Selenium‐Containing Polymer@Metal‐Organic Frameworks Nanocomposites as an Efficient Multiresponsive Drug Delivery System

The development of efficient multiresponsive drug delivery systems (DDSs) to control drug release has been widely explored. Herein, a facile strategy is reported that enables the micelles of the selenium‐containing polymer with the drug to be encapsulated in metal‐organic frameworks (MOFs), which serves as multiresponsive drug release by employing the selenium‐containing polymers with redox‐triggered property and the MOFs with pH‐triggered property in DDS. In this case, the micelles of selenium‐containing polymers, as core easily disassembles in the presence of redox agents, can then release the drug in MOFs matrixes. The ZIF‐8 (one type of MOFs) crystal frameworks serving as shell can collapse only under low pH conditions, and the drug can be further released. In the presence of external redox agents as well as the pH stimuli, the prepared nanocomposite (P@ZIF‐8) drug system exhibits the capability of multiresponsive release of the doxorubicin (DOX) and possesses good selectivity in releasing the DOX under low pH conditions instead of normal pH conditions. In addition, the merits of P@ZIF‐8 such as good biocompatibility, multiresponsive release properties, and especially the selective release properties under different pH conditions make the materials highly promising candidates for the realization of controlled drug delivery in tumor tissue systems.     

Covalent Organic Frameworks: Structures,Synthesis, and Applications

Covalent organic frameworks (COFs) are crystalline porous polymers formed by a bottom‐up approach from molecular building units having a predesigned geometry that are connected through covalent bonds. They offer positional control over their building blocks in two and three dimensions. This control enables the synthesis of rigid porous structures with a high regularity and the ability to fine‐tune the chemical and physical properties of the network. This Feature Article provides a comprehensive overview over the structures realized to date in the fast growing field of covalent organic framework development. Different synthesis strategies to meet diverse demands, such as high crystallinity, straightforward processability, or the formation of thin films are discussed. Furthermore, insights into the growing fields of COF applications, including gas storage and separations, sensing, electrochemical energy storage, and optoelectronics are provided.     

Multi Variant Surface Mounted Metal–Organic Frameworks

Hybrid surface mounted metal–organic frameworks (h‐SURMOFs) of multi variant core‐shell (cs) and core–shell–shell (css) structures (SURMOF A ‐ B and A ‐ B ‐ C , A : [Cu₂(bdc)₂(dabco)]; B : [Cu₂(NH₂‐bdc)₂(dabco)]; C : [Cu₂(ndc)₂(dabco)], bdc = 1,4‐benzenedicarboxylate; NH₂‐bdc = 2‐amino‐1,4‐benzenedicarboxylate; ndc = 1,4‐naphtalenedicarboxylate; dabco = 1,4‐diazabicyclo[2.2.2]octane) with specific crystallographic [001] orientation and incorporated amino groups at a controllable depth within the bulk are deposited via liquid phase epitaxial (LPE) approach on pyridyl‐terminated self‐assembled monolayers (SAM). The location of the (amino) functionality can be precisely controlled through tuning the thickness (number of deposition cycles) of each sub‐multilayer block according to the LPE deposition protocol. The chemo‐selective and location‐specific post deposition (chemical) modification of the amino groups in the cs and css‐type h‐SURMOF samples is achieved. The h‐SURMOFs allow one to probe functional groups at certain location in the volume of hybrid MOF crystallites attached to surfaces as thin film coatings. Multiplex adsorption kinetics of FPI (FPI = 4‐fluorophenyl isothiocyanate) is observed in h‐SURMOFs due to their multi‐variant pore structures in samples of A‐B and A‐B‐C . Conceptually, the stepwise LPE growth method enables fabrication of hybrid SURMOFs and incorporation of multi‐variant functionalities into one homogeneous thin film material, providing precisely tunable pore environment for selective adsorption, separation, etc.     

