Electrochemical Bleaching Research Articles

Some Significant Trends in Textile Bleaching

The article highlights some recent trends in the bleaching of textile materials. An attempt has been made to compare the effect of electrochemical bleaching with conventional bleaching of cotton. Electric current is used in the preparation of a bleaching agent to replace bleaching powder. The sodium hypochlorite generated from electrolyte cell is sufficient to produce powerful bleaching agent with available chlorine. Electrochemical bleaching with sodium hypochlorite offers numerous advantages like prevention of effluent problem, economy, reliability, cleanliness, and convenience in working. Attempts have been made to use sodium perborate as a bleaching agent with potassium persulphate as an activator at lower temperature in combined pre treatment of cotton fabric. Experimental trials have been designed by using taguchi technique. This bleaching technique promises to be eco-friendly process. In yet another interesting work, effort has been taken to bleach the scoured cotton fabric with sodium perborate as bleaching agent and tetreacetyl ethylenediamine as bleaching activator. The concentrations of these chemicals, temperature and time of the treatment have been varied. The utilization of hydrogen peroxide is much higher as compared with that of conventional bleaching process. Other advantages include less requirement of water and energy, thereby satisfying needs of eco-friendly process, lesser loss in weight, tearing strength, and tensile strength, in comparison with conventional bleaching process without compromising whiteness index.

Cover Picture: Selective Electrochemical Bleaching of the Outer Leaflet of Fluorescently Labeled Giant Liposomes (Chem. Eur. J. 28/2017)

Cover Picture: Selective Electrochemical Bleaching of the Outer Leaflet of Fluorescently Labeled Giant Liposomes (Chem. Eur. J. 28/2017)

Selective Electrochemical Bleaching of the Outer Leaflet of Fluorescently Labeled Giant Liposomes

AbstractInvited for the cover of this issue is the project team of Oliver Buriez at the Ecole Normale Supérieure of Paris. The image depicts the electrochemical bleaching of vesicles with retained fluorescence. Read the full text of the article at 10.1002/chem.201605786.

Selective Electrochemical Bleaching of the Outer Leaflet of Fluorescently Labeled Giant Liposomes.

Electrochemistry and confocal fluorescence microscopy were successfully combined to selectively bleach and monitor the fluorescence of NBD (7-nitrobenz-2-oxa-1,3-diazole)-labeled phospholipids of giant liposomes. Three types of giant unilamellar vesicles have been investigated, the fluorescent phospholipids being localized either mainly on their outer-, inner-, or both inner/outer leaflets. We established that only the fluorescent lipids incorporated in the outer leaflet of the vesicles underwent electrochemical bleaching upon reduction. The relative fluorescence intensity decay was quantified all along the electrochemical extinction through an original fluorescence loss in electrobleaching (FLIE) assay. As expected, the reorganization of the fluorescent phospholipids followed diffusion-driven dynamics. This was also evidenced by comparison with fluorescence loss in photobleaching (FLIP) and the corresponding numerical model. The value of the lateral diffusion coefficient of phospholipids was found to be similar to that obtained by other methods reported in the literature. This versatile and selective bleaching procedure appears reliable to explore important biological and pharmacological issues.

Study of electrochemical bleaching of p-nitrosodimethylaniline and its role as hydroxyl radical probe compound

In the present paper, research on the electrochemical bleaching of p-nitrosodimethylaniline (RNO) in different electrolyte systems is presented with special attention to the role of RNO as a selective hydroxyl radical probe compound. At a Ti/Pt90–Ir10 anode, RNO was found to be bleached in 0.050 M sodium sulphate electrolyte due to lattice active oxygen without hydroxyl radicals being intermediately present. In 0.050 M sodium chloride, the bleaching rate was greatly enhanced due to indirect bulk oxidation by active chlorine species, again without the presence of hydroxyl radicals in the oxidation mechanisms. Under galvanostatic electrolysis, a linear relationship was found between the concentration of added chloride to a supporting sodium sulphate electrolyte and the first order rate constant of the bleaching reaction, showing the importance of the indirect bulk chlorine bleaching in chloride electrolyte systems. In this fashion both the chemically bonded active oxygen and the chemical bulk oxidation by active chlorine species proved to be valid bleaching pathways of RNO that according to these findings cannot be regarded as a fully selective hydroxyl radical probe compound. In addition, the difference in the mechanisms of chloride electrolysis at Ti/Pt90–Ir10 and Si–BDD anodes was clearly demonstrated using t-BuOH as hydroxyl radical scavenger.

