Crystalline Metal-Organic Framework Coatings Engineered via Metal-Phenolic Network Interfaces.

Crystalline metal-organic frameworks (MOFs) have garnered extensive attention owing to their highly ordered porous structure and physicochemical properties. However, their practical application often requires their integration with various substrates, which is challenging because of their weakly adhesive nature and the diversity of substrates that exhibit different properties. Herein, we report the use of amorphous metal-phenolic network coatings to facilitate the growth of crystalline MOF coatings on various particle and planar substrates. Crystalline MOFs with different metal ions and morphologies were successfully deposited on substrates (13 types) of varying sizes, shapes, and surface chemistries. Furthermore, the physicochemical properties of the coated crystalline MOFs (e.g., composition, thickness) could be tuned using different synthesis conditions. The engineered MOF-coated membranes demonstrated excellent liquid and gas separation performance, exhibiting a high H2 permeance of 63200 GPU and a H2/CH4 selectivity of 10.19, likely attributable to the thin nature of the coating (~180 nm), which can be realized using the present strategy. Considering the vast array of MOFs available (>90,000) and the diversity of substrates, this work is expected to pave the way for creating a wide range of MOF composites and coatings with potential applications in biomedicine, environmental science, and agriculture.

Intelligent multifunctional ruthenium monoatomic/ZnAl-LDH photocatalysts for simultaneous detection and rapid degradation of antibiotics.

The construction and precise synthesis of materials based on functional and structural orientations have emerged as a pivotal platform in the field of environmental management. In this paper, an efficient and stable catalyst (RuLDH) was constructed to achieve this goal. RuLDH comprises individual Ru atoms that are uniformly dispersed on ZnAl-LDH, achieved by room temperature stirring. Remarkably, RuLDH exhibits exceptional performance under visible light, effectively triggering the photocatalytic degradation of tetracycline hydrochloride (TC) via peroxymonosulfate (PMS) with a remarkable efficiency of 100%, all while avoiding the generation of highly toxic intermediates. In addition, RuLDH0.2 demonstrated its utility in fluorescence detection of TC, showcasing commendable analytical performance characterized by rapid response, low detection limit, and robust resistance to environmental interferences (with a detection limit of 1.0 mg/L). Notably, the RuLDH0.2/PMS/Vis system exhibited remarkable efficacy in treating actual pesticide wastewater, effectively exerting bactericidal and disinfectant effects. This study serves as a source of inspiration for the design of multifunctional single-atom catalysts, thereby pushing the boundaries of "integration of diagnosis and treatment" in environmental management and control.

Low-cost flexible textile electrocatalyst for overall water splitting.

Through the braidability of cotton fiber and the richness of surface functional groups, cotton fiber can be woven into any shape, and catalytically active centers can be stably anchored on the fibers. During the electrocatalytic overall water splitting (OWS) process, catalyst shedding and activity reduction can be effectively avoided.

Direct Assembly of Metal-Phenolic Network Nanoparticles for Biomedical Applications.

Coordination assembly offers a versatile means to developing advanced materials for various applications. However, current strategies for assembling metal-organic networks into nanoparticles (NPs) often face challenges such as the use of toxic organic solvents, cytotoxicity because of synthetic organic ligands, and complex synthesis procedures. Herein, we directly assemble metal-organic networks into NPs using metal ions and polyphenols (i.e., metal-phenolic networks (MPNs)) in aqueous solutions without templating or seeding agents. We demonstrate the role of buffers (e.g., phosphate buffer) in governing NP formation and the engineering of the NP physicochemical properties (e.g., tunable sizes from 50 to 270 nm) by altering the assembly conditions. A library of MPN NPs is prepared using natural polyphenols and various metal ions. Diverse functional cargos, including anticancer drugs and proteins with different molecular weights and isoelectric points, are readily loaded within the NPs for various applications (e.g., biocatalysis, therapeutic delivery) by direct mixing, without surface modification, owing to the strong affinity of polyphenols to various guest molecules. This study provides insights into the assembly mechanism of metal-organic complexes into NPs and offers a simple strategy to engineer nanosized materials with desired properties for diverse biotechnological applications.