Porous Cu(I) Triazolate Framework and Derived Hybrid Membrane with Exceptionally High Sensing Efficiency for Gaseous Oxygen

Phosphorescent complexes of precious metal ions are widely studied as optical sensing materials for molecular oxygen. Combining the advantages of luminescent complexes and porous matrixes, porous coordination polymers show great potential for oxygen‐sensing, although their sensitivity, requirement of precious metal, and device fabrication remain challenging issues. In this work, the photoluminescence and oxygen‐sensing properties of the porous Cu(I) triazolate framework [Cu(detz)] (MAF‐2, Hdetz = 3,5‐diethyl‐1,2,4‐trizole) is studied in detail, which shows high chemical stability in moisture and water, very long phosphorescent lifetime (116 μs) and large Stokes shift (14 562 cm^?1), as well as considerable oxygen permeability (1.7 × 10^?11 mol cm^?1 s^?1 bar^?1) at ambient conditions, giving rise to exceptionally high luminescence quenching efficiency of 99.7% at 1 bar O₂ (I ₀/I ₁₀₀ = 356) with a perfectly linear Stern‐Volmer plot (K _SV = 356 bar^?1, R ² = 0.9998), fast response and good reversibility. Further, a counter‐diffusion crystal‐growth method was developed to fabricate MAF‐2 thin films protected by silicone rubbers as the first example of soft membrane oxygen sensor based on coordination polymer or metal‐organic framework, which exhibited extraordinary oxygen‐sensing performance (limit of detection = 0.047 mbar) and outstanding mechanical property, as well as outstanding chemical stability even in an acidic atmosphere.     

Novel Organic‐Dehydration Membranes Prepared from Zirconium Metal‐Organic Frameworks

Membranes with outstanding performance that are applicable in harsh environments are needed to broaden the current range of organic dehydration applications using pervaporation. Here, well‐intergrown UiO‐66 metal‐organic framework membranes fabricated on prestructured yttria‐stabilized zirconia hollow fibers are reported via controlled solvothermal synthesis. On the basis of the adsorption–diffusion mechanism, the membranes provide a very high flux of up to ca. 6.0 kg m^?2 h^?1 and excellent separation factor (>45 000) for separating water from i ‐butanol (next‐generation biofuel), furfural (promising biochemical), and tetrahydrofuran (typical organic). This performance, in terms of separation factor, is one to two orders of magnitude higher than that of commercially available polymeric and silica membranes with equivalent flux. It is comparable to the performance of commercial zeolite NaA membranes. Additionally, the membrane remains robust during a pervaporation stability test (≈300 h), including exposure to harsh environments (e.g., boiling benzene, boiling water, and sulfuric acid) where some commercial membranes (e.g., zeolite NaA membranes) cannot survive.     

Composite Salt in Porous Metal‐Organic Frameworks for Adsorption Heat Transformation

Adsorptive heat transformation systems such as adsorption thermal batteries and chillers can provide space heating and cooling in a more environmental friendly way. However, their use is still hindered by their relatively poor performances and large sizes due to the limited properties of solid adsorbents. Here, the spray‐drying continuous‐flow synthesis of a new type of solid adsorbents that results from combining metal‐organic frameworks (MOFs), such as UiO‐66, and hygroscopic salts, such as CaCl₂ has been reported. These adsorbents, commonly named as composite salt in porous matrix (CSPM) materials, allow improving the water uptake capabilities of MOFs while preventing their dissolution in the water adsorbed; a common characteristic of these salts due to the deliquescence effect. It is anticipated that MOF‐based CSPMs, in which the percentage of salt can be tuned, are promising candidates for thermal batteries and chillers. In these applications, it is showed that a CSPM made of UiO‐66 and CaCl₂ (38% w/w) exhibits a heat storage capacity of 367 kJ kg^?1 , whereas a second CSPM made of UiO‐66 and CaCl₂ (53% w/w) shows a specific cooling power of 631 W kg^?1 and a coefficient of performance of 0.83, comparable to the best solid adsorbents reported so far.     

Fluorous Metal–Organic Frameworks and Nonporous Coordination Polymers as Low‐κ Dielectrics

