functionalized magnetic nanoparticles for the decontamination of water polluted with cesium

Functionalized magnetic nanoparticles for the decontamination of water polluted with cesium Ahmed S Helal, Philippe Decorse, Christian Perruchot, Sophie Novak, Claude Lion, Souad Ammar, Jean, , Michel El Hage Chahine , and Miryana Hémadi Citation: AIP Advances 6, 056601 (2016); doi: 10.1063/1.4942825 View online: http://dx.doi.org/10.1063/1.4942825 View Table of Contents: http://aip.scitation.org/toc/adv/6/5 Published by the American Institute of Physics AIP ADVANCES 6, 056601 (2016) Functionalized magnetic nanoparticles for the decontamination of water polluted with cesium Ahmed S Helal,1,2 Philippe Decorse,1 Christian Perruchot,1 Sophie Novak,1 Claude Lion,1 Souad Ammar,1 Jean-Michel El Hage Chahine,1,a and Miryana Hémadi1,a ITODYS, Université Paris Diderot, PRES Sorbonne Paris Cité, CNRS-UMR 7086, 15 rue Jean-Antoine de Baïf, 75205 Paris 13, France Nuclear Materials Authority, P.O Box 540 El Maadi, Cairo, Egypt (Presented 14 January 2016; received November 2015; accepted 25 November 2015; published online 22 February 2016) Magnetic nanoparticles are attracting considerable interest because of their potential applications in practically all fields of science and technology, including the removal of heavy metals from contaminated waters It is, therefore, of great importance to adapt the surfaces of these nanoparticles according to the application In this work advanced nanoparticles (NPs) with well-tailored surface functionalities were synthesized using the polyol method The efficiency of a chelating agent, succinyl-βcyclodextrin (SBCD), was first investigated spectrophotometrically and by Isothermal Titration Calorimetry (ITC) SBCD was then grafted onto nanoparticles previously functionalized with 3-aminopropyl triethoxsilane (NP-APTES) The resulting NP-SBCD system was then incubated with a solution of cesium After magnetic separation, the solid residue was removed from the supernatant and characterized by X-Ray Photoelectron spectrometry (XPS), X-Ray Fluorescence spectrometry (XRF) and Superconducting QUantum Interference Device (SQUID) magnetometry These characterizations show the presence of cesium in the solid residue, which indicates Cs uptake by the NP-SBCD system This nanohybrid system constitutes a promising model for heavy metal decontamination C 2016 Author(s) All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License [http://dx.doi.org/10.1063/1.4942825] I INTRODUCTION The Chernobyl disaster and, more recently, that of Fukushima Daiichi led to the release of large amounts of 137Cs into the atmosphere and to its accumulation in the soil and vegetation.1,2 Naturally occurring cesium is an uncommon alkali metal with slight toxicity related to its interference with the sodium-potassium pump in muscles and red cells It is not therefore a particular health hazard However, 137Cs is a radioactive unnatural synthetic isotope, produced by nuclear chain reactions, with a half-life of 30 years This explains its highly negative impact on health, which is manifested in the Chernobyl and Fukushima regions by a recrudescence of cancers and other severe illnesses.3 Thus, the removal of 137Cs from areas contaminated by nuclear accidents is an absolute necessity for public health.4 Hence, there is an urgent need to develop new separation technologies to selectively remove the cesium while avoiding interference with the natural environmental metal balance.5,6 Magnetic nanoparticles (NPs) have attracted much interest over the past decades because of their physical and chemical properties The surface functionalization of such nanoparticles in conditioned by the application, such as drug targeting,7 imagery,8 extraction and separation of organic pollutants and heavy metal ions,9 etc In general, the strong point of magnetic a Author to whom correspondence should be addressed Electronic mail: hemadi@univ-paris-diderot.fr or chahine@univ- paris-diderot.fr 2158-3226/2016/6(5)/056601/6 6, 056601-1 © Author(s) 2016 056601-2 Helal et al AIP Advances 6, 056601 (2016) materials is that they can easily be collected and removed from a complex multiphase system by an external magnetic field.10 In this