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- ItemStable 15N isotopes in fine and coarse urban particulate matter(Philadelphia, Pa : Taylor & Francis, 2021) Wiedenhaus, Hanna; Ehrnsperger, Laura; Klemm, Otto; Strauss, HaraldParticulate nitrogen has far-reaching negative effects on human health and the environment, and effective strategies for reducing it require understanding its sources and formation processes. To learn about these factors, we recorded size-resolved nitrogen isotope ratios (δ15N) of total particulate N at an urban site in northwest Germany during a four-week measuring campaign. We observed a steady decrease in δ15N when going from fine to coarse particles, with values between +18 ‰ and −2 ‰. This difference based on particle size is caused by different isotope fractionation processes during particle formation: The fine particles contain ammonium nitrate, which is formed in an equilibrium process, leading to an enrichment of 15N. Moreover, fine particles are more reactive due to their larger surface areas and relatively long residence times in the atmosphere, which leads to an additional enrichment of 15N; a key step of this process likely occurs when the ammonium particles interact with ammonia from agricultural sources. In contrast to fine particles, coarse particles are formed by direct absorption of HNO3 on preexisting particles; the HNO3 stems from traffic emissions of NOx and subsequent oxidation in the atmospheric gas phase. Because only a small amount of isotope fractionation is associated with non-equilibrium processes during phase transitions, there is less 15N enrichment in the coarse particles. Overall, nitrogen isotopes clearly reflect the different formation processes of fine and coarse aerosol particles. © 2021 The Author(s). Published with license by Taylor & Francis Group, LLC.
- ItemDirect raman spectroscopic measurements of biological nitrogen fixation under natural conditions: An analytical approach for studying nitrogenase activity(Columbus, Ohio : American Chemical Society, 2016) Jochum, Tobias; Fastnacht, Agnes; Trumbore, Susan E.; Popp, Jürgen; Frosch, TorstenBiological N2 fixation is a major input of bioavailable nitrogen, which represents the most frequent factor limiting the agricultural production throughout the world. Especially, the symbiotic association between legumes and Rhizobium bacteria can provide substantial amounts of nitrogen (N) and reduce the need for industrial fertilizers. Despite its importance in the global N cycle, rates of biological nitrogen fixation have proven difficult to quantify. In this work, we propose and demonstrate a simple analytical approach to measure biological N2 fixation rates directly without a proxy or isotopic labeling. We determined a mean N2 fixation rate of 78 ± 5 μmol N2 (g dry weight nodule)-1 h-1 of a Medicago sativa-Rhizobium consortium by continuously analyzing the amount of atmospheric N2 in static environmental chambers with Raman gas spectroscopy. By simultaneously analyzing the CO2 uptake and photosynthetic plant activity, we think that a minimum CO2 mixing ratio might be needed for natural N2 fixation and only used the time interval above this minimum CO2 mixing ratio for N2 fixation rate calculations. The proposed approach relies only on noninvasive measurements of the gas phase and, given its simplicity, indicates the potential to estimate biological nitrogen fixation of legume symbioses not only in laboratory experiments. The same methods can presumably also be used to detect N2 fluxes by denitrification from ecosystems to the atmosphere. (Figure Presented).
- ItemHydrothermal Carbonization and Pyrolysis of Sewage Sludge: Effects on Lolium perenne Germination and Growth(Basel : MDPI, 2019) Paneque, Marina; Knicker, Heike; Kern, Jürgen; De la Rosa, José MaríaThe pyrolysis and hydrothermal carbonization (HTC) of sewage sludge (SS) resulted in products free of pathogens, with the potential for being used as soil amendment. With this work, we evaluated the impact of dry pyrolysis-treated (600 °C, 1 h) and HTC-treated (200 °C, 260 °C; 0.5 h, 3 h) SS on the germination, survival, and growth of Lolium perenne during an 80 day greenhouse experiment. Therefore, the hydrochars and pyrochars were amended to a Calcic Cambisol at doses of 5 and 25 t ha−1. The addition of sludge pyrochars to the Cambisol did not affect Lolium germination, survival rates or plant yields. However, the use 25 t ha−1 of wood biochar reduced germination and survival rates, which may be related to the low N availability of this sample. In comparison to the control, higher or equal plant biomass was produced in the hydrochar-amended pots, even though some hydrochars decreased plant germination and survival rates. Among all the evaluated char properties, only the organic and inorganic N contents of the chars, along with their organic C values, positively correlated with total and shoot biomass production. Our work demonstrates the N fertilization potential of the hydrochar produced at low temperature, whereas the hydrochar produced at 260 °C and the pyrochars were less efficient with respect to plant yields.
