Metal-organic frameworks for electrochemical reduction of carbon dioxide: The role of metal centers

Direct electrochemical reduction of CO_2 into valuable chemicals and fuel is one of the most promising approaches to address the current energy crisis and lower CO_2 emission. Recently, numerous metal-organic framework(MOF) and their derived materials have extensively been developed as electrocatalysts for CO_2 reduction owing to their unique structure including porosity, large specific surface area, and tunable chemical structures. In this review, the recent progress of MOF-based electrocatalysts for CO_2 reduction was summarized and discussed. Detailed discussions mainly focus on the synthesis and mechanism of pristine MOFs and MOF-derived materials for electrocatalytic CO_2 reduction. These examples are expected to provide clues to rational design and synthesis of stable and high-performance MOFs-based electrocatalysts for CO_2 reduction.     

Two-dimensional metal-organic framework nanosheet composites: Preparations and applications

As emerging two-dimensional materials, metal-organic framework(MOF) nanosheet composites possess many unique physical and chemical properties, thus being expected to be widely applied in gas separation and adsorption, energy conversion and storage, heterogeneous catalysis, sensing as well as biomedicine. In this review, we first introduce the methods for integrating MOF nanosheets with other materials to prepare multifunctional composites. Next, the applications of MOF nanosheet composites in ve...     

Rational design of Cu-based electrocatalysts for electrochemical reduction of carbon dioxide

The recent development of Cu-based electrocatalysts for electrochemical reduction of carbon dioxide(CO_2) has attracted much attention due to their unique activity and selectivity compared to other metal catalysts. Particularly, Cu is the unique electrocatalyst for CO_2 electrochemical reduction with high selectivity to generate a variety of hydrocarbons. In this review, we mainly summarize the recent advances on the rational design of Cu nanostructures, the composition regulation of Cu-based alloys, and the exploitation of advanced supports for improving the catalytic activity and selectivity toward electrochemical reduction of CO_2. The special focus is to demonstrate how to enhance the activity and selectivity of Cubased electrocatalyst for CO_2 reduction. The perspectives and challenges for the development of Cu-based electrocatalysts are also addressed. We hope this review can provide timely and valuable insights into the design of advanced electrocatalytic materials for CO_2 electrochemical reduction.     

Metal-Organic Framework Composites and Their Derivatives as Efficient Electrodes for Energy Storage Applications: Recent Progress and Future Perspectives

Metal-organic frameworks (MOFs) have been important electrochemical energy storage (EES) materials because of their rich species, large specific surface area, high porosity and rich active sites. Nevertheless, the poor conductivity, low mechanical and electrochemical stability of pristine MOFs have hindered their further applications. Although single component MOF derivatives have higher conductivity, self-aggregation often occurs during preparation. Composite design can overcome the shortcomings of MOFs and derivatives and create synergistic effects, resulting in improved electrochemical properties for EES. In this review, recent applications of MOF composites and derivatives as electrodes in different types of batteries and supercapacitors are critically discussed. The advantages, challenges, and future perspectives of MOF composites and derivatives have been given. This review may guide the development of high-performance MOF composites and derivatives in the field of EES.     

Selective electroreduction of carbon dioxide to formic acid on electrodeposited SnO_2@N-doped porous carbon catalysts

Electrocatalytic reduction of CO_2 is a promising route for energy storage and utilization. Herein we synthesized SnO_2 nanosheets and supported them on N-doped porous carbon (N-PC) by electrodeposition for the first time. The SnO_2 and N-PC in the SnO_2@N-PC composites had exellent synergistic effect for electrocatalytic reduction of CO_2 to HCOOH. The Faradaic efficiency of HCOOH could be as high as 94.1% with a current density of 28.4 mA cm-2 in ionic liquid-MeCN system. The reaction mechanism was proposed on the basis of some control experiments. This work opens a new way to prepare composite electrode for electrochemical reduction of CO_2.     

Robust Superhydrophobic/Superoleophilic Wrinkled Microspherical MOF@rGO Composites for Efficient Oil–Water Separation

Graphene/MOF‐based composite materials in three‐dimensional (3D) architectures are promising for the treatment of oil‐containing wastewater by absorption owing to their intrinsic properties of graphene and metal‐organic frameworks (MOFs), such as high porosity, ultralow density, and facilely tailored superwettability. In this study, novel wrinkled 3D microspherical MOF@rGO composites with both superhydrophobic and superoleophilic properties were developed by embedding MOF nanoparticles between graphene oxide (GO) nanosheets, followed by high‐temperature reduction self‐assembly. The microspherical composites feature a unique micro/nano hierarchy consisting of crumpled reduced GO (rGO) nanosheets intercalated with well‐dispersed MOF nanoparticles. Combined with the superwettability and abundant meso/microporosity, the peculiar architectures of wrinkled ZIF‐8@rGO microspheres show very fast absorption rates and high sorption selectivity for organic solvents and oils from water.     

