School of Geography, Earth and Environmental Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom.
School of Geography, Earth and Environmental Sciences, College of Life and Environmental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom; Center for Environmental Nanoscience and Risk, Department of Environmental Health Sciences, Arnold School of Public Health, University South Carolina, Columbia, SC 29208, United States.
Sci Total Environ. 2015 Dec 1;535:45-53. doi: 10.1016/j.scitotenv.2014.11.057. Epub 2014 Nov 26.
The dynamic nature of nanoparticle (NP) agglomeration behavior is of paramount interest to many current studies in environmental nanoscience and nano(eco)toxicology because agglomeration affects the NP bioavailability and toxicity. The present study investigates the surface charge and agglomeration behavior of TiO2 NPs in four different ecotoxicological media (OECD algae, OECD L_variegatus, hardwater and plant media) and two different electrolytes KCl (200 mM) and CaCl2 (50 mM). TiO2 NPs were positively charged, and the zeta potential varied from +1.9 mV in hardwater (at pH7.1) to +24.5 mV in CaCl2 electrolyte (at pH7.4) in all media except algae media, where the zeta potential was -6.7 mV (at pH7.7). Despite the differences in the pH and the surface charge of TiO2 NPs in the different media, an immediate agglomeration of the NPs in all standard ecotoxicological media was observed with aggregate sizes in the micrometer scale, as the measured zeta potentials were insufficient to prevent TiO2 NP agglomeration. The isoelectric point (pHiep) of TiO2 NPs in the studied media varied in the range (6.8-7.6), which was attributed to preferential association of anions and cations to TiO2; that is the pHiep decreases with the increased concentration of Cl and increases with the increased concentrations of Na and Mg. Despite the complexity of the ecotoxicological media and the presence of a mixture of different monovalent and divalent electrolytes, the agglomeration kinetics in the media follows the DVLO theory where two distinct agglomeration rates (slow, reaction limited regime and fast, diffusion limited regime) were observable. The critical coagulation concentration (CCC) of TiO2 NPs in the ecotoxicological media varied from 17.6 to 54.0% v/v standard media in UHPW, due to differences in media pH and TiO2 NP surface charge. In the ecotoxicological media (hardwater, L-variegatus and plant), where TiO2 NPs are positively charged, the CCC decrease with the increased divalent anions (act as counter ions) concentration in the media, again in good agreement with the DLVO theory.
纳米颗粒（NP）团聚行为的动态特性是当前环境纳米科学和纳米（生态）毒理学许多研究的关注重点，因为团聚会影响 NP 的生物利用度和毒性。本研究考察了 TiO2 NPs 在四种不同生态毒理学介质（OECD 藻类、OECD L-variegatus、硬水和植物介质）和两种不同电解质 KCl（200 mM）和 CaCl2（50 mM）中的表面电荷和团聚行为。TiO2 NPs 带正电荷，zeta 电位在所有介质中从硬水中的+1.9 mV（在 pH7.1 时）变化到 CaCl2 电解质中的+24.5 mV（在 pH7.4 时），除了藻类介质，其中 zeta 电位为-6.7 mV（在 pH7.7 时）。尽管不同介质中 TiO2 NPs 的 pH 和表面电荷存在差异，但在所有标准生态毒理学介质中，NP 立即发生团聚，形成微米级的团聚体，因为测量的 zeta 电位不足以防止 TiO2 NP 团聚。在研究的介质中，TiO2 NPs 的等电点（pHiep）在 6.8-7.6 范围内变化，这归因于阴离子和阳离子优先与 TiO2 结合；即 pHiep 随 Cl 浓度的增加而降低，随 Na 和 Mg 浓度的增加而增加。尽管生态毒理学介质复杂且存在混合的不同单价和二价电解质，但介质中的团聚动力学遵循 DVLO 理论，其中可以观察到两种不同的团聚速率（缓慢的，反应受限的状态和快速的，扩散受限的状态）。TiO2 NPs 在生态毒理学介质中的临界聚集浓度（CCC）在 UHPW 中从 17.6%至 54.0% v/v 标准介质变化，这是由于介质 pH 和 TiO2 NP 表面电荷的差异。在生态毒理学介质（硬水、L-variegatus 和植物）中，TiO2 NPs 带正电荷，CCC 随介质中二价阴离子（作为抗衡离子）浓度的增加而降低，这再次与 DLVO 理论一致。
