Effect of electrochemical regeneration on the surface of a graphite adsorbent loaded with an organic contaminant

Abstract

A regeneration efficiency of greater than 100% was obtained for electrochemical regeneration of a graphite interaction compound loaded with a phenol adsorbate. Time-of-flight secondary ion mass spectrometry was employed to study the effect of electrochemical regeneration on the graphite adsorbent. Using this technique, the elemental composition of the graphite surface was determined as a function of depth. The surface composition of the adsorbent was compared in three states: a fresh graphite before adsorption, after loading with a phenol adsorbate and after electrochemical regeneration. The fresh graphite exhibited a hydrogen and oxygen-rich surface layer approximately 150 nm thick. After loading with the adsorbate, the adsorbent had a thicker surface layer, approximately 370 nm, and significant enhancement in the hydrogen and oxygen abundance extending beyond 600 nm from the surface. After electrochemical regeneration, the graphite adsorbent showed an oxygen-rich layer, slightly thicker than the fresh case at approximately 220 nm, and a very much lower hydrogen enrichment at the surface. These results demonstrate that whilst the electrochemical regeneration effectively removes the phenol model pollutant, it also oxidises the exposed carbon surface. This oxidation may lead to new adsorption sites, but also has a significant impact on the estimation of adsorbent life.