*5.3.5 Comparison among physical, chemical, and physiochemical activation*

The selection of an activation method for deriving activated carbon depends on the precursor's properties and the intended application [59]. Physical activation is often preferred for industrial-scale production due to its ability to optimize the pyrolysis stage and achieve better control over microporosity development [60]. Physical activation also results in activated carbon that does not require chemical neutralization, reducing both the process costs and associated pollution. Moreover, the higher physical strength of physically activated carbon makes them ideal for use in high-pressure

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

**Figure 7.** *Thermal treatment scheme of two-step physiochemical method for preparation of activated carbon [58].*

columns [61]. As a result, physical activation is commonly used to prepare activated carbon for water treatment.

In contrast, chemical activation offers lower activation temperatures, shorter treatment times, reduced energy requirements, and higher activated carbon yields with a larger surface area and pore volume [62]. However, the process and chemical costs associated with chemical activation are higher than those of physical activation [63]. The lower activation temperature and homogeneously developed internal micropores result in superior physical and chemical properties compared to physical activation [64]. Physical activation results in a nonuniform shape and pore development, leading to higher weight losses and lower yields compared to chemical activation. However, the physiochemical activation method can produce activated carbon with even higher specific surface area, porosity, and pore volume than chemical or physical activation due to improved diffusion mass transfer within the carbon matrix, providing superior adsorption capacity [65]. **Table 1** shows the optimal conditions for preparing biomass-based activated carbon using physical, chemical, or physiochemical activation methods and their corresponding maximum adsorption capacities.

## **6. Environmental remediation**

Activated carbon has a wide range of applications, including purifying water and gas, treating sewage, extracting metals, producing medication, storing energy, controlling air pollution, and facilitating catalytic processes. Water treatment and purification, which involve removing contaminants from liquid-phase drinking water, groundwater, and wastewater, are the most significant areas of demand for activated carbon globally. High-quality activated carbon can effectively eliminate phenols, organic and inorganic toxic compounds from both drinking water and wastewater. In addition, activated carbon materials are effective adsorbents for heavy metals such as Cr, Pb, Cu, Cd, Zn, and Hg and can remove a wide range of contaminants and carcinogenic compounds [78]. The use of activated carbon for gas purification is an effective and environmentally friendly method for removing gaseous pollutants from


#### **Table 1.**

*Preparation of activated carbon from biomass using either physical, chemical, or physiochemical activation method, properties, and maximum adsorption capacities.*

industrial and domestic emissions. It is widely used in various industries, including petrochemicals, food and beverage, pharmaceuticals, and semiconductor manufacturing. Activated carbon is also a promising candidate for capturing CO2, which contributes to climate change and poses a threat to human health. Activated carbon, derived from waste biomass materials, exhibits CO2 uptake that is comparable to that of commercial adsorbents. Due to its large inner surface area, it is regarded as the most promising adsorbent for CO2 capture. In addition to CO2, activated carbon can effectively adsorb various gaseous pollutants such as CH4, H2S, NO2, and H2, making it an effective adsorbent for air pollution control [79]. Despite its relatively low density, activated carbon can be used for hydrogen storage due to its high surface area, abundant pore volume, acceptable pore size, large microporosity, and controlled pore size distribution. Highly microporous activated carbon is a suitable candidate for hydrogen storage at 77 K [80]. Various biomass-based activated carbons have been synthesized for hydrogen storage applications, providing sustainable and environmentally friendly alternatives to traditional fossil fuel-based materials. Activated carbons with a high surface area of up to 2700 m<sup>2</sup> /g have been obtained [81]. Overall, the use of activated carbon for hydrogen storage is an active area of research with great potential for practical applications. As new applications are discovered and more

sources of raw materials are utilized for its production, the use of activated carbon is expected to continue to increase.
