Bentonites are commonly used in scientific investigations and industrial applications due to their superior properties. As they have high cation exchange capacity (CEC), they are widely used as an adsorbent in pollution control. Although their cation adsorption capability is greater, their organic and anionic material adsorption ability is very limited or non-existent. Fortunately, this limitation can be eliminated by intercalation of organic or/and inorganic cations into their structure. Changes due to modification should be identified by characterization techniques in order to figure out realized structural changes. In this study, it is aimed to use X-ray powder diffraction (XRD) technique in order to clarify the expanding behavior and thermal stability of HDPy modified organo-bentonite. For this purpose, organo-bentonite (OBent) was synthesized by intercalation of organic surfactant, hexadecylpyridinium cation (HDPy), into purified bentonite (PBent). Products were characterized by X-ray powder diffraction (XRD) using CuK alpha radiation under various conditions: solvation with water and ethylene glycol (EG) and heat treatments at 100 degrees C, 350 degrees C and 550 degrees C. Existence of mixed-layer clay formation was investigated and PBent and OBent XRD patterns were simulated by NEWMOD software. The PBent sample contains small amounts of mixed layer illite/smectite. Results of XRD analysis supports the notion that HDPy+ is intercalated within interlayer and basal spacing increases from 12.29 to 18.84 angstrom. Degradation of the organic cation is observed, however some residues from intercalate still appears to remain in the structure upon heating up to 550 degrees C. The persistence of these intercalates in OBent over a wide range of temperature holds promise for their use in environmental remediation studies and gaining a better understanding of the mechanisms of interaction with pollutants. Furthermore, this study presents a new perspective in examining the expanding behavior and thermal stability of organo-bentonites and investigating the existence of mixed-layer clay in organo-bentonites by using X-ray powder diffraction (XRD) technique with different treatments. (C) 2016 Elsevier B.V. All rights reserved.