Hollow poly(cyclotriphosphazene-co-phloroglucinol) microspheres: An effective and selective adsorbent for the removal of cationic dyes from aqueous solution

Hollow poly(cyclotriphosphazene-co-phloroglucinol) (PCPP) microspheres, synthesized by a facile precipitation polymerization method and then a simple solvent-treatment procedure, were evaluated as a potential adsorbent for the removal of cationic dyes from aqueous solution. The adsorbent was characterized by SEM, TEM, FTIR, N2 adsorption/desorption isotherms, zeta potential and particle size analysis. The adsorption process with respect to operating parameters was investigated to evaluate the adsorption characteristics of the hollow PCCP microspheres for methylene blue (MB). Systematic research including equilibrium, kinetics and thermodynamic studies were performed. The results showed the hollow PCCP microsphere was a potential adsorbent with an adsorption capacity of 50.7 mg/g at 298 K. The adsorption behavior followed the pseudo-second-order kinetic model and the adsorption equilibrium data obeyed the Langmuir isotherm well. Thermodynamic analyses confirmed that the adsorption was a physisorption process with endothermic, spontaneous and random characteristics. In addition, the possible adsorption mechanism was also proposed based on the experimental results. The study of selective adsorption further indicated the hollow PCCP microspheres could also remove other cationic dyes efficiently and be used a selective adsorbent.