Metal-organic Gels Research Articles

Metal–organic gels and their derived materials for electrochemical applications

Metal–organic gels and their derived carbon and metal oxide materials are reviewed for their electrochemical applications in electricity/ion conductors, energy storage and conversion.

Metal-organic gels: recent advances in their classification, characterization, and application in the pharmaceutical field.

Metal-organic gels (MOGs) are a type of functional soft substance with a three-dimensional (3D) network structure and solid-like rheological behavior, which are constructed by metal ions and bridging ligands formed under the driving force of coordination interactions or other non-covalent interactions. As the homologous substances of metal-organic frameworks (MOFs) and gels, they exhibit the potential advantages of high porosity, flexible structure, and adjustable mechanical properties, causing them to attract extensive research interest in the pharmaceutical field. For instance, MOGs are often used as excellent vehicles for intelligent drug delivery and programmable drug release to improve the clinical curative effect with reduced side effects. Also, MOGs are often applied as advanced biomedical materials for the repair and treatment of pathological tissue and sensitive detection of drugs or other molecules. However, despite the vigorous research on MOGs in recent years, there is no systematic summary of their applications in the pharmaceutical field to date. The present review systematically summarize the recent research progress on MOGs in the pharmaceutical field, including drug delivery systems, drug detection, pharmaceutical materials, and disease therapies. In addition, the formation principles and classification of MOGs are complemented and refined, and the techniques for the characterization of the structures/properties of MOGs are overviewed in this review.

Ar plasma assists in enhanced oxygen evolution kinetics of MOG-derived multicomponent transition metal sulfides.

Transition metal sulfides are low-cost oxygen evolution reaction (OER) electrocatalysts that can potentially substitute noble metal catalysts. However, the adsorption process of their OER is impeded by their intrinsic poor catalytic activity. Constructing heterojunction and vacancy defects in transition metal sulfides is an efficient method to promote the process of oxygen evolution. Herein, a facile approach based on in situ sulfurization of metal-organic gels (MOGs) and a short-time plasma treatment was developed to fabricate vacancy-modified polymetallic sulfides heterojunction. The synergistic effect of the multi-component heterojunction and sulfur vacancy contributed greatly to improving the electron migration efficiency and OER ability of the electrocatalyst. As a result, the optimum oxygen evolution activity was achieved with appropriate surface vacancy concentrations by regulating the plasma radio frequency powers. The plasma-treated catalyst under 400 W showed the best OER performance (lower overpotential of 235 mV in 1 M KOH solution with the Tafel slope of 31 mV dec-1) and good durability over 11 h of chronopotentiometry testing. This work sheds new light on constructing multimetal-based heterojunction electrocatalysts with rich vacancy defects for oxygen evolution reactions.

A 5.3 nm giant metal-organic cage and its supramolecular gel for the formation of dye molecular ionic pairs.

A terpyridine-based supramolecular cage was successfully synthesized by the self-assembly of a hexapodal metal-organic ligand with Zn2+. This metallo-cage exhibited two large parallel planes on the top and bottom with diameters close to 6 nm and a face-to-face distance close to 3.5 nm, thus possessing a large cavity. Electrospray ionization mass spectrometry (ESI-MS), nuclear magnetic resonance (NMR), two-dimensional nuclear Overhauser (2D-NOESY), and diffusion-ordered (DOSY) spectroscopies as well as transmission electron microscopy (TEM) and atomic force microscopy (AFM) measurements, unambiguously supported the formation of a supramolecular cage. Furthermore, the corresponding metal-organic gel was felicitously prepared in CH3CN/H2O and displayed good adsorption performance for dye molecules.

A fluorescent test paper fabricated by in situ growth of a functional Zn-MOG for fast and effective detection of Cr(VI) and Fe(III)

Heavy metals, like iron and chromium(Cr), have been proved to be a serious pollutant to environmental and biological systems. Long-term exposure to Cr(VI) ions through drinking water is harmful to human and will cause some serious diseases. Therefore, exploring new method for selective and rapid detection of such specific pollutants in water is crucial for environmental protection and human health. Herein, a novel functional metal organic gel(MOG) was successfully fabricated. Its detection limit of Cr(VI) was 2.4 × 10−8 mol·L−1 in aqueous solution, and 1.2 × 10−6 mol·L−1 for Fe(III) Based on the excellent deformability of MOG materials, a fluorescent test paper which could realize visible detection of Cr(VI) was fabricated by the in situ growth of Zn-MOGs onto the filter paper. To the best of our knowledge, it is the first sample of Zn-MOGs Based Test Paper (Zn-MOGs-FP) fabricated by in situ growth.

