Downshift of the Ni d band center over Ni nanoparticles in situ confined within an amorphous silicon nitride matrix
DALTON TRANSACTIONS(2024)
摘要
Herein, nanocomposites made of Ni nanoparticles in situ distributed in an amorphous silicon nitride (Ni/a-Si3N4) matrix, on the one hand, and within an amorphous silicon dioxide (Ni/a-SiO2) matrix, on the other hand, were synthesized from the same Ni-modified polysilazane precursor. In both compounds, the Ni/Si atomic ratio (0.06-0.07), average Ni nanocrystallite size (7.0-7.6 nm) and micro/mesoporosity of the matrix were rigorously fixed. Hydrogen (H-2)-temperature-programmed desorption (TPD) profile analysis revealed that the activation energy for H-2 desorption at about 100-130 degrees C evaluated for the Ni/a-Si3N4 sample (47.4 kJ mol(-1)) was lower than that for the Ni/a-SiO2 sample (68.0 kJ mol(-1)). Mechanistic study with X-ray photoelectron spectroscopy (XPS) analysis and density functional theory (DFT) calculations revealed that, at Ni nanoparticle/matrix heterointerfaces, Ni becomes more covalently bonded to N atoms in the a-Si3N4 matrix compared to O atoms in the a-SiO2 matrix. Therefore, based on experimental and theoretical studies, we elucidated that nickel-nitrogen (Ni-N) interactions at the heterointerface lead to remarkable Ni d band broadening and downshifting of the d band center relative to those generated by Ni-oxygen (Ni-O) interactions at the heterointerface. This facilitates H-2 desorption, as experimentally observed in the Ni/a-Si3N4 sample.
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