Low Specific Area Research Articles

Trait‐based community assembly pattern along a forest succession gradient in a seasonally dry tropical forest

AbstractWe aimed to determine the important functional dimensions that may drive forest succession and community assembly patterns in dry tropical forests. We investigated whether there were patterns in specific functional strategies during succession in the dry tropical forests of the Florida Keys, whose unique physical setting includes nutrient‐stressed, salt‐stressed, and water‐limited environments. The study, which focused on ten traits, determined the leading trait dimensions by which species differentiate from one another in the study area. The general patterns of trait covariation at individual sites and among species were analyzed using principal component analysis. Trait niche overlap indices were calculated for all species sampled across all plots. Evidence for/against likely community assembly processes was tested using the coefficient of heterogeneity to determine whether variation within and among five key traits was clustered, random, or evenly distributed across young, old, or all measured forest stands. A combination of plant architecture, wood density, and three leaf traits (specific leaf area, leaf phosphorus, and leaf nitrogen) comprised a key set of functional traits that are important for understanding the community assembly process in dry tropical forest. Older forest stands were dominated by species with low specific area, low leaf nitrogen content, dense wood, and deeper and narrower canopies. Trees of old forests had leaves with lighter carbon isotope composition, suggesting that such individuals were making more efficient use of scarce water. Tests of trait distributions showed significant clustering across forests of all ages. When individual trait distributions in old stands were tested, they displayed either randomly or evenly distributed traits across trait niche space, indicating that resource partitioning was predominant in shaping community composition. Physical traits of trees in young communities are associated with resource acquisitive strategies, while old communities are dominated by species with traits that enhance survival in environments defined by competition or chronic resource scarcity.

Fabrication of high photoreactive carbon nitride nanosheets by polymerization of amidinourea for hydrogen production

As a typical visible-light-responsive organic semiconductor photocatalyst, graphitic carbon nitride (gCN) only exhibits moderate photoreactivity beacuse of its low specific area, limited light harvesting ability and quick recombination of photo-generated carriers. Herein, we report the fabrication of gCN nanosheets (gCN-NSs) with large BET surface area, excellent visible-light-absorptive property and efficient separation of carriers by direct polymerization of amidinourea, the product from the hydrolysis of dicyandiamine (DCDA). When compared with that of bulk gCN (S0) synthesized by direct polymerization of DCDA, the visible photocatalytic hydrogen evoluation rate of gCN-NSs (S2 sample) obtained by condensation of amidinourea improved 4.9 times, which is also 2.4 times higher than that of gCN-NSs (Su sample) which is prepared by polymerization of urea. The enhanced visible photocatalytic activity gCN-NSs (S2) toward hydrogen production can be ascribed to the combined effects of enlarged BET surface that provides more active sites for adsorption and photocatalytic reaction, compacted π-π layer stacking which facilitates the efficient separation of photo-generated carriers, negatively shifted CB potential and improved hydrophilic property that favor the electron transfer at the interfaces between gCN and water. In addition, the product yield of gCN-NSs (S2 sample) from the polymerization of amidinourea is 11.9%, which is 10.8 times higher than Su sample that prepared from urea (only 1.1%).

Structure dependence of Nb2O5-X supported manganese oxide for catalytic oxidation of propane: Enhanced oxidation activity for MnOx on a low surface area Nb2O5-X

A series of Nb2O5-x with different structures were prepared as a carrier to manganese oxide catalysts for total oxidation of propane. The results demonstrated that a monoclinic structure of Nb2O5-x pre-calcined at 1025 °C, leads to significantly and surprisingly higher catalytic oxidation activity when MnOx is deposited at 400 °C even with extremely low specific area (around 3.94 m2/g) relative to the performance of MnOx/Nb2O5-x (∼>50 m2/g pre-calcined at 500 °C). Conversion vs temperature profiles for fresh and aged catalysts were generated and performance compared for different materials. Brunauer Emmett Teller (BET) and X-ray diffraction (XRD) were conducted to reveal the textural and structural features of niobium-based catalysts. Raman, X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were performed to further understand the interaction between manganese and niobium oxides. Raman spectra indicated a new Nb-O-Mn species formed due to the strong interaction between the activated niobium oxide carrier at 1025 °C and manganese oxide. This study describes a synergistic catalytic oxidation effect between Mn oxides deposited on a specific phase structure of Nb2O5-x with very low specific surface area. The enhanced catalytic performance is directly related to the proper ratio of Mn3+/Mn4+ coupled with high ratio of Nb4+/Nb5+ on the surface and the oxygen vacancies generated between monoclinic Nb2O5-x and MnOx.

