Influence of Anions and Micelle and Submicellar Aggregates on the Alkaline Hydrolysis of Malachite Green: Tensiometric, Spectrophotometric, and Kinetic Investigations

Abstract

The influence of mono-and bivalent anions and micelle/submicellar clusters of different ionic and nonionic surfactants on the hydrolysis of malachite green (MG + ) was studied in the presence of low alkali concentrations. Large polarizable I − ion and bivalent SO 4 2− ion show specific interaction toward MG + with the formation of dye−anion ion-pair resulting in a retardation of the reaction rate. Tensiometric studies for anionic surfactants sodium dodecyl sulfate (SDS) and dioctyl sodium sulfosuccinate (AOT) in the presence of dye indicate the formation of ion-pair micelles which subsequently break down to form normal micelles. A change of the absorbance value accompanied by a red shift in the electronic spectra with increase in surfactant concentration also evidenced the formation of ion-pair. The observed rate inhibition by the anionic surfactants and the interaction behavior/nature of binding between the dye and surfactant in the premicellar region have been analyzed in terms of different kinetic models. The Piszkiewicz cooperativity index (n) suggests 1:1 association between the anionic surfactant monomer and MG + in the submicellar cluster. A catalyzing effect for the cationic surfactant, cetyltrimethylammonium bromide (CTAB), was noticed in the post-CMC region leading toward a limiting reaction rate, and the Menger−Portonoy pseudophase model was employed to explain the behavior with evaluation of the binding parameter. The nonionic surfactant poly(oxyethylene) (20) sorbitan monolaurate (Tween 20) exerts inhibition effect on the hydrolysis reaction which may be explained qualitatively by the dearth of HO − ions in the vicinity of the micelle-bound dye and quantitatively in light of the pseudophase model. Different equilibrium constants and binding constant parameters suggest appreciable binding between the dye and surfactant monomer/micelles owing to electrostatic/hydrophobic interactions.

Evidence of formation of dye–surfactant ion pair micelle in the anionic surfactant mediated alkaline fading of methyl violet carbocation

“…The normal CMC values for SDS and AOT in the presence of MV + are 4.75 and 1.93 mM, respectively. These CMC values are comparable to the values of 7.26 mM for SDS and 2.76 mM for AOT in an aqueous medium as studied in our recent investigation 29 . The small decrease in the CMC values of both SDS and AOT in the presence of MV + compared to that in the aqueous medium may be accounted for by the fact that as the system approaches the normal CMC value the free ionic species of the dye molecule increases the polarity of the medium which possibly lowers the CMC values of both the surfactants.…”

“…Since the medium is a cationic dye solution, there is a high possibility of the formation of ion pair with the addition of the anionic surfactant through electrostatic interaction as found in the previous reports 29 . A small number of such ion pairs tend to aggregate to form ion‐pair micelles or premicelles.…”

“…The CMC values of SDS and AOT in the presence of MV + obtained by tensiometric measurements are 4.75 and 1.93 mM, respectively. Such a kind of premicellar rate inhibition has been observed in a limited number of studies 18,29 . The dependence of fading reaction rate on the surfactant concentration was studied at four different temperatures, namely, 293, 298, 303, and 308 K by varying the concentration of SDS and AOT (0–2.5) mM in the reaction medium.…”

Environmental risks and toxicity of surfactants: overview of analysis, assessment, and remediation techniques

“…The pre-treatment procedure includes the mixture of extraction and or preconcentration of the analytes in the samples (van Os et al 1993;Wu et al 2020). Traditionally, the conductivity, surface tension, and intensity of fluorescence are indicators to determine the critical micelles concentration of surfactants (Scholz et al 2018;Ghosh et al 2020). However, this method is tedious and time-consuming and requires a large sample size (Harkins and Introduction 1947;Cui et al 2014).…”

Rational Design of Functional and Tunable Nanozymatic Networks

“…With the increase of the inhibitor SDS concentration, the inhibition effect became more evident (Figure S6). In this case, the inhibition was supposed to be ascribed to the electrostatic attraction between inhibitor and the cobalt center (zeta potential: 5.5 mV), [50][51][52] which reduced the active site density. This phenomenon was also observed in catalysts with other metal atom as the active center (Figure S7).…”