I am planning to prepare activated bio char, activating it with KOH. I am planning to follow the method that includes no heating. I wanted to know will it rally increase the BET surface area? If anyone have already followed such procedure, please share with me what result you have obtained. Also anyone please tell me the differences that could be obtained, while comparing bio char and activated bio char.
If you are use KOH as activating agent than your temperate should be in the range of 750-900 C. KOH is thermally stable in this range and produce large surface area & pore volume.
As mentioned in the other answer you need elevated temperatures (600 - 1200 C) for KOH activacation. if you are interested in the mechanism of KOH activation take a look at this paper: DOI: 10.1039/c2jm34066f
Alkaline hidroxides KOH, NaOH and carbonates K2CO3, Na2CO3 have been used as activation reagents in the preparation of activated carbons with high specific surface. In general , chemical activation by KOH and NaOH consists in a solid-solid or solid-liquid reaction involving the hydroxide reduction and carbon oxidation to generate greater porosity. KOH only produces a widening of micropore width whereas some other chemicals such as ZnCl2 additionally develops small mesoporosity and H3PO4 leads to a more heterogeneous pore size distribution.
Anil Kumar Sakhiya Nazgol Norouzi Aju Mathew George Thank you for answering, I am now able to understand the concept. But I have some more doubts like, can activation be done without heating? Does it be done my mass transfer also? Could you please go through the above attached file. This paper has a different method of activating the bio char, which excludes any heating.
Uddipta Nath Yes We can do activation without heating too. Your overall aim is to develop biochar. So the raw material (biomass ) from which you are aiming to develop charcoal can be initially given a chemical washing using acid/ alkali followed by thermal treatment. It helps to remove the organic matter present and the color which the your adsorbent may impart to the water which causes Secondary pollution.
It depends on the degree of activation. The activation will create porosity which in turn increases the specific surface area, however, at certain degree of activation the surface area may reduce too (excessive activation). So you need to question yourself to which extent of activation does your application require. For instance, pores below 0.7 nm (ultramicropores) are optimal for CO2 capture. Moreover, KOH is a strong activator. There are soft activators too, like CO2.
Some literature in the topic:
Importance of small micropores in CO2 capture by phenolic resin-based activated carbon spheres - DOI: 10.1039/C2TA00388K
Article Enhancement of CO2 adsorption on phenolic resin-based mesopo...
Article Potassium salt-Assisted synthesis of highly microporous carb...
Development of microporosity in carbons for carbon dioxide adsorption http://rave.ohiolink.edu/etdc/view?acc_num=kent1492043634249216
Alexandre A. S. Gonçalves Thank you for explaining, could you please mention other benefits of activation beside increase in surface area and porosity
Hi Uddipta Nath, I don't recall any specific example in literature to show you. But my answer would be surface modification, doping, and/or metal deposition; which will depend on the type of activation agent used.
One way of doing that is hydrothermal carbonization process otherwise you have to do some heating at higher temperature as mentioned by Uddipta Nath
Uddipta Nath A ativação química poderá aumentar a área superficial e consequentemente a porosidade, como já foi comentado. Esta ativação poderá também promover modificações na superfície como dito pelo Alexandre, especificamente em relação a sua química de superfície, onde encontram-se também os grupos funcionais. Sendo estes grupos funcionais responsáveis pela adsorção maior ou menor de alguns compostos, principalmente os inorgânicos.
Espero ter contribuído.
Uddipta Nath The chemical activation may increase the surface area and, consequently, the porosity, as already mentioned. This activation may also promote surface modifications as stated by Alexander, specifically in relation to its surface chemistry, where functional groups are also found. These functional groups are responsible for the greater or lesser adsorption of some compounds, mainly the inorganic ones.
I hope I contributed.
Yes, the surface area is increased because the chemical agents help in the development of porosity, by degrading the structure of the biomass. And, in general, activation promotes everything that Alexandre have previously cited, and can also change the PZC of the material. The adsorption of organic and inorganic compounds increases significantly after activation, this increase in adsorption can be promoted both by increasing the porosity and by increasing the functional groups on the surface of the material.
But you have to realize that most activations use heat at some point in the activation, this activation, for your material, can be efficient or not. I suggest you do it in small quantity and evaluate the efficiency of your material.
This review article provides an overview of the topic:
Article Activated carbon from lignocellulosics precursors: A review ...
Yes it modifies surface area depending on the carbon precursor. Refer to the Table 2.
Hi,
KOH activation is the best way to increase the surface area of the activated carbon. Also, you have to optimize the substrate/KOH ratio, temperature, and activation time.
All the best.
Activated carbon is prepared basically by two steps, carbonization, and activation. Activation can be done in two ways (physical or chemical) In the chemical activation method, you can use KOH as a chemical activation agent. But you have to realize that for the preparation of activated carbon you have to use heat at some point.