Journal of Hazardous Materials 416 (2021) 126226 Available online 26 May 2021 0304-3894/© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Research Paper Active and selective removal of Cs from contaminated water by self-propelled magnetic illite microspheres Chan Woo Park a, * , Taeeun Kim a, b , Hee-Man Yang a , Yeonsoo Lee a, c , Hyung-Ju Kim a a Decommissioning Technology Research Division, Korea Atomic Energy Research Institute, Daedeok-daero 989-111, Yuseong-gu, Daejeon, Republic of Korea b Department of Environmental Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea c Department of Organic Materials Engineering, Chungnam National University, 99 Daehak-ro, Yuseong-gu, Daejeon, Republic of Korea A R T I C L E INFO Editor: Dr. T. Meiping Keywords: Clay Illite Micrometer Cesium Adsorbent Self-propulsion ABSTRACT We report the fabrication of clay-mineral-based Janus microspheres that exhibit remotely steerable self- propulsion in water, facilitating their selective and active removal of radiocesium from a contaminated solu- tion. The spray-drying of slurries of intrinsically Cs-selective illite containing iron oxide nanoparticles led to magnetic illite microspheres with superior 137 Cs adsorption capability and superparamagnetic behavior. The Janus micromotor adsorbent was prepared by depositing catalytic Pt onto the half-surface of magnetic illite microspheres. The micromotor adsorbents exhibited self-propulsion at speeds as high as ~265 µm/s via asym- metric bubble generation in water containing H 2 O 2 as a fuel. The self-propulsion of the adsorbent improved the Cs adsorption kinetics six-folds compared with the kinetics in the corresponding stationary liquid. The magnetic properties of the micromotor adsorbent enabled convenient separation and direction control of the adsorbents under an external magnetic feld. In particular, the micromotor adsorbent could successfully remove more than 98.6% of 137 Cs from aqueous media containing competing ions including K + , Na + , Ca 2+ and Mg 2+ . 1. Introduction Radioactive Cs is one of the most hazardous radionuclides. It is generated by the nuclear fssion reactions; thus, liquid wastes containing 137 Cs, or radiocesium, are inevitably generated during the operation of nuclear power plants. Unintended leaks of contaminated liquids and nuclear accidents can lead to the release of radiocesium into the envi- ronment, where it contaminates soil and surface water (Kinoshita et al., 2011; Christoudias and Lelieveld, 2013; Vakulovsky et al., 1994). For example, the nuclear incident at Fukushima has resulted in environ- mental contamination of thousands of square kilometers, and hundreds of tons of liquid wastes containing 137 Cs are still produced every day (Kinoshita et al., 2011; Christoudias and Lelieveld, 2013; Strickland, 2014). Groundwater that fows into a damaged reactor building is mixed with radionuclides, and the contaminated liquid is continuously pum- ped out of the facility to prevent the migration of radionuclides (Strickland, 2014). Highly water-soluble 137 Cs behaves like K + in or- ganisms, and its ingestion poses various health risks (Avery, 1995; Redman et al., 1972). Both internal and external exposure of the human body to the gamma radiation of 137 Cs can cause cancers and genetic disorders (Bandazhevsky, 2000). Because the separation of Cs from liquid is critical for reducing the radiological impact on the environment, various Cs removal technolo- gies have been developed (Chen et al., 2020). Although water treatment processes such as membrane separation, chemical precipitation and ion exchange achieve satisfactory Cs removal effciency, such technologies produce enormous amount of secondary wastes, some of which are not suitable for selective Cs removal from mixed wastes (Chen et al., 2020; Combernoux et al., 2017; Rana et al., 2013; Han et al., 2012). Conse- quently, Cs-selective adsorption processes have attracted great interest because such technology enables the effcient and economical treatment of large volumes of liquid waste containing various competing ions while minimizing secondary waste generation (Chen et al., 2020). Synthetic materials based on transition-metal ferrocyanides, crystalline silicotitanate, metal sulfdes and vanadosilicates have shown promising Cs adsorption selectivity (Chen et al., 2020; Yang et al., 2021). However, 2:1 clay minerals are considered promising natural adsorbents for Cs because of their intrinsic cation-exchange capability and low material cost compared with synthetic Cs-selective materials (Zheng et al., 2017; Wang et al., 2019; Liu et al., 2014; Park et al., 2019). Like other Cs-selective adsorbents, however, clay minerals have a small particle size, which makes them diffcult to separate and also reduces the liquid * Corresponding author. E-mail address: chanwoo@kaeri.re.kr (C.W. Park). Contents lists available at ScienceDirect Journal of Hazardous Materials journal homepage: www.elsevier.com/locate/jhazmat https://doi.org/10.1016/j.jhazmat.2021.126226 Received 25 February 2021; Received in revised form 29 April 2021; Accepted 23 May 2021