Solvothermal Synthesis and Carbon Capture Performance of Terephthalate-Linked Zn0.75Mg0.25 MOF-74: Effects of Synthesis Conditions on Structure and CO2 Adsorption

Coal-fired power generation remains a major source of carbon dioxide (CO2) emissions, and metal–organic framework-74 (MOF-74) materials offer high adsorption capacity but rely on costly 2,5-dihydroxyterephthalic acid linkers that limit scalability. This study synthesized bimetallic Zn0.75Mg0.25-MOF-74 using terephthalic acid (TPA) as a cheaper alternative linker and evaluated the effect of synthesis reaction temperature (89–160 °C) and time (5–55.5 h) on its physicochemical properties for carbon capture. Samples were prepared solvothermally and characterized by FTIR, XRD, SEM-EDS, and N2 (77 K) and CO2 (293 K) adsorption analysis. FTIR confirmed metal–ligand coordination; XRD verified crystalline MOF-74 formation, and SEM showed well-defined rod-like morphology at 100 °C, 12 h and 125 °C, 30 h. Direct CO2 adsorption on the 125 °C, 30 h sample yielded a Type I isotherm characteristic of micropore filling, with an uptake of 0.31 mmol/g at ~1 bar and 0.072 mmol/g at flue-gas-relevant conditions (~0.135 bar). Its CO2-derived BET surface area (60.10 m2/g) and Dubinin–Astakhov micropore area (131.69 m2/g) far exceeded N2-derived values, confirming ultra-micropores accessible to CO2 but not to N2 at 77 K. TPA therefore yields a stable, microporous CO2-adsorbing framework, trading some capacity for lower cost and scalability. Future investigations should systematically evaluate long-term cycling stability and adsorption performance under mixed-gas operating conditions.