Effects of natural organic matter on separation of the hydroxylated fullerene nanoparticles by cross-flow ultrafiltration membranes from water

Transport, reactivity, and microbial toxicity of engineered nanomaterials (ENMs) are significantly influenced by the size and surface charge of the nanoparticle aggregates in the environmental media in which they are contained. To remove or separate the colloidal aggregates of ENMs from the aquatic environment, it is important to understand fate and transport of ENMs, and their interaction with other environmental components. Here, we explore the effects of natural organic matter (NOM) and NaCl concentrations on the removal efficiency of hydroxylated fullerene (fullerol) nanoparticle aggregates, nC₆₀(OH)₂₄ by cross-flow ultrafiltration (UF) membranes. We demonstrate that the removal efficiency of nC₆₀(OH)₂₄ (185 nm) by the UF membrane (nominal pore size = 30 nm) was limited at approximately 30%. As NaCl concentration increased from 0 to 1.5 M NaCl, the size of nC ₆₀(OH)₂₄ increased from 185 nm to 1405 nm but the maximum removal efficiency remained below 60%. The presence of NOM increased the stability of nC₆₀(OH)₂₄ and deteriorated the retention of nC₆₀(OH)₂₄ by the UF membranes. The more hydrophilic NOM (i.e., fulvic acid) resulted in lower separation efficiency of nC₆₀(OH)₂₄ by the UF membrane than the less hydrophilic NOM (i.e., humic acid).