Indoor direct air capture using amorphous MOF pellets from blast furnace slag: Waste to porous functional materials

Steel slag is a waste, could be a valuable source of metals, and these extracted metals from slag can serve as precursors for producing porous materials, such as metal–organic frameworks (MOFs). By refluxing blast furnace slag (BFS) in a 1 M HCl solution facilitates the dissolution of metals like Al, Mg, and Ca, while careful pH control enables effective separation of these metals. Therefore, the Al extracted from BFS was used to synthesize Al-1,3,5-benzene tricarboxylic acid (Al-BTC) and Al-fumarate (Al-FUM) MOFs. The MOFs powder was then formed into pellets and PEI-modified pellets were explored for CO₂ adsorption, using 1000 and 500 ppm CO₂ in N₂, which simulates indoor CO₂ concentrations. Pellets were examined to assess the impact of binders, and pellet shapes on adsorption capacity and kinetics. Pellets exhibited an average adsorption capacity of 0.6 to 1.2 mmol/g for 500 ppm CO₂, depending on the shape and binder. The most effective samples were subjected to 15 adsorption–desorption cycles from 500 ppm CO₂. MOF pellets demonstrated cyclic stability with an average adsorption capacity of approximately 1 mmol/g. This research presents a sustainable, circular method to utilize solid waste to synthesize MOFs, offering a significant reduction in production cost for CO₂ adsorption solid sorbents applications.