Spectrochimica Acta Part A 75 (2010) 1304–1307 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa Adsorption of isoniazid onto sepiolite–palygorskite group of clays: An IR study Sevim Akyuz a,∗ , Tanil Akyuz a , Elif Akalin b a Istanbul Kultur University, Science and Letters Faculty, Department of Physics, Atakoy Campus, 34156 Istanbul, Turkey b Istanbul University, Science Faculty, Department of Physics, Vezneciler, 34134 Istanbul, Turkey article info Article history: Received 19 November 2009 Accepted 31 December 2009 Keywords: Adsorption Clays IR spectroscopy Isoniazid Loughlinite Palygorskite Sepiolite abstract The adsorption of isoniazid (INH) on sepiolite, loughlinite (natural Na-sepiolite) and palygorskite from Anatolia was investigated by FT-IR spectroscopy. Experimental results indicated that INH molecules, adsorbed on sepiolite–palygorskite group of clays, are coordinated to surface hydroxyls by H-bonding interaction through the pyridine ring nitrogen lone pairs. Moreover, some of the adsorbed INH molecules may enter the interior channels of the sepiolite–palygorskite structure and involve H-bonding interaction with zeolitic water. Some intensity and frequency changes in the OH stretching band of surface hydroxyls (Si–OH) of the INH-treated sepiolite and loughlinite were observed. However, this band is found to be less affected by the adsorption of isoniazid in the case of palygorskite, probably because the surface Si–OH groups in palygorskite appear to be less abundant than in sepiolite or loughlinite. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Isoniazid (C 6 H 7 N 3 O, abbreviated as INH) is an important drug for the chemotherapy of tuberculosis. It also seems to be effective in the treatment of extrapulmonary illnesses such as meningitis and genito-urinary infections [1,2]. Sepiolite, loughlinite, and palygorskite form an important group of the (palygorskite–sepiolite) phyllosilicate class of clay minerals which has many industrial, catalytic and environ- mental applications [3–6]. Loughlinite is known as natural Na-sepiolite and is virtually identical in appearance to sepiolite, both in a hand specimen and microscopically [5,7]. However, field observations and mineralogical determinations indicate that loughlinite and sepiolite are formed authigenically and indepen- dently in different physicochemical environments rather than being the product of a transformation of one to the other [7]. The chemical formulas of loughlinite, sepiolite, and paly- gorskite are Na 2 Mg 3 Si 6 O 16 ·8H 2 O, Mg 4 Si 6 O 15 (OH) 2 ·6H 2 O, and (Mg,Al) 5 (Si,Al) 8 O 20 (OH) 2 ·8H 2 O, respectively [4–6]. Structurally, they consist of blocks and channels extending in the c-axis direction [8]. The width of the channels is different in sepiolite and paly- gorskite [8,9]. It is known that surface silanol (Si–OH) groups play an important role in the selective sorption on the external surfaces of the sepiolite group of clays [8]. ∗ Corresponding author. Tel.: +90 2124984401; fax: +90 2124658310. E-mail address: s.akyuz@iku.edu.tr (S. Akyuz). In our previous work we reported the spectroscopic results of the adsorption of isoniazid on natural montmorillonite and saponite [10]. As a continuation of our studies on clay–drug inter- actions, in this study the adsorption of isoniazid on sepiolite, loughlinite and palygorskite from Anatolia were investigated by FT-IR spectroscopy. 2. Experimental In the present work, natural sepiolite, loughlinite, and paly- gorskite samples from the Mihalliccik-Eskisehir region of Anatolia (Turkey) were employed. The clays were ground to a fine powder of <0.5 m particle size, and then were analyzed for purity by X-ray diffraction, differential thermal, and IR spectroscopic techniques. The results indicate that loughlinite is associated with analcime (approx. 8%) and Al 2 O 3 (approx. 6%), and has a detectable calcite impurity (IR; 1435 cm -1 ). The chemical compositions of starting clays were given in a previous paper [11]. Solid INH was reagent grade (Sigma) and was used as received. INH-treated clays were prepared by methods analogous to those given in literature [10] or by solid–solid reactions [12,13]. Solid–solid reactions are known as useful ways to introduce organic guest species into the interlayer species of clays [12,13]. The products were washed with solution to remove excess organic molecules and then dried. The FT-IR spectra of KBr discs of sam- ples were recorded on a Jasco 300E FT-IR spectrometer (2 cm -1 resolution) based on averaging 200 sample and 40 background scans. Spectral manipulations such as baseline adjustment, band fitting, and obtaining the second derivative were performed using 1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.12.069