纳米技术为深度水处理提供了新的机遇。然而，高活性超微（<5 nm）纳米颗粒材料的大规模生产仍存在挑战，且超微材料在实际水处理中也存在操作困难等问题，阻碍了纳米技术在水污染控制领域的推广应用。针对这些问题，我们提出了一种简便的解决方法，即以商用凝胶型离子交换树脂N201 为载体合成超微纳米颗粒。N201 是一种季铵化的毫米级聚（苯乙烯二乙烯基苯共聚）小球。在N201 中通过简单的浸渍-沉淀获得了水合氧化铁（HFO）、水合氧化锰（HMO）、硫化镉（CdS）和零价铁（ZVI）等纳米颗粒，所有纳米颗粒的尺寸都小于5 nm。中试生产表明该合成方法方便放大，并制备了大量亚5 nm HFO颗粒。关于超微纳米颗粒的合成机理，我们认为每个在水中溶胀的N201 小球内都包含连续均匀水相，使反应物可快速地扩散到树脂球内部（7 s 内从小球表面扩散到中心），从而实现纳米颗粒的爆发成核，形成超窄尺寸分布的晶核。此外，交联聚合物链间还可形成狭窄的孔隙（直径<5 nm），可防止在其中形成的纳米颗粒过度生长。由于N201 载体具有毫米级尺寸，所制备的复合纳米材料可方便用于连续流装置中。批次实验和柱吸附测试表明，超微HFO颗粒对As(III/V)的吸附性能比约17 nm的HFO显著增强。本研究有望进一步促进纳米技术在实际水处理中的推广应用。

Nanotechnology presents innovative solutions in advanced water treatment; however, its application is limited by the challenging large-scale production of ultrasmall (< 5 nm) nanoparticles (NPs) with extraordinary decontamination reactivity and the difficulty of handling such tiny NPs in engineering. To address these challenges, we propose a straightforward route for synthesizing ultrasmall NPs using the commercial gel-type anion exchange resin N201 as the host. N201 is a millimeter-scale poly(styrene-co-divinylbenzene) bead modified with quaternary ammonium groups. Nanoparticles of hydrated ferric oxide (HFO), hydrated manganese oxide (HMO), cadmium sulfide (CdS), and zero-valent iron (ZVI) were obtained through simple impregnation-precipitation in N201, and all of the NPs possessed an ultrasmall size of sub-5 nm. A pilot-scale production assay indicated that the synthetic system could be enlarged proportionally to prepare massive sub-5 nm HFO. Regarding the underlying mechanism, each N201 bead contained a continuous water phase, allowing the rapid diffusion of the reactants (7 s for diffusion from the bead surface to the center), resulting in burst nucleation to produce ultrasmall NPs with a narrow size distribution. Moreover, the crosslinked polymer chains provided a confined space (< 5 nm diameter) to prevent the excessive growth of the formed NPs. Owing to the millimetric N201 host, the resultant nanocomposite can be applied in flow-through systems. The batch and column adsorption assays demonstrate the dramatically enhanced adsorption performance of the ultrasmall HFO toward As(III/V) than the ∼17 nm analogs. This study can advance the widespread use of nanotechnology in practical water treatment.