The role of oxygen-containing groups on the adsorption of bisphenol-A on multi-walled carbon nanotube modified by HNO 3 and KOH

Abstract

Abstract The adsorption of bisphenol-A (BPA) on multi-walled carbon nanotubes (MWCNTs) was investigated in this study. To distinguish the influences of surface area and oxygen-containing functional groups, the as-purchased MWCNTs ( A -MWCNTs) were treated by HNO 3 ( N -MWCNTs) and KOH ( K -MWCNTs). The adsorption capacity of N -MWCNTs was less than that of A -MWCNTs at neutral pH due to the steric obstruction resulted from the oxygen-containing functional groups on the N -MWCNTs. The adsorption capacities of BPA on all three types of MWCNTs decreased when the pH values increase to 10 or 11, at which the electrostatic repulsions between the dissociated surface groups and BPA arose. Also, it was found that although the N -MWCNTs and the K -MWCNTs had about the same amount of the oxygen-containing surface groups, their ratios of the adsorption amount at solution pH 11 to that at pH 5 ( q 11 /q 5 ) were different. This indicated that not only the amount but also the types of the oxygen-containing groups would affect the interaction between aromatic compounds and MWCNTs. The dissociation of OH groups and water-clustering would have more significant hindering effects than the carboxylic groups for the adsorption of BPA by MWCNTs at high pH.