Prediction of sorption of aromatic and aliphatic organic compounds by carbon nanotubes using poly-parameter linear free-energy relationships

Abstract

The accurate prediction of distribution coefficients of organic compounds from water to carbon-based nanomaterials (CNM) is of major importance for the understanding of environmental processes and a risk assessment of released CNM. Poly-parameter linear free-energy relationships (ppLFER) have previously been shown to offer such an accurate prediction of sorption processes. The aim of this study was to identify and quantify the contribution of individual molecular interactions to overall sorption by multi-walled carbon nanotubes (MWCNTs). To this end, a large data set of experimental sorption isotherms by MWCNTs of 20 aliphatic and 14 aromatic compounds covering various relevant molecular interactions was produced. A thermodynamic cycle was used to obtain MWCNT-air distribution coefficients (KMWCNT/a) for the interpretation of direct sorbate-MWCNTs interactions. The thereby derived ppLFER log KMWCNT/a = (0.59 ± 0.59)E + (2.23 ± 0.59)S + (3.90 ± 0.67)A + (3.23 ± 0.71)B + (0.98 ± 0.17)L - (0.05 ± 0.50) shows the contribution of non-specific interactions, represented by the hexadecane-air partitioning constant (L), and specific interactions related to the solute polarity (S) as well as the H-bond interactions (A, B). Measured MWCNT-water distribution coefficients were clearly more accurately calculated by the ppLFER equations (R(2) 0.85-0.86) compared to the classical prediction by single parameter model based on the octanol-water partitioning constant (R(2) 0.64-0.78). In addition, the ppLFER presented here allow a more accurately prediction of sorption by MWCNTs compared to literature ppLFER, especially for aliphatic compounds and at environmentally relevant concentrations.

Keywords: Carbon nanomaterials; Interaction; LSER; Organic compounds.