Amidoxime-Modified β-Cyclodextrin-Based Microparticles for Ultrafast Selective Adsorption of Methylene Blue and Antibacterial Water Treatment

Abstract

β-Cyclodextrin/phosphazene microparticles bearing amidoxime groups (β-CDPO) were synthesized by first crosslinking β-CD with hexachlorocyclotriphosphazene (HCCP) and 2,3-diaminomaleonitrile (DAMN), followed by conversion of the nitrile groups using hydroxylamine hydrochloride. The submicron adsorbent combines a phosphazene network, β-CD inclusion cavities, and amidoxime-rich hydrophilic interfaces, facilitating the swift and selective extraction of cationic methylene blue (MB). Over 98% of MB was eliminated in under 1 minute, achieving adsorption equilibrium within 10 minutes. The β-CDPO-2 showed excellent MB uptake, and Langmuir fitting suggested a high theoretical adsorption capacity under the tested isotherm conditions. The exceptional performance is due to the synergy of negative surface charge, numerous amidoxime, hydroxyl, and phosphazene-derived interaction sites, enhanced wettability, submicron size, and β-CD host–guest inclusion. In an MB/CR mixed-dye system, β-CDPO-2 preferentially captured MB over CR, suggesting potential charge-selective adsorption under the tested conditions. β-CDPO also exhibited antibacterial inhibition rates close to 100% against E. coli and above 90% against S. aureus. After 10 adsorption–desorption cycles, β-CDPO-2 maintained stable MB removal performance. These results demonstrate that β-CDPO is a multifunctional β-CD-based adsorbent with potential for rapid dye removal, model charge-selective adsorption, and antibacterial water purification.