Facile fabrication of cyclotriphosphazene crosslinked quercetin hollow nanocapsules by dual catalyst strategy for superfast and efficient removal of crystal violet over a wide pH range

A novel cyclotriphosphazene crosslinked quercetin (QuH) nanoadsorbent was manufactured at room temperature through precipitation copolycondensation between quercetin and hexacyclotriphosphazene (HCCP) with the help of dual catalyst. The obtained QuH had a hollow porous structure with specific surface area of 30.18 m² g⁻¹, an average diameter of 178 nm, and a huge negative surface charge. The adsorption efficiency of QuH was evaluated using water sample polluted with cationic dye crystal violet (CV). Results revealed that the QuH nanoadsorbent delivered an amazing adsorption amount of 840 mg g⁻¹ within one minute and an equilibrium adsorption capacity of 1159 mg g⁻¹ in 120 min for CV at 298.15 K and an initial CV concentration of 300 mg L⁻¹. Moreover, the nanoadsorbent kept a high adsorption ability for CV over a wide pH range of 3–9. The coexisting ion Na⁺ could promote the CV adsorption, whereas Ca²⁺ inhibited the CV adsorption. The retention of adsorption capacity could be up to 96 % after five cycles. The superior adsorption performance of QuH for CV was proposed to be the collaborative contribution of electrostatic interaction, ion exchange, hydrogen bonding, π-π stacking and pore filling effect based on the study of adsorption kinetics, isotherm, thermodynamics, and mechanism analysis.