Phosphate ions functionalized spinel iron cobaltite derived from metal organic framework gel for high-performance asymmetric supercapacitors

Spinel iron cobaltite (FeCo2O4) with high theoretical capacity is a promising positive electrode material for building high-performance supercapacitors. However, its inherent poor conductivity and deficient electrochemical active sites hinder the improvement of its electrochemical kinetics behavior. Herein, phosphate ions modified FeCo2O4 is obtained in the presence of oxygen vacancies (P-FeCo2O4-x) by a simple metal organic framework gel-derived strategy. Phosphate ions added on the surface of P-FeCo2O4-x greatly enhances its surface activity, thus prompting the faster charge storage kinetics of the electrode material. Due to its ample electrochemical active sites and rapid ion diffusion and electron mobility, the optimized P-FeCo2O4-x electrode delivers a superior specific capacity of 1568.8 F g−1 (784.4 C g−1) at a current density of 1 A/g and has an excellent cycling stability with 93.3 % initial capacity retention ratio after 5000 cycles. More impressively, the assembled asymmetric supercapacitor consisting of P-FeCo2O4-x and activated carbon which act as positive and negative electrode materials, respectively displays a favorable energy density of 60.2 Wh kg−1 at a power density of 800 W kg−1 and has a long cycling lifespan. These results demonstrate the potential importance of modifying the surface of spinel cobaltite with phosphate ions and incorporating oxygen defects in it as a facile strategy for enhancing the electrochemical kinetics of electrode materials.

Antibiofouling Performance of a Metal‐Organic Gel Based on 2‐Amino‐5‐Mercapto‐1,3,4‐Thiadiazole and CuI

AbstractMetal–organic gels or metallogels (MOGs), which usually made up with metal ions and organic ligands, are promising in the area of medicine, environment, and biology. Herein, a new metal–organic gel containing Cu+ (Cu‐MOG‐5) is prepared at room temperature using 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole (AMT) and CuI. Considering the excellent low surface energy characteristics of polydimethylsiloxane (PDMS), the as‐prepared Cu‐MOG‐5 is infused into porous PDMS to obtain Cu‐MOG‐5/PDMS coating, which combines the bactericidal properties of Cu+ containing hydrogels and the low surface energy of PDMS. The morphology of the Cu‐MOG‐5 and Cu‐MOG‐5/PDMS coating is investigated by FE‐SEM, and the structure of the new Cu‐MOG‐5 is verified by FT‐IR, 1H NMR, XPS, EDS, and elemental analysis. The antibiofouling properties are assessed using Escherichia coli (E. coli) and mussel. The results show that the newly prepared Cu‐MOG‐5/PDMS coating exhibits superior antibiofouling performance because of the synchronous action of hydrogel including Cu+ and PDMS.

Oral Metal-Organic Gel Protected Whole-Cell Biosensor for in Situ Monitoring Nitrosamines in the Gastrointestinal Tract.

Nitrite, a type of food additive, has been proved convertible to genotoxic nitrosamines in the gastrointestinal tract by intestinal flora. There is no appropriate method for in situ detection of nitrosamines. Herein, plasmid-introduced Saccharomyces cerevisiae, which can respond to nitrosamine-induced DNA damage and activate pMAG1-based DNA damage repair (DDR), was designed as whole-cell biosensors (WCBs) for monitoring the in situ generated nitrosamines by a reporter gene expressing enhanced green fluorescent protein (EGFP). In order to protect the validity of WCBs (pMAG1 yeast) from the gastric acid environment, a type of metal-organic gel (MOG), coordinated by Fe3+ and 2,2'-thiodiacetic acid (TDA), was prepared to embed the WCBs. The MOG(Fe-TDA) is gastric acid resistant and can deliver the pMAG1 yeast to the gut without compromising the performance of pMAG1 yeast to detect in situ generated nitrosamines. The genotoxicity of nitrosamines converted from nitrite was successfully detected in the gastrointestinal tract of mice.