context, our approach was to graft a specific chelating agent for cesium onto maghemite nanoparticles The main advantage of maghemites is their chemical stability Moreover these nanoparticles have high surface areas, enabling the attachment of a large number of chelating molecules This should produce a confinement effect, which enhances the affinity for the metal, thus augmenting the decontamination efficiency We started by investigating the affinity of succinyl-β-cyclodextrin (SBCD) for Cs+ by UV-visible absorption and by Isothermal Titration Calorimetry (ITC) Potassium, an alkali metal with chemical properties close to cesium, was chosen as a reference to analyze SBCD selectivity for Cs+ Our main goal here is to synthesize the best nanohybrid NP-SBCD system capable of chelating cesium efficiently and selectively II EXPERIMENTAL SECTION A Synthesis and functionalization of maghemite nanoparticles Maghemite nanoparticles (γ-Fe2O3), 10 nm in diameter, were synthesized by the polyol method11 and then functionalized with 3-aminopropyl-triethoxysilane (APTES).12 The functionalized nanoparticles, after cooling to room temperature, were then collected by sedimentation on a laboratory magnet They were washed several times with ethanol and dried overnight at 50 ◦C The resulting hybrids were conjugated with succinyl-β-cyclodextrin, C71H100O55 (SBCD) by the formation of an amide bond between the amine of the nanoparticle (NP) and the carboxylic acid groups of SBCD, which were activated by adding N-hydroxy-succinamide (NHS, final concentration: 3.75 mM) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiamide (EDC, final concentration: 1.5 mM) B Materials All chemicals were of purest grade Succinyl-β-cyclodextrin, C71H100O55 and cesium acetate Cs(OCOCH3) were purchased from SIGMA-ALDRICH and KCl suprapur from Merck C Stock solution For the complexation test performed by differential absorption and ITC, solutions of SBCD, cesium acetate and potassium chloride were prepared in distilled water D Chelation test Two samples of SBCD (50 mg) were stirred overnight at room temperature, one with a solution of cesium chloride (0.5 mM) and the other with potassium chloride (0.5 mM) Magnetic sedimentation was performed to separate the supernatant from the pellet containing NP-SBCD (Fig 1) The pellet was afterwards characterized by X-Ray Photoelectron spectrometry (XPS), X-Ray Fluorescence spectrometry (XRF) and Superconducting QUantum Interference Device (SQUID) FIG A- Suspension of maghemite nanoparticles in presence of cesium B- Magnetic separation 056601-3 Helal et al AIP Advances 6, 056601 (2016) E Instrumentation Nano-ITC titrations were carried out at 25 ◦C in water by using a Nano-ITC calorimeter (TA Instruments, USA) with an active cell volume of 0.988 mL and a 250 or 100 µL stirring syringe The power curve (heat flow as a function of time) was integrated by means of the NanoAnalyze program to obtain the overall heat produced or absorbed during the reaction All solutions were thoroughly degassed by stirring under vacuum Titrations were accomplished by an automated sequence of 50 injections, each of µL cesium or potassium solutions (1.2 mM), into the sample cell containing the succinyl-β-cyclodextrin solution (0.1 mM) The injections were spaced at 300 s intervals to ensure complete equilibration Three titrations were carried out for each measurement The reported experimental data are the best-fit values (Nano Analyze software) Absorption measurements were performed at (25 ± 0.5)◦C on a Cary 4000 spectrophotometer equipped with a thermostated cell-carrier XPS was performed with an ESCALAB 250, Thermo VG Scientific spectrometer equipped with a monochromatic Al KαX-ray source The samples were fixed on holders using conductive double-sided adhesive tape and pumped overnight in the fast entry lock at ∼5 10−10 mbar prior to transfer to the analysis chamber Chemical analysis of selected elements (Fe, Cs) was performed (on dried powder deposited on a clean cellulose membrane) by X-ray Fluorescence (XRF) spectroscopy using a MINIPAL4 spectrometer equipped with a rhodium X-ray tube operating at 30 kV and 87 µA current emission The intensities of the Fe and Cs peaks on each XRF spectrum were compared to those