Sequential Reduction Processes Research Articles

Revisit the role of hydroxylamine in sulfur-driven autotrophic denitrification

Through dedicated batch tests using the enriched sludge dominated by sulfur-oxidizing bacteria (SOB), the potential transformation of hydroxylamine (NH2OH) by SOB and the effects of NH2OH on the rate-limiting sequential reduction processes of sulfur-driven autotrophic denitrification (SDAD) were systematically explored in this study. The results indicated that NH2OH might be first converted to NO by SOB and then participate in the SDAD process, thus accelerating the utilization of S2- and contributing to the formation of N2O. Up to 3.5 mg-N/L NH2OH didn't affect the NO3- or NO2- reduction of SDAD, during which no significant changes were observed for the NH2OH concentration. Comparatively, even though NH2OH had no direct impact on the N2O reduction of SDAD, it could be consumed and therefore affect the depletion of N2O indirectly by regulating the toxic effect and electron supply of S2-. These findings provide novel implications for applying NH2OH to SDAD-based integrated processes for biological nitrogen removal.

Hydrogen generation over Ni@Pd NCs through an active H-exchange from formic acid-water system

The use of Formic acid as an alternative to fossil fuels is promising, both from economical and ecological standpoints, and has received great of attention owing to its inherently superiority in recent decades. Nevertheless, efficient and low-cost solid catalyst for formic acid dehydrogenation at room temperature still constitutes a biggish challenge. Moreover, comparing to increase the catalytic performance of catalysts, very little attention payed to the kinetic mechanism of dehydrogenation reaction because of the lack of effective characterization artifice. Here, the as-prepared Ni@Pd nanoparticles by a sequential reduction process can be useful catalyst for formic acid decomposition at room temperature without a promoter. Thanks to the effective catalyst and isotope distribution technique, preliminary mechanistic results firstly reveal that hydrogen is obtained via a H-atom recombination on isolated sites after the proton exchange randomly between activated H and solvent.

Forecasting the Long-Term Trends of Coronavirus Disease 2019 (COVID-19) Epidemic Using the Susceptible-Infectious-Recovered (SIR) Model.

A simple model for predicting Coronavirus Disease 2019 (COVID-19) epidemic is presented in this study. The prediction model is presented based on the classic Susceptible-Infectious-Recovered (SIR) model, which has been widely used to describe the epidemic time evolution of infectious diseases. The original version of the Kermack and McKendrick model is used in this study. This included the daily rates of infection spread by infected individuals when these individuals interact with a susceptible population, which is denoted by the parameter β, while the recovery rates to determine the number of recovered individuals is expressed by the parameter γ. The parameters estimation of the three-compartment SIR model is determined through using a mathematical sequential reduction process from the logistic growth model equation. As the parameters are the basic characteristics of epidemic time evolution, the model is always tested and applied to the latest actual data of confirmed COVID-19 cases. It seems that this simple model is still reliable enough to describe the dynamics of the COVID-19 epidemic, not only qualitatively but also quantitatively with a high degree of correlation between actual data and prediction results. Therefore, it is possible to apply this model to predict cases of COVID-19 in several countries. In addition, the parameter characteristics of the classic SIR model can provide information on how these parameters reflect the efforts by each country to prevent the spread of the COVID-19 outbreak. This is clearly seen from the changes of the parameters shown by the classic SIR model.

Synthesis of Hierarchical Nanoporous Microstructures via the Kirkendall Effect in Chemical Reduction Process.

A series of novel hierarchical nanoporous microstructures have been synthesized through one-step chemical reduction of micron size Cu2O and Co3O4 particles. By controlling the reduction time, non-porous Cu2O microcubes sequentially transform to nanoporous Cu/Cu2O/Cu dented cubic composites and hollow eightling-like Cu microparticles. The mechanism involved in the complex structural evolution is explained based on oxygen diffusion and Kirkendall effect. The nanoporous Cu/Cu2O/Cu dented cubic composites exhibit superior electrochemical performance as compared to solid Cu2O microcubes. The reduction of nonporous Co3O4 also exhibits a uniform sequential reduction process from nonporous Co3O4 to porous Co3O4/CoO composites, porous CoO, porous CoO/Co composites, and porous foam-like Co particles. Nanoscale channels originate from the particle surface and eventually develop inside the entire product, resulting in porous foam-like Co microparticles. The Kirkendall effect is believed to facilitate the formation of porous structures in both processes.

Formation and Characterization of Ni Nanofiber Catalysts on Nickel Metallic Foam by Electrospinning Process.

