Effective and Selective Sorption of Iodide by Thin Film of Multilayered MnO2 Intercalated with Cationic Surfactants

Abstract

Following the magnitude-9.0 Tohoku earthquake on 11 March 2011 and the subsequent failure of the Fukushima No. 1 nuclear power plant, radioactive iodine was released into the environment.1 Radioactive isotopes of iodine 131 and 129 are produced during the fission of uranium atoms, and can be liberated during the normal operation of nuclear reactors and fuel reprocessing facilities, 2 as well as in the cases of nuclear accidents. Although 129 I is much less radioactive than 131I with a half-life of 8.02 days, its long half-life (1.57 × 10 7 years) allows it to diffuse over a long period of time in the hydrosphere, including groundwater and seawater, as anions (most often as iodide, I -). To date, several procedures have been developed for the recovery of iodide anions from aqueous solutions. I -can form precipitates with metal cations, such as Bi 3+ and Pb 2+ , at the high concentration. Lefèvre et al. found an affinity of cuprous oxide (Cu2O) toward I -, where the sorption capacity was unaffected by the presence of a 1000 fold excess of Cl -ions. 3 However, the potential region at which Cu2O existed stably was as small as about 0.2 V. Polyethylenimine-epichlorohydrin resins showed the maximum sorption capacity values, as high as 600 mg/g; however, the addition of background electrolytes (NaCl and Na2SO4) remarkably reduced their performance. 4 Layered or porous minerals, such as clays and zeolites, possess a negatively charged surface and exhibit cation-exchange properties as a result. Organoclays, which are produced from natural clays through a modification with cationic surfactants, provide an affinity for non-polar organic species and inorganic anions. 5Dultz and Bors 6 and Riebe et al. 7,8 modified bentonite clay minerals by replacing natural inorganic cations with tetra-alkylammonium ions. The resulting organoclays exhibited a high sorption capacity for I -, compared to untreated samples, especially when samples were treated with hexadecylpyridinium (HDPy) cations. When a large volume of contaminated water is treated, we must keep it in mind that the sorbents possess a sufficient selectivity toward the object with respect to major cations and anions existing in wastewater. In the present study, a thin film of organo-modified multilayered MnO2, whose interlayer is occupied with HDPy surfactants, was fabricated on an electrode substrate through a simple electrochemical approach. The electrode-supported film was investigated with regard to the sorption capability for iodide anions in both the absence and presence of NaCl and Na2SO4. To the best of our knowledge, this is the first iodide sorbent with a thin-film form. The preparation process, an anodic electrodeposition, can readily supply thin and uniform films with a large surface area, even on a substrate of complex shape.Non-radioactive NaI (99.5%) and hexadecylpyridinium chloride (HDPyCl, >99.0%) were purchased from Wako Pure Chemicals, and used without further purification. The electrodeposition of MnO2 was made in a standard three-electrode cell using a ...

Electrosynthesis of Layered Organo-Manganese Dioxide Framework-Doped with Cobalt for Iodide Sensing

“…30−34 In our previous study, the layered MnO 2 film intercalated with hexadecylpyridinium cations (HDPy + ) was utilized for the sorption of iodide anions. 35 The inherent advantages of an electrochemically grown film over conventional powdered sorbents are (i) thin film sorbent is much less bulkier than powder-type sorbent, (ii) the electrode-supported film can be easily separated from the solution being treated and does not need the secondary collection, and (iii) the oxidation state of the film sorbent can be controlled by an external electrical circuit. The HDPy/MnO 2 film selectively captured iodide from the major components of seawater through hydrophobic (organophilic) interaction between the interlayer organic phase of the MnO 2 film and iodide ions in solution.…”