The two nanoparticles (NPs), TiO2 and ZnO, in aqueous suspensions were identified in nanoscale by a transmission electron microscopy (TEM) and dynamic light scattering (DLS). Pretreatment process including filtration, centrifugation, and settling was evaluated for the analysis of NPs in the aquatic environment. Centrifugation(4060 G, 2 min) can be used to remove large particles on DLS analysis and the recovery was 74%-87%. For dissolved NPs, the solution can be filtered with a centrifugal ultrafilter and then calculated the real NPs concentration by the difference from total NPs concentration. The combination of the centrifugation before the DLS and concentration measurement after digestion are suggested. Finally, the size should be also confirmed by electron microscopies. For various aquatic parameters, the particle concentration from 10 mg/L to 1 g/L and 100 mg/L to 1 g/L did not affect the particle size of TiO2 and ZnO, respectively. We used 100 mg/L as the experiment concentration. The temperature in the range of 15~35℃ did not affect the stability of NPs. When the pH value closes to pHpzc of NPs, around 6.0±0.7 for TiO2 and 10.3±0.6 for ZnO, the obvious aggregation and sedimentation behaviors were found. With an increase of ionic strength, the particle size of NPs increased more quickly. The critical aggragation concentration (CAC) values for TiO2 NPs were 100 meq/L and 1.5 meq/L for Cl- and SO42-, respectively. Also, for ZnO, the CAC values were 10 meq/L and 0.2 meq/L for Cl- and SO42-, respectively. DLVO analysis consists with CAC results. When humic acid (HA) concentrations were 20 mg/L and 1 mg/L for TiO2 and ZnO NPs, NPs aggregated due to the surface of particles covered by SRHA to let surface charge near zero. For pH, NaCl and SRHA interaction, the most significant factors are SRHA concentration and pH for aggreagation and sedimentation, respectively, in TiO2 NPs suspensions. However, there are no significant interactions for two factors. For TiO2 NPs suspensions under different pH, Na2SO4 and SRHA, the most significant factors for aggregation and sedimentation are both SRHA and pH. The interaction between SRHA and pH value is significant. For ZnO NPs, with different pH, NaCl and SRHA, the most significant factor is SRHA. The interaction between SRHA and pH is significant for sedimentation. For ZnO under different pH, Na2SO4 and SRHA, the most significant factor for aggregation is SRHA and also the interaction between SRHA and pH. However, no significant factor can be observed for sedimentation. Overall, these factors generally affect the aggregation and sedimentation significantly.

nanoparticle suspension;aggregation;sedimentation