We report the fabrication of nickel nanofiber catalysts supported on nickel metallic foam using a modified electrospinning with a grounded rotor and sequential reduction process. The robust deposition of aligned Ni nanofibers with a uniform morphology on the highly porous surfaces of the metallic foam could be achieved by controlling electrospinning parameters such as applied voltage, tip-collector-distance (TCD), concentration of polymer, and humidity. The diameters of the obtained nanofibers decreased with increasing voltage and TCDs. The uniform and thinnest Ni nanofibers on the Ni foam were obtained at a humidity of less than 30%, 15 kV applied voltage, and 17 cm TCD when using a precursor composed of nickel nitrate salt and poly(vinyl) pyrrolidone. The Ni foam catalyst support exhibited the superior thermal conducting property than other supports of MgO-MgAl2O4, Al2O3, and SiC, enabling to a higher heat transfer during catalytic reaction. As a result, the Ni nanofiber catalyst with a high surface area and superior heat transfer performance, which is supported on the metallic foam, were successfully fabricated via a modified electrospinning for potential application of XTL process converting anything to liquids, such as for Gas-to-Liquid (GTL), Coal-to-Liquid (CTL), and Biomass-to-Liquid (BTL).

Synthesis, structural characterization and magnetic properties of Fe/Pt core-shell nanoparticles

Structural and magnetic properties of Fe/Pt core-shell nanostructure prepared by a sequential reduction process are reported. Transmission electron microscopy shows nearly spherical particles fitting a lognormal size distribution with Do = 3.0 nm and distribution width λD = 0.31. In x-ray diffraction, Bragg lines only from the Pt shell are clearly identified with line-widths yielding crystallite size = 3.1 nm. Measurements of magnetization M vs. T (2 K–350 K) in magnetic fields up to 90 kOe show a blocking temperature TB = 13 K below which hysteresis loops are observed with coercivity HC increasing with decreasing T reaching HC = 750 Oe at 2 K. Temperature dependence of the ac susceptibilities at frequencies fm = 10 Hz–5 kHz is measured to determine the change in TB with fm using the Vogel-Fulcher law. This analysis shows the presence of significant interparticle interaction, the Neel-Brown relaxation frequency fo = 5.3 × 1010 Hz and anisotropy constant Ka = 3.6 × 106 ergs/cm3. A fit of the M vs. H data up to H = 90 kOe for T > TB to the modified Langevin function taking particle size distribution into account yields magnetic moment per particle consistent with the proposed core-shell structure; Fe core of 2.2 nm diameter and Pt shell of 0.4 nm thickness.

Dechlorination of Pentachlorophenol by Palladium/Iron Nanoparticles Immobilized in a Membrane Synthesized by Sequential and Simultaneous Reduction of Trivalent Iron and Divalent Palladium Ions

Abstract Dechlorination of pentachlorophenol (PCP) by zero-valent iron (Fe0) and palladium (Pd)/iron (Fe) bimetallic nanoparticles (NPs) immobilized in nylon 6,6/PEG membranes was investigated at room temperature. Pd/Fe bimetallic NPs were synthesized by two different approaches, sequential and simultaneous reduction of trivalent iron (Fe3+) and divalent palladium (Pd2+) ions. Pd/Fe NPs prepared by simultaneous reduction showed a much smaller particle size, only 30 nm in average, and significantly higher reactivity toward PCP dechlorination than the other two materials. Almost 85% PCP removal within 45 min was qualified in terms of both phenol emergence and chlorine ion release. In contrast, dechlorination efficiency by Pd/Fe NPs immobilized by sequential reduction was insignificant. Iron oxides between Fe0 and Pd0 during the sequential reduction process impeded their effective contact, and enhanced PCP sorption on membranes. Spectra of X-ray photoelectron spectroscopy confirmed the existence of both Fe0 ...

Methane oxidation and methane driven redox process during sequential reduction of a flooded soil ecosystem

