Metal-Organic Framework Based on α-Cyclodextrin Gives High Ethylene Gas Adsorption Capacity and Storage Stability

Selective adsorption for dimethyl trisulfide to remove fish off-odors by edible calcium-based metal-organic frameworks: Structure, adsorption behavior, and removal mechanism

In this study, an edible calcium-based metal-organic frameworks (Ca-MOFs) were constructed to remove off-odors. The adsorption behavior and mechanisms of Ca-MOFs for various off-odors were evaluated using kinetic models, isotherms, molecular dynamics, and density functional theory. Compared with zeolite and aluminum oxide, Ca-MOFs exhibited superior adsorption capacity for fish odors, attributed to its plentiful COO- sites and unsaturated Ca2+ sites. Moreover, Ca-MOFs showed selective adsorption for dimethyl trisulfide (DMTS) with an adsorption rate of 97.3 %, surpassing other odors (42.4-84.7 %). Ca-MOFs can completely remove DMTS from surimi and also reduce the levels of aldehydes, alcohols, and heterocyclic substances. Hydrogen bonding and van der Waals forces were identified as the primary driving forces for five off-odors adsorption, with the additional involvement of weak coordination bonds in adsorption of DMTS and trimethylamine (TMA). Overall, this study offers a novel strategy for removing off-odors and broadening the potential applications of MOFs.

Sustained release of gaseous chlorine dioxide from alpha-cyclodextrin: An innovative method for strawberry preservation

The traditional method of generating chlorine dioxide (ClO2) involves reacting sodium chlorite with acid on-site, posing high safety risks of concentrated ClO2. This study encapsulates ClO2 molecules directly in α-cyclodextrin (α-CD) to form inclusion complexes (ClO2@α-CD). This approach enables stable storage and safe handling of gaseous ClO2, while its sustained-release property also provides long-term microbial inhibition. Fumigation with 0.25 g of ClO2@α-CD completely inhibited Aspergillus niger growth on potato dextrose agar (PDA). A 0.5 g dose reduced the 6-day decay incidence of A. niger-inoculated strawberries from 91.67 % (control) to 5.00 % and the severity from 58.75 % (control) to 1.25 %. In commercial storage simulations, 5 g of ClO2@α-CD reduced the natural incidence from 53.33 % (control) to 26.67 %, while preserving the weight, color, firmness, and total soluble solids (TSS)/titratable acidity (TA) ratio of strawberries. These findings suggest that ClO2@α-CD is a viable approach for controlling postharvest diseases and prolonging fruit shelf-life.

Eco-friendly one-pot hydrothermal synthesis of cyclodextrin metal-organic frameworks for enhanced CO2 capture

Polysaccharide-based metal-organic frameworks have attracted widespread attention due to their combination of the biocompatibility and flexibility of polysaccharides. Cyclodextrin are interesting bio-ligands in the construction of polysaccharide-based MOFs. Conventional methods for preparing cyclodextrin metal-organic frameworks (CD-MOFs) are often time-consuming and inefficient. In this study, cost-effective and environmentally friendly α- and β-CD-MOFs were successfully synthesized using a hydrothermal method, with optimized incubation time and solvent ratios. The materials were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and N₂ adsorption/desorption measurements. The CO₂ adsorption mechanism was also examined using Fourier transform infrared spectroscopy (FTIR). The results demonstrated excellent thermal and cycling stability of the materials. The CO₂ uptake capacities of α- and β-CD MOF-K were 10.8 and 11.2 cm3/g, respectively. Additionally, the CD-MOFs showed strong selectivity for CO₂ over N₂. Given the straightforward operational procedures, safety characteristics, and mild reaction conditions of CD-MOFs, it is reasonable to conclude that they are promising candidates for use as CO₂ adsorption materials.

Sustainable Active Packaging from On-Demand Degradable PLA/PBAT and Zn-Doped TiO2 Composites

Shelf life extendable packaging and ethylene scavenger technologies for climacteric fruits and vegetables have garnered much attention in recent years. These products effectively enable food quality to be maintained, ensure food safety, and prolong food storage life, which are key to helping reduce food waste. Current technologies - both in terms of academic research and broader commercial application - imply the use of chemicals that are of low activity, of high toxicity, or difficult to handle. Therefore, in this work, we prepared Zn-doped TiO2 photocatalysts, containing 0.1 and 2.0 mol % of Zn dopant (Zn 0.1% -TiO 2 and Zn 2% -TiO 2 ), through a simple sol-gel method, which were then applied to be used as ethylene scavenger fillers in the preparation of on-demand degradable active packaging. TiO2 particles were also prepared under identical conditions for comparison. The active composite film containing Zn 0.1% -TiO 2 was shown to be a better active packaging than the one containing TiO2 and was able to extend the shelf life of bananas for up to 8 days. In addition, the incorporation of Zn-doped TiO2 particles did not significantly compromise either the mechanical properties of the polymer composite film or change its degradation behavior; it slightly improved the thermal stability. Moreover, the active composite film could be degraded on demand by immersing it into a 3 M KOH solution - leading to almost complete polymer film degradation after 4 h at room temperature. The developed active packaging model is a very promising candidate and could serve for future optimization as sustainable active food packaging.

Native Cyclodextrin-Based Metal-Organic Frameworks (MOFs): Synthesis, Characterization, and Potential Applications in Food Industry

Metal-organic frameworks (MOFs) have become a highly usable system in various sectors because of their highly ordered structure and high porosity providing them with high storage capacity. However, their use is sometimes forbidden in the food industry due to the presence of some organic compounds which have undesirable effects. Cyclodextrins, which are considered GRAS (Generally Recognized as Safe) by the FDA, comes as a very good alternative to previously used compounds for the development of the MOFs to be used in the food packaging industry, especially in the packaging sector. The cyclodextrin MOF does possess edible, biocompatible, as well as biodegradable characteristics and due to these reasons, they have gained attention from researchers in the food industry. In this review, we focus on the recent advancements in the field of CD MOFs. We have emphasized the synthesis of these MOFs through different techniques, formations of their inclusion complex with bioactive compounds, and their characterization. Finally, we discussed the use of CD MOFs as carriers for various highly volatile bioactive compounds and their ability to increase the solubility and stability of these bioactive compounds.

