The material, dubbed CS@UiO-66-NH2@rGO, is assembled in a two-stage process. First, chitosan, a natural polysaccharide derived from crustacean shells, is combined with reduced graphene oxide and shaped into beads, which are then solidified. Second, the team grows the metal-organic framework UiO-66-NH2 directly on the beads through an in situ solvothermal treatment, in which the framework crystallizes from its molecular building blocks while anchored to the bead surface. The result is a millimeter-scale bead with a deliberately rough, hierarchical surface texture rather than a smooth exterior. That texture matters, because the researchers found that scanning electron microscopy, rather than gas-adsorption measurements alone, revealed an enlarged interfacial region where polystyrene particles could actually make contact and stick.

The nitrogen-accessible Brunauer-Emmett-Teller surface area of the finished beads came in at 298.76 square meters per gram, a figure that reflects the porous framework grown throughout the composite. Yet the authors are careful to distinguish between surface area measured by nitrogen adsorption and the effective contact area available to micron-scale polystyrene particles, which are far too large to enter most of the framework’s internal pores. This is a subtle but important point in microplastic adsorption science: what matters most is not the total internal surface but the external, accessible architecture. The rough, corrugated morphology of the beads multiplies the real-world contact area, letting particles wedge into crevices and lodge against the composite surface, a mechanism the researchers term roughness-assisted retention.

Performance figures from the study are striking. Under the selected experimental conditions, the beads removed 97.6 plus or minus 0.6 percent of polystyrene particles from solution and achieved an adsorption capacity of 390.4 milligrams of polystyrene per gram of adsorbent, approaching equilibrium in roughly 45 minutes. That combination of speed and capacity places the material among the more effective adsorbents reported for polystyrene capture, and the bead format itself solves a practical problem that has long plagued nanoscale adsorbents: fine powders are efficient but difficult to separate from treated water, whereas millimeter-scale beads can be retrieved by simple physical means and reused.

To understand how the beads capture their quarry, the team fitted their kinetic data to the two workhorse adsorption models. At the standard test temperature of 303 kelvin, the constrained pseudo-first-order model described the data better than the pseudo-second-order model, yielding root-mean-square errors of 15.66 and 20.71 milligrams per gram respectively. Importantly, the authors note that both models face boundary limitations and that neither consistently outperformed the other across the full temperature range investigated, a candid acknowledgment that kinetic model selection in adsorption studies is often less clear-cut than a single R-squared value might suggest. For equilibrium behavior, nonlinear Langmuir fitting based on four quantifiable data points at 303 kelvin yielded a maximum adsorption capacity of 506.24 milligrams per gram, with a coefficient of determination of 0.9840, indicating a favorable, saturable uptake process.

Durability and real-world robustness were tested as well. After six consecutive adsorption-desorption cycles, the beads still removed 91.8 plus or minus 1.1 percent of polystyrene, demonstrating that the capture interface survives repeated regeneration without collapsing. Perhaps more telling, when the researchers spiked natural-water matrices with polystyrene, the beads maintained removal efficiencies above 82 percent, suggesting that dissolved organic matter, ions and other natural constituents do not catastrophically poison the adsorption sites. For any water-treatment technology, performance in clean laboratory water is easy; holding up in actual environmental water is the harder test that many candidate materials fail.

Beyond simple physical sticking, the composite carries an optoelectronic dimension. Incorporating reduced graphene oxide narrowed the apparent band gap of the material to 2.56 electronvolts, bringing it into the visible-light range. Photoluminescence measurements showed suppressed emission, photocurrent response was enhanced, and electrochemical impedance spectroscopy revealed a reduced Nyquist semicircle diameter. Taken together, these signatures are consistent with a visible-light-responsive interface in which charge carriers separate more efficiently and transfer across the composite junction more readily. In other words, when light strikes the beads, the UiO-66-NH2 and reduced graphene oxide components act as a coupled system for moving electrons, a property more commonly exploited in photocatalysis than in microplastic capture and one that could open avenues for coupling adsorption with light-driven degradation of captured particles in future work.

