Activated charcoal/carbon (AC) is a widely utilized adsorbent material with uses in a wide range of industries. For more than 2000 years, charcoal’s adsorption abilities have been widely recognized.
Activated carbon is powdered charcoal that has been purified. It is mechanically or chemically processed to create micro fissures that greatly enhance its adsorptive surface area. A broad variety of polar molecules, especially phenols and their derivatives, may be successfully adsorbate by their large surface areas (500-1500 m2/g) and electrical charge.
What is Activated Charcoal?
Activated carbon, often known as activated charcoal, is a porous material that traps organic chemicals in a gas or liquid. It is the most extensively used purifying agent by humans. Activated charcoal (or activated carbon) is made up of microscopic black beads or a solid black porous sponge. It’s utilized in water filters, medications that remove poisons selectively, and chemical purification procedures.
Charcoal is mainly carbon when heated in a low-oxygen atmosphere. Heat or chemical treatment “activates” the charcoal. High-temperature pyrolysis in an argon or nitrogen environment, or oxidation in heated oxygen or steam, are two methods of heating. Acids, strong bases, and salts are examples of chemical activators. The resultant material is riddled with small holes.
Activated charcoal is a microcrystalline, non-graphitic carbon with a porous structure that has been treated to increase its internal porosity.
Activated charcoal has a large porosity, a broad surface area, and a strong surface reactivity. Its huge number of very small holes (microspores) offers the activated charcoal a broad inner surface, which is the foundation of its exceptional adsorption characteristics. As a result, they are excellent adsorbents for a wide range of pollutant substances (organic, inorganic, microbial, and biological) in water and wastewater treatment.
Preparation of Activated Carbon
Any carboneous substance (animal, plant, or mineral origin) with a high carbon content can be easily converted into activated carbon (by chemical or gas activation processes). For the production of activated carbon, the most frequent raw materials include wood, charcoal, nut shells, fruit pits, brown and bituminous coals, lignite, peat, bone, and paper mill waste (lignin), as well as synthetic polymers such as PVC. Because charcoal derived from soft wood, such as pinewood, is highly unstable and easily crumbles, activated carbon obtained from hard wood is preferred for adsorption. The finest grades of AC have been reported to be derived from coconut shells and apricot pits.
Activated carbons are typically produced using two methods:
- Physical or gas activation
- Chemical activation.
The technique of activation used is also determined by the starting material and whether low or high density, powdered or granular carbon is required. In the gas activation method, raw material with less than 25% moisture is carbonized first at 400 – 500oC to remove the majority of the volatile matter, and then the carbon is exposed to oxidizing gases, usually carbon dioxide or steam at 800-1000oC or and with air at law temperature, for selective oxidation. Usually, the oxidation is preceded by a first carbonization of the source material.
Wood pyrolysis begins at around 225oC. Carbon is converted to CO2 by ambient oxygen, hence air should be removed or extremely tightly regulated during carbonizing and activating.
Classifications of Activated Charcoal
Activated charcoal/carbons (AC) are typically classified into three types depending on their physical properties.
Powdered Activated Carbon (PAC): Activated carbons are typically manufactured as powders or tiny granules with an average diameter of.15 to.25 mm. PAC is composed of crushed or ground carbon particles, 95-100% of which will pass through a sieve with a mesh size of 50 to 80.
Granular Activated Carbon (GAC): Granular activated carbon has higher particle size than powdered activated carbon. Because GAC has a smaller exterior surface area than PAC, it is sometimes claimed incorrectly that GAC has a smaller overall surface area. It should be noted that the surface area of activated carbon is primarily internal rather than exterior. GAC is preferable for all gas and vapor adsorption because its diffusion rates are quicker. Granulated activated carbons are also utilized for water treatment, deodorization, and component separation in a flow system.
Extruded Activated Carbon (EAC): Extruded or Pellet AC is made up of cylindrically formed activated carbon with diameters ranging from 0.8 to 45 mm. Because of the minimal pressure drop when the air/gas goes through, as well as the excellent mechanical strength and low dust content, they are commonly utilized for air/gas applications.
