Article Characterization of Ag-exchanged clinoptilolite treated with a plasma jet at atmospheric pressure Sedef Dikmen* , Neslihan Şahin, Zafer Dikmen and Murat Tanışlı Eskişehir Technical University, Faculty of Science, Department of Physics, 26470 Eskisehir, Turkey Abstract This study reports on the effects of dielectric barrier discharge-like (DBD-like) plasma jet treatment at atmospheric pressure on Ag cation-exchanged clinoptilolite. In the plasma treatment process, argon plasma was applied to the surface of pellet samples prepared with Ag-clinoptilolite. After DBD-like plasma jet treatment for 30 and 60min, remarkable colour changes were observed in the pellet samples. These changes indicate that the DBD-like plasma jet application led to the successful reduction of Ag + to its metallic forms, which was further confirmed by the results of ultraviolet–visible diffuse reflectance spectroscopy. The structural, composition and morphological properties of the DBD-like plasma jet-treated samples were characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray analyses, and they were compared to the untreated Ag-clinoptilolite. The DBD-like plasma jet treatment caused no detectable structural changes in clinoptilolite within the analytical limitations of the methods used. The FTIR spectra show that the plasma treatment causes discharge-induced functional changes in the hydroxyl stretching region. The peaks appearing in the XRD patterns confirmed the reduction of Ag + to Ag 0 after expos- ure to the plasma. The present study indicates that the reduction of Ag + cations to their metallic forms can be performed successfully using the proposed method without collapsing the crystal structure of the Ag-clinoptilolite. Keywords: Ag-exchanged clinoptilolite, characterization, DBD-like plasma jet, FTIR, SEM, UV–Vis DRS, XRD (Received 7 March 2020; revised 5 October 2020; Accepted Manuscript online: 15 October 2020; Editor: George E. Christidis) Zeolites are important crystalline micro- and meso-porous mate- rials (Schwanke et al., 2017). They represent a group of naturally occurring hydrous aluminosilicate minerals with a cage-like crys- tal structure that can be synthesized in the laboratory (Altare et al., 2007). The structural properties of zeolites make them unique among inorganic materials. They have many applications in industry due to their high porosity, chemical stability, specific active sites, ion-exchange capacity and large specific surface area (Gottardi & Galli, 1985). Despite the abundance and low cost of natural zeolites, they have been less preferred than expensive synthetic zeolites because of their variable physical–chemical properties and impure mineralogical compositions. Because the cost of these synthetic porous materials is significant, research has focused on studies that deal with the modification of natural zeolites for various potential applications. Applications in cataly- sis and adsorption generally require an additional modification of the zeolite, such as dealumination or ion exchange (Tsitsishvili & Andronikashvili, 1992). Zeolites possess a net negative charge due to the isomorphic substitutions of Si 4+ by Al 3+ in the tetrahedral sites. This residual negative charge is balanced by the presence of exchangeable cations (Na + ,K + , Ca 2+ and Mg 2+ ) in the cages, which allows excellent performance in terms of thermal stability, acid resistance, etc., depending on the cationic composition (Tsitsishvili & Andronikashvili, 1992; Bertetti & Pabalan, 2001). Due to their variable physicochemical properties, zeolites have been exploited in large-scale industrial applications such as adsorption/separation, ion exchange, molecular sieving and catalysis (Gottardi & Galli, 1985). In addition to these conven- tional uses, which have a significant economic impact on various sectors of industry, there are specific uses of zeolites in new emer- ging applications, including luminescence, electricity, magnetism, microelectronics and biomedical processes. Recent studies have revealed that cation-exchange modification of natural zeolites with transition metals such as silver, zinc, copper, etc., also pro- vides interesting pharmaceutical properties (Hotta et al., 1998; Rivera-Garza, 2000; Top & Ulku, 2004; Akhigbe et al., 2014; Demirci et al., 2014; Milenkovic et al., 2017; Youssefa et al., 2019; Dutta & Wang, 2019; Hubner et al., 2020). The use of silver, which has antimicrobial properties in the form of AgNO 3 , dates back to ancient times. Today, the unique antibacterial activity of silver means that it is used in various applications, such as common consumer products and even in complicated medical devices. However, AgNO 3 is not suitable for direct usage. Recently, research has been carried out on sup- porting materials for silver ions, which, in turn, will form stable structures that are resistant to atmospheric oxidation and have long-lasting antibacterial properties. Zeolites have been consid- ered as potential candidates for delivering the properties above as cation carriers, and their porous structure allows for slow Ag release (Tosheva et al., 2017; Dutta & Wang, 2019). The *E-mail: sdikmen@eskisehir.edu.tr © The Author(s), 2020. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland Cite this article: Dikmen S, Şahin N, Dikmen Z, Tanışlı M (2020). Characterization of Ag-exchanged clinoptilolite treated with a plasma jet at atmospheric pressure. Clay Minerals 55, 238–247. https://doi.org/10.1180/clm.2020.33 Clay Minerals (2020), 55, 238–247 doi:10.1180/clm.2020.33