New insights into atomic layer BiOBr quantum dot/ZnAl-LDH composites in photocatalytic water treatment: Performance and mechanism.

Insufficient absorption sites and low charge separation notably limit the activation of photocatalytic molecular oxygen. In this study, atomic-layer BiOBr (BiOBr-QDs)/ZnAl-LDH composites with a considerable number of edges were developed to address the above-mentioned problems. The result of this study indicated the spatial separation of atomic-layer BiOBr-QDs/ZnAl-LDH's conduction band maximum (CBM) and valence band minimum (VBM). As a result, holes were produced on the substrate surface based on irradiation, and electrons were generated at the sites of the edge, such that ultra-fast charge separation can be carried out. The edges exposed massive adsorption sites in terms of oxygen molecules. Thus, electrons at the sites of the edge led to the reduction of absorbed oxygen molecules, thus exhibiting stronger photocatalytic •O2- production. Furthermore, the result confirmed that the atomic layer BiOBr-QDs/ZnAl-LDH are promising in environmental catalytic degradation for its increased activity of •O2- production. In this study, a novel insight into advanced photocatalyst design based on edge unsaturated ligand engineering at an atomic level is provided.

Engineering Flexible Metal-Phenolic Networks with Guest Responsiveness via Intermolecular Interactions.

Flexible metal-organic materials are of growing interest owing to their ability to undergo reversible structural transformations under external stimuli. Here, we report flexible metal-phenolic networks (MPNs) featuring stimuli-responsive behavior to diverse solute guests. The competitive coordination of metal ions to phenolic ligands of multiple coordination sites and solute guests (e.g., glucose) primarily determines the responsive behavior of the MPNs, as revealed experimentally and computationally. Glucose molecules can be embedded into the dynamic MPNs upon mixing, leading to the reconfiguration of the metal-organic networks and thus changes in their physicochemical properties for targeting applications. This study expands the library of stimuli-responsive flexible metal-organic materials and the understanding of intermolecular interactions between metal-organic materials and solute guests, which is essential for the rational design of responsive materials for various applications.

Thermoresponsive MXene composite system with high adsorption capacity for quick and simple removal of toxic metal ions from aqueous environment.

High-performance adsorption and easy-to-recycle property of adsorbents are desirable in wastewater treatment, and a suitably smart adsorbent with responsive phase separation capacity is promising in this regard. Herein, a thermoresponsive composite system is designed through the combination of transition metal carbides (MXene) and poly(N-isopropylacrylamide) (PNIPAM) for removal of toxic metal ions from water. As a thermoresponsive switch, the PNIPAM endows such composite system with superior thermoresponsiveness (i.e., gel-water phase separation) in water, which facilitates to the control of adsorption. The gel phase triggered by an elevated temperature (e.g., 40 °C) quickly adsorbs toxic metal ions, and then a solid-liquid extraction way is used to conveniently separated the gel phase from water phase for simple removal of toxic metal ions. A very high adsorption capacity (e.g., ~224 mg·g-1 for Cu2+) can be achieved due to the synergistic effects of the composite system. Moreover, the separated gel can be back to a redispersed state at low temperature (e.g., 20 °C), enabling its effective regeneration and recovery. Notably, the PNIPAM as a protective agent prevents the oxidation of MXene so as to retain good stability during the multiple adsorption/desorption cycles. This simple and smart adsorption strategy is great promising for water purification application.

Polyphenol-Functionalized Cubosomes as Thrombolytic Drug Carriers.