Impregnated Activated Carbon (IAC): These are porous activated carbons that have been impregnated with inorganic elements like iodine or silver, as well as cations like Al, Mn, Zn, Fe, Li, and Ca. These are used to clean flu gasses in coal-fired power plants or to manage air pollution in museums and galleries. Silver impregnated activated carbon is utilized as an adsorbent in earth-bound water filtration systems due to its antimicrobial/antiseptic qualities.
Polymers Coated Activated Carbon (PCAC): Activated carbons can be coated with a physiologically friendly polymer to provide a smooth, permeable coating that does not obstruct the pores. The generated PCAC can be used to improve hemoperfusion. Large amounts of blood are circulated over/through a bed of GAC or PCAC in AC hemoperfusion to eliminate harmful chemicals from the blood.
Activated Carbon Cloth (ACC): Activated carbon is also available in the form of cloths and fibers. The military use ACC for Nuclear Biological Chemical (NBC) protective garments, socks, and gloves. It is also utilized in wound dressings, protective masks, tarnish and deterioration prevention for antiques, oil mist filters for compressors, gas sensors, electrodes, water purification, and other applications.
Biochar Activated Charcoal (BAC): Biochar is the newest member of the activated carbon family. Biochar carbons are those created by a pyrolysis method with exceptionally low carbon emissions, a carbonization process that takes raw materials directly through to the activation stage in less than an hour depending on the temperature range. The pyrolysis process may be optimized to provide energy to power electrical turbines or biofuels. Both techniques produce low activity biochar with a high ash content.
Uses and Benefits of Activated Charcoal
- It absorbs toxins and overdoes from intake in medication. It does not work on ethanol, methanol, cyanide, iron, lithium, petroleum compounds, ethylene glycol, strong acids, or strong bases.
- It is a nonprescription medication used to treat gas and flatulence, diarrhea, indigestion, and skin infections.
- Activated charcoal filters volatile organic compounds and contaminants from water and air. Chlorine, chloramine, tannins, phenol, volatile odor-producing chemicals, and mercury compounds are also trapped. Ammonia, nitrates, nitrites, fluoride, salt, heavy metals, hydrocarbons, or microorganisms are not removed.
- It is also useful in spill cleaning and environmental remediation for the same reason.
- It is used in extraction and purification in analytical chemistry.
- It is used as a pesticide, disinfectant, feed addition, and processing aid in agriculture.
- Activated charcoal does not occur naturally in foods. It is, however, an additive that adds a smokey flavor and a black hue.
- A common deodorant is activated charcoal powder.
- It is used as an abrasive, whitener, and impurity remover in several toothpastes and skin treatments.
- Activated charcoal may or may not be beneficial in reducing hangover symptoms. While it does not eliminate alcohol, it does gather pollutants (congeners) that might aggravate a hangover.
Factors Affecting Activated Charcoal Effectiveness
Raw Materials: In general, bio-waste with a high carbon concentration is ideal for the manufacturing of AC. When selecting the raw material to generate activated carbon with a high degree of porosity, criteria such as low ash (inorganic), high carbon content, low degradation, economy, safety, low volatility, low moisture content, and high density should be considered. Because of their volatility, hardness, and high density, coconut shells and olive stones are the most commonly utilized economically.
Molecular Mass: Because the molecules are less soluble in water as the molecular weight increases, activated carbon’s adsorption capability increases. The carbon pore structure, on the other hand, should be big enough to allow molecules to flow within. A blend of low and high-molecular-weight molecules would be required to remove a higher number of difficult-to-remove particles.
Activation Temperature and Time: The activation process in commercial AC manufacturing is typically carried out at 800 °C. Several studies have found that increasing the temperature has an effect on surface area, volatile content, and AC generation. It also reduces the viscosity of the solution as the diffusion rate increases, resulting in an increase in the adsorption process. Adsorption is often increased by cold water since high temperatures can disrupt the adsorptive link, resulting in a modest reduction in adsorption depending on the organic chemical being removed. The production of AC and the volatilization of organic compounds from agricultural bio-waste are similarly affected by activation time.
pH: The pH of the liquid or aqueous solution is an important component in determining the surface charge density as well as whether the surface is cationic or anionic. A solution with a high pH will attract cations, whereas a solution with a low pH will attract anions. In other words, acidic carbons will be better at keeping cations, whereas basic carbons will be better at removing anion. As a result, the absorption of cationic and anionic groups may be regulated by adjusting the pH of the solution. When the pH rises, the elimination of pollutants reduces, resulting in a lower adsorption rate.
