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157462 
Journal Article 
Stability of commercial metal oxide nanoparticles in water 
Zhang, Y; Chen, Y; Westerhoff, P; Hristovski, K; Crittenden, JC 
2008 
1 
Water Research
ISSN: 0043-1354
EISSN: 1879-2448 
42 
8-9 
2204-2212 
WOS:000255825500037 
The fate of commercial nanoparticles in water is of
significant interest to health and regulatory authorities. This research investigated the
dispersion and stability of metal oxide nanoparticles in water as well as their removal by
potable water treatment processes. Commercial nanoparticles were received as powder aggregates,
and in water neither ultrasound nor chemical dispersants could break them up into primary
nanoparticles. Lab-synthesized hematite was prepared as a primary nanoparticle (85nm) suspension;
upon drying and 1-month storage, however, hematite formed aggregates that could not be dispersed
completely as primary nanoparticles in water. This observation may explain why it is difficult to
disperse dry commercial nanoparticles. Except for silica, other nanoparticles rapidly aggregated
in tap water due to electric double layer (EDL) compression. The stability of silica in tap water
is related to its low Hamaker constant. For all these nanoparticles, at an alum dosage of 60
mg/L, coagulation followed by sedimentation could remove 20-60% of the total nanoparticle mass.
Filtration using a 0.45 mu m filter was required to remove more than 90% of the nanoparticle
mass. (C) 2007 Elsevier Ltd. All rights reserved. 
nanoparticles; disaggregate; aggregate; stability; removal