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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]

Wastewater containing highly toxic and non-biodegradable heavy metals and organic dyes poses a serious threat to ecological environment and human health. Adsorption has been regarded as a promising technology to purify this kind of wastewater. Therefore, it is of great importance to develop efficient adsorbents. Herein, a magnetically recyclable adsorbent Fe 3 O 4 -CS/PDAC was facilely fabricated by coating poly(acryloyloxyethyltrimethyl ammonium chloride)-modified chitosan on the surface of Fe 3 O 4 nanoparticles. The morphology, physical-chemical and magnetic properties of as-prepared Fe 3 O 4 -CS/PDAC was fully characterized by various techniques. Its adsorption behaviors towards heavy metal Cr(VI) and organic dye sunset yellow (SY) were systematically investigated. Evidently, Fe 3 O 4 -CS/PDAC exhibited adsorption capacities of 163.93 and 769.23 mg/g for Cr(VI) and SY respectively, much higher than other reported adsorbents. Besides, batch experiment results showed that adsorption capacities decreased slightly with pH increasing from 2.0 to 10.0. Furthermore, Fe 3 O 4 -CS/PDAC could be easily separated and effectively regenerated after adsorption. The superior adsorption performance of Fe 3 O 4 -CS/PDAC could be attributed to the electrostatic interaction and ion exchange between target pollutants and the grafted cationic polymer. Owing to its high adsorption capacity over a wide pH range, rapid separation, easy regeneration and good reusability, Fe 3 O 4 -CS/PDAC has great potential for practical application in water treatment. Unlabelled Image • Novel cationic polymer modified magnetic chitosan beads (Fe 3 O 4 -CS/PDAC) were synthesized. • Fe 3 O 4 -CS/PDAC exhibits a high adsorption capacity towards Cr(VI) and sunset yellow over a wide pH range (2.0-10.0). • Superior adsorption performance is attributed to high density of quaternary ammonium groups on the grafted polymer chains. • Electrostatic interaction and ion exchange are involved in the adsorption process. [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]

A multifunctional carboxylate-rich magnetic chitosan flocculant (Mag@PIA-g-CS) was prepared through surface graft copolymerization on magnetite particles. The effect of monomer molar ratio, initiator and pre-neutralized degree on polymerization rate was determined. Various analytical methods were applied to characterize Mag@PIA-g-CS, exhibiting the successful grafting of polymers, good magnetic feature and core-shell structure. The kinetic process of Ni(II) and malachite green (MG) flocculation by Mag@PIA-g-CS reached equilibrium within <60 min with the optimal uptake rate of 98.3% and 87.4%, and exhibited satisfactory removal effect in wide pH range (4.0–8.0 for Ni(II), 5.0–10.0 for MG). Mag@PIA-g-CS exhibited superior flocculation performance over chitosan magnetic flocculant (Mag@CS). The pH-dependent behavior, rapid responsiveness and sensitivity to ionic strength in batch flocculation tests indicated the distinct effect of ionic groups. Moreover, sweeping action of linear molecular chains facilitated further flocculation. Mag@PIA-g-CS showed high stability in extreme environments, and can be easily regenerated and separated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Self-floating cyclodextrin-modified polymer was prepared. • The adsorption performance of TFCD and FTFCD was compared. • FTFCD simplified the recycling process by wrapping a hollow glass microsphere. • Porous structure and hydrophobic cavity favor the dye adsorption. • Polymers exhibited excellent selectivity toward cationic dyes. The separation and recycling processes of current cyclodextrin (CD)-based adsorbents are complicated. Thus, a novel composite based on a large surface area, porous, and self-floating tetrafluoroterephthalonitrile (TFN)-crosslinked CD polymer (FTFCD), was fabricated, characterized and applied to treat cationic dye pollutants. The characterization showed a porosity, good thermal stability, a stable crystal structure, and abundant functional groups on the prepared FTFCD, which had demonstrated great improvement on its adsorption capacity towards attention grabbing pollutants. The removal efficiency of the adsorbents for malachite green (MG) remained above 95% at pH 1 ∼ 10. In addition, the adsorbents were found to rapidly reach equilibrium governed by the pseudo-second-order kinetic model, and the maximum adsorption capacity of FTFCD was 1390.263 mg/g, as corroborated by the Langmuir isotherm model. While the phenolate groups of FTFCD found to electrostatically interacts with the MG strong cationic quaternary amine group, hydrogen-bonding was responsible for the hydroxyl group of FTFCD and the quaternary amine group binding. Meanwhile, the triangular cone configuration of MG makes it easy to be entrapped and absorbed in the hydrophobic cavity. Besides, after regeneration of exhausted FTFCD for five successive cycles, the MG removal efficiency still reached more than 80%. Thus, FTFCD could be applied as a potential alternative adsorbent for cationic dye removal owing to its excellent adsorption performance, convenient recycling, wide pH application, and environmental friendliness. [ABSTRACT FROM AUTHOR]