Recent advances in process engineering and upcoming applications of metal-organic frameworks

Stimulus-Responsive Metal-Organic Framework Signal-Reporting System for Photoelectrochemical and Fluorescent Dual-Mode Detection of ATP

Dual-mode bioanalysis integrating photoelectrochemical (PEC) and other modes is emerging and allows signal cross-checking for more reliable results. Metal-organic frameworks (MOFs) have been shown to be attractive materials in various biological applications. This work presents the utilization of MOF encapsulation and stimuli-responsive decapsulation for dual-mode PEC and fluorescence (FL) bioanalysis. Photoactive dye methylene violet (MV) was encapsulated in zeolitic imidazolate framework-90 (ZIF-90) to form an MV@ZIF-90 hybrid material, and MV could be released by adenosine triphosphate (ATP)-induced ZIF-90 disintegration. The released MV not only had FL emission but also had a sensitization effect on the ZnIn₂S₄ (ZnInS) photoanode. Based on the MV-dependent sensitization effect and FL emission characteristic, a dual-mode PEC-FL strategy was established for ATP detection with low detection limits, that is, 3.2 and 4.1 pM for PEC and FL detection, respectively. This study features and will inspire the construction and implementation of smart MOF materials for dual-mode bioanalysis.

Heterometallic Europium(III)–Lutetium(III) Terephthalates as Bright Luminescent Antenna MOFs

A new series of luminescent heterometallic europium(III)–lutetium(III) terephthalate metal–organic frameworks, namely (Eu_xLu_1−x)₂bdc₃·nH₂O, was synthesized using a direct reaction in a water solution. At the Eu³⁺ concentration of 1–40 at %, the MOFs were formed as a binary mixture of the (Eu_xLu_1−x)₂bdc₃ and (Eu_xLu_1−x)₂bdc₃·4H₂O crystalline phases, where the Ln₂bdc₃·4H₂O crystalline phase was enriched by europium(III) ions. At an Eu³⁺ concentration of more than 40 at %, only one crystalline phase was formed: (Eu_xLu_1−x)₂bdc₃·4H₂O. All MOFs containing Eu³⁺ exhibited sensitization of bright Eu³⁺-centered luminescence upon the 280 nm excitation into a ¹ππ* excited state of the terephthalate ion. The fine structure of the emission spectra of Eu^{3+ 5}D₀-⁷F_J (J = 0–4) significantly depended on the Eu³⁺ concentration. The luminescence quantum yield of Eu³⁺ was significantly larger for Eu-Lu terephthalates containing a low concentration of Eu³⁺ due to the absence of Eu-Eu energy migration and the presence of the Ln₂bdc₃ crystalline phase with a significantly smaller nonradiative decay rate compared to the Ln₂bdc₃·4H₂O.

Fluorescent Eu3+/Tb3+ Metal-Organic Frameworks for Ratiometric Temperature Sensing Regulated by Ligand Energy

This work presents three series of Eu/Tb metal-organic frameworks (MOFs) containing benzophenone-4,4'-dicarboxylic acid (H₂BPNDC), 4,4'-dicarboxydiphenyl ether (H₂OBA), and terephthalic acid (H₂BDC) as the ligands. Eu/Tb MOFs have the same structural features in that their 3D frameworks are simplified as 2,3,10-connected {4².6}₂{4⁶.6¹⁸.8¹⁹.10²}{4}₂ topological networks. The solid-state fluorescence spectra of three Eu/Tb MOF series are attributed to the combined emissions of ⁵D₀ → ⁷F_J (J = 1-4) transitions in Eu³⁺ and ⁵D₄ → ⁷F_J (J = 6-5) transitions in Tb³⁺. The n_Eu:n_Tb of Eu/Tb MOFs is optimized as 1:69 based on the relationships between I_Tb(545)/I_Eu(614) and n_Eu:n_Tb; that is, Eu_0.0143Tb_0.9857-L (L = BPNDC^2-, OBA^2-, and BDC^2-) were selected to carry out the following temperature (T)-sensing tests. The fluorescence mechanism of Eu_0.0143Tb_0.9857-L can be explained by a ligand-to-metal charge transfer combined with an intermetallic Tb³⁺ → Eu³⁺ energy transfer. The T-dependent fluorescence indicates linear relationships with sensitivities of 1.85% K^-1 for Eu_0.0143Tb_0.9857-BPNDC, 6.49% K^-1 for Eu_0.0143Tb_0.9857-OBA, and 0.28% K^-1 for Eu_0.0143Tb_0.9857-BDC. The influence of T on the lowest excited triplet energy levels (T1 values) of the ligands reveals that the ligand energy regulation impacts their fluorescence properties, including the sensitivity, fluorescence quenching rate, quantum yield, and fluorescence lifetime. This shows that Eu_0.0143Tb_0.9857-BPNDC is sufficiently sensitive to T, making it applicable in noncontact T measurements.

