Multi-walled carbon nanotubes as collector for the removal of cationic red X-GRL from wastewater by foam fractionation: shortcoming and remedy

Abstract

In this work, the removal of cationic red X-GRL from its aqueous solution by foam fractionation using multi-walled carbon nanotubes (MWCNTs) as the collector was investigated. MWCNTs were modified by nitric acid oxidation. The oxidized MWCNTs (o-MWCNTs) had high capacity of adsorbing cationic red X-GRL due to electrostatic attraction. However, the adhesive attraction of o-MWCNTs on the bubble surface would weaken after adsorbing cationic red X-GRL. In order to overcome this obstacle, small bubbles were used to provide plenty of plateau borders and large available surface area for loading dye-o-MWCNTs. Subsequently, a novel strategy on strengthening foam drainage was developed by creating a foam layer, in which large bubble layer was placed below small bubble layer. Experimental results indicated that above strategy contributed to weakening capillary phenomenon inside the foam without causing significant mass loss of dye-o-MWCNTs. Under the suitable conditions, the maximum removal percentage and enrichment ratio of cationic red X-GRL reached 96.4% and 13.5, respectively. This work is expected to facilitate the application of foam fractionation for wastewater treatment and provide a new method for strengthening foam drainage in the presence of nanoparticles.