Experimental Investigation of Fluid Dynamics in Sandwich Packings with Ultrafast X-ray Tomography

Sandwich packings consist of two layers of corrugated sheet structured packings with higher (holdup layer) and lower (de-entrainment layer) specific surface area alternatingly placed in the column. They are preferentially operated between the flooding points of both layers, which results in zones of bubbly flow, froth regime and liquid film flow in each sandwich element. Compared to conventional packed columns, sandwich packings can reach higher capacity and also higher separation efficiency as a result of intensive phase interactions. In the scope of a collaborative project, sandwich packings are experimentally and theoretically investigated. To provide detailed information on the heterogeneous flow patterns to derive reliable process models, ultrafast X-ray tomography is applied as a non-invasive measurement technique with high temporal and spatial resolution. In addition to local liquid holdup in the different layers of the packing, cross-sectional liquid distribution and axial transitions between the flow regimes are estimated. Furthermore, a method for the detection of the gas-liquid interfacial area is proposed.

Postsynthesis Growth of CoOOH Nanostructure on SrCo0.6Ti0.4O3−δ Perovskite Surface for Enhanced Degradation of Aqueous Organic Contaminants

The deployment of an efficient catalyst is critical for successful application of peroxymonosulfate-based advanced oxidation processes to the rapid degradation of retardant organics in wastewater. Considering the rich properties of perovskite oxides and their drawbacks of low specific area and easy cation leaching, we reported a facile postsynthesis hydrothermal treatment method for preparing SrCoTiO@CoOOH (SCT@CoOOH) nanocomposite as an efficient catalyst for PMS activation here. Surprisingly, CoOOH nanosheets were grown in situ over the surface of SCT substrate, resulting in a significantly increased surface area (22.1 m g), enhanced charge transfer capability, more generated surface oxygen defects and a strongly synergistic effect created between the bulk SCT and CoOOH surface layer. Remarkably, SCT@CoOOH exhibited higher (1.7 times) catalytic activity (0.84 mg L min) for phenol degradation than SCT. Additionally, suppressed cobalt leaching was demonstrated in the SCT@CoOOH/PMS system. Notably, singlet oxygen as additional oxidative species were formed to accelerate phenol degradation in the radical-based SCT@CoOOH/PMS system due to the surface oxygen defects. The beneficial effect of higher pH value and different influence of foreign anions on the reation rate were also investigated. As a universal method, it may be also useful for the development of innovative functional materials for other various applications.

Textural, structural and catalytic behavior of low specific area silica-supported copper catalysts: effect of preparation method

Supported copper catalysts on low surface area silica were prepared by several methods and characterized by AAS, XRD, N2 adsorption, SEM, H2-TPR, N2O titration, TGA-DTA, UV–Vis techniques. Their hydrogenating properties were examined in the gas-phase hydrogenation of benzaldehyde. The analysis of characterization results revealed that the choice of preparation method affected the texture, composition, and structure of the calcined and reduced Cu/SiO2 catalysts. The dispersion and size distribution of copper species was present in different forms in the catalysts that exhibited low specific surface areas. In gas-phase hydrogenation of benzaldehyde to benzyl alcohol, the catalysts tested at the reaction temperatures of 160 and 200 °C were stable and conducted to a good catalytic activity and benzyl alcohol selectivity ranging between 5 and 39 µmol min−1 g−1 and 0–95%, respectively. The activity of the catalysts in gas-phase hydrogenation also depended on the particle size and the nature of copper species formed on low surface area silica.

Three-dimensional hierarchical aggregation growth of perovskite ferroelectric microplates with a high-efficient methylene blue adsorption performance

Square-shape and single-crystal-like perovskite PbTiO3 (PT) microplates have been prepared via a facile one-step hydrothermal route by employing ethanol as surfactant. The as-synthesized PT microplates were characterized to exhibit a side length of 4–6µm and a height of ~ 150–200nm. It is interesting to find that the PT microplates were formed via a complex three-dimensional aggregation and oriented attachment process, where small sized precursor-transformed-PT nanoplates were determined to be the building blocks. Such process was proposed to arise from a long-distance electric dipole interaction and short-distance molecular interaction, giving rise to the square-shape and single-crystal-like microplates with large-scale polar {001} exposed. Moreover, these microplates demonstrate a remarkable adsorption performance of methylene blue (MB) from aqueous solution, despite of a low specific area (~ 3.48m2/g). It was revealed that the high-efficient adsorption could be attributed to an electrostatic interaction between MB and polar {001} of the microplates, offering a promising approach to selectively treating pollutant solution with organic molecules.

Structure of Carbon-Coated C12A7 Electride via Solid-State NMR and DFT Calculations

C12A7 calcium aluminate electride (C12A7:e–) is a novel inorganic functional material with mayenite crystal structure. Because of its physical and chemical properties, C12A7:e– can find application as a catalyst carrier in various reactions, including ammonia synthesis. However, the low specific area of this material imposes limitations on its use in catalysis. This limitation can be circumvented by synthesis within carbon nanoreactors as the carbon-coated particles resist sintering. We investigate by solid-state 27Al nuclear magnetic resonance (NMR) spectroscopy the structure of C12A7 electride prepared by the carbon nanoreactor process. An accurate determination of NMR parameters via simultaneous application of both DFT calculations and solid-state NMR proved the structure of carbon-coated C12A7 electride to be identical to the one of materials synthesized by more conventional routes. It was shown that the conducting electrons of C12A7:e– do not alter the cage structure, thus leading to similar NMR para...

Significant Enhancement of Thermal Conductivity in Polymer Composite via Constructing Macroscopic Segregated Filler Networks

The low efficiency of thermal conductive filler is an unresolved issue in the area of thermal conductive polymer composites. Although it is known that minimizing phonon or electron interfacial scattering is the key for achieving high thermal conductivity, the enhancement is generally limited by preparation methods that can yield the ideal morphology and interfaces. Herein, low temperature expandable graphite (LTEG) is added into a commercial impact modifier (Elvaloy4170), which is then coated onto poly(butylene terephthalate) (PBT) particles with various sizes at millimeter scale between their melting temperatures. Thus, macroscopic segregated filler networks with several considerations are constructed: high LTEG loading leads to a short distance between fillers and a robust filler network; continuous Elvaloy-LTEG phase leads to a continuous filler network; and good interaction among filler and matrix leads to good interfacial interaction. More importantly, the rather large size of PBT particles provides the filler networks with low specific interfacial area, which minimizes the interfacial scattering of phonons or electrons. Relative to homogeneous composites with an identical composition, the thermal conductivity is enhanced from 6.2 to 17.8 W/mK. Such an enhancement span is the highest compared with results reported in the literature. Due to possible "shortcut" behavior, much higher effectiveness can be achieved for the current system than found in literature results when the Elvaloy-LTEG phase is considered as filler, with the effectiveness even exceeding the upper limit of theoretical calculation for highly loaded Elvaloy-LTEG phase with relatively large PBT particle sizes. This could provide some guidelines for the fabrication of highly thermal conductive polymer composites as well as multifunctional polymer composites.

New Process to Synthesize Rh2S3 Precursor for Rhxsy Catalyst for HER/HOR in HBr Solution By Na2S and Pretreated Carbon