Metal-organic aerogels based on titanium(IV) for visible-light conducted CO2 photoreduction to alcohols

Metal-organic frameworks (MOFs) imply an appealing source of photocatalysts as they combine porosity with tailorable electronic properties and surface chemistry. Herein, we report a series of unprecedented metal-organic aerogels (MOAs) comprised by Ti(IV) oxo-clusters and aromatic dicarboxylic linkers as an alternative to microporous MIL-125 and MIL-125-NH2 MOFs. Discrete titanium oxo-clusters polymerized upon the addition of the dicarboxylic linkers to give rise to a metal-organic gel. Their supercritical drying led to aerogels comprised by nanoscopic particles (ca. 5–10 nm) cross-linked into a meso/macroporous microstructure with surface area ranging from 453 to 617 m2·g−1, which are comparatively lower than the surface area of the microporous counterparts (1336 and 1145 m2·g−1, respectively). However, the meso/macroporous microstructure of MOAs can provide a more fluent diffusion of reagents and products than the intrinsic porosity of MOFs, whose narrower channels are expected to imply a more sluggish mass transport. In fact, the assessment of the continuous visible-light-driven photocatalytic CO2 reduction into methanol shows that MOAs (221–786 μmol·g−1·h−1) far exceed not only the performance of their microporous counterparts (49–65 μmol·g−1·h−1) but also surpass the production rates provided by up-to-date reported photocatalysts.

An adjustable amyloid-β oligomers aptasensor based on the synergistic effect of self-enhanced metal-organic gel luminophore and triple-helix DNA system

Amyloid-β oligomers (AβOs) was the core-biomarker of Alzheimer's disease (AD), and the detection of AβOs is very important for the early diagnosis of AD. However, existing tests for AβOs are majorly suffering from complex process and poor sensitivity. Thus, an adjustable AβOs electrochemiluminescence (ECL) aptasensor based on the synergistic effect of self-enhanced metal-organic gel (AgCNS) and triple-helix DNA system (THS) was successfully constructed. AgCNS was prepared by an extremely simple one-pot method and was an innovative luminophore with excellent ECL performance. The AgCNS-labeled complementary sequence (AgCNS@CP) was interlaced with the unlabeled aptamer (Apt) carrying two short-arms fixed on the gold electrode (GE) to form the THS. Along with the specific-binding of AβOs and Apt, the THS was disrupted and adjusted flexibly between “on” and “off”, resulting in significant changes in the ECL signals. Thus, ECL detection of AβOs was sensitively achieved with a detection limit as low as 0.23 fM and the different forms of Aβ can be specifically distinguished. The aptasensor also exhibited satisfactory selectivity, stability and reproducibility. Moreover, when proposed method and ELISA-kit were simultaneously applied to artificial cerebrospinal fluid (A-CSF) samples, the obtained results were completely consistent, reflecting the potential clinical application value of this work.

Three-in-one multifunctional luminescent metal-organic gels/sodium alginate beads for high-performance adsorption and detection of chlortetracycline hydrochloride, and high-security anti-counterfeiting

Effective elimination and real-time detection of chlortetracycline hydrochloride (CTC) contamination in aqueous solutions, and the establishment of fluorescent state security labels for deterring counterfeits, remain formidable challenges. Herein, two hierarchically porous luminescent metal-organic gels (denoted as Tb-MOG and Eu-MOG) are fabricated by an ultrafast aqueous-based synthetic strategy at room temperature, exhibiting exceptional adsorption capacities (297.68 mg·g−1 and 258.78 mg·g−1), high sensitivities (1.48*106 M−1 and 1.12*106 M−1), and low detection limits (0.044 μM and 0.057 μM) towards CTC. More importantly, MOGs/SA beads are constructed by immobilizing MOGs into sodium alginate (SA) matrix, which addresses the deficiencies of difficult recyclability and easy agglomeration of powdered MOGs, accompanied by the enhanced adsorption capacities and excellent reusability. By virtue of exceptional adsorption performances, MOGs/SA beads allow for the continuous treatment of 100 bed volumes (BV) CTC in various water samples. Aside from that, MOGs/SA beads inherit the fluorescence properties of MOGs, which are capable of reflecting the CTC concentrations in real-time and visualizing adsorption processes assisted by smartphones, as well as ensuring their authenticity as anti-counterfeiting materials. Overall, this work furnishes a rational design of multifunctional carrier-based MOGs, and provides valuable insights for dealing with CTC wastewater pollution and counterfeits.

Magnetic porphyrin-based metal organic gel for rapid RhB removal and enhanced antibacterial activity by heterogeneous Photo-Fenton reaction under visible light.

Nanomaterials with visible light-driven catalytic ability are beneficial in controlling environmental pollutants. Porphyrin-based metal organic gel (MOG) was herein synthesized in one step and magnetic metal organic gel (MMOG) was successfully prepared via in-situ reaction of MOG and Fe3O4. This MMOG was developed as a novel visible light assisted Fenton-like catalyst. The catalytic experiments showed the high photo-Fenton activity of MMOG in the degradation of Rhodamine B (RhB) in the presence of visible light and H2O2 with a RhB degradation efficiency of 94.2% within 40min. Notably, the obtained MMOG can kill E. coli and S. aureus with high killing rate (>99.999%) under visible light. Importantly, the MMOG can be recovered simply by an external magnetic field due to the unique magnetic property. This easily synthesized MMOG with photo-Fenton activity under visible light and magnetic property makes MOG based on the photo-Fenton reaction a prospective material for the environmental and biomedical applications.

