In this blog post, we’ll explore the characteristics and applications of carbon materials used in the environmental field, with a particular focus on activated carbon fibers.
What are activated carbon fibers?
Have you ever used charcoal at home to purify the air? Charcoal is made by burning wood; it consists mostly of carbon and has a large surface area due to its numerous pores. The principle behind air purification is that odors and pollutants enter these pores and adhere to the surface. The fact that even a small piece of charcoal has a very large effective surface area helps us understand the powerful adsorption capacity of activated carbon.
Applying this principle, scientists have developed an artificial carbon material—activated carbon fiber (ACF)—that possesses a surface area far greater than that of charcoal and superior adsorption capacity. Activated carbon fiber is also manufactured through a process that activates a precursor fiber; it is characterized by a dense, porous structure and polar functional groups on its surface, such as -OH (hydroxyl) and -COOH (carboxyl). Functional groups are atomic groups within a molecule that exhibit specific properties; the surface functional groups of activated carbon fiber facilitate chemical bonding with pollutants.
Adsorption is broadly categorized into physical adsorption (binding due to intermolecular forces) and chemical adsorption (ionic bonding, covalent bonding, etc.), and both types occur in activated carbon fiber. Contaminants are drawn into the microscopic pores and held in place by physical forces, while simultaneously forming chemical bonds with the surface functional groups. Since the number of pores per unit area is much higher than that of charcoal, it can bind more contaminants per unit weight, resulting in significantly superior purification capacity.
Examples of Activated Carbon Fiber Applications in the Environmental Sector
Chemical plants around the world recover and reuse hazardous solvents. Since chlorine- and fluorine-containing solvents—used in the cleaning of semiconductor materials and precision equipment—can deplete the ozone layer, recovery processes are essential. These recovery processes utilize two cylindrical adsorption towers made of activated carbon fiber. While one tower adsorbs the solvent, the other is passed through heated steam to desorb, concentrate, and recover the adsorbed solvent; by operating the two towers alternately, the solvent can be recovered continuously.
Large amounts of sulfur oxides (SOx) and nitrogen oxides (NOx) emitted from thermal power plants cause smog and contribute to acid rain. While conventional processes have faced issues such as poor reaction rates at low concentrations or byproducts clogging reaction tubes, the process using activated carbon fibers offers an alternative approach. Sulfur oxides and nitrogen oxides are adsorbed into the microscopic pores of activated carbon fibers, where they react with oxygen and moisture in the air and are ultimately converted into substances such as sulfuric acid. Furthermore, when iron oxide is dispersed on the surface of the activated carbon fibers, it draws the gases into the micropores and promotes a reaction that reduces them to nitrogen, thereby aiding in the removal of NOx. Such ACF-based processes can mitigate the clogging and reaction rate issues inherent in existing methods and accelerate the reaction.
Activated carbon-based materials are also used to respond to oil spills. Since South Korea relies on imported crude oil, there is a risk of spills occurring during maritime transport; traditionally, the spread of oil has been contained and treated using oil booms, oil-absorbent paper, and surfactants. Recently, expanded graphite—a type of activated carbon fiber—has garnered attention. This material, produced by expanding natural graphite, can absorb crude oil equivalent to 85 times its own volume and demonstrates the ability to absorb approximately 75% of heavy oil. Although its adsorption performance is about eight times better than that of currently widely used adsorbents, its high manufacturing costs limit its commercialization. If research to reduce unit costs continues, it is highly likely to establish itself as a more effective oil adsorbent.
Future Challenges and Prospects
As described, activated carbon fibers have a wide range of potential applications in the environmental sector, including air and gas purification, solvent recovery, and oil spill cleanup. Since research in some areas is still limited, there is significant room for further development. In particular, if research to reduce manufacturing costs and ensure process stability is conducted in parallel, activated carbon fibers and related carbon materials will become key materials for solving various environmental problems in the future.
