# Biochar as a Multifunctional Component of the Environment--A Review
## 5 Biochar as a Activated Carbons
For example, carbons were prepared from combination of the waste tea and K\({}_{2}\)CO\({}_{3}\) have high surface area and pore volume [98]. The production of active carbons takes place within two mechanisms, i.e., physical activation and chemical activation. Physical activation, also known as thermal activation, consists of two successive stages. The first step is the pyrolysis of the starting material, carried out at a high temperature (usually 500-1000 \({}^{\circ}\)C). During the second step, the carbonization product obtained is activated by exposure to a high temperature (800-1000 \({}^{\circ}\)C) using an oxidizing agent such as water vapor, carbon monoxide (IV) or a mixture of these gases. If the above-mentioned stages of physical activation take place at the same time, then it is direct activation process. In the process of chemical activation, the precursor is subjected to high-temperature treatment in an inert gas atmosphere after prior impregnation or mixing with an activating agent. The activators used in chemical activation are mainly potassium and sodium hydroxide, sodium and potassium carbonates, zinc chloride, and phosphoric acid (V). The disadvantage of this method is its high cost caused by the necessity to use expensive activating agents and to introduce a stage aimed at removing the excess of the activating agent and the by-products. The physical and chemical properties of active carbons such as porous structure, highly developed specific surface area or sorbent capacity are strictly dependent on the substrates used, activation methods and conditions of the process. The properties of carbon sorbents can also be significantly altered by means of appropriate chemical modifications both during the manufacturing process and after the activation process. These processes consist mainly of the introduction of functional groups into the structure of the carbon material or on its surface, which significantly change its chemical character. Modification of carbon materials can be carried out using e.g., liquid oxidants, to which we include, primarily HNO\({}_{3}\), H\({}_{2}\)O\({}_{2}\) and (NH\({}_{4}\))\({}_{2}\)S\({}_{2}\)O\({}_{8}\). The surface of active carbons can also be modified with various types of organic and inorganic compounds, e.g., pyridine, compounds of platinum, of chromium, of silver, of copper, of potassium, of zinc, of sodium and of cobalt. This type of modification is aimed at obtaining materials with significantly increased and selective sorbent capacity. Table 6 presents the surface area values for physically and chemically activated carbons obtained from different materials [99; 100; 101]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multicolumn{2}{c}{**Physically Activated Carbons**} & \multicolumn{3}{c}{**Chemically Activated Carbons**} \\ \hline \multirow{2}{*}{Initial Material} & Activation & Surface & Activation & Surface \\  & Agent & Area\({}^{\text{m2}}\) g\({}^{-1}\) & Initial Material & Agent & Area\({}^{\text{m2}}\) g\({}^{-1}\) \\ Rice [103] & Steam & 1122 & Rice [104] & KOH & 3263 \\ Peanut shells [105] & Steam & 757 & Hazelnut shells [106] & KOH & 1700 \\ Cornstarch [107] & Thermal & 686 & Corncob [108] & KOH & 3054 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Surface area values for physically and chemically activated carbons obtained from different material. Activated carbons can be used in many sectors e.g., pharmaceutical, food industrial as additives or the emerging use. A series of studies demonstrated that activated biochar could be available for pharmaceuticals removal, such as acetaminophen, caffeine, atrazine, diclofenac, glyphosate, naproxen, ibuprofen and sulfamethazine [118]. [PERSON] et al. conducted a study to identify the maximum adsorption capacities of amitriptyline and paracetamol, separately and in combination, to activated charcoal [119]. The rapid adsorption tendencies of activated carbon have also extended the biochar applications to biomedical sciences.