What is activated carbon fiber? What is the material of activated carbon fiber

Activated carbon fiber (ACF), also known as fibrous activated carbon, is a kind of high-efficiency active adsorption material and environmental engineering material with better performance than activated carbon. More than 50% of its carbon atoms are located on the inner and outer surfaces, forming a unique adsorption structure, which is called surface solid. It is formed by carbonization and activation of fibrous precursor by a certain procedure. Because of its developed specific surface area and narrow pore size distribution, it has faster adsorption and desorption speed and larger adsorption capacity, and because it can be easily processed into different shapes such as felt, cloth, paper, etc., and has acid and alkali resistance and corrosion resistance characteristics, it has attracted extensive attention and in-depth research since its appearance. At present, it has been widely used in environmental protection, catalysis, medicine, military industry and other fields.

Since American patent first involved in the use of activated carbon fiber to filter radioactive iodine radiation in American ORNL in 1962, the research and application of organic fibers and activated carbon fibers with different precursors have developed rapidly. The United States, the United Kingdom, the former Soviet Union and Japan in particular are major countries in the research and use of ACF, with an annual output of nearly one thousand tons. Domestic ACF research started in the late 1980s, and industrial devices appeared successively in the late 1990s. Most of them are in the stage of laboratory research.

Manufacturing method: the production process and product structure of ACF are obviously different with different precursor materials. The production of ACF is generally to stabilize the organic precursor fiber at a low temperature of 200 ℃ ~ 400 ℃, and then activate it. The commonly used activation methods are as follows: physical activation with CO2 or water vapor and chemical activation with znci2, H3PO, H2PO4, KOH. The treatment temperature is 700 ℃ ~ 1000 ℃. Different treatment processes (time, temperature, activation dose, etc.) have different pore structure and performance. The main organic fibers used as ACF precursors are cellulose, pan, phenolic, pitch, polyvinyl alcohol, styrene / olefin copolymers and lignin fibers. The first four are mainly commercialized.

Structural characteristics: activated carbon fiber is a typical microporous carbon (MPAC), which is considered as a "combination of ultrafine particles, irregular surface structure and very narrow space", with a diameter of 10 μ M-30 μ M. The pores are directly open to the surface of the fiber, and the ultrafine particles are combined in various ways to form a rich nano space. The size of these spaces is in the same order of magnitude as the ultrafine particles, thus creating a large specific surface area. It contains many irregular structures - heterocyclic structures or micro structures with surface functional groups, which have great surface energy. It also creates a strong molecular field by the interaction between micropores and pore wall molecules, and provides a high-pressure system for the physical and chemical changes of adsorbed molecules. The diffusion path of adsorbate to adsorption site is shorter than that of activated carbon, driving force is larger and pore size distribution is concentrated, which is the main reason for the larger specific surface area, faster adsorption and desorption rate and higher adsorption efficiency of ACF than that of activated carbon.

Functionalization method: functionalization is mainly through pore structure control and surface chemical modification to meet the efficient adsorption and transformation of specific substances.

ACF is usually suitable for adsorption of low molecular weight molecules (Mw = 300 or below) in gas and liquid phases. When the micropore size of adsorbent is about twice the critical size of adsorbate, adsorbate is easier to adsorb. The purpose of pore size adjustment is to make the pore size of ACF equal to the molecular size of adsorbate. Generally, the following methods are used: 1) change of activation process or activation degree (to nanometer level); 2) add metal compounds or other substances to the raw fiber for carbonization activation, or add metal compounds to the raw fiber for reactivation (mainly mesopores). The raw fiber has a pore size (large) close to the large pore in advance Pore); 3) the pyrolysis of hydrocarbons deposited on the pore wall and treated at high temperature.

The surface chemical modification mainly changes the surface acidity and basicity of ACF, and introduces or removes some surface functional groups. The surface oxygen-containing groups can be removed (reduced) by high temperature or hydrogenation, and the acid surface can be obtained by gas-phase oxidation and liquid-phase oxidation. The influence of physical structure and chemical structure should be considered.