A fluorous metal–organic framework [Cu(FBTB)(DMF)] (FMOF‐3) [H₂FBTB = 1,4‐bis(1‐H‐tetrazol‐5‐yl)tetrafluorobenzene] and fluorous nonporous coordination polymer [Ag₂(FBTB)] (FN‐PCP‐1) are synthesized and characterized as for their structural, thermal, and textural properties. Together with the corresponding nonfluorinated analogues lc‐[Cu(BTB)(DMF)] and [Ag₂(BTB)], and two known (super)hydrophobic MOFs, FMOF‐1 and ZIF‐8, they have been investigated as low‐dielectric constant (low‐κ) materials under dry and humid conditions. The results show that substitution of hydrogen with fluorine or fluoroalkyl groups on the organic linker imparts higher hydrophobicity and lower polarizability to the overall material. Pellets of FMOF‐1, FMOF‐3, and FN‐PCP‐1 exhibit κ values of 1.63(1), 2.44(3), and 2.57(3) at 2 × 10⁶ Hz, respectively, under ambient conditions, versus 2.94(8) and 3.79(1) for lc‐[Cu(BTB)(DMF)] and [Ag₂(BTB)], respectively. Such low‐κ values persist even upon exposure to almost saturated humidity levels. Correcting for the experimental pellet density, the intrinsic κ for FMOF‐1 reaches the remarkably low value of 1.28, the lowest value known to date for a hydrophobic material.     

Regulating Uniform Li Plating/Stripping via Dual‐Conductive Metal‐Organic Frameworks for High‐Rate Lithium Metal Batteries

Lithium metal anodes show immense scope for application in high‐energy electronics and electric vehicles. Unfortunately, lithium dendrite growth and volume change leading to short lifespan and safety issues severely limit the feasibility of lithium metal batteries. A rational design of metal–organic framework (MOF)‐modified Li metal anode with optimized Li plating/stripping behavior via one‐step carbonization of ZIF‐67 is proposed. Experimental and theoretical simulation results reveal that carbonized MOFs with uniformly dispersed Co nanoparticles in N‐graphene (Co@N‐G) exhibit an electronic/ionic dual‐conductivity and significantly improved affinity with Li, and so serve as an ideal host for dendrite‐free lithium deposition, consequently leading to uniform lithium plating/stripping during cycling. As a result, the anode delivers highly stable cyclic performance with high coulombic efficiency (CE) at ultrahigh current densities (CE = 91.5% after 130 cycles at 10 mA cm^?2, and CE = 90.4% after 80 cycles at 15 mA cm^?2). Moreover, the practical applicability and functionality of such anodes are demonstrated through assembly of Li‐Co@N‐G/NCM full batteries exhibiting a long cycle life of 100 cycles with a high capacity retention of 92% at 1 C.     

Nanoscale Metal‐Organic Frameworks: Synthesis,Biocompatibility, Imaging Applications,and Thermal and Dynamic Therapy of Tumors

Nanoscale metal‐organic frameworks (NMOFs) have attracted increasing attention for biomedical applications due to their large specific surface area, good biocompatibility, adjustable structures, and diverse functions. By choosing appropriate metal ions and ligands, NMOFs can be synthesized and regulated to assist the diagnosis and treatment of cancer, acting as imaging agents, drug carriers, and cancer therapeutic agents. This review summarizes the recent advances of NMOFs in synthesis, biocompatibility, imaging, and applications in cancer therapies. Among these, the term “biocompatibility” is used to outline their various biological characteristics, and it is mainly discussed from the aspects of size and surface properties of NMOFs. The imaging section mainly emphasizes the application advantages of NMOFs as imaging agents in magnetic resonance, computed tomography, and fluorescence imaging. The applications of NMOFs in four cancer therapies, including phototherapy, radiotherapy, microwave therapy, and ultrasonic therapy, are addressed, especially for thermal and dynamic therapy. Finally, the prospects and challenges of NMOFs in imaging and cancer therapies are also discussed.     

Liquid Phase Heteroepitaxial Growth of Moisture‐Tolerant MOF‐5 Isotype Thin Films and Assessment of the Sorption Properties by Quartz Crystal Microbalance

The moisture‐tolerant metal‐organic frameworks (MOFs) of formula [Zn₄O(L)₃]_n (L = di‐substituted carboxypyrazolate derivatives) are fabricated as thin films on self‐assembled monolayer (SAM) functionalized gold substrates by employing the step‐by‐step liquid phase epitaxial (LPE) deposition method in a continuous operation mode. The in situ monitoring of the deposition by quartz crystal microbalance (QCM) and grazing incidence X‐ray diffraction reveal different growth regimes and crystallinities of the obtained thin films in dependence of the chosen alkyl side chain functionality at the carboxypyrazolate linkers, L. To overcome the relatively poor crystallinity and low porosity of a particular homostructured metal‐organic framework type B film, the step‐by‐step heteroepitaxial growth of this MOF B on top of the crystallite surfaces of a well‐grown and lattice‐matched MOF type A is applied. This approach enables the fabrication of oriented, core‐shell‐like MOF B @ A surface mounted heterocrystals as an intergrown homogeneous coating for the selective adsorption of volatile organic compounds. The accessible pore volumes of the individual components and the heterostructured films are characterized by performing adsorption measurements of different organic probe molecules using an environmentally controlled QCM instrument. The results show good adsorption capacity, excellent size exclusion selectivity for alcohols, and a high degree of moisture‐tolerance of the heteroepitaxial MOF films.     