A twofold interpenetrated three-dimensional barium(II) metal-organic framework constructed from 2,2'-[terephthaloylbis(azanediyl)]diacetate: synthesis, structure, dihydrogen bonding and spectroscopic properties

A new twofold interpenetrated 3D metal-organic framework (MOF), namely, poly[[μ-aqua-diaqua{μ4-2,2'-[terephthaloylbis(azanediyl)]diacetato}barium(II)] dihydrate], {[Ba(C12H10N2O6)(H2O)3]·2H2O}n, (I), has been assembled through a combination of the reaction of 2,2'-[terephthaloylbis(azanediyl)]diacetic acid (TPBA, H2L) with barium hydroxide and crystallization at low temperature. In the crystal structure of (I), the nine-coordinated BaII ions are bridged by two μ2-aqua ligands and two carboxylate μ2-O atoms to form a 1D loop-like Ba-O chain, which, together with the other two coordinated water molecules and μ2-carboxylate groups, produces a rod-like secondary building unit (SBU). The resultant 1D polynuclear SBUs are further extended into a 3D MOF via the terephthalamide moiety of the ligand as a spacer. Two intramolecular dihydrogen bonds (DHBs) between the imine H atoms and the arene H atoms contribute to maintaining the 3D structure. In the crystal, two independent MOFs interpenetrate each other, thereby producing a twofold interpenetrated 3D architecture with a 4-connected PtS-X topology. Intermolecular hydrogen bonding and π-π interactions contribute to the stability of the twofold interpenetrated 3D architecture. The noncovalent interactions in the coordination polymer (CP) were further investigated by Hirshfeld surface analysis and the results show that the prominent interactions are H...O (39.6%) and H...H (34.4%), as well as Ba...O (9.8%), contacts. The 3D CP (I) exhibits a fluorescence emission with a quantum yield of 0.134.

Metal-anchored oxidized starch-pullulan nanofiber films enhance ethylene adsorption and banana preservation

The development of novel strategies to control ethylene accumulation of fruit is crucial for improving food preservation and reducing spoilage-related losses. In this study, an oxidized starch-pullulan (OS-PUL) nanofiber films were prepared with silver, copper, and iron to control ethylene accumulation. The starch nanofiber film exhibited an average diameter of 96 nm at an OS-PUL concentration of 25 % (wt/wt). Adsorption test showed the maximum ethylene adsorption capacity (21.86 mg·m-2) of metal-nanofiber film with typical hierarchical microporous and mesoporous structure. Oxidized starch-pullulan-metal-nanofiber film extended the shelf life of bananas from 8 to 15 days by efficiently absorbing ethylene. This work will contribute to the development of innovative packaging materials with ethylene adsorption properties, which can help reduce food waste.

Gas Delivery Relevant to Human Health using Porous Materials

Gases are essential for various applications relevant to human health, including in medicine, biomedical imaging, and pharmaceutical synthesis. However, gases are significantly more challenging to safely handle than liquids and solids. Herein, we review the use of porous materials, such as metal-organic frameworks (MOFs), zeolites, and silicas, to adsorb medicinally relevant gases and facilitate their handling as solids. Specific topics include the use of MOFs and zeolites to deliver H2S for therapeutic applications, 129Xe for magnetic resonance imaging, O2 for the treatment of cancer and hypoxia, and various gases for use in organic synthesis. This Perspective aims to bring together the organic, inorganic, medicinal, and materials chemistry communities to inspire the design of next-generation porous materials for the storage and delivery of medicinally relevant gases.

Cyclodextrin in drug delivery: Exploring scaffolds, properties, and cutting-edge applications

Cyclodextrins (CDs) are unique cyclic compounds that can form inclusion complexes via host-guest complexation with a wide range of molecules, thereby altering their physicochemical properties. These molecules offer the formation of inclusion complexes without the formation of covalent bonds, making them suitable for a variety of applications in pharmaceutical and biomedical fields. Due to their supramolecular host-guest properties, CDs are being utilized in the fabrication of biomaterials, metal-organic frameworks, and nano-drug carriers. Additionally, CDs in combination with biomolecules are biocompatible and can deliver nano to macromolecules at the site of drug actions. However, the availability of free hydroxyl groups and a simple crosslinking process for supramolecular fabrication show immense opportunities for researchers in the field of tissue engineering and biomedical applications. In this review article, we have covered the historical development, various types of chemical frameworks, unique chemical and physical properties, and important applications of CDs in drug delivery and biomedical sciences.

Symmetry-Breaking and Symmetry-Retaining Morphological Evolution of the Single Crystals of Cyclodextrin Metal-Organic Frameworks

The morphological symmetry-retaining and symmetry-breaking of single crystals of the γ-cyclodextrin metal-organic framework have been achieved via introducing lower symmetric β-cyclodextrins and α-cyclodextrins, respectively. β-cyclodextrins led to a morphological evolution with retained symmetry from cubic to rhombic dodecahedra, while α-cyclodextrins resulted in the original cubic crystal missing a vertex angle presenting symmetry-breaking behavior. The crystal structures of rhombic dodecahedra and angle-deficient crystals were confirmed through X-ray crystallography, and the mechanisms underlying the morphological transformation evolution were further analyzed. Our work not only provides a rare case realizing two different paths of morphological evolution in one system, but also encourages future efforts towards the evolution of artificial crystal systems in a natural way.

