Synergy between Zeolite Framework and Encapsulated Sulfur for Enhanced Ion-Exchange Selectivity to Radioactive Cesium

To eliminate the radioisotope 137Cs+ from contaminated water, various inorganic ion-exchange materials have been developed. Many selective ion-exchange materials are relatively expensive and difficult to prepare, whereas conventional materials such as aluminosilicate zeolites lack ion-exchange selectivity in the presence of competing cations. Here, we report a simple but powerful strategy to significantly increase the Cs+ selectivity of conventional zeolites. We demonstrate that encapsulation of elemental sulfur in the micropores of zeolites (NaA, NaX, chabazite, and mordenite) via vacuum sublimation can remarkably increase the selectivity toward Cs+ in the presence of competing ions. It appears that the elemental sulfur does not provide additional adsorption sites for Cs+ ions but increases the ion-exchange selectivity toward Cs+ by providing additional interaction. Various analyses show that sulfur partially donates its electron to the ion-exchanged Cs+ cations in zeolites, indicating significant Lewis acid–base interaction. According to the hard soft acid base (HSAB) theory, the enhanced Cs+ ion-exchange selectivity can be explained by the fact that sulfur, a soft Lewis base, interacts more strongly with Cs+, which is a softer Lewis acid than other alkali and alkaline earth metal cations. Because of the high intrinsic Cs+ selectivity of bare zeolites and selectivity enhancement resulting from sulfur encapsulation, the sulfur-modified chabazite and mordenite showed highly promising Cs+ capture ability in the presence of various competing ions

A Novel Combination of Anaerobic Bioleaching and Electrokinetics for Arsenic Removal from Mine Tailing Soil

This study provides evidence that a hybrid method integrating anaerobic bioleaching and electrokinetics is superior to individual methods for arsenic (As) removal from mine tailing soil. Bioleaching was performed using static reactors in batch tests and flow conditions in column test, and each test was sequentially combined with electrokinetics. In the bioleaching, indigenous bacteria were stimulated by the injection of carbon sources into soil, leading to the mobilization of As with the concurrent release of Fe and Mn. Compared with the batch-type bioleaching process, the combined process showed enhanced removal efficiency in the equivalent time. Although the transport fluid bioleaching conditions were inadequate for As removal, despite long treatment duration, when followed by electrokinetics the combined process achieved 66.5% removal of As from the soil. The improvement of As removal after the combined process was not remarkable, compared with single electrokinetics, whereas a cost reduction of 26.4% was achieved by the reduced duration of electrokinetics. The As removal performance of electrokinetics was significantly dependent on the chemical species of As converted via microbial metal reduction in the anaerobic bioleaching. The synergistic effect of the combined process holds the promise of significant time and cost savings in As remediation

Monolayer Hexagonal Boron Nitride Nanosheets as Proton-Conductive Gas Barriers for Polymer Electrolyte Membrane Water Electrolysis

In a proton exchange membrane (PEM) water electrolyzer, the poor gas barrier property of conventional perfluorosulfonic acid (PFSA) membranes results in membrane degradation and safety-related explosion issues. In this report, we investigate the potential of monolayer hexagonal boron nitride (hBN) as an effective hydrogen gas barrier for PEMs in a water electrolyzer. An hBN/Nafion composite membrane is prepared by transferring large-area monolayer hBN (∼25 cm2), which is prepared using chemical vapor deposition, onto Nafion 117. This one-atom-thick monolayer hBN, which is known as an impermeable material to most molecules except protons, significantly enhances the hydrogen barrier property of Nafion 117, even at high temperatures, and increases the mechanical stability of the membrane. Although a trade-off between proton conductivity and hydrogen barrier properties is observed, the water electrolysis efficiency of the cell containing the composite membrane is improved by increasing the operating temperature while minimizing the decrease in proton conductivity. By employing monolayer hBN, hydrogen permeability is significantly reduced by approximately 40%, and the corresponding electrolysis efficiency decreases by 19% compared to that of pristine Nafion. Furthermore, the enhanced gas barrier property of the composite shows slightly higher long-term (100 h) stability than that of Nafion 117