Two isostructural Co/Ni fluorine-containing metal-organic frameworks for dye adsorption and supercapacitor

Advances in metal-organic frameworks for water remediation applications

Rapid industrialization and agricultural development have resulted in the accumulation of a variety of harmful contaminants in water resources. Thus, various approaches such as adsorption, photocatalytic degradation and methods for sensing water contaminants have been developed to solve the problem of water pollution. Metal-organic frameworks (MOFs) are a class of coordination networks comprising organic-inorganic hybrid porous materials having organic ligands attached to inorganic metal ions/clusters via coordination bonds. MOFs represent an emerging class of materials for application in water remediation owing to their versatile structural and chemical characteristics, such as well-ordered porous structures, large specific surface area, structural diversity, and tunable sites. The present review is focused on recent advances in various MOFs for application in water remediation via the adsorption and photocatalytic degradation of water contaminants. The sensing of water pollutants using MOFs via different approaches, such as luminescence, electrochemical, colorimetric, and surface-enhanced Raman spectroscopic techniques, is also discussed. The high porosity and chemical tunability of MOFs are the main driving forces for their widespread applications, which have huge potential for their commercial use.

Bismuth-Rich Co/Ni Bimetallic Metal-Organic Frameworks as Photocatalysts toward Efficient Removal of Organic Contaminants under Environmental Conditions

Active photocatalysts with an efficiency of 99% were prepared for the degradation of the industrial dye, methylene blue (MB), under visible light irradiation. These photocatalysts comprised Co/Ni-metal-organic frameworks (MOFs), to which bismuth oxyiodide (BiOI) was added as a filler to prepare Co/Ni-MOF@BiOI composites. The composites exhibited remarkable photocatalytic degradation of MB in aqueous solutions. The effects of various parameters, including the pH, reaction time, catalyst dose, and MB concentration, on the photocatalytic activity of the prepared catalysts were also evaluated. We believe that these composites are promising photocatalysts for the removal of MB from aqueous solutions under visible light.

A three-dimensional Mn-based MOF as a high-performance supercapacitor electrode

Developing new high-performance electrode materials for improving the energy density of supercapacitors is an important task. Herein, a new three-dimensional (3D) metal-orgainc framework (MOF) [Mn(BGPD)(H₂O)₂] (Mn-BGPD; BGPD = N,N'-bis(glycinyl)pyromellitic diimide) was synthesized. When Mn-BGPD is used as the electrode material of supercapacitors, in a three-electrode setup, it shows an outstanding specific capacitance of 832.6 F g^-1 at a current density of 1 A g^-1. The asymmetrical supercapacitor of Mn-BGPD shows an attractive specific capacitance of 100 F g^-1 at 1 A g^-1, which corresponds to an excellent energy density of 35.5 W h kg^-1. Moreover, better cycling stability with a capacitance retention of 46.7% is also shown. The high electrochemical performance makes Mn-BGPD a very promising electrode material for supercapacitors.

Fluorinated metal-organic frameworks for gas separation

Fluorinated metal-organic frameworks (F-MOFs) as fast-growing porous materials have revolutionized the field of gas separation due to their tunable pore apertures, appealing chemical features, and excellent stability. A deep understanding of their structure-performance relationships is critical for the synthesis and development of new F-MOFs. This critical review has focused on several strategies for the precise design and synthesis of new F-MOFs with structures tuned for specific gas separation purposes. First, the basic principles and concepts of F-MOFs as well as their structure, synthesis and modification and their structure to property relationships are studied. Then, applications of F-MOFs in adsorption and membrane gas separation are discussed. A detailed account of the design and capabilities of F-MOFs for the adsorption of various gases and the governing principles is provided. In addition, the exceptional characteristics of highly stable F-MOFs with engineered pore size and tuned structures are put into perspective to fabricate selective membranes for gas separation. Systematic analysis of the position of F-MOFs in gas separation revealed that F-MOFs are benchmark materials in most of the challenging gas separations. The outlook and future directions of the science and engineering of F-MOFs and their challenges are highlighted to tackle the issues of overcoming the trade-off between capacity/permeability and selectivity for a serious move towards industrialization.