The researchers propose a multicomponent capture mechanism rather than a single dominant interaction. Polystyrene particles adhere to the external bead surface through hydrophobic interactions and pi-related interactions, the latter arising between the aromatic rings of polystyrene and the graphitic domains of reduced graphene oxide as well as the organic linkers of the framework. Dispersion forces contribute universally, while the corrugated topography physically entraps particles that settle into surface depressions. Electrostatic attraction may also play a role under acidic conditions, specifically at pH values below the isoelectric point of the material, when surface charges reverse and favor attraction to negatively charged polystyrene particles. This layered mechanistic picture helps explain why the beads perform well across varied water chemistries: if one interaction weakens under a given condition, others remain to hold the particles in place.

The work sits within a fast-growing research frontier exploring metal-organic frameworks as microplastic scavengers. Zirconium-based frameworks such as UiO-66 and its amine-functionalized variant are prized for their exceptional chemical and thermal stability, and earlier studies have shown that amine modification and hydrogel integration can enhance adsorption performance. Other groups have pursued ZIF-67 frameworks, magnetic carbon nanotubes, quaternary-ammonium-modified biochars and cellulose nanofiber aerogels for the same task, each with trade-offs between capacity, recyclability and ease of separation. The chitosan scaffold is a strategic choice here: it is abundant, biodegradable and readily forms beads, while its amine-rich chemistry coordinates well with the zirconium nodes of the growing framework, producing the intimate interface that the optoelectronic measurements probe.

The study was funded by Malaysia’s Ministry of Higher Education through the Higher Institution Centre of Excellence program, along with a Universiti Malaya Matching Grant and a Fundamental Research Grant Scheme award, and was published online on 18 October 2026 after acceptance in late September. Whether such beads can be scaled from beaker to treatment plant remains the defining question for the field, and the authors frame their material as a reusable platform for rapid polystyrene capture coupled with a photoresponsive interface rather than a finished remediation solution. Still, the combination of near-complete removal, sub-hour equilibration, six-cycle reuse, tolerance of natural waters and a light-active surface gives this hydrogel bead an unusually complete portfolio of traits. As microplastic contamination continues its march through the global water cycle, materials that can grab plastic particles quickly, hold them securely and come back for more will be in steadily rising demand.

Subject of Research: Recoverable chitosan-MOF-reduced graphene oxide hydrogel beads for capturing polystyrene microplastics from water

Article Title: Recoverable CS@UiO-66-NH2@rGO hydrogel beads for efficient capture of polystyrene microplastics with a visible-light-responsive interface

Article References: Li, Y., Zhang, S. Y., Xiang, P., Lai, C. W., & Chang, C. J. (2026). Recoverable CS@UiO-66-NH2@rGO hydrogel beads for efficient capture of polystyrene microplastics with a visible-light-responsive interface. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13897-0

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13897-0

Keywords: microplastics, polystyrene, hydrogel beads, chitosan, metal-organic framework, UiO-66-NH2, reduced graphene oxide, water treatment, adsorption, visible-light response, photocatalysis, environmental remediation

The environmental problem the team targeted is both persistent and growing. Mining, processing, and industrial use of rare earth elements generate acidic leachate streams and tailings laden with dissolved lanthanide ions. When discharged untreated, these effluents contaminate groundwater, surface water, and marine ecosystems. Yet the same streams represent an opportunity: recovering rare earths from industrial process water, acid mine drainage, and electronic waste leachates offers a double dividend, cutting pollution while reclaiming strategically valuable materials. Conventional treatment routes such as chemical precipitation, ion exchange, solvent extraction, and membrane filtration all carry limitations in cost, selectivity, or performance in dilute solutions, which is why adsorption has long been viewed as the most promising alternative.

