Visible-Light Activation of Photocatalytic for Reduction of Nitrogen to Ammonia by Introducing Impurity Defect Levels into Nanocrystalline Diamond

• Main Authors: Rui Su, Zhangcheng Liu, Haris Naeem Abbasi, Jinjia Wei, Hongxing Wang
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: Materials
• Subjects: diamond; impurity levels; nitrogen vacancy center; solvated electrons; ammonia synthesis
• Online Access: https://www.mdpi.com/1996-1944/13/20/4559

Nitrogen impurity has been introduced in diamond film to produce a nitrogen vacancy center (NV center) toward the solvated electron-initiated reduction of N₂ to NH₃ in liquids, giving rise to extend the wavelength region beyond the diamond’s band. Scanning electron microscopy and X-ray diffraction demonstrate the formation of the nanocrystalline nitrogen-doped diamond with an average diameter of ten nanometers. Raman spectroscopy and PhotoLuminescence (PL) spectrum show characteristics of the NV⁰ and NV⁻ charge states. Measurements of photocatalytic activity using supraband (λ < 225 nm) gap and sub-band gap (λ > 225 nm) excitation show the nitrogen-doped diamond significantly enhanced the ability to reduce N₂ to NH₃ compared to the polycrystalline diamond and single crystal diamond (SCD). Our results suggest an important process of internal photoemission, in which electrons are excited from negative charge states into conduction band edges, presenting remarkable photoinitiated electrons under ultraviolet and visible light. Other factors, including transitions between defect levels and processes of reaction, are also discussed. This approach can be especially advantageous to such as N₂ and CO₂ that bind only weakly to most surfaces and high energy conditions.