Martin Šala

New Insight into Platinum Dissolution from Nanoparticulate Platinum‐Based Electrocatalysts Using Highly Sensitive In Situ Concentration Measurements

Time‐ and potential‐resolved electrochemical Pt dissolution from commercial Pt and prepared PtCu alloy nanoparticulate catalysts have been studied under potentiodynamic conditions in 0.1 M HClO4 by using on‐line inductively coupled plasma mass spectrometry (ICP‐MS). For the first time the exact amount of dissolved Pt per cycle has been measured on real electrocatalysts. Results show clearly that Pt dissolution depends on the particle size: approximately seven times as much Pt is released into the solution from commercial 3 nm Pt particles as from a commercial 30 nm Pt sample. The stability of our prepared PtCu electrocatalyst is higher than that of a commercial 3 nm electrocatalyst, which is, however, still slightly lower than that of a commercial 30 nm Pt electrocatalyst.

Multi-element analysis of wines by ICP-MS and ICP-OES and their classification according to geographical origin in Slovenia

Inductively coupled plasma mass spectrometry and optical emission were used to determine the multi-element composition of 272 bottled Slovenian wines. To achieve geographical classification of the wines by their elemental composition, principal component analysis (PCA) and counter-propagation artificial neural networks (CPANN) have been used. From 49 elements measured, 19 were used to build the final classification models. CPANN was used for the final predictions because of its superior results. The best model gave 82% correct predictions for external set of the white wine samples. Taking into account the small size of whole Slovenian wine growing regions, we consider the classification results were very good. For the red wines, which were mostly represented from one region, even-sub region classification was possible with great precision. From the level maps of the CPANN model, some of the most important elements for classification were identified.

Ion attachment mass spectrometry combined with infrared image furnace for thermal analysis: evolved gas analysis studies.

A well-established ion attachment mass spectrometer (IAMS) is combined with an in-house single-atom infrared image furnace (IIF) specifically for thermal analysis studies. Besides the detection of many chemical species at atmospheric pressure, including free radical intermediates, the ion attachment mass spectrometer can also be used for the analysis of products emanating from temperature-programmed pyrolysis. The performance and applicability of the IIF-IAMS is illustrated with poly(tetrafluoroethylene) (PTFE) samples. The potential of the system for the analysis of oxidative pyrolysis is also considered. Temperature-programmed decomposition of PTFE gave constant slopes of the plots of temperature versus signal intensity in a defined region and provided an apparent activation energy of 28.8 kcal/mol for the PTFE decomposition product (CF(2))(3). A brief comparison with a conventional pyrolysis gas chromatography/mass spectrometry system is also given.

3D laser ablation-ICP-mass spectrometry mapping for the study of surface layer phenomena – a case study for weathered glass

In this work, a multi-elemental 3D laser ablation-ICP-mass spectrometry mapping procedure for high-resolution depth information retrieval to investigate surface layer phenomena is presented. The procedure is based on laser drilling on a virtual grid on the surface, followed by extraction of depth maps along the z-axis (for each element monitored). Using a burst of 50 laser pulses at 1 Hz on each point of the grid, a penetration rate of ca. 150 nm per pulse (in glass) was obtained and a lateral resolution in the order of the laser beam diameter. By ultrafast ICP-MS monitoring of individual ablation pulses (58 ms for a set of 19 elements) using a laser ablation cell with fast signal washout (less than 0.5 s for whole laser pulse), the corresponding peak areas could be consistently integrated, resulting in spatial elemental data associated with individual pulses. The usual laser drilling limitations such as pulse mixing and signal tailing are avoided with this approach. After manipulation of the spatial elemental datasets and quantification, stacks of 50 2D depth maps (for each element monitored) were produced which could be visualized as volume images or time-lapse movies. As a proof of concept, this approach was successfully used to investigate the degradation mechanisms of a medieval, weathered glass artifact by colocalization analysis of selected cross-sectional 2D elemental images in arbitrary planes of the volume images. It was shown that degradation must have started as a result of dealkalinization leading to depletion of alkalis/earth alkalis in glass surface layers and enrichment of network formers (Si and Al), and subsequent worsening by cracking and formation of corrosion pits and so-called spatiotemporal Liesegang rings indicative of radial leaching.

Potentiometric and 31P NMR studies on inositol phosphates and their interaction with iron(III) ions

Potentiometric, conductometric and ³¹P NMR titrations have been applied to study interactions between myo-inositol hexakisphosphate (phytic acid), (±)-myo-inositol 1,2,3,5-tetrakisphosphate and (±)-myo-inositol 1,2,3-trisphosphate with iron(III) ions. Potentiometric and conductometric titrations of myo-inositol phosphates show that addition of iron increases acidity and consumption of hydroxide titrant. By increasing the Fe(III)/InsP(6) ratio (from 0.5 to 4) 3 mol of protons are released per 2 mol of iron(III). At first, phytates coordinate iron octahedrally between P2 and P1,3. The second coordination site represents P5 and neighbouring P4,6 phosphate groups. Complexation is accompanied with the deprotonation of P1,3 and P4,6 phosphate oxygens. At higher concentration of iron(III) intermolecular P-O-Fe-O-P bonds trigger formation of a polymeric network and precipitation of the amorphous Fe(III)-InsP(6) aggregates. (31)P NMR titration data complement the above results and display the largest chemical shift changes at pD values between 5 and 10 in agreement with strong interactions between iron and myo-inositol phosphates. The differences in T(1) relaxation times of phosphorous atoms have shown that phosphate groups at positions 1, 2 and 3 are complexated with iron(III). The interactions between iron(III) ions and inositol phosphates depend significantly on the metal to ligand ratio and an attempt to coordinate more than two irons per InsP(6) molecule results in an unstable heterogeneous system.

