A cyclophosphazene-derived porous organic polymer with P-N linkage for environmental adsorption applications

Porous organic polymers (POPs) have great potential in air and water pollutant treatments. However, the cost-effective syntheis of novel POPs remains a challenge. In this work, we fabricated a new porous organic polymer with P-N linkage (PCPD) via a low-cost catalyst-free polycondensation between 3,3′-diaminobenzidine and hexachlorocyclotriphosphazene under solvothermal conditions. The chemical composition, microstructure and thermal property were characterized by FT-IR, SEM, TEM NMR, DSC, TGA and N₂ sorption. The adsorption performance of PCPD was also studied. The results revealed that PCPD owns good microporosity, N-rich skeleton as well as abundant amino/imine groups. Tested for CO₂ adsorption at 273 K/1 bar and 298 K/1 bar, PCPD exhibited superior CO₂ uptakes of 127.6 mg g⁻¹ and 83.6 mg g⁻¹, respectively. Moreover, the isosteric heats of adsorption at low adsorption values was up to 33.3 kJ mol⁻¹. PCPD also delivered a superior removal performance towards toxic Cr (VI) from aqueous solution with equilibrium adsorption capacity of 205 mg g⁻¹ and instantaneous adsorption capacity of 148 mg g⁻¹ within 5 min at pH= 2. The Cr (VI) adsorption process is spontaneous and exothermic and well obeys intraparticle diffusion model, pseudo-second order kinetics, and Langmuir isotherm model. The plausible removal mechanism included electrostatic interaction, hydrogen bonding interaction, pore filling and the concurrent Cr (VI) reduction followed by in situ chelation on polymer adsorbent. PCPD would open a new field for efficient treatment of air and water pollutants due to its fascinating structure feature and excellent adsorption performance.