Direct Air Capture of CO₂: Mechanism-Guided Materials, Process Integration, and Scalable Carbon Removal

Direct air capture of CO₂ (DAC) is an emerging engineered carbon removal technology designed to extract CO₂ directly from ambient air and support long-term net-negative emission pathways. Unlike point-source carbon capture, DAC operates under ultradilute CO₂ conditions, where the low partial pressure of CO₂, large air-processing demand, humidity fluctuations, and regeneration energy requirements impose coupled thermodynamic, kinetic, and engineering constraints. While numerous reviews have addressed DAC materials or specific process configurations, a systematic account of how capture performance is progressively lost through the transition from molecular binding to material shaping, contactor operation, regeneration, and final storage remains lacking. This review fills this gap by adopting a performance-transfer framework that bridges capture chemistry, sorbent architecture, contactor engineering, and scalable deployment. We systematically survey the literature of the past decade across capture chemistries, sorbent design principles, structured contactors, regeneration strategies, and system integration, with a focus on studies that report cyclic working capacity, regeneration energy, and material stability under realistic conditions. Rather than enumerating material properties, we analyze the cascading losses introduced at each scale and identify the key bottlenecks limiting net carbon removal. Based on this analysis, we propose a staged roadmap from standardized material reporting to integrated DAC with carbon storage, aiming to guide future research toward verifiable and durable CO₂ removal.