Carbon dioxide capture and storage (CCS) is an important technological path for realizing “carbon neutrality,” where carbon capture is one of the three key CCS technologies. At present, mature carbon capture technologies still have technical shortcomings and difficulties, such as low capture efficiency and high energy consumption, which limit their large-scale popularization and application. In this study, a solid–liquid phase change absorbent (PCA) system with isophorone diamine (IPDA) as the only carbon dioxide (CO₂) capture carrier and ketone-based organic molecules as the phase change medium was developed. The solid–liquid PCA system has a wide range of applicability, with highly efficient CO₂ capture (1.11 mol·mol⁻¹) at concentrations ranging from typical values in air to those in coal-fired industrial emissions (400 to 150 000 ppm) and low-energy consumption regeneration, as revealed by a two-phase integrated engineering model. The CO₂ absorption product IPDA(NHCOO⁻)₂ was characterized by materials science analysis, molecular dynamics (MD) calculations and quantum chemistry. The results indicate that in noncyclic ketone-based phase-change media, the hydrogen bonding in IPDA(NHCOO⁻)₂ is modulated by noncovalent bond interaction (NCI) forces to form a small-scale hydrogen-bonding network. These properties ensure that the product can be easily regenerated by low-temperature thermal treatment (333 K, 60 °C), and characterization and calculations revealed a reaction mechanism different from that of the aqueous system. The technoeconomic evaluation (TEA) results show that this type of ketone-based PCA has an obvious low-cost advantage over traditional carbon capture technologies. This study provides a new perspective on the application and practical feasibility of PCAs for direct air capture of carbon dioxide.