Enhanced Solar Utilization Implemented by Defect Engineered Graphitic Carbon Nitrides
- Publication Type:
- Thesis
- Issue Date:
- 2022
Open Access
Copyright Clearance Process
- Recently Added
- In Progress
- Open Access
This item is open access.
Graphitic carbon nitrides (g-C₃N₄) are emerging as promising photocatalysts for various solar applications. Nevertheless, the insufficient solar utilization of bulk g- C₃N₄ arising from poor visible light absorption and severe recombination of photo-generated electron-hole pairs remains a persisting challenge. Fortunately, defect engineering that aims to tailor the electronic band structure and optimize surface states has been regarded as an all-in-one strategy to address the above issues. Therefore, this PhD thesis focus on how the defects (dopants, vacancies, functional groups, crystallinity) would affect the solar light harvesting ability and photocarrier transfer of g- C₃N₄ towards solar H₂ evolution and photocathodic protection of metals.
We synthesized the S-doped and N vacant g- C₃N₄ (DCN-ES) with non-deteriorative surface states via a dual-solvent-assisted synthetic approach. The precise defect control was realized by the addition of ethylene glycol (EG) into precursor formation and molten sulfur into the pyrolysis process, which simultaneously induced DCN-ES with shallow defect states. This is critical to lower the electron excitation energy and moderately trap the electrons migrated from CB, further enhancing the solar harvesting ability and suppressing the bulky photocarrier recombination. Additionally, the optimized surface states were reflected by the highest electron-trapping resistance (Rtrapping) of 9.56×10³ Ω cm² and the slowest decay kinetics of surface carriers (0.057 s⁻¹), which guaranteed the smooth surface charge transfer rather than being the recombination sites. Therefore, DCN-ES exhibited a superior H₂ evolution rate of 4219.9 μmol g⁻¹ h⁻¹, which is 29.1-fold higher than unmodified g- C₃N₄.
We fabricated a high-pressure mediated crystalline g- C₃N₄ (CCN-P) with optimized spatial charge transfer via an ion thermal synthetic strategy. The presence of NaCl/KCl eutectic mixture significantly promoted the in-plane and cross-plane crystallinity of CCN-P while the high strain inside the precursor tablet further induced a narrower interlayered distance, and both situations enabled an accelerated bulky photocarriers transfer. More importantly, the high pressure rendered CCN-P with better surface states as the concentrations of -C≡N and -NHₓ were maintained at more reasonable levels in comparison to the crystalline g- C₃N₄ without high-pressure regulation (CCN-NP). Therefore, CCN-P exhibited the highest Rtrapping (11.36 kΩ cm²) and the slowest photocarrier decay kinetics (0.013 s⁻¹), leading to a dramatically suppressed surface photocarrier recombination. Along with its enhanced light harvesting ability, CCN-P delivered a superior photocatalytic H₂ evolution rate of 2168.8 μmol g⁻¹ h⁻¹ and excellent photocathodic protection of 304 stainless steels with a highest potential retention efficiency of 78.5% after 7500 s, far more exceeding bulk g-C₃N₄ and CCN-NP.
Please use this identifier to cite or link to this item: