Activated carbon fibers (ACF) are highly microporous, showing better adsorption characteristics than granulated active carbons [l-3]. Surface m~i~cation of ACF by treatment with iron or copper oxides enhances micropore filling of supercritical NO and a mechanism involving a chemisorption-assisted micropore filling mechanism has been proposed [4-71. EXAF spectroscopic studies showed that oxides dispersed on ACF are ultrafine particles [6,7]. The adsorption activities for nof only NO, but also vapors such as SO2, NH3, CO2, and benzene were extensively examined [8,9]. Furthermore, the iron oxide-dispersed ACF exhibited selectivity for NO adsorption from a mixed gas [lo].
Enhancement of adsorptivity from solution is expected due to dispersed iron oxides on ACF. In this work, the adsorptivity of iron oxide-dispersed ACF for Hg(II) ions was investigated. The Hg(II) ion chemically interacts with the carbon surface [11,12] and the chemisorptivity of iron oxides dispersed on ACF will probably play an important role in the Hg(II) adsorption.
~ellullose-based ACF (Toyobo, KFlS~) was treated in the same way as reported earlier [4,5]. ACF and ACF preoxidized with HN03 treated in 0.6 M ferric sulfate solution at 303 K and pH 13 for 6 h were designed a-ACF and a-ox-ACF, respectively. The ACF treated in 0.2 M ferric chloride solution at 373 K was designated P-ACF. The granular activated carbons of 20-50 mesh from coconut shells (Takeda Yakuhin) and chelate resins for HE (III adsoration (Sumitomo Kagaku, Sumichelate Q-l@'w'&e u&l for cbmparison. The chelate resins are most effective in the pH region of 4-7 [13]. The ACF samples were characterized by Nz adsorption at 77 K after pre-evacuation at 383 K and 1mPa for 15 h. The specific surface areas determined from t-plots, micropore volumes obtained by DR plots and micropore widths by MP analysis for the t-plots are shown in Table 1. The surface area of a-ox-ACF is signi~cantly smaller (605 m2/g) than the other samples (1410-1650 mz/g). The micropore widths are a11 within the range 0.7-1.1 nm.
The dynamic Hg(I1) adsorption by all the adsorbents was measured at 303 K in a flow system constructed of glass and teflon tubes. A solution (1 ppm HgCl2, pH 5.5, 303 Kf was passed at a rate of 200