Nanomaterial Extraction of Radioactive Metals from Wastewater

The production of low-carbon energy has considerable global influence on social, economic, and environmental development. Nuclear energy offers a very high energy density with extremely low greenhouse gas emissions with unparalleled advantages as compared to other energies. Uranium is mainly used as fuel in nuclear power plants for electricity production in several countries, such as France, United States, etc. To a lesser extent, it is also used in reactors for the propulsion of naval vessels, for basic and applied research, and for the production of radioisotopes for multiple applications such as the treatment of cancer or for medical imaging. Our aim is to design a cheap, highly adsorbant, easily recyclable composite which can be used under conditions where saturation adsorption is reached in a very short time. This should make it possible to treat large quantities of radioactively contaminated wastewaters and reduce the contaminants to a small volume thereby economizing on storage space. The economic, environmental and societal advantages of mitigating nuclear contamination by such a process are obvious.<br/>The synthesis and elaboration of multifunctional nanomaterials are increasingly finding applications in different fields, in particular environmental science [1]. Among the best candidates are magnetic and carbon nanomaterials whose efficacy and specificity can be enhanced by functionalization. Grafting chelators and other small molecules onto these materials can provide a decisive advantage for their use in the decontamination of wastewater from heavy metals. Heavy metals adsorbed on magnetic materials can be easily recovered by magnetic harvesting. Interesting results on the extraction of cesium and uranium [2] were obtained by exploiting the high sorption capacity of calixarene [3], cyclodextrin [1] and amidoxime [4] groups.<br/>We have developed a fast, inexpensive system, based on the use of superparamagnetic nanoparticles (NPs) carrying carbon dots (CDs) [5] for the sequestration of radioactive elements. CDs are cheap and easy to produce by a variety of methods. Preparing them from glucose by ultrasonic treatment gives monodisperse spherical particles with excellent optical and photoluminiscent properties. These were grafted onto the surface of maghemite NPs and observed by fluorescence nanoscopy. Preliminary tests show that the hybrid material is able to extract slightly more than with cyclodextrin but at a much lower cost. Photothermia (PT) is a technique whereby heat is generated by irradiating NPs with a laser. In this study, PT is used for the first time to enhance the adsorption capabilities of NPs. Preliminary results show that the maximal adsorption capacity (q_max) of maghemite is increased by 230 % by irradiation at 680 nm for only 5 minutes. Work is in hand to apply the same procedure to CD@maghemite with uranium and other metals (Cs, Pb, As, etc.).<br/>[1] Helal AS, Mazario E, Mayoral A, Decorse P, Losno R, Lion C, Ammar S and Hémadi M<b>. Environmental Science: Nano. 2018</b>, 5, 158-168.<br/>[2] Mazario E, Stemper J, Helal AS, Mayoral A, Decorse P, Losno R, Lion C, Ammar S, Le Gall T and Hémadi M. <b>Journal of Nanoscience and Nanotechnology, 2019,</b> 19, 4911-4919<br/>[3] Kumar N, Pham-Xuan Q, Depauw A, Hemadi M, Ha-Duong NT, Lefevre JP, Ha-Thi MH and Leray I. <b>New Journal of Chemistry</b>, <b>2017</b>, 41, 7162<br/>[4] Stemper J, Tuo W, Mazarío E, Helal AS, Djurovic A, Lion C, El Hage Chahine JM, Maurel F, Hémadi M and Le Gall T. <b>Tetrahedron, 2018,</b> 74, 2641-2649.<br/>[5] H. Belkahla, R. Boudjemaa, V. Caorsi, D. Pineau, A. Curcio, J.S. Lomas, P. Decorse, A. Chevillot-Biraud, T. Azaïs, C. Wilhelm, H. Randriamahazaka and M. Hémadi. <b>Nanoscale Advances</b>, <b>2019</b>, 1, 2571-2579.