THERMAL-STABILITY OF OXYGENATED FUNCTIONS IN ACTIVATED CARBONS

Activated carbons with various degrees of oxidation were prepared by t reatment with concentrated nitric acid at various temperatures. Select ive removal of the oxygen complexes by heating under nitrogen flow at 573, 773 and 1073 K was also considered. The samples were characterise d through temperature-programmed desorption (TPD), Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XP S) techniques, FTIR and XPS techniques were found to be very useful fo r relating the shape of CO2 desorption profiles during pyrolysis with the nature of the functional groups desorbed. Three steps in TPD profi les were observed: (i) the desorption of carboxylic acid groups in the form of CO2 in the lower temperature range, 400-623 K; (ii) the decom position of lactone groups created during HNO3 treatment and, to some extent, originated during heating rearrangements, in the temperature r ange 623-823 K; and (iii) the elimination of the more stable ether gro ups upon treatment at temperatures above 823 K. The combination of the se three techniques (TPD, FTIR and XPS) gives a reasonable picture of the surface chemistry of the oxidised activated carbons. (C) 1997 Else vier Science B.V.