Effect of electrochemical treatments on the surface chemistry of activated carbon R. Berenguer a , J.P. Marco-Lozar b , C. Quijada c , D. Cazorla-Amoro ´s b , E. Morallo ´n a, * a Departamento de Quı ´mica Fı ´sica e Instituto Universitario de Materiales, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain b Departamento de Quı ´mica Inorga ´nica, Universidad de Alicante, Apartado 99, E-03080 Alicante, Spain c Departamento de Ingenierı ´a Textil y Papelera, Universidad Polite ´cnica de Valencia, Paseo Viaducto, 1, E-03801 Alcoy, Alicante, Spain ARTICLE INFO Article history: Received 10 June 2008 Accepted 4 December 2008 Available online 16 December 2008 ABSTRACT The effect of the electrochemical treatment (galvanostatic electrolysis in a filter-press elec- trochemical cell) on the surface chemistry and porous structure of a granular activated car- bon (GAC) has been analyzed by means of temperature-programmed desorption and N 2 (at 77 K) and CO 2 (at 273 K) adsorption isotherms. The anodic and cathodic treatments, the applied current (between 0.2 and 2.0 A) and the type of electrolyte (NaOH, H 2 SO 4 and NaCl) have been studied as electrochemical variables. Both anodic and cathodic treatments lead to an increase in the surface oxygen groups. A suitable choice of the electrochemical vari- ables allows a selective modification of the amount and the nature of the surface oxygen groups of the GAC. In general, the electrochemical treatment does not modify significantly the textural properties of the GAC. However, an increase in the porosity of the activated car- bon occurs during the cathodic treatment in oxygen-saturated solutions. This result is interpreted as a consequence of carbon gasification driven by reaction with peroxide spe- cies generated by electroreduction of oxygen. The anodic treatment in NaCl produces oxi- dation degrees comparable to those achieved by classical chemical oxidations. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction The relevance of surface chemistry in the performance of activated carbons (ACs) is known for more than 20 years and a very intense research on the modification and charac- terization of the surface chemistry of carbon materials can be found [1–5]. Since an appropriate modification of the sur- face chemistry can be useful to improve the efficiency of the carbon material, different methods are usually applied to modify the concentration and nature of surface functional groups. The methods widely used are, essentially, chemical reactions in either gas or liquid phase with an appropriate oxidizing or reducing agent and further heat treatments in an inert atmosphere. However, the electrochemical methods are not so often applied to modify the surface chemistry of carbon materials [6–14] and few studies focus on activated carbons [12–14]. Electrochemical methods present several advantages [15]: (i) one of the reagents is the electron, which can be easily sup- plied by a direct current (DC) source and do not need any transport or handling; (ii) they can be applied in situ; (iii) the treatment can be immediately interrupted and can be run at room temperature and atmospheric pressure; (iv) the reaction conditions can be very precisely reproduced; and (v) oxidation and reduction processes are more selective and easily controlled by means of the electrode potential. Concerning the work done on electrochemical modifica- tion of AC, Barton et al. [12] estimated the anodic oxidation degree of a granular activated carbon (GAC) in a 0.5 M K 2 SO 4 solution at two constant currents and during different periods 0008-6223/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbon.2008.12.022 * Corresponding author: Fax: +34 965903537. E-mail address: morallon@ua.es (E. Morallo ´ n). CARBON 47 (2009) 1018 – 1027 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/carbon