The safe administration of thrombolytic agents is a challenge for the treatment of acute thrombosis. Lipid-based nanoparticle drug delivery technologies present opportunities to overcome the existing clinical limitations and deliver thrombolytic therapy with enhanced therapeutic outcomes and safety. Herein, lipid cubosomes are examined as nanocarriers for the encapsulation of thrombolytic drugs. The lipid cubosomes are loaded with the thrombolytic drug urokinase-type plasminogen activator (uPA) and coated with a low-fouling peptide that is incorporated within a metal-phenolic network (MPN). The peptide-containing MPN (pep-MPN) coating inhibits the direct contact of uPA with the surrounding environment, as assessed by an in vitro plasminogen activation assay and an ex vivo whole blood clot degradation assay. The pep-MPN-coated cubosomes prepared with 22 wt% peptide demonstrate a cell membrane-dependent thrombolytic activity, which is attributed to their fusogenic lipid behavior. Moreover, compared with the uncoated lipid cubosomes, the uPA-loaded pep-MPN-coated cubosomes demonstrate significantly reduced nonspecific cell association (<10% of the uncoated cubosomes) in the whole blood assay, a prolonged circulating half-life, and reduced splenic uPA accumulation in mice. These studies confirm the preserved bioactivity and cell membrane-dependent release of uPA within pep-MPN-coated lipid cubosomes, highlighting their potential as a delivery vehicle for thrombolytic drugs.

Site-Selective Coordination Assembly of Dynamic Metal-Phenolic Networks.

Coordination states of metal-organic materials are known to dictate their physicochemical properties and applications in various fields. However, understanding and controlling coordination sites in metal-organic systems is challenging. Herein, we report the synthesis of site-selective coordinated metal-phenolic networks (MPNs) using flavonoids as coordination modulators. The site-selective coordination was systematically investigated experimentally and computationally using ligands with one, two, and multiple different coordination sites. Tuning the multimodal Fe coordination with catechol, carbonyl, and hydroxyl groups within the MPNs enabled the facile engineering of diverse physicochemical properties including size, selective permeability (20-2000 kDa), and pH-dependent degradability. This study expands our understanding of metal-phenolic chemistry and provides new routes for the rational design of structurally tailorable coordination-based materials.

Superhydrophobic nanocomposites of erbium oxide and reduced graphene oxide for high-performance microwave absorption.

Engineering of electromagnetic wave absorbing materials featuring long-term durability in harsh outdoor environments (e.g., humidity, acid, and alkali conditions) is meaningful for their effective and sustainable implementation. Herein, morphology-controlled erbium oxide-reduced graphene oxide composites are designed for effective absorption of electromagnetic microwaves either in an acidic or alkaline environment. The engineered nanocomposites with chrysanthemum-like structures display good impedance matching, moderate attenuation constant, exchange resonance, natural resonance, multiple reflections, and polarization relaxations, therefore exhibiting excellent microwave absorption capacity with a minimum reflection loss of -37.18 dB and an effective absorption bandwidth of 5.1 GHz. In addition, the chrysanthemum-like composite also displays self-cleaning property, strong weatherability, and acid- and alkali-resistance, enabling sustained electromagnetic wave absorbing performance even in corrosive conditions (1 M HCl, 1 M NaOH). The findings indicate that, through structural engineering, erbium oxide-reduced graphene oxide composites can serve as a promising microwave absorber in harsh outdoor environments.

Exploiting Molecular Dynamics in Composite Coatings to Design Robust Super-Repellent Surfaces.

Fluorinated motifs are promising for the engineering of repellent coatings, however, a fundamental understanding of how to effectively bind these motifs to various substrates is required to improve their stability in different use scenarios. Herein, the binding of fluorinated polyhedral oligomeric silsesquioxanes (POSS) using a cyanoacrylate glue (binder) is computationally and experimentally evaluated. The composite POSS-binder coatings display ultralow surface energy (≈10 mJ m-2 ), while still having large surface adhesions to substrates (300-400 nN), highlighting that super-repellent coatings (contact angles >150°) can be readily generated with this composite approach. Importantly, the coatings show super-repellency to both corrosive liquids (e.g., 98 wt% H2 SO4 ) and ultralow surface tension liquids (e.g., alcohols), with ultralow roll-off angles (<5°), and tunable resistance to liquid penetration. Additionally, these coatings demonstrate the potential in effective cargo loading and robust self-cleaning properties, where experimental datasets are correlated with both relevant theoretical predictions and systematic all-atom molecular dynamics simulations of the repellent coatings. This work not only holds promise for chemical shielding, heat transfer, and liquid manipulations but offers a facile yet robust pathway for engineering advanced coatings by effectively combining components for their mutually desired properties.

