Nada Mehio

Acidity of the amidoxime functional group in aqueous solution: a combined experimental and computational study.

Poly(acrylamidoxime) adsorbents are often invoked in discussions of mining uranium from seawater. While the amidoxime-uranyl chelation mode has been established, a number of essential binding constants remain unclear. This is largely due to the wide range of conflicting pK(a) values that have been reported for the amidoxime functional group. To resolve this existing controversy we investigated the pK(a) values of the amidoxime functional group using a combination of experimental and computational methods. Experimentally, we used spectroscopic titrations to measure the pK(a) values of representative amidoximes, acetamidoxime, and benzamidoxime. Computationally, we report on the performance of several protocols for predicting the pK(a) values of aqueous oxoacids. Calculations carried out at the MP2 or M06-2X levels of theory combined with solvent effects calculated using the SMD model provide the best overall performance, with a root-mean-square deviation of 0.46 pK(a) units and 0.45 pK(a) units, respectively. Finally, we employ our two best methods to predict the pK(a) values of promising, uncharacterized amidoxime ligands, which provides a convenient means for screening suitable amidoxime monomers for future generations of poly(acrylamidoxime) adsorbents.

Thickness- and Particle-Size-Dependent Electrochemical Reduction of Carbon Dioxide on Thin-Layer Porous Silver Electrodes.

The electrochemical reduction of CO2 can not only convert it back into fuels, but is also an efficient manner to store forms of renewable energy. Catalysis with silver is a possible technology for CO2 reduction. We report that in the case of monolithic porous silver, the film thickness and primary particle size of the silver particles, which can be controlled by electrochemical growth/reduction of AgCl film on silver substrate, have a strong influence on the electrocatalytic activity towards CO2 reduction. A 6 μm thick silver film with particle sizes of 30-50 nm delivers a CO formation current of 10.5 mA cm(-2) and a mass activity of 4.38 A gAg (-1) at an overpotential of 0.39 V, comparable to levels achieved with state-of-the-art gold catalysts.

Synthesis of metal–organic framework particles and thin films via nanoscopic metal oxide precursors

Metal–organic frameworks (MOFs) are a diverse family of hybrid inorganic–organic crystalline solids synthesized by assembling secondary building units (SBUs) and organic ligands into a periodic and porous framework. Microporous MOF materials, due to their high permeability and size selectivity, have attracted tremendous interest in gas storage and separation, large molecule adsorption, catalysis, and sensing. Despite the significant fabrication challenges, nanosized MOF particles can be fabricated to display enhanced gas storage and separation abilities in comparison to the parent MOF bulk counterparts under special synthesis conditions. So far, the majority of MOF nanocrystals have been derived from the controlled nucleation and growth of molecular precursors in homogeneous solutions. However, synthesis protocols based on nucleation and growth from dilute solution precursors are difficult to adapt to the synthesis of other nanoscopic materials, such as thin film and mixed-matrix membranes, which limits the practical applications of MOFs. This article discusses the current status of synthetic methods that have been utilized to fabricate MOF-based nanoscopic materials and ultrathin membranes from nanoscopic metal oxide precursors.

Separating Rare-Earth Elements with Ionic Liquids

The rare-earth elements (REEs) are a group of 17 chemically similar metallic elements; this group consists of scandium, yttrium, and 15 lanthanides. Due to their essential role in permanent magnets, lamp phosphors, catalysts, and rechargeable batteries, the REEs have become an essential component of the global transition to a green economy. Currently, with China producing over 90 % of the global REE output and its increasingly tightening export quota, the rest of the world is confronted with the potential risk of REE shortage. As such, many countries will have to rely on recycling REEs from pre-consumer scrap, industrial residues, and REE-containing end-of-life products. Over the course of the last two decades, ionic liquids have been increasingly used to separate REEs in the recycling process. Ionic liquids (ILs) are a class of molten salts that are liquid at temperatures below 100 °C. ILs are amenable to the recycling of REEs because the cation and anion components are readily tailored to a given process, and they offer numerous advantages over typical organic solvents, such as low volatility, low flammability, a broad temperature range of stability, the ability to dissolve both inorganic and organic compounds, high conductivity, and wide electrochemical windows. In this chapter, we discuss the performance of several IL-based extraction systems used to separate and recycle REEs.