K+ doped graphitic carbon nitride modified layered double oxide nanocomposite towards high-efficiency CO2 adsorption at intermediate temperature

As a novel medium-temperature CO(2 )adsorbent, K+ doped and graphitic carbon nitride modified layered double oxide composite (xK/CN-LDO, x = 15, 20, and 25 wt%) were prepared via in-situ synthesis and impregnation methods. Their adsorption performance was evaluated by thermal gravimetric analyzer. g-C3N4-modified LDO (CN-LDO) exhibited a CO2 adsorption capacity of 0.46 mmol/g, 1.39 times higher than the 0.33 mmol/g observed for LDO. This enhancement was attributed to the increased specific surface area and the exposure of additional extractable sites. Further doping with K significantly enhanced the adsorption uptake of xK/CN-LDO. Notably, 20 K/CN-LDO achieved the highest CO2 adsorption uptake of 0.82 mmol/g, representing a 2.48-fold increase compared to LDO. This further enhancement can be ascribed to K's ability to alter the distribution of chemical adsorption sites, thereby providing an optimal number of basic sites. In-situ DRIFTS analysis revealed that CO(2 )predominantly existed in the form of carbonate species, while adsorption kinetics studies show that the dominant mechanism is chemical adsorption, with external diffusion being the primary adsorption process. Furthermore, 20 K/CN-LDO exhibited significantly higher regeneration efficiency of 72.4 % after 10 cycles, showcasing its promising practical prospects for application in the SEWGS process.