Removal of iodide from water using halloysite/Ag2O composites as efficient adsorbent

Abstract

The efficient removal of iodide (I−) from water is challenging to accomplish because of the large size and low charge of I−. In this study, halloysite/Ag2O composites were prepared, characterized, and used to remove I− from water. The Ag2O nanoparticles primarily resided in the lumen of halloysite in the composites, whose amount and size can be readily controlled by adjusting the concentration of Ag+ during the preparation process. Moreover, there is rapid adsorption of I− by the composites, whose kinetics followed a pseudo-second-order model. With a solid/liquid ratio of 50 mg/20 mL and an initial pH of 7.5 ± 0.2, the maximum I− adsorption capacity of composites with an approximately 0.98% and 2.42% Ag2O content was 13.7 mg/g and 39.99 mg/g, which is 48 and 142 times higher than that of raw halloysite, respectively. Importantly, the composites exhibited high selective adsorption to I−, and their I− removal efficiency is barely affected by the presence of Cl−, Br−, or SO42−. The high adsorption capacity of the composite is driven by the small particle sizes of Ag2O due to the spatial confinement of the lumen of halloysite and the newly formed nanopores between Ag2O particles and the inner wall of halloysite. After capturing the radioactive I−, the composites are expected to constitute a low radiological hazard because of the shielding provided by the halloysite wall. Taken together, these results suggest the halloysite/Ag2O composites could be a promising adsorbent suitable for use in the efficient removal of radioactive I− from nuclear wastewater.