A Review of Advanced Solid Adsorbents for Direct Air Capture of CO2: From Material Design to Process Integration

Abstract Direct air capture (DAC) has emerged as a pivotal technology for regulating atmospheric CO2 levels, with solid adsorbents serving as critical components in high-efficiency capture systems. Despite their fundamental importance, prior research has lacked a systematic and comprehensive review of adsorbent classification and core characteristics in DAC applications. Earlier review articles primarily focused on cost analyses and economic feasibility, leaving significant gaps in the coverage of adsorbent types, properties, and performance metrics. Addressing this critical gap, our review presents a rigorous and exhaustive assessment of solid adsorbents for DAC, based on an extensive evaluation of recent literature. We first establish the thermodynamic foundations of DAC and outline the main CO2 capture technologies. Subsequently, we provide an in-depth analysis of both physical adsorbents, including zeolites, activated carbon, and metal-organic frameworks (MOFs), and chemical adsorbents, such as alkali-based adsorbents, amine-modified solids, and humidity-swing materials, evaluating their CO2 adsorption efficiency, operational conditions, and long-term stability in ambient air. Furthermore, we examine integrated CO2 adsorption-conversion technologies and the performance of dual-functional materials (DFMs) designed for such applications. In summary, this review consolidates current knowledge on solid adsorbents for DAC, identifies critical challenges, and proposes key research priorities to optimize adsorbent performance and accelerate technological deployment.