THE AQUEOUS PHOTOLYSIS OF ETHYLENE GLYCOL ADSORBED ON GOETHITE

Abstract— Suspensions of goethite (α-FeOOH) were photolyzed in aerated ethylene glycol-water solutions at pH 6.5, with ultraviolet light in the wavelength range300–400 nm. Under these conditions, formaldehyde and glycolaldehyde were detected as photoproducts. Quantum yields of formaldehyde production ranged from 1.9 7times; 10^-5 to 2.9 × 10^-4 over the ethylene glycol concentration range of 0.002-2.0 mol/ℓ, and gave evidence that the reaction occurred at the goethite surface. Quantum yields of glycolaldehyde were 20% less than those of formaldehyde, and displayed a concentration-dependent relationship with ethylene glycol similar to that of formaldehyde. Immediately after photolysis, Fe²⁺ was measured to be 4.6 × 10^-7 mol/ℓ in an aerated suspension containing 1.3 mol/ℓ ethylene glycol, and 8.5 × 10^-6 mol/ℓ in the corresponding deoxygenated suspension. Glycolaldehyde was not generated in the deoxygenated suspensions. These results are consistent with a mechanism involving the transfer of an electron from an adsorbed ethylene glycol molecule to an excited state of Fe³⁺ (Iron[III]) in the goethite lattice, to produce Fe²⁺ and an organic cation. In a series of reactions involving O₂, FeOOH, and Fe²⁺, the organic cation decomposes to form formaldehyde and the intermediate radicals "OH and" CH₂OH. OH reacts further with ethylene glycol in the presence of O₂ to yield glycolaldehyde. Aqueous photolysis of ethylene glycol sorbed onto goethite is typical of reactions that can occur in the aquatic environment.     

Zur ma?analytischen Bestimmung von Wolfram und Uran

Zusammenfassung Die für die technische Bestimmung von Molybdän brauchbare fällungsanalytische Titration mit Silbernitrat und potentiometrischer Endpunktsanzeige ist für Wolfram und Uran wegen der ungünstigeren Löslichkeitsverhältnisse nicht brauchbar.Die Reduktion im Silberreduktor und anschließende Titration mit Dichromat anstatt mit dem bisher verwendeten Cer(IV)-sulfat mit Endpunktsanzeige durch Farbumschlag (Diphenylamin) oder auf potentiometrischem Wege ist für Uran bei Einhaltung entsprechender Arbeitsbedingungen (Reduktion in 4 n Salzsäure bei 60°C, 2 · 10^–3 Mol Uran/l als obere Grenze bei der Titration) gut verwendbar. Der Silberreduktor hat jedoch keine erkennbaren Vorteile gegenüber dem Bleireduktor.Für Wolfram ist diese Methode wegen der ungünstigen Lage der Redoxpotentiale nicht brauchbar.     

Synthese,Charakterisierung und EPR-spektroskopische Untersuchung von Heteropolyverbindungen mit tetraedrisch bzw. oktaedrisch koordiniertem Eisen(III)

Synthesis, Characterization, and EPR Studies of Heteropoly Compounds with Iron(III) in Tetrahedral and Octahedral Coordination The heteropoly compounds H₅[FeO₄W₁₂O₃₆] · 6 H₂O (a₀ = 1216 pm), H₃[Fe(OH)₆Mo₆O₁₈] · 4 H₂O, Na₅[FeO₄W₁₂O₃₆] · nH₂O and FeH₂[FeO₄W₁₂O₃₆] · 17 H₂O, for the first time obtained in this work by freeze-drying and characterized by means of chemical analysis, i.r. and u.v. spectroscopy, X-ray powder-photographs, and magnetic measurements, appear as suitable model systems for EPR investigations. They contain, like a number of known Fe^III-heteropoly compounds, Fe^III in FeO₄ or/and FeO₆ units, which are isolated from each other by structural reasons. In the Keggin-compounds M₅[E^IIIO₄W₁₂O₃₆] · nH₂O ( I ) (M = Na, Rb, TMA, TEA; E = Fe, Al, B) Fe^III occupies slightly distorted tetrahedral positions (g′ ≈? 2), which are characterized by zfs-values of ≈? 10 mT and line widthes ΔB of 2.0 ?15 mT. Unlike as for I cations with different physico-chemical characteristics have only little effect on the Fe^III-zfs. This holds for the Anderson-complexes M₃[Fe(OH)₆Mo₆O₁₈]·nH₂O, (M = H, K, NH₄, TMA; g′ ≈? 4.3 ΔB ≈? 67 mT) and for M5[SiO₄W₁₁O₃₅FeO₅(OH₂)]·nH₂O, (M = K, TMA; g′ = 4.3 ΔB = 26.5 mT). The FeO₆ octahedra are more distorted than the FeO₄ tetrahedra in I and therefore less susceptible for structural changes.     