There has been growing interest in electrical energy storage because of the challenge of integrating intermittent renewable energy sources such as wind and solar into the electrical grid. The hydrogen-bromine reversible fuel cell system serves as a promising technology to meet this need because of its high round-trip conversion efficiency and low cost. Since the commonly used catalyst, platinum, is not stable in the corrosive HBr and Br2 environment, an alternative catalyst which is durable and active is needed. RhxSy catalyst has been found to be stable in the HBr/Br2 environment1,2. The conventional synthesis of RhxSy/C has been developed by De Nora3, where (NH4)2S2O3 serves as sulfur source and XC72R is the carbon support. This kind of catalyst, however, has large and broad particle sizes (12-40 nm) and consequently low mass specific active area (< 10 m2/g) for HOR. Moreover, the exchange current density for the HOR/HER is also relatively lower than the commercial RhxSy catalyst from BASF, which can be seen from Figure 1. Other research groups4,5 have shown that smaller particle size can be achieved if preferable surface for precipitation of Rh cation is provided. Figure 2 shows the mass specific active surface area (ECSA) of the catalyst prepared with pretreated carbon and the commercial Rh2S3 synthesis process. In addition to the ECSA/mass enhancement, Na2S also serves as an appropriate sulfur source to modify the crystal structure of RhxSy, as shown in Figure 3. The modified crystal structure leads to improved exchange current density. This presentation will discuss the attempt to synthesize the RhxSy catalyst with pretreated carbon and Na2S. The characteristics and performance of this catalyst will also be presented. Reference 1. J. Masud, T. Van Nguyen, N. Singh, E. McFarland, M. Ikenberry, K. Hohn, C.J. Pan, and B.J. Hwang, Journal of the Electrochemical Society, 162, F455 (2015). 2. A. Ivanovskaya, N. Singh, R.-F. Liu, H. Kreutzer, J. Baltrusaitis, T. Van Nguyen, H. Metiu, and E. McFarland, Langmuir, 29, 480 (2013). 3. De Nora Elettrodi S.P.A, Synthesis of Noble Metal, Sulphide Catalysts in A Sulfide Ion- Free Aqueous Environment, US6967185 B2, 2005. 4. A. Eguizabal, L. Uson, V. Sebastian, J.L. Hueso, and M.P. Pina, RSC Advances, 5, 90691 (2015). 5. M.S. Shafeeyan, W.M.A.W. Daud, A. Houshmand, and A. Shamiri, Journal of Analytical and Applied Pyrolysis, 89, 143 (2010). Acknowledgments The work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000262 and the National Science Foundation under Grant No. EFRI-1038234 and No. 1416874, as a sub-award from Proton Onsite. Figure 1

Effect of Carbon Substrate Pretreatment on the Ecsa and Activity of RhxSy/C Catalyst

Electrical energy storage technologies are needed when significant fraction of intermittent renewable energy sources such as wind and solar are integrated into the electrical grids. The hydrogen-bromine (H2-Br2) reversible fuel cell system is one of the promising technologies because of its high round-trip conversion efficiency, high power density capability and low cost. In a hydrogen bromine fuel cell, while carbon can be used for the bromine reactions, a noble metal such as platinum is needed for the hydrogen reactions. Since platinum is not stable in HBr/Br2 environment and HBr and Br2 are expected to cross from the bromine electrode to the hydrogen electrode during operation, a more durable and active catalyst is needed for the hydrogen reactions. RhxSy catalysts have been found to be stable in the HBr/Br2 environment and as active as platinum per active area. 1,2 Commercial RhxSy catalysts have large and broad particle sizes (12-40 nm) and consequently low mass specific active area (< 10 m2/g) for HOR. By literatures3,4, smaller particle size can be achieved if more preferable surface for precipitation of Rh cation is provided. Figure 1 shows the mass specific active surface area (ECSA) of the catalyst with pretreated carbon and commercial RhxSy catalysts. It shows that the RhxSy catalyst with pretreated carbon material has much higher mass specific ECSA than commercial RhxSy. This presentation will discuss the approach used to synthesis the RhxSy catalyst with pretreated carbon and the characteristics and performance of this catalyst. Figure 1. CV of catalyst with pretreated carbon and commercial one , measured in 1M H2SO4 with 10 mV/s scan rate

