**4.6 Bromine doping**

A bromide doped graphite phase carbon nitride technique was proposed by Lan et al. [24]. While preserving the core structure of Triazine as the main component of the material, bromine alteration can increase the optical, conductance, and photocatalytic capabilities of g-C3N4. **Figure 6** depicts the photocatalytic mechanism of the CN-Br photocatalyst. The process can be used to modify a variety of g-C3N4 precursors, including urea, dicyandiamide, ammonium thiocyanate, and thiourea. This work also demonstrates a viable method for rationally designing and synthesizing g-C3N4-based photocatalysts.

Element doping can significantly improve catalytic performance, particularly for visible light. However, there are some drawbacks that cannot be overlooked, such as the lengthy preparation procedure, increased production costs, and decreased industrial production.

### **Figure 4.**

*(a) Schematic diagram illustrating the synthesis of phosphorus-doped carbon nitride quantum dots (CNPQDs). (b) Steady-state PL spectrum of CNPQDs and carbon nitride quantum dots (CNQDs) in water. Inset showing fluorescence of CNPQDs sample under UV light irradiation. (c) N and P CPMAS NMR spectra of CNPQDs. (d-e) the preparation of CNPQDs decorated square-shaped TNTAs. Reproduced with permission [21]. Copyright 2019, Wiley-VCH.*

#### **Figure 5.**

*Schematic of synthesizing N-vacant iodine doped mesoporous g-C3N4 nanosheets. Reproduced with permission [23]. Copyright 2019, Royal Society of Chemistry.*

#### **Figure 6.**

*Photocatalytic mechanism of CN-Br photocatalyst. Reproduced with permission from [24]. Copyright 2016, Elsevier.*