Fluorine-Induced Electric Field Gradient in 3D Porous Aromatic Frameworks for Highly Efficient Capture of Xe and F-Gases

The development of robust and efficient porous adsorbents is essential for capturing xenon (Xe) and perfluorinated electron specialty gases (F-gases) in semiconductor exhaust gases, as toxic and corrosive gases coexist in high-temperature plasma degradation off-gases. Herein, two three-dimensional (3D) fluorinated porous aromatic frameworks (PAFs) with abundant fluorine (labeled PAF-4F and PAF-8F) were synthesized. The two PAFs exhibit high IAST selectivity in capturing Xe and F-gases from semiconductor off-gases, as well as excellent physicochemical stability and reusability, which have been collaboratively verified by single-component gas adsorption and regeneration tests, etc. Density functional theory (DFT) simulation revealed that the entry of strongly electronegative fluorine atoms into PAFs causes localized charge separation on the polymer pore surface, resulting in the preferential adsorption of high-polarizability Xe and F-gases via induced electric field gradients. Systematic studies have sufficiently manifested the great potential of fluorine-functionalized porous materials to effectively capture Xe and F-gases, which provides practical insights into the fabrication of highly stable porous adsorbents for harsh operating conditions.

Metal-organic frameworks as a therapeutic strategy for lung diseases

Lung diseases remain a global burden today. Lower respiratory tract infections alone cause more than 3 million deaths worldwide each year and are on the rise every year. In particular, with coronavirus disease raging worldwide since 2019, we urgently require a treatment for lung disease. Metal organic frameworks (MOFs) have a broad application prospect in the biomedical field due to their remarkable properties. The unique properties of MOFs allow them to be applied as delivery materials for different drugs; diversified structural design endows MOFs with diverse functions; and they can be designed as various MOF-drug synergistic systems. This review concentrates on the synthesis design and applications of MOF based drugs against lung diseases, and discusses the possibility of preparing MOF-based inhalable formulations. Finally, we discuss the chances and challenges of using MOFs for targeting lung diseases in clinical practice.

Atomistic origin of nano-silver paracrystalline structure: molecular dynamics and x-ray diffraction studies

Classical molecular dynamics (MD) and x-ray diffraction (XRD) have been used to establish the origin of the paracrystalline structure of silver nanoparticles at the atomic scale. Models based on the face-centred cubic structure have been computer generated and their atomic arrangements have been optimized by the MD with the embedded-atom model (EAM) potential and its modified version (MEAM). The simulation results are compared with the experimental XRD data in reciprocal and real spaces, i.e. the structure factor and the pair distribution function. The applied approach returns the structural models, defined by the Cartesian coordinates of the constituent atoms. It has been found that most of the structural features of Ag nanoparticles are better reproduced by the MEAM. The presence of vacancy defects in the structure of the Ag nanoparticles has been considered and the average concentration of vacancies is estimated to be 3 at.%. The average nearest-neighbour Ag-Ag distances and the coordination numbers are determined and compared with the values predicted for the bulk Ag, demonstrating a different degree of structural disorder on the surface and in the core, compared to the bulk crystalline counterpart. It has been shown that the paracrystalline structure of the Ag nanoparticles has origin in the surface disorder and the disorder generated by the presence of the vacancy defects. Both sources lead to network distortion that propagates proportionally to the square root of the interatomic distances.

Dynamic Covalent Self-Assembly of Chloride- and Ion-Pair-Templated Cryptates

While supramolecular hosts capable of binding and transporting anions and ion pairs are now widely available, self-assembled architectures are still rare, even though they offer an inherent mechanism for the release of the guest ion(s). In this work, we report the dynamic covalent self-assembly of tripodal, urea-based anion cryptates that are held together by two orthoester bridgeheads. These hosts exhibit affinity for anions such as Cl- , Br- or I- in the moderate range that is typically advantageous for applications in membrane transport. In unprecedented experiments, we were able to dissociate the Cs⋅Cl ion pair by simultaneously assembling suitably sized orthoester hosts around the Cs+ and the Cl- ion.