recorded for calibrated Fe and Cs standards Magnetic studies on raw and functionalized NPs were run on a Quantum Design MPMS-5S SQUID magnetometer The saturation magnetization was recorded at 300 K as a function of the magnetic field H at -50 to 50 kOe III RESULTS AND DISCUSSION Thermodynamic measurements were performed to determine the chelation capacity of SBCD in water towards cesium and potassium Differential absorption was studied by using cuvettes (reference and work) filled with SBCD A constant volume of cesium or potassium solution was repeatedly added to the work cuvette while the same volume of water was added to the reference This was done to maintain the same SBCD concentration in both cuvettes Fig shows at λ = 300 nm a decrease in differential absorption (∆A) with increasing cesium concentration FIG Differential absorption after cesium addition in water (pH = 6.8) at (25 ± 0.5) ◦C Baseline was run with [SBCD] = 10−5 M 056601-4 Helal et al AIP Advances 6, 056601 (2016) FIG Isothermal titration calorimetry (ITC) bind-ing curves for complexation of SBCD with Cs+ Cesium does not absorb at this wavelength This variation was therefore ascribed to the formation of a complex between cesium and SBCD (eq.(1)) SBCD + Cs+ (SBCD-Cs) [SBCD][Cs+] with KD = [(SBCD − CS)] (1) The same experiments were performed for potassium (data not shown) A SPECFIT analysis allowed the determination of the KD values for both metals (Cs+ and K+) These results were confirmed by nano-ITC (Fig 3) ITC is among the most quantitative means available for measuring the binding thermodynamic parameters directly by determining the heat variation during the association of a ligand with its binding partner In a single experiment, the values of the binding constant (Ka), the stoichiometry (n), and the enthalpy of binding (∆Hb) are determined Fig shows a regular heat variation with cesium injections, which establishes that there is an interaction between SBCD and cesium and that the complexation is endothermic In contrast, the experiment with potassium did not show any heat variation (see insert in Fig 3) The affinity constant of SBCD for K+ is at least one order of magnitude lower than that for cesium (Table I) This can be explained by the cation radii of K+ and Cs+ The Cs+ cation fits into the SBCD cavity, but not K+ Maghemite NPs were synthesized, functionalized by APTES and characterized, as described elsewhere,7,12 by Transmission Electron Microscopy (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD) SBCD was grafted onto 10 nm-diameter maghemite nano-particles The nanohybrid sytem thus obtained was characterized by XPS (Fig 4) The atomic ratio N/Fe is 1.39 for NP-SBCD (green spectrum) and 0.27 for NP-APTES (red spectrum) The ratio O/Fe increases for NP-SBCD to 14.27 while that for NP-APTES is 5.42 The atomic percentage TABLE I Values of –logKD obtained by differential absorption and by nano-ITC measurements for complex formation between SBCD and K+ or Cs+ SBCD Ionic radii (Å) SPECFIT (-logKD) Nano Analyze (-logKD) Cs+ K+ 1,67 5.1 ± 0.2 4.5 ± 0.3 1,38 3.6 ± 0.3 - 056601-5 Helal et al AIP Advances 6, 056601 (2016) FIG XPS survey spectra for NP (green), NP-SBCD (red) and NP-SBCD-Cs (black) of silicon, a specific elemental marker for APTES, is the same in both spectra (2%) This underlines the efficiency of SBCD grafting at the NP-APTES surface NP-SBCD was then tested for its cesium chelation capacity Cesium is an alkali with physical and chemical properties similar to potassium.13 Since the latter is much more abundant in nature, its chelation can compete with that of Cs+ Consequently, the high selectivity for Cs+ of the chelator when compared to that of K+ is a necessity for cesium decontamination Therefore, the chelation capacities of NP-SBCD towards both alkalis were determined A blank was performed with functionalized nanoparticles (NP-APTES): mg of NP-APTES and NP-SBCD were incubated separately with a fixed concentration of cesium (10−4 M) and potassium (10−4 M) Magnetic separation was performed and the solid phase was characterized by XPS and XRF For NP-SBCD, the XPS spectrum (Fig 4, black spectrum) shows an additional peak at 749 eV, which represents 1.3 % of the atomic percentage and is attributed to cesium (Cs3d3/2) Thus, the cesium is complexed to SBCD while no specific peak for potassium was observed In contrast, NP-APTES does not complex either K+ or Cs+ Since the XPS analysis depth does not exceed some nanometers, XRF measurements were performed to determine, for each hybrid prepared, the total atomic Cs/Fe ratio XRF is representative of the whole particle volume In the case of NP-SBCD-Cs, the overall masses of Fe and Cs are 11.4 and 0.4 µg, respectively This implies atomic percentages of 98.4 at.