A novel chitosan-urea encapsulated material for persulfate slow-release to degrade organic pollutants.

A novel eco-friendly material (CS-U@PS) for persulfate slow-release to effectively degrade organic pollutants (methyl orange and pyrene) was synthesized using chitosan and urea as the encapsulated framework materials via an emulsion cross-linking method for the first time. The obtained CS-U@PS exhibits spherical shapes with a uniform size of approximately 2–3 µm according to the particle-size distribution and SEM image results. The slow-release mechanism was proposed through a kinetics model study and the Ritger–Peppas model fit well (r2 = 0.9699) to indicate that the slow-release process is non-Fickian diffusion. The influences of urea and PS dosages and oxidative conditions on methyl orange degradation were studied, and all the results suggested that urea played an important role in PS slow-release and can also catalyze the activation of PS by iron to further produce radicals and improve the removal efficiency of pollutants. A pyrene removal rate of 90.53% was achieved in aqueous solutions and an above 80% removal rate was obtained in weakly acidic or neutral soil environments by CS-U@PS activated by Fe2+ with citric acid as the chelating agent. Therefore, the fabricated slow-release oxidation materials exhibit application potential for the remediation of organic polluted groundwater and soil. The degradation of MO can be inferred to possibly follow two main pathways as a result of preferential attack of ROS (mainly OH• and SO 4 ⋅ −) on MO molecules. The peak at m/z = 304 is the parent molecule of MO after losing Na+ due to dissolution in aqueous solution. Therefore, from this peak, it was confirmed that MO was not fully degraded. Initially, OH• oxidized the parent MO molecule to form the oxidation product of MO (m/z = 337.2). The other degradation pathway is that the N C bond of the dimethylamino group is broken down, leading to the replacement of the methyl group with protons to form new products corresponding to MO losing two methyl groups (m/z = 277). Then, the peaks found at m/z 139 and 173 proved the symmetric cleavage of the azo bond. The oxidative cleavage of the C and S bonds of the MO dye by free radicals generated the intermediate (m/z = 197.1). The peak at m/z 96.9 is ascribed to the formation of 2-cyclohexen-1-amine, and the peak at m/z 110 can be produced by hydroxylation. Further oxidation of hydroquinone resulted in the destruction (m/z = 171.9) and opening of aromatic rings and the formation of short linear aliphatic carboxylic acids (m/z = 116). Finally, aliphatic carboxylic acids can be directly converted into CO 2 and H 2 O. [Display omitted] • CS-U@PS is a novel chitosan-urea encapsulated material for persulfate slow-release. • The slow-release process is non-Fickian diffusion. • Urea was an excellent and vital sustained release component. • A moderate amount of urea can catalyze the Fe2 + activation of PS to further produce free radicals. • A pyrene removal rate of 90.53% and 80% were achieved in aqueous solutions and soil, respectively. [ABSTRACT FROM AUTHOR]