[thepAm][BF4] was molecularly designed, synthesized and characterized. [thepAm][BF4] showed high CO2 solubility and melting temperature at elevated pressures. An absorption-desorption procedure was proposed to test the stability of cyclic operation. A pressure swing absorption procedure was proposed to implement CO2 capture. Solid state of ionic liquid as an absorbent may open a new way for CO2 capture.