A Comparative Assessment of Nanostructured Adsorbents for Direct Air Capture

Direct air capture (DAC) is increasingly recognized as a critical component of net-zero emission strategies, as it enables the direct removal of CO₂ from ambient air. While carbon capture, utilization, and storage technologies are relatively mature for point sources, the ultra-low concentration of atmospheric CO₂ presents fundamental challenges for DAC, leading to high energy demand and elevated costs that currently constrain large-scale deployment. Recent advances in nanotechnology have enabled the development of nanostructured adsorbents with high surface areas, tunable pore architectures, and tailored surface chemistries capable of enhancing CO₂ capture under ultra-dilute conditions. In this study, a unified comparative evaluation framework is established to assess the performance of key classes of nanostructured adsorbents under DAC-relevant conditions. The analysis focuses on critical performance metrics, including CO₂ adsorption capacity, regeneration energy requirements, moisture tolerance, and cyclic stability. Representative material classes examined include MOFs, LDHs, porous carbons, graphene-based materials, and bio-derived nanostructures. Comparative assessment indicates that amine-functionalized LDH nanosheets exhibit rapid CO₂ uptake and stable performance over repeated adsorption–desorption cycles. At the same time, polyamidoamine-dendrimer-functionalized nanosilica demonstrates enhanced capture efficiency under both dry and humid conditions with relatively low-temperature regeneration. In parallel, charged-sorbent systems incorporating ions within activated carbon pores have emerged as a promising strategy, enabling fast CO₂ capture and electrically driven regeneration. Despite advances, substantial challenges remain. Reported techno-economic assessments frequently estimate capture costs in the approximate range of USD 300–1000 per ton of CO₂, depending on system configuration and scale, with associated energy penalties. Additional limitations include sensitivity to moisture, structural degradation during long-term cycling, and challenges related to scalable synthesis and deployment. No single adsorbent class currently satisfies all performance, cost, and scalability requirements. The comparative framework presented here highlights key trade-offs among material classes and underscores the need for integrated material- and system-level optimization to advance scalable, low-carbon DAC technologies.