Basic Product Introduction

What are Metal-Organic Frameworks (MOFs)?

Metal-Organic Frameworks (MOFs) are a class of porous crystalline materials formed by the self-assembly of metal ions/clusters (inorganic nodes) and organic linkers (organic struts) through coordination bonds, resulting in a periodic network structure.

MOFs represent one of the most breakthrough discoveries in materials chemistry over the past two decades. They are often referred to as "designer porous materials" due to their designable structures, tunable pores, and customizable functions.

Core Properties

MOFs possess ultra-high surface areas, far exceeding traditional porous materials such as zeolites and activated carbon, with BET surface areas reaching 3000-7000 m²/g. MOFs also exhibit high porosity, with pore volumes of 0.5-4.0 cm³/g, enabling them to accommodate large quantities of guest molecules. The pore sizes of MOFs can be precisely tuned by selecting organic linkers of different lengths, ranging from 3 to 100 Angstroms (0.3 to 10 nm). MOFs offer tremendous structural diversity, with nearly unlimited combinations of metals and linkers, and over 20,000 MOF structures have been reported to date. The pore interiors of MOFs can be functionalized with specific groups such as amino, carboxyl, sulfonic acid, and chiral sites. In terms of stability, MOFs typically decompose in the range of 200-500°C, with significant variation among different MOF types. Additionally, some MOFs remain stable in water, acids, and bases, with the UiO series exhibiting excellent chemical stability.

Key Application Areas

1. Gas Storage and Separation

The ultra-high surface areas and tunable pore sizes of MOFs make them ideal materials for gas adsorption.

For gas storage, materials such as MOF-5 and MOF-177 can store large amounts of hydrogen at low temperatures and high pressures, serving as hydrogen storage media for onboard fuel cell vehicles, with the U.S. Department of Energy targeting a system capacity of 5.5 wt%. MOF-519 exhibits excellent methane adsorption capacity at relatively low pressures and is used for adsorbed natural gas (ANG) technology in natural gas vehicles. Amine-functionalized MOFs (such as UiO-66-NH₂) show high selectivity and high adsorption capacity for CO₂, making them suitable for flue gas carbon capture and natural gas purification.

For gas separation, MOFs can be used for olefin/paraffin separations (such as ethylene/ethane and propylene/propane), achieving efficient separation through size exclusion effects or specific adsorption sites. MOFs can also be used for capturing VOCs (volatile organic compounds) from air.

2. Catalysis

MOFs as catalysts combine the advantages of both homogeneous and heterogeneous catalysts, featuring well-defined active sites, high surface areas, and recyclability.

For organic reaction catalysis, MOFs such as UiO-66-NH₂ can catalyze the reaction of CO₂ with epoxides to form cyclic carbonates, enabling CO₂ utilization. MOFs can also catalyze condensation reactions including Knoevenagel condensation and Aldol reactions. Porphyrin-based MOFs (such as PCN-222) mimic cytochrome P450 enzymes, catalyzing oxidation reactions such as olefin epoxidation. Pd-loaded MOFs can catalyze cross-coupling reactions such as Suzuki and Heck reactions.

For photocatalysis, porphyrin/porphyrin-based MOFs catalyze hydrogen production, CO₂ reduction, and organic pollutant degradation under visible light. Ti-based MOFs (such as MIL-125-NH₂) serve as photocatalytic hydrogen production materials.

For electrocatalysis, MOF derivatives (forming metal-nitrogen-carbon materials after pyrolysis) are used in oxygen reduction reactions (ORR), oxygen evolution reactions (OER), and hydrogen evolution reactions (HER).

3. Drug Delivery and Biomedicine

The degradability and high drug-loading capacity of MOFs make them emerging drug delivery systems. The pores of MOFs can encapsulate drug molecules, achieving drug loading capacities far exceeding conventional nanocarriers, reaching 30-50 wt%. Controlled drug release can be achieved through pH-responsive, enzyme-responsive, or light-responsive mechanisms. In terms of MOF selection, Fe-based MOFs (MIL-100, MIL-101) and Zn-based MOFs (ZIF-8) offer good biocompatibility and degradability. MOFs can also simultaneously load drugs and imaging agents (such as fluorescent dyes and MRI contrast agents), enabling theranostic applications. For antibacterial applications, metal-based MOFs (Ag, Cu) or antimicrobial-loaded MOFs are used in wound dressings.

4. Chemical Sensing

The pores of MOFs can selectively adsorb specific analytes, resulting in fluorescence or electrochemical signal changes. For gas sensing, MOFs detect toxic and hazardous gases including H₂S, NO₂, and formaldehyde. The water-adsorbing properties of MOFs are used in humidity sensors. Nitroaromatic explosives (such as TNT) can quench the fluorescence emission of MOFs, making MOFs suitable for explosive detection. Additionally, MOFs can detect specific metabolites in urine or blood as biomarkers.

5. Water Harvesting and Environmental Remediation

For atmospheric water harvesting, materials such as MOF-303 adsorb water vapor from air under arid conditions and release clean water upon solar heating, providing drinking water for off-grid regions.

For environmental remediation, MOFs are used to adsorb heavy metal ions such as Pb²⁺, Hg²⁺, and Cd²⁺ from wastewater, as well as to remove organic dye pollutants.

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