Views: 2 Author: Site Editor Publish Time: 2024-04-07 Origin: Site
Specific surface area and pore structure
The surface area of the adsorbent material provides a place for the adsorption process and increases the probability of the adsorbent interacting with VOCs. A large specific surface area means superior adsorption performance. Generally, the specific surface area of the adsorbent is increased by opening closed pores or forming new pores.
The surface area of the adsorbent material provides a place for the adsorption process and increases the probability of the adsorbent interacting with VOCs. A large specific surface area means superior adsorption performance. Generally, the specific surface area of the adsorbent is increased by opening closed pores or forming new pores.
Activated carbon with the highest specific surface area does not always show the best adsorption capacity for organic compounds, which proves that the adsorption of VOCs by materials is affected by multiple factors. Using activated carbon as the adsorbent, the effects of specific surface area and pore structure on adsorption capacity were investigated. The results showed that the adsorption of VOCs was mainly controlled by pore diffusion, and the smaller the packing density of the adsorbent, the easier it was to penetrate.
The microstructure of carbonaceous adsorption materials, especially the pore size distribution, determines its adsorption capacity for VOCs.
When the pore diameter is larger than the molecular diameter of VOCs, VOCs molecules can enter the pores of the adsorbent material. Optimum adsorption occurs where the pore size matches the molecular size of the adsorbate. Micropores are conducive to the adsorption of small-volume VOCs, and large pores such as mesopores are more suitable for the adsorption of large-molecule VOCs.
2. Surface chemical properties
In addition to the morphological structure, the chemical functional groups on the surface of the adsorbent material also play a role in the adsorption of VOCs. Their type and quantity have a great impact on the adsorption capacity of VOCs. The surface chemical modification of the adsorbent can change its adsorption capacity and selectivity for VOCs. . The surface functional groups of carbonaceous adsorbents are related not only to the properties of the raw materials, but also to activation or modification methods such as heating, chemical and electrochemical treatments. Different modification methods produce different surface chemical functional groups.
Hydrophobic VOCs prefer to adsorb on activated carbon without surface oxygen groups. Among them, oxygen and nitrogen groups on porous carbon are considered to be the most important species in the adsorption process.
3. External detection environment
In addition to the effects of adsorbents and adsorbates, external conditions such as temperature and humidity also have a certain impact on the adsorption performance of VOCs. The effect of temperature on VOCs adsorption is more obvious.
When the actual sampling scene is a high-humidity environment and there is competitive adsorption between the target adsorbate and water on the adsorbent surface, the adsorption of water will have a huge impact on the adsorption of VOCs.