Oxygen chemisorption on well cleaned carbon surfaces

Abstract

Graphon, a highly graphitized carbon black, was first oxidized to 14.4% weight loss in O 2 at 625°C to introduce significant active surface area. Following the cleaning of the activated Graphon surface by heating at 975°C in a vacuum of 10 −8 torr, chemisorption of oxygen between 25–400°C was studied. The saturation amounts of oxygen adsorbed sharply increase at temperatures above 250°C, suggesting the presence of at least two types of active sites. The maximum amount of oxygen adsorbed is estimated to occupy 2.8 m 2/g or 2.6% of the total surface. The rate of oxygen adsorption on the more active sites is given by k o Cn∞(1− θ) 2, where k 0 = 7.14 × 10 9 exp (−7,400/RT) cc/sec mole O 2. Following a large number of adsorption-desorption cycles, the Graphon surface is additionally activated to yield (in part) a fraction of very active sites that are not produced at comparable burn-offs by higher temperature activation between 500–625°C.