Hierarchical porous metal-organic gels and derived materials: from fundamentals to potential applications

Metal-organic gels (MOGs) emerged as a novel class of functional soft materials in which the scaffolding framework is fabricated by metal-ligand coordination in combination with other supramolecular interactions (for example, hydrogen bonding or π-π stacking). Through the combination of organic and inorganic (metal/metal-oxo clusters) building blocks, significant steps forward have been made in the development of new electrochemical sensors, superhydrophobic materials and ion storage devices, among others. These leaps forward are to some extend induced by the intrinsic hierarchical microporous/mesoporous pore structure of these metal-organic materials. Within this review we give an overview of recent developments of this growing field. First, we shed light onto the parallels to the well-established field of conventional gels and outline similarities and differences. Afterwards, we classify different types of MOGs according to their architectural/structural nature: (1) pristine MOGs, (2) hybrid MOGs, (3) crosslinking-based MOGs and (4) MOG-derived materials. Furthermore, we look at the different properties of MOGs and the requirements for the preparation of spatially patterned macro-structured MOGs by emerging additive manufacturing technologies. Moreover, different potential fields of application for MOGs and MOG derived materials are critically evaluated and potential improvements and pitfalls in comparison to traditional gel-based materials are given. Finally, a comprehensive outlook into future directions for the development of MOGs is provided.</p

Carbon nanotube based metal-organic framework hybrids from fundamentals toward applications

Metal-organic frameworks (MOFs) materials constructed by the coordination chemistry of metal ions and organic ligands are important members of the crystalline materials family. Owing to their exceptional properties, for example, high porosity, tunable pore size, and large surface area, MOFs have been applied in several fields such as gas or liquid adsorbents, sensors, batteries, and supercapacitors. However, poor conductivity and low stability hamper their potential applications in several attractive fields such as energy and gas storage. The integration of MOFs with carbon nanotubes (CNTs), a well-established carbon allotrope that exhibits high conductivity and stability, has been proposed as an efficient strategy to overcome such limitations. By combining the advantages of MOFs and CNTs, a wide variety of composites can be prepared with properties superior to their parent materials. This review provides a comprehensive summary of the preparation of CNT@MOF composites and focuses on their recent applications in several important fields, such as water purification, gas storage and separation, sensing, electrocatalysis, and energy storage (supercapacitors and batteries). Future challenges and prospects for CNT@MOF composites are also discussed.Web of Science184art. no. 210462

Hierarchical porous metal-organic framework materials for efficient oil-water separation

Oil contaminated water is a global issue, decreasing the quality of water sources and is posing a threat to the health of humans and many ecosystems. The utilization of industrial level strategies is limited mainly due to their complex and time-consuming processing. Considering this, we choose materials for separating oils from water based on their ease of handling and good performance. However, high surface area porous materials, such as linens, zeolites, cotton, etc., offer low efficiency for oil/water separation. Special wettability is the most promising property of materials and is helpful for oil-water separation. Metal-organic frameworks (MOFs), a class of highly tunable porous structures of metal clusters/ions and multidentate organic ligands, offer exciting prospects for various applications. The unique tunability of the structure and properties of these materials can endow them with special wettability for the treatment of oily water. This review focuses on hydrophobic-oleophilic, hydrophilic-underwater oleophobic and switchable wettability MOFs and their implementation as oil/water separating materials. We classify different MOF-based materials as filtration materials, absorbents or adsorbents based on the methodology they are used in for separating oil/water mixtures and emulsions. We discuss different subclasses of MOF-based filtration, absorbent and adsorbent materials and summarize recent developments in their oil/water separation applications. Finally, we end our discussion by critically analyzing the importance of these MOFs for separating oils from water and highlighting potential future directions for achieving improved performance.Web of Science1062785275

Emerging MXene@Metal–Organic Framework Hybrids: Design Strategies toward Versatile Applications

Rapid progress on developing smart materials and design of hybrids is motivated by pressing challenges associated with energy crisis and environmental remediation. While emergence of versatile classes of nanomaterials has been fascinating, the real excitement lies in the design of hybrid materials with tunable properties. Metal-organic frameworks (MOFs) are the key materials for gas sorption and electrochemical applications, but their sustainability is challenged by limited chemical stability, poor electrical conductivity, and intricate, inaccessible pores. Despite tremendous efforts towards improving the stability of MOF materials, little progress has made researchers inclined toward developing hybrid materials. MXenes, a family of two-dimensional transition-metal carbides, nitrides and carbonitrides, are known for their compositional versatility and formation of a range of structures with rich surface chemistry. Hybridization of MOFs with functional layered MXene materials may be beneficial if the host structure provides appropriate interactions for stabilizing and improving the desired properties. Recent efforts have focused on integrating Ti3C2Tx and V2CTx MXenes with MOFs to result in hybrid materials with augmented electrochemical and physicochemical properties, widening the scope for emerging applications. This review discusses the potential design strategies of MXene@MOF hybrids, attributes of tunable properties in the resulting hybrids, and their applications in water treatment, sensing, electrochemical energy storage, smart textiles, and electrocatalysis. Comprehensive discussions on the recent efforts on rapidly evolving MXene@MOF materials for various applications and potential future directions are highlighted. © 2021 American Chemical Society

