Emerging amine-functionalized layered double hydroxides as solid sorbents for direct air capture

Direct air capture (DAC) has emerged as an indispensable negative emission technology to mitigate climate change by removing CO₂ from ambient air. However, its further development is constrained by the limitations of conventional CO₂ adsorbents, which face significant challenges such as low uptake under ultra-dilute conditions, insufficient stability, high costs, and difficulties in scalable synthesis and shaping. This review critically evaluates amine-functionalized layered double hydroxides (LDHs) as a promising class of solid adsorbents specifically designed for DAC applications. We comprehensively compare the amine functionalization strategies for LDHs, including in situ incorporation and post-synthetic modification techniques (physical impregnation and covalent grafting), assessing their impacts on DAC performance metrics such as adsorption capacity, amine efficiency, kinetics, and cyclic stability under realistic humid conditions. Furthermore, we discuss scalable synthesis routes and advanced shaping techniques (e.g., 3D printing) essential for transitioning laboratory-scale LDH powders into structured contactors for industrial DAC processes. Finally, we outline future research directions, emphasizing the need for synergistic optimization across molecular design, macroscopic structuring, and low-energy regeneration process integration. This review aims to serve as a foundational reference and provide rational guidance for developing high-performance, cost-effective LDH-based sorbents to bridge the gap between material innovation and large-scale DAC implementation.