Core-Shell Rhodium Sulfide As Catalyst for HER/HOR in HBr Solution

Electrical energy storage technologies are needed when significant fraction of intermittent renewable energy sources such as wind and solar are integrated into the electrical grids. The hydrogen-bromine (H2-Br2) reversible fuel cell system is one of the promising technologies because of its high round-trip conversion efficiency, high power density capability and low cost. In a hydrogen bromine fuel cell, while carbon surface can be for the bromine reactions, a noble metal such as platinum is needed for the hydrogen reactions. Since platinum is not stable in HBr/Br2 environment and HBr and Br2 are expected to cross from the bromine electrode to the hydrogen electrode during operation, a more durable and active catalysts is needed for the hydrogen reactions. RhxSy catalysts have been found to be stable in the HBr/Br2 environment and as active as platinum per active area.1, 2 Commercial RhxSy catalysts have large and broad particle sizes (12-40 nm) and consequently low mass specific active area (< 10 m2/g) for HOR. To address this problem, we explore the core-shell approach used by others 3 as a way to increase the mass specific area of these RhxSy catalysts. Figure 1 shows the mass specific active surface area (ECSA) of the core-shell and commercial RhxSy catalysts, and Table 1 shows a comparison of the mass specific ECSA and durability of commercial 20 wt. % Pt/C and commercial and core-shell RhxSy catalysts. These results show that the core shell RhxSy catalyst has much higher mass specific ECSA than commercial RhxSy catalyst and superior durability over platinum catalyst. This presentation will discuss the approach used to synthesis the core-shell RhxSy catalyst and the characteristics and performance of this catalyst. Figure 1. CV of core-shell and commercial RhxSy catalysts, measured in 1M H2SO4 at 10mV/s KU Core-Shell RhxSy/C 20 wt.% Pt/C Commercial RhxSy/C Time in 1M HBr (hr) m2/g % m2/g % m2/g % 0 61.4 100 127.3 100 7.8 100 24 60.2 98 82.7 65 48 58.4 97 42.2 51 Table 1. Durability in 1M HBr solution of Pt/C and commercial and core-shell RhxSy catalysts References Anna Ivanovskaya, Nirala Singh, Ru-Fen Liu, Haley Kreutzer, Jonas Baltrusaitis, Trung Van Nguyen, Horia Metiu, Eric W McFarland, “Transition Metal Sulfide Hydrogen Evolution Catalysts for Hydrobromic Acid Electrolysis,” Langmuir, 29(1), 480-492 (2013).Jahangir Masud, Trung Van Nguyen, Nirala Singh, Eric McFarland, Myles Ikenberry, Keith Hohn, Chun-Jern Pan, and Bing-Joe Hwang, “A RhxSy/C Catalyst for the Hydrogen Oxidation and Hydrogen Evolution Reactions in HBr,” J. Electrochem. Soc., 162 (4), F455-F462 (2015).Hee-Young Park, Tae-Yeol Jeon, Jong Hyun Jang, Sung Jong Yoo, Kug-Seung Lee, Yoon-Hwan Cho, Kwang-Hyun Choi, Yong-Hun Cho, Namgee Jung, Young-Hoon Chung and Yung-Eun Sunga, “Hydrogen Oxidation Reaction Activity of Sub-Monolayer Pt-Shell/Pd-Core Nanoparticles,” J. Electrochem. Soc., 160 (1), H62-H66 (2013). Acknowledgements The work presented herein was funded in part by the Advanced Research Projects Agency-Energy (ARPA-E), U.S. Department of Energy, under Award Number DE-AR0000262 and the National Science Foundation under Grant No. EFRI-1038234 and No. 1416874, as a sub-award from Proton Onsite. Figure 1

Seasonal Dynamic of Morpho-Physiological Properties and the Lipid Composition ofPlantago Media(Plantaginaceae) in the Middle Volga Region

Seasonal Dynamic of Morpho-Physiological Properties and the Lipid Composition of Plantago Media (Plantaginaceae) in the Middle Volga Region The changes in morpho-physiological properties and lipid composition have been studied in the leaves of the plant Plantago media collected from two different places in the Middle Volga region during the summer 2011. The plants gathered from the first plot (P1 plants) grew on plane ground in the midst of typical meadowsteppe perennial plants. The plants of the second group (P2 plants) grew on a flat slope of the South-West exposition, in the grass community. The leaves of the plants Р 1 had lower specific area densities but larger areas and masses; they accumulated more levels lipid peroxide products. The changes in lipid compositions depended on the growth phase and habitats. Correlations between morpho-physiological parameters and certain lipids have been established. The amounts of galactolipids have been shown to correlate with the leaf areas. When the leaf areas were reduced, a ratio between phosphatidylcholine and phosphatidylethanolamine decreased. The result of our study showed that gradual changes of morphometrical parameters were accompanied by the alterations in biomass structure and modifications in lipids and FA..