-% for Fe and 1.6 at.-% for Cs (See Table II.) Additional experiments are needed to estimate the efficiency of cesium chelation by NP-SBCD Magnetic studies were performed in order to see whether the diamagnetic contribution of SBCD and cesium at the surface of the NPs strongly affects the magnetization Interestingly, the TABLE II Surface chemical compositions of NP-APTES, NP-SBCD and NP-SBCD-Cs as inferred from XPS analysis At.-% Signal NP-APTES NP-SBCD NP-SBCD-Cs C1s Cs3d3 Fe2p3 N1s O1s Si2s 54.9 6.4 1.7 34.6 2.3 48.9 2.9 4.1 42.0 2.1 39.2 1.4 10.4 1.4 46.6 1.1 056601-6 Helal et al AIP Advances 6, 056601 (2016) FIG First magnetization recorded at K on bare NPs (NP-APTES) and NP-SBCD before cesium chelation At 300 K, spectra of NP-APTES, in red (65.5 emu.g−1) and in blue NP-SBCD (42.1 emu.g−1) saturation magnetization (Msat) of bare NP (NP-APTES) at K is as high as that of bulk maghemite (γ-Fe2O3), whereas the decrease in Msat after SBCD grafting does not exceed 20% (Fig 5) Thus, NP-SBCD remains sufficiently magnetized to be attracted by a simple magnet The saturation magnetization (Msat) at 300 K (see insert in Fig 5) of NP-APTES and NP-SBCD are slightly lower than those at K Needless to say, further investigations are still required to fully estimate the efficiency and the selectivity of the system for Cs+ Adsorption studies and ICP analysis are currently in progress IV CONCLUSION The reported nanohybrid NP-SBCD seems to be efficient in cesium chelation and removal by magnetic harvesting It, therefore, constitutes a promising model for heavy metal decontamination by magnetic separation ACKNOWLEDGMENT This work was supported by the National Research Agency program “DECRET” (ANR ANR13-SECU-0001) A.S Helal was supported by French Foreign Ministry (Campus France program) The authors are grateful to Dr J S Lomas for constructive discussions I A E Agency, Chernobyl’s Legacy: Health, Enviromental and Socio-Economic Impacts and Recommendations to the Governments of Belarus, the Russian Federation and Ukraine, International Atomic Energy Agency (2006) I A E Agency, Fukushima Nuclear Accident: Information Sheet, International Atomic Energy Agency (2011) H Miyazaki, H Kato, Y Kato, T Tsuchiyama, and H Terada, J Food Soc Jpn 54, 151-155 (2013) P Melnikov and L Z Zanoni, Biol Trace Elem Res 135, 1-9 (2010) M S H Bader, J Hazard Mater B82, 139-182 (2001) I Urban, N M Ratcliffe, J R Duffield, G R Elder, and D Patton, Chem Commun 46(25), 4583-4585 (2010) H Piraux, J Hai, P Verbeke, N Serradji, S Ammar, R Losno, N T Ha-Duong, M Hemadi, and J M El Hage Chahine, Biochim Biophys Acta 1830(8), 4254-4264 (2013) J Xie, J Huang, X Li, S Sun, and X Chen, Curr Med Chem 16(10), 1278-1294 (2009) A Künküla and T Abbasovb, Powder Technol 149(1), 23-28 (2004) 10 D Feng, C Aldrich, and H Tan, Hydrometallurgy 56(3), 359-368 (2000) 11 H Basti, L Ben Tahar, L S Smiri, F Herbst, M J Vaulay, F Chau, S Ammar, and S Benderbous, J Colloid Interface Sci 341(2), 248-254 (2010) 12 H Piraux, J Hai, T Gaudisson, S Ammar, F Gazeau, J M El Hage Chahine, and M Hémadi, J Appl Phys 117, 17A336 (2015) 13 W H McCaroll, J Phys.Chem Solids 26(1), 191-195 (1965)  ... compete with that of Cs+ Consequently, the high selectivity for Cs+ of the chelator when compared to that of K+ is a necessity for cesium decontamination Therefore, the chelation capacities of NP-SBCD... from contaminated waters It is, therefore, of great importance to adapt the surfaces of these nanoparticles according to the application In this work advanced nanoparticles (NPs) with well-tailored...AIP ADVANCES 6, 056601 (2016) Functionalized magnetic nanoparticles for the decontamination of water polluted with cesium Ahmed S Helal,1,2 Philippe Decorse,1 Christian