Degradation of Carbon Nanomaterials Using Electrochemical Oxidation on BDD Electrodes

Abstract

Toxic potential of carbon nanomaterials (CN) to environmental species and humans is well documented. As carbon nanomaterials are produced in kiloton quantities worldwide, so is the risk of environmental contamination through industrial discharge and use (1). Eventually such discharge may diffuse through aquifers and residential drinking water. Significant challenges exist in decontaminating the effluent water, containing carbon nanomaterials. Carbon nanomaterials can be destroyed or degraded by incineration, however it requires the ability to locate, collect and concentrate carbon nanomaterial sample from the environment, which is often quite complicated. We have investigated the way to rapidly and significantly decrease the CN concentration in aqueous suspensions, thus reducing its toxic potential. Carbon nanomaterial degradation is based on generating strong oxidizing agents on a boron doped diamond anode, combined with a vigorous solution turbulence due to gas evolution inside a thin layer flow-through cell at high current densities. These agents react with carbon nanomaterials, damage them through multiple oxidations, destroy their structural integrity and rapidly reduce their concentration in aqueous solvents. In addition, the inert cathode surface facilitates hydrogen peroxide production due to the dissolved oxygen reduction reaction. As a result of strong oxidative reactions between nanomaterials and oxidative radicals, the outflowing water has a significantly lower concentration of suspended nanomaterials and, consequently is less toxic to the environment. The method was tested with pristine single and multiwall carbon nanotube, graphene and fullerene aqueous suspensions. UV-VIS-NIR absorbance show that CN concentration is reduced below 1% in a single pass through the single compartment electrochemical cell, thus offering a much faster way to degrade environmental toxicants compared to enzymatic or Fenton reaction approaches (2). Raman spectroscopy and analysis of the reaction products shows that oxidative attack on CN sp 2 –based structure by electrochemically generated reactive oxygen species leads to nanoparticle integrity loss and subsequent oxidation to CO2 . References Petersen, E. J. et al., Environ. Sci. Technol. 2011, 45, 9837-9856.Allen, B. L. et al., J. Am. Chem. Soc. 2009, 131, 17194-17205.