Potential of biocompatible calcium-based metal-organic frameworks for the removal of endocrine-disrupting compounds in aqueous environments

Rapid urbanization, industrialization and population growth have accelerated the amount and variety of emerging contaminants being released into the aqueous environment, including endocrine-disrupting compounds (EDCs). The introduction of these compounds constitutes a threat to human health and the environment, even at trace levels. Hence, new water treatment technologies are urgently required to effectively remove EDCs from water. The currently available technologies used in water remediation processes are expensive and ineffective, and some produce harmful by-products. Calcium-based metal-organic frameworks (Ca-MOFs) are porous synthetic materials that can potentially be applied as adsorbents. These MOFs are hydrolytically stable, biocompatible and low-cost compared with conventional porous materials. The structure of Ca-MOFs is maintained even though calcium metal centers in the structure can easily coordinate with water. Ca-MOFs and their composite derivatives have the potential for use in water purification because these biocompatible adsorbents have been shown to selectively extract a significant quantity of contaminants. This review highlights the potential of Ca-MOFs to adsorb EDCs from aqueous environments and discusses adsorbent preparation methods, adsorption mechanisms, removal capacity, water stability and recyclability. This review will support future efforts in synthesizing new biocompatible MOFs as an environmental treatment technology that can effectively remove EDCs from water, thereby improving environmental and human health.

Rational synthesis of isomorphic rare earth metal–organic framework materials for simultaneous adsorption and photocatalytic degradation of organic dyes in water

Two isomorphic rare earth metal–organic frameworks (MOFs) were synthesized by a solvothermal method. These MOFs have good removal effects on cationic and neutral dyes through simultaneous adsorption and photocatalysis.

A 2-Fold Interpenetrated Nitrogen-Rich Metal-Organic Framework: Dye Adsorption and CO2 Capture and Conversion

A bifunctional ligand strategy for modification of the functional pores is of great significance in the structural design of metal-organic frameworks (MOFs). Herein, a new 2-fold interpenetrated "pillared-layer" 3D Co-MOF, {[Co(HL)(4,4'-bipy)]·DMF·2H₂O}_n (1), was successfully synthesized by using two kinds of ligands, imidazolecarboxylic acid and pyridine. The metal-carboxylic layers are pillared by the 4,4'-bipy ligand, displaying a 3D framework with rectangular 3D channels (high BET surface of 190.9 m² g^-1 and maximum aperture of 3.9 Å) that are decorated with abundant uncoordinated N and O atoms. 1 shows good water stability and thermal stability (320 °C). The proper pores and active sites endowed 1 with a selective adsorption of Congo red in aqueous solution. In addition, a high CO₂ adsorption capacity and an excellent CO₂ chemical conversion were observed.

A series of porous 3D inorganic–organic hybrid framework crystalline materials based on 5-aminoisophthalic acid for photocatalytic degradation of crystal violet

Seven 3D metal-organic frameworks have been designed and synthesized by the hydrothermal synthetic method based on the ligand 5-aminoisophthalic acid. Complexes 1-4 have better photocatalytic degradation properties for dyes CV.

Metal-Organosulfide Coordination Polymer Nanosheet Array as a Battery-Type Electrode for an Asymmetric Supercapacitor

Metal-organosulfide coordination polymers (MOSCPs) are important functional materials with attractive application prospects. Herein a two-dimensional structural MOSCP was fabricated on nickel foam with nanosheet array morphology. When as the binder-free battery-type electrode for a supercapacitor, the as-prepared Co-based MOSCP showed high specific capacitance (759 F g^-1/379.5 C g^-1/105.4 mAh g^-1 at 0.5 A g^-1), excellent rate performance (58.8% after the current density increased 20 times), and good cycle stability (73.4% after 5000 cycles). In addition, a maximum energy density of 31.97 Wh kg^-1 was obtained at a power density of 375.01 W kg^-1 in the assembled asymmetric supercapacitor device. These results indicated that this work would open up a new path to design and prepare the battery-type electrode for a supercapacitor by exploring nanoscale MOSCP materials.

Incorporating Ni-MOF structure with polypyrrole: enhanced capacitive behavior as electrode material for supercapacitor

Herein, Ni-MOF sheet incorporated with polypyrrole is fabricated via a simple wet-chemical approach, and the obtained PPy-MOF composite is investigated as an electrode material for supercapacitors. The composite is systematically investigated by a series of characterization studies including X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. Besides that, the electrochemical capacitive behaviors of the products are examined by electrochemical measurements. Electrochemical results show varying the ingredient ratio can lead to different electrocapacitive behavior, and PPy-MOF-0.2 is proved to possess the best performance in the investigated recipes. Furthermore, an asymmetric supercapacitor employing PPy-MOF and activated carbon as positive and negative electrodes is also assembled, which exhibits high energy density.

A polythreaded MnII-MOF and its super-performances for dye adsorption and supercapacitors

One new polythreaded Mn^II-MOF was successfully prepared by employing a tridentate N-donor ligand with three long arms. Its excellent performances in dye adsorption and supercapacitor have been investigated in detail.