Spectrochimica Acta Part A 82 (2011) 389–395 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy j ourna l ho me page: www.elsevier.com/locate/saa Comparison of structural, textural and thermal characteristics of pure and acid treated bentonites from Aleksinac and Petrovac (Serbia) Zorica P. Tomi ´ c a , Vesna P. Logar b , Biljana M. Babic c , Jelena R. Rogan d , Petre Makreski e,∗ a Faculty of Agriculture, Institute of Soil and Melioration, Belgrade University, 11080 Belgrade, Serbia b Faculty of Mining and Geology, Belgrade University, 11000 Belgrade, Serbia c Vinca Institute of Nuclear Sciences, P.O. Box 522, 11000 Belgrade, Serbia d Department of General and Inorganic Chemistry, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia e Institute of Chemistry, Faculty of Science, SS. Cyril and Methodius University, Arhimedova 5, 1000 Skopje, Macedonia a r t i c l e i n f o Article history: Received 8 June 2011 Received in revised form 15 July 2011 Accepted 19 July 2011 Keywords: Bentonite Acid activation Smectite Cation exchange capacity Specific surface area a b s t r a c t Bentonite samples collected from vicinity of Petrovac and Aleksinac were treated with different sulfuric acid molarities. Acid attack dissolved the octahedral sheets by interlayer and edge attack. The effects of the H 2 SO 4 acid caused an exchange of Al 3+ , Fe 3+ and Mg 2+ with H + ions leading to a modification of the smectite crystalline structure. The Mg and Fe substitution in the octahedral sheets promoted the dispersion of corresponding layers and formation of amorphous silicon. The activated bentonites, after the treatment of sulfuric acid, exhibited a lower cation-exchange capacity (CEC) and significant increase of specific surface area from 6 to 387 m 2 g -1 (bentonite from Petrovac) and from 11 to 306 m 2 g -1 (bentonite from Aleksinac). The acid reaction caused a splitting of particles within the octahedral sheet which led to an increase in specific surface area and decrease in CEC in both bentonites. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Due to unique characteristics and wide range of application, clay minerals are considered to be one of the most promising future materials. The variable chemical composition influencing the layer charge, the cation-exchange capacity (CEC), the specific surface area (S BET ) and pore volume (V) are some of the charac- teristics that, promote clay minerals to have broad application in many industries. In the chemical industry they are used for deter- gents, as catalysts [1–3], for catalytic support [4–6], and also in beverage technology [7]. Their big role in the future is reflected in environmental protection, water purification and in the sci- ence of the nanocomposites. Bentonites are used either in their natural form or after modification (acids, alkali or organic). Acid modified natural bentonites are the subject of several studies [8–11]. Furthermore, acid bentonite activation is a useful method for altering the catalytic behavior of clay minerals and adsorp- tion features [12,13]. Hydrochloric acid is most commonly used for studying bentonite structure modification [13–16]. To the best of our knowledge, there is a very short list on researchers that have used sulfuric acid for modifying the smectite structure [12,17–19]. ∗ Corresponding author. Tel.: +389 23249 902; fax: +389 23226 865. E-mail address: petremak@iunona.pmf.ukim.edu.mk (P. Makreski). The first step in modifying the clay mineral structure with acid is separation of exchangeable cations from protons. The second step includes flushing of Al, Mg and Fe from octahedral and tetrahedral sheets. Afterwards, at lower acid concentration, the SiO 4 groups of tetrahedral sheets remain mostly intact and acid corrodes the octahedral sheets (at higher acid concentration, tetrahedral sheets are also affected). However, this procedure poses a dilemma for many authors regarding its completeness. A combination of several methods is imperative for monitoring the structural and textural changes of all phases in the studied material. An increase of the specific surface area and pore volume represent physical changes [7,20–22,6,23] important to monitor the structural properties, i.e. dissolving of octahedral sheets [24]. The focus of this work is structural modification of bentonites that will retain their layered structure, develop a large specific sur- face area and preserve the ability of CEC by sulfuric acid treatment. 2. Experimental 2.1. Materials and methods Natural bentonites from Petrovac and Aleksinac (Serbia) were treated with different sulfuric acid molarities (98%, Zorka ˇ Sabac). Bentonite particles below 2 m were separated by decantation. Typically, 10 g of bentonite were dispersed in 1 L of distilled water and left to precipitate for 24 h. A fraction was separated, which 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.07.068