Tailoring the Surface Chemistry of Activated Carbon by Nitric Acid: Study Using Response Surface Method

Tailoring the surface chemistry of adsorbents, especially activated carbons, make them suitable to specific applications. Many times oxidation is the first step and greatly affects the next steps of tailoring. We modified the surface chemistry of a microporous activated carbon (AC) by nitric acid solutions at different conditions of acid concentration, time, and oxidation temperature. The oxidized AC samples were inspected with the aid of physical adsorption-desorption of nitrogen at 77 degrees C and temperature-programmed desorption (TPD). It was shown that oxidation by nitric acid lowers surface area of the studied AC even at mild severity. Moreover, different instrumental analysis pointed out creation of a considerable amount of oxygen-containing functional groups, especially acidic ones on the surface. Central composite design (CCD) was applied to evaluate the individual and interactive effects of oxidation parameters and to provide a compromise between the amount of oxygen groups and BET surface area as two of studied responses. The significant factors and interactions on each response were recognized by Analysis of Variance (ANOVA). A linear model and a two factor interaction (2FI) model were developed to correlate the oxidation conditions to BET surface area and the amount of oxygen surface groups. In addition, optimized oxidation conditions were established.