Electronic structure and photocatalytic mechanism of graphitic carbon nitride modified with plasmonic Ag@SiO2 core-shell nanoparticles by X-ray adsorption spectroscopy
Yu-Cheng Huang1*, Jeng-Lung Chen3, J. Chen5, Shaohua Shen5, W. Y. Lee1, Y. X. Chen1, Ying-Rui Lu1, Wu-Ching Chou4, Chung-Li Dong2
1Program for Science and Technology of Accelerator Light Source, National Chiao Tung University, Hsinchu, Taiwan
2Department of Physics, Tamkang University, New Taipei City, Taiwan
3National Synchrotron Radiation Research Center (NSRRC), Hsinchu, Taiwan
4Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
5Xi’an Jiaotong University Xi’an, Shaanxi, China
* presenting author:Yu-Cheng Huang, email:waney200@yahoo.com.tw
In order to enhance photocatalytic solar hydrogen evolution under visible light, graphitic carbon nitride (g-C3N4) modified with plasmonic Ag@SiO2 core-shell nanoparticles are fabricated. The SiO2 shell generates the nanogap separating the plasmonic Ag nanoparticles and g-C3N4. By controlling the size of nanogap (ranges from 8 to 21 nm), different photocatalytic activities are observed. The highest performance of hydrogen generation is obtained in the g-C3N4/Ag@SiO2 with nanogap around 12 nm. In this system, plasmon resonance energy transfer (PRET) and energy-loss Förster resonance energy transfer (FRET) are both induced by localized surface plasmon resonance (LSPR). The former increases while the latter decreases the photocatalytic ability. In situ x-ray absorption spectroscopy (XAS) are employed to investigate the electronic structure of these photocatalysts. The C and N K-edge are conducted to reveal the density of unoccupied states in the conduction band and how these states vary under the light irradiation and in the dark condition. In situ XAS directly probes the charge redistribution dynamic and indicates the shift of conduction band edge and modification of density of unoccupied states is responsible for the improved photocatalytic activity. A tradeoff between PRET and FRET by controlling the SiO2 thickness is critical for the photocatalytic performance of g-C3N4/Ag@SiO2.

Keywords: Localized surface plasmon resonance, X-ray absorption spectroscopy, Photocatalytic mechanism, Solar hydrogen evolution