Practical evaluation of monometallic MOFs for efficient ammonia capture and regeneration under humid and acidic conditions

Despite the extensive development of metal–organic frameworks (MOFs) for ammonia (NH₃) adsorption, comparative studies under realistic humid and acidic conditions remain limited. A series of monometallic MOFs, including HKUST-1, MIL-88A, MIL-53(Al), UiO-66, MOF-801, and ZIF-8, were synthesized and systematically evaluated for NH₃ adsorption. Among them, HKUST-1 exhibited the highest surface area (1140 m 2 g⁻ 1 ) and NH₃ uptake (9.0 mg g⁻ 1 ), attributed to the presence of open Cu 2 ⁺ sites that facilitate both physisorption and chemisorption. The thermal stability of the MOFs followed the order UiO-66 > MOF-801 > MIL-53(Al) ≈ ZIF-8 > MIL-88A > HKUST-1, consistent with the strength of metal–oxygen coordination. HKUST-1 maintained over 90% of its adsorption capacity after five consecutive cycles and was fully regenerable at 75 °C. Structural analysis revealed that its framework remained stable under mildly acidic (pH 4) and humid environments but degraded under strong acidity (pH 2) due to Cu–O bond hydrolysis. The presence of PM₂.₅ slightly reduced NH₃ removal efficiency (> 90% retained) through partial pore blockage. Overall, NH₃ adsorption on HKUST-1 proceeds via a synergistic physisorption–chemisorption mechanism, offering high capacity, excellent reversibility, and strong potential for NH₃ capture in semiconductor exhaust abatement systems. The findings provide important structure–property insights for the rational design of next-generation NH₃ adsorbents operating under humid and acidic industrial environments.