NH2-MIL-53(Al) prepared sustainably and assisted by cationic surfactant as H2 and CO2 adsorbent.

The development of metal-organic frameworks (MOFs) with improved textural properties is a key strategy for enhancing their performance in adsorption. For this purpose, three NH2-MIL-53(Al) MOFs were synthesized via room temperature and hydrothermal approaches in the presence of cetyltrimethylammonium bromide surfactant using water as the only solvent. Firstly, parent and cetyltrimethylammonium-assisted NH2-MIL-53(Al) MOFs were synthesized at room temperature in water. In a different route, post hydrothermal treatment of cetyltrimethylammonium-assisted room-temperature-synthesized NH2-MIL-53(Al) and conventional hydrothermal synthesis of cetyltrimethylammonium-assisted NH2-MIL-53(Al) were performed at 100 °C in an autoclave. All the as-obtained MOFs were crystalline, except the cetyltrimethylammonium-assisted room-temperature-synthesized NH2-MIL-53(Al), which was semi-crystalline. The washing protocol using water and ethanol was found to be successful in removing the bulk of surfactant or unreacted precursors from the final products as confirmed by thermal analysis. Room-temperature-synthesized parent MOF showed rice or worm-like shapes and surfactant-templated room-temperature-synthesized MOF displayed shape-less agglomerated morphology as revealed by transmission electron microscopy. Conventionally and post hydrothermally synthesized surfactant-templated MOFs showed well-formed morphology. Textural analysis showed that surfactant tailored the porosity of NH2-MIL-53(Al) synthesized in water at room temperature by introducing small intercrystalline mesoporosity. The conventional hydrothermally synthesized NH2-MIL-53(Al) exhibited low surface area compared to the other three samples. The cetyltrimethylammonium-templated room-temperature synthesis in water produced a high-surface area sample with improved hydrogen and carbon dioxide uptakes compared to the parent NH2-MIL-53(Al).