Supramolecular Metal-Organic Framework for the High Stability of Aqueous Rechargeable Zinc Batteries

Aqueous rechargeable Zn batteries (AZBs) are considered to be promising next-generation battery systems. However, the growth of Zn dendrites and water-induced side reactions have hindered their practical application, especially with regard to long-term cyclability. To address these challenges, we introduce a supramolecular metal-organic framework (SMOF) coating layer using an α-cyclodextrin-based MOF (α-CD-MOF-K) and a polymeric binder. The plate-like α-CD-MOF-K particles, combined with the polymeric binder create dense and homogeneous Zn2+ ion conductive pore channels that can vertically transport Zn2+ ions through the cavity while restricting the contact of water molecules. Molecular dynamics (MD) simulation verifies that Zn2+ ions can reversibly migrate through the pores of α-CD-MOF-K by partial dehydration. The uniform Zn deposition/dissolution promotes a smooth solid-electrolyte interface layer on the Zn metal anode and effectively suppresses side reactions with free water molecules. The α-CD-MOF-K@Zn symmetric cell exhibits stable cycling and a small polarization voltage of 70 mV for 800 h at 5 mA cm-2, and the α-CD-MOF-K@Zn|α-MnO2 full cell shows only 0.12% capacity decay per cycle at a rate of 1 A g-1.

Purification of gamma-cyclodextrin via selective coordination with potassium ions to form metal-organic frameworks

Efficient purification of gamma-cyclodextrin (γ-CD) is always challenging due to its structural similarity to other CDs and low crystallinity in water. In addressing this issue, an approach was proposed based on the formation mechanism of cyclodextrin metal-organic frameworks (CD-MOFs). This method involved the selective coordination of CDs mixture with potassium ions in water, facilitated by ethanol-induced crystallization, leading to the purification of γ-CD. The results showed that potassium ions enhanced γ-CD crystallization, and ethanol was crucial to selectively coordinating potassium ions with γ-CD. The characterizations revealed that the resulting CD-MOFs exhibited a small particle size, high surface area, and high thermal stability, and was identical to γ-CD-MOF, further indicating the final γ-CD with high purity. The separation factors of γ-CD/α-CD and γ-CD/β-CD were 309 and 260, respectively. Moreover, this method was validated through its application to the industrial enzymatic CDs mixture. The purification of γ-CD could achieve 99.99 ± 0.01 % after four crystallization cycles. Therefore, selectively coordinating with potassium ions to form MOFs provided a valuable reference for the purification of γ-CD and even the direct synthesis of γ-CD-MOF from CDs mixture. This advancement will also benefit the future production and application of γ-CD.

Lutein Loaded in β-Cyclodextrin Metal-Organic Frameworks for Stability and Solubility Enhancements

Lutein (Lut) is a recognized nutritional supplement known for its antioxidative and anti-inflammatory properties, crucial in mitigating ocular disease. However, enhancements to Lut stability and solubility remain challenges to be addressed in the healthcare industry. Herein, we fabricated and evaluated a food-grade highly porous β-cyclodextrin metal-organic framework (β-CD-MOF) for its ability to encapsulate Lut. Lut stability considerably improved when loaded into β-CD-MOF to form a Lut@β-CD-MOF complex, which exhibited better stability than Lut loaded into the γ-cyclodextrin metal-organic framework (Lut@γ-CD-MOF), Lut@β-CD, and commercial product (Blackmores™) at 40°C, 60°C, and 70°C, respectively. The solubility of Lut@β-CD-MOF in water increased by 26.8-fold compared to raw Lut at 37°C. Lut@β-CD-MOF exhibited greater hydrophilicity, as determined by measuring the water contact angle. Molecular docking and other characterizations of Fourier transform infrared spectroscopy and powder X-ray diffraction confirmed that Lut was successfully encapsulated in the chamber formed by the three cyclodextrins in β-CD-MOF. Thermogravimetric analysis and Raman spectroscopy demonstrated that Lut distributed in the β-CD-MOF cavity deeply improved Lut stability and solubility. In conclusion, our findings underscored the function of β-CD-MOF in enhancing Lut stability and solubility for formulation applications.

An O/N/S-rich porous Fe-based metal-organic framework (MOF) for gold recovery from the aqueous phase with excellent performance

Recovering gold from wastewater has both economic and environmental benefits. However, how to effectively recover it is challenging. In this work, a novel Fe-based metal-organic framework (MOF) was synthesized and decorated with 2,5-thiophenedicarboxylic acid to have a well-developed porous architecture to effectively recover Au(III) from water. The maximum Au(III) sorption capacity by the finally-synthesized porous material MIL-101(Fe)-TDCA reached 2350 mg/g at pH = 6.00 ± 0.15, which is one of the highest among all literature-reported relevant materials including MOFs, and high sorption strength can be maintained within a wide pH range from 2.0 to 10.0. Besides, Au(III) sorption efficiency at low concentrations (i.e., 3.5 × 104 mg/mL) reached over 99%. Mechanically, outstanding Au(III) sorption by MIL-101(Fe)-TDCA resulted from the O/N/S-containing moieties on its surface, large surface area and porosity. The N- and S-containing functionalities (CS, CONH) served as electron donors to chelate Au(III). The O-containing (FeOFe, COFe, COOH, and coordinated H2O) and N-containing (CONH) moieties on MIL-101(Fe)-TDCA interacted with OH groups on the hydrolyzed species of Au(III) (AuCl3(OH)-, AuCl2(OH)2-, and AuCl(OH)3-) by hydrogen bond, which further increased Au(III) sorption. Furthermore, about 45.71% of Au(III) was reduced to gold nanoparticles by CS groups on the decorated 2,5-dithiophene dicarboxylic acid during sorption on MIL-101(Fe)-TDCA. Over 98.35% of Au(III) was selectively sorbed on MIL-101(Fe)-TDCA at pH 4.0, much higher than that of the coexisting heavy metal ions including Cu(II), Zn(II), Pb(II), and Ni(II) (< 5%), despite their same concentration at 0.01 mg/mL. Although sorption selectivity of a noble metal Pt(IV) by MIL-101(Fe)-TDCA is relatively poor (68.23%), it could be acceptable. Moreover, reusability of MIL-101(Fe)-TDCA is also excellent, since above 90.5% Au(III) still can be sorbed after two sorption-desorption cycles. Overall, excellent sorption performance and the roughly-calculated gold recycling benefits (26.30%) highlight that MIL-101(Fe)-TDCA is a promising porous material for gold recovery from the aqueous phase.

