In this study, the disaggregation behavior and the strength of heteroaggregates composed of multiwalled carbon nanotubes (CNTs) and hematite nanoparticles (HemNPs) were investigated in different solution chemistries. Negatively charged CNTs and positively charged HemNPs were first allowed to undergo favorable heteroaggregation at pH 5.5 and 0.1 mM NaCl before the CNT–HemNP heteroaggregates were disaggregated through the use of an ultrasonication bath. The heteroaggregate sizes before and after ultrasonication were measured by dynamic light scattering (DLS) in order to determine the degree of disaggregation. When the solution chemistry was unchanged, the heteroaggregates underwent partial disaggregation and heteroaggregate re-growth was observed after ultrasonication. Conversely, when the pH was raised to 11.0 immediately before ultrasonication, the heteroaggregates were almost completely disaggregated and no aggregation took place after disaggregation. Similarly, the introduction of humic acid led to a near complete disaggregation of the CNT–HemNP heteroaggregates. The elevated pH, as well as the adsorption of humic acid on the nanoparticles, was likely to weaken the particle–particle bonds within the heteroaggregates and hence increase the propensities of the heteroaggregates to undergo disaggregation.

Environ. Sci.: Processes Impacts, 2014, 16, 1371-1378