The surface characteristics of activated carbon as affected by ozone and alkaline treatment Hung-Lung Chiang a , C.P. Huang b, * , P.C. Chiang c a Department of Environmental Engineering, Fooyin Institute of Technology, Kaohsiung Hsien, 831, Taiwan, ROC b Department of Civil and Environmental Engineering, University of Delaware, Newark, DE 19716, USA c Graduate Institute of Environmental Engineering, National Taiwan University, Taipei, Taiwan, ROC Received 17 April 2000; received in revised form 6 July 2001; accepted 13 August 2001 Abstract The surface chemical characteristics of activated carbon treated by ozone and alkaline are determined in terms of surface functional groups and surface acidity. Surface functional groups are analyzed by the IR spectroscopic method and Boehm’s titration technique. The surface acidity of activated carbon is determined by electrophoretic mobility measurements. The oxygen concentration of activated carbon increases upon ozone and NaOH treatment. Surface functional groups increase mostly in the hydroxyl and carboxyl categories rather than the carbonyl category upon ozone and NaOH treatment. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Activated carbon; Ozone; Alkaline; Oxygen concentration; Surface functional groups 1. Introduction Activated carbon can be produced from a great va- rietyofcarbonaceousmaterialsincludingcoconutshells, sawdust, wood char, coal, petroleum coke, bone char, molasses, peat and paper-mill waste (lignin) (Mattson and Mark, 1971; Hassler, 1974; Bansal et al., 1990). Depending on the extent of oxidation reaction, two typesofactivatedcarboncanbeproduced(Mattsonand Mark, 1971; Hassler, 1974; Corapcioglu and Huang, 1987; Bansal et al., 1990): H-type and L-type. H-type activated carbons exhibit positive charge in water, ad- sorb strong acid and are hydrophobic. L-type activated carbons display negative charge in water, neutralize strong bases and are hydrophilic. Much has been re- ported on the oxidation of activated carbon. Steebberg (1944) characterized the activation and oxidation of carbon at various temperatures and classified those carbons that were oxidized at low-temperature and ad- sorbed primarily hydroxide ion as L-carbons, and those activatedathightemperaturesandadsorbedstrongacid as H-carbons. The L-carbon behavior is expected to intensify after long exposure to the atmosphere even at ambient temperatures. Cookson (1978) and Huang (1978) reported the adsorption of electrolytes and non- electrolytesanditseffectonthestructureoftheelectrical doublelayerandtheroleofsurfacefunctionalgroupon the nature of adsorption. Bailey (1982) proposed two mechanistic extremes for the oxidation of carbon by ozone: a radical type, ozone-initiated autoxidation, and a concerted reaction, i.e., l, 3-dipolat insertion. Schubert and Pease (1956a) reported that in the high temperature range, molecular oxygen participates in the reaction as the temperature increases up to 270 °C. The reaction then becomes a slow combustion process that is indistinguishable from thereactionwithoxygenalone.Atlowtemperature,the mechanism of vapor-phase reaction is similar to that of liquid-phase ozonation, at least when only molecular Chemosphere 47 (2002) 257–265 www.elsevier.com/locate/chemosphere * Corresponding author. Tel.: +1-302-831-8428; fax: +1-302- 831-3640. E-mail address: huang@mail.ce.udel.edu (C.P. Huang). 0045-6535/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0045-6535(01)00215-6