Enhancing antibacterial property of porous titanium surfaces with silver nanoparticles coatings via electron-beam evaporation

Antibacterial activity is one of the most vital characteristics for Titanium (Ti) dental implants. Coating antibacterial material onto Ti surfaces is an effective approach to enhance their intrinsic antibacterial ability. However, a cost-effective but efficient coating strategy for realizing this objective still remains challenging. In this study, we proposed a novel implant surface modification strategy for coating silver nanoparticles onto the porous Ti surface via a facile electron beam evaporation (EBE) approach. Porous Ti surfaces were firstly prepared by sand-blasting large grit acid-etching (SLA) process. Then, the silver nanoparticles coating thickness on the porous Ti surface was adjusted and optimized by altering the duration of EBE process. Consequently, composite porous Ti surfaces with different silver thicknesses were synthesized. Polished Ti (PT) surface without SLA or EBE process was also prepared as the controlled blank group. The surface characterizations were analyzed by SEM, AFM, and XPS. After that, the antibacterial properties of all groups were tested with bacteria counting method, bacterial viability test, live/dead bacterial staining, and SEM examination. Results show that silver nanoparticles were uniformly distributed on the porous Ti surfaces after the SLA and EBE processes. After being incorporated with silver nanoparticles, the composite surfaces successfully inhibited the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The antibacterial ratio (AR) values of SLA-Ag groups increased with the increasing silver thickness and are significantly higher than those of PT and SLA groups. Therefore, by the SLA and EBE processes, the composite porous Ti surfaces modified with silver nanoparticles coatings demonstrate superior antibacterial property compared with pure Ti surfaces, which is highly promising for enhancing the antibacterial functions of dental implants. Graphical abstract.

3D Printing of Metal-Organic Framework-Based Ionogels: Wearable Sensors with Colorimetric and Mechanical Responses

Soft ionotronics are emerging materials as wearable sensors for monitoring physiological signals, sensing environmental hazards, and bridging the human-machine interface. However, the next generation of wearable sensors requires multiple sensing capabilities, mechanical toughness, and 3D printability. In this study, a metal-organic framework (MOF) and three-dimensional (3D) printing were integrated for the synthesis of a tough MOF-based ionogel (MIG) for colorimetric and mechanical sensing. The ink for 3D printing contained deep eutectic solvents (DESs), cellulose nanocrystals (CNCs), MOF crystals, and acrylamide. After printing, further photopolymerization resulted in a second covalently cross-linked poly(acrylamide) network and solidification of MIG. As a porphyrinic Zr-based MOF, MOF-525 served as a functional filler to provide sharp color changes when exposed to acidic compounds. Notably, MOF-525 crystals also provided another design space to tune the printability and mechanical strength of MIG. In addition, the printed MIG exhibited high stability in the air because of the low volatility of DESs. Thereafter, wearable auxetic materials comprising MIG with negative Poisson's ratios were prepared by 3D printing for the detection of mechanical deformation. The resulting auxetic sensor exhibited high sensitivity via the change in resistance upon mechanical deformation and a conformal contact with skins to monitor various human body movements. These results demonstrate a facile strategy for the construction of multifunctional sensors and the shaping of MOF-based composite materials.

Functionalization of Diamine-Appended MOF-Based Adsorbents by Ring Opening of Epoxide: Long-Term Stability and CO2 Recyclability under Humid Conditions

Although diamine-appended metal-organic framework (MOF) adsorbents exhibit excellent CO₂ adsorption performance, a continuous decrease in long-term capacity during repeated wet cycles remains a formidable challenge for practical applications. Herein, we present the fabrication of diamine-appended Mg₂(dobpdc)-alumina beads (een-MOF/Al-Si-Cx; een = N-ethylethylenediamine; x = number of carbon atoms attached to epoxide) coated with hydrophobic silanes and alkyl epoxides. The reaction of epoxides with diamines in the portal of the pore afforded sufficient hydrophobicity, hindered the penetration of water vapor into the pores, and rendered the modified diamines less volatile. een-MOF/Al-Si-C17-200 (een-MOF/Al-Si-C17-y; y = 50, 100, and 200, denoting wt % of C17 with respect to the bead, respectively), with substantial hydrophobicity, showed a significant uptake of 2.82 mmol g^-1 at 40 °C and 15% CO₂, relevant to flue gas concentration, and a reduced water adsorption. The modified beads maintained a high CO₂ capacity for over 100 temperature-swing adsorption cycles in the presence of 5% H₂O and retained CO₂ separation performance in breakthrough tests under humid conditions. This result demonstrates that the epoxide coating provides a facile and effective method for developing promising adsorbents with high CO₂ adsorption capacity and long-term durability, which is a required property for postcombustion applications.