Metal-organic frameworks, or MOFs, have changed the calculus for adsorption chemistry. These materials consist of metal clusters connected by organic linkers into porous, crystalline lattices with surface areas that can reach thousands of square meters per gram, far exceeding conventional adsorbents like activated carbon, zeolites, and clays. Among the most studied families is UiO-66, a zirconium-based framework prized for exceptional chemical, thermal, and mechanical stability in water. The researchers in this work went a step further by incorporating amine groups into the framework, replacing the standard terephthalic acid linker with 2-aminoterephthalic acid. The lone electron pairs on nitrogen atoms can interact directly with lanthanum ions, adding a chemical binding dimension on top of simple pore-based capture.

Synthesis of the material followed a solvothermal route. Zirconium chloride and 2-aminoterephthalic acid were dissolved in dimethylformamide, acetic acid was added as a modulator, and the mixture was heated at 120 degrees Celsius for 16 hours. The resulting powder was washed and vacuum-dried. X-ray diffraction confirmed a highly crystalline structure with characteristic peaks matching the known UiO-66-NH2 pattern, while field-emission scanning electron microscopy revealed multimodal spherical particles averaging below 200 nanometers in size, though with some aggregation. Nitrogen adsorption measurements yielded a Brunauer-Emmett-Teller surface area of 682 square meters per gram, a dominant pore size of 1.79 nanometers, and a pore volume of 0.27 cubic centimeters per gram, values consistent with the 600 to 1,200 square meter per gram range reported in the literature for this material family.

To find the best operating conditions, the team turned to response surface methodology, specifically a Box-Behnken design. Thirteen experimental trials varied adsorbent dosage and contact time, and a quadratic polynomial model was fitted to the removal data. Analysis of variance confirmed the model was statistically significant, with an F-value of 6.44 and a p-value of 0.0149. The adsorbent dose emerged as the dominant factor, while the coefficient of determination reached 0.82, explaining most of the variability in lanthanum removal. The statistical exercise converged on an optimal recipe: 10 milligrams of adsorbent per 10 milliliters of solution, a pH of 9, and 150 minutes of contact time.

The influence of pH proved particularly revealing. As pH rose from 3 to 7, lanthanum removal actually fell from 98.5 percent to 75.21 percent. The explanation lies in acid-base chemistry at the adsorbent surface: in acidic conditions, the amine groups accept protons and become positively charged, while hydrogen ions compete directly with lanthanum for binding sites. Above pH 7, the picture reverses. The framework surface becomes negatively charged, electrostatic attraction between the surface and the positively charged trivalent lanthanum ions strengthens, and removal efficiency climbs, peaking at pH 9. Adsorbent dosage showed a similar decisive effect, with removal rising from 64 percent to 99.86 percent as the dose increased from 3 to 10 milligrams, reflecting the growing availability of active sites.

Modeling the equilibrium and kinetics of the process provided mechanistic insight. The Freundlich isotherm, which describes multilayer adsorption on heterogeneous surfaces, fit the data better than the Langmuir model, with an R-squared value of 0.9986 and a heterogeneity coefficient of 1.98 indicating favorable adsorption. The Langmuir fit still yielded a maximum capacity of 312.5 milligrams per gram, placing UiO-66-NH2 well above most conventional adsorbents reported for lanthanum, including magnetic clay composites at around 111 milligrams per gram and silica xerogels at under 7. Kinetic analysis showed the pseudo second-order model best described the uptake, with an R-squared of 0.9971, suggesting that chemisorption, the formation of chemical bonds through electron exchange, is the rate-limiting step rather than simple mass transfer.

The Weber-Morris intraparticle diffusion model added a final layer of understanding. The plot produced a single linear line across the entire time interval examined, with a diffusion rate constant of 7.14 milligrams per gram per minute to the one-half power and a positive intercept of 12.8 milligrams per gram. The non-zero intercept indicates that intraparticle diffusion is not the sole rate-limiting factor; boundary-layer resistance and external mass transfer also contribute. Crucially, the absence of multiple linear segments means no transition between diffusion regimes occurred during the experiment, pointing to a single, consistent mass-transfer mechanism governing the process from start to finish.