High Active Surface Area and Durable Multi-Wall Carbon Nanotube-Based Electrodes for the Bromine Reactions in H2-Br2 Fuel Cells

The commercially available carbon gas diffusion electrodes (GDEs) with low specific active area but high permeability are often used as Br2 electrodes in the H2-Br2 fuel cell. In order to increase the specific active surface area of the existing carbon GDEs, a study was conducted to grow multi-wall carbon nanotubes (MWCNTs) directly on the surface of carbon fibers of a commercial carbon electrode. Experimental fixtures were developed to promote the electrodeposition of cobalt and the growth of MWCNTs on the carbon GDE. The MWCNT growth across the carbon electrode was confirmed by SEM. The carbon GDE with a dense distribution of short MWCNTs evaluated in a H2-Br2 fuel cell has 29 times higher active surface area than a plain carbon electrode and was found to be highly durable at an electrolyte flow rate of 10 cc/min/cm2. The performance of the best single layer MWCNT GDE measured at 80% discharge voltage efficiency in a H2-Br2 fuel cell was found to be 16% higher compared to that obtained using three layers of plain carbon electrodes. Finally, the preliminary material cost analysis has shown that the MWCNT-based carbon electrodes offer significant cost advantages over the plain carbon electrodes.

Ageing process of some pyrogenic silica samples exposed to controlled relative humidities

Abstract The kinetic of the ageing process of 3 pyrogenic silica samples, exhibiting increasing surface areas (Wacker N20, T30 and T40), was followed through gravimetric measurements, during about 1000 h at 22.5 °C, under different relative humidities (RH) from 62% up to100%. Silanol chemical titration, and IR spectroscopy were also called on to evidence the change of the surface chemistry induced by the ageing process. This study evidenced that pyrogenic silicas are, at room temperature, sensitive to RH humidity over a threshold of about 50% of RH. Exposed to high RH, a strong change of the surface functionality occurs bound to an important chemisorption of water. At RH of 100%, the silanol density could increase up to quite 40%. It is more important for low specific area samples than for the higher ones. The limit value of 3.5–3.8 SiOH/nm 2 suggests that no polysilicic layer are formed. Moreover IR spectroscopy indicates that the new silanol groups appear in the vicinity of the pre-existing silanol groups at the border between hydrophilic and hydrophobic domains. It is hence evidenced that the patch like distribution of the silanol groups and the surface morphology, flat or rough play a main role on the ageing process.

Effect of the doping agent nature on the characteristic and catalytic properties of aerogel zirconia catalysts doped with sulfate groups or heteropolytungstic acid

Zirconia catalysts doped with sulfates or heteropolytungstic acid (HPW) prepared by sol–gel method and dried in supercritical conditions of solvent have been evaluated in n-hexane isomerization in the temperature range 150–220°C. Using HPW as dopant, the obtained catalyst is active at 220°C and selective towards isomers having higher Individual Octane Number, i.e., 2,2-DMB and 2,3-DMB compared with using sulfates as dopant. Based on N2-physisorption, XRD, SEM and TEM analyses, low specific area, particular morphology of grains and the lack of tetragonal ZrO2 particles reduce the adsorption of n-hexane reactant and led to inefficient catalyst throughout the temperature range 150–200°C. The catalyst doped with sulfur deactivates at T>200°C since agglomerates of zirconia particles (TEM and SEM results) favor the coke formation. Using HPW, agglomerates of W oxide as well as phosphate groups (revealed by TGA, FTIR, EDX and UV/visible DRS) favor the formation of more valuable isomers at 220°C.

Catalytic oxidation of toluene over Au–Co supported on SBA-15

Au–Co supported on mesoporous silica materials SBA-15 was prepared with about 15wt.% cobalt then deposition-precipitation with 2wt.% Au. The results showed that while SBA-15 provided the long ordered arrangement of the channels for support, mixtures of cobalt oxides and gold nanoparticles are dispersed in the mesoporous channels. The sample exhibited excellent catalytic activity for toluene combustion, a complete decomposition (about 100%) of toluene had been achieved at the reaction temperature over 573K and space velocity 30,000h−1. The kinetics showed that the activation energy of the sample was 96.06kJ/mol (22.96kcal/mol) and frequency factor was 1.05×1010s−1, respectively. All these results indicate that while mesoporous materials give a high surface area support for metals, cobalt offers active supports for gold particles, which might be a combined way to overcome the shortcomings of low specific area for reducible transition metal oxides and low activity for inert oxides.

