The magical family of activated carbon

Activated carbon is a black, porous solid carbonaceous material.It is a specially treated form of carbon produced by heating organic

 raw materials—such as fruit shells, coal, or wood—in the absence of air to reduce non-carbon components (a process known as

 carbonization), and subsequently reacting the material with a gas to erode its surface and generate a highly developed microporous

 structure (a process known as activation). Since activation is a microscopic process—specifically, the surface erosion of the

 carbonaceous material occurs at countless discrete points—the resulting activated carbon surface is characterized by a myriad of

 minute pores. The diameters of these surface micropores typically range from 2 to 50 nanometers; consequently, even a small quantity

 of activated carbon possesses an immense surface area, with each gram offering a surface area of 500 to 1,500 square meters. Virtually

 all applications of activated carbon are predicated upon this distinctive characteristic.

Chinese national standards classify activated carbon into two categories: one based on the primary raw materials used in

 manufacturing, and the other based on a combination of the raw materials used and the corresponding product shape.

Based on the primary raw materials used in their manufacture, activated carbons are divided into four classes: coal-based activated

 carbon, wood-based activated carbon, synthetic-material-based activated carbon, and other types of activated carbon. When classified

 according to the combination of primary raw materials and corresponding product shapes, they are categorized into 16 specific types.

 Specifically, coal-based activated carbons are subdivided into: columnar granular, crushed granular, powdered, and spherical forms.

 Wood-based activated carbons are subdivided into: columnar granular, crushed granular, powdered, and spherical forms. Synthetic-

material-based activated carbons are subdivided into: columnar granular, crushed granular, powdered, shaped, and spherical forms, as

 well as fabric-based (carbon fiber cloth) and felt-based (carbon fiber felt) forms. "Other types of activated carbon" refers to activated

 carbons prepared from raw materials other than the three aforementioned classes—such as coal pitch or petroleum coke. Within the

 product shape classification, this category currently lists pitch-based microspherical activated carbon.

Physicochemical Activation Method

(1) Integrated Physicochemical Preparation Technology

As the name implies, the physicochemical activation method involves the combined application of physical and chemical activation

 techniques; specifically, the carbonaceous material is first treated chemically and subsequently subjected to further activation using

 physical methods (typically steam or CO₂). Researchers abroad have successfully synthesized "super-activated carbon"—possessing a

 specific surface area as high as 3,700 m²/g—through a combined H₃PO₄ and CO₂ activation process. The specific procedure entails first

 impregnating the lignocellulosic raw material with H₃PO₄ at 85°C, followed by carbonization at 450°C for 4 hours, and finally, activation

 using CO₂. By integrating physical and chemical methods—specifically by utilizing the off-gases generated during the physical

 carbonization stage to provide thermal energy for the chemical activation stage—the production process can be rendered entirely free

 of coal consumption, while simultaneously yielding both physically activated and chemically activated carbon products.

(2) Microwave-Assisted Chemical Activation

Traditional furnace heating methods employed in activated carbon production suffer from several drawbacks: they are labor-intensive,

 time-consuming, and result in uneven heating of the raw materials. The introduction of microwave technology addresses these issues

 by enabling uniform internal heating of the material; furthermore, it facilitates rapid and convenient process start-up and shut-down,

 significantly reducing the overall processing time compared to conventional methods. Consequently, microwave-assisted chemical

 activation can drastically shorten production cycles, thereby substantially boosting production efficiency while simultaneously

 mitigating environmental pollution. Standard chemical activation techniques—such as the phosphoric acid method, zinc chloride

 method, and potassium hydroxide method—can all be effectively adapted to utilize microwave heating. Moreover, research indicates

 that microwave-assisted heating yields high-performance activated carbon, proving particularly well-suited for the synthesis of

 supercapacitor-grade activated carbon via the KOH activation route. However, the production of activated carbon using microwave

 heating remains largely in the experimental stage, primarily due to the substantial capital investment required for equipment and the

 high associated energy consumption.

(3) Catalytic Activation

Metal-based catalysts, when deposited on the surface of carbonaceous raw materials, create active sites that lower the activation

 energy required for the reaction between the carbon and activating agents (such as steam or CO₂). This effect serves to reduce the

 requisite activation temperature, accelerate the reaction rate, and facilitate the development of a highly porous structure; additionally,

 the migration of metal particles across the carbon surface during the process contributes to the formation of distinct pore channels. In

 the context of synthesizing super-activated carbon, catalysts play a pivotal role by lowering the activation temperature and

 dramatically accelerating the reaction kinetics, while also ensuring a uniform pore size distribution within the resulting activated

 carbon product. Although the catalytic activation method for preparing activated carbon offers the aforementioned numerous

 advantages, an excessively rapid reaction rate may burn through the walls of the micropores, thereby destroying the microporous

 structure.