Abstract
The differences in effectiveness of multi-walled carbon nanotubes (MWCNTs) as the dispersive solid-phase extraction (dSPE) sorbent for the selective extraction of polycyclic aromatic hydrocarbons (PAHs) were explained on the basis of theoretical study. It was observed that for low molecular weight PAHs, the recoveries using non-helical and helical MWCNTs were similar. In contrary, for PAHs containing five or more aromatic rings, the extraction efficiency was higher using HMWCNTs than for non-helical ones. Principle component analysis (PCA) as well as providing structural parameters and interaction energies for adsorption processes (PAH + CNT → PAH-CNT) have been used for this purpose. All the PAH + CNT → PAH-CNT adsorption processes considered were found to be thermodynamically favorable. However, the adsorption energies (Eads) for PAHs and the helical carbon nanotube surface estimated for the B(a)P-HCNT and I(1,2,3-cd)P-HCNT are substantially less negative than those observed for PAH molecules interacting with the non-helical CNT. Namely, the Eads calculated in simulated aqueous environment for the B(a)P-MWCNT(6,2) and I(1,2,3-cd)P-MWCNT(6,2) were respectively − 43.32 and − 59.98 kcal/mol, while values of only − 7.75 kcal/mol (B(a)P-HCNT) and − 9.13 kcal/mol (I(1,2,3-cd)P-HCNT) were found for the corresponding PAH-HCNT systems. Therefore, we conclude that the replacement of MWCNTs with HCNTs leads to PAH-HCNT systems in which the interaction energies are much smaller than those estimated for the corresponding PAH-MWCNT systems. HMWCNTs are therefore recommended as the dSPE sorbent phase for the extraction of both low and high molecular weight PAHs from water samples.
Highlights
The use of carbon nanotubes (CNTs) as sorbents in extraction techniques is one of the most discussed topics in analytical chemistry (Ravelo-Pérez et al 2010; 253 Page 2 of 15Pyrzynska 2011, 2013; Scida et al 2011; Paszkiewicz et al 2016; Jakubus et al 2017)
Two Multi-walled carbon nanotubes (MWCNTs), i.e., 8MWCNT (BET-specific surface area 437.5 ± 1.5 m2 g−1) and 50MWCNT (BET-specific surface area 86.0 ± 0.6 m2 g−1), and helical MWCNTs (HMWCNT; BET-specific surface area 103.3 ± 0.4 m2 g−1) were chosen as sorbents to test their capability for the sorption of polycyclic aromatic hydrocarbons (PAHs)
Because the CNTs have a high sorption ability for PAHs (Table 1), the composition of the eluent was optimized for both MWCNTs and for HMWCNTs
Summary
The use of carbon nanotubes (CNTs) as sorbents in extraction techniques is one of the most discussed topics in analytical chemistry (Ravelo-Pérez et al 2010; 253 Page 2 of 15Pyrzynska 2011, 2013; Scida et al 2011; Paszkiewicz et al 2016; Jakubus et al 2017). The use of carbon nanotubes (CNTs) as sorbents in extraction techniques is one of the most discussed topics in analytical chemistry The results have shown that the extraction efficiency was comparable or higher than with using conventional stationary phases. The best results were obtained when methanol was used as the elution solvent and the carbon nanotubes had an outer diameter of 60–100 nm. Another method of sample preparation and the enrichment of PAHs from environmental matrices using hybrid magnetic carbon nanotubes (mCNTs) has been proposed by Menezes et al (2015). The hybrid mCNTs contain hydrophilic and hydrophobic parts which allow
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