General Synthesis and Solution Processing of Metal-Organic Framework Nanofibers

A Versatile Shaping Method of Very-High Loading Porous Solids Paper Adsorbent Composites

Owing to their high porosity and tunability, porous solids such as metal-organic frameworks (MOFs), zeolites, or activated carbons (ACs) are of great interest in the fields of air purification, gas separation, and catalysis, among others. Nonetheless, these materials are usually synthetized as powders and need to be shaped in a more practical way that does not modify their intrinsic property (i.e., porosity). Elaborating porous, freestanding and flexible sheets is a relevant shaping strategy. However, when high loadings (>70 wt.%) are achieved the mechanical properties are challenged. A new straightforward and green method involving the combination softwood bleached kraft pulp fibers (S) and nano-fibrillated cellulose (NFC) is reported, where S provides flexibility while NFC acts as a micro-structuring and mechanical reinforcement agent to form high loadings porous solids paper sheets (>70 wt.%). The composite has unobstructed porosity and good mechanical strength. The sheets prepared with various fillers (MOFs, ACs, and zeolites) can be rolled, handled, and adapted to different uses, such as air purification. As an example of potential application, a MOF paper composite has been considered for the capture of polar volatile organic compounds exhibiting better performance than beads and granules.

Fibrous Zr-MOF Nanozyme Aerogels with Macro-Nanoporous Structure for Enhanced Catalytic Hydrolysis of Organophosphate Toxins

Metal-organic frameworks (MOFs) with Lewis acid catalytic sites, such as zirconium-based MOFs (Zr-MOFs), comprise a growing class of phosphatase-like nanozymes that can degrade toxic organophosphate pesticides and nerve agents. Rationally engineering and shaping MOFs from as-synthesized powders into hierarchically porous monoliths is essential for their use in emerging applications, such as filters for air and water purification and personal protection gear. However, several challenges still limit the production of practical MOF composites, including the need for sophisticated reaction conditions, low MOF catalyst loadings in the resulting composites, and poor accessibility to MOF-based active sites. To overcome these limitations, a rapid synthesis method is developed to introduce Zr-MOF nanozyme coating into cellulose nanofibers, resulting in the formation of processable monolithic aerogel composites with high MOF loadings. These composites contain Zr-MOF nanozymes embedded in the structure, and hierarchical macro-micro porosity enables excellent accessibility to catalytic active sites. This multifaceted rational design strategy, including the selection of a MOF with many catalytic sites, fine-tuning the coating morphology, and the fabrication of a hierarchically structured monolithic aerogel, renders synergistic effects toward the efficient continuous hydrolytic detoxification of organophosphorus-based nerve agent simulants and pesticides from contaminated water.

Regulating Intramolecular Electron Transfer of Nickel-Based Coordinations through Ligand Engineering for Aqueous Batteries

The integration of electronic effects into complexes for the construction of novel materials has not yet attracted significant attention in the field of energy storage. In the current study, eight one-dimensional (1D) nickel-based salicylic acid  complexes (Ni-XSAs, X = pH, pMe, pMeO, mMe, pBr, pCl, pF, and pCF3 ), are prepared by ligand engineering. The coordination environments in the Ni-XSAs are explored using X-ray absorption fine structure spectroscopy. The charge transfer of the complexes is modulated according to the difference in the electron-donating ability of the substituents, in combination with frontier orbital theory. Furthermore, density functional theory is used to investigate the effect of the substituent position on the electronic properties of the complexes. Ni-mMeSA exhibits better electrical conductivity than Ni-pMeSA. The electrochemical performance of Ni-mMeSA as an aqueous battery cathode is remarkably improved with a maximum energy density of 0.30 mWh cm-2 (125 Wh kg-1 ) and a peak power density of 33.72 mW cm-2 (14.03 kW kg-1 ). This study provides ideas for the application of new coordination chemistry in the field of energy materials science.

Organized mineralized cellulose nanostructures for biomedical applications

Cellulose is the most abundant naturally-occurring polymer, and possesses a one-dimensional (1D) anisotropic crystalline nanostructure with outstanding mechanical robustness, biocompatibility, renewability and rich surface chemistry in the form of nanocellulose in nature. Such features make cellulose an ideal bio-template for directing the bio-inspired mineralization of inorganic components into hierarchical nanostructures that are promising in biomedical applications. In this review, we will summarize the chemistry and nanostructure characteristics of cellulose and discuss how these favorable characteristics regulate the bio-inspired mineralization process for manufacturing the desired nanostructured bio-composites. We will focus on uncovering the design and manipulation principles of local chemical compositions/constituents and structural arrangement, distribution, dimensions, nanoconfinement and alignment of bio-inspired mineralization over multiple length-scales. In the end, we will underline how these cellulose biomineralized composites benefit biomedical applications. It is expected that this deep understanding of design and fabrication principles will enable construction of outstanding structural and functional cellulose/inorganic composites for more challenging biomedical applications.

Versatile Assembly of Metal-Phenolic Network Foams Enabled by Tannin-Cellulose Nanofibers

Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive metal-phenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe^(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Blood-Coagulation-Inspired Dynamic Bridging Strategy for the Fabrication of Multiscale-Assembled Hierarchical Porous Material

Porous materials, from macroscopic bulk materials (MBs) with (sub-)millimeter-scale pores to tiny particles (TPs) with (sub-)nanometer-scale pores, have attracted ever-growing interest in various fields. However, the integration of multi-scale pores in one composite is promising but challenging, owing to the considerable gap in the scale of the pores. Inspired by blood coagulation, a fibrin-based dynamic bridging strategy is developed to fabricate a multiscale-assembled hierarchical porous material (MHPM), in which fibrin formed as the sub-framework for the weaving-narrow of MBs and the enwinding-load of TPs. The bio-polymerization nature makes the fabrication rapid, facile, and universal for the customizable integration of seven kinds of TPs and four kinds of MBs. Besides, the integration is controllable with high load capacity of TPs and is stable against external shock forces. The unique multi-level structure endows the MHPM with large and accessible surface area, and efficient mass transfer pathways, synergistically leading to high adsorption capacity and rapid kinetics in multiple adsorption models. This work suggests a strategy for the rational multi-level design and fabrication of hierarchical porous architectures.

Metal-Organic Frameworks and Their Composites for Environmental Applications

From the point of view of the ecological environment, contaminants such as heavy metal ions or toxic gases have caused harmful impacts on the environment and human health, and overcoming these adverse effects remains a serious and important task. Very recent, highly crystalline porous metal-organic frameworks (MOFs), with tailorable chemistry and excellent chemical stability, have shown promising properties in the field of removing various hazardous pollutants. This review concentrates on the recent progress of MOFs and MOF-based materials and their exploit in environmental applications, mainly including water treatment and gas storage and separation. Finally, challenges and trends of MOFs and MOF-based materials for future developments are discussed and explored.