Laboratory for Earth Surface Processes, College of Urban and Environmental Sciences, Peking University, Beijing 100871, China.
Department of Civil and Environmental Engineering, University of Nevada, Reno, NV 89557, USA.
Water Res. 2018 May 15;135:85-94. doi: 10.1016/j.watres.2018.02.018. Epub 2018 Feb 7.
Stable dispersion of nanoparticles with environmentally-friendly materials is important for their various applications including environmental remediation. In this study, we systematically examined the mechanisms of stable dispersion of two types of TiO nanoparticles (TNPs) with anatase and rutile crystalline structures by naturally occurring dissolved organic matter (humic acid) at different pHs, including at, below and above the Point of Zero Charge (PZC). The results showed that stable dispersion of TNPs by humic acid (HA) at all pHs tested can only be achieved with the assistance of ultra-sonication. The dispersion of TNPs by HA differed at the three pHs tested. Generally, HA greatly decreased the hydrodynamic diameters of TNPs at a very low concentration. The dispersion of TNPs became relatively stable when the HA concentration exceeded 5 mg/L, indicating that this HA concentration is required for stable dispersion of TNPs. The mechanisms involved in dispersion of TNPs by HA included electrostatic repulsion, steric hindrance and hydrophobic interaction. Electrostatic repulsion was identified to be the dominant mechanism. The dispersion of TNPs was enhanced when HA was added before ultra-sonication to avoid the partly irreversible re-aggregation of TNPs after sonication. The crystalline phases and concentrations of TNPs were also found to influence their stable dispersion. The findings from this work enhance understanding of the combined effects of HA, pH, ultra-sonication and crystalline structures of TNPs on their stable dispersion. The mechanisms identified can improve applications of TNPs in environmental water pollution control.
稳定地分散纳米颗粒与环保材料对于它们的各种应用是很重要的，包括环境修复。在这项研究中，我们系统地研究了两种类型的 TiO 纳米颗粒（TNPs）具有锐钛矿和金红石晶型结构在不同 pH 值下，包括在零电荷点（PZC）以下和以上的天然存在的溶解有机物（腐殖酸）稳定分散的机制。结果表明，在所有测试的 pH 值下，只有在超声波的辅助下，腐殖酸（HA）才能稳定地分散 TNPs。HA 在三个测试 pH 值下对 TNPs 的分散作用不同。一般来说，HA 在非常低的浓度下大大降低了 TNPs 的水动力直径。当 HA 浓度超过 5mg/L 时，TNPs 的分散变得相对稳定，这表明需要这个 HA 浓度来稳定分散 TNPs。HA 分散 TNPs 的机制包括静电排斥、空间位阻和疏水相互作用。静电排斥被确定为主要机制。当 HA 在超声之前加入以避免超声后 TNPs 的部分不可逆再聚集时，TNPs 的分散得到增强。TNPs 的晶相和浓度也被发现影响它们的稳定分散。这项工作的结果增强了对 HA、pH 值、超声波和 TNPs 晶型结构对其稳定分散的综合影响的理解。确定的机制可以提高 TNPs 在环境水污染控制中的应用。
