Adsorption of Benzoic Acid: Structural Organization on the Surfaces of Pristine and Functionalized Single-Walled Carbon Nanotubes

We present the results of a classical molecular dynamics simulation of the adsorption of neutral benzoic acid on the surface of single-walled carbon nanotubes (SWNTs) with varying amounts of carboxyl functional groups. Here we show that a small increase in the level of surface oxygenation of SWNTs led to greater retention of benzoic acid in the first adsorption shell while the combined mass retained in the first two adsorption shells decreased with surface functionalization, likely due to the loss of aromatic-aromatic interfacial interaction between benzoic acid and tube surfaces. However, the aromatic-aromatic alignment angle was similar at different degrees of surface functionalization. Benzoic acid attained the optimal packing orientation in the adsorption region, an effect that was propagated even outside the adsorption region when there are few or no surface oxygens. The findings suggest that the primary adsorption mechanism of molecular benzoic acid on SWNTs is aromatic-aromatic interfacial interaction. Interestingly, surface carboxylation provides stronger per-molecule interfacial energy to both benzoic acid and water, which is attributed to the increased opportunity for nondissociative hydrogen bonding. The mechanistic understanding obtained here can be transferred to a wide range of amphiphilic emerging water contaminants during carbon nanotube-based targeted adsorption.

Automated summary

This study investigated the adsorption behavior of benzoic acid on single-walled carbon nanotubes with varying levels of surface functionalization through classical molecular dynamics simulations. The results showed that the retention of benzoic acid in the first adsorption shell increased with higher surface oxygenation, while the total mass retained in the first two adsorption shells decreased with surface functionalization due to the loss of aromatic-aromatic interactions. Interestingly, surface carboxylation enhanced per-molecule interfacial energy between benzoic acid and water, attributed to increased nondissociative hydrogen bonding opportunities.