What is activated charcoal?

Whether used in respiratory masks, nuclear power plants, cigarette filters, cosmetics, food, medicines, water filters, exhaust gas purifiers or aquariums: activated carbon is a versatile adsorbent and, as sustainably produced carbon, a material with great potential for the future. Guidebook We will therefore talk about the “jack of all trades activated carbon” and clarify all important questions from A to Z.

Extraction of activated carbon [Production]

As is well known, coal is produced when carbon-containing materials - e.g. wood, nutshells and kernels - are burned in the absence of oxygen. By burning organic materials, the production of coal is much faster than if, for example, hard coal was produced naturally in a process lasting several million years.¹ over several million years.

This is also how barbecue charcoal² is produced under exclusion of air and without oxygen by combustion - this is called carbonization. Charcoal and activated charcoal can be made from various plant, animal, mineral or artificial substances. 

(Active) coal from wood, plants, blood, bones, sugar...

The combustion process during charring is also known as "pyrolysis".³ is also known as "pyrolysis". Regardless of whether you "burn" wood, peat, fruit stones or nutshells (without oxygen supply): What remains is the carbon in the form of biochar, which - unlike in a campfire - does not turn to ash (or escape as gas). Incidentally, the term biochar is used when the following materials are carbonized as raw materials during production:

• Wood
• Peat
• Coconut fibers / shells
• or other nutshells / kernels.

The carbonization of animal blood or bones is referred to as blood charcoal or bone charcoal. Sugar charcoal is (activated) charcoal that is obtained from sugar (e.g. glucose or molasses). But how exactly is charcoal turned into activated charcoal? 

Activation of activated carbon

The carbonization process is followed by "activation" during production. Activated carbon is only created through this eponymous step. Two methods can be used for activation:

Activated charcoal has particularly small pores

The special thing about activated carbon is the ultra-fine pores, which are connected to each other in a labyrinth and therefore form a huge surface structure. Even a 1cm³ cube (made of activated carbon) would have an inner surface area 10,000 times larger than the outer surface - and this is due to the many fine pores. This is why activated carbon can bind or adsorb dirt or pollutants so well. 

What does adsorption mean?

 In contrast to absorption, the "soaking up" of substances, which generally refers to the "taking in of something", adsorption refers to the binding of foreign substances to a starting material.

When foreign (toxic) substances adhere to the surface of activated carbon and accumulate on its surface, this is called adsorption.

When light or sound is absorbed by foreign bodies, colloquially: swallowed, we speak of absorption.

Both terms come from the Latin: "adsorbere" = "(to) suck in" "absorbere" = "(to) absorb".

A distinction is made between pore sizes:

• Mikroporen (<1 Nanometer), 
• Mesopores (1-25 nanometers) 
• Macropores (>25 nanometers)
  

The quantity and distribution of the pore sizes ultimately determine the adsorption properties of the activated carbon, i.e. how well it can bind these or those substances. This is because pores of different sizes absorb dirt particles of different sizes. And depending on the area of application, a different distribution may be advantageous.

Areas of application for activated carbon

Activated carbon is therefore primarily used as an adsorbent - e.g. to remove unwanted odors or flavors, to filter toxic gases or to remove dyes. As a powerful cleaning and filtering medium, activated carbon is of great value in medicine, chemistry, water treatment, ventilation technology, agriculture and - more recently - the cosmetics and food industries.

Activated carbon as an air filter

It is hard to imagine the automotive industry without air filters made of activated carbon. Activated carbon has been used successfully in air conditioning systems since the 1990s at the latest. Activated carbon is therefore not only used in cars to remove unwanted substances such as dust, gases, odors or other suspended particles from the air.

Passengers on planes or trains are also protected from odors and pollutants by activated carbon in the air conditioning systems. The production of these cabin air filters, which have a layer of activated carbon, consumes more than 5000 tons of activated carbon per year worldwide.

