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The development of adsorbents with outstanding adsorption capacities, wide versatility, and excellent recyclability for the removal of organic dyes remains a challenge. In this study, a quaternised chitosan-based aerogel (QCSA) was fabricated via a facile method to effectively treat concomitant anionic dyes. Porous QCSA with high hydrophilicity, nontoxicity, excellent thermal stability, and sustainability exhibits adsorption properties superior to most previously reported adsorbents. The equilibrium adsorption capacities for Congo red, Sunset yellow, and Methyl orange were 1259.6, 550.2, and 607.5 mg/g, respectively. Notably, the spent QCSA exhibits excellent cyclic performance. The multilayer adsorption, external-internal mass transfer resistance, and adsorption on the active site models were employed to enable a more accurate description of the dynamic characteristics, confirming that double-layer chemisorption was the dominant process. A quantitative analysis of the electrostatic potential and the independent gradient model further verified that electrostatic interactions, hydrogen bonding, and van der Waals forces led to the highly efficient adsorption of dye molecules. Therefore, the eco-friendly and recyclable QCSA is a promising adsorbent for trapping anionic dyes from aquatic systems., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

In this study, novel green in situ quaternary-ammonium-functionalized magnetic chitosan microspheres (IQMCM) were synthesised. The resulting adsorbent was characterised by Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, vibrating sample magnetometry, X-ray photoelectron spectroscopy, and zeta potential analysis. The characterization results indicated that the IQMCMs possessed spherical morphology and superior specific thermal stability, magnetic properties, and surface charges. Batch adsorption experiments revealed that the adsorption capacities of the IQMCM microspheres to Congo red (CR) was 630.21 mg/g at a dosage of 0.15 g/L, temperature of 333 K, pH of 5.0, and initial dye concentration of 100 mg/L, and the corresponding removal rate reached 94.53 %. According to the kinetics, adsorption isotherms, and thermodynamics experiment results, the adsorption of CR dye coincided with a spontaneous endothermic monolayer chemisorption process. After saturated adsorption, this magnetic adsorbent could be rapidly separated from water and reused with little adsorption capacity loss. Overall, these results show that IQMCMs are potentially applicable in wastewater treatment., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022. Published by Elsevier Ltd.)