Recent Advances in Hierarchical Porous Engineering of MOFs and Their Derived Materials for Catalytic and Battery: Methods and Application

Hierarchical porous materials have attracted the attention of researchers due to their enormous specific surface area, maximized active site utilization efficiency, and unique structure and properties. In this context, metal-organic frameworks (MOFs) offer a unique mix of properties that make them particularly appealing as tunable porous substrates containing highly active sites. This review focuses on recent advances in the types and synthetic strategies of hierarchical porous MOFs and their derived materials. Furthermore, it highlights the relationship between the mass diffusion and transport of hierarchical porous structures and the pore size with examples and simulations, while identifying their potential and limitations. On this basis, how the synthesis conditions affect the structure and electrochemical properties of MOFs based hierarchical porous materials with different structures is discussed, highlighting the prospects and challenges for the synthetization, as well as further scientific research and practical applications. Finally, some insights into current research and future design ideas for advanced MOFs based hierarchical porous materials are presented.

Construction of continuous flow catalytic reactor-HPLC system with ultrahigh catalytic activity using 2D nanoflower MOF-derived Cu2O/Cu/PDA/CF catalyst

Currently, metal-organic frameworks (MOFs) derived materials have been widely concerned for the reduction of 4-nitrophenol (4-NP). However, complex recovery of powder catalysts and low utilization ratio of active sites make their application challenging. Herein, a novel Cu2O/Cu/PDA/CF catalyst has been developed for the rapid reduction of 4-NP to 4-aminophenol (4-AP). The catalyst was constructed by compositing a two-dimensional nanoflower MOF-derived nanoporous Cu2O/Cu network on a polydopamine (PDA)-modified porous copper foam by a mild and controllable in-situ reduction synthesis. Notably, an enhanced catalytic performance of Cu2O/Cu/PDA/CF was obtained for 4-NP reduction with a rate constant (k) of 0.8001 min-1, outperforming Cu/PDA/CF-X (X = 400, 500 and 600 ℃ pyrolysis temperature) catalysts (2.3-6.4 folds), and even many reported catalysts (2.3-46.5 folds). The ultrafast degradation of 4-NP was completed in 70 s. Moreover, an ingenious online continuous flow catalytic reactor (CFCR)-high performance liquid chromatography (HPLC) system was constructed for automatic and real-time monitoring of the reduction reaction. System stability experiments over 300 min revealed a surprisingly high reaction k value of 76.68 min-1 at low NaBH4 usage, significant increasing by 2-3 orders of magnitude compared with Cu2O/Cu/PDA/CF batch catalysis, due to the high aspect ratio of 2D nanoflower MOF and convection-accelerated mass transfer. This work offers new insights for the rational design of catalytic reactor and its potential application in wastewater treatment.

CO2 Cycloaddition under Ambient Conditions over Cu-Fe Bimetallic Metal-Organic Frameworks

Carbon dioxide cycloaddition into fine chemicals is prospective technology to solve energy crisis and environmental issues. However, high temperature and pressure are usually required in the conventional cycloaddition reactions of CO2 with epoxides. Moreover, metal active sites play a vital role in the CO2 cycloaddition, but it is still unclear. Herein, we select the isostructural MOF-919-Cu-Fe and MOF-919-Cu-Al as models to promote the performance and clarify the effects of metal type on the CO2 cycloaddition. The MOF-919-Cu-Fe with exposed Fe and Cu Lewis acid sites reaches the CO2 cycloaddition with over 99.9% conversion and over 99.9% selectivity at room temperature and a 1 bar CO2 atmosphere, 3.0- and 52.6-fold higher than those of the MOF-919-Cu-Al with Al and Cu sites (33.8%) and the 1H-pyrazole-4-carboxylic acid, Fe, and Cu mixed system (1.9%), respectively. The proposed mechanism demonstrated that the exposed Fe3+ sites facilitate the ring opening of epoxide and CO2 activation to boost the CO2 cycloaddition reaction. This work provides a new insight to tune the catalytic sites of MOFs to achieve high performance for CO2 fixation.

Recyclable TPA-Modified MIL-88-Supported Ionic Pt as a Highly Efficient Catalyst for Alkene Hydrosilylation

The hydrosilylation reaction driven by a homogeneous catalyst has been widely used in the industrial synthesis of functionalized silicone compounds. However, the homogeneous catalyst for hydrosilylation has the shortcomings of nonrecyclability, undesirable side reactions, and high cost. In this work, a highly efficient heterogeneous catalyst was prepared by loading Pt ions on MIL-88 modified with trimethoxy[3-(phenylamino)propyl]silane. In comparison with previous research studies, the resulting catalyst can exhibit high catalytic activity and excellent stability during the hydrosilylation reaction, which was attributed to the presence of a pyrrolic nitrogen structure between TPA-MIL-88 and the Pt ion. Besides them, 1.2%Pt/TPA-MIL-88 showed the highest catalytic activity and can be reused five times without significant deactivation. Importantly, 1.2%Pt/TPA-MIL-88 also achieved satisfactory results when it was used to catalyze the hydrosilylation reaction for other olefins, implying great potential for application in the silicone industry.

