Analysis of Primary Degradation and Decolourization of Dyes in Water by an H2O2/UV Advanced Oxidation Process

Abstract

Synthetic dyes are extensively used in textile dyeing, paper printing, colour photography, pharmaceuticals, food, cosmetics and other industries. In spite of their diversity there are a certain number of properties common to many dye compounds, such as aromatic constitution, chromophore groups and others. Similarly to other dyes and due to the formation of colour intermediates, in the case of Rhodamine 6G colour capacity is maintained in the initial steps of dye degradation. For this reason in the degradation of a dye it is necessary to distinguish between two processes that take place simultaneously: dye removal and decolourization. This study was conducted by using a water solution of 50 mg/L of Rhodamine 6G (Rh-6G), as a model of a dye wastewater, in the hydrogen peroxide/UV system. The kinetic model proposed in this paper for the removing of Rh- 6G is a sequential first-order reaction. This model describes acceptably the changes in two kinds of compound for a wide interval of H

Lumped-intermediates analysis in the photooxidation of Rhodamine 6G in the H2O2/UV system

“…However, Elmorsi et al [19] considered the absorbance not only by the dye but also by the intermediates produced without independently analyzing both. Nevertheless, recent works have proved that the rate of degradation of the dye (analyzed by means of HPLC) does not match the absorbance-decrease rate which would be justified by the presence of other colored intermediates with chromophore groups similar to that of Rh-6G absorbing at its maximum absorbance wave length (λ max =528 nm) [9]. For this reason, in this work two processes were considered individually: dye elimination and water decoloration.…”

“…The proposed model is an improvement on an earlier two-stage model based solely on colored intermediates derived from Rhodamine 6G [9]. The new lumped kinetic model describes oxidation up to complete degradation by modelling a reaction system in which, apart from colored intermediates absorbing at 528 nm (CI), two new lumps of colorless intermediates are considered based on the complexity of their structures.…”

“…Thus far the kinetic model is identical with the classic series model used previously [9], in which the lump of colorless compounds was assumed to be the final product of the reaction mechanisms and was therefore called CLC (colorless compounds) rather than CLI (colorless intermediates) as in this new model. The innovation of the present model over the previous one is that the CLI is understood as a lump of intermediates, whereas before the reaction was modelled as ending with these colorless compounds.…”

“…In another study on the specific case of dye removal and water decoloration, a basic lumped kinetic model was proposed [9]. In the present work, an improvement of the preceding model is proposed; more lumps with higher complicity and consequently more paths were considered.…”

“…Previous studies have defined simple series reaction models to describe the degradation of well-defined compounds by an H 2 O 2 /UV system [3,4] and others have proposed lumped kinetic models applied to a wet-oxidation process [5][6][7]. In our previous work, a lumped kinetic model for the degradation of a linear alkylbenzenesulphonate (LAS) surfactant in an H 2 O 2 /UV system was proposed [8]. That model was based on prior observations and assumed the formation of intermediate lumps with different absorption behaviors at the two wavelengths which are characteristic of the initial compound and which have common chemical structures.…”