Developing a sustainable route to environmentally relevant metal–organic frameworks: ultra-rapid synthesis of MFM-300(Al) using microwave heating

Abstract

NO₂, SO₂ and CO₂ are major air pollutants causing significant environmental and health problems. Metal–organic frameworks (MOFs), in particular [Al₂(OH)₂(C₁₆O₈H₆)](H₂O)₆ (trivial names: NOTT-300/MFM-300(Al)), have shown great promise for capturing these gases. However MOF syntheses often involve toxic solvents and long durations which are inherently energy intensive, an environmental burden, and have serious safety risks. There is a pressing need to develop environmentally-friendly routes to MOFs that require less energy and implement safer solvents particularly when considering scale-up beyond the laboratory for industrial application. We report the rapid synthesis of MFM-300(Al) in aqueous conditions and 10 minutes using microwave heating. This is the fastest reported synthesis of MFM-300(Al) to date with a 99.77% reduction in reaction time compared to the current reported 3-day conventionally heated route. The microwave synthesized sub-micron crystalline material exhibits gas uptake capacities of 8.8 mmol g⁻¹ at 273 K and 1.0 bar for CO₂, 8.5 mmol g⁻¹ at 298 K and 0.17 bar for SO₂, and 1.9 mmol g⁻¹ at 298 K and 0.01 bar for NO₂. These are 26%, 70%, and 90% greater for CO₂, SO₂, and NO₂, respectively, when compared to previously reported MFM-300(Al) materials produced via a 3-day conventionally heated route demonstrating the production of high quality materials in a fraction of the time with enhanced gas properties. Crucially, this offers an opportunity to move from batch to continuous processing owing to reduced reaction times underpinned by targeted heating.