CD-MOFs: From preparation to drug delivery and therapeutic application

Cyclodextrin metal-organic frameworks (CD-MOFs) show considerable advantages of edibility, degradability, low toxicity, and high drug loading, which have attracted enormous interest, especially in drug delivery. This review summarizes the typical synthesis approaches of CD-MOFs, the drug loading methods, and the mechanism of encapsulation and release. The influence of the structure of CD-MOFs on their drug encapsulation and release is highlighted. Finally, the challenges CD-MOFs face are discussed regarding biosafety assessment systems, stability in aqueous solution, and metal ion effect.

The green synthesis and applications of biological metal-organic frameworks for targeted drug delivery and tumor treatments

Biological metal-organic frameworks (bio-MOFs) constitute a growing subclass of MOFs composed of metals and bio-ligands derived from biology, such as nucleobases, peptides, saccharides, and amino acids. Bio-ligands are more abundant than other traditional organic ligands, providing multiple coordination sites for MOFs. However, bio-MOFs are typically prepared using hazardous or harmful solvents or reagents, as well as laborious processes that do not conform to environmentally friendly standards. To improve biocompatibility and biosafety, eco-friendly synthesis and functionalization techniques should be employed with mild conditions and safer materials, aiming to reduce or avoid the use of toxic and hazardous chemical agents. Recently, bio-MOF applications have gained importance in some research areas, including imaging, tumor therapy, and targeted drug delivery, owing to their flexibility, low steric hindrances, low toxicity, remarkable biocompatibility, surface property refining, and degradability. This has led to an exponential increase in research on these materials. This paper provides a comprehensive review of updated strategies for the synthesis of environmentally friendly bio-MOFs, as well as an examination of the current progress and accomplishments in green-synthesized bio-MOFs for drug delivery aims and tumor treatments. In conclusion, we consider the challenges of applying bio-MOFs for biomedical applications and clarify the possible research orientation that can lead to highly efficient therapeutic outcomes.

Cyclodextrin-based metal-organic framework materials: Classifications, synthesis strategies and applications in variegated delivery systems

Metal-organic frameworks (MOFs) are coordination compounds that possess an adjustable structure and controllable function. Despite their wide applications in various industries, the use of MOFs in the fields of food and biomedicine is limited mainly due to their potential biological toxicity. Researchers have thus focused on developing biocompatible MOFs to address this issue. Among them, cyclodextrin-based metal-organic frameworks (CD-MOFs) have emerged as a promising alternative. CD-MOFs are novel MOFs synthesized using naturally carbohydrate cyclodextrin and alkali metal cations, and possess renewable, non-toxic, and edible characteristics. Due to their high specific surface area, controllable porosity, great biocompatibility, CD-MOFs have been widely used in various delivery systems, such as encapsulation of nutraceuticals, flavors, and antibacterial agents. Although the field of CD-MOF materials is still in its early stages, they provide a promising direction for the development of MOF materials in the delivery field. This review describes classification and structural characteristics, followed by an introduction to formation mechanism and commonly used synthetic methods for CD-MOFs. Additionally, we discuss the status of the application of various delivery systems based on CD-MOFs. Finally, we address the challenges and prospects of CD-MOF materials, with the aim of providing new insights and ideas for their future development.

Energy-efficient extraction of linear alkanes from various isomers using structured metal-organic framework membrane

Extraction of low concentration linear alkanes (C5-C7) from various isomers is critical for the petrochemical industry. At present, the separation of alkane isomers is mainly accomplished by distillation, which results in substantial energy expenditure. Metal-organic frameworks (MOFs) with well-tailored nanopores have been demonstrated to be capable of realizing molecule-level separation. In this study, oriented HKUST-1 membranes are formulated according to the morphology-biased principle and finally realized with a low dose synthesis method for terminating undesired crystal nucleation and growth. The fully exposed triangular sieving pore array of the membrane induces configuration entropic diffusion to split linear alkanes from mono-branched and di-branched isomers as well as their cyclical counterparts. Typically, the current separation technique consumes 91% less energy than vacuum distillation. Furthermore, our membranes can realize one-step extraction of normal-pentane, normal-hexane and normal-heptane from a ten-component alkane isomer solution that mimics light naphtha.

