Superhydrophilic COFs with D–A structure accelerate photocatalytic synthesis of H₂O₂using water as a proton supply reservoir.

As a green, visible-light-driven metal-free semiconductor material, graphitic carbon nitride (g-C₃N₄) has generated tremendous significance in the fields of environmental purification and energy conversion. Inducing a polarization effect by creating defects in g-C₃N₄ is a promising strategy for improving photocatalytic properties. The polarization effect in photocatalysts could be created by manufacturing vacancies, doping impurity atoms, constructing heterostructure, etc. Recently, defective g-C₃N₄ has attracted wide attention due to its remarkable performance in the separation and migration of photogenerated charge carriers. However, the relationship between defects and the polarization effect remains to be clarified in terms of improving the photocatalytic performance. In this minireview, we summarize the recent advances on how the polarization effect and defect engineering expedite the photogenerated carrier migration and separation to improve the photocatalytic properties of g-C₃N₄. Is it pure synergy or is there some degree of antagonism? Ultimately, the major challenges for simply constructing the polarization effect and internal electric field in g-C₃N₄ and inspiring perspectives for future opportunities in polarization-defect type photocatalysis are discussed. It is believed that this work can provide a new idea for the design of novel and efficient photocatalysts in the future.

Inspired by electric field engineering applied to photocatalysts, herein, the synergy of highly crystalline and surface polarization electric field generated by introducing fluorine (F) atoms in graphitic carbon nitride (g-C₃N₄) played a crucial role in enhancing charge separation. Systematic experiments and theoretical analysis proved that the introduction of F atoms with the most electronegativity can effectively induce charge density promotion to generate high-crystallized g-C₃N₄, which usefully enhance the charge conductivity, thus boosting the charge transfer on the C–F bond, forming a surface polarization electric field. This field is favorable for the separation of holes and electrons, finally increasing the charge density and further improving the crystallinity. Therefore, the improved photodegradation performance of F-doped g-C₃N₄ for phenol, bisphenol A, diclofenac sodium, and methylene blue under simulated solar irradiation are attributed to the synergistic effect of high crystallinity and surface polarization electric field. This work provides an innovative strategy that could combine the crystal structure with electric field engineering, and may stimulate in-depth insights for green degradation.

High crystallinity and extended conjugated system improve the polarization of O-doped g-C ₃ N ₄ , which efficiently promotes carrier separation.

Photocatalytic self-Fenton technology is regarded as a promising strategy for the removal of pollutants in wastewater, and the in situ H₂O₂ production rate is one of the main factors affecting contaminant degradation performance. However, insufficient utilization of molecular oxygen results in poor activity in photocatalytic H₂O₂ production. Herein, we propose a single-layer BiOCl nanoflower induced by biosurfactant with surface micelles to increase the oxygen adsorption and reduction rate. The DFT results demonstrated that hydrophobic groups (–CH₂–) on the surface of micelles increased the O₂ adsorption sites and then expanded the O₂ adsorption capacity of BiOCl samples, which was also confirmed by the enhancement of the O 1s peak intensity in the XPS spectra. The charge concentrated on the micelle surface can accelerate the reduction of molecular oxygen to reactive oxygen species, thus enhancing H₂O₂ production to reach 108.6 μM within 60 min in pure water. Simultaneously, single-layer BiOCl increased the utilization rate of H₂O₂ by decreasing the decomposition of H₂O₂ itself, resulting in a 16.8-fold increase in sulfamethoxazole degradation efficiency. These results can inspire further developments in the photocatalytic degradation of antibiotics based on in situ H₂O₂ production.

A schematic mechanism of the photocatalytic degradation process of SMX by solvothermal synthesis of hydrogen-bonded organic framework materials.