Green synthesis of a hydrophobic metal-organic gel for the capture of trace odorous hexanal from humid air

The development of superhydrophobic adsorbents for the capture of trace volatile organic compounds (VOCs) from humid indoor air is still a challenge. Herein, we reported the formation of a granular zinc-based metal-organic gel, i.e., ZIF-412(gel) by optimizing the synthesis conditions. The thermally stable xerogel exhibited high surface area (1008 m2/g), hydrophobicity, and viscosity for self-depositing on the substrate such as non-woven fibers. Dynamic adsorption experiments under various humidity conditions demonstrated as-synthesized ZIF-412(gel) owned excellent VOC (hexanal) adsorption performance with adsorption capacity higher than commercial activated carbon and some water-stable MOFs including ZIF-8, ZIF-67, MIL-101(Cr) and ZIF-414. ZIF-412(gel) could be regenerated at temperature as low as 358 K without obvious loss in adsorption capacity. The adsorption mechanism of hexanal over ZIF-412(gel) is also simulated by Grand canonical Monte Carlo (GCMC).

Self-Healable Poly(vinyl alcohol)─Metal–Organic Hybrid Gel Electrolyte for Flexible Capacitor Sensors

Supramolecular gels based on noncovalent interaction are attractive self-healable polymeric electrolytes due to their repeatable spontaneous recovery of mechanical and electrochemical performance. Herein, we report such a hybrid supramolecular gel electrolyte system composed of a poly(vinyl alcohol) (PVA)–palladium-coordination metal–organic gel (MOG) by controlling ligand conformation transition from cis to trans. The reversible coordination and hydrogen bonding interactions endow the PVA/MOG hybrid gels with 17 consecutive self-healing in 10000S and ultrafast self-healable ability in both mechanical and electrochemical time scales of 180 and 60 s, respectively. The polyaniline (PANI)-based printed interdigital capacitor (IDC) sensor with the hybrid gel electrolyte exhibits a wide voltage window of 0–2.75 V, stable charge–discharge cycle at a high scan rate of 500 mV/s. When printed onto a glove, our sensor can recognize the hand fist and open with good sensitivity. This work provides a promising direction for designing flexible capacitor sensors with self-healable MOGs.

Highly Efficient Aggregation-Induced Electrochemiluminescence of Al(III)-Cbatpy Metal-Organic Gels Obtained by Ultrarapid Self-Assembly for a Biosensing Application.

Aggregation-induced electrochemiluminescence (AIECL) has attracted extensive interest due to the significant increase in ECL response by restricting free intramolecular rotation and torsion, but traditional AIECL emitters suffer from limited ECL efficiency, high cost, and complex synthetic steps, dramatically limiting their applications. Herein, novel Al(III)-Cbatpy metal-organic gels (Al(III)-Cbatpy-MOGs) with nanofiber morphology and ultrarapid coordination of Al3+ and 4'-carboxylic acid-2,2':6',2″-terpyridine (Cbatpy) are developed, which demonstrates an excellent AIECL enhancement behavior far beyond that reported in ECL supramolecular gels. In view of the strong affinity of N and O atoms in Cbatpy toward Al3+, Al(III)-Cbatpy-MOGs with high viscosity and stability can be assembled in one step within about 15 s, easily conquering the main predicaments of current AIECL emitters: complicated synthesis steps and poor film formation. Impressively, the ECL efficiency of Al(III)-Cbatpy-MOGs with superemission is about 20 times higher than that of individual Cbatpy molecules, which is attributed to the aggregation of the organic ligand Cbatpy restricting intramolecular rotation and torsion to reduce nonradiative relaxation. Furthermore, compared with traditional metal complexes, Al(III)-Cbatpy-MOGs show the benefits of remarkable biocompatibility and low cost without the involvement of any organic solvents, noble metals, and rare metals. As proof, a "signal-off" sensing platform based on an Al(III)-Cbatpy-MOGs/S2O82- system was constructed for the sensitive detection of dopamine (DA) with a low detection limit of 0.34 nM. This strategy provides a novel method to prepare cheap metal-organic gels as a highly efficient AIECL emitter, which is promising as a luminescent molecular device and biosensor for clinical diagnostic applications.

