Tracking the Seconds of a Clock Reaction: A Multiparametric Experimental Study on the Catalytic Reduction of Methylene Blue

Abstract

The catalytic reduction and subsequent reoxidation of methylene blue (MB) is a well-known reaction, commonly referred to as a "clock reaction". Specifically, the reduction process is accompanied by a color change from intense blue to clear and can be readily monitored by UV−vis spectroscopy via the decrease in absorbance at λ max = 664 nm, providing facile access to valuable reaction kinetics. Unsurprisingly, the reduction of methylene blue has become a widely used probe for heterogeneous catalyst reactivity. Yet, despite its broad utility, the mechanism of reduction is not well-understood. Herein, we report an experimental study on the mechanism of MB reduction using Pt/C nanoparticles. Through a multiparametric study incorporating in situ probing of reaction kinetics, pH, dissolved oxygen, and variable catalyst and reductant loading, the multiple factors impacting the reaction are disentangled. We demonstrate that the reaction steps that limit the reduction of MB are the H 2 evolution and reoxidation sequences. We limit these competitive reactions by optimizing reductant concentration and catalyst loading, N 2 purging, and restriction of O 2 redissolution. This achieves a highly competitive activity parameter of 25,740 min −1 g Pt −1 L.

Poly(ionic liquid)-Flocculated Chlorella Loading Bactericidal and Antioxidant Hydrogel as a Biological Hydrogen Therapy for Diabetic Wound Dressing

“…H 2 release from the flocculated Chlorella and HAP-Chl hydrogels was measured using methylene blue (MB) as an H 2 probe. MB can be reduced by H 2 to induce an absorption decrease at 664 nm in the UV spectrum . First, an MB standard curve was plotted.…”

“…MB can be reduced by H 2 to induce an absorption decrease at 664 nm in the UV spectrum. 45 First, an MB standard curve was plotted. H 2 production by Chlorella was studied first.…”

Exfoliated MXene–AuNPs hybrid in sensing and multiple catalytic hydrogenation reactions

“…One of the water pollutants that endangers the aquatic ecosystem is the cationic MB dye, which depletes the water's dissolved oxygen. The reduction of MB and subsequent leucomethylene blue (LMB) [54] formation can be monitored through UV-vis spectrophotometry in the hybrid structure CIT-AuNPs@MXene. This is evidenced by a reduction in absorbance at λ max = 662 nm for MB and a corresponding rise at λ max = 260 nm, indicating the formation of LMB (figure 5(c)).…”