The effects of activated carbon fibers (ACFO, ACFH, and ACFN) on the degradation of methyl orange were investigated in a pulsed discharge reactor. ACFO fibers were modified with nitric acid (to yield ACFH fibers) or ammonia (to yield ACFN fibers) to create fibers with different porous structures and chemical properties. The adsorption properties of ACFO, ACFH, and ACFN depended on their pore diameter, but the catalytic properties were independent of their chemical properties. Acidic and basic surfaces both accelerated ozone decomposition, resulting in formation of hydroxyl radicals. Boehm titration and Fourier-transform infrared spectral studies indicated that the numbers of acidic and basic groups on ACFO. ACFH, and ACFN surfaces could be increased by this process, as could the surface areas and pores volumes. ACFO, ACFH, and ACFN could also be regenerated in situ after repeated use. (C) 2010 Elsevier B.V. All rights reserved.