- ItemEffects of synthesis catalyst and temperature on broadband dielectric properties of nitrogen-doped carbon nanotube/polyvinylidene fluoride nanocomposites(New York, NY [u.a.] : Pergamon Press, 2016) Ameli, A.; Arjmand, M.; Pötschke, Petra; Krause, Beate; Sundararaj, U.This study reports on nitrogen-doped carbon nanotube (N-CNT)/polymer nanocomposites exhibiting relatively high and frequency independent real permittivity (ϵ′) together with low dielectric loss (tan δ). N-CNTs were synthesized by chemical vapor deposition, and their nanocomposites were prepared by melt-mixing with polyvinylidene fluoride (PVDF). In the synthesis of N-CNTs, three catalysts of Co, Fe and Ni, and three temperatures of 650, 750 and 950 °C were employed. The morphology, aspect ratio, synthesis yield, remaining residue, nitrogen content, nitrogen bonding type, and powder conductivity of N-CNTs, and the morphology, polar crystalline phase, and broadband dielectric properties of N-CNT/PVDF nanocomposites were investigated. The results revealed that by proper selection of synthesis catalyst (Fe) and temperature (650 °C and 950 °C), nitrogen doping generated polarizable nanotubes via providing local polarization sites, and resulted in nanocomposites with favorable dielectric properties for charge storage applications at N-CNT loadings as low as 1.0 wt%. As a result, 3.5 wt% (N-CNT)Fe/950°C/PVDF nanocomposites exhibited an insulative behavior with ϵ' = 23.12 and tan δ = 0.05 at 1 kHz, a combination superior to that of PVDF, i.e., ϵ' = 8.4 and tan δ = 0.03 and to those of percolative nanocomposites, e.g., ϵ' = 71.20 and tan δ = 63.20 for 3.5 wt% (N-CNT)Fe/750°C/PVDF. Also, the relationships between the dielectric properties, N-CNT structure, and nanocomposite morphology were identified.
- ItemEffect of synthesis catalyst on structure of nitrogen-doped carbon nanotubes and electrical conductivity and electromagnetic interference shielding of their polymeric nanocomposites(New York, NY [u.a.] : Pergamon Press, 2016) Arjmand, Mohammad; Chizari, Kambiz; Krause, Beate; Pötschke, Petra; Sundararaj, UttandaramanDifferent catalysts including Co, Fe, and Ni were used to synthesize nitrogen-doped carbon nanotubes (N-CNTs) by chemical vapor deposition technique. Synthesized N-CNTs were melt mixed with a polyvinylidene fluoride (PVDF) matrix using a small scale mixer at different concentrations ranging from 0.3 to 3.5 wt%, and then compression molded. The characterization techniques revealed significant differences in the synthesis yield and the morphological and electrical properties of both N-CNTs and nanocomposites depending on the catalyst type. Whereas Co and Fe resulted in yields comparable to industrial multiwalled CNTs, Ni was much less effective. The N-CNT aspect ratio was the highest for Co catalyst, followed by Ni and Fe, whereas nitrogen content was the highest for Ni. Raman spectroscopy revealed lowest defect number and highest N-CNT crystallinity for Fe catalyst. Characterization of N-CNT/PVDF nanocomposites showed better dispersion for N-CNTs based on Co and Fe as compared to Ni, and the following order of electrical conductivity and electromagnetic interference shielding (from high to low): Co > Fe > Ni. The superior electrical properties of (N-CNT)Co nanocomposites were ascribed to a combination of high synthesis yield, high aspect ratio, low nitrogen content and high crystallinity of N-CNTs combined with a good state of N-CNT dispersion.
