Kinetics and Mechanism of Cationic Micelle/Flexible Nanoparticle Catalysis: A Review

Abstract

The aqueous surfactant (Surf) solution at [Surf] > cmc (critical micelle concentration) contains flexible micelles/nanoparticles. These particles form a pseudophase of different shapes and sizes where the medium polarity decreases as the distance increases from the exterior region of the interface of the Surf/H 2 O particle towards its furthest interior region. Flexible nanoparticles (FNs) catalyse a variety of chemical and biochemical reactions. FN catalysis involves both positive catalysis (i.e. rate increase) and negative catalysis (i.e. rate decrease). This article describes the mechanistic details of these catalyses at the molecular level, which reveals the molecular origin of these catalyses. Effects of inert counterionic salts (MX) on the rates of bimolecular reactions (with one of the reactants as reactive counterion) in the presence of ionic FNs/micelles may result in either positive or negative catalysis. The kinetics of cationic FN (Surf/MX/H 2 O)-catalysed bimolecular reactions (with nonionic and anionic reactants) provide kinetic parameters which can be used to determine an ion exchange constant or the ratio of the binding constants of counterions.

Bifunctional carbon dots as cocatalyst and reactor decorating an organic photocatalyst for H2 production from water-splitting in an emulsion

“…Furthermore, the larger concentration of SDS that leads to the larger concentration of micelles is not beneficial for the reaction kinetics according to the PIE model. 43 In Fig. 6b, when SDS is replaced with CDs, the diameters of the emulsion droplets increase with the increase of CDs content instead, suggesting that more water is combined in the emulsion droplets.…”

“…51 According to the PIE model, the apparent reaction kinetics should increase monotonously. 43 However, the monotonous increase only occurs when the ratio of CDs/p(DB) changes from 1% to 5%. This can be ascribed to the factor that apart from serving as the emulsifying agent, CDs also act as the cocatalyst and excessive CDs will occupy the active sites on p(DB), resulting in a worse photocatalytic performance.…”

“…Moreover, according to the pseudo-phase ion exchange (PIE) model, the change trend of H 2 evolution with the mass of SDS can be explained from the perspective of reaction kinetics. 43 Because photocatalytic water-splitting occurs at oil–water interfaces, the rate constant for the reaction occurring in the bulk water phase is larger than that in the micellar pseudo-phase. When the concentration of micelles ([M]) is larger than the critical micelle concentration, the apparent rate constant of H 2 ( K obs ) is a monotonically decreasing function with [M].…”