An iron-based metal-organic framework as a novel dispersive solid-phase extraction sorbent for the efficient adsorption of tetrabromobisphenol A from environmental water samples

For environmental safety, it is important to establish a simple, rapid, and sensitive method for emerging pollutants. Here, a dispersive solid-phase extraction (d-SPE) method based on an iron-based metal-organic framework (Fe-MIL-88-NH₂) combined with high-performance liquid chromatography (HPLC) was developed for tetrabromobisphenol A (TBBPA) in water samples. Fe-MIL-88-NH₂ was synthesized using a solvothermal method and completely characterized. Fe-MIL-88-NH₂ had good water stability and gave a maximum adsorption capacity of 40.97 mg g^-1 for TBBPA. The adsorption of TBBPA on Fe-MIL-88-NH₂ followed Langmuir adsorption models and a pseudo-second-order kinetic model. The bromine ion and the hydroxyl group of TBBPA could form strong hydrogen bond interactions with the amino protons around the cavity of Fe-MIL-88-NH₂, which was in accord with the molecular simulation calculations. Furthermore, several important d-SPE parameters were optimized, such as the amount of materials, extraction time, pH, ionic strength, elution solvent type, and volume. The established method showed good linearity in the concentration range of 0.005-100 μg g^-1 (r² ≥ 0.9996). This method's limits of detection (LOD) and quantification (LOQ) were 0.001 μg g^-1 and 0.005 μg g^-1, respectively. The recoveries in spiked water samples ranged from 87.5% to 104.9%. The proposed method was applied successfully to detect TBBPA in environmental water samples.

Room temperature design of Ce(iv)-MOFs: from photocatalytic HER and OER to overall water splitting under simulated sunlight irradiation

A new synthetic approach is reported to synthesize redox-active Ce(iv) MOFs at room temperature for efficient and reusable photo-induced overall water splitting.

Applications of water-stable metal-organic frameworks in the removal of water pollutants: A review

Because the pollutants produced by human activities have destroyed the ecological balance of natural water environment, and caused severe impact on human life safety and environmental security. Hence the task of water environment restoration is imminent. Metal-organic frameworks (MOFs), structured from organic ligands and inorganic metal ions, are notable for their outstanding crystallinity, diverse structures, large surface areas, adsorption performance, and excellent component tunability. The water stability of MOFs is a key requisite for their possible actual applications in separation, catalysis, adsorption, and other water environment remediation areas because it is necessary to safeguard the integrity of the material structure during utilization. In this article, we comprehensively review state-of-the-art research progress on the promising potential of MOFs as excellent nanomaterials to remove contaminants from the water environment. Firstly, the fundamental characteristics and preparation methods of several typical water-stable MOFs include UiO, MIL, and ZIF are introduced. Then, the removal property and mechanism of heavy metal ions, radionuclide contaminants, drugs, and organic dyes by different MOFs were compared. Finally, the application prospect of MOFs in pollutant remediation prospected. In this review, the synthesis methods and application in water pollutant removal are explored, which provide ways toward the effective use of water-stable MOFs in materials design and environmental remediation.

Immobilization of MIL-88(Fe) anchored TiO2-chitosan(2D/2D) hybrid nanocomposite for the degradation of organophosphate pesticide: Characterization, mechanism and degradation intermediates

In this study, we have rationally designed and grafted a bio-assisted 2D/2D TiO₂/MIL-88(Fe) (TCS@MOF) heterojunction by growing granular TiO₂ on the surface of MIL-88(Fe) nanosheet, as hybrid photocatalyst. The hierarchical TCS@MOF composite was prepared via the one-pot solvothermal process and employed for monocrotophos (MCP) degradation under visible light region, since its persistent nature on soil and water causes major threat to the environment. The TCS@MOF promotes a number of packed high-speed nano-tunnels in the (p-n) heterojunctions, which significantly enhance the migration of photo-induced electrons (e^-) and holes (h⁺), respectively and thus limits the charge recombination of e^-s. The optimized photocatalyst achieves significant catalytic activity of ~98.79% for the degradation of MCP within 30 min of irradiation. The prominent oxidative radicals namely •OH, •O₂^- etc., were involved in the oxidation of organic pesticide. Besides, TCS@MOF exhibits outstanding stability even after five repetitive cycles for the oxidation of MCP with a negligible decrease in photo-activity. The proposed mechanism and oxidative pathways of MCP were rationally deduced in detail subject to experimental results. The mechanism renders insight into the oxidation and consequent bond rupture of pollutant as well as into the formation of products such as H₂O, CO₂, etc. This report unveils a novel architecture of proficiently optimized TCS@MOF material structure for the perceptive oxidation of organic contaminants.

Quest for an Efficient 2-in-1 MOF-Based Catalytic System for Cycloaddition of CO2 to Epoxides under Mild Conditions

We have devised a straightforward tandem postsynthetic modification strategy for Zr-based metal-organic framework (MOF) materials, which resulted in a series of well-defined 2-in-1 heterogeneous catalysts, cat1-cat8, exhibiting high catalytic activity in the synthesis of cyclic carbonates under solvent-free and co-catalyst-free conditions. The materials feature precisely located co-catalyst moieties decorating the metal nodes throughout the bulk of the MOF and yield cyclic carbonates with up to 99% efficiency at room temperature. We use diffuse reflectance infrared Fourier transform (DRIFT) and solid-state nuclear magnetic resonance (NMR) measurements to elucidate the role of each component in this model catalytic reaction. Establishing a method to precisely control the co-catalyst loading allowed us to observe the cooperativity between Lewis acid sites and the co-catalyst in the 2-in-1 heterogeneous system.

A facile fabrication of a multi-functional and hierarchical Zn-based MOF as an efficient catalyst for CO2 fixation at room-temperature

Multi-functional and hierarchical Zn-MOF was rapidly synthesized by room-temperature stirring using an organic amine as a protonation agent and exhibited remarkable improvement for CO₂ cycloaddition to bulky epoxides.