Perhaps the most compelling demonstration came in seawater, a brutally competitive environment for any adsorbent. Spiked with 100 parts per million of lanthanum, real seawater contains roughly 9,000 parts per million of sodium ions and 1,000 parts per million of magnesium ions, both of which could theoretically crowd out the target metal. Yet when 10 milligrams of UiO-66-NH2 were added and the mixture agitated for 150 minutes, inductively coupled plasma mass spectrometry showed the material captured 87.5 percent of the lanthanum while taking up only 1.1 percent of sodium and 0.5 percent of magnesium in the first cycle. Over five sequential adsorption and acid-elution cycles, lanthanum recovery declined only modestly to 85 percent, while competing ion uptake rose to just 3.2 percent for sodium and 2.2 percent for magnesium.

The authors attribute this selectivity and capacity to two factors working in concert: the microporous architecture with its substantial surface area and pore volume, and the electrostatic and coordinative interaction between electronegative nitrogen atoms in the linkers and the trivalent lanthanum ions. Because lanthanum concentrations in real contaminated waters are typically far lower than those of coexisting cations, the framework’s preference for lanthanum over sodium and magnesium is exactly the property a practical separation technology requires. The researchers suggest that this class of amine-functionalized zirconium MOFs could be extended to remove heavy metals and rare earth elements from seawater and industrial streams alike, turning a stubborn pollution problem into a source of recoverable strategic materials.

Subject of Research: Amine-functionalized zirconium metal-organic framework adsorbent for lanthanum removal from water

Article Title: Amine-terminated zirconium metal-organic framework as an efficient adsorbent for lanthanum removal

Article References: Saranya, J., Ramesh, S., Kumar, R. T. R., & Haldorai, Y. (2026). Amine-terminated zirconium metal-organic framework as an efficient adsorbent for lanthanum removal. Frontiers in Materials, 13, Article 1944659. https://doi.org/10.3389/fmats.2026.1944659

Image Credits: AI Generated

DOI: 10.3389/fmats.2026.1944659

Keywords: metal-organic frameworks, UiO-66-NH2, lanthanum, rare earth elements, adsorption, water treatment, response surface methodology, Freundlich isotherm, adsorption kinetics, seawater selectivity, zirconium MOF, heavy metal removal

The research team, led by Khadega A. Al-Maqdi of UAE University together with colleagues at Khalifa University, the University of Arkansas at Little Rock, and collaborators, chose horseradish peroxidase (HRP) for good reason. Peroxidases are oxidoreductase enzymes that use hydrogen peroxide to oxidize a broad range of substrates, and HRP in particular has long attracted attention for water remediation because of its high catalytic efficiency and selectivity. The catch is operational: free enzymes in solution are fragile, difficult to recover, and quickly lose activity under the temperature swings, pH extremes, and oxidative conditions of real treatment scenarios. Poor reusability drives up cost and has largely confined enzyme-based remediation to the laboratory. Immobilization on a solid support is the standard remedy, and the nature of that support can make or break the technology.

The support selected here was UiO-66-NH2, a zirconium-based metal–organic framework (MOF) built from zirconium chloride and 2-aminoterephthalic acid. MOFs are crystalline, highly porous materials in which metal ions or clusters are coordinated to organic linkers, producing enormous internal surface areas and tunable pore architectures. UiO-66-NH2 brings additional advantages: the strong zirconium–oxygen coordination bonds confer exceptional structural and aqueous stability, while pendant amino groups on the linkers promote hydrogen bonding and electrostatic interactions at the enzyme–MOF interface, helping the protein adhere and remain stable. Immobilization was deliberately simple and gentle. Five milligrams of the MOF were dispersed in solutions of HRP at concentrations ranging from 0.5 to 4 milligrams per milliliter, shaken for four hours, and then collected by centrifugation and washed to remove unbound enzyme. This physical adsorption approach preserves the enzyme’s native structure better than covalent coupling or crosslinking, at the cost of a need to verify that the protein does not leach away.

