Adsorption of carbon dioxide, methane, nitrogen, oxygen and argon in NaETS-4

The NaETS-4 sample was synthesized and the effect of heat treatment on the adsorption of CO2, CH4, N2, O2 and Ar in NaETS-4 was studied at 373 K and 423 K. The synthesized NaETS-4 sample was characterized by scanning electron microscopy, X-ray powder diffraction and TGA/DTA analysis. The XRD pattern shows that the NaETS-4 structure starts collapsing at around 473 K. NaETS-4 degassed at 373 K shows the highest equilibrium adsorption capacity for CO2 among the above gases and also shows higher equilibrium selectivity for CO2 over N2 and CH4. NaETS-4 sample degassed at 373 K showed moderate equilibrium selectivity of 1.4 for O2 over Ar. However, the NaETS-4 sample degassed at 423 K showed infinite selectivity for O2 over Ar and, N2 over CH4 due to the pore contraction of NaETS-4 at this temperature. The equilibrium adsorption capacity for CO2 also decreased drastically in NaETS-4 degassed at 423 K and the isotherm was irreversible. The chemisorption of CO2 in NaETS-4 degassed at 423 K is evidenced by DRIFT spectrum of CO2 adsorption in NaETS-4 degassed at 373 K and 423 K.