Mechanisms and thermodynamic modelling of iodide sorption on AFm phases

Retention of Iodide by Chloride Green Rust and Magnetite

Green rust (GR), a layered double hydroxide (LDH) containing Fe, and magnetite can be found in natural and engineered environments. The ability of chloride GR (GR-Cl) and magnetite to retain iodide as a function of various parameters was investigated. Sorption equilibrium is achieved within 1 day of contact time between iodide and preformed GR-Cl in suspension. pH_m variations (7.5-8.5) have no significant influence, but the iodide sorption decreases with increasing ionic strength set by NaCl. Sorption isotherms of iodide suggest that the uptake operates via ionic exchange (IC), which is supported by geochemical modeling. The short-range binding environment of iodide associated with GR is comparable to that of hydrated aqueous iodide ions in solution and is not affected by pH_m or ionic strength. This finding hints at an electrostatic interaction with the Fe octahedral sheet, consistent with weak binding of charge balancing anions within an LDH interlayer. The presence of sulfate anions in significant amounts inhibits the iodide uptake due to recrystallization to a different crystal structure. Finally, the transformation of iodide-bearing GR-Cl into magnetite and ferrous hydroxide resulted in a quantitative release of iodide into the aqueous phase, suggesting that neither transformation product has an affinity for this anionic species.

Facile preparation of CoFe-based oxide nanosheets derived from CoFe-layered double hydroxide for the thermal catalytic decomposition of ammonium perchlorate

In this work, CoFe-based oxide nanosheets were prepared by a facile method and its catalysis effects on the thermal decomposition of ammonium perchlorate (AP) were studied. CoFe-based oxide nanosheets were obtained from hydrothermal process and high-temperature treatment of CoFe-layered double hydroxide. The samples were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The thermal catalytic decomposition of AP with CoFe-based oxide nanosheets as catalysts was investigated by differential scanning calorimetry and coupling Fourier transform infrared spectrometer. The results showed that the CoFe-based oxide samples with the width size of 200–300 nm and the thickness size of ∼10 nm show the inherent catalytic ability. With 10 wt% of CoFe-based oxide nanosheets added, the decomposition temperature of AP was reduced by 127.5 °C from 431.0 °C to 303.5 °C. The apparent activation energy was decreased by 61.1 kJ/mol from 177.3 kJ/mol of raw AP to 116.2 kJ/mol of AP with 10 wt% of CoFe-based oxide nanosheets added. The thermal catalysis decomposition mechanism of AP with CoFe-based oxide nanosheet material promoting was proposed. This work offered a novel idea toward preparation and application of functional material layered double hydroxide in the field of energetic materials.