Cyclophosphazene-Based Hybrid Nanoporous Materials as Superior Metal-Free Adsorbents for Gas Sorption Applications.

Cyclophosphazene-based inorganic-organic hybrid nanoporous materials (CHNMs) have been synthesized by a facile solvothermal method. The condensation of pyrrole with the reaction product of phosphonitrilic chloride trimer and 4-hydroxybenzaldehyde resulted in the formation of high-surface-area CHNMs. The maximum specific surface area (SABET) of 1328 m2 g-1 with hierarchical pore structures having micropores centered at 1.18 nm and mesopores in the range of 2.6-3.6 nm was estimated from the N2 sorption analysis. Observation of high SABET could be attributed to the synergy effect exerted by the cyclophosphazene moiety owing to its three-dimensional paddle wheel structure. The metal-free adsorbent exhibited a high and reversible CO2 uptake of 22.8 wt % at 273 K and 1 bar. The performance is on the higher side among the reported metal-free inorganic-organic hybrid nanoporous adsorbents. Moreover, the high H2 uptake of 2.02 wt % at 77 K and 1 bar is an added advantage. The superior performance of the adsorbents for the gas sorption applications could be attributed to the combined effect of high SABET and hierarchical pore structure, which has made CHNMs good candidates for energy and environmental applications.