Selective Chemical Reduction Research Articles

Highly selective chemical reduction of nitrate in water in carbon-based contactor catalytic membrane reactors

A carbon-based catalytic membrane reactor in a contactor (interfacial) configuration has been used as an approach to control selectivity in the reduction of NO3- in water. Water and hydrogen fed to the reactor circulate tangentially on opposite sides of the membrane, which acts as a separator and contactor, enabling hydrogen transfer to the water phase. Powdered carbons (carbon black, carbon nanofiber, and activated carbon) were used to prepare catalytic membranes that also acted as contactors to transfer H2 from the gas phase to water. The membranes based on the Pd-Cu/carbon black catalyst showed lower selectivity towards unwanted NH4+ than the Pd-Cu and Pd-Sn catalysts supported on carbon nanofibers and activated carbon, due to a good balance among conductivity, external surface area, and particle size. Sensitivity analysis for H2 partial pressure demonstrated that the contactor membrane reactor can be operated with control of H2 mass transfer, hence enabling enhanced control of the selectivity to NH4+. Additional control of selectivity was achieved by reducing the catalytic layer thickness of the membrane, which improved NO3- transport and decreased the H/N ratio at the active centers. With these approaches, NO3- conversion values above 40 % with negligible NH4+ production and NO3- conversions close to 60 % with NH4+ selectivity values around 3 % were achieved.

Amorphous-Co@Nd(BO2)3/rGO magnetic nanocomposites as high-frequency, wide-bandwidth and light-weight microwave absorbing materials

It is necessary to broaden absorption bandwidth, regulate applied frequency, reduce the weight and maintain strong absorption for magnetic microwave absorbing materials by constructing suitable material structures to satisfy the requirements for wide applications in various electromagnetic devices. In this work, well-structured amorphous-Co@Nd(BO2)3/rGO nanocomposites have been fabricated using a selective chemical reduction in a mixed aqueous solution containing Co2+ and Nd3+ ions along with GO sheets reduced by NaBH4 as the reductant, in which only Co2+ and GO but no Nd3+ ions were reduced. Very low coercivity of 0.4 Oe is achieved in amorphous-Co@Nd(BO2)3/rGO nanocomposites due to amorphous Co@Nd(BO2)3 core-shell nanoparticles uniformly anchored on rGO sheets. These soft magnetic rGO-based nanocomposites exhibit high-frequency microwave absorption performance including a minimum reflection loss (RLmin) value of −84.09 dB at 15.38 GHz for a 2.1 mm thickness at an applied frequency range (12.31–18 GHz) covering almost the entire Ku band. Moreover, a much wider absorption band of 7.24 GHz (10.67–17.89 GHz, RL ≤ −10 dB) with a 2.3 mm thickness along with a RLmin value of −35.92 dB is also achieved. These rGO-based magnetic composites also show good structural stability, low density and easily controlled material compositions along with facile chemical fabrication suitable for mass production, which promises their latent use in high-performance microwave absorbing devices. Crystallization behavior of a new amorphous Nd(BO2)3 phase was also investigated.

Dissecting ZnOX/Cu interfacial self-encapsulation and methanol-induced strong metal-support interaction of the highly active alloyed CuZn and ZnO for methanol steam reforming

A highly durable non-noble metal catalyst like copper for high-temperature methanol steam reforming is necessary for a compact hydrogen reactor. Herein, deactivation of copper-based catalysts with strong metal-support interaction is extremely sluggish even at 550 °C when using a selective chemical reduction approach paired with various induced activation procedures. The adsorbate methanol could enhance the migration of ZnOx onto the Cu and increase the number and electronic modulation of high-activity CuZn alloy sites. The Zn pre-deposited on the Cu surface induces continuous morphology and structural reorganization of the catalytic surface, which constantly refreshes the catalyst surface. The adsorbate methanol led to abundant CuZn alloy-ZnO synergism, which sped up the dissociation of·H2O and the dehydrogenation of *CH3O in accordance with the density functional theory and, ultimately, exhibited the highest methanol conversion (99.55 %) and hydrogen yield (97.73 %) compared to the hydrogen induction.

Choosing sides: unusual ultrafast charge transfer pathways in an asymmetric electron-accepting cyclophane that binds an electron donor.

