Electrochemical and sonoelectrochemical monitoring of indigo reduction by glucose

The reduction of indigo (dispersed in water) to leuco-indigo (dissolved in water) is an important industrial process and investigated here for the case of glucose as an environmentally benign reducing agent. In order to quantitatively follow the formation of leuco-indigo two approaches based on (i) rotating disk voltammetry and (ii) sonovoltammetry are developed. Leuco-indigo, once formed in alkaline solution, is readily monitored at a glassy carbon electrode in the mass transport limit employing hydrodynamic voltammetry. The presence of power ultrasound further improves the leuco-indigo determination due to additional agitation and homogenization effects. While inactive at room temperature, glucose readily reduces indigo in alkaline media at 65 degrees C. In the presence of excess glucose, a surface dissolution kinetics limited process is proposed following the rate law d eta(leuco-indigo)/dt = k x c(OH-) x S-indigo where eta(leuco-indigo) is the amount of leuco-indigo formed, k = 4.1 x 10(-9) m s(-1) (at 65 degrees C, assuming spherical particles of I gm diameter) is the heterogeneous dissolution rate constant,c(OH-) is the concentration of hydroxide, and Sindigo is the reactive surface area. The activation energy for this process in aqueous 0.2 M NaOH is E-A = 64 U mol(-1) consistent with a considerable temperature effects. The redox mediator 1,8-dihydroxyanthraquinone is shown to significantly enhance the reaction rate by catalysing the electron transfer between glucose and solid indigo particles. (c) 2006 Elsevier Ltd. All fights reserved

M A Muthukumaran, Potentiostatic studies on indirect electrochemical reduction of vat dyes. Dyes and Pigments

Abstract Dispersed vat dyestuffs can be electrochemically reduced by indirect electrolysis using ironetriethanolamine complex as a reducing agent. The application and mechanism of indirect electrolysis as a reduction technique are described in detail in this paper. Electrochemically reduced vat dye is tested on a laboratory scale in dyeing experiments, and the results of different reduction conditions are discussed. The influence of the concentration of the complex-system on the build-up of colour depth, shade and fastness is discussed and compared with samples of the standard dyeing procedure using sodium dithionite as the reducing agent. The new process offers environmental benefits as well as prospects for improved process stability, because the state of reduction in the dye-bath can be readily monitored by measuring the reduction potential

Anthraquinone catalysis in the glucose-driven reduction of indigo to leuco-indigo

Anthraquinone immobilised onto the surface of indigo microcrystals enhances the reductive dissolution of indigo to leuco-indigo. Indigo reduction is driven by glucose in aqueous NaOH and a vibrating gold disc electrode is employed to monitor the increasing leuco-indigo concentration with time. Anthraquinone introduces a strong catalytic effect which is explained by invoking a molecular "wedge effect'' during co-intercalation of Na+ and anthraquinone into the layered indigo crystal structure. The glucose-driven indigo reduction, which is in effective in 0.1 M NaOH at 65 degrees C, becomes facile and goes to completion in the presence of anthraquinone catalyst. Electron microscopy of indigo crystals before and after reductive dissolution confirms a delamination mechanism initiated at the edges of the plate-like indigo crystals. Catalysis occurs when the anthraquinone-indigo mixture reaches a molar ratio of 1:400 (at 65 degrees C; corresponding to 3 mu M anthraquinone) with excess of anthraquinone having virtually no effect. A strong temperature effect ( with a composite E-A approximate to 120 kJ mol(-1)) is observed for the reductive dissolution in the presence of anthraquinone. The molar ratio and temperature effects are both consistent with the heterogeneous nature of the anthraquinone catalysis in the aqueous reaction mixture

Light cured networks containing metal organic frameworks as efficient and durable polymer electrolytes for dye-sensitized solar cells

We describe the preparation of a polymer composite containing Mg-based metal-organic framework (MOF) through a rapid and environmental friendly UV-induced free-radical process. The composite is used as electrolyte for quasi-solid dye-sensitized solar cells (DSSCs): noticeable solar energy conversion efficiencies were obtained (Eff = 4.8%), together with a outstanding long-term durability. Besides being an effective candidate for the enhancement of DSSC performances, this first ever MOF-based polymeric composite proves to be potentially exploitable also for other applications, e.g. in the field of supported catalysis