Two-dimensional MOF-based liquid marbles: surface energy calculations and efficient oil-water separation using a ZIF-9-III@PVDF membrane

Superhydrophobic MOF-nanosheets assembled on the outside of an aqueous droplet form 'liquid marbles'. A facile mechanochemical-based synthesis followed by ultrasonication was used to prepare two-dimensional superhydrophobic-oleophilic MOF nanosheets of a Co2+-based zeolitic imidazolate framework, namely ZIF-9-III ([Co-4(bIm)(16)] with bIm(-) = benzimidazolate). The resulting ZIF-9-III showed excellent hydrophobicity (advancing water contact angle of 144 degrees) and oleophilicity (oil contact angle of approximate to 0 degrees). The superhydrophobic behavior originated from its predominant outer (002) surface, which featured nanoscale corrugation caused by the exposed benzimidazole groups. This behavior was corroborated by inverse gas chromatography measurements to determine the surface energies of bulk exfoliated 2D ZIF-9-III nanosheets and 3D ZIF-9-I. Taking advantage of the unique surface properties, including low surface energy and good moisture stability, we prepared ZIF-9-III@PVDF (PVDF = polyvinylidene fluoride) membranes following the non-solvent induced phase inversion (NIPS) process. The resulting membranes were exploited in real-time oil/water separation and featured remarkably high adsorption capacity and anti-staining properties. Therefore, this work opens the door to developing new superhydrophobic MOF-based composite materials with permeant porosity, which may enable applications in self-cleaning membranes for oil-water separation.Web of Science941236592365

Rational design of graphene derivatives for electrochemical reduction of nitrogen to ammonia

The conversion of nitrogen to ammonia offers a sustainable and environmentally friendly approach for producing precursors for fertilizers and efficient energy carriers. Owing to the large energy density and significant gravimetric hydrogen content, NH3 is considered an apt next-generation energy carrier and liquid fuel. However, the low conversion efficiency and slow production of ammonia through the nitrogen reduction reaction (NRR) are currently bottlenecks, making it an unviable alternative to the traditional Haber-Bosch process for ammonia production. The rational design and engineering of catalysts (both photo- and electro) represent a crucial challenge for improving the efficiency and exploiting the full capability of the NRR. In the present review, we highlight recent progress in the development of graphene-based systems and graphene derivatives as catalysts for the NRR. Initially, the history, fundamental mechanism, and importance of the NRR to produce ammonia are briefly discussed. We also outline how surface functionalization, defects, and hybrid structures (single-atom/multiatom as well as composites) affect the N-2 conversion efficiency. The potential of graphene and graphene derivatives as NRR catalysts is highlighted using pertinent examples from theoretical simulations as well as machine learning based performance predictive methods. The review is concluded by identifying the crucial advantages, drawbacks, and challenges associated with principal scientific and technological breakthroughs in ambient catalytic NRR.Web of Science1511172981727

Covalent graphene-MOF hybrids for high-performance asymmetric supercapacitors

In this work, the covalent attachment of an amine functionalized metal-organic framework (UiO-66-NH2 = Zr6O4(OH)(4)(bdc-NH2)(6); bdc-NH2 = 2-amino-1,4-benzenedicarboxylate) (UiO-Universitetet i Oslo) to the basal-plane of carboxylate functionalized graphene (graphene acid = GA) via amide bonds is reported. The resultant GA@UiO-66-NH2 hybrid displayed a large specific surface area, hierarchical pores and an interconnected conductive network. The electrochemical characterizations demonstrated that the hybrid GA@UiO-66-NH2 acts as an effective charge storing material with a capacitance of up to 651 F g(-1), significantly higher than traditional graphene-based materials. The results suggest that the amide linkage plays a key role in the formation of a pi-conjugated structure, which facilitates charge transfer and consequently offers good capacitance and cycling stability. Furthermore, to realize the practical feasibility, an asymmetric supercapacitor using a GA@UiO-66-NH2 positive electrode with Ti3C2TX MXene as the opposing electrode has been constructed. The cell is able to deliver a power density of up to 16 kW kg(-1) and an energy density of up to 73 Wh kg(-1), which are comparable to several commercial devices such as Pb-acid and Ni/MH batteries. Under an intermediate level of loading, the device retained 88% of its initial capacitance after 10 000 cycles.Web of Scienceart. no. 200456