In recent years, metal-organic framework materials(MOFs) have attracted the attention of many researchers because of their excellent framework structure, rich porosity and versatility. A variety of MOFs materials and MOF-based composites have been developed. However, since most MOFs exist in the form of crystals and powders, their rigidity and fragility limit its practical application. Meanwhile, the instability of MOFs in solution can cause the decomposition of the material. Some high-crystallinity MOFs are also very fragile and difficult to process, so researchers combine MOFs with hydrogels and develop many MOF-based hydrogel materials with excellent properties. This review presents current developments of MOF-based hydrogels with emphasis on the specific categories and the synergistic effects of MOF-derived hydrogels between MOFs and additional materials. Particular emphasis is placed on discussing the advantages of MOF-based hydrogels in applications such as sensors, catalysts, water treatment, wound dressings, drug carriers, etc. MOF-based hydrogels can provide valuable guidance for the investigation of MOFs towards practical applications with processability, stability, and easy handling. Specifically, the recent progress of pure MOF hydrogels, MOF@bioorganic macromolecule hydrogels, MOF@biocompatible hydrogels, other MOF-based composite hydrogels, and the applications of these composite materials are summarized.

Metal-organic frameworks(MOFs) have a large number of pore structures and active sites, which enable them to play a huge role in gas adsorption, catalysis, medical treatment and other fields. As a crystal powder, MOFs are brittleness, easy hydroxylation, difficulty in recycling and so on which limits its application. MOFs combining to flexible polymers, in particular combining to hydrogels greatly improve the flexibility, dispersibility in water, recyclability, and processability of composite materials, which broadens the application fields of MOFs. In the present paper, it is elaborated that the progress of the preparation of MOFs/hydrogel composites are based on three different methods including MOFs in situ growing from hydrogel, MOFs/hydrogel simultaneous generation, and hydrogel encapsulated MOFs. The characteristics of the above three preparation methods and their resulting product properties are summarized. Additionally, the applications of composite materials in biomedicine, catalysis, wastewater treatment, and gas adsorption are further summarized. Finally, preparation method improvement and future application of MOFs/ hydrogel composites are discussed and prospected.

Ultra-thin two dimensional metal-organic framework(MOF) nanomaterial is a kind of MOF materials. Different from the traditional bulk MOF materials, the ultra-thin sheet structure endows it with unique properties such as high specific surface area, rich coordination unsaturated metal sites and so on, which can effectively improve the performance of MOF in catalysis, separation and sensors. In this paper, the research progress on the construction and preparation methods of ultra-thin two dimensional MOF nanomaterials in recent years is reviewed, including top-down method, bottom-up method and 2D oxide sacrifice approach. At the same time, this paper discusses the application prospects of ultra-thin two dimensional MOF nanomaterials in the fields of gas adsorption and gas separation, catalysis, energy storage, sensing platform, and further analyzes the challenges and opportunities faced by the research of ultra-thin two dimensional MOF nanomaterials in the future.

The emergence of emerging organic contaminants(EOCs) has attracted increasing attention due to their wide distribution and persistence in aquatic ecosystems, as well as the potential threat to the health and safety of aquatic organisms. Traditional water treatment processes represented by activated sludge processes are generally insufficient to eliminate these persistent pollutants. For efficient removal of EOCs, advanced oxidation technology based on new materials is one of the most important advanced treatment technologies. Fe-MOFs and their composites have been widely used in many fields, especially in the catalytic oxidation of pollutants in wastewater. With the aid of the improvement of synthesis methods, post-synthetic modification and being composited with specific functional materials, Fe-MOFs can be used to effectively improve the adsorption performance, enhance the light absorption characteristics, and promote the effective separation of charge carriers. The review focuses on the progress of advanced oxidation processes(photocatalysis, Fenton-like reaction and sulfate radical($SO_{4}^{-·}$) mediated oxidation) of Fe-MOFs and their composites to remove emerging organic contaminants in wastewater. As well, the opportunities and challenges of Fe-MOFs in the field of EOCs removal are proposed.