Bioresponsive Polyphenol-Based Nanoparticles as Thrombolytic Drug Carriers.

Thrombolytic (clot-busting) therapies with plasminogen activators (PAs) are first-line treatments against acute thrombosis and ischemic stroke. However, limitations such as narrow therapeutic windows, low success rates, and bleeding complications hinder their clinical use. Drug-loaded polyphenol-based nanoparticles (NPs) could address these shortfalls by delivering a more targeted and safer thrombolysis, coupled with advantages such as improved biocompatibility and higher stability in vivo. Herein, a template-mediated polyphenol-based supramolecular assembly strategy is used to prepare nanocarriers of thrombolytic drugs. A thrombin-dependent drug release mechanism is integrated using tannic acid (TA) to cross-link urokinase-type PA (uPA) and a thrombin-cleavable peptide on a sacrificial mesoporous silica template via noncovalent interactions. Following drug loading and template removal, the resulting NPs retain active uPA and demonstrate enhanced plasminogen activation in the presence of thrombin (1.14-fold; p < 0.05). Additionally, they display lower association with macrophage (RAW 264.7) and monocytic (THP-1) cell lines (43 and 7% reduction, respectively), reduced hepatic accumulation, and delayed blood clearance in vivo (90% clearance at 60 min vs 5 min) compared with the template-containing NPs. Our thrombin-responsive, polyphenol-based NPs represent a promising platform for advanced drug delivery applications, with potential to improve thrombolytic therapies.

Macromolecular Engineering of Thermoresponsive Metal-Phenolic Networks.

Dynamic nanostructured materials that can react to physical and chemical stimuli have attracted interest in the biomedical and materials science fields. Metal-phenolic networks (MPNs) represent a modular class of such materials: these networks form via coordination of phenolic molecules with metal ions and can be used for surface and particle engineering. To broaden the range of accessible MPN properties, we report the fabrication of thermoresponsive MPN capsules using FeIII ions and the thermoresponsive phenolic building block biscatechol-functionalized poly(N-isopropylacrylamide) (biscatechol-PNIPAM). The MPN capsules exhibited reversible changes in capsule size and shell thickness in response to temperature changes. The temperature-induced capsule size changes were influenced by the chain length of biscatechol-PNIPAM and catechol-to-FeIII ion molar ratio. The metal ion type also influenced the capsule size changes, allowing tuning of the MPN capsule mechanical properties. AlIII-based capsules, having a lower stiffness value (10.7 mN m-1), showed a larger temperature-induced size contraction (∼63%) than TbIII-based capsules, which exhibit a higher stiffness value (52.6 mN m-1) and minimal size reduction (<1%). The permeability of the MPN capsules was controlled by changing the temperature (25-50 °C)─a reduced permeability was obtained as the temperature was increased above the lower critical solution temperature of biscatechol-PNIPAM. This temperature-dependent permeability behavior was exploited to encapsulate and release model cargo (500 kDa fluorescein isothiocyanate-tagged dextran) from the capsules; approximately 70% was released over 90 min at 25 °C. This approach provides a synthetic strategy for developing dynamic and thermoresponsive-tunable MPN systems for potential applications in biological science and biotechnology.

Origins of Structural Elasticity in Metal-Phenolic Networks Probed by Super-Resolution Microscopy and Multiscale Simulations.

