Department of Civil and Environmental Engineering, University of Iowa, United States.
Department of Chemical and Environmental Engineering, University of California, Riverside, United States.
Water Res. 2017 Jun 15;117:207-217. doi: 10.1016/j.watres.2017.04.007. Epub 2017 Apr 4.
Via a single-pot electrospinning synthesis, we developed a functionalized polymer-metal oxide nanofiber filter for point of use (POU) water treatment of metal oxyanions (e.g., arsenate and chromate). Polyacrylonitrile (PAN) functionalization was accomplished by inclusion of surface-active, quaternary ammonium salts (QAS) [cetyltrimethylammonium bromide (CTAB) or tetrabutylammonium bromide (TBAB)] that provide strong base ion exchange sites. Embedded iron oxide [ferrihydrite (Fh)] nanoparticles were used for their established role as metal sorbents. We examined the influence of QAS and Fh loading on composite properties, including nanofiber morphology, surface area, surface chemical composition, and the accessibility of embedded nanoparticles to solution. Composite performance was then evaluated using kinetic, isotherm, and pH-edge sorption experiments with arsenate and chromate, and benchmarked to unmodified PAN nanofibers and freely dispersed Fh nanoparticles. We also assessed the long-term stability of QAS in the composite matrix. For composites containing QAS or Fh nanoparticles, increasing QAS/Fh nanoparticle loading generally yielded increasing metal oxyanion uptake. The optimized composite (PAN 7 wt%, Fh 3 wt%, TBAB 1 wt%) exhibited two distinct sites for simultaneous, non-competitive metal binding (i.e., iron oxide sites for arsenate removal via sorption and well-retained QAS sites for chromate removal via ion exchange). Moreover, surface-segregating QAS enriched Fh abundance at the nanofiber surface, allowing immobilized nanoparticles to exhibit reactivity comparable to that of unsupported (i.e., suspended or freely dispersed) nanoparticles. To simulate POU application, the optimized composite was tested in a dead-end, flow-through filtration system for arsenate and chromate removal at environmentally relevant concentrations (e.g., μg/L) in both idealized and simulated tap water matrices. Performance trends indicate that dual mechanisms for uptake are maintained in kinetically limited regimes. Although chromate removal via ion exchange is more susceptible to interfering counter-ions, arsenate removal in simulated tap water indicates that ∼130 g of the composite could produce an individual's annual supply of drinking water (assuming an influent contaminated with 100 μg As/L, which is 10 times the current MCL).
通过一锅静电纺丝合成，我们开发了一种功能化聚合物-金属氧化物纳米纤维过滤器，用于现场（POU）处理金属含氧阴离子（如砷酸盐和铬酸盐）的水。通过包含表面活性剂季铵盐（QAS）[十六烷基三甲基溴化铵（CTAB）或四丁基溴化铵（TBAB）]来实现聚丙烯腈（PAN）的功能化，这些 QAS 提供了强碱性离子交换位点。嵌入的氧化铁[水铁矿（Fh）]纳米颗粒因其作为金属吸附剂的既定作用而被使用。我们研究了 QAS 和 Fh 负载对复合性质的影响，包括纳米纤维形态、比表面积、表面化学成分以及嵌入纳米颗粒对溶液的可及性。然后使用动力学、等温线和 pH 边缘吸附实验评估了复合材料对砷酸盐和铬酸盐的性能，并与未改性的 PAN 纳米纤维和自由分散的 Fh 纳米颗粒进行了基准测试。我们还评估了 QAS 在复合基质中的长期稳定性。对于含有 QAS 或 Fh 纳米颗粒的复合材料，增加 QAS/Fh 纳米颗粒的负载通常会导致金属含氧阴离子的摄取增加。优化的复合材料（PAN 7wt%，Fh 3wt%，TBAB 1wt%）表现出两个同时发生的非竞争性金属结合的独特位点（即，通过吸附去除砷酸盐的氧化铁位点和通过离子交换去除铬酸盐的保留良好的 QAS 位点）。此外，表面分离的 QAS 使 Fh 在纳米纤维表面富集，从而使固定化纳米颗粒表现出与未负载（即悬浮或自由分散）纳米颗粒相当的反应性。为了模拟 POU 应用，在环境相关浓度（例如理想化和模拟自来水中的μg/L）下，将优化的复合材料在死端、流动通过过滤系统中进行了砷酸盐和铬酸盐的去除测试。性能趋势表明，在动力学受限的情况下，摄取的两种机制得以维持。虽然通过离子交换去除铬酸盐更容易受到干扰的抗衡离子的影响，但在模拟自来水中去除砷酸盐表明，大约 130 克的复合材料可以产生一个人每年的饮用水供应量（假设进水受污染，浓度为 100μg As/L，这是当前 MCL 的 10 倍）。