High‐resolution experiments on chemical oxidation of DNAPL in variable‐aperture fractures

AbstractChemical oxidation of dense nonaqueous‐phase liquids (DNAPLs) by permanganate has emerged as an effective remediation strategy in fractured rock. We present high‐resolution experimental investigations in transparent analog variable‐aperture fractures to improve understanding of chemical oxidation of residual entrapped trichloroethylene (TCE) in fractures. Four experiments were performed with different permanganate concentrations, flow rates, and initial TCE phase geometry. The initial aperture field and evolving entrapped‐phase geometry were quantified for each experiment. The integrated mass transfer rate from the TCE phase for all experiments exhibited three time regimes: an early‐time regime with slower mass transfer rates limited by low specific interfacial area; an intermediate‐time regime with higher mass transfer rates resulting from breakup of large TCE blobs, which greatly increases specific interfacial area; and a late‐time regime with low mass transfer rates due to the deposition of MnO2 precipitates. In two experiments, mass balance analyses suggested that TCE mass removal rates exceeded the maximum upper bound mass removal rates derived by assuming that oxidation and dissolution are the only mechanisms for TCE mass removal. We propose incomplete oxidation by permanganate and TCE solubility enhancement by intermediate reaction products as potential mechanisms to explain this behavior. We also speculate that some intermediate reaction products with surfactant‐like properties may play a role in lowering the TCE‐water interfacial tension, thus causing breakup of large TCE blobs. Our quantitative experimental measurements will be useful in the context of developing accurate computational models for chemical oxidation of TCE in fractures.

Continuous within-plant variation as a source of intraspecific functional diversity: Patterns, magnitude, and genetic correlates of leaf variability in Helleborus foetidus (Ranunculaceae).

Continuous within-plant variation in quantitative traits of reiterated, homologous structures is a component of intraspecific variation, but its contribution to functional diversity remains largely unexplored. For the perennial Helleborus foetidus, we measured functional leaf traits to quantify the contribution of within-plant variation to intraspecific functional variance and evaluate whether within-plant variability itself deserves separate consideration. Within-individual variation in eight leaf traits was quantified for 138 plants sampled from 10 widely spaced locations in the Sierra de Cazorla, southeastern Spain. An amplified fragment length polymorphism (AFLP) technique was used to look for associations between within-plant variability and specific AFLP markers. Leaflets from basal positions in ramets were longer, heavier, had greater surface area and larger stomata, and lower specific area, stomatal index, and stomatal density than those from distal positions. Continuous variation between leaves from the same ramet was the main source of population-wide variance for most traits. Within-plant variability differed among populations. Individuals differed in within-plant variability, which was largely independent of trait means and associated with genetic characteristics. Up to four AFLP markers were associated with the within-plant variability level of a given leaf trait. Subindividual variability in continuous leaf traits was independent of plant means and related to genetic features. The within-individual component generally exceeded the between-individual component of intraspecific variance. Within-plant variation may broaden the ecological breadth and enhance stability and persistence of plant populations and communities and may provide novel insights when incorporated in trait-based community ecology models.

Effect of the Transition Metal on Metal–Nitrogen–Carbon Catalysts for the Hydrogen Evolution Reaction

The effect of the nature of the transition metal on the structure and activity for hydrogen evolution of Metal-N-C catalysts synthesized via the pyrolysis of metal salts and a Zn-based metal organic framework was investigated. It is found that W, Mo, Cu and Zn lead to amorphous carbons with high specific area while Cr, Mn, Fe, Co and Ni lead to more graphitic carbons with a lower specific area. Metal salts with a high redox potential are fully reduced during pyrolysis while others are only partially reduced. Electrochemical activity toward hydrogen evolution was investigated at pH 1 and pH 13. Hydrogen evolution on these Metal-N-C catalysts is generally more facile at pH 1 than at pH 13, paralleling the trends observed for noble metal surfaces. The Co-, Ni- and Fe-N-C catalysts are the most active at pH 13 while Co-N-C and Cr-N-C are the most active at pH 1. The activity of the latter catalysts stems from metallic cobalt particles encapsulated in carbon and from a chromium carbo-nitride phase, respectively.