中文摘要：

纳米粒子的聚集和再分散行为是影响纳米粒子在环境中归趋的重要因素.选取赤铁矿纳米粒子作为研究对象,用Zeta电位和粒径测定仪系统研究其在不同pH条件下的聚集和再分散过程.结果表明,当pH在7.0～8.7之间时,赤铁矿纳米粒子发生较快的聚集（如当pH为8.2时平均粒径在400s内由31nm增加到1400nm）.当pH≤6.3时,赤铁矿纳米粒子几乎不发生聚集.不经老化聚集的赤铁矿纳米粒子均能发生再分散,但是再分散过程并不完全可逆,而是呈现一定的非线性.老化使得更多的赤铁矿纳米粒子发生不可逆的聚集,在等电点处老化后的样品不发生再分散.当pH为7.0和8.9时,老化的样品再分散后的平均粒径（约500nm）大于不老化的样品（约250nm）.纳米粒子聚集-再分散过程的非线性对预测其在环境中的存在状态和生态效应带来了大的困难.

英文摘要：

The aggregation and deaggregation behaviors have profound impacts on the fate of nanoparticles in the environment.In this work,the aggregation and deaggregation kinetics of hematite nanoparticles at different pHs were examined using a Zetasizer.In the pH range of 7.0-8.7,aggregation occurred quickly（e.g.,the average size increased from 31 nm to 1 400 nm with 400 s at pH = 8.2）,whereas at pH below 6.2,no aggregation was observed.Deggregation of hematite nanoparticles without aging was slower than aggregation and not completely reversible,demonstrating hysteresis.Aging caused more hematite nanoparticles to aggregate irreversibly.At point of zero charge（pH = 8.2）,no deaggregation of aged particles was observed.At pH = 7.0 and 8.9,the average sizes of aged samples（about 500 nm） after deaggregation was greater than those of the samples without aging（about 250 nm）.The hyteresis of the aggregation-deaggregation process poses significant difficulty to predict the fate and ecological effects of nanoparticles in the environment.