Optimization experiments showed that relative activity rose as the HRP loading concentration increased from 0.5 to 1 milligram per milliliter but plateaued beyond that point, indicating that the MOF had reached its maximum uptake capacity at 1 milligram per milliliter, which was used for all subsequent work. Leaching tests addressed the Achilles heel of physical immobilization: after the first wash, minimal enzyme was detected in the wash solution, and after the second wash no unbound HRP appeared in the supernatant at all, confirming that the enzyme was effectively anchored. The composite was then subjected to a battery of characterization techniques. Scanning electron microscopy revealed that the MOF crystallized as ball-shaped particles whose morphology was unchanged by enzyme loading, while energy-dispersive X-ray spectroscopy detected increases in the carbon, nitrogen, and oxygen signals after immobilization, consistent with protein incorporation. Powder X-ray diffraction showed that the characteristic diffraction peaks of the framework survived intact, and thermogravimetric analysis revealed an additional low-temperature weight loss in the composite attributable to protein decomposition, further evidence of successful binding.

Brunauer–Emmett–Teller surface area measurements added a telling detail. The bare MOF had a surface area of 256.27 square meters per gram, which dropped to 207.33 square meters per gram after enzyme loading, with pore volume falling from 0.17 to 0.14 cubic centimeters per gram. Both materials displayed Type I nitrogen adsorption isotherms, indicating predominantly microporous character. The reduction suggests that HRP molecules partially blocked the framework’s pores, a pattern seen repeatedly in other enzyme–MOF systems such as laccase on MIL-53(Al) and beta-lactamase on ZIF-8. Fourier-transform infrared spectroscopy told a complementary story: the amide I and amide II bands characteristic of the protein’s peptide bonds overlapped with the framework’s own absorptions in the 1500 to 1700 per centimeter region, producing broadened signals without shifts or signs of framework degradation. Together the data confirmed that immobilization neither destroyed the MOF’s crystallinity nor its thermal stability, which persisted up to roughly 350 to 400 degrees Celsius.

Functional testing revealed that immobilization did more than just fix the enzyme in place; it changed its operating envelope. Both free and immobilized HRP performed best at pH 4, with a narrow operational window from pH 3 to 5, but the immobilized enzyme showed roughly 30 percent higher activity than the free enzyme at pH 3, hinting at improved stability or substrate accessibility under acidic conditions. More striking was the temperature shift: free HRP peaked at 30 degrees Celsius, while HRP@UiO-66-NH2 reached maximum activity at 40 degrees and outperformed the free enzyme by around 10 percent or more at 50 and 70 degrees. The peroxide story was equally significant. Free HRP achieved maximum activity at about 0.72 millimolar hydrogen peroxide and then declined sharply, because excess peroxide drives the enzyme’s heme into irreversibly inactive species. The immobilized enzyme peaked at 1.08 millimolar and retained substantial activity at 1.62 and 2.43 millimolar, indicating that the framework shields the protein from oxidative damage and restricts the conformational changes that lead to heme destruction.

Reusability, the economic linchpin of any immobilized enzyme, proved robust. Over four consecutive reaction cycles, HRP@UiO-66-NH2 retained approximately 95 percent of its initial activity, with a decline to around 60 percent only in the fifth cycle, likely from leaching or denaturation. The authors are careful to note, however, that post-use characterization was not performed, so retained catalytic activity demonstrates functional reusability but does not directly prove that the framework’s crystallinity and morphology survived the cycles; future work combining post-cycle diffraction, spectroscopy, microscopy, and leaching measurements is needed to distinguish enzyme deactivation, mass-transfer limitations, and possible structural changes in the MOF.

The real test came with pollutants. The team challenged the biocatalyst with a mixture of nine structurally diverse emerging pollutants detected in water sources across China, the United Arab Emirates, Poland, and Brazil: 2-mercaptobenzothiazole (a rubber-industry chemical), paracetamol, the antibiotic sulfamethoxazole, the preservative methylparaben, salicylic acid, the antibiotic lincomycin hydrochloride, the beta-blocker atenolol, the fungicide thiabendazole, and the insect repellent DEET. Degradation was quantified by liquid chromatography–tandem mass spectrometry in multiple-reaction-monitoring mode, a sensitive approach that tracks the disappearance of each compound’s characteristic molecular transitions. Within 30 minutes, HRP@UiO-66-NH2 degraded 99.7 percent of 2-mercaptobenzothiazole and 97.4 percent of paracetamol, while the remaining pollutants were removed far less efficiently, a pattern consistent with earlier reports that certain peroxidases struggle with specific substrates, possibly because of competition or inhibition within the mixture rather than inherent inability.

