Dispersibility and dispersion stability of carbon nanotubes in synthetic aquatic growth media and natural freshwater

Abstract

The dispersion behavior of carbon nanotubes (CNTs) is influenced by both their physicochemical properties and by the aqueous media properties (e.g. ionic strength, presence of divalent cations and natural organic matter) in which they are dispersed. In the current study, the dispersibility and dispersion stability of four multi-walled CNTs (MWCNT) and a single walled CNT (SWCNT) with different physicochemical properties were investigated in three freshwater growth media (with and without natural organic matter; NOM) used in algae and daphnia ecotoxicity studies. CNT dispersion behavior was also investigated in a natural freshwater for comparison. SWCNTs and non-functionalized MWCNTs showed similar dispersibility irrespective of the media type (SWCNTs = 0.5-0.9 mg/L; MWCNTs = 1.5-2.8 mg/L). Functionalized MWCNTs exhibited higher dispersion concentrations, but were more dependent upon the ionic strength and divalent cation concentration of each media (MWCNT-COOH = 3.0-6.6 mg/L). In contrast, CNT surface oxygen content had no influence on CNT dispersibility in the natural water (all MWCNTs = 0.9-1.4 mg/L). Functionalized MWCNTs were affected more by the differences in media properties than non-functionalized MWCNTs. The dispersed CNT concentration decreased over time for all CNT types and in all media due to sedimentation, but was influenced by both CNT and media properties. The study shows how a complex interplay between CNT and media properties can influence the environmental fate of CNTs. Furthermore, the study demonstrates how different CNT types and/or ecotoxicological media in aquatic tests influences the dispersion behavior of the CNTs, and thus their exposure and toxicity to aquatic organisms.

Purification of Boron Nitride Nanotubes Enhances Biological Application Properties

“…We also tested whether these dispersed BNNTs and pBNNTs can retain their dispersibility over the time course of the storage period. We and several other groups previously reported that CNTs dispersed in aqueous solution can be stable for up to several months [34][35][36][37]. However, unlike pBNNTs, dispersed BNNTs quickly aggregated and sedimented over the 60 d storage period.…”

Sorption and Desorption Analysis of Nitrobenzene on Differently Functionalized Multiwalled Carbon Nanotubes and Implications on the Stability

“…Turbidity is the cloudiness or haziness of a fluid caused by individual particles (suspended solids). The higher the turbidity, the smaller the particles that remain in solution, which could increase the surface area of MWCNTs and consequently be expected to enhance the nitrobenzene adsorption [10,42].…”

“…Once released into the aquatic environment, CNTs inevitably interact with the co-existing media in water. Due to their strong hydrophobicity and high specific surface area, CNTs concentrate pollutants in water, especially organic pollutants, and enter the food chain together, through the ingestion of floating organisms, thus, posing potential threats to the environment and human health [10]. On the one hand, adsorption and desorption of organic compounds molecules by CNTs can affect the transport and bioavailability of organic compounds in water.…”

“…This can also affect the cloudiness or haziness (turbidity) of CNTs suspension. Changes in size and diffusion efficiency and surface structure caused by aggregation behavior, directly affect the migration behavior (such as, outward migration distance (in m or km) from source of pollution) and the bioavailability of CNTs in water, and change their reactivity and toxicological properties in water [9,10]. The changes also affect the efficacy of absorption and reusability cycles when used as sorbents in the treatment of polluted water, which determine the removal rate of pollutants and cost of wastewater treatment [5].…”

The Effect of Multi-Walled Carbon Nanotubes-Additive in Physicochemical Property of Rice Brand Methyl Ester: Optimization Analysis

“…Carbon nanotubes are categorized as multi-walled nanotubes (MWCNTs) or single-walled nanotubes (SWCNTs). MWCNTs are cheaper to produce and have better dispersion compared to SWCNTs [32,33]. It is undeniable that the cost of preparing carbon nanotube materials is higher than metal oxides.…”