Katalytische Dechlorierung von Chlorkohlenwasserstoffen aus kontaminierten Grundw?ssern

Im Rahmen des Forschungsverbundes SAFIRA wurden zwei neue Katalysatorsysteme zur reduktiven Dehalogenierung von CKW mit H2 entwickelt und am Standort Bitterfeld in Grundwasser-Durchflussreaktoren untersucht. Die katalytisch aktive Komponente Pd wurde zum Schutz vor Vergiftung durch ionische Verbindungen zum einen in hydrophobe Polymermembranen eingebettet, zum anderen wurden Pd-Cluster in den Poren hydrophober Zeolithe erzeugt. Die erreichten Standzeiten beider Katalysatoren waren trotzdem bedingt durch die Bildung von H ₂ S und organischen Schwefelverbindungen durch mikrobiologische Sulfatreduktion gering. Die Katalysatoren waren zwar durch eine Spülung mit Hypochlorit regenerierbar, unterlagen aber nach wenigen Tagen erneuter Vergiftung. Der Einsatz von Pd-Katalysatoren unter Bitterfelder Grundwasserbedingungen wird deshalb als problematisch eingesch?tzt.     

Large-area nanopatterned graphene for ultrasensitive gas sensing

Chemical vapor deposited （CVD） graphene is nanopatterned using a spherical block copolymer etch mask. The use of spherical rather than cylindrical block copolymers allows homogeneous patterning of cm-scale areas without any substrate surface treatment. Raman spectroscopy was used to study the con- trolled generation of point defects in the graphene lattice with increasing etching time, confirming that alongside the nanomesh patterning, the nanopatterned CVD graphene presents a high defect density between the mesh holes. The nanopatterned samples showed sensitivities for NO2 of more than one order of magnitude higher than for non-patterned graphene. NO2 concentrations as low as 300 ppt were detected with an ultimate detection limit of tens of ppt. This is the smallest value reported so far for non-UV illuminated graphene chemiresistive NO2 gas sensors. The dramatic improvement in the gas sensitivity is believed to be due to the high adsorption site density, thanks to the combination of edge sites and point defect sites. This work opens the possibility of large area fabrication of nanopatterned graphene with extremely high densities of adsorption sites for sensing applications.     

Beryllium-7 as a tracer of short-term sediment deposition and resuspension in the Fox River, Wisconsin

Short-term (approximately monthly) sediment deposition and resuspension rates of surficial bed sediments in two PCB-laden impoundments on the Fox River, WI, were determined in the summer and fall of 1998 using 7Be, a naturally occurring radioisotope produced in the atmosphere. Decay-corrected activities and inventories of 7Be were measured in bed sediment and in suspended particles. Beryllium-7 activities generally decreased with depth in the top 5-10 cm of sediments and ranged from undetectable to approximately 0.9 pCi cm(-3). Inventories of 7Be, calculated from the sum of activities from all depths, ranged from 0.87 to 3.74 pCi cm(-2), and the values covaried between sites likely reflecting a common atmospheric input signal. Activities of 7Be did not correlate directly with rainfall. Partitioning the 7Be flux into "new" and "residual" components indicated that net deposition was occurring most of the time during the summer. Net erosion, however, was observed at the upstream site from the final collection in the fall. This erosion event was estimated to have removed 0.10 g (cm of sediment)(-2), corresponding to approximately 0.5 cm of sediment depth, and approximately 6-10 kg of polychlorinated biphenyls (PCBs) over the whole deposit. Short-term accumulation rates were up to approximately 130 times higher than the long-term rates calculated from 137Cs profiles, suggesting an extremely dynamic sediment transport environment, even within an impounded river system.     

Oscillating Combustion of Gun Propellants in the Closed Vessel. I. preliminary investigation

The oscillating combustion, which takes place in the closed vessel when certain colloidal gun propellants are fired has been investigated. The amplitude of the oscillation depended on the geometry and flame temperature of the propellant. For propellants having the same composition but different geometry, the amplitude of the oscillation varied inversely with the maximum pressure in the vessel. This was tentatively ascribed to vortex formation during combustion.