Interactions of graphene with oxidants in a mixed atmosphere: synergistic effects of O2/H2O and O2/CO2 on gasification reactivity and kinetics.

The gasification of carbon with O2, CO2, and H2O oxidants plays an important role in several energy-based applications. As most of the industrial gasification processes are conducted under mixed-atmosphere conditions, the oxidation of carbon in binary oxidant mixtures becomes crucially important. Using reactive force-field (ReaxFF) potentials, extensive MD simulations were carried out on the oxidation behavior of graphene in mixed O2/H2O and O2/CO2 environments for a range of gas compositions and temperatures. A graphene sheet with a line defect comprising of eight and four-membered rings was used as the starting carbon structure. In addition to enhanced carbon gasification with oxygen additions, MD simulations showed synergistic interactions between different oxidants and their net influence on the overall reactivities. The gasification levels achieved under the binary system were higher than the linear combination of contributions from individual oxidants. The addition of ∼40% O2 in the binary mix was identified as the region with the highest reactivity during the initial stages of gasification. The oxidation reactions with oxygen were found to start instantaneously in the presence of H2O or CO2 instead of the usual initial delay. A very fast reaction kinetics was also observed in the initial stages in the presence of oxygen. Our results show that the gasification reactions under H2O and CO2 started at lower temperatures than O2 thereby creating a partially oxidized structure. Due to the presence of a large number of activation sites, very high rates of gasification were achieved with oxygen. These findings could help identify optimal oxidant compositions towards maximizing carbon gasification and minimizing CO2 emissions.

Formation of carbyne-like materials during low temperature pyrolysis of lignocellulosic biomass: A natural resource of linear sp carbons.

The exploration, understanding and potential applications of 'Carbyne', the one-dimensional sp allotrope of carbon, have been severely limited due to its extreme reactivity and a tendency for highly exothermic cross-linking. Due to ill-defined materials, limited characterization and a lack of compelling definitive evidence, even the existence of linear carbons has been questioned. We report a first-ever investigation on the formation of carbyne-like materials during low temperature pyrolysis of biobased lignin, a natural bioresource. The presence of carbyne was confirmed by detecting acetylenic -C≡C- bonds in lignin chars using NMR, Raman and FTIR spectroscopies. The crystallographic structure of this phase was determined as hexagonal: a = 6.052 Å, c = 6.96 Å from x-ray diffraction results. HRSEM images on lignin chars showed that the carbyne phase was present as nanoscale flakes/fibers (~10 nm thick) dispersed in an organic matrix and showed no sign of overlapping or physical contact. These nanostructures did not show any tendency towards cross-linking, but preferred to branch out instead. Overcoming key issues/challenges associated with their formation and stability, this study presents a novel approach for producing a stable condensed phase of sp-bonded linear carbons from a low-cost, naturally abundant, and renewable bioresource.

Identification of the Escherichia coli K-12 ybhE gene as pgl, encoding 6-phosphogluconolactonase.

We report identification of the Escherichia coli ybhE gene as the pgl gene that encodes 6-phosphogluconolactonase. A tentative identification was first made based on the known approximate location of the pgl gene and the similarity of the presumptive ybhE-encoded protein sequence to a known Pgl enzyme. To test this notion, the ybhE gene was deleted and replaced with a drug marker. Like previously characterized pgl mutants, the ybhE deletion mutant had a Blu- phenotype (dark-blue staining with iodine due to accumulation of starch after growth on minimal maltose) and demonstrated impaired growth on minimal glucose medium when combined with a pgi mutation. Biochemical assay of crude extracts for 6-phosphogluconolactonase enzymatic activity showed that ybhE encodes this activity. The ybhE gene was transferred from the E. coli chromosome to an expression vector. This ybhE clone complemented both the precise deletion of the ybhE gene and a larger deletion, pglDelta8, for the Blu- phenotype and for phosphogluconolactonase activity, confirming that ybhE is the pgl gene. A newly observed phenotype of pgl strains is a lowered frequency of appearance of Bgl+ mutants that can utilize the beta-glucoside salicin. This is likely due to poor growth of Bgl+ pgl strains on salicin due to the accumulation of 6-phosphogluconolactone.