Selected sustainably synthesized metal–organic frameworks for hydrogen and carbon dioxide storage

Abstract

Selected metal–organic frameworks (MOFs) including Al–MIL-53–NH₂, Fe–MIL-100, Zr–BDC and Zr–BDC–NH₂ were synthesized via a sustainable approach and tested for hydrogen and carbon dioxide storage. The synthesis was conducted at room temperature in the presence of water acting as a solvent. Crystalline Fe–MIL-100, nanocrystalline Al–MIL-53–NH₂, and semi-crystalline Zr–BDC and Zr–BDC–NH₂ were formed as confirmed by powder X-ray diffraction. Fourier transform infrared spectroscopy further confirmed the successful metal–ligand coordination in the MOFs. Thermogravimetric analysis shows that Zr–BDC was the most stable among the synthesized MOFs as it started to decompose above 500 °C. Morphological evaluation using field emission scanning electron microscopy reveals that Fe–MIL-100 consisted of octahedral-shaped crystals while Al–MIL-53–NH₂, Zr–BDC and Zr–BDC–NH₂ manifested as agglomerated particles. The agglomeration, further validated by transmission electron microscopy, results from the clustering of nanocrystals or small particles. This occurs due to the rapid formation of the precipitate during the room-temperature synthesis, where water serves as the solvent for the specified MOFs. The highest Brunauer–Emmett–Teller (BET) surface area (2013 m² g⁻¹), determined from nitrogen sorption, was recorded for Fe–MIL-100. Accordingly, Fe–MIL-100 exhibited the highest H₂ uptake (1.0 wt% at 77 K and 1 bar) and CO₂ storage (8.5 wt% at 298 K and 1 bar). This study illustrates the potential of certain sustainably produced MOFs for gas storage applications. Sustainably prepared MOFs provide the benefit of scalable synthesis suitable for industrial production by reducing reaction times and employing environmentally friendly solvents.