In situ temperature measurements of reaction spaces under microwave irradiation using photoluminescent probes

Abstract

We demonstrate two novel methods for the measurement of the temperatures of reaction spaces locally heated by microwaves, which have been applied here to two example systems, i.e., BaTiO₃ particles covered with a SiO₂ shell (BaTiO₃–SiO₂) and layered tungstate particles. Photoluminescent (PL) probes showing the temperature-sensitivity in their PL lifetimes are located in the nanospaces of the above systems. In the case of BaTiO₃–SiO₂ core–shell particles, rhodamine B is loaded into the mesopores of the SiO₂ shell covering the BaTiO₃ core, which generates the heat through the dielectric loss of microwaves. The inner nanospace temperature of the SiO₂ shell is determined to be 28 °C higher than the bulk temperature under microwave irradiation at 24 W. On the other hand, Eu³⁺ is immobilized in the interlayer space of layered tungstate as the PL probe, showing that the nanospace temperature of the interlayer is only 4 °C higher than the bulk temperature. This method for temperature-measurement is powerful for controlling microwave heating and elucidates the ambiguous mechanisms of microwave special effects often observed in chemical reactions, contributing greatly to the practical application of microwaves in chemistry and materials sciences.