Activated carbon in nuclear power plants

The use of activated carbon filters in nuclear power plants serves a similar purpose. The activated carbon binds short-lived radioactive noble gases for a certain period of time. This process, known as "temporary adsorption", significantly reduces the amount of radioactive noble gases in the exhaust air.

Activated carbon in agriculture?

Whether the use of biochar⁴ can increase agricultural yields and contribute to climate protection is the subject of much research. In 2013, a field trial was even carried out to investigate the extent to which the use of sulphur fertilizer mixed with activated carbon can increase crop yields.

The result? If a certain concentration of the additions was not exceeded, the addition of activated carbon to the fertilizer had a positive effect on the dry matter yield⁵ of the plants.

Activated carbon in medicine

Most readers will be familiar with the medicinal use of activated charcoal for gastrointestinal complaints. The most common form is over-the-counter activated charcoal tablets, which are available from any pharmacy. The most common medical applications of activated charcoal tablets include

• Feeling of fullness
• Flatulence
• Diarrhea
  
• Vomiting

Activated charcoal for poisoning

It is probably less well known that activated charcoal is used in medicine to treat poisoning. In fact, the World Health Organization (WHO) includes activated charcoal in its list of essential medicines.⁶ . In Germany, some emergency services are even obliged to carry activated charcoal with them.

The surface of activated charcoal also acts as a kind of sponge in the gastrointestinal tract. It can therefore bind (adsorb) any plant or chemical toxins (noxae) in the event of poisoning, prevent them from being released into the intestinal mucosa and remove them from the body - e.g. an overdose of medication.

Activated carbon in the food industry

The use of activated charcoal in the food industry should be treated with caution. Not because activated charcoal is harmful to health, but because many false promises are circulating that are hardly scientifically tenable. As colorant E153⁸ activated charcoal has long been approved by the European Union for the food industry.

Black foods with activated charcoal - e.g. burger buns, fruit juices, jellies, smoothies, jams, confectionery or cheese - may look exotic, but they are hardly beneficial to health. On the contrary, it should be borne in mind that activated charcoal can bind not only toxins but also valuable substances such as minerals and vitamins.

And since, according to NDR⁹ a "single smoothiealreadycontains about the drug dose of three to four activated charcoal tablets", the use of activated charcoal in food can certainly be viewed with skepticism. All the more so as many marketing promises that the consumption of activated charcoal is beneficial to health cannot be scientifically proven.

Activated charcoal in cosmetics

Similar to the positive effect of activated charcoal on food, many promises made by the cosmetics industry cannot be scientifically proven. Toothpaste with activated charcoal, for example, does not clean teeth any better than conventional products. Quite the opposite: it is much more likely that the charcoal particles have a negative abrasive effect.¹⁰ have a negative abrasive effect.

The use of activated charcoal in other cosmetics, e.g. creams, face masks or shower gels, is rather unproblematic, but here too there is a lack of studies that prove its effectiveness for cleaner skin, for example. However, this is not surprising - for two reasons:

• Almost all cosmetic effects are marketing.
• Activated charcoal only works really well if something flows through it - e.g. water!

Activated carbon as a filter medium for water

The fine surface structure of activated carbon can of course also be used to filter water, with many positive effects. In industry, contaminated water is recycled or purified on a large scale. For example, wastewater from textile dyeing plants contains dyes that can often only be removed by adsorption with activated carbon.

Wastewater treatment plants in German municipalities and large cities also make use of the properties of activated carbon. Municipal wastewater can contain a variety of contaminants, which are divided into different pollutant groups, including

• dissolved and undissolved substances,
• easily or poorly degradable organic substances, 
• Plant nutrients,
• Heavy metals,
• Chlorine,
• Salts, 
• and much more.

Although activated carbon is particularly suitable for contaminating organic compounds, for some substances its effectiveness is limited or ineffective.

What activated carbon can filter out of water - and what it can't

Activated carbon filter for drinking water at home?