金属有机骨架复合材料生物传感器检测肿瘤标志物的应用进展

生物传感器是传统肿瘤标志物检测方法的有效替代方法,而基于金属有机骨架(MOF)复合材料的生物传感器在肿瘤标志物检测方面具有速度快、灵敏度高、检出限低、成本低等优点。综述了MOF及其复合材料的分类,介绍了基于MOF复合材料的生物传感器在检测肿瘤标志物方面的应用进展,并对基于MOF复合材料的生物传感器未来发展趋势进行了展望。     

An updated review of metal–organic framework materials in photo(electro)catalytic applications: From CO2 reduction to wastewater treatments

This review summarizes recent advances in the development of metal–organic framework (MOF) materials, focusing on their photocatalytic and photoelectrocatalytic activities for different applications, such as CO₂ reduction, water splitting, elimination of inorganic contaminants, and degradation of organic pollutants. In each section, the first applications described focus on the photocatalysts developed using MOF materials. Meanwhile, the latest are centered on photoelectrode applications using these materials. The last advances in the synthesis process are discussed in terms of improvement in electron transfer and charge separation, which enhance the activity of the photo (electro)catalysts. Finally, some insights about the upcoming applications of MOF materials are provided.     

Amine-silica composites for CO_2 capture: A short review

Amine-silica composite materials for post-combustion CO_2 capture have attracted considerable attention because of their high CO_2 uptake at low CO_2 concentrations, excellent CO_2 capture selectivity in the presence of moisture, and lower energy requirements for sorbent regeneration. This review discusses the recent advances in amine-silica composites for CO_2 capture, including adsorbent preparation and characterization, CO_2 capture under dry and moisture conditions at different CO_2 partial pressures, sorbent regeneration, and stability after many cyclic sorption-desorption runs.     

金属-有机框架衍生的多功能光催化剂

在光催化过程中,光催化剂被太阳能激发产生光生电子和空穴,来实现环境净化或能量转换,是应对全球变暖和能源短缺的有效途径之一.然而,光催化技术面临的主要瓶颈问题是光生载流子的低分离效率和高反应能垒.而催化剂本身的特性对这一点起到了决定性的作用.因此,催化剂的合理设计和改性是提高光催化效率的关键.金属有机框架(MOFs)是一...     

A multiunit catalyst with synergistic stability and reactivity: a polyoxometalate-metal organic framework for aerobic decontamination

A combination of polyanion size and charge allows the Keggin-type polyoxometalate (POM), [CuPW(11)O(39)](5-), a catalyst for some air-based organic oxidations, to fit snuggly in the pores of MOF-199 (HKUST-1), a metal-organic framework (MOF) with the POM countercations residing in alternative pores. This close matching of POM diameter and MOF pore size in this POM-MOF material, [Cu(3)(C(9)H(3)O(6))(2)](4)[{(CH(3))(4)N}(4)CuPW(11)O(39)H] (1), results in a substantial synergistic stabilization of both the MOF and the POM. In addition, this heretofore undocumented POM-MOF interaction results in a dramatic increase in the catalytic turnover rate of the POM for air-based oxidations. While 1 catalyzes the rapid chemo- and shape-selective oxidation of thiols to disulfides and, more significantly, the rapid and sustained removal of toxic H(2)S via H(2)S + 1/2 O(2) → 1/8 S(8) + H(2)O (4000 turnovers in <20 h), the POM or the MOF alone is catalytically slow or inactive. Three arguments are consistent with the catalytic reactions taking place inside the pores. POM activation by encapsulation in the MOF likely involves electrostatic interactions between the two components resulting in a higher reduction potential of the POM.     

