Investigation of the sequestration mechanisms of Cd(II) and 1-naphthol on discharged multi-walled carbon nanotubes in aqueous environment.

The increasing exploitation of multi-walled carbon nanotubes (MWCNTs) into many industrial processes has raised considerable concerns as they are likely to be released into the environment. The interactions of the pollutants in water with discharged MWNCTs will further influence the environmental behavior and fate of these contaminants. In this context, our work aims to quantify the sequestration mechanisms and species distribution of Cd(II) and 1-naphthol on discharged MWCNTs by using batch technique. The uptake of Cd(II) on oxidized MWCNTs is greatly enhanced by the coexistent 1-naphthol, whereas the uptake of 1-naphthol on oxidized MWCNTs is not influenced by the coexistent Cd(II) in solution. Based on the experimental results, one can deduce that ion exchange or outer-sphere surface complexation mainly contributes to Cd(II) uptake on oxidized MWCNTs at low pH values, and inner-sphere surface complexation is the main uptake mechanism at high pH values. The uptake of 1-naphthol on oxidized MWCNTs is attributed to the π-π conjugate action between the aromatic ring of 1-naphthol and the graphitic structure of oxidized MWCNTs. The above-mentioned laboratorial results are further verified by the investigation conducted in actual effluent disposal system. The findings in the present study can provide more precise information on the real impact and changes in aqueous environment caused by the simultaneous presence of Cd(II), 1-naphthol and discharged oxidized MWCNTs.