Solid sorbents for direct air capture: a technological and environmental perspective

Direct air capture (DAC) is a pivotal technology for achieving net-zero emissions, yet its scalability is constrained by energy intensity and material limitations. This work critically examines the current landscape of solid sorbents for DAC, focusing on their performance, durability, and environmental impact. Key sorbent classes — amine-functionalized materials, carbonates, zeolites, and metal-organic frameworks — are evaluated in terms of CO₂ uptake, energy requirements, and life cycle emissions. A novel exergetic efficiency metric is introduced, incorporating sorbent degradation to better reflect real-world performance. Structured supports such as laminates and monoliths are discussed for their role in enhancing mass transfer and reducing pressure drop, though often at increased cost and environmental burden. Life cycle assessment (LCA) results highlight that energy consumption dominates DAC’s carbon footprint, with sorbent-related impacts becoming significant only for short-lived or energy-intensive materials. Emerging materials like hydroxylated activated carbon, along with alternative processes such as moisture swing adsorption and electrochemical DAC, offer promising pathways to reduce energy demand and improve sustainability. The work underscores the need for integrated assessments that link sorbent properties, process design, and environmental metrics from early development stages. Future research should prioritise sorbent longevity, comprehensive kinetic data, and inclusion of support structures in LCA models to enable cost-effective and climate-positive DAC deployment. • There is not a “one-fit-all” solution for DAC • LCA shows that the carbon footprint is dominated by the energy demand. • Novel materials and processes show promise to reduce footprint and energy load