*5.3.3.4 H2SO4*

The activation method involves the diffusion of H2SO4 into a char matrix, which prevents the formation of tar substances and promotes the development of oxygencarbon functional groups on the surface of activated carbon [53]. However, the yield of carbon obtained by this method is typically low due to the carbon burn-off caused by the water vapor generated during H2SO4 dehydration [54]. The chemical equation for the reaction between H2SO4 and carbon is:

$$2\text{H}\_2\text{SO}\_4 + \text{C} \to 2\text{SO}\_2 + \text{CO}\_2 + 2\text{H}\_2\text{O}.\tag{4}$$

*5.3.3.5 NaOH*

The following reactions may occur during NaOH activation:

$$\text{6NaOH} + \text{C} \to 2\text{Na} + \text{3H}\_2 + 2\text{Na}\_2\text{CO}\_3.\tag{5}$$

$$\text{Na}\_2\text{CO}\_3 + \text{C} \to \text{Na}\_2\text{O} + 2\text{CO}\_2.\tag{6}$$

$$2\text{Na} + \text{CO}\_2 \to \text{Na}\_2\text{O} + \text{CO}.$$

The chemical reactions between alkaline, carbonate metals, CO, CO2, and H2 gases have a crucial impact on the development of microporosity and mesoporosity and the stabilization and enlargement of pores in activated carbon. The ratio of NaOH to char is a significant determinant of BET surface area and pore volume, which consequently influences adsorption capacity [55]. An increase in the NaOH to char ratio can enhance adsorption capacity, but an excessive amount of NaOH can damage the carbon structure, decrease the BET surface area and adsorption capacity, and reduce carbon yield due to the gasification reaction of NaOH and the deposition of excessive amounts on the carbon pore wall [56]. The activation process leads to the formation of an irregular pore structure, as shown in **Figure 6**, in activated carbon.

**Figure 6.** *Irregular pore structure of activated carbon, as a result of its activation treatment [57].*
