Microstructure, dangling bonds and impurities in activated carbons Original Research Article

Wide-angle X-ray diffraction (WAXD), magnetometry, electron spin resonance (ESR) and Raman spectroscopy are used to investigate three activated PICA carbons (viz. GX203, P1400, Med 50) with surface areas of 1000, 1150 and 2000 m2/g, respectively. Although WAXD showed the absence of any minerals in these carbons, temperature and magnetic field variations of the magnetization shows significant magnetic impurities with concentrations in the order GX203>Med 50>P1400. Analysis of WAXD and Raman spectra shows these carbons to consist of graphitic crystallites with La≃30 Å and Lc≃10 Å. All three carbons give an ESR line due to dangling bonds with g=2.0028(3) but the linewidth ΔH and the spin concentration Ns are strongly affected by air/oxygen. The linewidths are reduced from ΔH∼4 Oe for the as-received samples to ΔH∼1.2 Oe for the evacuated samples. The Ns values are enhanced upon evacuation, with the enhancement factors of about 40, 130 and 670 for GX203, P1400 and Med 50 respectively, correlating well with the increase in the relative surface areas of these carbons. Magnetization studies using a SQUID magnetometer show that below about 30 K, all three carbons yield Curie-law variations with Ns∼1019/gram, in good agreement with the Ns values obtained from the room temperature ESR studies on evacuated samples.