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

[Display omitted] •1. A novel isosorbide-based cyclomatrix polyphosphazene (HISP) microsphere was synthesized.•2. The HISP microsphere exhibits a highly selective adsorption ability of cationic dyes from aqueous solution.•3. The adsorption behavior of MB follows pseudo-second-order adsorption kinetic model and Langmuir model.•4. The mechanism of adsorption between MB and HISP was revealed by experiment and DFT simulation.•5. The incorporation of isosorbide promotes the cationic dyes adsorption capacity of the HISP microsphere. 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.