Surface oxygenation of biochar through ozonization for dramatically enhancing cation exchange capacity

Abstract

Biochar cation exchange capacity (CEC) is a key property that is central to biochar environmental applications including the retention of soil nutrients in soil amendment and removal of certain pollutants in water-filtration applications. This study reports an innovative biochar-ozonization process that dramatically increases the CEC value of biochars by a factor of 2. The ozonized biochars also show great improvement on adsorption of methylene blue by as much as a factor of about 5. In this study, biochar samples treated with and without ozone were analyzed by means of pH and CEC assays, water field capacity measurement, elemental analysis, methylene blue adsorption, and Raman spectroscopy. Gaseous products’ analyses were carried out using an online universal gas analyzer over the duration of ozone treatments, and temperature changes were monitored using a thermal imaging camera. The results demonstrate a doubling of CEC with a concomitantly large drop in pH of the ozonized biochar compared with the untreated sample, brought about by the creation of acidic oxygen-functional groups on biochar surface, which may represent a significant progress toward the viability of employing biochar as a soil amendment for sustainability on Earth. This biochar-ozonization process technology has the potential to effectively convert conventional biochars into surface-oxygenated products with dramatically higher CEC values.