Mixed-Ligand Metal-Organic Frameworks for All-in-One Theranostics with Controlled Drug Delivery and Enhanced Photodynamic Therapy

Mixed-ligand metal-organic frameworks (MOFs) multiply the properties and improve the versatility of conventional MOFs for theranostic applications. A tumor targeting and tumoral microenvironment-responsive system is significant for specific and efficient cancer theranostics. Herein, we report a kind of versatile mixed-porphyrin ligand MOF as a multifunctional matrix for multimodality-imaging-guided synergistic therapy. Tetrakis(4-carboxyphenyl)porphyrin (TCPP) shows the properties of fluorescence (FL) and photodynamic therapy (PDT), while Mn-TCPP owns magically the properties of T1-weighted magnetic resonance (MR) imaging and photothermal conversion for photothermal imaging and photothermal therapy (PTT). Because of the same coordination capacity and mode of TCPP and Mn-TCPP to Zr4+ ions, MOFs with adjustable ligand ratios were easily prepared. The mixed-ligand MOFs exhibited a high drug loading capacity for 10-hydroxycamptothecin (HCPT, 65%). After modification with hyaluronic acid (HA) through a disulfide bond (-S-S-), the MOF-S-S-HA composites possess enhanced PDT and tumor-targeted redox-responsive drug release properties due to the -S-S- bond. Thus, excellent fluorescence, MR, and photothermal trimodality imaging, redox-responsive drug release, and enhanced PDT/PTT are integrated together in the mixed-ligand MOFs as "all-in-one" theranostic agents.

Ultrafast Degradation and High Adsorption Capability of a Sulfur Mustard Simulant under Ambient Conditions Using Granular UiO-66-NH2 Metal-Organic Gels

Zirconium-based metal-organic frameworks (Zr-MOFs) have been considered as prospective materials for the degradation of nerve chemical warfare agents (CWAs) but show poor catalytic performance toward blister agents. Moreover, the powder issues and the poor adsorption capability also remain as the major challenges for the application of Zr-MOFs in practical CWA detoxification. Herein, a series of defected granular UiO-66-NH2 metal-organic gels are synthesized via adjusting the amount of added concentrated hydrochloric acid for the decontamination of 2-chloroethyl ethyl sulfide (2-CEES), a sulfur mustard simulant. The half-life of 2-CEES decontaminated by defected granular UiO-66-NH2 metal-organic gels can be shortened to 7.6 min, which is the highest reported value for MOFs under ambient conditions. The mechanism of decontamination is that the amino group on the linkers in UiO-66-NH2 MOGs undergoes a substitution reaction with 2-CEES to yield 2-(2-(ethylthio)ethylamino)terephthalic acid, which is less toxic and fixed in the frameworks. The recycling test corroborates that the granular UiO-66-NH2 xerogels possess good stability and reusability. Static adsorption and desorption tests show that UiO-66-NH2 xerogels possess a high 2-CEES vapor adsorption capacity of 802 mg/g after exposure for 1 d and only 28 wt % desorption capacity after air exposure for 7 d. The dual function of ultrafast degradation and high adsorption capability provide a firm foundation for using UiO-66-NH2 xerogels as a future protection media.

Multivariate Metal-Organic Framework/Single-Walled Carbon Nanotube Buckypaper for Selective Lead Decontamination

The search for efficient technologies empowering the selective capture of environmentally harmful heavy metals from wastewater treatment plants, at affordable prices, attracts wide interest but constitutes an important technological challenge. We report here an eco-friendly single-walled carbon nanotube buckypaper (SWCNT-BP) enriched with a multivariate amino acid-based metal-organic framework (MTV-MOF) for the efficient and selective removal of Pb2+ in multicomponent water systems. Pristine MTV-MOF was easily immobilized within the porous network of entangled SWCNTs, thus obtaining a stable self-standing adsorbing membrane filter (MTV-MOF/SWCNT-BP). SWCNT-BP alone shows a moderately good removal performance with a maximum adsorption capacity of 180 mg·g-1 and a considerable selectivity for Pb(II) ions in highly concentrated multi-ion solutions over a wide range of lead concentration (from 200 to 10000 ppb). Remarkably, these features were outperformed with the hybrid membrane filter MTV-MOF/SWCNT-BP, exhibiting enhanced selectivity and adsorption capacity (310 mg·g-1, which is up to 42% higher than that of the neat SWCNT-BP) and consequently enabling a more efficient and selective removal of Pb2+ from aqueous media. MTV-MOF/SWCNT-BP was able to reduce [Pb2+] from the dangerous 1000 ppb level to acceptable limits for drinking water, below 10 ppb, as established by the current EPA and WHO limits. Thus, the eco-friendly composite MTV-MOF/SWCNT-BP shows the potential to be effectively used several times as a reliable adsorbent for Pb2+ removal for household drinking water or in industrial treatment plants for water and wastewater lead decontamination.