That gap is where redox mediators enter the picture. The team added 1-hydroxybenzotriazole (HOBT), a small molecule that HRP oxidizes to a reactive species capable of transferring oxidative equivalents to pollutants that interact poorly with the enzyme’s active site. The effect was dramatic and pollutant-dependent. Degradation of sulfamethoxazole rose from 23.3 to 53.1 percent, methylparaben from 14.5 to 57.6 percent, and salicylic acid from 12.4 to 54.3 percent, while MBT and paracetamol, already nearly eliminated, showed no further change, and thiabendazole, lincomycin, and atenolol remained largely untouched. Comparisons with free HRP added nuance: free enzyme plus HOBT pushed sulfamethoxazole degradation to 80.2 percent, roughly 30 percentage points higher than the immobilized version, possibly because minor conformational changes imposed by the support alter substrate selectivity. Yet the immobilized enzyme outperformed free HRP on DEET by more than 10 percent, encouraging for a notoriously recalcitrant compound. Unlike MOF-based adsorption, which merely accumulates pollutants on finite surface sites and requires regeneration, the enzyme–MOF composite catalytically transforms susceptible molecules through repeated oxidation cycles powered by hydrogen peroxide.

The authors are candid about limitations. The experiments were conducted in a controlled buffered model-water system, so performance may differ in real wastewater laden with organic matter, dissolved ions, and competing contaminants. Removal of a parent compound does not confirm complete mineralization or reduced toxicity, and transformation products were not identified, meaning the proposed mediator-assisted mechanisms remain plausible rather than proven pathways. Still, the study demonstrates that a zirconium MOF can simultaneously protect a fragile enzyme, extend its thermal and peroxide tolerance, enable four-cycle reuse, and, with a selectively applied redox mediator, broaden its reach across chemically diverse micropollutants. The researchers propose evaluating HRP@UiO-66-NH2 as a targeted polishing treatment for emerging pollutants, with mediators deployed according to pollutant-specific effects, and call for follow-up work on transformation products, toxicity before and after treatment, real-matrix performance, and scalability. If those hurdles are cleared, enzyme–MOF composites of this kind could move from the laboratory bench toward a genuine role in safeguarding drinking water.

Subject of Research: Immobilization of horseradish peroxidase on the metal–organic framework UiO-66-NH2 for enzymatic degradation of emerging water pollutants

Article Title: Efficient enzyme-mediated degradation of various emerging pollutants, including 2-mercaptobenzothiazole, paracetamol, and sulfamethoxazole, using HRP@UiO-66-NH2

Article References: Al-Maqdi, K. A., Alneyadi, S., Elmerhi, N., Siddig, L. A., Alzamly, A., Shah, I., & Ashraf, S. S. (2026). Efficient enzyme-mediated degradation of various emerging pollutants, including 2-mercaptobenzothiazole, paracetamol, and sulfamethoxazole, using HRP@UiO-66-NH2. Environmental Science and Pollution Research. https://doi.org/10.1007/s11356-026-38269-8

Image Credits: AI Generated

DOI: 10.1007/s11356-026-38269-8

Keywords: horseradish peroxidase, UiO-66-NH2, metal–organic framework, enzyme immobilization, emerging pollutants, water remediation, bioremediation, redox mediator, HOBT, sulfamethoxazole, paracetamol, LC–MS/MS

