Natural and modified nanomaterials as sorbents of environmental contaminants

Nanotechnology is a revolutionary scientific and engineering concept that will have a large impact on our life. A core piece of this technology is the production of nanomaterials for electronic, chemical, medical, pharmaceutical, and environmental applications. In the last case, natural and modified natural nanomaterials would be good reference points for comparison of the functionality, cost, and potential ecological implications of synthetic nanomaterials. Here we investigated the performance of natural and modified nanomaterials (an allophane and a surface-modified smectite) in adsorbing copper (a common heavy metal contaminant), naphthalene (a representative polycyclic aromatic hydrocarbon), or 17beta-estradiol (an endocrine-disrupting chemical). Allophane is an effective sorbent of copper (Cu): at pH 5.5 it can take up 4448 mg Cu/kg at the equilibrium concentration of 10mg Cu/L. On the other hand, the surface-modified smectite is an excellent sorbent for naphthalene and 17beta-estradiol. It can sorb 1180mg naphthalene/kg at the equilibrium concentration of 1 mg/L or remove 98% of 17beta-estradiol from a solution after 4h of reaction. While the environmental impact and health effects of synthetic nanomaterials are essentially unknown and their use is of concern, natural nanomaterials (e.g., allophane and smectites) have been part of human existence since antiquity. As such, they do not pose much risk either to the physical environment or to human health.