Synthesis and structural characterization of a luminescent cadmium(II) complex with bis(4-(1H-imidazole-1-yl)phenyl)amine and 4,4′-sulfonyldibenzoate ligands

A new coordination polymer {[Cd(BIPA)(DCPS)](H2O)} n (1) was constructed with bis(4-(1H-imidazole-1-yl)phenyl)amine and 4,4′-sulfonyldibenzoate ligands. The complex 1 features (BIPA–Cd–BIPA) n and (DCPS–Cd–DCPS) n helical chains in a 3D architecture assembled via hydrogen bonds. A spectroscopic study of complex 1 in the crystalline state showed an intense red-shifted photoluminescence as compared with the ligands BIPA and DCPS2−, which can be attributed to the ligand-to-metal charge transfer (LMCT) transitions.

Understanding Solvothermal Growth of Metal-Organic Framework Colloids for CO2 Capture Applications

A quantitative study of the synthesis of metal-organic framework (MOF) colloids via a solvothermal growth process was demonstrated using electrospray-differential mobility analysis (ES-DMA), a gas-phase electrophoresis approach. HKUST-1, a copper-based MOF (Cu-MOF), was selected as the representative MOF of the study. The effects of the synthetic parameters, including ligand concentration (C_BTC), synthetic temperature (T_s), and synthetic time (t_s) versus material properties of the Cu-MOF, were successfully characterized based on the mobility size distributions measured by ES-DMA. The results show that the mobility size of Cu-MOF was proportional to T_s, t_s, and C_BTC during the solvothermal growth. X-ray diffraction and Brunauer-Emmett-Teller analyses were employed complementarily to the ES-DMA, confirming that the increase in mobility size of Cu-MOF was correlated to the increase in crystallinity (i.e., larger specific surface area and crystallite size). The results of CO₂ pulse adsorption show that the synthesized Cu-MOF possessed a good CO₂ adsorption ability under 1 atm, 35 °C, and the cumulative amount of CO₂ uptake was proportional to the measured mobility size of Cu-MOF. The work provides a proof of concept for the controlled synthesis of MOF colloids with the support of gas-phase electrophoretic analysis, and the quantitative methodology is useful for the development of MOF-based applications in CO₂ capture and utilization.

Metal-organic Framework ZIF-67 Functionalized MXene for Enhancing the Fire Safety of Thermoplastic Polyurethanes

In this work, a novel functionalization strategy for ZIF-67-modified layered MXene was proposed, aiming at improving the fire safety of thermoplastic polyurethanes (TPU). The ZIF-67@MXene was verified by microscopic morphology, elemental composition, functional group species and crystal structure, and then the successfully prepared ZIF-67@MXene was introduced into the TPU material. When ZIF-67@MXene content was only 0.5 wt%, the peak heat release rate, total heat release rate, peak smoke release rate, total smoke release rate, and CO yield of the TPU/ZIF-67@MXene composites were reduced by 26%, 9%, 50%, and 22%, respectively, compared with the pure TPU. The thermogravimetric tests showed that the residual char of TPU/ZIF-67@MXene composites was the most in all samples. In short, the high-quality carbon layer of TPU/ZIF-67@MXene composites acts as a physical barrier to the transfer of heat and toxic gases, greatly improving the flame retardant properties of the TPU polymer.

Facile in Situ Transformation of NiOOH into MOF-74(Ni)/NiO OH Heterogeneous Composite for Enchancing Electrocatalytic Methanol Oxidation

A new MOF-74(Ni)/NiOOH heterogeneous composite was synthesized via NiOOH microsphere precursor. The electrocatalytic methanol oxidation reactions' (MOR) performance was assessed. The as-prepared MOF-74(Ni)/NiOOH exhibited excellent activity with high peak current density (27.62 mA·cm^-2) and high mass activity (243.8 mA·mg^-1). The enhanced activity could be a result of the synergistic effect of the MOF-74(Ni)/NiOOH heterocomposite providing more exposed active sites, a beneficial diffusion path between the catalyst surface and electrolyte, and improved conductivity, favorable for improving MOR performance.

Efficient Heparin Recovery from Porcine Intestinal Mucosa Using Zeolite Imidazolate Framework-8

Heparin is one of the most valuable active pharmaceutical ingredients, and it is generally isolated from porcine intestinal mucosa. Traditionally, different types of commercial resins are employed as an adsorbent for heparin uptake; however, using new, less expensive adsorbents has attracted more interest in the past few years to enhance the heparin recovery. Zeolite imidazolate framework-8 (ZIF-8), as a metal–organic framework (MOF) with a high surface area, porosity, and good stability at high temperatures, was selected to examine the heparin recovery. In this research, we demonstrate that ZIF-8 can recover up to ~70% (37 mg g⁻¹) of heparin from porcine intestinal mucosa. A mechanistic study through kinetic and thermodynamic models on the adsorption revealed appropriate surface conditions for the adsorption of heparin molecules. The effect of different variables such as pH and temperature on heparin adsorption was also studied to optimize the recovery. This study is the first to investigate the usage of MOFs for heparin uptake.

