Editing Adsorption (section)

===Activated carbon===

The term "adsorption" itself was coined by [[Heinrich Kayser]] in 1881 in the context of uptake of gases by carbons.<ref>{{cite web |url=https://application.wiley-vch.de/books/sample/3527324712_c01.pdf 
|title=Water and Wastewater Treatment: Historical Perspective of Activated Carbon Adsorption and its Integration with Biological Processes |website=application.wiley-vch.de
|first=Ferhan |last=((&Ccedil;e&ccedil;en)) |access-date=23 Aug 2024 |date=7 July 2011}}</ref>

[[Activated carbon]] is a highly porous, amorphous solid consisting of microcrystallites with a graphite lattice, usually prepared in small pellets or a powder. It is non-polar and cheap. One of its main drawbacks is that it reacts with oxygen at moderate temperatures (over 300&nbsp;°C).[[Image:Demac isoth.jpg|right|thumb|230px|Activated carbon nitrogen isotherm showing a marked microporous type I behavior]]

Activated carbon can be manufactured from carbonaceous material, including coal (bituminous, subbituminous, and lignite), peat, wood, or nutshells (e.g., coconut). The manufacturing process consists of two phases, [[carbonization]] and activation.<ref>Spessato, L. et al. KOH-super activated carbon from biomass waste: Insights into the paracetamol adsorption mechanism and thermal regeneration cycles. Journal of Hazardous Materials, Vol. 371, Pages 499-505, 2019.</ref><ref>Spessato, L. et al. Optimization of Sibipiruna activated carbon preparation by simplex-centroid mixture design for simultaneous adsorption of rhodamine B and metformin. Journal of Hazardous Materials, Vol. 411, Page 125166, 2021.</ref> The carbonization process includes drying and then heating to separate by-products, including tars and other hydrocarbons from the raw material, as well as to drive off any gases generated. The process is completed by heating the material over {{convert|400|°C|F|sigfig=2}} in an oxygen-free atmosphere that cannot support combustion. The carbonized particles are then "activated" by exposing them to an oxidizing agent, usually steam or carbon dioxide at high temperature. This agent burns off the pore blocking structures created during the carbonization phase and so, they develop a porous, three-dimensional graphite lattice structure. The size of the pores developed during activation is a function of the time that they spend in this stage. Longer exposure times result in larger pore sizes. The most popular aqueous phase carbons are bituminous based because of their hardness, abrasion resistance, pore size distribution, and low cost, but their effectiveness needs to be tested in each application to determine the optimal product.

Activated carbon is used for adsorption of organic substances<ref>{{Cite journal|title=Tea waste derived activated carbon for the adsorption of sodium diclofenac from wastewater: adsorbent characteristics, adsorption isotherms, kinetics, and thermodynamics|doi=10.1007/s11356-018-3148-y|pmid=30221322|year=2018|last1=Malhotra|first1=Milan|last2=Suresh|first2=Sumathi|last3=Garg|first3=Anurag|journal=Environmental Science and Pollution Research|volume=25|issue=32|pages=32210–32220|bibcode=2018ESPR...2532210M |s2cid=52280860}}</ref> and non-polar adsorbates and it is also usually used for waste gas (and waste water) treatment. It is the most widely used adsorbent since most of its chemical (e.g. surface groups) and physical properties (e.g. pore size distribution and surface area) can be tuned according to what is needed.<ref>{{Cite journal |last1=Blankenship |first1=L. Scott |last2=Mokaya |first2=Robert |date=2022-02-21 |title=Modulating the porosity of carbons for improved adsorption of hydrogen, carbon dioxide, and methane: a review |journal=Materials Advances |language=en |volume=3 |issue=4 |pages=1905–1930 |doi=10.1039/D1MA00911G |s2cid=245927099 |issn=2633-5409|doi-access=free }}</ref> Its usefulness also derives from its large micropore (and sometimes mesopore) volume and the resulting high surface area. Recent research works reported activated carbon as an effective agent to adsorb cationic species of toxic metals from multi-pollutant systems and also proposed possible adsorption mechanisms with supporting evidences.<ref>{{Cite journal|title=Comparative study of separation of heavy metals from leachate using activated carbon and fuel ash|doi=10.1061/(ASCE)HZ.2153-5515.0000520|pmid=04020031|year=2020|last1=Mohan|first1=S|last2=Nair|first2=Vijay V|journal=Journal of Hazardous, Toxic & Radioactive Waste|volume=24|issue=4|pages=473–491 |s2cid=219747988 }}</ref>