Nitrogen-Doped Carbon Dots Encapsulated a Polyoxomolybdate-Based Coordination Polymer as a Sensitive Platform for Trace Tetracycline Determination in Water

The requirement of simple, efficient and accurate detection of tetracycline (TC) in water environments poses new challenges for sensing platform development. Here, we report a simple method for TC sensing via fluorescence detection based on metal-organic coordination polymers (MOCPs, (4-Hap)4(Mo8O26)) coated with nitrogen-doped carbon dots (NCDs). These NCDs@(4-Hap)4(Mo8O26) composites showed excellent luminescence features of NCDs with stable bright-blue emission under UV light. The results of the sensing experiment showed that the fluorescence of NCDs@(4-Hap)4(Mo8O26) can be quenched by TC (166 µM) with 94.1% quenching efficiency via the inner filter effect (IFE) in a short time (10 s), with a detection limit (LOD) of 33.9 nM in a linear range of 8-107 µM. More significantly, NCDs@(4-Hap)4(Mo8O26) showed a high selectivity for TC sensing in the presence of anions and metal cations commonly found in water environments and can be reused in at least six cycles after washing with alcohol. The potential practicality of NCDs@(4-Hap)4(Mo8O26) was verified by sensing TC in real water samples with the standard addition method, and satisfactory recoveries from 91.95% to 104.72% were obtained.

Adenosine/β-Cyclodextrin-Based Metal-Organic Frameworks as a Potential Material for Cancer Therapy

Recently, researchers have employed metal-organic frameworks (MOFs) for loading pharmaceutically important substances. MOFs are a novel class of porous class of materials formed by the self-assembly of organic ligands and metal ions, creating a network structure. The current investigation effectively achieves the loading of adenosine (ADN) into a metal-organic framework based on cyclodextrin (CD) using a solvent diffusion method. The composite material, referred to as ADN:β-CD-K MOFs, is created by loading ADN into beta-cyclodextrin (β-CD) with the addition of K⁺ salts. This study delves into the detailed examination of the interaction between ADN and β-CD in the form of MOFs. The focus is primarily on investigating the hydrogen bonding interaction and energy parameters through the aid of semi-empirical quantum mechanical computations. The analysis of peaks that are associated with the ADN-loaded ICs (inclusion complexes) within the MOFs indicates that ADN becomes incorporated into a partially amorphous state. Observations from SEM images reveal well-defined crystalline structures within the MOFs. Interestingly, when ADN is absent from the MOFs, smaller and irregularly shaped crystals are formed. This could potentially be attributed to the MOF manufacturing process. Furthermore, this study explores the additional cross-linking of β-CD with K through the coupling of -OH on the β-CD-K MOFs. The findings corroborate the results obtained from FT-IR analysis, suggesting that β-CD plays a crucial role as a seed in the creation of β-CD-K MOFs. Furthermore, the cytotoxicity of the MOFs is assessed in vitro using MDA-MB-231 cells (human breast cancer cells).

Construction of TiO2/starch nanocomposite cryogel for ethylene removal and banana preservation

Perishability caused by natural plant hormone ethylene has attracted great attention in the field of fruit and vegetable (F&V) preservation. Various physical and chemical methods have been applied to remove ethylene, but the eco-unfriendliness and toxicity of these methods limit their application. Herein, a novel starch-based ethylene scavenger was developed by introducing TiO₂ nanoparticles into starch cryogel and applying ultrasonic treatment to further improve ethylene removal efficiency. As a porous carrier, the pore wall of cryogel provided dispersion space, which increased the area of TiO₂ exposed to UV light, thereby endowing starch cryogel with ethylene removal capacity. The photocatalytic performance of scavenger reached the maximum ethylene degradation efficiency of 89.60 % when the TiO₂ loading was 3 %. Ultrasonic treatment interrupted starch molecular chains and then promoted their rearrangement, increasing the material specific surface area from 54.6 m²/g to 225.15 m²/g and improving the ethylene degradation efficiency by 63.23 % compared with the non-sonicated cryogel. Furthermore, the scavenger exhibits good practicability for removing ethylene as a banana package. This work provides a new carbohydrate-based ethylene scavenger, utilizing as a non-food contact inner filler of F&V packaging in practical applications, which exhibits great potential in F&V preservation and broadens the application fields of starch.

Encapsulating functionalized graphene quantum dot into metal-organic framework as a ratiometric fluorescent nanoprobe for doxycycline sensing

A distinctive fluorescent nanoprobe with the function of doxycycline identification was designed by encapsulating histidine and serine-functionalized graphene quantum dots (His-GQDs-Ser) into the luminescent metal-organic frameworks (MOF). The synthesized nanoprobe displayed the merits of prominent selectivity, wide detection range, and high sensitivity. The interaction of doxycycline and the fabricated fluorescent nanoprobe contributed to the phenomenon of the suppression of the fluorescence of the His-GQDs-Ser and enhancement of the MOF fluorescence. Linear relation between the concentration of doxycycline and the ratio fluorescence intensity of the nanoprobe was observed, which evidenced the brilliant capability in the ranges 0.003-6.25 μM and 6.25-25 μM with a detection limit of 1.8 nM. Additionally, the practicability of the probe was verified in analysis of spiked milk sample, and the satisfactory recoveries of doxycycline varied from 97.39 to 103.61%, with relative standard deviations in the range 0.62-1.42%. A proportional fluorescence sensor for doxycycline detection in standard solution was constructed, which provides a potential for the development of other fluorescence detection systems.

MOF-Based Active Packaging Materials for Extending Post-Harvest Shelf-Life of Fruits and Vegetables

Active packaging that can extend the shelf-life of fresh fruits and vegetables after picking can assure food quality and avoid food waste. Such packaging can prevent the growth of microbial and bacterial pathogens or delay the production of ethylene, which accelerates the ripening of fruits and vegetables after harvesting. Proposed technologies include packaging that enables the degradation of ethylene, modified atmosphere packaging, and bioactive packaging. Packaging that can efficiently adsorb/desorb ethylene, and thus control its concentration, is particularly promising. However, there are still large challenges around toxicity, low selectivity, and consumer acceptability. Metal-organic framework (MOF) materials are porous, have a specific surface area, and have excellent gas adsorption/desorption performance. They can encapsulate and release ethylene and are thus good candidates for use in ethylene-adjusting packaging. This review focuses on MOF-based active-packaging materials and their applications in post-harvest fruit and vegetable packaging. The fabrication and characterization of MOF-based materials and the ethylene adsorption/desorption mechanism of MOF-based packaging and its role in fruit and vegetable preservation are described. The design of MOF-based packaging and its applications are reviewed. Finally, the potential future uses of MOF-based active materials in fresh food packaging are considered.

