Inﬂuence of Thermal, Hydrothermal, and Acid–Base Treatments on Structural Stability and Surface Properties of Macro-, Meso-, and Microporous Carbons D. B. Akolekar and S. K. Bhargava 1 Department of Applied Chemistry, RMIT, GPO Box 2476V, Melbourne, Victoria 3001, Australia Received January 19, 1999; accepted April 27, 1999 Effects of thermal treatment (at 723 K), hydrothermal treat- ment [low-pressure steam vapor (34 Torr) at 723 and 923 K and water (at autogenous pressure) at 398 and 473 K], and acid–base treatment (at 473 K) on the structural stability and physical properties of porous carbon samples prepared from both natural and synthetic sources have been studied. These thermally, hydrothermally, and acid–base-treated car- bons have been characterized using BET, thermogravimetric, and infrared techniques. Investigations of the treated carbon samples revealed that the thermal stability, pore structure, pore size distribution, and surface area are strongly affected by the thermal, hydrothermal, and acid–base treatments. The method of sample treatment inﬂuences the order of thermal stability and porosity and surface area (differences in sur- face area were attributed to differences in porosity, based on micropore and total pore volume). FTIR studies show that the carbon structures are signiﬁcantly inﬂuenced by the hy- drothermal and acid–base treatments. The surface and pore structure modiﬁcations of the microporous carbon have also been studied by controlled air decomposition and high temper- ature aliphatic and aromatic organic vapor deposition. © 1999 Academic Press Key Words: macro-, meso-, and microporous carbons; surface area; pore size distribution; controlled decomposition; FTIR; ther- mal, hydrothermal, acid–base treatment; TGA; BET. INTRODUCTION In many adsorption–separation processes, with both lab- oratory and industrial scale applications, activated car- bons are widely used as adsorbents for the removal of organicsgas puriﬁcations and as a support material in various catalytic processes (1–5). The macro-, meso-, and microporous carbons are of considerable interest as adsor- bents for the removal of bulkier organics from various industrial processes (6 – 8). The activated carbons are of great research interest because of their high surface area, chemical inertness, and ability to endure harsh chemical environments. In our earlier studies (9), the preparation and charac- terization of heat-treated carbons obtained from natural and synthetic (artiﬁcial) sources and the ability of these carbons to remove Bayer active organic compounds from simple aqueous systems were investigated. In various ad- sorption processes, the functioning of an activated carbon material is strongly dependent on the factors such as sur- face area, macro-, meso-, and mircopore size/volume, pore size distribution, and structure. Thus, from the point of view of activated carbon application as an adsorbent and/or cat- alyst support, knowledge of the inﬂuence of various ther- mal, hydrothermal, and acid– base treatment on its surface and structural stability is of great interest. In the present study, the inﬂuence of thermal, hydrothermal, and acid– base treatments on the thermal stability, surface area, pore size distribution, and structure of activated carbons are investigated. Effects of the controlled decomposition and high temperature organic vapors on the surface area and pore size distribution of the microporous carbon have also been studied. EXPERIMENTAL Preparation of Carbon Samples Heat-treated carbons were prepared from pure (100%) mus- tard oil (C1), almond oil (C2), and olive oil (C3). In each case, the heat-treated carbon sample was prepared by controlled burning of the source at 900 –1123 K for 5– 6 h. The carbon sample C4 was obtained commercially. The procedures used for the thermal, hydrothermal, and acid– base treatment of carbon samples are as follows. Thermal Treatment Microporous carbon (C4) (4 g) was calcined at 723 K for 7 h (in the presence helium) in a stainless steel tube reactor fur- nace. 1 To whom correspondence should be addressed. E-mail: rcmsb@rmit.edu.au. Journal of Colloid and Interface Science 216, 309 –319 (1999) Article ID jcis.1999.6306, available online at http://www.idealibrary.com on 309 0021-9797/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.