Cover Picture: Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water (Angew. Chem. Int. Ed. 32/2022)

A unique anion exchangeable hybrid composite aerogel material was fabricated by strategically implanting a stable cationic metal–organic polyhedron in a hierarchically porous metal–organic gel material by Sujit K. Ghosh and co-workers in their Research Article (DOI: 10.1002/anie.202203385). The composite scavenger efficiently and selectively sequestrates various metal-based toxic oxoanions from natural and simulated industrial waste-water samples in both batch and dynamic column exchange sorption experiment.

Bimetallic metal-organic gel for effective removal of chlortetracycline hydrochloride from aqueous solution：Adsorption isotherm, kinetic and mechanism studies

A novel bimetallic metal–organic gel (JLUE-MOG-Fe/Y) was fabricated through solvothermal method and employed for adsorptive removal of chlortetracycline hydrochloride (CTC) from aqueous solution. JLUE-MOG-Fe/Y, with outstanding stability, wide adaptability and excellent recyclability, showed strong CTC adsorption capacity as high as 584.83 mg·g−1 at 25 °C. The process of CTC adsorption on JLUE-MOG-Fe/Y was exothermic and spontaneous, and fitted well with the pseudo-second-order kinetic model and Freundlich isotherm model. Based on the adsorption experiments and characterization results, pore filling, coordination bonds, electrostatic interactions, π-π interactions, hydrogen bonds and hydrophilic/hydrophobic interaction participated in the adsorption process.

Trap Inlaid Cationic Hybrid Composite Material for Efficient Segregation of Toxic Chemicals from Water

AbstractMetal‐based oxoanions are potentially toxic pollutants that can cause serious water pollution. Therefore, the segregation of such species has recently received significant research attention. Even though several adsorbents have been employed for effective management of chemicals, their limited microporous nature along with non‐monolithic applicability has thwarted their large‐scale real‐time application. Herein, we developed a unique anion exchangeable hybrid composite aerogel material (IPcomp‐6), integrating a stable cationic metal–organic polyhedron with a hierarchically porous metal–organic gel. The composite scavenger demonstrated a highly selective and very fast segregation efficiency for various hazardous oxoanions such as, HAsO42−, SeO42−, ReO4−, CrO42−, MnO4−, in water, in the presence of 100‐fold excess of other coexisting anions. The material was able to selectively eliminate trace HAsO42− even at low concentration to well below the AsV limit in drinking water defined by WHO.

Oxygen-rich ligands tailored for novel metal–organic gel electrocatalyst to promote two-electron selectivity electrocatalysis

More extensive attention has been garnered about the H2O2 electroproduction via two-electron oxygen reduction reaction (2e- ORR). Aiming to develop a more active, more selective and more stable catalyst, herein we reported an unconventional raw metal–organic gels (MOGs) toward this process. This pioneering work, by ingeniously designing and altering the precursor ligands, achieving precisely controlling the number of oxygen groups (OGs). By elaborately comparing more than 70 samples, uncovered the significance that OGs could sufficiently promote the selectivity for H2O2 electrochemical synthesis through the two-electron pathway (realizing enhancement more than 20% in this work). The most potential Fe0.1Co0.9 MOG (H6L), performing an onset potential of 0.76 V (low overpotential), a high selectivity up to 93% ranging 0.15 V to 0.65 V (large voltage window) and 2.1 electron transfer number (implying the 2e- process dominate). This study, unlike other oxidation treatment, through the precise regulation of precursors, further confirmed the feasibility of oxygen-containing functional groups (OGs) tailoring strategy, providing a possibility for low-cost and efficient potential candidate of 2e- ORR.

Novel acylhydrazone-based supramolecular gel for super-sensitive detection of Fe3+ and alternant detection of CN− in aqueous medium

Specific detection of ultratrace levels of ions in aqueous solution without costly equipment and advanced technical is a hot research topic for environmental monitoring. A new gelator molecular, (E)-N’-(4-bromobenzylidene)-4-methoxybenzohydrazide (BM), has been simply synthesized via a 1-step pathway. The obtained molecular BM could self-assembled in N,N-Dimethylformamide (DMF) and formed a stable organogel (OBM) via multi-self-assembly driving forces. Interestingly, OBM had a fluorescence ‘‘turn-off’’ detection signal for Fe3+ and formed a complex OBM-Fe3+. When CN− ions are added to the Fe3+ coordinated metal-organic gel, the fluorescence intensity was increased to the original strength of the supramolecular gel OBM again. The sensing mechanism of CN− was determined through the competitive coordination action of supramolecular gel OBM, Fe3+ cations and CN− anions. Simultaneously, the organogel sensor OBM could also serve as ion responsive films for the detection of Fe3+ and CN−.