Purpose

Fulvic acid (FA) is a series of organic macromolecular compounds with many oxygen-containing functional groups and is easy to complex with nanoparticles (NPs) in the environment, thus affecting the stability and mobility of NPs in the water environment. Therefore, it is necessary to investigate the transport behavior of nano titanium dioxide (nTiO₂) particles with FA in the presence of phosphate (P).

Materials and methods

A series of transport experiments were conducted by using nTiO₂ suspended in phosphate background electrolyte with and without the addition of FA passing through water-saturated sand columns. The zeta potentials, hydrodynamic radii, and aggregation kinetics were measured, and the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory and two-site kinetic attachment model (TSKAM) were employed to explain the underlying mechanism.

Results and discussion

The experimental results showed that the presence of FA compressed the transport of nTiO₂ in phosphate electrolyte due to formation of larger complex via the adsorption of organic FA molecules onto nTiO₂, which can strongly compete with phosphate adsorption, leading to reduced electrostatic repulsive forces between nTiO₂ and sand. In the absence of FA at low pH (6.0), transport of individual nTiO₂ was increased by low phosphate adsorption in response to increased phosphate levels, and then, transport was decreased with the increased number of cations (Na⁺) from the phosphate (P ≥ 1.0 mM) electrolyte due to the compressed electric double layer. From the goodness-of-fit of the modeling results, the TSKAM provided a good prediction for the retention and transport of nTiO₂ in the copresence of FA and phosphate.

Conclusions

The compressed transport of nTiO₂ in the copresence of FA and phosphate was distinct from the synergistic transport in the copresence of humic acid.

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中文翻译：

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黄腐酸与磷酸盐介导的表面性能之间的竞争以及砂多孔介质中二氧化钛纳米颗粒的运输

目的

富勒酸（FA）是一系列具有许多含氧官能团的有机大分子化合物，易于与环境中的纳米颗粒（NPs）络合，从而影响NPs在水环境中的稳定性和迁移性。因此，有必要研究在磷酸盐（P）存在下纳米二氧化钛（nTiO ₂）颗粒与FA的传输行为。

材料和方法

通过使用悬浮在磷酸盐本底电解液中的nTiO _2（添加和不添加FA穿过水饱和砂柱）进行了一系列运输实验。测量了ζ电势，流体动力学半径和聚集动力学，并使用扩展的Derjaguin-Landau-Verwey-Overbeek（DLVO）理论和两点动力学吸附模型（TSKAM）来解释其潜在机理。

结果和讨论

实验结果表明，FA的存在压缩了nTiO ₂在磷酸盐电解质中的迁移，这是由于有机FA分子在nTiO ₂上的吸附形成了较大的络合物而形成的，这可以与磷酸盐吸附产生强烈的竞争，从而降低了静电排斥力nTiO ₂和沙子。在低pH（6.0）下不存在FA的情况下，响应于磷酸盐水平的提高，低磷酸盐吸附降低了单个nTiO _2的运输，然后，磷酸盐中阳离子（Na ⁺）的数量增加，运输的nTiO ₂降低了（P ≥1.0 mM）的电解质归因于双电层的压缩。从建模结果的拟合优度来看，TSKAM为FA和磷酸盐共存时nTiO ₂的保留和运输提供了良好的预测。

结论

FA和磷酸盐共存时nTiO ₂的压缩转运不同于腐殖酸共存时的协同转运。

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