ZIF-8 Membrane Permselectivity Modification by Manganese(II) Acetylacetonate Vapor Treatment

Cations induced in situ electrochemical amorphization for enhanced oxygen evolution reaction

Surface reconstruction is widely existed on the surface of transition metal-based catalysts under operando oxygen evolution reaction (OER) condition. The design and optimize the reconstruction process are essential to achieve high electrochemical active surface and thus facilitate the reaction kinetics, whereas still challenge. Herein, we exploit electrolyte engineering to regulate reconstruction on the surface of Fe2O3 catalysts under operando OER conditions. The intentional added cations in electrolyte can participate the reconstruction process and realize a desirable crystalline to amorphous structure conversion, contributing abundant well-defined active sites. Spectroscopic measurements and density functional theory calculation provide insight into the underlying role of amorphous structure for electron transfer, mass transport, and intermediate adsorption. With the assistant of Co2+ cations, the enhanced current density as large as 17.9 % can be achieved at 2.32 V (vs RHE). The present results indicate the potential of electrolyte engineering for regulating the reconstruction process and provide a generalized in-situ strategy for advanced catalysts design.

Facilitating Proton Coupled Electron Transfer Reaction through the Interfacial Micro Electric Field with Fe─N4 ─C in FeMOFs Glass

The proton-coupled electron transfer(PCET) reaction plays a crucial role in the chemical transformation process andhas become one of the most concerned elementary reactions. However, the complex kinetics of PCET reaction, which requires the simultaneous transfer of protons and electrons, leads to the dilemma that thermodynamics and kinetics cannot bebalanced and restricts its further development. In this, an interface micro-electric field (IMEF) basedon Fe─N4 in FeMOFs (Fe-Based Metal-Organic Frameworks) glass is designed tosynchronize proton/electron interface behavior for the first time to realizeefficient PCET reaction and optimize reaction thermodynamics and kinetics. The IMEF facilitates the separation of photogenerated electrons and holes, and accelerates Fe(III)/Fe(II) cycle. Driven by near-surface electric field force, the protons near surfacemigrate to Fe sites and participate in Fe(IV)═O formation and reaction, lowering the reaction energy barrier. Based on the interface regulation ofIMEF, a high-efficiency PCET reaction is realized, and kinetic reactionrate constant of photocatalytic oxidation of emerging contaminants is increasedby 3.7 times. This study highlights a strategy for IMEFs to modulate PEC Treactions for a wide range of potential applications, including environmental and ecological applications.

Metal-Organic Framework Membrane Hybridized with Graphitic Materials for Gas Separation

Metal-organic frameworks (MOFs) are an exceptional class of crystalline materials that have been extensively used to fabricate membranes for various applications such as gas separation, ion transport, and desalination due to their well-defined pore structure, chemical features, and simple synthesis process. The incorporation of graphitic carbon materials in MOFs has garnered significant attention as it can provide abundant nucleation sites and modulate gas transport by influencing the orientation or rigidity of MOF crystals without changing their porous structure. This review insights of previous studies utilizing graphene, graphene oxide, carbon nanotubes, and graphene nanoribbons for MOF-based gas separation membranes, particularly focusing on polycrystalline MOF membrane hybridization with graphitic materials. We also briefly discuss the use of carbon/MOF hybrid materials for preparing mixed matrix membranes.

Fluoropolymer-MOF Hybrids with Switchable Hydrophilicity for 19F MRI-Monitored Cancer Therapy

Cancer theranostics that combines cancer diagnosis and therapy is a promising approach for personalized cancer treatment. However, current theranostic strategies suffer from low imaging sensitivity for visualization and an inability to target the diseased tissue site with high specificity, thus hindering their translation to the clinic. In this study, we have developed a tumor microenvironment-responsive hybrid theranostic agent by grafting water-soluble, low-fouling fluoropolymers to pH-responsive zeolitic imidazolate framework-8 (ZIF-8) nanoparticles by surface-initiated RAFT polymerization. The conjugation of the fluoropolymers to ZIF-8 nanoparticles not only allows sensitive in vivo visualization of the nanoparticles by ¹⁹F MRI but also significantly prolongs their circulation time in the bloodstream, resulting in improved delivery efficiency to tumor tissue. The ZIF-8-fluoropolymer nanoparticles can respond to the acidic tumor microenvironment, leading to progressive degradation of the nanoparticles and release of zinc ions as well as encapsulated anticancer drugs. The zinc ions released from the ZIF-8 can further coordinate to the fluoropolymers to switch the hydrophilicity and reverse the surface charge of the nanoparticles. This transition in hydrophilicity and surface charge of the polymeric coating can reduce the "stealth-like" nature of the agent and enhance specific uptake by cancer cells. Hence, these hybrid nanoparticles represent intelligent theranostics with highly sensitive imaging capability, significantly prolonged blood circulation time, greatly improved accumulation within the tumor tissue, and enhanced anticancer therapeutic efficiency.