A laboratory incubation study conducted to assess the temporal variation of CH4 oxidation during soil reduction processes in a flooded soil ecosystem. A classical sequence of microbial terminal electron accepting process observed following NO3 − reduction, Fe3+ reduction, SO4 2− reduction and CH4 production in flooded soil incubated under initial aerobic and helium-flushed anaerobic conditions. CH4 oxidation in the slurries was influenced by microbial redox process during slurry reduction. Under aerobic headspace condition, CH4 oxidation rate (k) was stimulated by 29 % during 5 days (NO3 − reduction) and 32 % during both 10 days (Fe3+) and 20 days (early SO4 2− reduction) over unreduced slurry. CH4 oxidation was inhibited at the later methanogenic period. Contrastingly, CH4 oxidation activity in anaerobic incubated slurries was characterized with prolonged lag phase and lower CH4 oxidation. Higher CH4 oxidation rate in aerobically incubated flooded soil was related to high abundance of methanotrophs (r = 0.994, p < 0.01) and ammonium oxidizers population (r = 0.184, p < 0.05). Effect of electron donors NH4 +, Fe2+, S2− on CH4 oxidation assayed to define the interaction between reduced inorganic species and methane oxidation. The electron donors stimulated CH4 oxidation as well as increased the abundance of methanotrophic microbial population except S2− which inhibited the methanotrophic activity by affecting methane oxidizing bacterial population. Our result confirmed the complex interaction between methane-oxidizing microbial groups and redox species during sequential reduction processes of a flooded soil ecosystem.

Magnetically Recyclable Fe@Pt Core−Shell Nanoparticles and Their Use as Electrocatalysts for Ammonia Borane Oxidation: The Role of Crystallinity of the Core

Carbon-supported Fe@Pt core-shell nanoparticle (NP) catalysts with Fe cores in different crystal states have been successfully synthesized by a sequential reduction process. Unexpectedly, in contrast to its crystallized counterpart, iron in the amorphous state exerts a distinct and powerful ability as the core for the Fe@Pt NPs. The resultant NPs are far more active for ammonia borane oxidation (by up to 354%) than the commercial Pt/C catalysts. Furthermore, these NPs combine low cost, long-term stability, and easy recovery functions.

Formation of stable Cu 2O from reduction of CuO nanoparticles

In situ time-resolved X-ray diffraction (TR-XRD) using synchrotron radiation has been used to capture the dynamics of the reduction of nanocrystalline CuO using a normal supply of CO gas. Copper(II) oxide nanoparticles 4–16 nm in width, as measured by XRD peak broadening, are synthesized using an aqueous organic-nitrate method and reduced in isothermal and temperature ramping reduction experiments. Temperature-programmed reduction of CuO nanoparticles using a ramping heating profile was observed to result in the sequential reduction process CuO → Cu 2O → Cu, with CuO reducing completely to the intermediate Cu 2O phase before further reduction to metallic copper. Isothermal reduction experiments at 250 °C show that CuO nanoparticles completely reduce to Cu 2O, and this phase remains stable without further reduction with continued exposure to CO. In contrast to what is typically observed in bulk CuO in both isothermal and ramping reduction conditions, nanocrystalline CuO reduces to a stable Cu 2O phase rather than forming metallic copper directly. The behavior of the CuO nanoparticles in temperature ramping reducing conditions is controlled by the particle size, with the smaller CuO nanoparticles exhibiting a greater stability and withstanding a higher temperature before their reduction to Cu 2O and then to metallic copper nanoparticles.

Archaeal population dynamics during sequential reduction processes in rice field soil.

The population dynamics of Archaea after flooding of an Italian rice field soil were studied over 17 days. Anoxically incubated rice field soil slurries exhibited a typical sequence of reduction processes characterized by reduction of nitrate, Fe(3+), and sulfate prior to the initiation of methane production. Archaeal population dynamics were followed using a dual approach involving molecular sequence retrieval and fingerprinting of small-subunit (SSU) rRNA genes. We retrieved archaeal sequences from four clone libraries (30 each) constructed for different time points (days 0, 1, 8, and 17) after flooding of the soil. The clones could be assigned to known methanogens (i.e., Methanosarcinaceae, Methanosaetaceae, Methanomicrobiaceae, and Methanobacteriaceae) and to novel euryarchaeotal (rice clusters I, II, and III) and crenarchaeotal (rice clusters IV and VI) lineages previously detected in anoxic rice field soil and on rice roots (R. Grosskopf, S. Stubner, and W. Liesack, Appl. Environ. Microbiol. 64:4983-4989, 1998). During the initiation of methanogenesis (days 0 to 17), we detected significant changes in the frequency of individual clones, especially of those affiliated with the Methanosaetaceae and Methanobacteriaceae. However, these findings could not be confirmed by terminal restriction fragment length polymorphism (T-RFLP) analysis of SSU rDNA amplicons. Most likely, the fluctuations in sequence composition of clone libraries resulted from cloning bias. Clonal SSU rRNA gene sequences were used to define operational taxonomic units (OTUs) for T-RFLP analysis, which were distinguished by group-specific TaqI restriction sites. Sequence analysis showed a high degree of conservation of TaqI restriction sites within the different archaeal lineages present in Italian rice field soil. Direct T-RFLP analysis of archaeal populations in rice field soil slurries revealed the presence of all archaeal lineages detected by cloning with a predominance of terminal restriction fragments characteristic of rice cluster I (389 bp), Methanosaetaceae (280 bp), and Methanosarcinaceae/rice cluster VI (182 bp). In general, the relative gene frequency of most detected OTUs remained rather constant over time during the first 17 days after flooding of the soil. Most minor OTUs (e.g., Methanomicrobiaceae and rice cluster III) and Methanosaetaceae did not change in relative frequency. Rice cluster I (37 to 30%) and to a lesser extent rice cluster IV as well as Methanobacteriaceae decreased over time. Only the relative abundance of Methanosarcinaceae (182 bp) increased, roughly doubling from 15 to 29% of total archaeal gene frequency within the first 11 days, which was positively correlated to the dynamics of acetate and formate concentrations. Our results indicate that a functionally dynamic ecosystem, a rice field soil after flooding, was linked to a relatively stable archaeal community structure.

