School of Civil Engineering, Chang'an University, Xi'an, 710061, China.
School of Civil Engineering, Chang'an University, Xi'an, 710061, China; Key Laboratory of Northwest Water Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an, 710055, China.
Chemosphere. 2023 Dec;345:140421. doi: 10.1016/j.chemosphere.2023.140421. Epub 2023 Oct 13.
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.
金属有机骨架（MOFs）被认为是有效去除磷酸盐的吸附剂，但其超细粉末限制了其实际应用。在这项研究中，我们制备了两种壳聚糖（CS）凝胶珠，分别添加了不同的基于铈的 MOFs 并涂覆了 PDA 以用于吸附磷酸盐。掺杂在珠中的 MOFs 是 CM1 和 CM2，其中 Ce(III)/Ce(IV) 的比值为 0.36 和 1.46，表明 CM2 是 Ce(III) 为主，更适合去除磷酸盐。然而，在制备凝胶珠的过程中，壳聚糖和 CM1/CM2 的混合物是逐滴滴加到 NaOH 溶液中的，这导致两种珠子中的 Ce(III) 含量由于氧化而降低。在此基础上，为了提高磷酸盐的吸附性能并增强机械强度，将聚多巴胺（PDA）涂覆在外面。CS-CM1 和 CS-CM2 的吸附容量比纯 CS 高不超过 20mg/g，与 CS@PDA（63mg/g）的磷酸盐吸附量相当。由于 PDA 的减少，两个吸附剂中 Ce(III) 的含量明显增加。CS-CM1@PDA 和 CS-CM2@PDA 的最大磷酸盐吸附容量分别为 146.8mg/g 和 114.8mg/g。CS-CM2@PDA 在固定床柱研究中表现出最大的处理体积约为 1166BV，远高于 CS-CM1@PDA（976BV）。主要原因是 Ce(III) 可以通过配体交换和沉淀与磷酸盐形成结合。这些内球相互作用比 Ce(IV) 和磷酸盐之间的静电吸引强得多。因此，由于这种强亲和力，具有较高 Ce(III) 含量的 CS-CM2@PDA 可以在低浓度下更容易地捕获磷酸盐。综上所述，由于 PDA 的减少，成功地将基于铈的 MOFs 引入 CS 中，实现了优异的磷酸盐去除效果，在应用中具有广阔的前景。