Multifunctional Integrated Superhydrophobic Coatings with Unique Fluorescence and Micro/Micro/Nano-Hierarchical Structures Enabled by In Situ Self-Assembly

Conferring versatility to superhydrophobic materials is extremely desirable to advance their utility. Herein, we have developed a superhydrophobic material with montmorillonite as microskeleton supports and in situ grown ZIF-8 nanoparticles and loaded them with newly developed fluorescent carbon dots. In situ growth of the ZIF-8 on OMMT constructs a dense nanoscale rough structure and meanwhile self-assembly generates abundant microporous, thus forming unique hierarchical microporous/microsheet/nanoparticle tri-tier micro and nano structures. Then the multifunctional superhydrophobic coating is fabricated by a facile spraying technique using polydimethylsiloxane (PDMS) as a multifunctional polymer binder. The PDMS/RB-CDs/ZIF-8@OMMT exhibits superhydrophobicity with a water contact angle of 164.7° and a water sliding angle of 1.4°, which also possesses good self-cleaning performance. Moreover, novel carbon dots are developed in this work which can confer unique fluorescent properties and photothermal properties to materials. Fluorescence characterization reveals the multiple emission peaks among 300-800 nm and excitation wavelength dependence and independence. Photothermal experiments unveil an efficient light-to-heat conversion caused by the light traps and absorption wavelengths associated with photothermal heating. Benefiting from the dense microporous/microsheet/nanoparticle structures, the superhydrophobicity is still maintained after 120 cycles of abrasion. Moreover, electrochemical impedance spectroscopy (EIS) reveals a significant increase in impedance, which is associated with excellent corrosion resistance. The superhydrophobic coating also exhibits superior UV resistance and good thermal stability. Multifunctional fluorescent superhydrophobic materials will enable the development of various and potential applications in different fields.

Zeolitic Imidazolate Framework Membranes: Novel Synthesis Methods and Progress Toward Industrial Use

In the last decade, zeolitic imidazolate frameworks (ZIFs) have been studied extensively for their potential as selective separation membranes. In this review, we highlight unique structural properties of ZIFs that allow them to achieve certain important separations, like that of propylene from propane, and summarize the state of the art in ZIF thin-film deposition on porous substrates and their modification by postsynthesis treatments. We also review the reported membrane performance for representative membrane synthesis approaches and attempt to rank the synthesis methods with respect to potential for scalability. To compare the dependence of membrane performance on membrane synthesis methods and operating conditions, we map out fluxes and separation factors of selected ZIF-8 membranes for propylene/propane separation. Finally, we provide future directions considering the importance of further improvements in scalability, cost effectiveness, and stable performance under industrially relevant conditions. Expected final online publication date for the Annual Review of Chemical and Biomolecular Engineering, Volume 13 is October 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Tailoring the Void Space Using Nanoreactors on Carbon Fibers to Confine SnS2 Nanosheets for Ultrastable Lithium/Sodium-Ion Batteries

Herein, a rational design of SnS₂ nanosheets confined into bubble-like carbon nanoreactors anchored on N,S doped carbon nanofibers (SnS₂ @C/CNF) is proposed to prepare the self-standing electrodes, which provides tunable void space on carbon fibers for the first time by introducing hollow carbon nanoreactors. The SnS₂ @C/CNF provides the stable support with greatly enhanced ion and electron transport, alleviates aggregation and volume expansion of SnS₂ nanosheets, and promotes the formation of abundant exposed edges and active sites. The volume balance between SnS₂ nanosheets and hollow carbon nanoreactors is reached to accommodate the expansion of SnS₂ during cycles by controlling the thickness of SnO₂ shells, which achieves the best space utilization. The doping of N,S elements enhances the wettability of the carbon nanofiber matrix to electrolyte and Li ions and further improves the electrical conductivity of the whole electrode. Thus, the SnS₂ @C/CNF benefits greatly in structural stability and pseudocapacitive capacity for improved lithium/sodium storage performance. As a result of these improvements, the self-standing SnS₂ @C/CNF film electrodes exhibit the highly stable capacity of 964.8 and 767.6 mAh g^-1 at 0.2 A g^-1 , and excellent capacity retention of 87.4% and 82.4% after 1000 cycles at high current density for lithium-ion batteries and sodium-ion batteries, respectively.

