Understanding adsorption and desorption behaviors of toxic organic chemicals on/from carbon nanotubes (CNTs) is critical for the application of CNTs as superior sorbents and the environmental risk assessment of both CNTs and toxic chemicals. Adsorption and Desorption hysteresis of polar and nonpolar organic compounds on/from five multiwalled carbon nanotubes (MWCNTs) containing varied amounts of surface oxygen-containing groups were investigated in this study to examine the influence of functional groups of organic chemicals and MWCNTs on the adsorption affinity and capacity and the desorption hysteresis. We observed that surface oxidation of MWCNTs reduced the surface area-normalized adsorption capacity of organic compounds significantly because of the competition of water molecules but not altered the adsorption affinity. Moreover, the decrease of surface area-normalized adsorption capacity of the organic compound with more polarity and higher adsorption affinity by surface oxidation was less because of the heterogeneous nature of hydrophilic sites of MWCNTs' surface. Desorption hysteresis was not observed for nitrobenzenes and phenols from all MWCNTs. Significant desorption hysteresis was observed for aniline and 4-methylaniline on surface oxidized MWCNTs but not on non-oxidized MWCNTs. Amidation reaction, an endothermic nucleophilic acyl substitution reaction and irreversible binding between amino-substituted aromatics and oxidized MWCNTs, could interpret the hysteresis of anilines from MWCNTs successfully, where amino groups of anilines acted as nucleophile and could form amidation reaction with carboxyl or lactonic groups on MWCNTs surface. Substitute groups with electron-withdrawing ability (e.g., �NO2, �Cl) could weaken the nucleophilicity of amino-substituted aromatics, the strength of amidation reaction and thus the hysteresis, while the substitute groups with electron-donating ability (e.g., �CH3) could enhance the hysteresis.

Adsorption and desorption of organic compounds on/from carbon nanotubes in water: Influence of surface oxidation of carbon nanotubes and chemical functional groups

247th National Meeting (2014)

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