Details: I'll show you part of my undergraduate thesis. Although it is mesoporous carbon, it is also a kind of activated carbon.

This section will summarize and compare the influencing factors of pore parameters of three main mesoporous carbon preparation methods: direct carbonization method, activation method and template method

(1) direct carbonization method

For the direct carbonization method with biomass materials as carbon source, the pore structure of porous carbon materials is quite different due to the different particle size and composition of biomass materials. In Wang Gang's research [93], the BET specific surface areas of mesoporous carbon materials prepared from pig hair and sheep manure with the same treatment and preparation process are 865,438+0.3m2/g and 629 m2 /g, respectively, with a difference of 29.23%. However, Wang Gang only mentioned that the difference of biomass particle size caused this difference, and did not give a specific mechanism explanation for this difference.

Pacioni et al. [129] observed that the existence of volatiles and alkali metal elements in biomass materials will affect the morphology of porous carbon materials, among which alkali metal elements can play an activating role, and the pore structure of biomass materials itself also provides convenient conditions for the formation of pores [83].

In addition to raw materials, the temperature of carbonization and calcination also has a certain influence on the formation of pores: Chen [9 1] summarized the pore size distribution of products at different carbonization temperatures in the process of preparing mesoporous carbon by direct carbonization, as shown in Figure 3-9. It is found that with the increase of temperature, the pore size becomes smaller due to the collapse of pores, but in the process of further temperature increase, the pore size distribution begins to be uniform. Encanacio? N et al. [120] found that when the calcination temperature increased from 600℃ to 900℃, the adsorption period of N2 remained unchanged, but the BET specific surface area increased from 746 m2 /g to 1307 m2 /g, which indicated that the mesoporous structure of the material remained unchanged and a large number of micropores were produced.

(2) Template method

Because of the template, the morphological characteristics and parameters of the template product mainly depend on the properties of the template itself. For the hard template method, whether there is micropore connection between the pores of the template material is the key to whether the product is orderly. Taking SBA- 15 as a template to prepare hexagonal mesoporous carbon CMK-3 as an example: if the template materials are not interconnected, the mesoporous carbon will collapse after removing the template; On the contrary, due to the support of carbon entering micropores, the whole structure will remain orderly, as shown in figure 1- 10. At the same time, different carbon sources have little effect on the morphology of mesoporous carbon due to the role of templates [97].

For soft template method, due to the self-assembly characteristics of soft template and carbon precursor, the morphology and structure of the final product can be controlled by changing the soft template material. In addition to changing the soft template material, long-chain alkanes can also be added as catalysts to change the pores of the products [104]. In addition, the use of mixed carbon sources will also affect the formation of mesopores. Tanaka et al. [130] used resorcinol, phloroglucinol and methanol as mixed carbon sources and F 127 as template to synthesize ordered membrane materials with extremely rich mesoporous structures. In the process of principle explanation and pore formation, it is mentioned that the pore structure of mesoporous carbon materials prepared by soft template method is initially formed when carbon precursors are combined with soft template, so the formation of mesopores can be controlled by changing the degree of combination.

Hu et al. [13 1] controlled the degree of polymerization by adding surfactants and changing reaction conditions, and finally prepared ordered mesoporous carbons with different mesoporous contents. Mesoporous carbon structures with different morphologies can also be obtained by changing the ratio of raw materials to templates. Yang et al. [132] used F 127 as template to prepare resin as mixed carbon source. Three-dimensional body-centered cubic and two-dimensional hexagonal mesoporous carbon materials can be obtained by simply adjusting the mass ratio of the two. To sum up, for the hard template method, the hard template material is the most important factor affecting the product form expression; For the soft template method, the mesoscopic structure of the product can be selectively controlled by changing the self-assembly reaction process by different means.

(3) Activation method

According to the different activation mechanism, different activators will have an impact on the final activation results. Comparing CO2 and H2O, the two most commonly used physical activators, the reactivity of CO2 is less than that of H2O, so the reaction speed is less than that of H2O [133]. There are also some differences in the reaction process between the two gases: as mentioned above, the pore-forming by physical activation is in three aspects: opening, reaming and new pore. In the activation process, CO2 first opens the pores and then reams, while in the activation process, H2O finally obtains the mesopore and macropore structure through continuous reaming [108]. The activation mechanism of chemical activation method is not completely clear. At present, it is considered that the activation mechanisms of different activators are different: when phosphoric acid is used as the activator, it promotes the bond cracking and cross-linking of carbon precursors through cyclic condensation [134]; Zinc chloride will dehydrogenate the raw materials during activation, forming porous materials with concentrated pore size [133]; KOH is the best activator for activating products at present. It is considered that K2O and other substances with oxidation properties are formed through a series of reactions, and the specific surface area after KOH activation is much higher than that of physical activators such as steam and CO2 [135].

Besides the activator, other activation conditions will also affect the formation of pores. Lilo-Rodenas et al. [127] explored the activation effect of NaOH in different atmospheres. The specific experimental conditions and activation results are shown in Figure 3- 1 1 and Figure 3- 12. By comparison, it is found that the greater the N2 gas flow rate, the greater the specific surface area. As an atmosphere, CO2 will not produce pores in the process of NaOH activation. And the specific surface area will not be increased by adding steam during the heat preservation process. Wu Jian et al. [136] studied the activation effect of KOH at different activation temperatures. According to the comparison of three groups of results at 700℃, 800℃ and 900℃, it is found that with the increase of temperature, the etching effect of KOH on carbon precursors is enhanced, and the pore size is gradually increased. At 800℃, a large number of mesopores with the pore size of 4-6nm appear.