Hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeletons for highly efficient and selective adsorption of anionic dyes from water

An amino-rich hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeleton (HTCM) was facilely prepared by a one-step precipitation polycondensation of hexachlorocyclotriphosphazene and tetraethylenepentamine at room temperature, which exhibited a highly efficient, rapid and selective adsorption behavior towards anionic dyes. [Display omitted] •HTCM was facilely synthesized by one-step polymerizaiton at room temperature.•HTCM owned hollow structure and rigid-flexible coupling cationic skeleton.•The average adsorption capacity of HTCM for MO reached 1009.66 mg g−1 at 25 °C.•The α values of MO for MB, CV and RhB reached 124.22, 124.87 and 136.35 respectively.•The adsorption mechanism of HTCM involved electrostatic interaction and H-bonding. An amino-rich hollow polyphosphazene microcapsule with rigid-flexible coupling cationic skeleton (HTCM) was facilely prepared by one-step polycondensation from hexachlorocyclotriphosphazene and tetraethylenepentamine. The systematic adsorption studies for six single dye systems and three binary mixed dye systems showed that HTCM possessed a highly-efficient and selective adsorption behavior towards anionic dyes from water. Especially, the adsorption capacity of HTCM towards methyl orange (MO) at equilibrium reached 1009.66 mg g−1 at 25 °C, and the relative separation factors of anionic dye MO for three cationic dyes (methylene blue, Crystal violet and Rhodamine B) was up to 124.22, 124.87 and 136.35, respectively. The adsorption rate of MO onto HTCM was very rapid, attaining 68.6 % of adsorption equilibrium capacity for MO within the first 30 min. The adsorption kinetics, isotherm and thermodynamic analysis revealed that the uptake behavior of HTCM towards MO obeyed pseudo-second-order kinetic model, intraparticle diffusion model and Langmuir model, and the uptake process was spontaneous and endothermic. As verified from FT-IR and XPS analysis for HTCM before and after MO adsorption, the adsorption mechanism of HTCM for MO involved electrostatic interaction and hydrogen bonding. The present study promises the potential of HTCM for highly selective separation of anionic dyes from wastewater.