Binding Materials for MOF Monolith Shaping Processes: A Review towards Real Life Application

Metal–organic frameworks (MOFs) could be utilized for a wide range of applications such as sorption, catalysis, chromatography, energy storage, sensors, drug delivery, and nonlinear optics. However, to date, there are very few examples of MOFs exploited on a commercial scale. Nevertheless, progress in MOF-related research is currently paving the way to new industrial opportunities, fostering applications and processes interconnecting fundamental chemistry with engineering and relevant sectors. Yet, the fabrication of porous MOF materials within resistant structures is a key challenge impeding their wide commercial use for processes such as adsorptive separation. In fact, the integration of nano-scale MOF crystallic structures into bulk components that can maintain the desired characteristics, i.e., size, shape, and mechanical stability, is a prerequisite for their wide practical use in many applications. At the same time, it requires sophisticated shaping techniques that can structure nano/micro-crystalline fine powders of MOFs into diverse types of macroscopic bodies such as monoliths. Under this framework, this review aims to bridge the gap between research advances and industrial necessities for fostering MOF applications into real life. Therefore, it critically explores recent advances in the shaping and production of MOF macro structures with regard to the binding materials that have received little attention to date, but have the potential to give new perspectives in the industrial applicability of MOFs. Moreover, it proposes future paths that can be adopted from both academy and industry and can further boost MOF exploitation.

Transformation of the coordination nanostructures of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzoic acid molecules on HOPG triggered by the change in the concentration of metal ions

The modulation effects of Cu2+/Fe3+ ions on the hydrogen-bonded structure of 4,4',4''-(1,3,5-triazine-2,4,6-triyl) tribenzoic acid (TATB) on a HOPG surface have been investigated at the liquid-solid interface by scanning tunneling microscopy (STM). STM observations directly demonstrated that the self-assembled honeycomb network of TATB has been dramatically transformed after introducing CuCl2/FeCl3 with different concentrations. The metal-organic coordination structures are formed due to the incorporation of the Cu2+/Fe3+ ions. Interestingly, a Cu2+ ion remains coordinated to two COOH groups and only the number of COOH groups involved in coordination doubles when the concentration of Cu2+ ions doubled. A Fe3+ ion changes from coordination to three COOH groups to two COOH groups after increasing the concentration of Fe3+ ions in a mixed solution. Such results suggest that the self-assembled structures of TATB molecules formed by metal-ligand coordination bonds can be effectively adjusted by regulating the concentration of metal ions in a mixed solution, which has rarely been reported before. It explains that the regulatory effect of concentration leads to the diversity of molecular architectures dominated by coordination bonds.

Ultralow-temperature-driven water-based sorption refrigeration enabled by low-cost zeolite-like porous aluminophosphate

Thermally driven water-based sorption refrigeration is considered a promising strategy to realize near-zero-carbon cooling applications by addressing the urgent global climate challenge caused by conventional chlorofluorocarbon (CFC) refrigerants. However, developing cost-effective and high-performance water-sorption porous materials driven by low-temperature thermal energy is still a significant challenge. Here, we propose a zeolite-like aluminophosphate with SFO topology (EMM-8) for water-sorption-driven refrigeration. The EMM-8 is characterized by 12-membered ring channels with large accessible pore volume and exhibits high water uptake of 0.28 g·g-1 at P/P0 = 0.2, low-temperature regeneration of 65 °C, fast adsorption kinetics, remarkable hydrothermal stability, and scalable fabrication. Importantly, the water-sorption-based chiller with EMM-8 shows the potential of achieving a record coefficient of performance (COP) of 0.85 at an ultralow-driven temperature of 63 °C. The working performance makes EMM-8 a practical alternative to realize high-efficient ultra-low-temperature-driven refrigeration.

Embedding an extraordinary amount of gemifloxacin antibiotic in ZIF-8 framework with one-step synthesis and measurement of its H2O2-sensitive release and potency against infectious bacteria

GEM@ZIF-8 has DLC = 69.82% and DLE = 89.03%, with controlled release dependent on H2O2 concentration, and it shows significant antibacterial activity.

A ratiometric fluorescent sensor made of a terbium coordination polymer for the anthrax biomarker 2,6-dipicolinic acid with on-site detection assisted by a smartphone app

Tb-NDBC is a quantitative ratiometric fluorescence sensor for DPA detection with high sensitivity and selectivity, a rapid response, and durability.

