Separation is an important industrial step with critical roles in the chemical, petrochemical, pharmaceutical, and nuclear industries, as well as in many other fields. Although much progress has been ...made, the development of better separation technologies, especially through the discovery of high‐performance separation materials, continues to attract increasing interest due to concerns over factors such as efficiency, health and environmental impacts, and the cost of existing methods. Metal–organic frameworks (MOFs), a rapidly expanding family of crystalline porous materials, have shown great promise to address various separation challenges due to their well‐defined pore size and unprecedented tunability in both composition and pore geometry. In the past decade, extensive research is performed on applications of MOF materials, including separation and capture of many gases and vapors, and liquid‐phase separation involving both liquid mixtures and solutions. MOFs also bring new opportunities in enantioselective separation and are amenable to morphological control such as fabrication of membranes for enhanced separation outcomes. Here, some of the latest progress in the applications of MOFs for several key separation issues, with emphasis on newly synthesized MOF materials and the impact of their compositional and structural features on separation properties, are reviewed and highlighted.
The development of advanced separation materials is central to address challenging separation tasks in a number of essential industrial processes in the petrochemical, pharmaceutical, and nuclear industries. The emerging class of metal–organic frameworks (MOFs) has shown a great promise. The latest advances in MOF materials used for such applications are reviewed.
Reported herein are two new polymorphic Co‐MOFs (CTGU‐5 and ‐6) that can be selectively crystallized into the pure 2D or 3D net using an anionic or neutral surfactant, respectively. Each polymorph ...contains a H2O molecule, but differs dramatically in its bonding to the framework, which in turn affects the crystal structure and electrocatalytic performance for hydrogen evolution reaction (HER). Both experimental and computational studies find that 2D CTGU‐5 which has coordinates water and more open access to the cobalt site has higher electrocatalytic activity than CTGU‐6 with the lattice water. The integration with co‐catalysts, such as acetylene black (AB) leads to a composite material, AB&CTGU‐5 (1:4) with very efficient HER catalytic properties among reported MOFs. It exhibits superior HER properties including a very positive onset potential of 18 mV, low Tafel slope of 45 mV dec−1, higher exchange current density of 8.6×10−4 A cm−2, and long‐term stability.
HER choice of surfactants: Two new Co‐MOFs phase‐selected by anionic and neutral surfactants exhibit differential affinity for entrapped water molecules, leading to a difference in the spatial accessibility of active metal sites. A composite material made from such Co‐MOFs shows impressive performance in electrocatalytic hydrogen evolution reaction (HER) as well as long‐term stability.
Polymer electrolyte membrane water electrolysis (PEMWE) has been regarded as a promising technology for renewable hydrogen production. However, acidic oxygen evolution reaction (OER) catalysts with ...long‐term stability impose a grand challenge in its large‐scale industrialization. In this review, critical factors that may lead to catalyst's instability in couple with potential solutions are comprehensively discussed, including mechanical peeling, substrate corrosion, active‐site over‐oxidation/dissolution, reconstruction, oxide crystal structure collapse through the lattice oxygen‐participated reaction pathway, etc. Last but not least, personal prospects are provided in terms of rigorous stability evaluation criteria, in situ/operando characterizations, economic feasibility and practical electrolyzer consideration, highlighting the ternary relationship of structure evolution, industrial‐relevant activity and stability to serve as a roadmap towards the ultimate application of PEMWE.
The large‐scale application of polymer electrolyte membrane water electrolysis (PEMWE) is suffering from long‐term stability challenges in anodic oxygen evolution reaction (OER). This review provides a thorough discussion of degradation mechanisms, catalyst design principles and future research opportunities to serve as a cornerstone for overcoming the dilemma in acidic OER stability and achieving the industrialization of water electrolysis.
The integration of heterometallic units and nanostructures into metal–organic frameworks (MOFs) used for the oxygen evolution reaction (OER) can enhance the electrocatalytic performance and help ...elucidate underlying mechanisms. We have synthesized a series of stable MOFs (CTGU‐10a1–d1) based on trinuclear metal carboxylate clusters and a hexadentate carboxylate ligand with a (6,6)‐connected nia net. We also present a strategy to synthesize hierarchical bimetallic MOF nanostructures (CTGU‐10a2–d2). Among these, CTGU‐10c2 is the best material for the OER, with an overpotential of 240 mV at a current density of 10 mA cm−2 and a Tafel slope of 58 mV dec−1. This is superior to RuO2 and confirms CTGU‐10c2 as one of the few known high‐performing pure‐phase MOF‐OER electrocatalysts. Notably, bimetallic CTGU‐10b2 and c2 show an improved OER activity over monometallic CTGU‐10a2 and d2. Both DFT and experiments show that the remarkable OER performance of CTGU‐10c2 is due to the presence of unsaturated metal sites, a hierarchical nanobelt architecture, and the Ni–Co coupling effect.