Effect of atmosphere and catalyst on reducing bisphenol A (BPA) emission during thermal degradation of polycarbonate.

Bisphenol A (BPA), a well-known endocrine disruptor, is one of the major products in the thermal degradation of polycarbonate (PC) and is also leached out from various PC products. Because of the high acute toxicity of BPA, reducing BPA production during degradation of PC is an important topic. A combined Infrared Image Furnace with Ion attachment mass spectrometry technique was used to investigate the evolution of BPA from a PC sample during heating in either nitrogen or air atmosphere and with or without a CuCl(2) catalyst. Thermal treatment in the presence of CuCl(2), in nitrogen atmospheres and at lower degradation temperatures, substantially reduced the BPA emission.

Functionalization of cellulose fibres with oxygen plasma and ZnO nanoparticles for achieving UV protective properties

Low-pressure oxygen plasma created by an electrodeless radiofrequency (RF) discharge was applied to modify the properties of cellulosic fibrous polymer (cotton) in order to improve adsorption properties towards zinc oxide (ZnO) nanoparticles and to achieve excellent ultraviolet (UV) protective properties of cotton fabric. The chemical and physical surface modifications of plasma-treated cotton fabric were examined by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The mechanical properties of plasma-treated samples were evaluated, measuring strength and elongation of the fabrics. The quantity of zinc on the ZnO-functionalized cotton samples was determined using inductively coupled plasmamass spectrometry (ICP-MS) and the effectiveness of plasma treatment for UV protective properties of cotton fabrics was evaluated using UV-VIS spectrometry, measuring the UV protection factor (UPF). The results indicated that longer plasma treatment times cause higher concentration of oxygen functional groups on the surface of fibres and higher surface roughness of fibres. These two conditions are crucial in increasing the content of ZnO nanoparticles on the fibres, providing excellent UV protective properties of treated cotton, with UPF factor up to 65.93.

Synthesis of 3-(α- and β-d-arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3-b]pyridazine

Abstract Di- O -isopropylidene- and O -methanesulfonyl-protected 1- C -(6-chloro-1,2,4-triazolo[4,3- b ]pyridazin-3-yl)pentitols were prepared in three to four steps from d -galactose, d -glucose, d -mannose, and 2,3:5,6-di- O -isopropylidene-α- d -mannofuranose. Acid-catalysed treatment of (1 S )- and (1 R )-1- C -(6-chloro-1,2,4-triazolo[4,3- b ]-pyridazin-3-yl)-2,3:4,5-di- O -isopropylidene-1- O -methanesulfonyl- d -arabinitols in refluxing 1,2-dimethoxyethane furnished 3-(α- and β- d -arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3- b ]pyridazine, respectively. Several structures, including the structure of the 3-(β- d -arabinofuranosyl)-6-chloro-1,2,4-triazolo[4,3- b ]pyridazine, were also determined by single-crystal X-ray diffraction analysis.

Evaluation of a method for treatment of iron gall ink corrosion on paper

AbstractIron gall ink was the most widely used writing ink for paper from the Middle Ages to the twentieth century. Unfortunately, the ink ingredients contain corrosive transition metal ions and acids that cause severe damage to the paper carrier. New or improved paper conservation methods for iron gall ink stabilization are constantly sought. The aim of the study was evaluation of a recently proposed stabilization treatment, adapted to lower relative humidity, applied to various model and historical paper samples containing iron gall ink. The effect of stabilization treatment on paper samples during artificial thermal aging was followed by the determination of the molecular weight distribution by size exclusion chromatography and colorimetry. Migration of iron and copper compounds from the ink lines was monitored by laser ablation inductively coupled plasma mass spectrometry. The results demonstrate that effective stabilization of iron gall ink-containing paper can be successfully achieved by interleaving with papers impregnated with the antioxidant tetrabutylammonium bromide and alkaline buffer under experimental conditions. Negative side effects of the stabilization treatment, such as migration of iron or copper ions from the ink lines and changes of color after the treatment and after accelerated thermal degradation, were limited, proving that the proposed stabilization treatment can be considered for future use by conservators.

Electrochemical Dissolution of Iridium and Iridium Oxide Particles in Acidic Media: Transmission Electron Microscopy, Electrochemical Flow Cell Coupled to Inductively Coupled Plasma Mass Spectrometry, and X-ray Absorption Spectroscopy Study

Iridium-based particles, regarded as the most promising proton exchange membrane electrolyzer electrocatalysts, were investigated by transmission electron microscopy and by coupling of an electrochemical flow cell (EFC) with online inductively coupled plasma mass spectrometry. Additionally, studies using a thin-film rotating disc electrode, identical location transmission and scanning electron microscopy, as well as X-ray absorption spectroscopy have been performed. Extremely sensitive online time-and potential-resolved electrochemical dissolution profiles revealed that Ir particles dissolve well below oxygen evolution reaction (OER) potentials, presumably induced by Ir surface oxidation and reduction processes, also referred to as transient dissolution. Overall, thermally prepared rutile-type IrO2 particles are substantially more stable and less active in comparison to as-prepared metallic and electrochemically pretreated (E-Ir) analogues. Interestingly, under OER-relevant conditions, E-Ir particles exhibit superior stability and activity owing to the altered corrosion mechanism, where the formation of unstable Ir(>IV) species is hindered. Due to the enhanced and lasting OER performance, electrochemically pre-oxidized E-Ir particles may be considered as the electrocatalyst of choice for an improved low-temperature electrochemical hydrogen production device, namely a proton exchange membrane electrolyzer.