Contents lists available at ScienceDirect Materials Research Bulletin journal homepage: www.elsevier.com/locate/matresbu Crown-ether functionalized graphene oxide for metal ions sequestration S. Petrescu a , S. Avramescu b , A.M. Musuc a , F. Neatu c , M. Florea c , P. Ionita a,b, ⁎ a Institute of Physical Chemistry, 202 Spl. Independentei, Bucharest, Romania b Department of Organic Chemistry, Biochemistry and Catalysis, University of Bucharest, Panduri 90-92, Bucharest, Romania c National Institute of Materials Physics, 405A Atomistilor, Magurele, Romania ARTICLE INFO Keywords: Graphene oxide Crown-ether Organic functionalization Supramolecular ABSTRACT Graphene oxide has been synthesized, additionally derivatized with chloroacetic acid for increase the number of available carboxylic groups and further functionalized with crown-ether moieties. The thus obtained material was characterized by IR, thermal analysis, SEM, Raman, and XPS. Tests on adsorption of several metal cations showed that cooper and iron are more retained than potassium. 1. Introduction Carbon-based adsorbents are known from long time, the most used being activated carbon [1]. Recent novel allotropes of carbon, like graphene and graphene oxide (GO), have attracted huge attention due of their remarkable physical and chemical properties [2]. It is worth to remind that graphene oxide is a 2D material based on the hexagonal carbon network that contains functional groups holding oxygen atoms. Such groups, like carboxyl ones, are very important for various purposes and applications; besides, they allow covalent func- tionalization with other compounds of interest. In this way, GO has been functionalized with a plethora of organic compounds, including free radicals [3], ferrocene [4], porphyrins [5], and so on. The thus functionalized GO has not only mixed properties, but moreover, inter- esting and co-lucrative behavior emerges [6]. Although GO has been discovered long time ago [7,8], its out- standing properties were evidenced in the recent decade [9], and nowadays literature data contains a tremendous amount of information about its characteristics and conceivable high-tech applications [10,11]. GO is a very promising adsorbent material for wastewater treatment and water purification [12]. The carboxylic groups (usually negative charged) and the presence in the GO structure of conjugated CeC bonds allow a strong interaction with inorganic metal ions (charged posi- tively) and other organic pollutants (aromatics, dyes). On the other way, crown-ethers are well known cyclic polyethyleneglycols that have as well a strong interaction with cations; in addition, the host-guest interaction can be tailored by the size of the macrocyclic cavity [13,14]. Up to date, there are very few articles that deal with GO covalently functionalized with crown ethers, and none of them are employing such hybrid material in a study of metal cations adsorption; until now, for organic functionalization, the researchers took advantage of the epoxy groups contained by GO, and the materials thus obtained showed en- hanced electrochemical properties [15–17]. However, there is an in- creasing interest in graphene-embedded crown ethers as materials used as ion channels [18]. In this work, starting from plain graphite, we obtained GO that was subsequently functionalized with benzo-15-crown-5 ether moieties (denoted herein as GO-CE) and tested this new material as possible adsorbent for the cations of copper, iron, sodium and potassium. 2. Material and methods All chemicals were purchased from Sigma-Aldrich or Chimopar and used as received. As our previous experience [3] showed that powder synthetic graphite (size < 20 μm) has some advantages, therefore this was used as starting material in our work. All experiments were run at least in duplicate. Synthesis of GO was performed as described previously [3,19], with the amend that we used a longer oxidation reaction time (12 h) and the solid was separated first by decantation, followed by centrifugation and then washed extensively with diluted hydrochloric acid and finally with methanol. Derivatization with chloroacetic acid, for the synthesis of GO-COOH, followed a similar Zhang [20] procedure (1 g GO was sus- pended in water, to which 1 g NaOH was added under stirring, followed by 0.5 g chloroacetic acid; next day, the solution was acidulated with concentrated HCl, centrifugated, and the solid was washed with plenty of water, followed by methanol, and then dried). The synthesis of GO- https://doi.org/10.1016/j.materresbull.2019.110643 Received 17 July 2019; Received in revised form 14 September 2019; Accepted 23 September 2019 ⁎ Corresponding author at: Institute of Physical Chemistry, 202 Spl. Independentei, Bucharest, Romania. E-mail address: pionita@icf.ro (P. Ionita). Materials Research Bulletin 122 (2020) 110643 Available online 27 September 2019 0025-5408/ © 2019 Elsevier Ltd. All rights reserved. T