Abstract
The rate of electron transfer is critical in determining the efficiency of photoenergy conversion systems and is controlled by changing the relative energy gap of components, their geometries, or surroundings. However, the rate of electron transfer has not been controlled by the remote input of an external field without changing the geometries or materials of the systems. We demonstrate here that an applied microwave field can enhance the photocatalytic reduction of bipyridinium ion using CdS quantum dots (QDs) by accelerating electron transfer. Analysis of the time-resolved emission decay profiles of CdS quantum dots immersed in aqueous solutions of bipyridinium exhibited the shortening of their emission lifetimes, because of the accelerated electron transfer from QDs to bipyridinium under microwave irradiation. This discovery leads us to a new methodology using microwaves as an external field to enhance photocatalytic reactions.
Highlights
The mechanism of microwave heating in which the alternating electromagnetic fields interact with substances
Because SiO2 particles with anchored CdS quantum dots (QDs) were dispersed in the reaction solution by ultrasonication before starting the reaction and the solutions were not stirred during the experiments, they were sinking during the reaction time
According to Marcus theory, electron transfer rates depend on the electronic coupling matrix element related to the electron orbital overlap of the donors and acceptors (HAB2) and the reorganization energy (λ ), which is described as follows: k ET
Summary
The mechanism of microwave heating in which the alternating electromagnetic fields interact with substances. Microwave non-thermal effects have been extensively studied in the organic synthesis field and in reactions at solid surfaces in several systems. Our group reported[14] that the dechlorination reactions of an organohalide by Fe particles were accelerated under microwave heating compared with those reactions performed under conventional heating. These observations of the enhanced reaction rates under microwaves have led us to a hypothesis that the electron transfer reaction occurring at the interface between a solid surface and a liquid phase is accelerated by microwaves, which may be the origin of the microwave non-thermal effect observed in redox reactions. This study exhibits a direct evidence of microwave non-thermal effects observed as the acceleration of electron transfer
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