The effects of anodic treatment on the surface chemistry of a Graphite Intercalation Compound

Abstract

Graphite intercalation compounds (GIC) can be used as adsorbents for the removal of dissolved organic contaminants in water, and can be rapidly regenerated by electrochemical treatment. After electrochemical regeneration, the adsorption capacity of the GIC is often observed to increase compared to fresh adsorbent. This increase has been attributed to roughening of the surface as well as changes in surface chemistry. Specific surface areas of fresh and electrochemically treated GICs have been measured, and show no significant variation. Consequently, the electrochemical anodic oxidation process used to regenerate the material has been investigated, and these changes, specifically the transformation of the oxygen containing functional groups which is believed to give the GIC its surface chemistry properties, has been measured and studied. Analytical techniques including Scanning Electron Microscopy, Attenuated Total Reflectance Fourier Transform Infra-red spectroscopy, X-ray Photoelectron spectroscopy, Energy Dispersive X-ray spectroscopy and Boehm titrations were used to detect and estimate the relative amounts of functionalities such as carboxylic, quinone and lactonic functional groups. Results showed that fresh GICs have acidic quinone and carboxyl groups on the surface. These functional groups increase upon regeneration, however sustained regeneration leads to the formation of basic lactones which offset the relative amounts of the acidic groups. Acidic functional groups have been reported to increase adsorption, and consequently, there is an initial increase in adsorption due to surface acidic functionalities. Subsequent regeneration leads to the formation of basic functional groups which limit this enhanced adsorption.