Construction of a Luminescent Cadmium-Based Metal-Organic Framework for Highly Selective Discrimination of Ferric Ions

Fluorescent metal–organic frameworks (MOFs) are ideal materials for sensors because of their adjustable pore size and functional groups, which provide them with favorable metal ion selective recognition. In this paper, a new cadmium-based MOF was synthesized using Cd(NO₃)₂·4H₂O and 3,3′,5,5′-biphenyltetracarboxylic acid by solvothermal method. CdBPTC owned three types of channels with dimensions of approximately 8.4 × 8.3 Å, 6.0 × 5.2 Å, 9.7 × 8.4 Å along a, b, and c axis, respectively. This MOF has high selectivity to ferric ions and shows excellent anti-inference ability toward many other cations. The results indicate that the fluorescence quenching efficiency of CdBPTC is close to 100% when the concentration of Fe³⁺ reaches 1.0 × 10⁻³ mol·L⁻¹. Moreover, the luminescent intensity at 427 nm presents a linear relationship at a concentration range of 2.0 × 10⁻⁴~7.0 × 10⁻⁴ mol·L⁻¹, which can be quantitatively expressed by the linear Stern–Volmer equation I₀/I = 8489 [Fe³⁺] − 0.1400, which is comparable to the previously reported better-performing materials. Competitive energy absorption and ion exchange may be responsible for the variation in fluorescence intensity of CdBPTC in different Fe³⁺ concentrations.

Encapsulation of Dyes in Luminescent Metal-Organic Frameworks for White Light Emitting Diodes

The development of white light emitting diodes (WLEDs) holds great promise for replacing traditional lighting devices due to high efficiency, low energy consumption and long lifetime. Metal-organic frameworks (MOFs) with a wide range of luminescent behaviors are ideal candidates to produce white light emission in the phosphor-converted WLEDs. Encapsulation of emissive organic dyes is a simple way to obtain luminescent MOFs. In this review, we summarize the recent progress on the design and constructions of dye encapsulated luminescent MOFs phosphors. Different strategies are highlighted where white light emitting phosphors were obtained by combining fluorescent dyes with metal ions and linkers.

Antioxidative Composites Based on Multienzyme Systems Encapsulated in Metal-Organic Frameworks

Skin is exposed to ultraviolet radiation from the sun constantly, which may induce overproduction of reactive oxygen species (ROS) causing oxidative stress to cells and tissues. Enzymes and small molecules work together to maintain the redox homeostasis, among which superoxide dismutase (SOD) and catalase (CAT) are two kinds of most important antioxidants that suffer from the fragile nature of proteins. Moreover, the proportion of two enzymes used in products must be precisely controlled to reduce the damage caused by the toxic intermediate H₂O₂. Metal-organic frameworks (MOFs) are emerging as promising candidates for multiple enzyme encapsulation due to their high porosity, easy synthesis, and good biocompatibility. Herein, we developed enzyme-MOF composites, SC@ZIF-8, which exhibited an excellent antioxidative activity in vitro. Chemically protective cages formed by MOFs endow the encapsulated enzymes the long-term stability under unnatural conditions in cosmetic and biomedical materials. The pH-dependent protein release profile of SC@ZIF-8 facilitated the successful delivery of enzymes into the cytoplasm to scavenge toxic ROS. The nanocomposites protected human cells from paraquat-induced oxidative stress, paving a new path for the stable and efficient application of antioxidative enzymes in cosmetic and dermatological fields.

Organic guest molecule induced ultrafast breathing of an epitaxially grown metal-organic framework on a self-assembled monolayer

We report epitaxially grown new two-dimensional metal-organic framework (MOF) thin films on a self-assembled monolayer (SAM). We fabricated these epitaxial thin-films using stepwise layer-by-layer seeding followed by solvothermal treatment. The MOF thin films exhibit ultrafast structural flexibility (through breathing) compared to their bulk samples upon uptake of organic guest molecules.

Bimetallic MOF-Derived Synthesis of Cobalt-Cerium Oxide Supported Phosphotungstic Acid Composites for the Oleic Acid Esterification

The impregnation of phosphotungstic acid (HPW) with porous cobalt-cerium oxide (HPW@CoCeO) has been prepared by pyrolysis of CoCe-MOF and used for the production of methyl oleate from oleic acid and methanol. FTIR, XRD, SEM, TEM, N2 adsorption/desorption, and NH3-TPD were characterized for the prepared composites. Simultaneously, the effects of reaction time, substrate molar ratio, temperature, and catalyst loading on catalytic activity were highlighted, and the conversion of 67.2% was reached after 4 h at 60°C. Importantly, HPW@CoCeO was reusabe and reused more than eight times, and the oleic acid conversion could be maintained at 61.8% without significant activity loss. Thus, the HPW@CoCeO composite could be used as acid catalysts for sustainable energy production.

