Benzo(a)pyrene Due diligence
Benzo(a)pyrenes are formed from the incomplete combustion of organic material. They can be found in coal tar, tobacco smoke, and grill meat. These compounds can be very carcinogenic. Activated carbon can be a nice binder for detoxification.
Different types of coal
Allen, C. S., Ghamouss, F., Boujibar, O., & Harris, P. J. F. (2022). Aberration-corrected transmission electron microscopy of a non-graphitizing carbon. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, 478(2258).Peter Harris was the corresponding author. At the time he was at Electron Microscopy Laboratory, JJ Thomson Building, University of Reading, Whiteknights, Reading RG6 6AF, UK.;
This post is working off image and what appears to be the full text of the above publication. It is good to know that Roslind Franklin, the woman responsible for the X-ray crystal structure of DNA, instrumental for the Noble Prize awarded to Crick and Watson. Franklin did other interesting things in her too short life.
Franklin RE. 1951 Crystallite growth in graphitizing and non-graphitizing carbons. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences 209, 196–218. (doi:10.1098/rspa.1951.0197)
Franklin described the effect of high temperature heat treatment carbons prepared from polymers, coals, and pitch. Franlkin found that the carbons fell into two distinct and well-defined classes. According to the Harris group summary of Franklin’s work:
- Graphitizing carbons could be converted into crystalline graphite by heating to 3000oC, Cokes are graphitizing carbons.
- Non-graphitising carbons (NGCs), as the name suggests, cannot be converted to graphite. Chars are non-graphitizing carbons.
“Graphitising carbons are soft and non-porous, while non-graphitising carbons are hard, microporous, low density materials. Non-graphitising carbons are of great commercial importance. When activated by chemical treatment they can develop extremely high surface areas, and in this form are widely used in the purification of air and water supplies”
The diversity of pure carbon structures
An image of electronic configurations of carbon in the basic state, a transition excited state, and sp3 hybrid orbitals associated with diamonds
In school I was taught that sp2 orbitals are found in pure carbon pencil graphite. It was generally assumed that the s orbital contained both paired orbitals. One of these electrons could be kicked out into the higher energy p sub oribital in an excited state. These four electrons can become equalized in what we called an sp3 hybrid oribital.
The Harris group’s continuation of Franklin’s work is of interest to clinicians giving their patients activated carbon because we do not want to be eating any form of carbon resembling diamonds that could rip apart our GI tracts. Note that graphite has a very planar array of six member rings.
And the porous carbon structures we want in binders
Panel C is an enlarged image of the boxed in region of panel B Note the the red dots marking carbons in panel d contain five and seven member rings..
Wikipedia has a good page on carbon bonds that puts the lengths in the Harris paper in perspective.
Comments regrading sp2-sp3 stuff
- Aberration-corrected transmission electron microscopes (ACTEM) has resulted ine direct imaging of atomic structure in both sp2 and sp3 carbons. The technique has been extensively applied to graphene
- There is some uncertainty about the edge structure of the individual fragments. In some cases these would undoubtedly be terminated with oxygen-containing functional groups. The presence of a small amount of oxygen in the sample studied here has already been noted. There may also that sp and sp3-bonded carbon atoms at the edges
- Defects containing pentagons and heptagons have been quite frequently imaged in sp2 carbons. The first direct image of such a defect was reported by Suenaga et al. in an AC-TEM study of single-walled carbon nanotubes
- Defects containing pentagons and heptagons have been quite frequently imaged in sp2 carbons. 5-7 pairs do not introduce any curvature into a hexagonal network; only individual pentagons and heptagons can do this.
Figures not shown
- There are two types of pore: around 2 – 3 nm in size and a smaller one in the sub-nanometer range with spaces between the fragments. .
- not reported in text
- mentions pentagon and hexagon rings as in Buckyball
- Heptagonal rings are introduced with pentagon rings.
- rows of hexagons curved rather than straight, heptagon-pentagon pairs…
- See above
- seems to be a summary figure linking back to work of Franklin. Pentagons and heptagons impede graphinization.
There is nothing to indicate that the non graphite carbon structures are hare like diamonds or easy to fracture. If the activated carbon was prepared correctly, there should not be any benzo (a) pyrenes. It wouldn’t hurt to ask for a certificate of analysis or for studies on the binding capacity.