Stability of oxidized single-walled carbon nanotubes in the presence of simple electrolytes and humic acid Original Research Article

The stability of nanoparticles is closely related to the fate, transport, and bio-toxicity of nanomaterials in the aquatic environment. Surface treatments and the presence of natural organic matter (NOM) have significant impacts on the aggregation behavior of nanoparticles. The aggregation kinetics of oxidized single-walled carbon nanotubes (O-SWCNT) was investigated in the presence of humic acid (HA). Results indicated that O-SWCNT was relatively stable in water with a critical flocculation concentration (CFC) of 0.16, 4.2 × 10−3 and 5.4 × 10−5 M for NaCl, CaCl2 and AlCl3, respectively. The aggregation of O-SWCNT was not sensitive to pH over the range of 3–8. The presence of HA can enhanced the stability of O-SWCNT dependent on the type of electrolyte present. The CFC of NaCl increased from 0.16 in the absence of HA to 0.19, 0.23, and 0.25 M at HA concentration of 1, 5, and 20 ppm, respectively. However, the effect of HA on the aggregation of O-SWCNT was negligible in the presence of CaCl2 and AlCl3. The findings highlighted the importance of surface treatments, water chemistry, and the presence of NOM on the aggregation behavior of nanomaterials, which should be considered when dealing with the fate and environmental impacts of engineered nanomaterials.