Isosorbide-based cyclomatrix polyphosphazene for high-efficient and selective adsorption of cationic dyes: Experimental and computational studies

Abstract

A novel bio-based cyclomatrix polyphosphazene microsphere, namely poly(cyclotriphosphazene-co-isosorbide) (HISP), for efficient cationic-dyes adsorption was prepared by solvothermal method using hexachlorocyclotriphosphazene (HCCP) and isosorbide (IS). The chemical structure and morphology of HISP microsphere were characterized by Fourier transform infrared (FTIR), solid-state 31P nuclear magnetic resonance (NMR) spectroscopy, X-Ray photoelectron spectroscopy (XPS), andscanning electron microscope (SEM). The adsorption study towards different organic dyes and their mixtures showed that HISP exhibits an over 850 mg/g adsorption capacity for cationic dyes (e.g., rhodamine B (RhB), methylene blue (MB), and bismarck brown Y (BY)), respectively, and highly selective adsorption ability for MB. Using the adsorption of MB as a model system, the results show that alkaline condition is able to promote the adsorption performance. A high adsorption capacity of 1143.6 mg/g can be obtained towards 200 mg/L MB solution at 25 °C and pH = 10 using 6 mg of HISP. Adsorption kinetics and isotherm studies indicate that the adsorption behavior of HISP can be well described by pseudo-second-order kinetic model and Langmuir isotherm model. Importantly, the adsorption mechanism of HISP was demonstratedto be the electrostatic attractions derived from the numerous electron-rich O atoms in isosorbide, which was clarified by the electrostatic screening experiment and density functional theory (DFT) calculation. This systematic work paves a path to the preparation of highly selective dye adsorbents.