Piranha solution | EPFL Graph Search

Piranha solution, also known as piranha etch, is a mixture of sulfuric acid () and hydrogen peroxide (). The result of the mixture gives rise to a strong union of two acids called per-hexa-sulfuric acid (H4SO6) that is used to clean organic residues off substrates. Because the mixture is a strong oxidizing agent, it will decompose most organic matter, and it will also hydroxylate most surfaces (by adding –OH groups), making them highly hydrophilic (water-compatible). This means the solution can also easily dissolve fabric and skin, potentially causing severe damage and chemical burns in case of inadvertent contact. It is so named after the fish, piranha. Preparation and use Many different mixture ratios are commonly used, and all are called piranha. A typical mixture is 3 parts of concentrated sulfuric acid and 1 part of hydrogen peroxide solution; other protocols may use a 4:1 or even 7:1 mixture. A closely related mixture, sometimes called "base piranha", is a 3:1 mixtur

Safe non-smooth black-box optimization with application to policy search

Andreas Krause, Ilnura Usmanova

For safety-critical black-box optimization tasks, observations of the constraints and the objective are often noisy and available only for the feasible points. We propose an approach based on log barriers to find a local solution of a non-convex non-smooth black-box optimization problem minf0(x)minf0(x)\min f^0(x) subject to fi(x)≤0,i=1,…,mfi(x)≤0,i=1,…,mf^i(x)\leq 0, i = 1,\ldots, m, at the same time, guaranteeing constraint satisfaction while learning with high probability. Our proposed algorithm exploits noisy observations to iteratively improve on an initial safe point until convergence. We derive the convergence rate and prove safety of our algorithm. We demonstrate its performance in an application to an iterative control design problem.

PMLR2020

Synthesis, reactivity, and environmental relevance of uranyl(V) complexes.

Radmila Faizova

Knowledge of fundamental chemical properties of all environmentally relevant uranium species is essential to understand environmental uranium mobility and develop novel remediation strate-gies. A myriad of uranium(VI) and uranium(IV) compounds has been studied for decades but the uranyl(V) analog was traditionally thought of as a highly unstable species of limited environmen-tal importance. This understanding has changed in the last decade with studies demonstrating uranyl(V) to be a persistent species in Fe rich environments and an intermediate in the biological /abiotic transformations of soluble uranyl(VI) compounds into insoluble uranium(IV) polynuclear species. These processes are imperative for drinking water remediation but their mechanism and the role of U(V) remains unclear. A stable uranyl(V) complex in organic media was first reported more than 10 years ago and this led to rapid development in the field. However, a stable compound in aqueous media at environ-mentally relevant pH could not be obtained and this was selected as the primary goal of this the-sis. Our research produced the first uranyl(V) complex that is stable in both organic and aqueous me-dia. This was achieved using an aminopicolinate ligand, combining the pentadentate binding mode with the ability to form stable complexes with metal ions in water. This molecule has al-lowed us to investigate the persistence of U(V) in certain environments, its conversion to insolu-ble complexes, and the mechanism of bacterial reduction of uranium with collaborators in micro-biology. The effect of Fe2+ on the stability of U(V) towards proton-induced disproportionation and redox reactions was investigated. Cation-cation interaction between uranyl(V) oxygen and Fe2+ was shown to stabilize U(V), explaining its unusual persistence in Fe-rich environments. Additionally, the effect of iron and the impact of a supporting ligand on the electronic structure of U(V) was investigated in collaboration by a high-resolution X-ray absorption spectroscopy and computational study.
Several rational routes for the preparation of uranium polyoxometalates (POM) were developed. The resulting clusters provide a good model of uranate species formed upon environmental reduc-tion of uranyl(VI). An insoluble well-defined molecular trinuclear U(IV) oxo/hydroxo cluster was isolated in a good yield from the direct reduction of a uranyl(VI) complex in aqueous media. This unprecedented 2-electron reduction was accomplished by utilizing a readily available and non-toxic reductant (Na2S2O4). Finally, controlled hydrolysis of UCl4 in organic solution was explored to investigate the factors that govern the assembly of uranium POMs. The formation of discrete uranium(IV) clusters of various nuclearities (U6 â U38) was shown to be dependent on multiple factors, however, the time variable was found to be paramount.

EPFL2020

Sintered metal fibers coated with transition metal oxides as structured catalysts for hydrogen peroxide decomposition

Julien Haber, Lioubov Kiwi

This study aimed at the development of active and stable structured catalyst for the decomposition of hydrogen peroxide under industrial conditions. Sintered metal fibers of stainless steel (SMFss) in the form of flat panels were surface coated by different catalytic metal oxides. The oxide coating has been carried out by incipient wetness impregnation of SMFss with suitable precursors followed by calcination in air at temperatures between 500 and 600 degrees C. The coating of SMFss renders a very thin homogeneous oxide layer of less than 1 mu m covering the individual fibers and ensures an optimal accessibility of the treated H2O2 solution to the catalytically active phase without any mass-transfer limitations. In the decomposition of hydrogen peroxide, the 5 wt.% MnOx/5 wt.% (Al2O3 + MgO)/SMFss was found to be the most active and stable catalyst in a range of pH = 4-7 at 25 degrees C exhibiting a significant first order rate constant of 5.2 min(-1) at pH 7. The same catalyst was tested in the back end of the epoxidation of soybean oil process demonstrating its suitability for industrial application. (c) 2013 Elsevier B.V. All rights reserved.

Elsevier2013

Synthesis, reactivity, and environmental relevance of uranyl(V) complexes.

Radmila Faizova

EPFL2020