Electrochemical bleaching of kraft bagasse pulp using a new cell design

AbstractIn situ single‐stage electrochemical bleaching of kraft bagasse pulp was carried out in a cylindrical agitated vessel fitted with four graphite rod anodes and a cylindrical stainless steel screen cathode, using NaCl as an electrolyte. The effect of current density, pH, NaCl concentration, impeller rotational speed, temperature, and pulp consistency on the rate of bleaching was studied. It was found that the rate of bleaching increased with increasing current density, NaCl concentration, and temperature and decreased with increasing pH and pulp consistency. The effect of temperature was found to fit Arrhenius equation with an activation energy of 0.515 kcal/mol, which denotes a diffusion‐controlled mechanism. Energy consumption (EC) calculation showed that EC ranged from 0.225 to 3.11 kWh/kg dry pulp depending on the current density. The strength of bleached pulp was little affected by bleaching lying within an acceptable range.

P-Nitrosodimethylaniline (RNO)-Based Evaluation of Enhanced Oxidative Potential During Electrochemical Treatment of High-Salinity Wastewater

The electrochemical bleaching of p-nitrosodimethylaniline (RNO) was investigated in order to apply its reactions to evaluating electrochemical oxidation. The bleaching rate of RNO during electrochemical treatment was accelerated by the presence of chloride ions. The initial bleaching rate of RNO was found to be accelerated during the electrolysis of NH4Cl, suggesting that electrochemically generated chloramines are sufficiently strong oxidants to convert RNO. A method of evaluating direct or indirect oxidative potential for electrochemical treatment was proposed, provided that the initial bleaching rate of RNO is consistent with low concentrations of RNO. The saline wastewater of Japanese pickle production processes (brown mustard and Japanese radish) was electrochemically treated. The ammonium ion (18 and 8 mg L−1) was almost completely removed after 1h of treatment in the presence of NaCl (3%). The removal rate of total organic carbon (TOC) exceeded 90% for 7 mg L−1 and 60% for 352 mg L−1, indicating that electrochemical treatment is useful in removing ammonium ions and organic substances from high-salinity wastewater.

Effect of a chromium salt on the electrochemical bleaching of sulphite pulp

Electrochemical bleaching of sulphite pulp was carried out by using NaCl solution as an electrolyte. At pH 10, a temperature of 35 °C and a pulp consistency of 2%, the rate of bleaching was found to increase with increasing current density and salt concentration. The power consumption ranged from 0.4 to 3.3 kW h per kilogram of pulp, depending on the current density or salt concentration. The addition of 0.02% K 2Cr 2O 7 increased the degree of bleaching by 6% and the current efficiency by 7% with no deterioration effect on the pulp quality.

A new electrochemical technique for bleaching cellulose pulp

A study of electrochemical bleaching of cellulose pulp was carried out in an electrolyte cell composed of a horizontal graphite anode and a parallel stainless screen steel cathode, using NaCl as electrolyte. Variables studied were: current density, sodium chloride concentration, pulp concentration, pH and temperature. The rate of bleaching was found to increase with increasing current density, salt concentration and temperature. The rate of bleaching was found to decrease with increasing pH and pulp concentration. Energy consumption ranged from 0.1 kWh kg−1 (pulp) to 1.75 kWh kg−1 (pulp), depending on current density and degree of bleaching. The quality of electrochemically bleached pulp was found to compare favourably with that of chemically bleached pulp.

Photoinduced Coloration and Electrochemical Bleaching of an Electrochromic Material Mixed with Photosensitive Powders

Photoinduced Coloration and Electrochemical Bleaching of an Electrochromic Material Mixed with Photosensitive Powders

The electrochemical bleaching of ferric thiocyanate in acidic solution

Abstract The bleaching phenomena of ferric thiocyanate in acidic solution were investigated electrochemically. The cyclic voltammogram showed only a cathodic wave, and two waves appeared in the dc polarogram; ie the limiting current of the Fe(III) complex and the reduction of Fe(II) at −1.3 V( sce ). The rate determining step of the bleaching reaction was diffusion control in solution for small values of the ratio [SCN]/[Fe(III)], but it shifted toward the chemical reaction control with an increase in the ratio.