Xylanase itself is a fascinating target. The enzyme, classified as endo-1,4-beta-xylanase (EC 3.2.1.8), specifically attacks xylan, the complex polysaccharide that ranks as the second most abundant polymer in nature after cellulose and forms a major structural component of plant cell walls. By cutting the beta-1,4-glycosidic bonds threaded through xylan chains, the enzyme releases xylose and xylooligosaccharides, sugars with enormous commercial value. Xylanases are sorted by the carbohydrate-active enzymes database into glycoside hydrolase families, with GH10 and GH11 by far the best characterized; their members differ subtly in substrate specificity, catalytic mechanism, and optimal operating conditions, which in turn shapes their industrial niches. In food processing, xylanases modify the water-binding behavior of bread dough, increasing loaf volume and improving crumb structure, while in animal feed they reduce the viscosity of non-starch polysaccharides to boost nutrient absorption. Beyond food, the same enzyme pre-bleaches kraft pulp in the paper industry and helps open up lignocellulosic biomass for bioethanol production.

The enzyme is sourced from an impressively diverse biological roster. Bacterial genera such as Bacillus, Streptomyces, and Clostridium produce xylanases prized for their thermal and pH robustness — Bacillus species in particular yield thermostable variants suited to high-temperature processing. Fungal producers, including Aspergillus, Trichoderma, and Penicillium, dominate food and feed applications thanks to their efficiency at degrading complex xylans. Plants make xylanases during germination and fruit ripening, and certain herbivorous insects and termites harbor gut microbes that degrade plant cell walls with the enzyme’s help, though plant and animal sources remain marginal industrially. Recombinant DNA technology now allows xylanase genes to be cloned and expressed in hosts such as Escherichia coli and Pichia pastoris, multiplying yields far beyond what natural fermentation achieves. Even so, free enzymes remain fragile in industrial reactors, which is precisely where immobilization — attaching the enzyme to a solid support — enters the picture, a concept dating back to 1916 when charcoal-embedded invertase was first shown to hydrolyze sucrose.

Metal-organic frameworks emerged in the late 1990s as a new class of crystalline solids built from metal ions or clusters coordinated to organic linkers into extended, lattice-like networks. Their defining feature is porosity taken to an extreme: some MOFs boast surface areas exceeding 7000 square meters per gram, among the highest of any known material, offering a vast internal landscape for hosting guest molecules. Just as importantly, MOFs are programmable. By swapping metal nodes and organic struts, chemists can tune pore size, pore shape, and surface functionality with a precision unavailable to conventional carriers such as chitosan beads, alginate gels, or polyaniline films. Synthesis routes are equally varied, ranging from conventional hydrothermal heating under pressure to solvent-free mechanochemical grinding, electrochemical deposition on electrodes, and rapid microwave-assisted growth that produces highly crystalline particles in a fraction of the usual time.

For xylanase, the review highlights several standout MOF platforms. Manganese-doped ZIF-67, a zeolitic imidazolate framework, was used in a comparative study to immobilize xylanase via an in-situ method, with striking results. Encapsulated xylanase retained 85.7 percent of its activity after two hours at 70 degrees Celsius, while the free enzyme plummeted to 28.7 percent. Both the standard and manganese-doped versions kept more than 70 percent of their initial activity through eight consecutive reaction cycles, and the doped variant showed the highest substrate affinity. Functionalized UiO-66-NH2, a zirconium-based framework, served as the scaffold for co-immobilizing beta-xylosidase and endoxylanase, a pairing that maintained over 95 percent relative activity at 95 degrees Celsius in a 50 percent acetone solution and halved the enzyme’s Km value, indicating markedly improved substrate binding. A magnetic Fe3O4@polydopamine@MOF composite achieved protein loading of 80.67 milligrams per gram through multipoint interactions while tolerating both acidic and alkaline conditions.

The immobilization chemistry itself spans a spectrum of strategies, each with distinct trade-offs. Physical adsorption, the simplest approach, relies on weak van der Waals forces, hydrogen bonds, and electrostatic attraction to tether the enzyme to the MOF surface, preserving the protein’s native structure but risking gradual leaching into the product. Covalent bonding forms durable chemical links between amine, carboxyl, or thiol groups on the enzyme and complementary groups on the framework, essentially eliminating leaching at the cost of more elaborate preparation and occasional active-site interference. In-situ encapsulation is arguably the most elegant: enzyme molecules are trapped inside the growing MOF crystal as it assembles around them, creating a protective environment from which escape is nearly impossible. Covalent cross-linking with bifunctional reagents builds a stable enzyme network throughout the pores and across the surface, boosting resistance to harsh conditions. In one demonstration, beta-xylosidase cross-linked onto FeSO4-chitosan-encapsulated MOF microparticles retained 40 percent activity after ten reuse cycles and functioned at temperatures five degrees higher than the free protein, with double the activity at 70 degrees.

