Switchgrass-and pine wood-derived biochars produced by fast pyrolysis were characterized to estimate the degree of thermochemical transformation and to assess their potential use as a soil amendment and to sequester carbon. The feedstocks were pyrolyzed to biochars in an auger reactor at 450, 600, and 800 °C with a residence time of 30 s. Ash contents of switchgrass and pine wood biochars varied from 13 to 22% and from 1.3 to 5.2%, respectively. Nutrients, such as N, P, K, S, Mg, and Ca, in switchgrass biochars ranged from 0.16 to 1.77%. Under combustion conditions, switchgrass chars were decomposed at lower temperatures than pine wood biochars because of the structural differences between the two feedstocks. Principal component analysis of the Fourier transform infrared (FTIR) spectra allowed for the discrimination of all biochars by significant contributions of cellulose-derived functionality at low pyrolysis temperatures, while the same analysis of the Raman spectra presented apparent separation of all biochars by two broad bands at 1587 and 1350 cm À1 . These two broad peaks were deconvoluted into pseudo-subpeaks, which revealed that the number of aromatic rings linearly increased with the pyrolysis temperature. Cross-linkages between aromatic rings were also found to increase with thermal treatment, and switchgrass biochars contained a higher number of aromatic rings and cross-linkages than pine wood biochars, which was consistent with turbostratic carbon crystallites in the X-ray diffraction (XRD) pattern.

No abstract

A practical approach for adsorption modeling of heterogeneity of single-walled carbon nanotube (SWNT) bundles has been developed. The method integrates experimental analysis with grand canonical Monte Carlo (GCMC) simulation of a small probe molecule, such as nitrogen at 77 K. Using this method, it is possible for one to separately estimate adsorption inside the nanotubes, adsorption on the external surface of the bundles, and adsorptive contributions from the impurities present in samples. By introducing a scaling parameter for adsorption in the internal porous volume of the bundles, the predicted adsorption isotherm results in a near replication of the experimental N 2 adsorption isotherm. We refer to this parameter as the volume fraction of open-ended nanotubes. Our GCMC-assisted experimental characterization method has been applied successfully to several commercial samples obtained from different suppliers, such as MER Corp., Carbon Nanotechnologies Inc., Carbon Solutions Inc., Carbolex Inc., and BuckyUSA. It was found that the volume fraction of openended SWNTs in these samples ranged between 0 and 55%. The majority of the samples were subjected to some purification treatment by the manufacturer and exhibited an already high BET surface area of hundreds of square meters per gram. The near-perfect reproduction of the experimental N 2 (77 K) adsorption isotherm for each of the tested samples shows that our characterization method is not specific to a particular sample and can be extended to most SWNTs successfully. The fraction of open-ended SWNTs cannot otherwise be estimated by visual characterization of the samples because of the large aspect ratio of nanotubes and the spaghetti-like arrangement of the bundles. Our method has the potential to become a standard technique to quantify this structural property of SWNT samples.