Fabrication of Glyco‐Metal‐Organic Frameworks for Targeted Interventional Photodynamic/Chemotherapy for Hepatocellular Carcinoma through Percutaneous Transperitoneal Puncture

Hepatocellular carcinoma (HCC) causes high morbidity and mortality due to a lack of adequate treatments. Cancer treatments have benefited from nanotechnology approaches that integrate multimodal synergistic therapies. A synergistic, minimally invasive strategy of interventional photodynamic therapy (IPDT) and chemotherapy for HCC treatment through percutaneous transperitoneal puncture is disclosed that is based on photosensitive porphyrinic galactose‐modified metal‐organic frameworks (PCN‐224) first used as hepatic targeting and encapsulated with anticancer drug doxorubicin (DOX@Gal‐PCN‐224). Real‐time imaging reveals the effective accumulation of the integrated nanosystem in the HCC cells and tumor tissues due to hepatic targeting. Evaluation of the anti‐tumor efficiency of this nanosystem on orthotopic transplantation tumors with the aid of minimally invasive intervention shows a tumor inhibition rate of 98%. The synergistic effects induce high‐level cell apoptosis and tissue necrosis in vitro and in vivo. This bimodal IPDT/chemotherapy strategy holds great potential in the clinical treatment for HCC.     

Electrolyte Interphase Built from Anionic Covalent Organic Frameworks for Lithium Dendrite Suppression

Lithium (Li) metal batteries hold considerable promise for numerous energy-dense applications. However, the dendritic Li anode produced during Li⁺/Li deposition-stripping endangers battery safety and shortens cycle lifespan. Herein, an electrolyte interphase built from 2D anionic covalent organic frameworks (ACOF) is coated on Li for dendrite suppression. The ACOF with Li⁺-affinity facilitates rapid and exclusive passage of Li-ions from the electrolyte, yielding near-unity Li⁺ transference number (0.82) and ionic conductivity beyond 3.7 mS cm^-1 at the interphase. Such high transport efficiency of Li-ions can fundamentally circumvent the Li⁺ deficiency that results in dendrite formation. Pairing the ACOF-coated Li against a high-voltage LiCoO₂ cathode (4.5 V) achieves exceptional cycle stability, mitigated polarization, as well as improved rate capability. Accordingly, this strategy vastly expands the pool of electrolyte interphases that can be used for coating and protecting Li anode.     

Tuning Local Molecular Orientation–Composition Correlations in Binary Organic Thin Films by Solution Shearing

A general impact of solution shearing on molecular orientation correlation is observed in polymer:fullerene organic solar cells in which one of the components forms fibrils or aggregates. Further investigation with polarized soft X‐ray scattering reveals that solution shearing induces more face‐to‐face orientation relative to the interface of two components compared to spin‐coating. This impact is shearing speed dependent, that is, slow shearing speed can induce more face‐to‐face orientation than a fast shearing speed. These results demonstrate that solution shearing is an effective method to control the relative molecular orientation. Solution shearing can also modify the domain size and average composition variations.     

Solvent‐Induced Morphology in Polymer‐Based Systems for Organic Photovoltaics

Studies on the influence of four different solvents on the morphology and photovoltaic performance of bulk‐heterojunction films made of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl‐C₆₁ butyric acid methyl ester (PCBM) via spin‐coating for photovoltaic applications are reported. Solvent‐dependent PCBM cluster formation and P3HT crystallization during thermal annealing are investigated with optical microscopy and grazing‐incidence wide‐angle X‐ray scattering (GIWAXS) and are found to be insufficient to explain the differences in device performance. A combination of atomic force microscopy (AFM), X‐ray reflectivity (XRR), and grazing‐incidence small‐angle X‐ray scattering (GISAXS) investigations results in detailed knowledge of the inner film morphology of P3HT:PCBM films. Vertical and lateral phase separation occurs during spin‐coating and annealing, depending on the solvent used. The findings are summarized in schematics and compared with the IV characteristics. The main influence on the photovoltaic performance arises from the vertical material composition and the existence of lateral phase separation fitting to the exciton diffusion length. Absorption and photoluminescence measurements complement the structural analysis.     