Finding the right balance: The integration of heterometallic clusters and nanostructures into stable hierarchical nanosheet‐based bimetal–organic frameworks allows to increase the oxygen evolution reaction performance of electrocatalysts. The ideal ratio between Co and Ni leads to one of the best performances of pure‐phase MOF–OER electrocatalysts.
Nitrogen doping represents an effective way to induce charge/spin polarization in nanocarbons for promoting oxygen reduction reaction (ORR) activity. However, it remains elusive to define the ...dominant active sites with respect to two critical N‐configurations of pyridinic‐N and graphitic‐N. Herein, a tandem catalytic graphitization and nitrogen modification strategy for the synthesis of metal‐free nitrogen‐doped carbon nanoflakes (NCF) featuring the edge‐suffused and graphite‐analogous structure is presented. NCF exhibits superb Pt‐like ORR activity (0.85 V for half‐wave potential and 5.9 mA cm−2 for diffusion‐limited current density) but much stronger robustness in the alkaline medium. The experimental and theoretical studies suggest the key role of graphitic‐N in ORR. Furthermore, it unveils that the high activity of NCF should be traced to a synergistic polarization of the edge‐type pyridinic‐N/graphitic‐N dipole spaced by one edge peak carbon atom on the armchair edges. This study sheds light on the understanding of ORR active sites in the nitrogen‐doped nanocarbons for ORR.
Edge‐suffused and graphite‐analogous nitrogen‐doped carbon nanoflakes (NCF) are fabricated using a tandem catalytic graphitization and nitrogen modification strategy. The key electronic synergism of the edge‐type pyridinic‐N/graphitic‐N dipole is identified to empower NCF with superior electrocatalytic oxygen reduction performances.
With ever‐increasing energy consumption and continuous rise in atmospheric CO2 concentration, electrochemical reduction of CO2 into chemicals/fuels is becoming a promising yet challenging solution. ...Sn‐based materials are identified as attractive electrocatalysts for the CO2 reduction reaction (CO2RR) to formate but suffer from insufficient selectivity and activity, especially at large cathodic current densities. Herein, we demonstrate that Cu‐doped SnS2 nanoflowers can undergo in situ dynamic restructuring to generate catalytically active S‐doped Cu/Sn alloy for highly selective electrochemical CO2RR to formate over a wide potential window. Theoretical thermodynamic analysis of reaction energetics indicates that the optimal electronic structure of the Sn active site can be regulated by both S‐doping and Cu‐alloying to favor formate formation, while the CO and H2 pathways will be suppressed. Our findings provide a rational strategy for electronic modulation of metal active site(s) for the design of active and selective electrocatalysts towards CO2RR.
Sn‐based materials have been extensively explored in the electrochemical CO2 reduction reaction to formate, but reaching high selectivity and durability at large current densities remains challenging. Here, a catalytically active S‐doped Cu/Sn alloy was formed in situ through dynamic restructuring of Cu‐doped SnS2 nanoflowers, leading to an excellent CO2 to formate performance over a wide potential window.
The photocatalytic reduction of CO2 to energy carriers has emerged as one of the most promising strategies to alleviate the energy crisis and CO2 pollution, for which the development of catalyst was ...considered as the determining factor for the accomplishment of this conversion process. In this study, three stable and isostructural metal–organic frameworks (denoted as MOF-Ni, MOF-Co, and MOF-Cu) have been synthesized and used as heterogeneous catalysts in photocatalytic CO2 reduction reaction (CO2RR). It is worth noting that the MOF-Ni exhibited very high selectivity of 97.7% for photoreducing CO2 to CO, which has exceeded most of the reported MOF-based catalysts in the field. Significantly, the MOFs associated with a monometallic catalytic center offer a simple and precise structural model which allows us to understand more definitively the specific effects of different metal-ion species on photoreduction of CO2 as well as the reactive mechanism.
•Surfactant-assisted strategy for synthesis of single crystal MOFs.•Surfactant-assisted strategy for separating the pure single-phase of MOFs.•Surfactant-assisted strategy for the control of MOFs’ ...morphology.
Extensive attention has been paid to metal-organic frameworks (MOFs) due to their interesting structures and plenty of potential applications in catalysis, chemical sensors, magnetism, drug delivery, gas separation and storage. A variety of synthetic methodologies for the synthesis of multifunctional MOFs with complicated structures and attracting properties (such as solvothermal, hydrothermal, urothermal and ionothermal methods), have been developed. Recently, the surfactant-assisted strategy for the synthesis, adjustment and control of multifunctional MOFs has attracted extensive research interest, because surfactants forcefully determine the dimensions, phases, and morphologies of MOFs materials via acting as emulsifiers, detergents, foaming agents, wetting agents or dispersants. This review offers recent developments and prospects in the surfactants as promising templates in the field of growing MOFs, namely, surfactant-assisted strategy for the synthesis of crystalline MOFs, the separation of the pure single-phase of MOFs, the control of the pore’s sizes and morphologies of MOFs (such as core/shell, nanodisks, nanoplates, nanorods, nanosheets) as well as their mechanism.
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