Cyclodextrin-metal-organic frameworks in molecular delivery, detection, separation, and capture: An updated critical review

Metal-organic frameworks (MOFs) are coordination compounds with tuneable structures and controllable functions. However, the biological toxicity of traditional MOFs materials is often inevitable, making their application in the biological field have many limitations. Therefore, frontier research increasingly focuses on developing biocompatible MOFs materials. Cyclodextrins (CDs), derived from starch, are favored by various biomaterials due to their good biosafety and are often seen in the preparation and application of MOFs materials. This review describes the features of MOFs materials, and the various preparation methods of CD-MOFs are analyzed in detail from the perspective of CD classification. Additionally, the promising applications of CD-MOFs materials for delivery, detection, separation, and capture of active molecules in recent studies are systematically discussed and summarized. In terms of safety, the CD-MOFs materials are meticulously summarized. Finally, this review presents the challenges and future prospects regarding the current CD-MOFs-based materials, which will shed new light on the application of such materials in various fields.

Progress and opportunities for metal-organic framework composites in electrochemical sensors

Metal-organic framework composites have the advantages of large surface area, high porosity, strong catalytic efficiency and good stability, which provide a great possibility of finding excellent electrode materials for electrochemical sensors. However, MOF composites still face various challenges and difficulties, which limit their development and application. This paper reviews the application of MOF composites in electrochemical sensors, including MOF/carbon composites, MOF/metal nanoparticle composites, MOF/metal oxide composites and MOF/enzyme composites. In addition, the application challenges of MOF composites in electrochemical sensors are summarized. Finally, the application prospect for MOF composites is considered to promote the synthesis of more MOF composites with excellent properties.

2D bimetallic organic framework nanosheets for high-performance wearable power source and real-time monitoring of glucose

Diabetics often prick their fingertips to measure the glucose levels in their blood. However, this traditional method not only causes prolonged pain but also increases the risk of infection. Hence, in this study, a non-invasive flexible glucose biosensor with high sensitivity was fabricated. Specifically, NiCo metal-organic frameworks (NiCo-MOFs) served as the electrode material of a micro-supercapacitor and sensing material of a glucose sensor. The electrochemical tests verified that the prominent sensitivity of the NiCo bimetal product is 1422.2 μA mM^-1 cm^-2. The micro-supercapacitor based on the as-fabricated NiCo-MOFs showed a high energy density of 11.5 mW h cm^-2 at the power density 0.26 mW cm^-2. In addition, the as-designed glucose device exhibited an excellent sensitivity of 0.31 μA μM^-1. Furthermore, a flexible energy storage and glucose detection system was successfully prepared by further integrating the micro-supercapacitor and glucose sensor. The smart detector could accurately and conveniently measure the glucose concentration in sweat in real-time. Therefore, the wearable real-time sensing device displays feasible application for non-invasive glucose monitoring and health management.

Preparation of polyethyleneimine-modified chitosan/Ce-UIO-66 composite hydrogel for the adsorption of methyl orange

In this work, a polyethyleneimine-modified chitosan/Ce-UIO-66 composite hydrogel (PEI-CS/Ce-UIO-66) was prepared using the ex-situ blend method. The synthesized composite hydrogel was characterized by SEM, EDS, XRD, FTIR, BET, XPS, and TG techniques, while the zeta potential was recorded for sample analysis. The adsorbent performance was studied by conducting adsorption experiments using methyl orange (MO), which showed that PEI-CS/Ce-UIO-66 exhibited excellent MO adsorption properties (900.5 ± 19.09 mg/g). The adsorption kinetics of PEI-CS/Ce-UIO-66 could be explained by the pseudo-second-order kinetic model, and its isothermal adsorption followed the Langmuir model. Thermodynamics showed that the adsorption was spontaneous and exothermic at low temperatures. MO could interact with PEI-CS/Ce-UIO-66 via electrostatic interaction, π-π stacking, and hydrogen bonding. The results indicated that the PEI-CS/Ce-UIO-66 composite hydrogel could potentially be used for the adsorption of anionic dyes.

Controlled Release of Thymol by Cyclodextrin Metal-Organic Frameworks for Preservation of Cherry Tomatoes

Thymol is a phenol monoterpene with potential antifungal, antioxidant and antibacterial activities. Due to the low water solubility and high volatility of thymol, encapsulation serves as an effective tool during application. In the present study, cyclodextrin (CD)-based metal-organic-frameworks (MOFs) were synthesized using α-CD, β-CD, and γ-CD as organic building blocks, and further complexed with thymol to produce three CD-MOF-THY inclusion complexes (ICs). The encapsulation content, release kinetics and fruit preservation effect of ICs were analyzed. Results showed that thymol was well embedded in γ-CD-MOFs, with the highest encapsulation content of 286.7 ± 8.4 mg/g. Release kinetics revealed that CD-MOFs exhibited a controlled release effect toward thymol for 35 days. The release kinetics of three ICs fit the Rigter-Peppas model well, with γ-CD-MOF-THY showing the lowest release rate constant of 2.85 at 50 °C, RH 75%. Moreover, γ-CD-MOF-THY exhibited a remarkable preservation performance on cherry tomatoes with the lowest decay index (18.75%) and weight loss (5.17%) after 15 days of storage, suggesting this material as a potential fresh-keeping material for fruit and vegetable preservation.

