Magnetic hollow poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol)-Fe₃O₄ hybrid nanocapsules for adsorbing Safranine T and catalytic oxidation of 3,3′,5,5′-tetramethylbenzidine

The development of novel adsorbents with high adsorption capacity and easy recovery property is imperative in the field of wastewater treatment. In this study, a hard template-induced assembly strategy was developed to fabricate the magnetic hollow poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol)-Fe₃O₄ (PZS-Fe₃O₄) hybrid nanocapsules, in which Fe₃O₄ nanoparticles were well embedded in the cross-linked PZS shell. The resulting samples were well characterized using SEM, TEM, EDS, FT-IR, VSM, XPS, XRD and N₂ sorption. Then, using Safranine T (ST) as model dye, the adsorption behavior of as-prepared hollow PZS-Fe₃O₄ nanocapsules including adsorption kinetics, adsorption isotherms, adsorption mechanism, and recyclability were systematically evaluated and discussed. The results revealed that the magnetic hollow PZS-Fe₃O₄ nanocapsules own high adsorption capacity towards ST dye and outstanding magnetic separation functionality. The pseudo-second-order kinetic model and the Langmuir model can well describe the experimental data, and the adsorption process is controlled by more than one diffusion step. The interaction between ST dye and hollow PZS-Fe₃O₄ nanocapsules is ascribed to π-π interaction and electrostatic interaction. The thermodynamic parameters demonstrated that the adsorption processes were physical, endothermic, and spontaneous. Additionally, the magnetic hollow PZS-Fe₃O₄ nanocapsules also shows excellent peroxidase-like catalytic activity in the oxidation of 3,3′,5,5′-tetramethylbenzidine with H₂O₂, indirectly confirming the adsorption kinetic results.