Influence of ions on the coagulation and removal of fullerene in aqueous phase

Increased attention has been paid to the transportation and removal efficiencies of nanoparticles during water treatment. Here, C₆₀ was selected as nano-pollutant to investigate its removal efficiency in the process of coagulation by Al(3+) in regard to different ions. Negatively charged C₆₀ tends to adsorb hydrated Al(3+) to form positively charged C₆₀-Al(OH)(n)((m-δ)+) particles, leading to the restabilization of C₆₀. Multivalent anions, i.e., CO₃(2-), SO₄(2-), HPO₄(2-),and humic acid (HA), were shown to bridge the C₆₀-Al (OH)(n)((m-δ)+) particles together and induce the formation of flocs, resulting in enhanced C₆₀ removal (>80%). Monovalent anions, such as OH(-), NO₃(-) and the surfactant SDS, were not able to bridge the C₆₀-Al (OH)(n)((m-δ)+) particles together; hence, they had no effect on the C₆₀ removal. The addition of Na(+) and Ca(2+) increased the ionic strength of the aqueous solution, which compressed the electric double layer and induced the C₆₀-Al(OH)(n)((m-δ)+) particles to aggregate. However, they are not the essential factors for flocs formation. This is the first study to report the bridging phenomena between multivalent anions and C₆₀-Al(OH)(n)((m-δ)+) in water treatments, and it highlights that the presence of multivalent anions and cations in raw water are important for the effective removal of C₆₀.