Synchronous Moderate Oxidation and Adsorption on the Surface of γ-MnO 2 for Efficient Iodide Removal from Water.

Long-term exposure to excessive iodine via drinking water presents health risks. Moderate oxidation of iodide (I - ) to iodine (I 2 ) has a better iodine removal effect than excessive oxidation to iodate (IO 3 - ). This study combines computational and experimental methods to construct a heterogeneous interface with synchronous I - moderate oxidation and I 2 adsorption to increase the total iodine removal. Compared to other forms of crystal manganese dioxide (MnO 2 ), theoretical calculations predict that MnO 2 with a γ-crystal structure has the lowest adsorption energy, that is, -1.20 eV, and a slight overlap between the conduction and valence bands, which favors electron transfer between I - and Mn(IV) and I 2 adsorption. Thus, γ-type MnO 2 was designed by adjusting the precursor Mn sources and hydrothermal reaction conditions. The liquid chromatography-inductively coupled plasma-mass spectrometry and high-performance liquid chromatography confirmed that the total iodine concentration in water decreased from 173.7 to 36.3 μg/L after 2 h, with 200 mg/L γ-MnO 2 dosage lower than the national standard of 0.1 mg/L. A minute proportion of I - in water was converted to IO 3 - (approximately 1.1 μg/L). The current I - adsorbent performed better than previously reported ones. During iodine removal, most of the I - migrated from water to the surface of γ-MnO 2 , and the ratio of I - to I 2 was determined to be 1:0.6 by X-ray photoelectron spectroscopy. This study evaluates iodine species transformation and an optimum strategy for heterogeneous interface design; it is promising for treating high-iodine groundwater.