Real-world food applications are already validating the concept. A xylanase from a novel Bacillus pumilus strain, immobilized on the copper-based framework Cu-BTC, clarified pineapple and pomegranate juices with enhanced catalytic efficiency and remarkable durability, retaining 61 percent of its activity after 21 cycles. In apple juice trials, Xyl@ZIF-67 raised juice transmittance from 65.61 to 94.73 percent within an hour of treatment, while the manganese-doped version lifted it from 77.80 to 84.13 percent, simultaneously increasing reducing sugar content. Xylooligosaccharide production — a booming market for prebiotic ingredients that selectively nourish beneficial Bifidobacteria and Lactobacilli in the human gut — has proven equally receptive. The magnetic Fe3O4@PDA@MOF-xylanase system converted corncob xylan into xylooligosaccharides at a 23 percent yield, outperforming the free enzyme by a factor of 1.15, while a green-synthesized Xy-Cu-BTC composite achieved an 87.4 percent conversion yield, boosting xylopentose output and suppressing unwanted xylose formation to just 0.88 percent of the product mix.

Challenges remain, and the review does not gloss over them. Leaching persists whenever weak non-covalent interactions are disrupted by shifts in pH, ionic strength, or temperature. Mass-transfer limitations loom large because xylan is a bulky, high-molecular-weight polymer; if MOF pore apertures are too narrow, substrate chains simply cannot reach the immobilized active sites, dragging down reaction rates compared with free enzyme. Aqueous stability is a further concern, as water molecules can competitively displace organic linkers from metal centers, collapsing some frameworks — a problem researchers counter by turning to chemically robust series such as ZIF and MIL frameworks, which simultaneously act as a molecular corset restricting protein unfolding. Food safety adds a final layer of scrutiny: frameworks built from toxic metals such as chromium or cobalt risk contaminating food matrices, so current research favors biocompatible MOFs assembled from iron, zinc, or calcium nodes with Generally Recognized as Safe ligands such as amino acids or citric acid, validated by rigorous leaching assays in food-simulating solvents.

The path forward, the review concludes, lies in hierarchical pore engineering that integrates mesopores large enough for xylan polymers, a transition to aqueous green synthesis routes, and continuous-flow biocatalysis in packed-bed reactors for pulp, bioethanol, and food production. The economics, too, must balance out: MOF supports cost more upfront than silica or chitosan, a premium justified only if exceptional reusability and extended enzyme half-life reduce replacement frequency and simplify downstream recovery. With the immobilized enzyme market projected to reach USD 27.29 billion by 2031 at a compound annual growth rate of 9.45 percent, the commercial incentive to solve these problems is unmistakable. If MOF-encapsulated xylanase delivers on its laboratory promise at industrial scale, the crystal cages now being grown around this humble enzyme could quietly reshape how the world’s food — from breakfast juice to prebiotic supplements — is made.

Subject of Research: Metal-organic framework composites for xylanase enzyme immobilization and their applications in the food industry

Article Title: Metal organic framework composites for xylanase immobilization and their applications in food industry

Article References: Jana, U. K. (2026). Metal organic framework composites for xylanase immobilization and their applications in food industry. Discover Industrial Chemistry and Materials, 1(1), Article 9. https://doi.org/10.1007/s44508-026-00011-0

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00011-0

Keywords: metal-organic frameworks, xylanase, enzyme immobilization, biocatalysis, xylooligosaccharides, fruit juice clarification, ZIF-67, UiO-66-NH2, food safety, prebiotics, nanobiotechnology, food industry