Sorption Studies of Chromate by Iron Oxide from Drinking Water

Chromium is well-thought-out heavy metal which is one of the enormously lethal due to its cancer-causing nature. In this study, iron oxide is used as adsorbent for chromate removal from aqueous solution as a function of pH, time, temperature, concentration of adsorbate and media dosage. The influence of pH on Cr (VI) sorption by iron oxide reveals that adsorption is significantly increased as pH is decreased from 8 to 2. The sorption rate is detected to be higher in the beginning and then it remains constant after 120 min of equilibrium time. The removal of Cr (VI) is found to be greater at higher temperature, which confirms the endothermic nature of Cr (VI) adsorption by iron oxide. Whereas, the kinetic investigations confirm that the chromate adsorption follows the pseudo second order with kinetic energy in the range of 8.4–83.7 kJ mol−1.

Volatility of Amorphous Solid Water

Amorphous solid water is probably the most abundant form of solid water in the universe. Its saturation vapor pressure and thermodynamic properties, however, are not well known. We have investigated the saturation vapor pressure over vapor-deposited amorphous ice at temperatures between 133 and 147 K using a novel experimental method. The new method determines the absolute vapor pressures and the sublimation rates by measuring the mass growth rates of ice-covered nanoparticles under supersaturated water vapor conditions. We find that the vapor pressure of amorphous solid water is up to a factor of 3 higher than that predicted by current parameterizations, which are based in part on calorimetric measurements. We demonstrate that the calorimetric measurements can be reconciled with our data by acknowledging the formation of nanocrystalline ice as an intermediate ice phase during the crystallization of amorphous ice. As a result, we propose a new value for the enthalpy of crystallization of amorphous solid water of Δ H = 2312 ± 227 J/mol, which is about 1000 J/mol higher than the current consensus. Our results shine a new light on the abundance of water ice clouds on Mars and mesospheric clouds on Earth and may alter our understanding of ice formation in the stratosphere.