ELECTRON PARAMAGENTIC RESONANCE STUDIES OF AN ACTIVE-CARBON - THE INFLUENCE OF PREPARATION PROCEDURE ON THE OXYGEN RESPONSE OF THE LINEWIDTH

Active carbons have been prepared from sucrose, using chemical activating agents (KOH and ZnCl2) to yield carbons with BET surface areas of 430-1170 m2 g-1, which are dependent on the amount of activating agent present during carbonization. Adsorption studies with nitrogen at 77 K have demonstrated type I adsorption/desorption isotherms with well-defined plateaus and no hysteresis. The adsorbent pore volume determined by the BJH technique is mostly microporous, with pore radii smaller than 20 angstrom, the degree of microporosity being dependent on preparation conditions. Additional characterization has been performed by monitoring the electron paramagnetic resonance (EPR) linewidth DELTAB(pp) of the active carbons in the presence of various pressures of oxygen. The carbons give a single resonance line at g almost-equal-to 2.00, the free electron value. Subsequent analysis of the EPR characterization has shown a reversible dependence of the linewidth on the pressure of oxygen, P(O2), and a dependence of the response d(DELTAB(pp))/dP(O2) on the BET surface area. Thus active carbon oxygen sensors with differing responses to oxygen can be produced for oximetry applications.