Activated carbon is just as suitable for treating drinking water and improving water quality in the home as it is for industry and sewage treatment plants. However, there are major differences in quality that are related to the manufacturing method. There are two different types of activated carbon for water filters for private use at home:

• Poured activated carbon as granulate (table can filter)
• extruded activated carbon (with binder) 
• (sintered) activated carbon block filters

Activated charcoal filters - different types at a glance

Poured activated carbon

• Conventional table-top can filters work on the basis of loose activated carbon. 
• If the activated carbon is only poured in loosely, the filter improves the taste and smell of the water, but largely fails to filter out harmful substances. 
• A table-top jug filter is good against limescale, but the ion exchange resin added to it is quickly saturated. 
• In addition, a table-top jug filter is not able to reliably filter out residues of microplastics, medicines or hormones. 
• And because a table water filter comes into contact with more sunlight, there is a greater risk of contamination
• Contamination occurs in particular if the filter medium is not changed in good time.

Extruded activated carbon

• An activated carbon block can also consist of extruded activated carbon.
• In this variant, (a lot of) binding agent is used to "activate" the coal.
• However, extruded activated carbon does not offer the same high porosity as sintered activated carbon.

(Sintered) activated carbon blocks

• High-quality activated carbon block filters can remove the pollutants listed in the table above from the water.
• Particularly high-quality activated carbon block filters can also be manufactured with sintered activated carbon. 
• The process of sintering optimizes the "performance" of the activated carbon by maximizing the absorption capacity of the activated carbon. 
• Sintered activated carbon therefore has a particularly high adsorptive (i.e. "sucking in") effect and thus a strong filter performance

Curious?

Find out all about activated charcoal filters for water here.

How ecological and sustainable is activated carbon?

Over 1 million tons of activated carbon are produced worldwide every year. A maximum of one fifth of this is obtained from renewable resources. These include, among others:

• Wood
• Sawdust (from certain types of wood)
• Coconut fibers (and shells)
• Corn on the cob
• Lignin
• Bamboo
• Fruit kernels (e.g. apricot)
• Nutshells
• Seeds
• Sawdust
• and much more.

In any case, the production of activated carbon devours resources and is also energy-intensive. For this reason, the choice of raw material for sustainable activated carbon should be carefully considered and a resource-conserving production process should be selected.

Finally, some good news: saturated activated carbon that has lost its filter performance can be reactivated at high temperatures and thus recycled. This means that there is basically no waste in the activated carbon industry, as every gram of carbon can be renewed. Especially in view of the wide range of applications, the "jack-of-all-trades" activated carbon has great potential - now and in the future.

Frequently asked questions explained briefly

What is activated charcoal good for?

Although activated carbon is also known as "medical carbon", its use in medicine (e.g. for gastrointestinal diseases) does not make up the whole story. As a purifying filter medium, activated carbon is also used extensively in air conditioning systems, industrial plants, nuclear power stations and even in the military.

How does activated charcoal work?

The special thing about activated charcoal is the ultra-fine pores, which are labyrinthine and therefore form a large surface area. There is enough space for any harmful or toxic substances to adhere. This makes activated carbon a highly valued material precisely because of its enormous binding properties (adsorption capacity).

What is sintered activated carbon?

Sintered activated carbon is a special form of activated carbon. Sintering optimizes the "performance" of the activated carbon by maximizing the absorption capacity, i.e. the number of pores.

Is activated charcoal harmful?

Apart from the activated charcoal in toothpaste, which may accelerate the abrasion of tartar, activated charcoal is harmless. However, experts warn against it in food: Charcoal not only binds harmful substances and toxins in the body, but also vitamins and minerals. These should be better absorbed by the body through food. 

Is activated carbon flammable?

Activated carbon consists mainly of carbon (usually > 90 %) with a highly porous structure and is combustible¹².

What does an activated charcoal filter do?

As a powerful cleaning and filtering medium, activated carbon is of great value in medicine, chemistry, water treatment, ventilation technology, agriculture and, more recently, the cosmetics and food industries. However, its value in the last two areas of application is highly controversial in scientific terms.

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