Benchmarking CO2 Adsorbents for Direct Air Capture with an Amine-Grafted Metal–Organic Framework

Abstract

Direct air capture (DAC) is a promising strategy for mitigating atmospheric CO2 accumulation, yet sorbent evaluation remains dominated by equilibrium uptake under static conditions that fail to capture kinetic, humid, and process-level constraints relevant to real operation. Here we establish a dynamic evaluation framework that replaces equilibrium-centric metrics with a unified platform integrating high-precision gravimetric measurements, ppm-level CO2 nondispersion infrared detection, and capacitive humidity sensing, enabling direct quantification of adsorption kinetics, H2O/CO2 coadsorption, breakthrough behavior, and regeneration energy under low CO2 concentration and dry/humid conditions. Using TAEA@MIL-101(Cr) as a benchmark system, we introduce a sonication-assisted impregnation strategy that enables coordinated amine anchoring with preserved porosity and strong CO2 chemisorption. The optimized material exhibits a high equilibrium CO2 of 3.12 mmol g–1 (13.8 wt %) at 298 K, a dynamic breakthrough capacity of 12.4 wt % under dry conditions, and a retained capacity of 9.7 wt % at 50% relative humidity. Complete regeneration is achieved at 50 °C, enabling low-energy temperature-swing operation. This work establishes a generalizable dynamic benchmarking framework for DAC sorbents and positions TAEA@MIL-101(Cr) as a reference platform bridging molecular design, kinetic performance, and process-level energy requirements to complement conventional equilibrium evaluation.