Adsorption of cationic dye (methylene blue) from aqueous solution using poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) nanospheres

•We reported a novel polymer adsorbent which can be facilely synthesized.•The adsorbent owns numerous electron-rich N, P and S atoms and hydroxyl groups.•The adsorbent was an efficient and specific adsorbent for the removal of MB.•The pseudo-second-order model could be better to describe the adsorption of MB. Poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanospheres were prepared by a simple precipitation polymerization method and used as an efficient and specific adsorbent for the removal of methylene blue (MB), a cationic dye from aqueous solution. The as-synthesized PZS nanospheres were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The effects of initial solution pH, initial MB concentration, adsorbent dosage, and contact time on MB adsorption have been investigated. Results showed that the neutral and basic solutions benefited MB adsorption. The pseudo-second-order model could be better fit to the experimental data compared with the pseudo-first-order kinetic adsorption model. In addition, Weber's intraparticle diffusion model was used to further understand the adsorption process. The mechanism of efficient and specific adsorption possibly involved the presence of numerous electron-rich N, P and S atoms in PZS, the electrostatic attraction and π-π stacking interactions between PZS nanospheres and MB.