ARS | Publication request: Solid-state NMR and ESR studies of activated carbons produced from pecan shells

Submitted to: Carbon
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2010
Publication Date: August 1, 2010
Repository URL: http://hdl.handle.net/10113/43983
Citation: Cheng, H.N., Wartelle, L.H., Klasson, K.T., Edwards, J.C. 2010. Solid-state NMR and ESR studies of activated carbons produced from pecan shells. Carbon. 48:2455-2469.

Interpretive Summary: In this work, we showed that solid state NMR and ESR are effective methods of characterizing activated carbons. The activated carbons are known to remove metal ions and organic species in industrial waste water. They are also used in sugar refining, in geosmin adsorption, and even as a soil fertility agent. Despite their usefulness, the chemistry is only partly known. Through NMR and ESR, we can now more fully characterize the chemical structures involved and gain a better understanding of reaction mechanisms. These characterization tools enable us to have a more rational way of designing future, improved activated carbon systems. Although the work shown here deals with activated carbon from pecan, carbonaceous materials from other sources can be likewise studied. This work will benefit farmers and growers who have agriculturally based waste materials that can be converted to activated carbon.

Technical Abstract: Activated carbon from pecan shells has shown promise as an adsorbent in water treatment and sugar refining. However, the chemistry of the material is complex and not fully understood. We report here the application of solid state NMR and ESR to study the chemical structure, mobility, and pore volume of pecan shell-based carbon. We use a model system where the pecan shells are activated with phosphoric acid, and carbonized at 450 degrees C for 4 hours with varying amounts of air flow. With carbonization, aliphatic groups quickly disappear and aromatic clusters form. With increasing air flow, the fractions of carboxy and phenolic groups increase due to oxidation, and aromatic clusters partly break down. Using 31P NMR, we observed that the two main species are phosphoric acid and alkyl phosphate, the latter increasing with increasing air flow. There are suggestions of small amounts of polyphosphates present, but no phosphonic acid and phosphonates are found under the present reaction conditions.