**3. Applications of g-C3N4 materials**

#### **3.1 Friedal: crafts reaction**

Friedel–Crafts reactions are a type of aromatic C–H activation reaction that is known to be one of the least environmentally friendly industrial processes, creating roughly 88 percent waste. AlCl3 boosted the standard version. According to Goettmann et al. [9] that meso-g-C3N4 is an important Lewis base catalyst allowed for some quite strange aromatic substitution reactions to take place. A Friedel–Crafts type that has been generalized. This metal-free catalyst is not just good for the

environment. Only environmentally friendly alkylation agents, such as alcohols or acids, but they also showed unexpected reactivity in the direction of urea and quaternary ammonium compounds.

### **3.2 Selective oxidation reaction**

The selective oxidation of hydrocarbons using pure oxidants is an important step in the synthesis of a wide range of products, from commodity chemicals to specialty medications. Chen et al. [10] proved that the Fe/g-C3N4 catalyst was capable of converting benzene to phenol without the use of hydrogen peroxide. The yield of phenol synthesis might be significantly increased by utilizing the photocatalytic capabilities of g-C3N4. Su et al. [11] demonstrated that under visible light irradiation, meso-g-C3N4 can operate as a photocatalyst to activate O2 for the selective oxidation of benzyl alcohols.

#### **3.3 Oxygen reduction reaction in fuel cells**

Fuel cells have sparked a lot of interest since they provide cleaner, more sustainable energy. The high cost of Pt catalyst and the slow kinetics of ORR now limit the practical applications of fuel cells. Carbon compounds containing nitrogen, such as g-C3N4, are worth exploring because they give enough active sites for ORR. However, the low electron transport of g-C3N4 limits its electrocatalytic effectiveness. One option for addressing this issue is to use conductive carbon materials as a support to boost electron accumulation and consequently electrocatalytic performance. Lyth et al. employed g-C3N4 as an oxygen reduction catalyst and discovered that, while the electrocatalytic activity of g-C3N4 was higher than pure carbon, the current densities were low, presumably due to its low surface area. It was discovered that combining C3N4 with carbon black boosted current densities. Yang et al. used nanocasting to make graphene-based C3N4 (G-CN) nanosheets. The G-CN nanosheets had a high nitrogen content and a large specific surface area, and their electrical conductivities were improved.