Metal-phenolic networks (MPNs) are amorphous materials that can be used to engineer functional films and particles. A fundamental understanding of the heat-driven structural reorganization of MPNs can offer opportunities to rationally tune their properties (e.g., size, permeability, wettability, hydrophobicity) for applications such as drug delivery, sensing, and tissue engineering. Herein, we use a combination of single-molecule localization microscopy, theoretical electronic structure calculations, and all-atom molecular dynamics simulations to demonstrate that MPN plasticity is governed by both the inherent flexibility of the metal (FeIII)-phenolic coordination center and the conformational elasticity of the phenolic building blocks (tannic acid, TA) that make up the metal-organic coordination complex. Thermal treatment (heating to 150 °C) of the flexible TA/FeIII networks induces a considerable increase in the number of aromatic π-π interactions formed among TA moieties and leads to the formation of hydrophobic domains. In the case of MPN capsules, 15 min of heating induces structural rearrangements that cause the capsules to shrink (from ∼4 to ∼3 µm), resulting in a thicker (3-fold), less porous, and higher protein (e.g., bovine serum albumin) affinity MPN shell. In contrast, when a simple polyphenol such as gallic acid is complexed with FeIII to form MPNs, rigid materials that are insensitive to temperature changes are obtained, and negligible structural rearrangement is observed upon heating. These findings are expected to facilitate the rational engineering of versatile TA-based MPN materials with tunable physiochemical properties for diverse applications.

Assembly of Bioactive Nanoparticles via Metal-Phenolic Complexation.

The integration of bioactive materials (e.g., proteins and genes) into nanoparticles holds promise in fields ranging from catalysis to biomedicine. However, it is challenging to develop a simple and broadly applicable nanoparticle platform that can readily incorporate distinct biomacromolecules without affecting their intrinsic activity. Herein, a metal-phenolic assembly approach is presented whereby diverse functional nanoparticles can be readily assembled in water by combining various synthetic and natural building blocks, including poly(ethylene glycol), phenolic ligands, metal ions, and bioactive macromolecules. The assembly process is primarily mediated by metal-phenolic complexes through coordination and hydrophobic interactions, which yields uniform and spherical nanoparticles (mostly <200 nm), while preserving the function of the incorporated biomacromolecules (siRNA and five different proteins used). The functionality of the assembled nanoparticles is demonstrated through cancer cell apoptosis, RNA degradation, catalysis, and gene downregulation studies. Furthermore, the resulting nanoparticles can be used as building blocks for the secondary engineering of superstructures via templating and cross-linking with metal ions. The bioactivity and versatility of the platform can potentially be used for the streamlined and rational design of future bioactive materials.

Luminescent Metal-Phenolic Networks for Multicolor Particle Labeling.

The development of fluorescence labeling techniques has attracted widespread interest in various fields, including biomedical science as it can facilitate high-resolution imaging and the spatiotemporal understanding of various biological processes. We report a supramolecular fluorescence labeling strategy using luminescent metal-phenolic networks (MPNs) constructed from metal ions, phenolic ligands, and common and commercially available dyes. The rapid labeling process (<5 min) produces ultrathin coatings (≈10 nm) on diverse particles (e.g., organic, inorganic, and biological entities) with customized luminescence (e.g., red, blue, multichromatic, and white light) simply through the selection of fluorophores. The fluorescent coatings are stable at pH values from 1 to 8 and in complex biological media owing to the dominant π interactions between the dyes and MPNs. These coatings exhibit negligible cytotoxicity and their strong fluorescence is retained even when internalized into intracellular compartments. This strategy is expected to provide a versatile approach for fluorescence labeling with potential in diverse fields across the physical and life sciences.

Fluorinated Metal-Organic Coatings with Selective Wettability.

