Z.R. Yue et al. /Carbon 37(1999)1785-1796 75.76% 348%488%2,18 91%553%487% (3) 6837% 2.19%12.38%2.279 2.90%6.76%318% 88 280 Fig. 12. High resolution XPS C Is spectra of (1)as-received carbon fiber; (2)electrochemically oxidized carbon fiber (5300 C/g, and oxidized fiber which was post-heat-treated at, (3)550C and (4)850C under flowing nitrogen upon oxidation. The o Is spectra(Fig. 4) revealed the decreased after post oxidation heating at 550C(see Figs. 9 ame trends. The oxygen-rich surface within the micropor- and 10)and further decreased to nearly 0 umol/g after ous region chemisorbed oxygen and/or water as revealed post heating to 850C. Therefore, a large quantity of by an o ls peak at 534.6-535.4 eV. The O 2s-C 2s peak carboxyl, phenolic hydroxyl and reducible groups had been separation gradually increased in the valence band spectra present on the pore surfaces. I, adsorption increased as the (Fig. 5)as the extent of oxidation increased, probably due post heating temperature was increased, possibly from an to a carbonyl group contribution. a broad carbonyl stretch- increase in the average micropore diameter upon loss of ing vibration(ketones and/or carboxyl groups)at-1727 oxygen complexes. "Pinch points" could have opened, cm increased significantly as the oxidation extent in- allowing iodine access to a larger internal surface area onto creased. Weight loss and NaoH titration data required that which it could adsorb electrochemical oxidation generated an oxygenated internal XPS analysis of oxidized fibers after heat treatment ore structure extending far below the XPS analysis depth. ( Figs. 1l and 12 and Table 2)illustrated a progressive loss As-received fiber samples exhibited no significant of the oxygen functions with higher heat treatment tem- weight loss after heating to 550C for 30 min. while perature and time oxidized fibers gave substantial weight loss. This weight functions that had been formed in direct proportion to the Acknowledgements extent of electrochemical oxidation. Increasing the post oxidation heating temperature increased the weight loss This research was supported in part by th magnitude as the more thermally stable carbon-oxygen Science Foundation through Grants No. OSr-9452857 and surface groups were progressively gasified No. EPS-9452857. Support from the State of Mississippi Ag adsorption and NaoH uptake by fibers rapidly and Mississippi State University is also gratefully ack-Z.R. Yue et al. / Carbon 37 (1999) 1785 –1796 1795 Fig. 12. High resolution XPS C 1s spectra of (1) as-received carbon fiber; (2) electrochemically oxidized carbon fiber (5300 C/g); and oxidized fiber which was post-heat-treated at, (3) 5508C and (4) 8508C under flowing nitrogen. upon oxidation. The O 1s spectra (Fig. 4) revealed the decreased after post oxidation heating at 5508C (see Figs. 9 same trends. The oxygen-rich surface within the micropor- and 10) and further decreased to nearly 0 mmol/g after ous region chemisorbed oxygen and/or water as revealed post heating to 8508C. Therefore, a large quantity of by an O 1s peak at 534.6–535.4 eV. The O 2s–C 2s peak carboxyl, phenolic hydroxyl and reducible groups had been separation gradually increased in the valence band spectra present on the pore surfaces. I adsorption increased as the 2 (Fig. 5) as the extent of oxidation increased, probably due post heating temperature was increased, possibly from an to a carbonyl group contribution. A broad carbonyl stretch- increase in the average micropore diameter upon loss of ing vibration (ketones and/or carboxyl groups) at |1727 oxygen complexes. ‘‘Pinch points’’ could have opened, 21 cm increased significantly as the oxidation extent in- allowing iodine access to a larger internal surface area onto creased. Weight loss and NaOH titration data required that which it could adsorb. electrochemical oxidation generated an oxygenated internal XPS analysis of oxidized fibers after heat treatment pore structure extending far below the XPS analysis depth. (Figs. 11 and 12 and Table 2) illustrated a progressive loss As-received fiber samples exhibited no significant of the oxygen functions with higher heat treatment tem￾weight loss after heating to 5508C for 30 min. while perature and time. oxidized fibers gave substantial weight loss. This weight loss was due to thermal decomposition of oxygenated functions that had been formed in direct proportion to the Acknowledgements extent of electrochemical oxidation. Increasing the post oxidation heating temperature increased the weight loss This research was supported in part by the National magnitude as the more thermally stable carbon–oxygen Science Foundation through Grants No. OSR-9452857 and surface groups were progressively gasified. No. EPS-9452857. Support from the State of Mississippi 1 Ag adsorption and NaOH uptake by fibers rapidly and Mississippi State University is also gratefully ack-