Synthesis of poly(hexachlorocyclotriphosphazene-co-phenolphthalein) microspheres with negative charges for the selective removal of cationic dyes

Abstract

Through the precipitation polymerization method, polyphosphazene microspheres (PHCPP) were prepared using hexachlorocyclotriphosphazene (HCCP) and phenolphthalein (PP) as precursors. Subsequently, PHCPP microspheres, which are enriched with abundant hydroxyl functional groups and named PHCPP-NaOH, were derived via an intramolecular ester ring-opening reaction under alkaline conditions. Their morphology, composition, and structure were thoroughly characterized using various techniques. Due to electrostatic attraction and hydrogen bonding between PHCPP-NaOH and dye molecules, PHCPP-NaOH exhibited a high adsorption capacity (481.25 mg g⁻¹) towards the cationic dye (methylene blue). The adsorption process can be described with both Langmuir and pseudo-second-order models, and this was spontaneous and favorable. DFT calculations corroborated the experimental findings and the adsorption models, thereby validating the analysis. The fabricated PHCPP-NaOH exhibits promising potential as an effective adsorbent for removing cationic dyes from aqueous solutions.