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

The attachment efficiency of O-SWCNT as a function of electrolyte concentration [(a) NaCl, (b) CaCl 2, and (c) AlCl 3] in the presence of humic acid (HA), indicating that NOM can prevent the aggregation of O-SWCNT in the presence of monovalent electrolyte but not multivalent ions [Display omitted] ► Surface oxidation significantly enhances the stability of carbon nanotubes. ► NOM prevents the aggregation of O-SWCNT induced by monovalent ions. ► NOM does not stabilize O-SWCNT when multivalent electrolytes are present. ► Surface modification and water chemistry are critical for CNT aggregation behavior. ► CNT should be readily removed by conventional wastewater treatment processes. 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, CaCl 2 and AlCl 3, 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 CaCl 2 and AlCl 3. 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.