Study of oxygen groups at a porous carbon surface by a new fast intermittent thermodesorption technique

Abstract

A threshold thermodesorption method, named fast Intermittent TPD (ITPD), was used to study the evolution of CO 2 and CO arising from the decomposition of oxygen groups at the surface of a porous carbon used in the wastewater treatment. Applied to the as-received carbon, CO 2-ITPD provided clear evidence for six values of the apparent activation energy of oxygen group decomposition ( E app ): 139, 168, 206, 237, 270 and 290 kJ mol −1. Corresponding apparent pre-exponential factors ( A app ) were also determined. The data ( E app and A app ) derived from ITPD for the six desorption steps allowed a successful description of the complete TPD profile, considering a Gaussian narrow distribution of E app for each step. CO-ITPD also showed the presence of six (possibly seven) distinguishable steps upon CO thermal desorption and further demonstrated the interest of the fast ITPD technique for studying carbon surface chemistry. The TPD and ITPD profiles of the carbon treated with sodium hypochlorite showed: (i) a sharp increase in the amount of desorbed species, (ii) the prevailing presence of less stable oxygen groups, mainly carboxylic acids, giving rise to CO 2 desorption at low temperature, and (iii) the progressive merging of the desorption steps detectable at low temperature upon increasing surface density of oxygen groups.