Removal of Pemetrexed from aqueous phase using activated carbons in static mode
Introduction
Water is not only an essential element for human beings but also an important factor in social and economic processes. However, water availability is threatened in recent years because of an increase in anthropogenic pollutants from the non–industrial and industrial sectors [1]. Approximately two million tons of wastewater is being discharged into freshwater every day [1]. In particular, conventional wastewater treatment plants (WWTPs) are not specifically designed to efficiently remove residual concentrations of bioactive compounds such as pharmaceutical ones [2]. As a consequence, a lot of these compounds are directly discharged into natural water contributing to new environmental issues. An effective process for removing these contaminants should be the addition of a tertiary treatment in WWTPs. Various technologies have been extensively developed and used in this context, such as precipitation, oxidation, membrane filtration, reverse osmosis, evaporation, ion exchange and adsorption [3], [4]. Among these different potential treatments, adsorption represents a promising and effective method, owing to its numerous advantages such as ease of implementation, relatively low cost, no addition and use of chemical products, and no generation of harmful by–products [5].
Activated carbon (AC) is a typical adsorbent obtained by carbonization of practically any carbonaceous material. The use of cheap and renewable raw materials (e.g. wood) as precursors not only reduces the production cost of AC but also limits the problems of environmental pollution caused since these raw materials are usually waste ones. Besides the carbonization process, an activation step involving chemical and/or physical methods, is required to further generate a structure with abundant pores. On the other hand, the gasification process using steam is an effective procedure for producing high surface area AC due to the favorable effect of the diffusion of smaller water molecules within the porous structure of the precursor [6]. Additionally, a previous study has shown that activated carbons with high apparent pore volume and surface areas were obtained by treating the endocarp of babassu coconut with phosphoric acid during the chemical activation procedure [7]. AC is used to eliminate contaminants from water relies mainly on its high specific surface area, well–developed pore structure, large pore volume as well as surface properties [8], [9]. For example, Baccar et al. used a homemade AC activated by phosphoric acid for the elimination of pharmaceutical compounds at a laboratory scale [10]. The adsorption capacities based on the Langmuir model were 56, 11, 25 and 40 mg.g−1 for diclofenac, ibuprofen, ketoprofen and naproxen, respectively, under the conditions of original solution pH 4 at 25 °C for 26 h. The adsorption characteristics of trimethoprim from aqueous solution onto a powdered AC from wood were investigated by Kim et al [11]. The experimental data is in good agreement with the Langmuir model; the maximum adsorption capacity calculated from the model was 258 mg.g−1 for AC. Kleywegt et al. reported that the use of granulated AC could increase the removal efficiency of carbamazepine from 71 to 93% for water treatment in Ontario, Canada [12].
Pemetrexed (PEME) is a novel generation of anti–folate pharmaceutical showing encouraging activity in the treatment of a variety of tumors, e.g., malignant mesothelioma, non–small cell lung cancer, breast cancer, bladder cancer, colorectal carcinoma and cervical cancer [13]. Consequently, PEME consumption increases year by year, especially in European countries and it is worth noting that PEME environmental concentrations in France for years 2004 and 2008 were reported to be 0.02 and 0.85 ng.L−1, respectively [14]. Additionally, it is estimated that ca. 78% of residual PEME is continuously released into the surface water from WWTPs due to its own characteristics (water–soluble, non–volatile and weakly metabolized) [15]. At the same time, its intended function may cause potential risks, including genotoxic, mutagenic, cytotoxic effects to aquatic organisms, which represents a new challenge to be solved [15].
To the best of our knowledge, there is currently no systematic study on the removal of PEME from water by any type of adsorbent. Considering the potential advantages of AC, it can be selected as a sorbent material to remove PEME. In this study, the adsorption behavior of PEME in water by different types of ACs was investigated. The main purposes of this article were to explore the effects of different factors such as the adsorbent dose, contact time, pollutant concentration, temperature and pH conditions on the adsorption of PEME to determine the best materials and experimental conditions for removing PEME from water. In addition, the adsorption mechanisms were researched using the Conductor–like Screening Model (COSMO) methodology in a computational procedure to determine the proton donor–acceptor centres and the polarized charge distribution in PEME. Finally, Raman spectrometry was carried out to assess the π–π interactions between PEME and ACs.
Section snippets
Materials
Pemetrexed disodium heptahydrate (CAS No. 357166–29–1) was purchased from Sigma–Aldrich. The physicochemical properties of PEME are listed in Table S1. Deionized water was prepared from a Millipore Milli–Q system (18.2 MΩ cm). High–performance liquid chromatography (HPLC) grade methanol was supplied by Carlo Erba Reagents. Other chemical reagents used in the work were of analytical grade.
Three commercial ACs powders produced from wood and activated either by steam (AC1) or H3PO4 (AC2, AC3) were
Characterizations of ACs
The International Union of Pure and Applied Chemistry (IUPAC) classifies porous substances into three categories depending upon their pore diameters: < 2 nm is micropore, 2–50 nm is mesopore, greater than 50 nm is macropore [25]. The N2 adsorption–desorption isotherms of ACs (Fig. S1) exhibited a type I isotherm with a slight hysteresis loop for AC1, and a IV type isotherm with H4–shaped hysteresis loop for AC2, as well as a type IV isotherm with H3 hysteresis loop for AC3 according to the
Conclusions
This is the first systematic study on the removal of PEME from water by adsorption. For this purpose, three ACs obtained from wood and activated either by steam (AC1) or phosphoric acid (AC2 and AC3) were characterized. In addition, the adsorption mechanism of PEME with the materials tested was tentatively explained. The results showed that experimental data obtained with AC1 and AC3 were better described by the Freundlich and Langmuir models, respectively, whereas both Freundlich and Langmuir
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Authors gratefully acknowledge the contribution of the China Scholarship Council in supporting a doctoral thesis study for Bomin FU. The authors are also very grateful to Université Claude Bernard Lyon 1, Centre National de la Recherche Scientifique, Institut de Recherches sur la Catalyse et l’Environnement de Lyon (IRCELYON) for their financial support. In particular, the authors would like to thank the IRCELYON for its technical services such as Raman, physical and chemical analysis on this
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