Surface modifications of activated carbon by gamma irradiation Inmaculada Velo-Gala, Jesu ´s J. Lo ´ pez-Pen ˜ alver, Manuel Sa ´ nchez-Polo * , Jose ´ Rivera-Utrilla Department of Inorganic Chemistry, Faculty of Science, University of Granada, 18071 Granada, Spain ARTICLE INFO Article history: Received 2 July 2013 Accepted 29 September 2013 Available online 7 October 2013 ABSTRACT Four commercial activated carbons with different chemical and textural characteristics were modified by gamma irradiation under five different conditions: irradiated in absence of water, in presence of ultrapure water, in ultrapure water at pH = 1.0 and 1000 mg L 1 Cl  , in ultrapure water at pH = 7.5 and 1000 mg L 1 Br  , and in ultrapure water at pH = 12.5 and 1000 mg L 1 NO 3  . Changes in surface chemistry were studied by X-ray photoelectron spec- troscopy; pH of point of zero charge, total acidic groups and total basic groups, which were determined by assessment with HCl and NaOH; and textural changes were determined by obtaining the corresponding adsorption isotherms of N 2 and CO 2 . Outcomes show that the activated carbon surface chemistry can be modified by gamma irradiation and that the changes depend on the irradiation conditions. Modifications in the sp 2 hybridization of the surface carbons suggest that the irradiated carbons undergo graphitization. Measure- ments of structural parameters indicate that the irradiation treatment does not modify the textural properties of the carbons. Finally, studies of pristine and irradiated activated carbons using diffuse reflectance spectroscopy with the Kubelka–Munk function revealed a reduction in band gap energy in the irradiated carbons associated with an increase in sp 2 hybridization of the carbon atoms. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Activated carbons (ACs) are employed as adsorbents, cata- lysts, and catalyst supports, among others, and are used to obtain new materials and for energy storage devices [1–6]. All of these varied applications take advantage of their extraordinary textural, and chemical properties (surface area, porous texture, and, surface chemistry), which largely depend on the hetero-atoms on their surface. Various researchers have investigated techniques for modifying the surface chem- istry of ACs in order to improve their performance and/or ex- pand their applications [7–10]. Among the hetero-atoms on the surface of ACs, we focus here on oxygen, because the presence of oxygenated groups determines their pH of point of zero charge (pH PZC ), their character as electron acceptor/donor, and their hydrophobic- ity, among other properties. They are also able to anchor func- tional molecules that can act as ligands or can incorporate other materials, such as oxides and nanoparticles. Various methods have been proposed to modify the oxygen content of ACs and the nature and concentration of their surface groups (Fig. 1) [10,11]. Gaseous or aqueous oxidation [10–14] is widely used to modify activated carbon (AC) surface chemistry, but it also 0008-6223/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.carbon.2013.09.087 * Corresponding author: Fax: +34 958243856. E-mail address: mansanch@ugr.es (M. Sa ´ nchez-Polo). Abbreviations: AC, activated carbon; ACs, activated carbons; C, Ceca activated carbon; D, absorbed dose; DRS, Diffuse Reflectance Spectra; Eg, band gap energy; M, Merck activated carbon; S, Sorbo activated carbon; SBW, spectral bandwidth; STP, standard temperature and pressure; W, Witco activated carbon; XPS, X-ray photoelectron spectroscopy CARBON 67 (2014) 236 – 249 Available at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/carbon