Preparation of hollow SiO 2 microspheres functionalized with amidoxime groups for highly efficient adsorption of U(VI) from aqueous solution Ying Dai 1 • Jieyun Jin 1,2 • Limin Zhou 1,3 • Tianqi Li 1 • Zhao Li 1 • Zhirong Liu 1,2 • Guolin Huang 1 • Adesoji A. Adesina 3 Received: 5 November 2016 Ó Akade ´miai Kiado ´, Budapest, Hungary 2016 Abstract The amidoxime-functionalized hollow SiO 2 microspheres (HSA) were prepared for highly efficient U(VI) adsorption. Results showed that amidoxime modi- fication could improve both sorption capacity and sorption selectivity for U(VI), however, excess functionalization might block the mesopores and thus restricting U(VI) sorption. The maximum U(VI) sorption capacity was 109.6 mg/g for HSA15 at 298 K and pH 5.0. The U(VI) sorption isotherms could be described by Langmuir model; whereas the sorption kinetics fitted well with the pseudo- second-order equation, indicating of monolayer chemisorption mechanism. The HSA sorbents could be efficiently regenerated by 0.6 M HNO 3 and reused for several sorption–desorption cycles. Keywords SiO 2 microspheres  Functionalization  Amidoxime  U(VI) sorption Introduction Uranium is an important fuel for nuclear reactors but the uranium resources are in shortage due to rapid increase of nuclear energy. On the other hand, uranium-containing wastewater arised from uranium processing is very dan- gerous and need to be treated because of its toxicity and radioactivity [1]. Different methods have been developed for the separation of uranium, among them sorption is mostly adopted since it has the advantages of easy opera- tion, low cost, and wide adaptability [2]. Many kinds of materials such as ion-exchange resins, alumina, activated carbon, and polymers have been investigated for uranium sorption [3–7]. However, most of these materials suffered from weak stability, low ion selectivity, or bad cost effectiveness, thus restricting their practical application. The mesoporous SiO 2 materials have excellent mechanical strength and radiation stability, as well as some unique features such as large surface area, tunable pore size, and facile modification [8, 9], and thus become ideal sorbents for the separation of radionuclides. Compared to conventional silica-based materials, the hollow meso- porous silica (HMS) microspheres have more suitable ap- parent density for better dispersion in solution; Moreover, HMS have much less inner-particle diffusion resistance, thus enhancing kinetic rate for radionuclide separation. The formation of ordered-mesopores in HSM provides a quick access of the sorption centers for radionuclides. The sorption capacity or the sorption selectivity of HMS for radionuclides could be improved by grafting different functional groups such as phosphoric acid [9], amino [10], thiol [11], thiadiazole [12], and amidoxime [13, 14]. These groups have high affinity towards various radionuclide ions (Lewis acid) since they contain electronegative donor atoms (Lewis base) such as N, P, O, and S, etc. For uranly Electronic supplementary material The online version of this article (doi:10.1007/s10967-016-5128-3) contains supplementary material, which is available to authorized users. & Jieyun Jin jingjieyun111@sohu.com & Limin Zhou minglzhecit@sohu.com 1 State Key Laboratory for Nuclear Resources and Environment, East China University of Technology, 418 Guanglan Road, Nanchang 330013, People’s Republic of China 2 Radioactive Geology and Exploration Technology Laboratory, East China University of Technology, 418 Guanglan Road, Nanchang 330013, People’s Republic of China 3 School of Chemical Sciences and Engineering, University of New South Wales, Sydney 2035, Australia 123 J Radioanal Nucl Chem DOI 10.1007/s10967-016-5128-3