Xingxing Li,Zaiyin Huang,Zuojiao Liu,Kaisheng Diao,Gaochao Fan,Zhan Huang,Xuecai Tan
Much effort has been expended recently to investigate photocatalytic mechanisms by in situ spectroscopy. We introduced an alternative method to study photocatalysis thermodynamically by tracing thermodynamics and kinetics in real-time using a light-emitting diode photocalorimeter that includes a commercial microcalorimeter and fiber optics. We were almost able to adjust its baseline to zero by tuning the incident light intensity. After calibration, we used the photocalorimeter to trace heat changes and kinetics in the photocatalysis of methylene blue over a visible-light-driven Ag@AgCl photocatalyst. Three main heat changes occurred: (і) photoresponse of methylene blue molecules and photocatalyst, (іі) balance between endothermic photoresponse and pollutant photodegradation, and (ііі) stable exothermic stage in pollutant photodegradation. The photocalorimeter underwent an initial endothermic reaction and a subsequent exothermic stage, and finally maintained a stable exothermic rate of −(0.1543 ± 0.0446) mJ s −1 with a pseudo-zero-order process. The heat effects of stages (і), (іі), and (ііі) are 73.8, 143.9, and −1939.2 mJ, respectively. The photocatalytic mechanism was discussed in detail. Results from this study are critical to the development of promising applications in in situ photochemistry, physics, and biomedicine.
Photothermal sensing is crucial for the creation of smart wearable devices. However, the discovery of luminescent materials with suitable dual-wavelength emissions is a great challenge for the construction of stable wearable optical fibre temperature sensors. Benefiting from the Mn 2+ -Mn 2+ superexchange interactions, a dual-wavelength (530/650 nm)-emitting material Li 2 ZnSiO 4 :Mn 2+ is presented via simple increasing the Mn 2+ concentration, wherein the two emission bands have different temperature-dependent emission behaviours, but exhibit quite similar excitation spectra. Density functional theory calculations, coupled with extended X-ray absorption fine structure and electron-diffraction analyses reveal the origins of the two emission bands in this material. A wearable optical temperature sensor is fabricated by incorporating Li 2 ZnSiO 4 :Mn 2+ in stretchable elastomer-based optical fibres, which can provide thermal-sensitive emissions at dual- wavelengths for stable ratiometric temperature sensing with good precision and repeatability. More importantly, a wearable mask integrated with this stretchable fibre sensor is demonstrated for the detection of physiological thermal changes, showing great potential for use as a wearable health monitor. This study also provides a framework for creating transition-metal-activated luminescence materials.
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