**5.2 Carbonization**

The thermal decomposition of biomass material at a temperature range of 600-800°C in an inert atmosphere is known as carbonization, which produces a fixed mass of carbon [39]. The most commonly used gas during carbonization is N2 because of its cleanliness, ease of handling, and low cost [40]. Thermal decomposition eliminates moisture, low molecular weight substances, and non-carbon elements such as H2, N2, O2, and S from the biomass precursor [41]. The carbonization process involves heating the biomass material in an electric furnace to the carbonization temperature while maintaining an inert gas flow rate, followed by cooling the produced biochar to room temperature before the activation stage. The key factors that influence the carbonization process include carbonization temperature, carbonization time, heating rate, and flow rate of the inert gas [42].

#### **5.3 Activation**

The activation process is designed to increase the porosity and surface area of activated carbon derived from biomass (**Figure 5**). The type and degree of the activation process can affect the physical and chemical properties, as well as the yield of biomass-based activated carbons [42]. The activation process involves the opening of

**Figure 5.** *Activation of the porosity.*

inaccessible pores, the development of new pores, and the widening of existing pores, leading to increased porosity. Three methods are used for activating carbonized biomass materials: physical, chemical, and physiochemical activation. Physical activation employs steam, N2, air, or CO2 as activating agents, while chemical activation uses different chemical agents such as ZnCl2, KOH, NaOH, HNO3, H2SO4, K2CO3, and H3PO4, and physiochemical are physical and chemical methods [15]. During carbonization, tar products fill the pore structures of the carbon material, obstructing their openings. To enhance porosity and remove these obstructions, activation is necessary, as depicted in **Figure 5**.
