**4. Activated carbon**

Activated carbon is a category of amorphous carbon-based materials that possess a high degree of porosity and a substantial surface area. The properties of activated carbon depend on the starting materials used and the conditions of activation, resulting in a wide range of activated carbons with specific uses. The most common method used to prepare activated carbon involves the carbonization of precursors at high temperatures in an inert atmosphere followed by activation. Activation can be achieved through physical, chemical, or physiochemical. Physical activation involves the treatment of char with oxidizing gases, such as steam or carbon dioxide, at high temperatures to create a porous structure [36]. Chemical activation involves impregnating a chemical agent with precursors and then heat-treating them in an inert

*Biomass-Based Activated Carbon DOI: http://dx.doi.org/10.5772/intechopen.111852*

**Figure 3.** *Structure of activated carbon.*

atmosphere to develop pores through dehydration and oxidation reactions. Activated carbons have various applications, including their use as adsorbents, catalysts, or catalyst supports. Activated carbons can be classified into gas-adsorbing and liquidphase carbons, based on their pore size distribution. **Figure 3** shows the pore structure of activated carbons is categorized into three groups based on pore size: micropores (pore size <2 nm), mesopores (pore size 2–50 nm), and macropores (pore size >50 nm), according to the International Union of Pure and Applied Chemistry classification [37]. Gas-adsorbing carbons have more pore volume in the micropore and macropore ranges, whereas liquid-phase carbons have significant pore volume in the mesopore or transitional pore range, allowing easy access for liquids to the micropore structure [30]. Activated carbons are widely used in industries, such as food processing, pharmaceuticals, chemical, petroleum, nuclear, and automobile, due to their high surface area and extensive internal pore structure. They are also commonly used in environmental processes for removing toxic gases and in wastewater and potable water treatments.
