration spikes that plague surface-deposited nanoparticles, while the microporous architecture can wick up biological fluids and improve interactions between the implant and surrounding tissue.

Corrosion testing in a brutal acidic chloride bath, one molar sodium chloride at pH 1.0, showed the coating earning its keep. Bare stainless steel started with a corrosion current density of 0.014 amperes per square centimeter, which climbed to 0.046 within days as chloride ions attacked the passive chromium oxide film. The Ag-Zeo coated samples moved in the opposite direction, with corrosion current falling from 0.03 to 0.021 amperes per square centimeter over five days of immersion, a sign that the coating-substrate interface was stabilizing rather than degrading. Electrochemical impedance spectroscopy reinforced the picture, showing larger semicircles and higher charge-transfer resistance for coated samples, consistent with a barrier that limits ion diffusion to the metal.

The drug delivery results may be the most clinically provocative. Cisplatin, a platinum-based chemotherapy used against osteosarcoma and other cancers, was loaded into the zeolite with an encapsulation efficiency of 88 percent and a loading capacity of 4.4 percent. When the loaded coating was tested across a pH gradient, it behaved like a smart material. At pH 5.6, which mimics the acidic microenvironment of bone tumors, cumulative cisplatin release climbed steadily to about 15 percent over 72 hours. At physiological pH 7.4, release was slower, reaching only about 10 percent in the same period. Crucially, the profile showed gradual, sustained liberation rather than the dangerous burst release common to many polymer carriers, a behavior the team attributes to host-guest interactions inside the zeolite channels and to a synergistic effect between silver and the platinum complex.

Antifungal performance rounded out the platform’s credentials. Implant-associated Candida albicans infections are notoriously difficult to treat because the fungus builds resilient biofilms that resist azoles, polyenes and other standard drugs. In adhesion assays using Candida albicans ATCC 14053, surfaces treated with Ag-Zeo at 16 milligrams per milliliter showed dramatically fewer adherent, viable fungal cells than untreated surfaces or surfaces treated with zeolite alone, which performed no better than the control. That comparison isolates silver as the active agent, delivered steadily from its zeolite host. The authors point to the established mechanisms of silver action, including reactive oxygen species generation, oxidative and nitrosative stress, membrane disruption and interference with microbial proteins and DNA, all sustained by the controlled ion release that the framework provides.

Taken together, the study sketches a next-generation implant surface that is simultaneously protective, therapeutic and antimicrobial, all from a clay-derived, template-free synthesis that the researchers describe as a sustainable strategy for implant coating technology. The work remains at the laboratory stage, and questions of long-term biocompatibility, mechanical wear and silver dosing in living patients will need to be answered before clinical translation. But the concept, a single green coating that resists corrosion, fights fungal colonization and dispenses chemotherapy on demand in response to tumor acidity, offers a compelling glimpse of where biomaterials engineering is heading: away from passive hardware and toward implants that actively participate in their own defense and in the treatment of the diseases that put them there.

Subject of Research: A green-synthesized silver-integrated ZSM-5 zeolite coating on AISI 316 L stainless steel implants for corrosion resistance, controlled cisplatin delivery and antifungal activity

Article Title: Sustainable silver-integrated ZSM-5 coating on AISI 316 L implants: a multifunctional platform for controlled cisplatin delivery and antifungal activity

Article References: Sustainable silver-integrated ZSM-5 coating on AISI 316 L implants: a multifunctional platform for controlled cisplatin delivery and antifungal activity. (n.d.). https://doi.org/10.1007/s44442-026-00108-3

Image Credits: AI Generated

DOI: 10.1007/s44442-026-00108-3

Keywords: zeolite coating, ZSM-5, silver nanoparticles, AISI 316L stainless steel, cisplatin delivery, antifungal activity, Candida albicans, corrosion resistance, hydrothermal synthesis, metakaolin, drug release, biomaterials