Metal-Organic Frameworks and Composites for Ammonia Capture

Abstract

The Haber-Bosch process has fueled surging ammonia (NH₃) demand for agriculture, pharmaceuticals, and energy, but its toxic, corrosive nature poses challenges for high-pressure storage and transport. Research on metal-organic frameworks (MOFs) for NH₃ storage emphasizes their exceptional porosity and functionalization capabilities, enabling high adsorption capacities However, their stability remains a challenge, as many degrade upon NH₃ exposure. Recent efforts aim to enhance both NH₃ uptake and stability through improved synthesis and post-synthetic modifications. This review highlights recent advances in MOFs for NH₃ adsorption, focusing on the key mechanisms involving open metal sites, µ-OH groups, structural defects, and functional surface modifications. The incorporation of unsaturated metal sites and Brønsted acidic µ-OH groups significantly improves NH₃ binding, while defect engineering introduces additional adsorption sites for increased capacity. Functional modifications, including anion insertion and hydroxyl group functionalization, further boost NH₃ adsorption capacity, even in cases of reduced surface area. Emerging MOF composites, such as metal halide-embedded and ionic liquid-loaded materials, demonstrate outstanding NH₃ capture performance due to synergistic effects and cooperative interactions. Finally, the future challenges and prospects of MOFs for NH₃ capture are discussed, highlighting current obstacles and potential advancements in the field.