Formation of oxygen structures by air activation. A study by FT-IR spectroscopy

Using cherry stones (CS) as starting material and commonly air as activatin g agent, formation of oxygen structures in activated carbon is investigated . In the preparation of samples, CS was first heated at temperatures betwee n 450 and 900 degrees C in N-2 atmosphere. Then, in a successive activation stage, the product carbonized at 600 degrees C was maintained in contact w ith an air stream at 25-325 degrees C for 24 h, 300-600 degrees C for 1 h, and 250 degrees C for 1-96 h. The rest of the carbonization products of CS were also heated at 250 degrees C in air for 24 h. Moreover. the product ca rbonized at 900 degrees C was activated at 750 or 900 degrees C in CO2 for 1 h. Furthermore, in a second activation stage, the products activated at s uch temperatures in CO2 and those at 300-600 degrees C in air were heated a t 250 degrees C in air for 24 h. The starting material, carbonized products , and activated carbons were examined by FT-IR spectroscopy. A number of ca rbon-hydrogen atomic groupings and of oxygen groups and structures, i.e., O H, C=O, and C-O-C) have been identified in CS, The yield of the activation and carbonization processes and also the chemical structure of the resultan t products are strongly dependent on the carbonization temperature. In the products carbonized at 600-900 degrees C, only ether type structures are de tected. The activation at 250 degrees C in air results in activated carbons that contain different oxygen structures when CS is carbonized at 450 or 6 00 degrees C. At 750 or 900, by contrast, oxygen structures are not formed as a result of the activation treatment. This also applies when the carboni zation product of CS at 900 degrees C is activated solely in CO2 or first i n CO2 and then in air. The heating conditions in air greatly influence the formation of oxygen structures (specifically, of lactonic and ion-radical t ypes) to a large extent. It only occurs when activating at relatively low t emperatures for a long time; at 300-600 degrees C for 1 h, however, the oxy gen structures are not formed. (C) 1999 Elsevier Science Ltd. All rights re served.