Acta Physico-Chimica Sinica ›› 2020, Vol. 36 ›› Issue (6): 1905087.doi: 10.3866/PKU.WHXB201905087

Special Issue: 热分析动力学和热动力学

• Article • Previous Articles     Next Articles

Temperature Effects on Photocatalytic Heat Changes and Kinetics via In Situ Photocalorimetry-Fluorescence Spectroscopy

Fanghong Qin1,Ting Wan2,Jiangyuan Qiu1,*(),Yihui Wang1,Biyuan Xiao1,Zaiyin Huang1,3,*()   

  1. 1 College of Chemistry and Chemical Engineering, Guangxi University for Nationalities, Nanning 530008, P. R. China
    2 The Sixth Geological Bureau, Xiaogan 432000, Hubei Province, P. R. China
    3 Guangxi Colleges and Universities Key Laboratory of Food Safety and Pharmaceutical Analytical Chemistry, Nanning 530008, P. R. China
  • Received:2019-05-31 Accepted:2019-07-17 Published:2019-07-19
  • Contact: Jiangyuan Qiu,Zaiyin Huang E-mail:gxqiujiangyuan@yeah.net;huangzaiyin@163.com
  • Supported by:
    the National Natural Science Foundation of China(21873022);the National Natural Science Foundation of China(21573048);Innovation Project of Guangxi Graduate Education, China(gxun-chxzs2018062)

Abstract:

The thermodynamics and kinetics of photocatalytic processes provide the scientific foundation for the optimization of reaction conditions and establishment of reaction mechanisms. Because of the limited availability of techniques that can provide in situ thermodynamics coupled with spectral information during photo-driven processes, research regarding the thermodynamics of the photo-driven processes is rare and in-depth studies on their kinetics remain inadequate. Herein, a novel photocalorimetry-fluorescence spectroscopy system composed of a photocalorimeter and laser-induced fluorescence spectrometer based on a 405 nm laser was developed. This system could simultaneously monitor the thermal and spectral information during photocatalytic processes, providing a correlation between nonspecific thermodynamic and specific molecular fluorescence spectral results. A highly efficient, bionic Z-type g-C3N4@Ag@Ag3PO4 nano-composite photocatalyst was developed and characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In situ thermodynamic and spectral kinetic information for Rhodamine B (RhB) degradation on g-C3N4@Ag@Ag3PO4 was obtained at five temperatures by synchronously monitoring the calorimetric and spectrometric results using the newly developed photocalorimetry-fluorescence spectroscopy system and the effects of temperature on various parameters were investigated. The catalytic decomposition comprised three stages at different temperatures: (ⅰ) photoresponse of RhB and photocatalyst, (ⅱ) competition between the endothermic photoresponse and exothermic RhB photodegradation, and (ⅲ) stable exothermic period of RhB photodegradation. The in situ heat flux and fluorescence spectra could be combined to estimate the concentration characteristics of the different photocatalytic reactions: (1) the spectral information suggested that the competitive endothermic and exothermic reactions followed first order kinetics, and the reaction rate constants (k) at five temperatures were calculated. The results also indicated that the degradation rate increased with increasing temperature. The activation energy at each temperature interval was determined, and yielded an average value of 23.82 kJ·mol−1. (2) The calorimetric results revealed that the subsequent stable exothermic period was a pseudo-zero-order process. The exothermic rates at 283.15, 288.15, 293.15, 298.15, and 303.15 K were determined to be 0.4668 ± 0.3875, 0.5314 ± 0.3379, 0.5064 ± 0.3234, 0.5328 ± 0.3377, and 0.5762 ± 0.3452 μJ·s−1, respectively. The novel photocalorimetry-fluorescence spectroscopy technique could concurrently obtain thermodynamic, thermo-kinetic, and molecular spectral information, allowing for the direct correlation of the thermodynamics, thermo-kinetics, and spectrokinetics with the underlying mechanisms of the reaction. This in situ technique integrated the thermal information with spectral information for improved understanding of the microscopic mechanisms of photo-driven processes, providing scientific support for the establishment of photothermal spectroscopy.

Key words: g-C3N4@Ag@Ag3PO4, Photocatalysis, Photocalorimetry-fluorescence spectroscopy, Thermodynamics, Temperature effect

MSC2000: 

  • O642