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[Display omitted] • Exploring the defluorination performance by different crystalline MnO 2. • Lanthanum-modified MnO 2 with four crystal forms for defluorination were prepared. • Lanthanum loading significantly enhanced the fluoride ions adsorption. • The quantity of surface hydroxyl groups strongly influenced the defluoridation. • Ion exchange was the main process for fluoride ions adsorption. MnO 2 has a large potential for defluoridation, however, the influences of its crystal forms on the performance and mechanism of defluoridation are unknown. The research systematically investigated the defluoridation performance and mechanism of a total of eight materials with different crystal forms of MnO 2 (α, β, γ, δ) before and after lanthanum modification, separately. It was indicated that the largest Langmuir adsorption of α-MnO 2 and La-γ-MnO 2 for fluoride achieved 5.04 mg/g and 42.39 mg/g, correspondingly. The surface hydroxyl group and lanthanum loading of the material proved to be the major contributors to defluoridation. For the adsorption performance of eight materials on fluoride, pH was a significant influencing factor, with the highest adsorption performance at pH 5 ∼ 6. The eight materials showed consistent selectivity for fluoride adsorption in the existence of different anions, with the order of influence on the removal efficiency: CO 3 2–> NO 3 –> SO 4 2–> Cl–. The studies of FTIR, XPS, and variation of solution pH further illustrated that the adsorption mechanism of the eight materials on fluoride was the ion-exchange interaction and the complexation reaction. In addition, the effect of crystal forms on the adsorption of fluoride ions was further elaborated by DFT analysis. Finally, this study provided an in-depth discussion of the parameters of the dynamic process as well as the nature of the penetration curves by applying the Thomas, Clark, and BDST models. [ABSTRACT FROM AUTHOR]

Currently, the hidden risk of microplastics in the coagulation process has attracted much attention. However, previous studies aimed at improving the removal efficiency of microplastics and ignored the importance of interactions between microplastics and natural organic matter (NOM). This study investigated how polystyrene micro/nano particles impact the release of NOM during the aging of flocs formed by aluminum-based coagulants Al 13 and AlCl 3. The results elucidated that nano-particles with small particle sizes and agglomerative states are more likely to interact with coagulants. After 7 years of floc aging, the DOC content of the nano system decreased by more than 40%, while the micron system did not change significantly. During coagulation, the benzene rings in polystyrene particles form complexes with electrophilic aluminum ions through π-bonding, creating new Al-O bonds. NOM tends to adsorb at micro/nano plastic interfaces due to hydrophobic interactions and conformational entropy. In the aging process, the structure of PS-Al 13 or PS-AlCl 3 flocs and the functional groups on the surface of micro/nano plastics control the absorption and release of organic matter through hydrophobic, van der Waals forces, hydration, and polymer bridging. In the system with the addition of nano plastics, several DBPs such as TCAA, DCAA, TBM, DBCM and nitrosamines were reduced by more than 50%. The reaction order of different morphological structures and surface functional groups of microplastics to Al 13 and AlCl 3 systems is aromatic C-H > C-OH > C-O > NH 2 > aromatic C C > aliphatic C-H and C-O>H-C O> NH 2 >C-OH> aliphatic C-H. The results provided a new sight to explore the effect of micro/nano plastics on the release of NOM during flocs aging. [Display omitted] • Polystyrene plastic particles complex with Al-based coagulants through Al-O bond. • Nano-plastic particles with small sizes are more likely to interact with coagulants. • Micro-nano plastics would affect the reactivity order of functional groups of NOM. • Flocs formed with plastic would adsorb and release NOM in the aging process. • The involvement of Micro-nano plastics may increase the formation of DBPs. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Fe 2 @BC 900℃ -PMS process achieves outstanding degradation rate for CBZ. • Nonradical oxidation acts as dominate role for CBZ degradation. • 1O 2 , electron transfer and Fe(IV) are determined in the Fe 2 @BC 900℃ -PMS process. • The degradation pathways of CBZ are proposed by DFT and LC-MASS. • The toxicity of intermediates is evaluated by ECOSAR. In this study, the synthesis of Fe@BC (biochar) was successfully achieved using a one-step calcination process. The catalyst exhibited notable pore structures, a considerable specific surface area, and surface functional groups. Heterogeneous catalytic experiments further demonstrated that the CBZ degradation was significantly improved in the Fe 2 @BC 900℃ -PMS process, in comparison to alternative catalytic processes. The quenching, ESR analyses, and electrochemical tests (CV, LSV, OCP, and EIS) provided evidence that the CBZ degradation occurred via nonradical pathways involving the participation of 1O 2 , electron transfer, and Fe (IV). Furthermore, the potential mechanisms of PMS activation in the Fe 2 @BC 900℃ -PMS process were systematically elucidated. DFT, LC-MASS tests and ECOSAR suggested that CBZ can be transformed into smaller, less toxic molecules during the treatment. Moreover, the cyclic experiments revealed that the Fe 2 @BC 900℃ -PMS process maintained a consistent oxidation capacity for CBZ even after undergoing ten cycles. Based on the above findings, it can be concluded that the Fe 2 @BC 900℃ -PMS process could effectively degrade organic pollutants in water. [ABSTRACT FROM AUTHOR]