Photothermal nanotube enhanced thermomorphic absorbents for efficient low-temperature CO2 release

Aqueous amines have been identified as effective agents for CO₂ capture. However, their significant energy consumption during the regeneration process presents a major challenge, impeding further progress. This study presents a thermomorphic absorbent capable of regenerating at low temperatures. At a temperature of 323 K, the absorbent achieves a regeneration efficiency of 86.73 % in a water bath. Building on this capability, the desorption efficiency was further improved by incorporating photothermal nanotubes into the solution, replacing steam with photothermal energy for CO₂ desorption. This modification resulted in desorption efficiency comparable to that of the water bath at the same temperature. Furthermore, the absorption performance of the thermomorphic absorbent was evaluated, revealing a maximum upper-layer absorption capacity of 0.03885 g/g solvent and a lower-layer capacity of 0.08945 g/g solvent. The incorporation of carboxylated multi-walled carbon nanotubes not only acted as photothermal materials during desorption but also increased the solution absorption capacity by 25.93 % and sustained high absorption rates over time. Additionally, the presence of nanotubes boosted the solvent’s cycling capacity by 86.44 % compared to its absence. Fourier transform infrared testing and liquid nuclear magnetic resonance carbon spectroscopy of the thermomorphic absorbents indicated the formation of HCO₃^–, an unstable compound prone to decomposition, which facilitates low-temperature CO₂ desorption. The regeneration energy consumption of the thermomorphic absorbent was evaluated to be 1.10 GJ/ton CO₂, representing a 72.43 % reduction in energy consumption compared to 30 % MEA. This finding underscores the potential of the thermomorphic absorbent as a promising candidate for CO₂ capture.