As the secondary battery with the highest specific energy, lithium ion battery is widely used in portable electronic devices, new energy vehicles and large-scale energy storage power stations. Currently, commercial lithium-ion batteries are facing some technical bottlenecks, such as low energy density and short service life. There are many reports about the anode materials of lithium ion batteries, but most of them cannot overcome the shortcomings such as the huge volume expansion before and after lithium, the pulverization of electrode materials, and the large electrode impedance. However, metal oxides derived from metal-organic frameworks(MOFs) and composites are widely used in lithium ion batteries due to their low level charge-discharge potential platform, high capacity and stable cycle performance. Therefore, in this paper, metal oxides derived from MOFs and composites are divided into four modules: mono-metal oxides, bi-metal oxides, bi-component metal oxide composites and metal oxide/carbon composites. The relationships between their synthesis methods, morphologies and electrochemical properties are summarized, and the opportunities and challenges for their future development are forecast.

Metal organic framework is a kind of three-dimensional framework porous materials self-assembly by a structure of organic ligands and metal centers. Because of the structure of metal organic complex framework, it has good chemical properties. Metal-organic frameworks have become more and more mature when applied to material analysis. Significant progress has also been achieved in the application of electrochemical sensors. In this paper, the newly found preparing approaches to the mental-organic frameworks, constructing electrochemical sensor methods as well as the summary of its application in electrochemical sensor based on MOF are presented. The problems and the limitations in metal-organic frameworks application to the electrochemical sensors are also involved. At the end, we briefly discuss the direction and expectations of electrochemical sensor based on metal-organic frameworks.
Contents
1 Introduction
2 Methods for preparing MOF modified electrode
2.1 Layer-by-Layer self-assembly
2.2 Electro polymerization
2.3 Solvothermal Method
3 The role of MOF in electrochemical sensor
3.1 Catalysis
3.2 Improvement of surface areas
3.3 Electroactive immobilization
3.4 Molecular recognition
4 Application in electrochemical sensor about MOF
4.1 Application in the determination of organics
4.2 Application in the determination of inorganic ions
4.3 Application in the determination of biomacromolecules
5 Conclusion

The development of global industries has brought serious problem of water pollution, therefore, the efficient treatment of wastewater containing various kinds of organic and inorganic pollutants is one of the most important research topics. Metal-organic frameworks(MOFs) have been widely applied in many fields, especially in the solid phase adsorption/separation owing to their large surface area, high porosity, ordered structure and tunable porous physico-chemical properties, thermal stability, easy synthesis and abundant open active sites. The functionalization methods of MOFs such as post-synthesis modification, in situ synthesis with linkers containing substituents, and hybridization with specific functional materials could effectively increase the adsorption active sites, thus enhancing the adsorption performance and adsorption selectivity. Compared to MOFs particles, MOFs/polymer composite membranes combine the special structure and physico-chemical properties of MOFs and excellent adsorption/carrier nature of polymer films and thus exhibit extraordinary adsorption/separation performances in the removal of pollutants. In this paper, we focus on the functionalization methods of MOFs which are applied in the adsorption/removal of dyes and heavy metal ions. We also summarize the fabrication technology of MOFs/polymer composite membranes and their applications in the wastewater treatment. Finally, the development direction and research prospect of MOFs-related composite materials are also proposed.

Benefiting from its high oxygen reduction activity comparable with platinum catalyst, the transition metal and nitrogen co-doped carbon catalyst(M-N/C) has become one of the most important non-noble metal catalysts, and it is recognized as the most promising non-noble metal catalyst, as substitute of precious platinum catalyst, in proton exchange membrane fuel cells in the future. Metal organic frameworks(MOFs), a new class of crystalline porous materials with regular porous structure, high porosity, controllable morphology and size, and tunable ligands, have been regarded as perfect precursors for preparing various high-performance doped carbon catalysts. The catalysts derived from MOF often show superior structure and performance compared with those derived from conventional precursors, making them more prospective for applying in the fuel cells. Actually, it has become one of the most attractive topics to prepare M-N/C catalysts with MOFs as precursors in recent years. In this paper, we systematically introduce the research works on MOFs derived M-N/C catalysts at home and abroad in recent years, including the preparation technologies of MOF derived M-N/C catalysts, the strategies of improving the structure and performance of MOF derived carbon catalysts, as well as the research progress on the characterization technologies of such catalysts. Finally, we indicate the problems and challenges existed in MOF derived M-N/C catalysts, propose possible strategies/measures to solve the problems. The development and application of this type of new catalysts are also prospected.

Judicious utilization of host-guest supramolecular interactions and flexibilities of both the host and guest enables metal-organic frameworks to show abnormal adsorption selectivities for the less polar, more saturated hydrocarbons, which is useful for efficient purification of high-value alkenes such as ethylene and butadiene.