J Incl Phenom Macrocycl Chem (2016) 85:49–58 DOI 10.1007/s10847-016-0604-5 ORIGINAL ARTICLE Synthesis and characterization of novel nanofiber based calixarene and its binding efficiency towards chromium and uranium ions 1,2 3 1 Fatih O¨ zcan • Mevlu¨t Bayrakcı • S¸ eref Ertul Received: 19 January 2016 / Accepted: 11 March 2016 / Published online: 18 March 2016 Ó Springer Science+Business Media Dordrecht 2016 Abstract The objective of this study is to obtain Introduction nanofibrous precursor based calixarene with high ion adsorption capacity by electrospinning of blended solution Nanotechnology has gained interest in recent years from of polyacrylonitrile (PAN) and upper rim functionalized both public and private sector organizations. Therefore, calix[4]arene bearing N-methylglucamine (Calix-NMG). nanotechnology has offered several novel products, which The obtained electrospun fibers were characterized using have superior properties making them valuable for a wide fourier transform infrared (FT-IR-ATR), scanning electron range of applications. One of the major successes of nan- microscope (SEM) equipped with energy-dispersive X-ray otechnology has been nanofibers. Nanofibers can be man- spectrometry (EDX) and thermogravimetric analyses (TGA ufactured by electrospinning which is a technique to obtain and DSC). Analysis indicated that preparation of nanofi- fiber structures that can range in diameter from nanometers bers based Calix-NMG was successfully achieved. The ion to micrometers [1–4]. Electrospun fibers can be made of binding studies exhibited that the nanofiber based Calix- many types of polymers and composite combinations that NMG could be efficiently used for the binding of chromate can be utilized to imitate properties of native extracellular anions and uranium cations. Nanofiber based calix[4]arene matrix or to optimize various chemical, mechanical, elec- with N-methylglucamine chelating groups may be a good trical, architectural, and biological properties. Polymeric candidate as a filter material for treatment of a large nanofibers have enormous specific surface area and high quantity of wastewater owing to their very large surface flexibility. As a result, nanofiber skeletons have large sur- area as well as both the inclusion and donor–acceptor face-to-volume ratio, micropores, and high porosity [5]. complexation capability of all surfaces associated with the Owing to the special properties of nanofibers, they are used calixarene skeleton. in a wide range of applications such as battery separators, aerospace, transistors, drug delivery systems, capacitors, Keywords Calixarene Á Nanofiber Á N-methylglucamine Á energy storage, information technology, filtration, super Uranium Á Chromate absorbents, as scaffolds for tissue engineering, wound dressings, fuel cells and many electronic applications [6– 16], Highly purified air, water, gasses, chemicals, biologi- cal agents without contaminants are needed intensively in & Mevlu¨t Bayrakcı food, pharmaceuticals and biotechnology industries. [email protected] Therefore, compared the microfibers, nanofibrous media undoubtedly hold great advantage in filtration and nanofi- 1 Department of Chemistry, Faculty of Science, Selcuk University, 42075 Konya, Turkey ber structures can act as protective materials against environmental and infectious agents in hospitals, offices 2 Advanced Technology Research and Application Center, 42075 Konya, Turkey and homes. From this point of view functionalized nano- fibers will be most important topic and used as affinity 3 Department of Bioengineering, Faculty of Engineering, Karamanog˘lu Mehmetbey University, Karaman 70200, membranes for filtering heavy metals and toxic anions that Turkey are difficult to purify by conventional purification methods. 123 50 J Incl Phenom Macrocycl Chem (2016) 85:49–58 Furthermore, it is estimated that the current nanofiber addition, the presence of functionalized calixarene in market worldwide may be $400 million and will be worth polymeric matrix provides the functional properties of more than $1 billion by 2020 [17]. This increase also shows solid supports. Electrospinning of nanofibers with cal- the importance of the investigations on functionalized ixarene units is of particular interest, since in this way, nanofibers. Careful examination of the literature reveals nanofibers with specific function groups can be produced. that considerable work has been reported on the design and The polystyrene structures based N-methylglucamine synthesis of nanofibers with supramolecules as cyclodex- (NMG) have been developed for boron removal from trins and their analytical applications [18, 19]. But very irrigation water [38]. Along with boron removal, (NMG) little information has appeared in the literature concerning containing