Design of a MOF based on octa-nuclear zinc clusters realizing both thermal stability and structural flexibility

An octa-nuclear zinc (Zn₈) cluster-based two-fold interpenetrated metal-organic framework (MOF) of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆]·7DMF (denoted as Zn8-as; H₂FDC = 9H-fluorene-2,7-dicarboxylic acid; DMF = N,N-dimethylformamide) was synthesized by the reaction of a hard base of a curved dicarboxylate ligand (H₂FDC) with the borderline acid of Zn(II) under solvothermal conditions. Zn8-as shows significant crystal volume shrinkage upon heating, yielding a solvate-free framework of [(CH₃)₂NH₂]₂[Zn₈O₃(FDC)₆] (Zn8-de). Zn8-de displays gated adsorption for C₂H₂ and type-I adsorption for CO₂, attributed to the framework flexibility and the different interactions between the gas molecules and the host framework.

Vapor-Phase Processing of Metal-Organic Frameworks

ConspectusPorous metal-organic frameworks (MOFs), formed from organic linkers and metal nodes, have attracted intense research attention. Because of their high specific surface areas, uniform and adjustable pore sizes, and versatile physicochemical properties, MOFs have shown disruptive potential in adsorption, catalysis, separation, etc. For many of these applications, MOFs are synthesized solvothermally as bulk powders and subsequently shaped as pellets or extrudates. Other applications, such as membrane separations and (opto)electronics, require the implementation of MOFs as (patterned) thin films. Most thin-film formation methods are adapted from liquid-phase synthesis protocols. Precursor transport and nucleation are difficult to control in these cases, often leading to particle formation in solution. Moreover, the use of solvents gives rise to environmental and safety challenges, incompatibility issues with some substrates, and corrosion issues in the case of dissolved metal salts. In contrast, vapor-phase processing methods have the merits of environmental friendliness, control over thickness and conformality, scalability in production, and high compatibility with other workflows.In this Account, we outline some of our efforts and related studies in the development and application of vapor-phase processing of crystalline MOF materials (MOF-VPP). We first highlight the advances and mechanisms in the vapor-phase deposition of MOFs (MOF-VPD), mainly focusing on the reactions between a linker vapor and a metal-containing precursor layer. The characteristics of the obtained MOFs (thickness, porosity, crystallographic phase, orientation, etc.) and the correlation of these properties with the deposition parameters (precursors, temperatures, humidity, post-treatments, etc.) are discussed. Some in situ characterization methods that contributed to a fundamental understanding of the involved mechanisms are included in the discussion. Second, four vapor-phase postsynthetic functionalization (PSF) methods are summarized: linker exchange, guest loading, linker grafting, and metalation. These approaches eliminate potential solubility issues and enable fast diffusion of reactants and guests as well as a high loading or degree of exchange. Vapor-phase PSF provides a platform to modify the MOF porosity or even introduce new functionalities (e.g., luminescence photoswitching and catalytic activity). Third, since vapor-phase processing methods enable the integration of MOF film deposition into a (micro)fabrication workflow, they facilitate a range of applications with improved performance (low-k dielectrics, sensors, membrane separations, etc.). Finally, we provide a discussion on the limitations, challenges, and further opportunities for MOF-VPP. Through the discussion and analysis of the vapor-phase processing strategies as well as the underlying mechanisms in this Account, we hope to contribute to the development of the controllable synthesis, functionalization, and application of MOFs and related materials.

Zinc-coordinated polydopamine surface with a nanostructure and superhydrophilicity for antibiofouling and antibacterial applications

A superhydrophilic nanostructured surface of zinc-coordinated polydopamine is formed by the growth and intertwining of the PDA/Zn nanowires via Zn–N and Zn–O bonds, which has potential for preventing biomaterial-associated biofouling and infections.

Integration of a Metal-Organic Framework Film with a Tubular Whispering-Gallery-Mode Microcavity for Effective CO2 Sensing

Carbon dioxide (CO₂) sensing using an optical technique is of great importance in the environment and industrial emission monitoring. However, limited by the poor specific adsorption of gas molecules as well as insufficient coupling efficiency, there is still a long way to go toward realizing a highly sensitive optical CO₂ gas sensor. Herein, by combining the advantages of a whispering-gallery-mode microcavity and a metal-organic framework (MOF) film, a porous functional microcavity (PF-MC) was fabricated with the assistance of the atomic layer deposition technique and was applied to CO₂ sensing. In this functional composite, the rolled-up microcavity provides the ability to tune the propagation of light waves and the electromagnetic coupling with the surroundings via an evanescent field, while the nanoporous MOF film contributes to the specific adsorption of CO₂. The composite demonstrates a high sensitivity of 188 nm RIU^-1 (7.4 pm/% with respect to the CO₂ concentration) and a low detection limit of ∼5.85 × 10^-5 RIU. Furthermore, the PF-MC exhibits great selectivity to CO₂ and outstanding reproducibility, which is promising for the next-generation optical gas sensing devices.