Moisture Swing Adsorption Materials for Direct Air Capture: A Critical Review

Moisture swing adsorption (MSA) technology has emerged as a promising approach for direct air capture (DAC) of CO 2 due to its energy efficiency and operational flexibility. This review examines the fundamental principles of MSA, with a focus on the thermodynamic and kinetic mechanisms governing humidity-driven CO 2 adsorption and desorption. Recent advancements in quaternary ammonium (QA)-based adsorbents are analyzed, focusing on optimized material carriers, advanced formation techniques, and targeted functionalization strategies. These approaches lead to improvements in cycling stability, mass transfer efficiency, and kinetic performance. Emerging non-QA adsorbents and process innovations, exemplified by the six-step MSA cycle, demonstrate substantial potential for improving scalability and reducing energy consumption. This work provides a framework for developing next-generation MSA materials and advancing DAC applications.