Pore Size and Pore Volume: The adsorption behavior of different adsorbents is dependent on the size of the pores. Steam-activated carbon revealed micro and mesopores in waste tyre-derived carbon, and the carbon’s adsorption capability increased with pore volume. It was also discovered experimentally that thin micropores formed during the early phases of steam activation of tyre char. When the activation period was increased, the structure changed from micro to mesoporous. The type of the chemicals used during chemical activation influences the pore volume of the AC.
Contaminant Concentration: The removal capacity of AC is determined by the contaminant concentration, which must be high since impurity molecules diffuse through the pores and get adsorbed. However, as concentration rises, so do effluent leakages. Contaminants have a maximum limit of roughly 100 ppm. For greater pollutant concentrations, more contact time with activated carbon is necessary
Health Risks of Activated Charcoal
- The usage of activated charcoal may result in black tongue, black feces, vomiting, and either diarrhea or constipation. A gastrointestinal obstruction is possible.
- Combining activated charcoal with constipation medications (magnesium citrate or sorbitol) may result in electrolyte abnormalities.
- It may limit supplement absorption.
- It also inhibits the absorption of some nutrients.
- Brushing your teeth with activated charcoal may cause tooth enamel damage since it is very abrasive.
- Inhaling activated charcoal dust might result in catastrophic lung damage.
- Contaminants may be present in charcoal depending on the raw material utilized.
- Using activated charcoal in aquarium filtration adds iron to the water over time, encouraging plant growth and algae infestation. Water changes aid in the reduction of metal buildup.
- Several medicines, including acetaminophen, digoxin, theophylline, tricyclic antidepressants, and birth control pills, are reduced or prevented from being absorbed by activated charcoal.
Difference Between Carbon and Activated Charcoal
Both carbon black and activated carbon are essential adsorbing agents. They have a high surface area to volume ratio, allowing the material to absorb as much as possible. The main distinction between carbon black and activated carbon is that carbon black has a lower surface-area-to-volume ratio than activated carbon.
| Carbon | Activated Charcoal |
| Carbon black is a kind of adsorbing agent produced by the incomplete combustion of heavy petroleum compounds. | Activated carbon is a kind of adsorbent formed from charcoal. As a result, it is also known as activated or active charcoal. This carbon-atom-based material has an extremely high surface-area-to-volume ratio. |
| Lower surface area-to-volume ratio than activated carbon. | High surface area-to-volume ratio |
| Greater than 95% carbon content. | Carbon content (80-90%) |
| Preparation by carbonization at high temperatures (700-1000°C) by physical or chemical procedures | Process of combustion with little or no air |
References
- https://www.ncbi.nlm.nih.gov/books/NBK482294/
- Helmenstine, Anne Marie, Ph.D. “Activated Charcoal and How It Works.” ThoughtCo, Aug. 27, 2020, thoughtco.com/how-does-activated-charcoal-work-604294.
- Bansal, Roop Chand, and Meenakshi Goyal. Activated Carbon Adsorption. Boca Raton: Taylor & Francis, 2005. ISBN 978-0824753443.
- Marsh, Harry, and F. Rodríguez-Reinoso. Activated Carbon. Amsterdam: Elsevier, 2006. ISBN 978-0080444635.
- https://chemistnotes.com/physical/activated-carbon-preparation-properties-and-10-reliable-uses/
- Activated Charcoal: Preparation, characterization and Applications : A review article
- https://www.vedantu.com/chemistry/charcoal
- Yang, R. T. Adsorbents: Fundamentals and Applications. Hoboken, NJ: Wiley-Interscience, 2003. ISBN 0471297410.
- Muttil, N.; Jagadeesan, S.; Chanda, A.; Duke, M.; Singh, S.K. Production, Types, and Applications of Activated Carbon Derived from Waste Tyres: An Overview. Appl. Sci. 2023, 13, 257. https://doi.org/10.3390/app13010257
