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The colour component from the bark of Macaranga peltata has been extracted and, using spectral techniques, the main colouring ingredient has been identified as ellagic acid. The dyeing properties of the extract on silk have been studied. The colour coordinates of the dyed samples were found to be in the yellow-red quadrant of the colour space diagram and the dyed samples exhibited acceptable fastness properties. The effect of temperature and dye concentration on the rate of dyeing has been studied. Adsorption studies revealed that the process fits well with the Langmuir isotherm model. The thermodynamic parameters of the dyeing process have been evaluated using an Arrhenius plot. The experimental results revealed that the adsorption was exothermic and spontaneous in nature, and exhibited first-order kinetics. Further, the effect of electrolyte on rate of dyeing has also been recorded. The rate of adsorption increases as the disrupting effect of the added electrolyte cation increases and follows the order: Al 3+ > Ca 2+ > Na + . ª

a b s t r a c tThe kinetics of oxidation of sunset yellow (SY) by sodium-N-chloro-p-toluenesulfonamide or chloramine-T (CAT) was studied spectrophotometrically in HClO 4 and NaOH media with Os(VIII) as a catalyst in the latter medium at 298 K and 303 K, respectively. In acid medium, the experimental rate law isÀ0.46 . Alkali accelerates the rate of reaction and the rate law takes the form. The solvent isotope effect was studied using D 2 O. Benzenesulfonic acid and 1,2-naphthoquinone-6-sulfonic acid were characterized as the oxidation products of SY. Under identical set of experimental conditions in alkaline medium, Os(VIII) catalyzed reaction is about seven-fold faster than the uncatalyzed reaction. Activation parameters for the overall reaction and also with respect to catalyst have been evaluated. The observed results have been explained by plausible mechanisms and the related rate laws have been deduced.

One of the most important thiazine dyes is methylene blue (MB), which is extensively used in the dyeing industry. It also facilitates a number of biological applications. Methylene blue dye is not significantly hazardous, but it can lead to various harmful effects. Among the physicochemical processes developed to remove this dye from wastewater textile and dyestuff manufacturing industries, the oxidative decolorization method alone seems to ensure the advantage of a low cost, simple, and efficient process. So we investigated a detailed oxidative decolorization kinetic study of MB by sodium-N-chloro-p-toluenesulfonamide (chloramine-T or CAT) in alkaline medium catalyzed by Os(VIII) spectrophotometrically at 664 nm (λ max of the dye). The reaction rate showed a first-order dependence each on [CAT] o and [MB] o , a fractional-order dependence on [Os(VIII)], and an inverse-fractional-order dependence on [NaOH]. A decrease of the dielectric constant of the medium by the addition of methanol decreased the rate. The solvent isotope effect k′ (H 2 O)/k′ (D 2 O) was equal to 1.37. Activation parameters were computed. The kinetics of oxidation of MB by CAT was also studied with other platinum metal ions. The relative reactivity of these catalysts are in the order Os(VIII) > Ru(III) > Ir(III) g Rh(III) g Pt(IV) > Pd(II). This trend may be attributed to the different d-electronic configurations of the metal ions. It was found that the catalyzed reactions are about 3-fold to 10-fold faster than the uncatalyzed reactions. The mechanism proposed and the derived rate law are consistent with the observed kinetics. This simple and economic redox system can also be adopted for removing the MB dye present in industrial wastewater.

The use of synthetic dyes causes environmental pollution as majority of these dyes are toxic and non-biodegradable. Natural dyes on the other hand have proved to be eco-friendly, biodegra- dable and highly compatible with the environ-ment. Consequently, dyes derived from natural sources have emerged as important alternatives to synthetic dyes. In the present work, the major color component isolated from the pods of G. sepium plant is morin, which is a flavonoid moiety. The dyeing behaviour of this component on silk yarn was investigated. Mordanting stu- dies have indicated that the post-mordanting method was found to be a better method com-pared to pre-mordanting. Variation of pH on dye extract pointed out that the maximum absorbance was at pH 4 and hence all the dyeing studies have been carried out at that pH. Thermodynamic parameters were determined by studying the dyeing process at different temperatures. Heat of dyeing was positive which indicated the dyeing process was endothermic. The adsorption process of morin on silk was tested with Langmuir, Freundlich and Tempkin- Pyzhev isotherm models. The adsorption process followed both the Langmuir and Freund- lich isotherms. The value of regression coefficient, however, indicated that the Langmuir isotherm was a better fit than the Freundlich isotherm. These results signified that the adsor- ption of morin on silk yarn was homogeneous in nature with the formation of a monolayer. Hence, the dye obtained from the pods of G. sepium plant may be an alternative source to synthetic dye for the dyeing of silk as well as other textile fabrics