A metal–organic framework/polymer derived catalyst containing single-atom nickel species for electrocatalysis

While metal–organic frameworks (MOF) alone offer a wide range of structural tunability, the formation of composites, through the introduction of other non-native species, like polymers, can further broaden their structure/property spectrum. Here we demonstrate that a polymer, placed inside the MOF pores, can support the collapsible MOF and help inhibit the aggregation of nickel during pyrolysis; this leads to the formation of single atom nickel species in the resulting nitrogen doped carbons, and dramatically improves the activity, CO selectivity and stability in electrochemical CO₂ reduction reaction. Considering the vast number of multifarious MOFs and polymers to choose from, we believe this strategy can open up more possibilities in the field of catalyst design, and further contribute to the already expansive set of MOF applications.

A metal–organic framework/polymer derived catalyst containing single-atom nickel species shows good performance for electroreduction of CO₂ to CO.     

二维金属有机框架纳米片的合成及在超电容和电催化领域的应用

二维金属有机框架(2D MOF)纳米片具有丰富且易暴露的表面活性位点、 高度有序的孔结构以及多样且可调的化学成分, 在电化学能量存储与转化中有利于降低反应电位, 提高扩散速率和反应速率. 关于2D MOF应用于电化学存储与转化的研究已有大量报道. 本文综合评述了近几年2D MOF的合成进展及其在超电容(SC)、 析氧反应(OER)、 析氢反应(HER)、 氧还原反应(ORR)和二氧化碳还原反应(CRR)的应用, 并对2D MOF作为电催化材料的研究现状和发展前景进行了总结与展望.     

Toward 3D printed hydrogen storage materials made with ABS‐MOF composites

The push to advance efficient, renewable, and clean energy sources has brought with it an effort to generate materials that are capable of storing hydrogen. Metal–organic framework materials (MOFs) have been the focus of many such studies as they are categorized for their large internal surface areas. We have addressed one of the major shortcomings of MOFs (their processibility) by creating and 3D printing a composite of acrylonitrile butadiene styrene (ABS) and MOF‐5, a prototypical MOF, which is often used to benchmark H₂ uptake capacity of other MOFs. The ABS‐MOF‐5 composites can be printed at MOF‐5 compositions of 10% and below. Other physical and mechanical properties of the polymer (glass transition temperature, stress and strain at the breaking point, and Young's modulus) either remain unchanged or show some degree of hardening due to the interaction between the polymer and the MOF. We do observe some MOF‐5 degradation through the blending process, likely due to the ambient humidity through the purification and solvent casting steps. Even with this degradation, the MOF still retains some of its ability to uptake H₂, seen in the ability of the composite to uptake more H₂ than the pure polymer. The experiments and results described here represent a significant first step toward 3D printing MOF‐5‐based materials for H₂ storage.     

Chemical Reduction of CO2 to Different Products during Photo Catalytic Reaction on TiO2 under Diverse Conditions： an Overview

The chemical reduction of CO_2 remains a challenge with respect to the reversal of the oxidative degradation of any organic materials.The conversion of CO_2 into useful substances is essential in developing al- ternative fuels and various raw materials for different in- dustries.This also aids in preventing the continuous rise in tropospheric temperature due to the green house effect of CO_2.In this article an overview of the growth taken place so far in the field of CO_2 chemical reduction is pre- sented.The discussion comprises of photochemical meth- ods for the development of different products,viz.CO, CH_3O_H and CH_4,through chemical reduction of CO_2. This includes the use of photo catalysts,mainly TiO_2, and the role of a hole scavenger(such as 2-propanol)for this purpose.     

Recent advances in Cu-based nanocomposite photocatalysts for CO_2 conversion to solar fuels

CO_2 conversion via photocatalysis is a potential solution to address global warming and energy shortage.Photocatalysis can directly utilize the inexhaustible sunlight as an energy source to catalyze the reduction of CO_2 to useful solar fuels such as CO, CH_4, CH_3OH, and C_2H_5OH. Among studied formulations, Cubased photocatalysts are the most attractive for CO_2 conversion because the Cu-based photocatalysts are low-cost and abundance comparing noble metal-based catalysts. In this literature review, a comprehensive summary of recent progress on Cu-based photocatalysts for CO_2 conversion, which includes metallic copper, copper alloy nanoparticles(NPs), copper oxides, and copper sulfides photocatalysts, can be found. This review also included a detailed discussion on the correlations of morphology, structure, and performance for each type of Cu-based catalysts. The reaction mechanisms and possible pathways for productions of various solar fuels were analyzed, which provide insight into the nature of potential active sites for the catalysts. Finally, the current challenges and perspective future research directions were outlined, holding promise to advance Cu-based photocatalysts for CO_2 conversion with much-enhanced energy conversion efficiency and production rates.     