Hierarchical Porous Te@ZnCo2O4 Nanofibers Derived from Te@Metal‐Organic Frameworks for Superior Lithium Storage Capability

1D hierarchical porous nanocomposites with tailored chemical composition are gaining popularity in lithium‐ion batteries. Here, with core@shell Te@ZIF‐8 (Zn, Co) nanofibers as a starting point, rational designed porous Te@ZnCo₂O₄ nanocomposite has been fabricated by a simple morphology‐maintained and calcination‐induced oxidative decomposition process, with the purpose of simultaneously settling the pulverization and conductivity issues of transition metal oxides. This is the first time to integrate Te and ZnCo₂O₄ into one architecture at nanometer level. The Te@ZnCo₂O₄ nanofibers combine both advantages of Te such as excellent electrical conductivity and ZnCo₂O₄ with high capacity as well as take full use of their synergistic effect. With the favorable 1D porous structure and the unique composition, this novel Te@ZnCo₂O₄ nanofiber manifests strong ability to improve the lithium storage performances with a high specific capacity of 1364 mA h g^?1 in the initial discharge and a reversible capacity of 956 mA h g^?1 after 100 cycles. When increased the current density to 2000 mA g^?1, the capacity still remains as 307 mA h g^?1, demonstrating superior rate capability. Furthermore, this general strategy can be extended to construct other core@shell Te@MOFs composites.     

Self‐Mineralized Photothermal Bacteria Hybridizing with Mitochondria‐Targeted Metal–Organic Frameworks for Augmenting Photothermal Tumor Therapy

A photothermal bacterium (PTB) is reported for tumor‐targeted photothermal therapy (PTT) by using facultative anaerobic bacterium Shewanella oneidensis MR‐1 (S. oneidensis MR‐1) to biomineralize palladium nanoparticles (Pd NPs) on its surface without affecting bacterial activity. It is found that PTB possesses superior photothermal property in near infrared (NIR) regions, as well as preferential tumor‐targeting capacity. Zeolitic imidazole frameworks‐90 (ZIF‐90) encapsulating photosensitizer methylene blue (MB) are hybridized on the surface of living PTB to further enhance PTT efficacy. MB‐encapsulated ZIF‐90 (ZIF‐90/MB) can selectively release MB at mitochondria and cause mitochondrial dysfunction by producing singlet oxygen (¹O₂) under light illumination. Mitochondrial dysfunction further contributes to adenosine triphosphate (ATP) synthesis inhibition and heat shock proteins (HSPs) down‐regulated expression. The PTB‐based therapeutic platform of PTB@ZIF‐90/MB demonstrated here will find great potential to overcome the challenges of tumor targeting and tumor heat tolerance in PTT.     

Massive Anisotropic Thermal Expansion and Thermo‐Responsive Breathing in Metal–Organic Frameworks Modulated by Linker Functionalization

Functionalized metal–organic frameworks (fu‐MOFs) of general formula [Zn₂(fu‐L)₂dabco]_n show unprecedentedly large uniaxial positive and negative thermal expansion (fu‐L = alkoxy functionalized 1,4‐benzenedicarboxylate, dabco = 1,4‐diazabicyclo[2.2.2]octane). The magnitude of the volumetric thermal expansion is more comparable to property of liquid water rather than any crystalline solid‐state material. The alkoxy side chains of fu‐L are connected to the framework skeleton but nevertheless exhibit large conformational flexibility. Thermally induced motion of these side chains induces extremely large anisotropic framework expansion and eventually triggers reversible solid state phase transitions to drastically expanded structures. The thermo‐responsive properties of these hybrid solid–liquid materials are precisely controlled by the choice and combination of fu‐Ls and depend on functional moieties and chain lengths. In principle, this combinatorial approach allows for a targeted design of extreme thermo‐mechanical properties of MOFs addressing the regime between crystalline solid matter and the liquid state.