Redox behavior of the molybdenum and tungsten metallafullerenes M(η2-C60)(CO)2(phen)(dbm) (phen = 1,10-phenanthroline; dbm = dibutyl maleate): (spectro)electrochemistry and theoretical considerations

Electrochemistry of M(η2-C60)(CO)2(phen)(dbm) (M = W 1, Mo 2; phen = 1,10-phenanthroline; dbm = dibutyl maleate) shows that the complexes undergo four sequential reduction processes. As with free C60, the first three electrons add reversibly (even if the relevant potentials are shifted ca. 0.15 V toward negative values), whereas the fourth reduction features chemical irreversibility. Cyclic voltammetry gives evidence that, as a consequence of the latter process, the metal fragment decomplexes and [C60]3– is released. In good agreement with this picture, a qualitative MO approach shows four close LUMOs for the ground state structure of the uncharged complexes. The first three levels are delocalized over C60 (somewhat extended to the dmb π system), while the fourth one is metal–fullerene antibonding (back donation dπ → π* C60) and its occupation causes fulleride dissociation. The EPR spectra of the electrogenerated [1]– and [2]– monoanions are significantly different from that of [C60]– and seem suggestive of metal character for these radical species. At present, this result is unexpected in that the unpaired electron in the anions [1]– and [2]– should be intuitively centered on the coordinated fullerene.

Sequential reduction processes and initiation of CH 4 production upon flooding of oxic upland soils

Sequential reduction processes were studied in four oxic upland soils (cultivated, forest, savanna and desert soil) which were slurried and incubated under anoxic conditions. NO 3 −1 reduction began almost immediately and was followed by reduction of manganese(IV), sulfate and iron(III). The phases of reduction of Mn 4+, SO 4 2− and Fe 3+ overlapped, with SO 4 2− being depleted long before accumulation of Mn 2+ and Fe 2+ was finished. CH 4 production and growth of methanogenic bacteria began when all the other reduction processes were finished. Radiotracer experiments showed that CH 4 was produced from H 2 (29–42%) and acetate. The respiratory index indicated that the acetate was predominantly degraded by methanogenic bacteria. The late onset of methanogenesis was not a consequence of limitation by the methanogenogenic precursors, since H 2 and acetate were present long before the initiation of methanogenesis. Thermodynamic calculations showed that the concentrations of these substrates were always sufficient to allow exergonic production of CH 4 at Gibbs free energies of ΔG < −30 kJ mol −1 CH 4. However, exergonic production of acetate from H 2 CO 2 was not possible. Propionate was also detected in the soil slurries. The redox potential in the soils decreased from > + 400 mV to final values of < − 150 mV, except in the forest soil where the redox potential stayed at + 50 mV. The onset of methanogenesis and of growth of methanogenic bacteria coincided with redox potentials between +70 and 0 mV, which is much higher than claimed in literature. We speculate that the redox-active substances in soil were the signal for methanogenic bacteria to initiate activity.

Effect of molecular hydrogen on the reduction process of submerged soil

When the paddy soil is submerged, several reduction reactions take place sequentially with the decrease in the release of free energy, as predicted by thermodynamic studies (9). Through this sequential reduction process the partial pressure of H2 in soil is generally kept low. However, when an air-dried soil rich in mineralizable organic matter is submerged, H2 evolution and its subsequent absorption occur within a few days after incubation (12). Furthermore, the reduced soil has the capacity to take up H2 (5). These facts suggest that H2 is transferred from one reduction process to another during the reduction process, because the observed H2 evolution results from the balance between H2 consumption and formation. In this report we describe the effect of H2-addition on the reduction process in the submerged soil.