Surface chemistry is a major factor that determines the wettability of materials, and devising broadly applicable coating strategies that afford tunable and selective surface properties required for next-generation materials remains a challenge. Herein, we report fluorinated metal-organic coatings that display water-wetting and oil-repelling characteristics, a wetting phenomenon different from responsive wetting induced by external stimuli. We demonstrate this selective wettability with a library of metal-organic coatings using catechol-based coordination and silanization (both fluorinated and fluorine-free), enabling sensing through interfacial reconfigurations in both gaseous and liquid environments, and establish a correlation between the coating wettability and polarity of the liquids. This selective wetting performance is substrate-independent, spontaneous, durable, and reversible and occurs over a range of polar and nonpolar liquids (60 studied). These results provide insight into advanced liquid-solid interactions and a pathway toward tuning interfacial affinities and realizing robust, selective superwettability according to the surrounding conditions.

Exploiting Supramolecular Dynamics in Metal-Phenolic Networks to Generate Metal-Oxide and Metal-Carbon Networks.

Supramolecular complexation is a powerful strategy for engineering materials in bulk and at interfaces. Metal-phenolic networks (MPNs), which are assembled through supramolecular complexes, have emerged as suitable candidates for surface and particle engineering owing to their diverse properties. Herein, we examine the supramolecular dynamics of MPNs during thermal transformation processes. Changes in the local supramolecular network including enlarged pores, ordered aromatic packing, and metal relocation arise from thermal treatment in air or an inert atmosphere, enabling the engineering of metal-oxide networks (MONs) and metal-carbon networks, respectively. Furthermore, by integrating photo-responsive motifs (i.e., TiO2 ) and silanization, the MONs are endowed with reversible superhydrophobic (>150°) and superhydrophilic (≈0°) properties. By highlighting the thermodynamics of MPNs and their transformation into diverse materials, this work offers a versatile pathway for advanced materials engineering.

Microemulsion-Assisted Templating of Metal-Stabilized Poly(ethylene glycol) Nanoparticles.

Poly(ethylene glycol) (PEG) is well known to endow nanoparticles (NPs) with low-fouling and stealth-like properties that can reduce immune system clearance in vivo, making PEG-based NPs (particularly sub-100 nm) of interest for diverse biomedical applications. However, the preparation of sub-100 nm PEG NPs with controllable size and morphology is challenging. Herein, we report a strategy based on the noncovalent coordination between PEG-polyphenolic ligands (PEG-gallol) and transition metal ions using a water-in-oil microemulsion phase to synthesize sub-100 nm PEG NPs with tunable size and morphology. The metal-phenolic coordination drives the self-assembly of the PEG-gallol/metal NPs: complexation between MnII and PEG-gallol within the microemulsions yields a series of metal-stabilized PEG NPs, including 30-50 nm solid and hollow NPs, depending on the MnII/gallol feed ratio. Variations in size and morphology are attributed to the changes in hydrophobicity of the PEG-gallol/MnII complexes at varying MnII/gallol ratios based on contact angle measurements. Small-angle X-ray scattering analysis, which is used to monitor the particle size and intermolecular interactions during NP evolution, reveals that ionic interactions are the dominant driving force in the formation of the PEG-gallol/MnII NPs. pH and cytotoxicity studies, and the low-fouling properties of the PEG-gallol/MnII NPs confirm their high biocompatibility and functionality, suggesting that PEG polyphenol-metal NPs are promising systems for biomedical applications.

Engineered Coatings via the Assembly of Amino-Quinone Networks.

Engineering coatings with precise physicochemical properties allows for control over the interface of a material and its interactions with the surrounding environment. However, assembling coatings with well-defined properties on different material classes remains a challenge. Herein, we report a co-assembly strategy to precisely control the structure and properties (e.g., thickness, adhesion, wettability, and zeta potential) of coatings on various materials (27 substrates examined) using quinone and polyamine building blocks. By increasing the length of the amine building blocks from small molecule diamines to branched amine polymers, we tune the properties of the films, including the thickness (from ca. 5 to ca. 50 nm), interfacial adhesion (0.05 to 5.54 nN), water contact angle (130 to 40°), and zeta potential (-42 to 28 mV). The films can be post-functionalized through the in situ formation of diverse nanostructures, including nanoparticles, nanorods, and nanocrystals. Our approach provides a platform for the rational design of engineered, substrate-independent coatings for various applications.