Advances of Metal‐Organic Frameworks in Energy and Environmental Applications

Nowadays, energy shortage and environmental pollution issues are increasingly severe and urgent to be solved. The effective storage and use of environmentally friendly fuels and removal of harmful gases from the environment are great challenges and of great importance both for the environment protection and for human health. Porous metal‐organic frameworks (MOFs) are highly ordered crystalline materials formed by the self‐assembly process of metal ions and organic ligands. Their good features such as ultrahigh porosity, large surface area, structural diversity and functionalities make them promising candidates for applications in energy and environmental fields. MOF thin films and MOF composites have also been investigated to further enhance the properties and introduce new functionalities. This review provides an overview of the synthesis methods of pristine MOFs, MOF thin films and MOF composites, and significant advances of MOFs in energy and environment applications such as energy storage (H₂, CH₄), CO₂ capture and separation, adsorption removal and sensing of harmful gases in the environment.     

Exploring the coordination chemistry of MOF-graphite oxide composites and their applications as adsorbents

Metal-organic frameworks (MOFs), besides being porous materials exhibit a very rich chemistry, which can be used for the synthesis of composites and/or the reactive adsorption of toxic gases. In this study, composites of MOFs (MOF-5, HKUST-1 or MIL-100(Fe)) and a graphitic compound (graphite or graphite oxide, GO) were synthesized and tested for the removal of NH(3), H(2)S and NO(2) under ambient conditions. The materials were characterized before and after exposure to the target gases by X-ray diffraction, thermogravimetric analysis, N(2) sorption measurement and FT-IR spectroscopy. The results indicate that strong chemical bonds exist between the MOF and GO as a result of the coordination between the GO oxygen groups and the MOFs' metallic centers. Depending on the structure of the MOF, such interactions induce the formation of a new pore space in the interface between the carbon layers and the MOF units, which enhances the physical adsorption capacity of the toxic gases. When unsaturated metallic sites are present in the MOFs, the target gases are also adsorbed via coordination to these centers. Further reaction with the framework leads to the formation of complexes. This is accompanied by the collapse of the MOF structure.     

The thermodynamics analysis and experimental validation for complicated systems in CO_2 hydrogenation process

Catalytic conversion of CO_2 into chemicals and fuels is an alternative to alleviate climate change and ocean acidification.The catalytic reduction of CO_2 by H_2 can lead to the formation of various products:carbon monoxide,carboxylic acids,aldehydes,alcohols and hydrocarbons.In this paper,a comprehensive thermodynamics analysis of CO_2 hydrogenation is conducted using the Gibbs free energy minimization method.The results show that CO_2 reduction to CO needs a high temperature and H_2/CO_2 ratio to achieve a high CO_2 conversion.However,synthesis of methanol from CO_2 needs a relatively high pressure and low temperature to minimize the reverse water-gas shift reaction.Direct CO_2 hydrogenation to formic acid or formaldehyde is thermodynamically limited.On the contrary,production of CH_4 from CO_2 hydrogenation is the thermodynamically easiest reaction with nearly 100%CH4 yield at moderate conditions.In addition,complex reactions with more than one product are also calculated in this work.Among the considered carboxylic acids(HCOOH,CH_3COOH and C_2H_5COOH),propionic acid dominates in the product stream(selectivity above 90%).The same trend can also be found in the hydrogenation of CO_2 to aldehydes and alcohols with the major product of propionaldehyde and butanol,respectively.In the process of CO_2 hydrogenation to alkenes,low temperature,high pressure,and high H_2 partial pressure favor the CO_2 conversion.C_4H_6 is the most thermodynamically favorable among all considered alkynes under different temperatures and pressures.The thermodynamic calculations are validated with experimental results,suggesting that the Gibbs free energy minimization method is effective for thermodynamically understanding the reaction network involved in the CO_2 hydrogenation process,which is helpful for the development of high-performance catalysts.     

Ruthenium-promoted reductive transformation of CO_2

The reductive transformation of CO_2 to energy related products including formic acid, CO, formamide, methanol and methylamine could be a promising option to supply renewable energy. In this aspect, ruthenium has found wide application in hydrogenation of various carbonyl groups, and has successfully been applied to reductive transformation of CO_2 with high catalytic efficiency and excellent selectivity. In addition, ruthenium complexes have also served as effective photosensitizers for CO_2 photoreduction.Classified by reductive products, this review summarizes and updates advances in the Ru-catalyzed reduction of CO_2 along with catalyst development on the basis of mechanistic understanding at a molecular level.