Journal of Colloid and Interface Science 275 (2004) 342–344 www.elsevier.com/locate/jcis Note Effect of acidic treatment on metal adsorptions of pitch-based activated carbon fibers Soo-Jin Park, a,∗ Jun-Sik Shin, a Jae-Woon Shim, b and Seung-Kon Ryu b a Advanced Materials Division, Korea Research Institute of Chemical Technology, P.O.Box 107, Yusong, Taejon 305-600, Republic of Korea b Department ofChemical Engineering, Chungnam National University, Yusong, Taejon 305-764, Republic of Korea Received 16 October 2003; accepted 5 January 2004 Available online 7 February 2004 Abstract In this work, the pitch-based activated carbon fibers (ACFs) were prepared by nitric acid to investigate the multi-metal adsorption in interfacial and textural points of view. N 2 /77 K adsorption isotherm characteristics, including the specific surface area and micropore volume, were studied by BET specific surface area and t -plot methods, respectively. As a result, the specific surface area of the almost neutral ACFs in nature significantly decreased with nitric acid treatment, probably due to the widening of micropores. However the total acidity, including the carboxyl groups, on carbon surfaces was extremely induced during the acidic surface treatment. From the adsorptions of Cu 2+ and Ni 2+ , it was revealed that the adsorption capacity of metal ions was mainly influenced by the weakly acidic functional groups such as lactones on the carbon surfaces at pH < pI (isoelectric point), and by the strongly acidic functional groups such as carboxyl groups at pH > pI .  2004 Elsevier Inc. All rights reserved. Keywords: Activated carbons; Adsorption; Specific surface area; Nitric acid; Metal ions Porous carbon materials have been widely used in sepa- ration, purification, and catalytic processes due to their ex- tended specific surface area, high adsorption capacity, mi- croporous structure, and functional surface reactivity. The adsorption of activated carbon fibers (ACFs) depends on many kinds of factors, such as raw materials, activation process, nature of pore structure, and surface functionali- ties [1]. Different methods of activation on the same raw material can yield totally different carbon characteristics. Chemical activation is performed in only one step for carbonization and activation at low temperatures (e.g., 673–1073 K). Oth- erwise, physical activation involves the carbonization of a carbonaceous precursor followed by the gasification of the resulting char in the presence of suitable oxidizing gasify- ing agents such as CO 2 and steam at high temperatures (e.g., 1073–1373 K) [1]. The existence of surface functional groups on carbons, such as carboxyl, phenol, lactone, and acid anhydrides, has * Corresponding author. E-mail address: psjin@krict.re.kr (S.-J. Park). been postulated as constituting the source of surface acid- ity [2–5]. Its active sites can determine the functional group interaction of its surface with other heteroatoms. The main objectives of the present work were to study the effect of nitric acid treatment on multi-metal adsorption by basic ACFs in interfacial and textural points of view. In this work, the precursor pitch was prepared by the ref- ormation of petroleum naphtha cracker bottom (NCB) oil for 12 h at 633–663 K under nitrogen flow condition and then melt–spun through a nozzle (D = 0.3 mm, L = 0.5 mm) at 593 K. The as-spun fibers were stabilized in an air convec- tion oven at 553 K for 6 h. Thereafter, the anisotropic fibers were carbonized at 1273 K with a heating rate of 10 ◦ C/min and holding for 2 h under nitrogen flow. These carbonized carbon fibers were activated in a cylindrical quartz tube by the steam diluted with nitrogen at 1173 K for 45 min. At this time, the nitrogen flow rate was 1.6 l min −1 and the volume ratio of H 2 O/N 2 was 0.44. Nitric acid of 1 M at boiling temperature was used in the oxidation of functional groups without damage of the fiber surfaces. Nitric acid was slowly added through the funnel. The oxidation was carried out at the boiling temperature for 2 h. The chemically acidic-treated activated carbon fibers 0021-9797/$ – see front matter  2004 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2004.01.010