**Abstract**

Biomass is a renewable and eco-friendly energy source, which is easily regenerated, pollution-free, and widely available. It is also naturally carbonaceous and has low disposal costs. Biomass activated carbon (BAC) is a highly effective adsorbent that can remove a wide range of organic and inorganic pollutants, as well as polar and nonpolar compounds in aqueous or gaseous environments. Additionally, it is also utilized for energy storage purposes. Converting biomass into activated carbon for carbon dioxide (CO2) adsorption is a practical solution for managing solid waste and reducing anthropogenic greenhouse gas emissions. Activated carbon is a microporous form of carbon that possesses a well-developed high internal surface area, pore volume, pore structure, and surface chemistry. The production of biomass-derived activated carbons is dependent on pyrolysis temperatures and physical and chemical activation conditions, which can alter their surface characteristics and adsorption behavior. Literature indicates that biomass-derived activated carbons possess a high surface and adsorption capacity, making them a suitable option for environmental remediation and energy storage.

**Keywords:** biomass, biomass activated carbon, pyrolysis temperatures, activation, environmental remediation

## **1. Introduction**

Biomass has the potential to be transformed into solid, liquid, and gaseous biofuels, as well as certain chemicals to generate bioenergy. This is due to the renewability of biomass, which enables CO2-neutral conversion, making biofuel combustion widely accepted as not contributing to the greenhouse effect. The increasing focus on bioenergy as a *viable* alternative to fossil energy has been driven by concerns over global warming, which largely stems from the combustion of fossil fuels [1]. In recent years, there has been a significant global effort to shift toward biomass as an alternative to fossil fuels for energy production [2]. Biomass is a diverse group of materials that includes wood, woody biomass, herbaceous and agricultural biomass, aquatic biomass, animal and human biomass waste, semi-biomass, and biomass mixtures, all of which can be utilized to produce biofuels and biochemicals [3]. Currently, around 95–97% of the world's bioenergy is generated through direct biomass combustion, and many countries are exploring the potential of large-scale combustion of natural biomass and its co-combustion with semi-biomass and solid fossil fuels, such as coal,

peat, and petroleum coke, to promote biofuel adoption [4]. Numerous studies [5, 6] have been conducted worldwide to investigate the advantages and disadvantages of using biomass fuels for various thermochemical processes such as combustion, pyrolysis, gasification, and liquefaction, as well as biochemical processes such as anaerobic digestion, alcoholic fermentation, and aerobic biodegradation. Additionally, research has been conducted on co-combustion, co-pyrolysis, and co-gasification of biomass with other solid fuels. The main technologies for producing biochar and activated carbon from biomass are pyrolysis, carbonization, gasification, and torrefaction [7]. All of these technologies involve thermal treatment of the biomass under oxygenlimited conditions to increase the carbon content [8]. Pyrolysis refers to the process of thermally breaking down organic matter, such as sawdust, tire waste, and sewage sludge, in the absence of oxygen, typically within a temperature range of 400–800°C. During this process, the resulting primary products from biomass are commonly known as condensable (tars) and non-condensable volatiles, as well as char [9]. During pyrolysis, the moisture and light volatiles are initially released, followed by the aromatic components and hydrogen gas. The remaining solid residues form biochar, which possesses well-defined porous structures and abundant carbon content. The specific surface area, porosity, total pore volume, and surface chemical properties of biochar depend on the pyrolysis conditions such as the heating rate, pyrolysis temperature, and residence time, as demonstrated in previous studies [10]. In general, higher heating rates and temperatures result in lower biochar yields but a higher surface area and pore volume [11]. Higher temperatures also increase the ash and fixed carbon content, while decreasing the volatile matter.

Due to the rapid growth of the world's population, increased urbanization, agricultural demands, and industrial development, global biomass has significantly expanded. By 2030, the world's population is projected to reach 8.5 billion, and solid waste production is expected to reach 2.59 billion tons [12]. **Figure 1** illustrates the global distribution of research activities on converting biomass into biochar, as well as the research collaborations among different countries. Notably, China, India, South Korea, Australia, and Malaysia are among the countries that prioritize the efficient use of biomass resources to address environmental challenges and produce biochar as part of their energy development strategies.

