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The metal organic frameworks (MOFs) are considered as the effective adsorbents for phosphate removal, while their ultrafine powders limit their practical application. In this study, we fabricate two chitosan (CS) gel beads added with different cerium-based MOFs and coated with PDA for phosphate adsorption. The MOFs doped in beads are CM1 and CM2, in which the Ce(III)/Ce(IV) ratio is 0.36 and 1.46, indicating CM2 is Ce(III) dominated and more suitable for phosphate removal. However, during the process of preparing gel beads, the mixture of chitosan and CM1/CM2 are added drop-by-drop to NaOH solution, leading to the decrease of Ce(III) contents in both of the two beads on account of oxidization. On this basis, in order to improve the phosphate uptake performance and enhance the mechanical strength, polydopamine (PDA) is applied to be coated on the outside. The adsorption capacities of CS-CM1 and CS-CM2 are no more than 20 mg/g higher than that of pure CS, which is also quite equal with the phosphate uptake of CS@PDA (63 mg/g). Due to the reduction of PDA, the content of Ce(III) increasing evidently in the two adsorbents. The maximum phosphate adsorption capacities are 146.8 mg/g and 114.8 mg/g for CS-CM1@PDA and CS-CM2@PDA, respectively. CS-CM2@PDA exhibits the largest treatment volume of ∼1166 BV in the fix-bed column study, much higher than that of CS-CM1@PDA (976 BV). The main reason is that Ce(III) could form binding with phosphate through ligand exchange and precipitation. Those inner-sphere interactions are much stronger than the electrostatic attraction between Ce(IV) and phosphate. Thus, due to this strong affinity, CS-CM2@PDA possessing a higher content of Ce(III) can capture phosphate more easier at low concentration. In summary, owing to reduction of PDA, the Cerium-based MOFs are successfully introduced in CS to realize excellent phosphate removal and exhibit a great prospect in application. [Display omitted] • The chitosan gel beads added with cerium-based MOFs and coated with PDA are fabricated. • The Ce(III) valence state is converted to Ce(IV) during the preparation of gel beads. • PDA coating reduces Ce(IV) and improves mechanical strength. • CS-CM1@PDA and CS-CM2@PDA exhibit high adsorption capacities. • CS-CM2@PDA can treat up to 1166 bed volumes of phosphate in column study. [ABSTRACT FROM AUTHOR]

Due to the complexity of contaminants, the effectiveness of traditional flocculants toward water purification is insufficient. To break the limitation, a novel polymer flocculant [chitosan grafted poly (acrylamide-itaconic acid), CS-g-P(AM-IA)] was synthesized via ultraviolet-initiated graft copolymerization reaction. Characterization results revealed that the graft copolymers were successfully synthesized and with rougher surface structure. The solubility of CS-g-P(AM-IA) and chitosan grafted polyacrylamide (CS-g-PAM) were greatly improved and they can dissolve in the wide pH range of 2.0–12.0. CaCl 2 was used as a source of cation bridge to enhance the flocculation of kaolin particles, and its optimum dosage was 150 mg·L −1 . At dosage of 30 mg·L −1 and pH of 5.0, the turbidity removal efficiency of CS-g-P(AM-IA) reached the maximum of 93.8%, whereas those of CS-g-PAM and CS were 96.7% and 76.9%, respectively. The patchwise adsorption of ionic groups embedded in the molecular chain on Ca 2+ -clay complexes took effect to generate flocs with larger particle size. Besides, the decolorization ability of cationic dyes by CS-g-P(AM-IA) was greatly enhanced due to the role of abundant carboxyl groups. In the crystal violet (CV) adsorption experiment, the maximum CV dye removal efficiency for CS-g-P(AM-IA) reached the maximum of 81.6% at dosage of 0.7 mg·mL −1 and pH of 9.0, while those for CS-g-PAM and CS were 51.7% and 36.5%, respectively. [ABSTRACT FROM AUTHOR]