- ItemCooperative catalytic methoxycarbonylation of alkenes: Uncovering the role of palladium complexes with hemilabile ligands(Cambridge : RSC, 2018) Dong, Kaiwu; Sang, Rui; Wei, Zhihong; Liu, Jie; Dühren, Ricarda; Spannenberg, Anke; Jiao, Haijun; Neumann, Helfried; Jackstell, Ralf; Franke, Robert; Beller, MatthiasMechanistic studies of the catalyst [Pd2(dba)3/1,1′-bis(tert-butyl(pyridin-2-yl)phosphanyl)ferrocene, L2] for olefin alkoxycarbonylation reactions are described. X-ray crystallography reveals the coordination of the pyridyl nitrogen atom in L2 to the palladium center of the catalytic intermediates. DFT calculations on the elementary steps of the industrially relevant carbonylation of ethylene (the Lucite α-process) indicate that the protonated pyridyl moiety is formed immediately, which facilitates the formation of the active palladium hydride complex. The insertion of ethylene and CO into this intermediate leads to the corresponding palladium acyl species, which is kinetically reversible. Notably, this key species is stabilized by the hemilabile coordination of the pyridyl nitrogen atom in L2. The rate-determining alcoholysis of the acyl palladium complex is substantially facilitated by metal-ligand cooperation. Specifically, the deprotonation of the alcohol by the built-in base of the ligand allows a facile intramolecular nucleophilic attack on the acyl palladium species concertedly. Kinetic measurements support this mechanistic proposal and show that the rate of the carbonylation step is zero-order dependent on ethylene and CO. Comparing CH3OD and CH3OH as nucleophiles suggests the involvement of (de)protonation in the rate-determining step.
- ItemControlling the speciation and reactivity of carbon-supported gold nanostructures for catalysed acetylene hydrochlorination(Cambridge : RSC, 2018) Kaiser, Selina K.; Lin, Ronghe; Mitchell, Sharon; Fako, Edvin; Krumeich, Frank; Hauert, Roland; Safonova, Olga V.; Kondratenko, Vita A.; Kondratenko, Evgenii V.; Collins, Sean M.; Midgley, Paul A.; López, Núria; Pérez-Ramírez, JavierCarbon-supported gold catalysts have the potential to replace the toxic mercuric chloride-based system applied industrially for acetylene hydrochlorination, a key technology for the manufacture of polyvinyl chloride. However, the design of an optimal catalyst is essentially hindered by the difficulties in assessing the nature of the active site. Herein, we present a platform of carbon supported gold nanostructures at a fixed metal loading, ranging from single atoms of tunable oxidation state and coordination to metallic nanoparticles, by varying the structure of functionalised carbons and use of thermal activation. While on activated carbon particle aggregation occurs progressively above 473 K, on nitrogen-doped carbon gold single atoms exhibit outstanding stability up to temperatures of 1073 K and under reaction conditions. By combining steady-state experiments, density functional theory, and transient mechanistic studies, we assess the relation between the metal speciation, electronic properties, and catalytic activity. The results indicate that the activity of gold-based catalysts correlates with the population of Au(i)Cl single atoms and the reaction follows a Langmuir-Hinshelwood mechanism. Strong interaction with HCl and thermodynamically favoured acetylene activation were identified as the key features of the Au(i)Cl sites that endow their superior catalytic performance in comparison to N-stabilised Au(iii) counterparts and gold nanoparticles. Finally, we show that the carrier (activated carbon versus nitrogen-doped carbon) does not affect the catalytic response, but determines the deactivation mechanism (gold particle aggregation and pore blockage, respectively), which opens up different options for the development of stable, high-performance hydrochlorination catalysts. © 2019 The Royal Society of Chemistry.
