静电纺丝制备无定形氧化钨/高分子复合纳米纤维膜及其在污水处理及贵金属回收方面的应用

Wastewater containing metal pollutants has raised concerns owing to their accumulation in the human body and the negative effects on human health. Meanwhile, metal pollutants in wastewater are valuable resources and their removal/recovery from wastewater is essential for both environmental protection and sustainable development. However, current technologies would not meet the requirements of high-efficiency removal/recovery of metal ions in ultralow concentrations from wastewater. Here we propose the fabrication of electrospun membranes with amorphous-WO3 (a-WO3) incorporated into polymeric nanofibers. By solar light irradiation the membrane can be switched to the blue color reduced state. Once immersing the reduced nanofiber membrane in aqueous solutions of metal ions, a variety of metal compounds can be reduced and deposited on the nanofiber membrane rapidly and simultaneously. In principle, the metal deposition on the membrane is an electroreduction/deposition process. The large-surface-area nanofiber membranes are negatively charged with relatively low redox potentials, which promote the metal reduction/deposition. More interestingly, the strong electrostatic attraction between the negatively charged nanofiber membrane and the metal ions endows the membranes highly efficient in removing trace amount of metal ions from water. Such a NFM achieves metal removal in ppb level without pumping water through complex filtration membranes and can potentially be a beneficial supplement of the current water purification systems. Also, the noble metals removed from wastewater are reduced and deposited on the membrane as elemental metal nanoparticles without further high temperature thermal reduction or chemical reduction. These noble metal nanoparticles can be facilely separated and recycled, converting metal pollutants into valuable materials. These membranes are low-cost, environmental benign and easy for large-scale production, indicate their great potential for rapid, efficient toxic metal removal/ noble metal recovery in ppb level from wastewater.

污水中的重金属离子严重威胁人类健康，对水中重金属离子的去除是一个重要的环保问题，另一方面，工业废水中往往包含低浓度的贵金属离子，对这些贵金属离子的还原回收对可持续发展及环境保护具有重要意义。目前对低浓度重金属/贵金属离子的去除/回收缺乏有效途径。本项目尝试通过静电纺丝手段制备无定形氧化钨/高分子纳米纤维膜，该复合纤维膜可以通过太阳光照射转变为还原态。无定形氧化钨的引入使纤维膜具有较低的氧化还原电位，而当将还原态的纤维膜置于水中时，带负电的纤维膜与带正电的金属离子之间的强静电吸引作用可使水中微量的金属离子还原沉积于纳米纤维膜表面，达到水中金属离子去除的目的。另一方面，不同于常规贵金属吸附回收材料，本复合膜回收所得的贵金属以金属单质颗粒的形式沉积于纤维膜上，极易于分离回收，避免了复杂的高温热处理或化学还原步骤。本项目的开展可以为含低浓度重/贵金属的污水处理提供一个可能的新途径。

贵金属具有特别的物理化学性质，在工业领域具有广泛的应用，随着全球工业的飞速发展，贵金属的需求日益增加，但是贵金属在地壳中含量较低，因此成为非常重要的战略性资源。而随着贵金属在工业领域中用量的增加，工业中排出的含贵金属离子的废水也在逐年增多，如何处理废水并回收贵金属引起了大家的广泛关注。本项目通过静电纺丝手段制备无定形氧化钨/高分子纳米纤维膜，并利用该复合膜材料合适的氧化还原电位，通过还原性离子交换机理对低浓度贵金属离子废水进行了处理。研究结果表明，制备所得纳米纤维膜对含低浓度贵金属离子的溶液具有优良的还原回收效率。如对低浓度Ag, Au, Pt, Pd等贵金属离子去除效率可达98 %以上(100 ppb)，对含低浓度Cu, Hg, Pb, Cr等重金属离子的污水去除处理后可使其达到WHO规定的饮用水标准。对可能影响纤维膜还原回收效果的相关因素，如不易还原的阳离子浓度、氧浓度、pH值等均进行了讨论。对纤维膜的贵金属回收机理进行了充分研究，提出还原性离子交换机理，将其扩展到其他类型的可电化学还原膜材料中。通过在前期实验室研究基础上，积极与相关企业合作，建设可进行高分子/无定形氧化钨复合纳米纤维膜连续生产的静电纺丝生产线，所得纳米纤维膜用于农药茚虫威生产后处理中，前期实验证实纤维膜处理可有效降低生产中贵金属催化剂损耗，实现工业贵金属催化剂绿色可持续利用，降低企业经营成本。本项目制备的复合静电纺丝纤维膜有望规模化应用于废弃工业催化剂后处理及电子废弃物回收利用中，为节能减排及贵金属可持续回收利用提供更好的解决方案。本项目提出的还原性离子交换机理有望拓展到其他可还原性膜材料体系，为水处理及贵金属回收提供新思路。

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