Highly-efficient and selective adsorption of anionic dyes onto hollow polymer microcapsules having a high surface-density of amino groups: Isotherms, kinetics, thermodynamics and mechanism

Organic dye pollution in the water environment is a problem of global concern. Adsorption is demonstrated as a promising technology to remove organic dyes from wastewater, in which the development of highly-efficient adsorbents is still the challenging task. Herein, we reported the facile fabrication of polyamine-based cyclophosphazene hybrid (PCP-NH 2 ) hollow microcapsules with cross-linked structure, generated by one-step precipitation polymerization between hexachlorocyclotriphosphazene and branched polyethyleneimine , and subsequent acetone treatment. Their morphology, composition and structure were confirmed by SEM, TEM, FTIR , TGA , and XPS . The endowment of hollow PCP-NH 2 microcapsules as potential adsorbents were thoroughly evaluated using eight organic dyes with different surface charges. The adsorption action of hollow PCP-NH 2 microcapsules highly depends on the surfaces charges, exhibiting highly-efficient and selective adsorption behavior towards anionic dyes. Especially, The adsorption capacity of the hollow PCP-NH 2 microcapsules towards anionic dyes of EY, ACBK, MO and EB reaches up to 1196.36, 1190.65, 1142.77 and 1040.92 mg/g at 25 °C, respectively. The adsorption kinetics shows a better fit to pseudo second-order kinetic model , compared to pseudo-first-order kinetic and Weber’s intraparticle diffusion models. The adsorption equilibrium data followed the Langmuir isotherm well. The adsorption thermodynamic experiments demonstrated that adsorption was a physisorption process with endothermic and spontaneous characteristic.