The preparation methods of activated carbon include physical method, chemical method, microwave radiation method, etc.(1) Physical method.
Physical method is to use carbon dioxide, water vapor or the mixture of both as activator, the carbonized carbon material and gas in the activation furnace at 500~1200℃ for carbon activation reaction, so that the pore size of the carbonized material to expand, the formation of activated carbon with porous microcrystalline structure.Gas activation method mainly includes carbonization and activation engineering.The so-called carbonization, refers to the low temperature (about 500℃) is small, the volatile coal tar molecules in the material and the thermal decomposition and curing process of asphalt, that is, to remove the volatile in advance, made suitable for the next step of activation with carbonization.
When the temperature is below 600℃, the specific surface area of carbonized material increases with the increase of temperature.When 600~900℃, the specific surface area reaches a certain value: 250~300 m2/g; when above1000℃, the specific surface area shrinks rapidly.
When the carbonization temperature is above 800℃, the reaction performance of carbonized compounds and activation gas gradually becomes weaker, so the carbonization temperature is generally below 1000℃. However, if the residual volatile content and thermal effect are taken into account, the most suitable temperature should be 600~700℃39].
The carbonized substance obtained from the carbonization process is placed in water vapor or a mixture of water vapor and combustion gas and heat treated at 800~1000℃, which is called the activation process.
The commonly used activation gases are carbon dioxide, water vapor, oxygen, etc., due to the oxidation reaction of these gases on the surface of the carbonized substance, eroding the carbonized substance, thus producing a rich porous structure.(2) Chemical method.
Chemical activation method is a method of preparing activated carbon by adding chemicals to the raw materials used or impregnation into the raw materials or carbonized materials, and then heating it at high temperature in inert gas.The chemicals used in chemical activation are generally dehydrating.The more commonly used activator is: inorganic acid varieties have phosphoric acid, sulfuric acid and boric acid, salt varieties have zinc chloride, calcium carbonate and potassium sulfate, alkali varieties have sodium hydroxide, potassium hydroxide, etc..
The main principle of chemical activation method is the raw materials in 0.5~5 times the chemical activator impregnation for a certain time, in the process of heating, because of the dehydration of chemicals, the H and О elements in the raw materials in the form of water vapor released, the results produced a developed porous structure of activated carbon.The method requires the oxygen content in the raw material.25%, hydrogen content ≥5%[4], and most of the materials that can meet the requirements of this index are rice husk, wood and coal, etcoxidation modification of activated carbon
Surface oxidation modification is mainly to oxidize the functional groups on the surface of activated carbon materials by using appropriate oxidants at appropriate temperatures, so as to improve the content of oxygen-containing groups on the surface of carbon materials, enhance the surface hydrophilicity and polarity, and enhance the adsorption capacity of polar substances.
The number and types of oxygen-containing functional groups are different after treatment with different oxidants.Oxidation treatment also changed the void structure of activated carbonThe commonly used modified oxidants mainly include HNO, HClO, HPO, H,SO4, HF, O and HO, etc. www.yrdcarbon.com
Oxidant HNO;After the modified activated carbon was treated with proper amount of nitric acid, the mesopore increased, the ratio of carboxylic hydroxyl increased, the surface polarity of activated carbon increased, and the adsorption capacity of some solutes with certain polarity increased.However, excessive nitric acid modification treatment will increase the unstable groups on the surface of activated carbon and fail to achieve the predetermined effect 18-20].activated charcoal bulk canada
After modified by HCIO with mild oxidation, the number of oxygen-containing groups on the surface of activated carbon increased, but the micropore structure and specific surface area did not change much.After ozonation treatment, the number of oxygen-containing acid functional groups on the surface of activated carbon and the surface acidity increased, and the adsorption rate and capacity of C** increased. P-Morwski et al. 2 used HNO to oxidize the carbon synthesized from phenols, and the adsorption performance of the treated activated carbon material to trihalomethane was greatly improved.Shan Xiaomei et al. 2 found that the surface area and pore volume of activated carbon decreasedafter high concentration of HNO treatment.
However, the surface and pore volume of activated carbon increased after low concentration HNO treatment.(NH4) S0.Oxidation changes the micropore size distribution of coal-based carbon, but has little effect on the micropore size distribution of coconut-shell carbon.
In addition, the number of carboxyl groups on the surface of activated carbon increased obviously after modification of HNO, (NH4)S
The amount of phenolic hydroxyl group and lactone group on the surface of activated carbon increased significantly after OG modification.Tsutsumi after 2 ⒂ activated carbon materials such as activation, first under the condition of the air cooled to about 400 ℃, and then with a good contact with air oxidation treatment, can increase the alkali activated carbon material surface oxide hydroxyl groups on the surface of the the surface polarity and hydrophilic increased, can adsorption in aqueous solution polarity organic matter and inorganic matter.