Membrane filtration of fullerene nanoparticle suspensions: effects of derivatization, pressure, electrolyte species and concentration.

Particle aggregation is induced in derivatized fullerene (fullerol) suspensions by introducing different counter-ion species (Na(+) Ca(2+) and Mg(2+)) and concentrations. The suspensions are filtered through 20 nm ceramic membranes under different transmembrane pressures, and the removal efficiency is compared. In all cases, the average hydrodynamic radius far exceeded the average pore diameter of the membrane. In the case of mono-valent counter-ions, removal efficiency is influenced by transmembrane pressure, with higher removal efficiencies achieved at lower pressures. In contrast, removal efficiencies of fullerol suspensions destabilized with di-valent ions are insensitive to transmembrane pressure, similar to what was found in the case of non-derivatized fullerene. Scanning Electron Microscope (SEM) images of post-filtration membranes indicate that fullerol aggregates destabilized with Mg(2+) ions deform and partially penetrate the membrane, but are ultimately trapped. The proposed mechanism suggests that di-valent ions act as bridges between fullerol aggregates, forming strong bonds that were not broken under the experimental conditions. These strong bonds may allow aggregated fullerol particles to deform under high pressure, and partially penetrate the membrane. Mono-valent ions are incapable of functioning as bridges, and subsequently, when sufficient pressure is applied, fullerol aggregates will break apart and pass through the membrane. 2010 Elsevier Inc. All rights reserved.