Abstract:

This study investigated the effects of typical anions such as Cl^-, NO₃^-, SO₄^2-, and PO₄^3- on the transport and deposition behaviors of titanium dioxide nanoparticles (nTiO₂) in iron oxide-coated sand under environmental related conditions (ionic strength and pH). In iron oxide-coated sand, the breakthrough curves and retained profiles of nTiO₂ were equivalent in NaCl, NaNO₃, and Na₂SO₄ solutions. However, under the same solution conditions (ionic strength and pH), the breakthrough curves of nTiO₂ in the NaH₂PO₄ solution were higher yet the retained profiles were lower relative to other three solutions. The results indicated that under the examined solution conditions (pH and ionic strength), Cl^-, NO₃^-, and SO₄^2- had similar effects on the transport of nTiO₂ in iron-coated sand, yet the presence of PO₄^3- could facilitate the transport of nTiO₂. The alteration of the surface properties of both nanoparticles and porous media, the change of particle sizes, as well as the competition of deposition sites on sand grain surfaces by PO₄^3- ions contributed to the increased nTiO₂ transport in iron oxide-coated sand in NaH₂PO₄ solutions.

Key words: titanium dioxide nanoparticles, anions, transport, deposition, porous media

摘要：

以纳米二氧化钛为研究对象, 考察系列环境相关条件下(不同pH、离子类型与离子强度)纳米二氧化钛在载铁石英砂多孔介质中的迁移规律。结果表明, 纳米二氧化钛在NaCl, NaNO₃和Na₂SO₄ 3种溶液中的穿透曲线和滞留曲线没有显著差异, 但与其他溶液相比, 在NaH₂PO₄溶液中的穿透曲线和滞留曲线分别有明显的升高和降低; 磷酸根离子会促进纳米二氧化钛在载铁石英砂多孔介质中的迁移行为。机理探究发现, 由于PO₄^3-会被吸附至纳米二氧化钛和载铁石英砂多孔介质的表面上, 增大纳米二氧化钛和多孔介质的表面Zeta电位, 导致纳米二氧化钛与介质表面之间静电斥力的增加, 从而加大纳米二氧化钛被吸附于多孔介质表面位点的难度, 减少沉积; 同时, 纳米二氧化钛Zeta电位的增加会减少纳米二氧化钛颗粒间的碰撞团聚, 导致其水力学粒径变小, 从而促进其迁移行为。此外, PO₄^3-会与纳米二氧化钛竞争多孔介质表面的吸附位点, 导致纳米二氧化钛可沉积位点的减少, 增加迁移能力。

关键词: 二氧化钛, 阴离子, 迁移, 沉积, 多孔介质