- ItemEnvironmental Effects over the First 2½ Rotation Periods of a Fertilised Poplar Short Rotation Coppice(New York, NY : Springer, 2017-12-7) Kern, Jürgen; Germer, Sonja; Ammon, Christian; Balasus, Antje; Bischoff, Wolf-Anno; Schwarz, Andreas; Forstreuter, Manfred; Kaupenjohann, MartinA short rotation coppice (SRC) with poplar was established in a randomised fertilisation experiment on sandy loam soil in Potsdam (Northeast Germany). The main objective of this study was to assess if negative environmental effects as nitrogen leaching and greenhouse gas emissions are enhanced by mineral nitrogen (N) fertiliser applied to poplar at rates of 0, 50 and 75 kg N ha−1 year−1 and how these effects are influenced by tree age with increasing number of rotation periods and cycles of organic matter decomposition and tree growth after each harvesting event. Between 2008 and 2012, the leaching of nitrate (NO3 −) was monitored with self-integrating accumulators over 6-month periods and the emissions of the greenhouse gases (GHG) nitrous oxide (N2O) and carbon dioxide (CO2) were determined in closed gas chambers. During the first 4 years of the poplar SRC, most nitrogen was lost through NO3 − leaching from the main root zone; however, there was no significant relationship to the rate of N fertilisation. On average, 5.8 kg N ha−1 year−1 (13.0 kg CO2equ) was leached from the root zone. Nitrogen leaching rates decreased in the course of the 4-year study parallel to an increase of the fine root biomass and the degree of mycorrhization. In contrast to N leaching, the loss of nitrogen by N2O emissions from the soil was very low with an average of 0.61 kg N ha−1 year−1 (182 kg CO2equ) and were also not affected by N fertilisation over the whole study period. Real CO2 emissions from the poplar soil were two orders of magnitude higher ranging between 15,122 and 19,091 kg CO2 ha−1 year−1 and followed the rotation period with enhanced emission rates in the years of harvest. As key-factors for NO3 − leaching and N2O emissions, the time after planting and after harvest and the rotation period have been identified by a mixed effects model. © 2017, The Author(s).
- ItemScanning single quantum emitter fluorescence lifetime imaging: Quantitative analysis of the local density of photonic states(Washington, DC : American Chemical Society, 2014) Schell, A.W.; Engel, P.; Werra, J.F.M.; Wolff, C.; Busch, K.; Benson, O.Their intrinsic properties render single quantum systems as ideal tools for quantum enhanced sensing and microscopy. As an additional benefit, their size is typically on an atomic scale that enables sensing with very high spatial resolution. Here, we report on utilizing a single nitrogen vacancy center in nanodiamond for performing three-dimensional scanning-probe fluorescence lifetime imaging microscopy. By measuring changes of the single emitter's lifetime, information on the local density of optical states is acquired at the nanoscale. Three-dimensional ab initio discontinuous Galerkin time-domain simulations are used in order to verify the results and to obtain additional insights. This combination of experiment and simulations to gather quantitative information on the local density of optical states is of direct relevance for the understanding of fundamental quantum optical processes as well as for the engineering of novel photonic and plasmonic devices.
- ItemImprovement of the optical properties after surface error correction of aluminium mirror surfaces(London : Biomed Central, 2021) Ulitschka, M.; Bauer, J.; Frost, F.; Arnold, T.Ion beam finishing techniques of aluminium mirrors have a high potential to meet the increasing demands on applications of high-performance mirror devices for visible and ultraviolet spectral range. Reactively driven ion beam machining using oxygen and nitrogen gases enables the direct figure error correction up to 1 μm machining depth while preserving the initial roughness. However, the periodic turning mark structures, which result from preliminary device shaping by single-point diamond turning, often limit the applicability of mirror surfaces in the short-periodic spectral range. Ion beam planarization with the aid of a sacrificial layer is a promising process route for surface smoothing, resulting in successfully reduction of the turning mark structures. A combination with direct surface smoothing to perform a subsequent improvement of the microroughness is presented with a special focus on roughness evolution, chemical composition, and optical surface properties. As a result, an ion beam based process route is suggested, which allows almost to recover the reflective properties and an increased long-term stability of smoothed aluminium surfaces.