several macroporous resins have been studied nanofibers derived from calixarene supramolecular and for its affinity towards oxoanions of Ge(IV), V(V), Mo(VI), their possible applications [15, 20]. Calixarenes are often As(V), As(III), W(VI), Se(IV), Se(VI), and Sn(IV) [39], referred to as the third generation of supramolecular uranium sorption studies were not observed. N-methyl- receptors after crown ethers and cyclodextrins [21, 22]. glucamine (NMG) has a high interaction capability with Calixarenes are cyclic oligomers made of several phenolic different types of species owing to the presence chelating units bound with methylene bridges [23–26]. The phenolic tertiary amine and vic diol groups that interacted with OH groups of the calixarene lower rim can be further different ion species. Therefore, there is a growing interest functionalized to give various ionic receptors for anions, on (NMG)-based support materials by surface modification cations, as well as hosts of neutral molecules [27–29]. This methods. Compared the support materials, nanofibers excellent skeleton enables calixarenes to act as ‘‘molecular mainly including higher durability in acidic environment, baskets’’ towards neutral or ionic guests. Many different large surface-to-volume ratio, micropores, high porosity studies about the chromate and dichromate anions and flexibility are excellent support materials especially for À2 À (Cr2O7 /HCr2O7 ) from contaminated water have been separation science. At this context, it is a good tentative reported, but the toxic effect of chromate is not well doc- idea to combine the multifunctional character of calixarene umented despite its importance as an environmental pol- skeleton based NMG and PAN nanofibers. Even though lutant [30]. Chromium is one of the most toxic pollutants surface modifications of fibers by calixarene compounds generated from industrial applications [31]. Chromium were reported [15, 20], to the best of our knowledge, the generally appears both in trivalent Cr(III) and hexavalent synthesis of nanofibers with calix [4] arene containing N- Cr(VI) forms in aqueous media. Especially, trivalent methylglucamine chelating groups and their extraction chromium is considered as an essential micronutrient for studies were not reported previously. With this in mind, we human, plant and animal metabolism and less toxic than set out to synthesize PAN nanofiber based calix [4] arene hexavalent chromium which is extremely toxic and car- containing N-methylglucamine chelating groups at upper cinogenic to living organism [32, 33]. Depending on pH rim of calixarene skeleton and explore its ion binding and the total concentration of the solution, Cr(VI) is existed properties towards chromate anions and uranium cations. in different oxy-anion forms. Cr(VI) is unstable and shows very oxidizing behaviors in the presence of the electron donor in acidic medium. At lower pH values, the dominant Experimental À 2À form of the chromium is HCrO4 and only CrO4 ions exist above pH 7. The synthesis of supports and hosts for General specific anions as dichromate is an important goal. Because Cr(VI) has well known effects on environment and living 1H and 13C NMR spectra were obtained using a Varian organism, it is necessarily to remove Cr(VI) from 400 MHz spectrometer operating at 400 MHz. IR spectra wastewater. Owing to the oxide moieties, the dichromate were recorded on a Perkin-Elmer spectrum 100 FT-IR ions are known as oxyanions. These oxide moieties are spectrometer (ATR). Thermogravimetric analysis (TGA) potential sites for hydrogen bonding to the host molecule. data were obtained with a Setaram SETSYS thermal ana- Pyridine, amino and imino derivatives of calixarene are lyzer. SEM images were received using a Zeiss LS-10 field extremely efficient extractant for oxoanions [34]. Nowa- emission SEM instrument. UV–Visible spectra were days many researchers are interested in surface modifica- recorded on Jenway 6105 and Shimadzu160A UV–Visible tion of all kinds of materials such as nanoparticles [35], recording spectrophotometers. Millipore Milli-Q Plus resin [36] and silica gel [37] with calixarene compounds to water purification system is used for the distilled water. For obtain new composite materials. Therefore, simple nano- the pH measurements, An Orion 410Aþ pH meter was fibers containing calixarenes may result in composites used. All of the reagents used in this study were obtained having a range of useful and interesting properties. In from analytical grade and used without further purification. 123 J Incl Phenom Macrocycl Chem (2016) 85:49–58 51 Arsenazo III, uranyl acetate dihydrate were purchased from performed three times. From the blank experiments data it Fluka. Standard stock solution of 0.9787 g/mL ura- was observed that