Electrochemical Deposition of ZnS Films from Electrolyte Based on Na2SO3

The paper considers the features of electrochemical growth of zinc sulfide from an aqueous electrolyte based on sodium sulfite and zinc sulfate. The conditions for the electrochemical production of ZnS films are determined. It is shown that the value of the potential at which a ZnS layer is formed is limited by the achievement of the critical current due to the diffusion limitations of the electrochemical process of reducing the sulfite ion. It is shown that the resulting films contain an excess of sulfur, which is removed, and the stoichiometric composition is obtained by heat treatment. Aed mechanism of reactions resulting in the formation of zinc sulfide is proposed.

Integrated all-solid-state sulfite sensors modified with two different ion-to-electron transducers: rapid assessment of sulfite in beverages

An integrated all-solid-state screen-printed ion-selective potentiometric sensor for rapid assessment of sulfite ion in beverages, based on analytical transduction, is described.

Reactivity Indices related to DFT Theory, the Electron Localization Function (ELF) and Non-Covalent Interactions (NCI) Calculations in the Formation of the non-Halogenated Pyruvic Esters in Solution

The non-halogenated pyruvic esters are essential compounds, considering that they exhibit particular properties, due to the proximity of two functional groups: carbonyl and ester. These molecules can be obtained from the approach of the Lewis acid MgI2 on the iodinated pyruvic ester by using sodium hydrogen sulfite in aqueous solution, which selectively reduces the carbon-iodine bond of the iodinated pyruvic ester. The sites of attack of hydrogen sulfite of this reaction remained uncertain and were the subject of a debate between the experimenters. Our aim in this work is to determine the more favorable sites of attack by using the local indices (Parr functions). To approve the structure of the reagents, we have conducted a topological analysis of electron localization function (ELF). To reveal the type of interaction in the "ester pyruvic-hydrogen sulfite" complex, we have performed a non-covalent interactions (NCI) calculation. The analysis of local indices and NCI analysis of electron density indicate that the approach of the hydrogen sulfite ion will take place on the iodine atom elucidating the preferable site of the attack.

Reaction kinetics of strong nucleophiles with a dimeric non-phenolic lignin model compound with α-carbonyl functionality (adleron) in aqueous alkali solution

The degradation kinetics of a non-phenolic lignin model compound with α-carbonyl functionality (adlerone) has been studied by varying temperature and concentrations of sodium hydroxide, sodium hydrogen sulfide, and sodium sulfite. The kinetics of adlerone degradation and formation of its reaction products were monitored by UV-Vis spectroscopy and their structures were analyzed by GC/MS. The two step degradation of adlerone was studied in two separate experimental setups. In the first alkali catalyzed step, adlerone is converted to a β-elimination product that reacts further in the second step with hydrogen sulfide or sulfite ion. The Arrhenius kinetic parameters were derived by the KinFit software. The activation energy for the 1st step was 69.1 kJ mol-1, and for the 2nd step with sulfide 42.4 kJ mol-1 and with sulfite ion 35.8 kJ mol-1. The reaction mechanisms presented are in line with those published earlier: β-ether bonds of structures having α-carbonyl functionality do not cleave under soda pulping conditions, whereas in kraft and sulfite pulping the cleavage of β-ether bonds proceeds via nucleophile attack and addition. The combination of hydroxyl and sulfite ions gives the fastest cleavage of β-ether bonds in non-phenolic lignin structures with the α-carbonyl functionality.

Effect of hydroxide and sulfite ion concentration in alkaline sulfite anthraquinone (ASA) pulping – a comparative study

Pulp and black liquor produced by alkaline sulfite anthraquinone (ASA) process were comprehensively characterized to evaluate the effects of ion concentration on the delignification and polysaccharide preservation. Scots pine wood meal was pulped at 160°C with a sulfite-to-hydroxide ion ratio of 0.75 and liquor-to-wood ratio of 200:1. Two concentration levels were studied in presence and absence of anthraquinone (AQ). Contrary to the expectations, already the lower concentration level (L-ASA) revealed rapid delignification in presence of AQ, while only moderate acceleration was obtained at the high concentration level (H-ASA). However, H-ASA liquor resulted in a slightly higher pulp yield of 1–2% (based on wood) but only in case of pulps with kappa numbers (KN) above 60. With progressing delignification, the yield advantage was gradually lost. The higher pulp yield at H-ASA conditions was mainly due to improved galactoglucomannan retention, which was around 2% on KN60 pulp and around 0.5% after prolonged delignification. The xylan content, on the other hand, was found to be 1% (based on wood) lower under H-ASA conditions compared to L-ASA conditions, which may be attributed to an increased solubility of short-chain polysaccharides at high alkali concentration.

A comparison of different methods to remove dissolved oxygen: Application to the electrochemical determination of imidacloprid

This study compares different methods for the removal of oxygen from the solution prior to the chronopotentiometric determination of the insecticide imidacloprid on glassy carbon electrode. The research included the application of the chemical method involving addition of sulfite ion, and the physical method of purging the sample with nitrogen stream, as well as their combination. By comparing analytical signals of imidacloprid, chemical method showed almost the same efficiency as conventional physical method, while the best reproducibility was achieved by applying chemical method with addition of the saturated sodium sulfite solution. The method is very simple and can be applied for deoxygenation of the solution prior to the chronopotentiometric analysis. The application of the chemical deoxygenation significantly shortened duration of the chronopotentiometric analysis of imidacloprid from approximately 15 min to 1 min.