#### **Figure 1.**

*Shows the bibliometric mapping of the conversion of biomass into biochar, as well as the research interrelations between various countries.*

The objective of this chapter is to provide a comprehensive summary and analysis of the recent advancements and research conducted on biomass resources, structure of biomass, and biomass-based activated carbons. This review will cover various preparation methods for biomass-based activated carbons and their applications.

## **2. Biomass resources**

Biomass resources encompass a wide range of materials, including wood waste, agricultural crops, industrial waste, municipal solid waste, animal waste, and byproducts from food processing. Annually, more than 140 billion metric tons of biomass waste are produced from agriculture alone, equivalent to approximately 50 billion tons of oil [13]. These materials can be utilized to produce renewable energy and fuels, referred to as bioenergy and biofuels. Through thermal and chemical treatment, agricultural waste can generate an array of valuable products, including biosolids, biogases, biooils, and biofuels [14]. The composition of the activated carbon derived from agricultural waste depends on whether it undergoes biochemical or thermochemical conversion processes [13]. Biomass is primarily composed of three natural fiber components: cellulose, hemicellulose, and lignin, with varying compositions depending on the material. Typically, cellulose, hemicellulose, and lignin make up 20–55 wt%, 20–45 wt%, and 15–35 wt% of biomass, respectively [15]. Activated carbon possesses desirable properties such as high porosity, excellent surface textural characteristics, and good adsorption capacity. **Figure 2** shows the chemical structures of cellulose, hemicellulose, and lignin, which are all components of lignocellulosic materials.

Agricultural waste is a plentiful, renewable, and eco-friendly resource that is also available at a low cost [17]. Examples of agricultural waste include bamboo waste [18], rattan sawdust [19], peanut hull [20], sesame seed shell [21], garlic peel [22], wood [23], cotton stalk [24], coffee grounds [25], almond shell [26], and waste tea [27]. Although activated carbon has numerous applications, there are certain limitations

**Figure 2.** *Lignocellulosic chemical structures of cellulose, hemicellulose, and lignin [16].*

that must be considered. In a study by Abbas and Ahmed [28], it was found that leaves are not suitable for activated carbon due to their low carbon content, high volume-toweight ratio, and ash content. Furthermore, research indicates that the digestibility of amorphous lignin is higher than that of biomass cellulose by the activating agent used in chemical activation. Thus, it is crucial to comprehend the properties of any substance utilized [17]. Activated carbon, which can be a promising CO2 adsorbent, can be produced from various materials, including carbonaceous raw materials, biomassbased residues, and lignocellulosic agricultural by-products [15].

## **3. Biomass-based activated carbon**

Biomass is an abundant energy source that possesses several desirable characteristics, including high porosity, renewability, ease of handling, storability, low pollution, wide availability, and inherent carbon content. Utilizing biomass energy has gained significant attention as a means of reducing carbon footprint [29]. In recent years, researchers have been actively exploring substitutes for solid adsorbents that are low in cost, easy to regenerate, and have a minimal environmental impact. Biomass-based adsorbents have emerged as a promising alternative. The choice of biomass for BAC production depends on the application area, such as wastewater treatment, supercapacitors, energy generation, and air pollution control [30]. The carbon content, such as cellulose, hemicellulose, and lignin, is a crucial criterion for selecting the appropriate biomass for pollutant removal processes, as these elements contribute to the porous structure of the BAC. Wood-type biomass, which contains wood biomass yields higher carbon content [31]. Cellulose is the most abundant lignocellulosic component in biomass, followed by hemicelluloses and lignin [32]. The carbon content of biomass varies depending on location and geographical conditions. Herbaceous biomass generally has a lower carbon content than wood-type biomass [33]. Lignocellulosic biomasses with unique characteristics are suitable for producing BAC in an easy and cost-effective manner. The energy required for activation is dependent on the properties of the biomass waste, including its structure and the chemical behavior of its constituents [34]. Selecting the appropriate biomass waste is crucial for BAC production while converting agricultural waste into value-added products. These factors impact the quality of the end product of BAC [35]. Thus, the next section will discuss the available carbonization methods for producing biochar from biomass and activation techniques.