Interparticle Forces of a Native and Encapsulated Metal-Organic Framework and Their Effects on Colloidal Dispersion

The colloidal properties of suspended metal-organic frameworks (MOFs) are critical for device fabrication and application. Herein, van der Waals attractive, electric double layer repulsive, and steric repulsive forces of a native and encapsulated MOF are quantified for the first time. The van der Waals attractive forces were investigated by conducting environmental ellipsometric porosimetry (EEP) and spectroscopic ellipsometry (SE) on submicron, optical-quality nanoparticle films. The repulsive forces were determined from colloid and material characterization measurements. These data were used to predict suspension properties via extended Derjaguin, Landau, Verwey, and Overbeek theory. The state of dispersion was quantified for comparison with theoretical predictions for nine solvents. The MOF encapsulated with a surface-selective modification showed superior suspension in hydrophobic solvents. These findings should expedite the formulation of MOF colloidal suspensions for future works.

Enhanced Fungicidal Efficacy by Co-Delivery of Azoxystrobin and Diniconazole with Cauliflower-Like Metal-Organic Frameworks NH2-Al-MIL-101

Long-term use of a single fungicide increases the resistance risk and causes adverse effects on natural ecosystems. Controlled release formulations of dual fungicides with different modes of action can afford a new dimension for addressing the current issues. Based on adjustable aperture and superhigh surface area, metal-organic frameworks (MOFs) are ideal candidates as pesticide release carriers. This study used Al3+ as the metal node and 2-aminoterephthalic acid as the organic chain to prepare aluminum-based metal-organic framework material (NH2-Al-MIL-101) with "cauliflower-like" structure and high surface area of 2359.0 m2/g. Fungicides of azoxystrobin (AZOX) and diniconazole (Dini) were simultaneously encapsulated into NH2-Al-MIL-101 with the loading content of 6.71% and 29.72%, respectively. Dual fungicide delivery system of AZOX@Dini@NH2-Al-MIL-101 demonstrated sustained and pH responsive release profiles. When the maximum cumulative release rate of AZOX and Dini both reached about 90%, the release time was 46 and 136 h, respectively. Furthermore, EC50 values as well as the percentage of inhibition revealed that AZOX@Dini@NH2-Al-MIL-101 had enhanced germicidal efficacy against rice sheath blight (Rhizoctonia solani), evidenced by the synergistic ratio of 1.83. The present study demonstrates a potential application prospect in sustainable plant protection through co-delivery fungicides with MOFs as a platform.

A green route to prepare metal-free phthalocyanine crystals with controllable structures by a simple solvothermal method

Exploring the environmentally friendly and low-cost synthesis strategies of phthalocyanine (Pc) crystals in just one step is an absolute challenge. The solvothermal synthesis of phthalocyanine crystals shows the advantages of high-quality crystalline products, facile reaction and purification, and low cost. Nevertheless, only a few metal phthalocyanine crystals have been successfully synthesized via solvothermal reactions. In this study, we found that the crystalline β metal-free phthalocyanine needles could be directly prepared via the tetrapolymerization of phthalodinitrile catalyzed by DBU in solvothermal reactions. Similar to the preparation of β-phthalocyanine crystals, the α metal-free phthalocyanine crystals with the specific multiply-laminated structures can be obtained through solvothermal reactions assisted by DBN. SEM characterization showed that the individual β metal-free phthalocyanine has a well-defined quadrangular shape with smooth faces. However, the α metal-free phthalocyanine exhibits a distinctive undulating surface morphology. Both phthalocyanines showed satisfactory thermal stability (from room temperature to about 300 °C), excellent resistance to acid/alkali solution, and fast photoelectric response properties (order of magnitude of response time, 10⁻⁶ s) as tested by TG-DSC and TPV, respectively. It is noted that ethanol was used as the reaction medium and the resulting phthalocyanine crystals can be facilely purified using hot ethanol to dissolve the impurities adsorbed on the surfaces of phthalocyanine crystals. Compared to the traditional methods, no re-crystallization operation was carried out for our method. To the best of our knowledge, this is the first report on the solvothermal synthesis of metal-free phthalocyanine crystals with controllable crystal form adjusted by DBU/DBN in one step.

The quadrangular β phthalocyanine and multiply-laminated α phthalocyanine crystals could be synthesized via a solvothermal route by using DBU and DBN, respectively.