Experimental and DFT studies of the removal of pharmaceutical metronidazole from water using polypyrrole

International Journal of Industrial Chemistry (2019) 10:269–279 https://doi.org/10.1007/s40090-019-0190-7 RESEARCH Experimental and DFT studies of the removal of pharmaceutical metronidazole from water using polypyrrole Nouh Aarab1 · Mohamed Laabd1 · Habiba Eljazouli1 · Rajae Lakhmiri2 · Hassan Kabli1 · Abdallah Albourine1 Received: 8 July 2018 / Accepted: 20 June 2019 / Published online: 29 June 2019 © The Author(s) 2019 Abstract The polypyrrole (PPy) was used as an adsorbent material for efficient removal of pharmaceutical metronidazole from aqueous solutions. The physiochemical parameters influencing the adsorption process such as adsorbent dose, temperature, pH, initial concentration and contact time were systematically investigated. The optimum adsorption efficiency is achieved at pH 6.17 after 120 min of contact time. In addition, the Langmuir isotherm and pseudo-second-order models were found to explain the metronidazole adsorption process on the PPy. The thermodynamic parameters indicate that the adsorption of metronidazole on the PPy is a spontaneous and exothermic process. The quantum calculations using density functional theory (DFT) was used to confirm the adsorption mechanism of metronidazole on the PPy. The obtained results of the interaction energy indicate that the adsorption was a physical process. The metronidazole was adsorbed by its oxygen atoms on the amine groups of PPy. Finally, the PPy polymer can be used as an efficient adsorbent for removal of pharmaceutical pollutants from wastewater. Keywords Adsorption · Density functional theory · Pharmaceutical metronidazole · Polypyrrole · Wastewater Introduction Pharmaceutical compounds are part of the so-called emerging contaminations because of their recent interest in environmental studies. The emerging contaminants are well known as toxic and biorefractory compounds, including pharmaceuticals, pesticides, personal care products, endocrine-disrupting chemicals, and other recalcitrant organic substances [1–3]. The pharmaceutical compounds include diverse groups, such as antibiotics, hormones and anticancer agents [4, 5]. The hospitals, households and drug industries are the major sources of pharmaceutical contaminants in aquatic systems [6]. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s40090-019-0190-7) contains supplementary material, which is available to authorized users. * Abdallah Albourine 1 Laboratory of Materials and Environment, Faculty of Sciences, Ibn Zohr University, Agadir, Morocco 2 Laboratory of Materials and Valorization of the Resources, Faculty of Sciences and Techniques, Abdelmalek Essaâdi University, Tangier, Morocco The metronidazole is an antiparasitic agent used for the treatment of Giardia lamblia, Trichomonas vaginalis and Helicobacter pylori infections [7, 8]. In addition, this pharmaceutical byproduct is a carcinogenic and mutagenic compound [9]. The genotoxic activity evaluation indicates that the metronidazole can induce DNA damage in human lymphocytes as well as freshwater and marine organisms [10, 11]. Therefore, its presence in water can cause harmful effects for living organisms and human health [12]. Furthermore, the metronidazole can be accumulated in the aquatic environment because of its non-biodegradability and high solubility in water [13]. For these reasons, the removal of this pollutant from wastewater is a major environmental challenge. In this context, several decontamination methods have been developed to remove emerging contaminants from water including adsorption [14, 15], heterogeneous catalytic ozonation [16] and flocculation [17]. Among these separation technologies, the adsorption is one of the most promising techniques for removal of the pharmaceuticals from aquatic ecosystems [18]. In this regard, the use of effective adsorbent materials is necessary. Various materials such as clays [19], agricultural waste [20] and organic polymers [21, 22] were used as adsorbents for wastewater treatment. 13 Vol.:(0123456789) 270 International Journal of Industrial Chemistry (2019) 10:269–279 Recently, the organic polymers (e.g., polypyrrole, polyaniline and polythiophene) were attracted considerable attention in various research fields such as gas sensors, solar cells, corrosion protection, and wastewater decontamination. [23–25]. The PPy is one of the most promising organic polymers because of its specific properties like chemical stability, biodegradability, non-toxicity, conductivity and ease of synthesis [26, 27]. The use of PPy as a novel alternative adsorbent material for removal of contaminants from water is mainly related to its large amounts of amino groups and redox reversibility [28]. The present study aims to investigate the adsorption of pharmaceutical metronidazole on the polypyrrole (PPy). The PPy was synthesized via chemical oxidative polymerization of pyrrole monomer in aqueous solution. The textural and structural properties of synthesized PPy were characterized using scanning electron microscopy (SEM) and infrared spectroscopy (IR). To find the optimum adsorption conditions, the effects of physiochemical parameters such as pH, adsorbent dose, contact time, initial concentration of metronidazole and temperature were systematically investigated. The kinetics, isotherms and thermodynamics of the metronidazole adsorption process were also studied. In addition, it was necessary to investigate the adsorption mechanism of the metronidazole on the PPy. The density functional theory (DFT) was recently used to identify the adsorption mechanism of contaminants on the conducting polymers in aqueous and gas phases [25, 29–31]. In this way, we examined the geometrical and electronic structures of PPy before and after adsorption of metronidazole using DFT to understand the mechanism involved in the adsorption process. Materials and methods Reagents The pyrrole monomer [98% pyrrole (Aldrich)] is distilled prior to polymerization. The ferric chloride [FeCl3· 6H2O (Aldrich)] with strength of 0.2 M was used as an oxidant agent. The metronidazole was purchased from Sigma-Aldrich as an analytical grade reagent and used as received without further purification. The stock solution of metronidazole is obtained by dissolving 200 mg of metronidazole in 1 L of distilled water. The solutions used in the experiments were obtained by dilutions to the desired concentrations. Fig. 1  Simplified polymerization reaction of pyrrole The oxidative polymerization of pyrrole using ferric chloride was carried out according to the reaction illustrated in Fig. 1. A typical synthesis procedure can be described briefly as follows: 775 µl of pyrrole was mixed with 37.5 ml of distilled water. Then, 12.5 ml of aqueous solution containing 0.2 M of FeCl3, 6H2O was gradually added to start the polymerization reaction [32]. The mixture was stirred for 2 h at room temperature. The resulting PPy was filtered on a filter paper an (...truncated)