Effect of potassium salts on the structure of γ-cyclodextrin MOF and the encapsulation properties with thymol

BACKGROUND

Thymol is a natural essential oil with strong volatility, low solubility, poor dispersion, strong irritation, and an unpleasant smell, which often requires appropriate porous materials to encapsulate thymol during the application process. However, the encapsulation efficiency of thymol in inclusion complexes is low, and new methods of encapsulation need to be developed. In the present study, the encapsulation capacity, storage stability, and antibacterial activity of thymol were investigated using γ-cyclodextrin (γ-CD) metal-organic frameworks (MOFs) by cocrystallization and high-temperature adsorption methods. The effect of different potassium salts (i.e. KOH, KCl, and KAc) on the structure and complexation of γ-CD-MOFs was also analyzed.

RESULTS

Compared with γ-CD, the thymol encapsulation capacity of γ-CD-MOFs was increased by two- to three-fold, with the encapsulation content following the order: KAc-γ-CD-MOF (293.8 mg g^-1 ) > KOH-γ-CD-MOF (287.7 mg g^-1 ) > KCl-γ-CD-MOF (249.3 mg g^-1 ). The anions in the solution participate in the coordination and influence the symmetry relationship between atoms and ions. This explains the differences in both the three-dimensional γ-CD-MOF structure and the thymol encapsulation amount, as well as the high storage stability of thymol.

CONCLUSION

The in vitro release kinetics and antibacterial experiments showed that the inclusion complexes prepared by γ-CD-MOFs had higher stability, sustainability, and antibacterial activity, which suggests that it is an excellent complex material for industrial and agricultural applications. © 2022 Society of Chemical Industry.

Biodegradable active packaging: Components, preparation, and applications in the preservation of postharvest perishable fruits and vegetables

The consumption of fresh fruits and vegetables is restricted by the susceptibility of fresh produce to deterioration caused by postharvest physiological and metabolic activities. Developing efficient preservation strategies is thus among the most important scientific issues to be urgently addressed in the field of food science. The incorporation of active agents into a polymer matrix to prepare biodegradable active packaging is being increasingly explored to mitigate the postharvest spoilage of fruits and vegetables during storage. This paper reviews the composition of biodegradable polymers and the methods used to prepare biodegradable active packaging. In addition, the interactions between bioactive ingredients and biodegradable polymers that can lead to plasticizing or cross-linking effects are summarized. Furthermore, the applications of biodegradable active (i.e., antibacterial, antioxidant, ethylene removing, barrier, and modified atmosphere) packaging in the preservation of fruits and vegetables are illustrated. These films may increase sensory acceptability, improve quality, and prolong the shelf life of postharvest products. Finally, the challenges and trends of biodegradable active packaging in the preservation of fruits and vegetables are discussed. This review aims to provide new ideas and insights for developing novel biodegradable active packaging materials and their practical application in the preservation of postharvest fruits and vegetables.

Chemo-Biocascade Reactions Enabled by Metal–Organic Framework Micro-Nanoreactor

The one-pot combination of biocatalytic and chemocatalytic reactions represents an economically and ecologically attractive concept in the emerging cascade processes for manufacturing. The mutual incompatibility of biocatalysis and chemocatalysis, however, usually causes the deactivation of catalysts, the mismatching of reaction dynamic, and further challenges their integration into concurrent chemo-biocascades. Herein, we have developed a convenient strategy to construct versatile functional metal–organic framework micro-nanoreactors (MOF–MNRs), which can realize not only the encapsulation and protection of biocatalysts but also the controllable transmission of substances and the mutual communication of the incompatible chemo-biosystems. Importantly, the MOFs serving as the shell of MNRs have the capability of enriching the chemocatalysts on the surface and improving the activity of the chemocatalysts to sufficiently match the optimum aqueous reaction system of biocatalysts, which greatly increase the efficiency in the combined concurrent chemo-biocatalysis. Such strategy of constructing MOF–MNRs provides a unique platform for connecting the “two worlds” of chemocatalysis and biocatalysis.

2-O-Methylated β-Cyclodextrin as an Effective Building Block to Construct Supramolecular Assemblies with Various Morphologies and Molecular Arrangements

The preparation of supramolecular cyclodextrin (CD) assemblies and control of their assembly mode through guest inclusion in CD cavities have been actively studied. Contrarily, there are limited reports on the control of the assembly mode of guest-free CD molecules by external stimuli. Herein, we report the use of 2-O-methylated β-cyclodextrin (2-Me-β-CD) as an effective building block in fabricating supramolecular assemblies with diverse morphologies and molecular arrangements through assembly mode control by various stimuli, such as temperature and solvent. When methanol and diethyl carbonate were used as good and poor solvents, respectively, 2-Me-β-CD formed an amorphous assembly through solvent evaporation on a polyethylene terephthalate (PET) substrate. Increasing the drying temperature and using crystalline substrates, such as highly oriented pyrolytic graphite (HOPG) and sapphire, changed the assembly mode of 2-Me-β-CD to a head-to-tail channel assembly. However, when a 2-Me-β-CD/1-propanol solution was mixed with linear alkanes as a poor solvent, 2-Me-β-CD with head-to-head channel assembly was formed as a precipitate. Additionally, when the corresponding cyclic alkane was used as an alternative poor solvent, an organogel composed of 2-Me-β-CD with head-to-head channel assemblies was obtained. The organogel obtained became a precipitate composed of 2-Me-β-CD with cage-type assembly upon heating at 50 °C. Among the supramolecular assemblies fabricated in this study, the head-to-tail channel assembly is a rare molecular assembly of β-CD and its derivatives. It possesses a modified columnar cavity that has potential applications in molecular recognition and sensing.

