Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
Key Laboratory of Yangtze River Water Environment, Ministry of Education, State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
Sci Total Environ. 2014 Jul 15;487:375-80. doi: 10.1016/j.scitotenv.2014.04.036. Epub 2014 May 3.
With the increasingly widespread use of titanium dioxide nanoparticles (TiO2 NPs), the particles' environmental impacts have attracted concern, making it necessary to understand the fate and transport of TiO2 NPs in aqueous media. In this study, we investigated TiO2 NP aggregation caused by the effects of humic acid (HA), ionic strength (IS) and different pH using dynamic light scattering (DLS) to monitor the size distribution of the TiO2 NPs continuously. It was determined that HA can influence the stability of TiO2 NPs through charge neutralization, steric hindrance and bridging effects. In the absence of IS, aggregation was promoted by adding HA only when the pH (pH=4) is less than the point of zero charge for the TiO2 NPs (pHPZC≈6) because HA reduces the zeta potential of the TiO2 NPs via charge neutralization. At pH=4 and when the concentration of HA is 94.5 μg/L, the zeta potential of TiO2 NPs is close to zero, and they reach an aggregation maximum. A higher concentration of HA results in more negatively charged TiO2 NP surfaces, which hinder their aggregation. When the pH is 5.8, HA enhances the negative zeta potential of the TiO2 NPs and increases their stability via electrostatic repulsion and steric hindrance. When the pH (pH=8) is greater than pHpzc, the zeta potential of the TiO2 NPs is high (~40 mV), and it barely changes with increasing HA concentration. Thus, the TiO2 NPs are notably stable, and their size does not grow at pH8. The increase in the critical coagulation concentration (CCC) of TiO2 NPs indicated that there is steric hindrance after the addition of HA. HA can enhance the coagulation of TiO2 NPs, primarily due to bridging effect. These findings are useful in understanding the size change of TiO2 NPs, as well as the removal of TiO2 NPs and HA from aqueous media.
随着二氧化钛纳米颗粒（TiO2 NPs）的广泛应用，其颗粒的环境影响引起了人们的关注，因此有必要了解 TiO2 NPs 在水介质中的归宿和迁移。在这项研究中，我们使用动态光散射（DLS）连续监测 TiO2 NPs 的尺寸分布，研究了腐殖酸（HA）、离子强度（IS）和不同 pH 值对 TiO2 NPs 聚集的影响。结果表明，HA 可以通过电荷中和、空间位阻和桥接作用影响 TiO2 NPs 的稳定性。在没有 IS 的情况下，只有当 pH（pH=4）小于 TiO2 NPs 的等电点（pHPZC≈6）时，添加 HA 才会促进聚集，因为 HA 通过电荷中和降低 TiO2 NPs 的动电电位。在 pH=4 且 HA 浓度为 94.5 μg/L 时，TiO2 NPs 的动电电位接近零，达到聚集最大值。HA 浓度较高会导致 TiO2 NP 表面带更多负电荷，从而阻碍其聚集。当 pH=5.8 时，HA 增强了 TiO2 NPs 的负动电电位，并通过静电排斥和空间位阻增加其稳定性。当 pH（pH=8）大于 pHpzc 时，TiO2 NPs 的动电电位较高（约 40 mV），且随着 HA 浓度的增加几乎不变。因此，TiO2 NPs 非常稳定，在 pH8 时其粒径几乎不增长。TiO2 NPs 的临界聚沉浓度（CCC）增加表明加入 HA 后存在空间位阻。HA 可以增强 TiO2 NPs 的凝聚，主要是因为桥接作用。这些发现有助于理解 TiO2 NPs 的粒径变化以及从水介质中去除 TiO2 NPs 和 HA。
