Modification of the surfaces of a gasactivated carbon and a chemically activated carbon with nitric acid, hypochlorite, and ammonia

A gas-activated carbon and a chemically activated carbon were chemically modified by oxidation with nitric acid or hypochlorite. Nitric acid oxidation appeared to be most effective, resulting in the largest amount of acidic surface groups. Hypochlorite is a much milder oxidant, giving the opportunity to adjust the surface properties to desired values. A number of modified carbonaceous materials were treated with ammonia at relatively low temperatures (200°C), which resulted in basic carbon surfaces with large ion exchange capacities. The parent and modified carbons and chars were characterized by using different techniques, such as acid/base adsorption, TGA/MS, FT-IR, and porosimetry. Reaction pathways for the different modifications are presented.