Calcium oxalate crystals in tomato and tobacco plants: morphology and in vitro interactions of crystal-associated macromolecules

Plants form calcium oxalate crystals with unique morphologies under well-controlled conditions. We studied the morphology of single calcium oxalate monohydrate (whewellite) crystals extracted from tomato and tobacco leaves. These crystals have a pseudotetrahedral shape. We identified the (101), (101) or (102), (110), and (hk0) faces as stable faces. The morphology is chiral with unique handedness. We also show that calcium oxalate monohydrate crystals isolated from tomato, tobacco, and bougainvillea leaves contain macromolecules rich in Gly, Glx, and Ser. Crystal-associated macromolecules extracted from tomato and tobacco influence the morphology of calcium oxalate monohydrate crystals grown in vitro, promoting preferential development of the [120] faces. Furthermore, crystal-associated macromolecules from tobacco promote nucleation of calcium oxalate monohydrate crystals, whereas model polypeptides do not have any significant effect on nucleation. These results imply an active role of the crystal-associated macromolecules in the formation of pseudotetrahedral shapes in vitro, and these properties may in part be responsible for the unique chiral morphology of the natural pyramidal-shaped crystals.     

Die ma?analytische Bestimmung des Molybd?ns

Zusammenfassung Die fällungsmaßanalytische Bestimmung von Molybdat kann durch potentiometrische Titration mit Silbernitrat in acetatgepufferter Lösung geschehen, wobei zweckmäßig noch ein Zusatz von Äthanol zur Lösung erfolgt. Die Analysenwerte streuen etwa ± 1%, sind demnach für technische, nicht aber exakte Bestimmungen brauchbar.Eine einfache und genaue Bestimmung des Molybdäns ist jedoch möglich durch Reduktion der salzsauren Lösung im Silberreduktor zu Mo⁵⁺, das anschließend nach Zusatz von Phosphorsäure als Reaktions-beschleuniger und Diphenylamin als Indicator mit Dichromat auf Farbumschlag nach Blau titriert wird.     

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

Large area single and bilayer graphene are grown on Pt/Ti/SiO₂ substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO₂ substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO₂ substrate at a low filament temperature. The approach paves a novel pathway towards the layer-controlled growth of graphene on Pt/Ti/SiO₂ substrates by HFCVD for frontier applications.     

Impurity distribution and electrical characteristics of boron-doped Si1−x Ge x /Si p +/N heterojunction diodes produced using pulsed UV-laser-induced epitaxy and Gas-immersion laser doping

A two-step pulsed UV-laser process which independently controls the metallurgical and electrical junction depth of a Si_1–x Ge _x /Si heterojunction diode has been implemented. Pulsed Laser-Induced Epitaxy (PLIE) combined with Gas-immersion Laser Doping (GILD) are used to fabricate boron-doped heteroepitaxial p ⁺/N Si_1–x Ge _x /Si layers and diodes. Borontrifluoride is used as the gaseous dopant source in the GILD process step. Boron incorporation and activation are investigated as a function of laser energy fluence and the number of laser pulses using SIMS and Halleffect measurements. The dose of incorporated dopant is on the order of 10¹³ cm^–2 per pulse. The B profiles obtained are flat except for a peak at the interface resulting from segregation effects. The B and Ge distributions are compared with shifts in the turn-on voltage of p ⁺/N Si_1–x /Si heterojunction diodes produced by the process. The GILD/PLIE process is spatially selective with the resulting diodes fabricated being quasiplanar. Hole mobilities in the heavily doped Si_1–x Ge _x films are found to be slightly lower than in comparable Si films.Presently at the Oregon Graduate Institute, Beaverton, OR 97006, USA     

Die titanometrische Bestimmung von Chlorat

Ohne Zusammenfassung     

Fast wavelength-parallel polarimeter for broadband optical networks

We describe a novel wavelength-parallel polarimeter operating in the light-wave band that measures the complete state of polarization of 256 wavelengths in parallel within 20 ms (software-limited), with the potential for submillisecond operation. By use of fast switching ferroelectric liquid crystals in conjunction with an InGaAs arrayed detector, selection and wavelength-parallel detection of individual polarization components can be achieved within approximately 150 microseconds. This instrument offers unprecedented sensing capability that is relevant to the compensation of polarization-related impairments in high-speed light-wave communications.