Encapsulation of catechin into nano-cyclodextrin-metal-organic frameworks: Preparation, characterization, and evaluation of storage stability and bioavailability

This study, nanoscale α-, β-, γ-cyclodextrin (CD)-metal-organic frameworks (MOFs) were successfully prepared using solvothermal assisted ultrasound method. CD-MOFs were used as nanocarriers to encapsulate catechin (CA), and their encapsulation capacities were evaluated. Encapsulation capacities of CD-MOFs to incorporate CA followed the order: β-CD-MOFs > γ-CD-MOFs > α-CD-MOFs. CA/CD-MOFs were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). DSC and SEM results provided evidence for the formation of CA/CD-MOFs. XRD results indicated the new solid crystalline phases formed in CA/CD-MOFs complex. Results of FT-IR showed that CA was combined with CD-MOFs through hydrogen bonding and van der Waals forces. Current research demonstrated that encapsulation of CA within CD-MOFs provided it against light, oxygen and temperature. Moreover, encapsulation by CD-MOFs improved storage stability and bioavailability of CA. Thus, these CA/CD-MOFs have potential to be used as nutritional supplements and functional foods.

Cyclodextrin metal-organic frameworks and derivatives: recent developments and applications

While there is a tremendous amount of scientific research on metal organic frameworks (MOFs) for gas storage/separation, catalysis and energy storage, the development and application of biocompatible MOFs still poses major challenges. In general, they can be synthesised from various biocompatible linkers and metal ions but particularly cyclodextrins (CDs) as cyclic oligosaccharides are an astute choice for the former. Although the field of CD-MOF materials is still in the early stages and their design and fabrication comes with many hurdles, the benefits coming from CDs built in a porous framework are exciting. Versatile host-guest complexation abilities, high encapsulation capacity and hydrophilicity are among the valuable properties inherent to CDs and offer extended and novel applications to MOFs. In this review, we provide an overview of the state-of-the-art synthesis, design, properties and applications of these materials. Initially, a rationale for the preparation of CD-based MOFs is provided, based on the chemical and structural properties of CDs and including their advantages and disadvantages. Further on, the review exhaustively surveys CD-MOF based materials by categorising them into three sub-classes, namely (i) CD-MOFs, (ii) CD-MOF hybrids, obtained via combination with external materials, and (iii) CD-MOF-derived materials prepared under pyrolytic conditions. Subsequently, CD-based MOFs in practical applications, such as drug delivery and cancer therapy, sensors, gas storage, (enantiomer) separations, electrical devices, food industry, and agriculture, are discussed. We conclude by summarizing the state of the art in the field and highlighting some promising future developments of CD-MOFs.

Gas sensing based on metal-organic frameworks: Concepts, functions, and developments

Effective detection of pollutant gases is vital for protection of natural environment and human health. There is an increasing demand for sensing devices that are equipped with high sensitivity, fast response/recovery speed, and remarkable selectivity. Particularly, attention is given to the designability of sensing materials with porous structures. Among diverse kinds of porous materials, metal-organic frameworks (MOFs) exhibit high porosity, high degree of crystallinity and exceptional chemical activity. Their strong host-guest interactions with guest molecules facilitate the application of MOFs in adsorption, catalysis and sensing systems. In particular, the tailorable framework/composition and potential for post-synthetic modification of MOFs endow them with widely promising application in gas sensing devices. In this review, we outlined the fundamental aspects and applications of MOFs for gas sensors, and discussed various techniques of monitoring gases based on MOFs as functional materials. Insights and perspectives for further challenges faced by MOFs are discussed in the end.

Characteristics and ethylene encapsulation properties of V-type linear dextrin with different degrees of polymerisation

The objective of this research was to investigate the effects of preparation method on the characteristics and ethylene loading capacity of V-type linear dextrin (LD). LD with different degrees of polymerisation were obtained from debranched starch by gradient ethanol precipitation. X-ray diffraction (XRD) patterns of samples obtained by precipitation and anti-solvent precipitation presented A + V-type crystalline structure. However, the percentage of V-type structure of samples obtained by anti-solvent precipitation was significantly higher than for samples prepared by precipitation, which was further confirmed by nuclear magnetic resonance spectroscopy (NMR), and molecular dynamics simulation supported the XRD and NMR results. The ethylene encapsulation capabilities of samples fabricated by different methods were in range of 1.15-4.68 cm³/g. Ethylene release from V-type LD was a physical process at different storage temperatures, and the higher percentage of V-type structure, the slower release rate. Thus, a higher V-type structure content was beneficial for encapsulation of gaseous molecules.

PDMS-coated γCD-MOF solid-phase microextraction fiber for BTEX analysis with boosted performances

Owing to the ubiquitous occurrence and chemotoxicity of BTEX (benzene, toluene, ethylbenzene and xylene), the development of stable and accurate analysis methods that can assess environment risks and can generate monitoring data rapidly is urgent. In this work, a new strategy was proposed for efficient detection of BTEX. By creatively utilizing thermal deposition method, a robust SPME fiber was fabricated, where the γCD-MOF acted as the adsorbent, while PDMS functionalized as the adhesive and protective coating. Benefiting from the protection of PDMS, the γCD-MOF fiber presented significantly better extraction performance and exhibited long-term structural stabilities in aqueous or methanol samples up to a week. The stable and improved properties of γCD-MOF demonstrated that the PDMS protected the MOF components from the adverse effects of solvent. The detection limits of PDMS modified γCD-MOF fiber for BTEX was as low as 0.13-0.29 ng L^-1 that accompanied with wide linear range of 1-1000 ng L^-1, which was significantly superior to commercial PDMS fiber and other MOF-based fibers. Besides, the feasibility of the proposed method was verified by the quantitative determination of BTEX in real water samples. This work presents an effective strategy for creating ultrasensitive and stable SPME fibers based on γCD-MOF for applications in aqueous samples or other poor solvent.