Fabrication of Phosphorus- and Nitrogen-Rich Inorganic–Organic Hybrid Hyper-Cross-Linked Polymers for CO₂ and I₂ Uptake

In this research, two types of metal-free organic–inorganic phosphazene based hybrid porous polymers (HPMs) enriched with phosphorus (P) and nitrogen (N) for gas sorption characteristics were reported. Cyclic phosphazenes were synthesized by condensation of biphenyl methanol with the hexachlorocyclophosphazenes (HCCPs) followed by cross-linking for the fabrication of porous and high surface area moiety designated as HCP-1. Whereas HCP-2 was synthesized with the replacement of polydichlorophosphazene (PDCP) chlorines with biphenyl methanol and later cross-linked in the same manner. Brunauer–Emmett–Teller surface areas of (SABETs) of HCP-1 and HCP-2 were 482 and 323 m2 g–1, respectively, whereas pore size distribution was under 1.10 nm. The observation of a higher surface area of HCP-1 is strongly indicative of cyclic N and P long chain backbone [-N═P-]. HCP-1 with a high surface area represented high carbon dioxide (CO2) adsorption (1.656 mmol g–1 with quantity adsorbed 37.13 cm3 g–1 at 273 K/1 bar and 1.35 mmol g–1 with quantity adsorbed 30.37 cm3 g–1 at 298 K/1 bar). HCP-2 with a low surface area showed moderate adsorption capacity (1.6 mmol g–1 with a quantity adsorbed 35.82 cm3 g–1 at 273 K/1 bar and 1.26 mmol g–1 with a quantity adsorbed 28.36 cm3 g–1 at 298 K/1 bar). The values of iodine uptake of HCP-1 and HCP-2 are 148 and 227 wt %, respectively, at 353 K. These results indicate a facile and convenient method to synthesize heteroatom-rich metal-free organic–inorganic phosphazene based hybrid porous polymers for CO2 and I2 sorption applications.