Synthesis, Characterization, and Roles of Vacancy Defects in Polymer and Graphitized Carbon Nitride Photocatalysts: A...

Area of Science:

• Materials Science
• Photocatalysis
• Defect Engineering

Background:

• Graphitic carbon nitride (g-C3N4) and conjugated polyimide (PI) polymers are promising metal-free photocatalysts with suitable bandgaps.
• Their photocatalytic performance is limited by narrow visible light absorption and rapid charge carrier recombination.
• Vacancies, such as oxygen vacancies (OVs) in PI and nitrogen (NVs) and carbon vacancies (CVs) in g-C3N4, can improve electronic structure and photocatalytic efficiency.

Purpose of the Study:

• To review the synthesis, characterization, and applications of vacancy-rich PI polymers and g-C3N4 in photocatalysis.
• To examine the specific roles of OVs, NVs, and CVs in enhancing photocatalytic activity.
• To provide a framework for vacancy-engineered design and a guide for material synthesis and characterization.

Main Methods:

• Summarizes various preparation approaches for introducing vacancies before, during, and after polymerization.
• Reviews spectroscopic characterization techniques including EPR, XPS, PAS, XRD, FTIR, and NMR for vacancy defect analysis.
• Analyzes the impact of vacancies on light absorption, charge carrier separation, and transfer dynamics.

Main Results:

• Vacancies significantly enhance photogenerated electron migration and improve the electronic structure and band gap width of PI and g-C3N4.
• Defect engineering via vacancy introduction is crucial for boosting photocatalytic efficiency.
• Specific vacancies (OVs, NVs, CVs) play distinct roles in optimizing photocatalyst performance.

Conclusions:

• Vacancy-rich PI polymers and g-C3N4 show great potential for advanced photocatalytic applications.
• Understanding and controlling vacancy defects are key to designing highly efficient metal-free photocatalysts.
• This review serves as a comprehensive resource for researchers in the field of defect-engineered photocatalysis.