Constructing functional molecular systems for solar energy conversion and quantum information science requires a fundamental understanding of electron transfer in donor-bridge-acceptor (D-B-A) systems as well as competitive reaction pathways in acceptor-donor-acceptor (A-D-A) and acceptor-donor-acceptor' (A-D-A') systems. Herein we present a supramolecular complex comprising a tetracationic cyclophane having both phenyl-extended viologen (ExV2+) and dipyridylthiazolothiazole (TTz2+) electron acceptors doubly-linked by means of two p-xylylene linkers (TTzExVBox4+), which readily incorporates a perylene (Per) guest in its cavity (Per ⊂ TTzExVBox4+) to establish an A-D-A' system, in which the ExV2+ and TTz2+ units serve as competing electron acceptors with different reduction potentials. Photoexcitation of the Per guest yields both TTz+˙-Per+˙-ExV2+ and TTz2+-Per+˙-ExV+˙ in <1 ps, while back electron transfer in TTz2+-Per+˙-ExV+˙ proceeds via the unusual sequence TTz2+-Per+˙-ExV+˙ → TTz+˙-Per+˙-ExV2+ → TTz2+-Per-ExV2+. In addition, selective chemical reduction of TTz2+ gives Per ⊂ TTzExVBox3+˙, turning the complex into a D-B-A system in which photoexcitation of TTz+˙ results in the reaction sequence 2*TTz+˙-Per-ExV2+ → TTz2+-Per-ExV+˙ → TTz+˙-Per-ExV2+. Both reactions TTz2+-Per+˙-ExV+˙ → TTz+˙-Per+˙-ExV2+ and TTz2+-Per-ExV+˙ → TTz+˙-Per-ExV2+ occur with a (16 ± 1 ps)-1 rate constant irrespective of whether the bridge molecule is Per+˙ or Per. These results are explained using the superexchange mechanism in which the ionic states of the perylene guest serve as virtual states in each case and demonstrate a novel supramolecular platform for studying the effects of bridge energetics within D-B-A systems.

Aging-resistant nanofluids containing covalent functionalized boron nitride nanosheets

Developing a thermally stable nanofluid that can maintain good thermo-conductive and flow performance at moderate or elevated temperatures for prolonged periods of time is a great challenge in heat transfer applications. Here, the thermal conductivity and rheological properties as well as their thermal stability characteristics of a nanofluid containing two-dimensional (2D) hexagonal boron nitride nanosheets (h-BNNSs) in ethylene glycol (EG) are presented, in comparison with those for a graphene oxide (GO) nanofluid as a counterpart. In place of a surfactant, hydroxyl functional groups covalently bound to the BNNS surface provided excellent compatibility and stable dispersion of the particles within EG at temperatures up to 90 °C. Owing to the percolation effect of the 2D sheets, the thermal conductivity of the EG base fluid was significantly enhanced by 80% at 5 vol% of BNNS, superior to that of the GO fluid. Moreover, the BNNS fluids exhibited excellent long-term stability at 90 °C for 5 d without loss of their high thermal conductivity, low viscosity and electrical insulating property, whereas the GO fluids underwent thermal degradation with irreversible particle aggregation and increasing viscosity due to the selective chemical reduction of the surface functional groups (i.e., C–O groups) of the GO.

Electrodeposition Though Polyelectrolyte Layers: Control of Interfacial Reaction, Deposition Rate, and Morphology of Deposited Thin Films

Demand for the development of deposition strategies of well-defined metal thin films with good chemical and physical characteristics has been rapidly growing in the field of various electronics applications. For example, copper electro- or electroless deposition has been widely utilized and investigated in microelectronics industry due to its low electrical resistivity and high electromigration resistance, as compared with aluminum. The conventional plating bath for electro- or electrolless copper deposition involves various chemical reagents such as deposition promoter (or inhibiter), brightening and smoothing agent, etc. These additives, typically organic molecules, sometimes cause mechanical problems due to inclusion of such additives during deposition process, and the discharge from the deposition bath can be a serious environmental issue. Therefore, the development of a facile process that enables additive-free deposition of metallic thin films as well as low environmental toxicity is an important challenge for the fabrication of microelectronic elements. In order to sustain the demand for generating multichip packaging systems for future electronic devices, it would be exceedingly useful to develop novel electrochemical deposition strategy with high-throughput capability that would allow stability of electrochemical reaction at higher deposition rate from plating bath without organic additives. In this context, direct metal deposition processes though ion conducting films have been investigated, such as the fabrication of metallic patterns on polymer substrates using ion-doped precursor films. A variety of direct deposition techniques have been introduced by several groups, including ours,1,2) based on photoinduced chemistry, thermal treatment, and selective chemical reduction for polyimide and other functional polymers. We have also reported a chemical metallization strategy that utilizes electrochemical constructive lithography with post lift-off process, which enables the fabrication of metal patterns on the polyimide substrate.3) The use of ion-doped precursors has triggered the development of new concept for electrochemical deposition. Herein we report for the first time that metallic thin films can be deposited through polyelectrolyte thin layers placed on the cathode electrode by the diffusion of metallic ions from the interior of polyelectrolyte, which is essentially different to conventional solution-phase electrodeposition processes (Fig. 1). By taking advantage of the cation-exchangeable nature of polyelectrolyte layers used for creation of solid interface, we demonstrate in this study how it is possible to merge the electrochemical deposition at cathode-polyelectrolyte interface and diffusion of cations through polyelectrolytes for development of novel solid electrodeposition (SED) process. As a proof of concept study, we herein present the successful electrochemical deposition of copper and nickel thin films at the interface between an electrode and ion-doped polyelectrolyte layers from the baths containing only metal salts (without any additives). The effect of cation concentration, temperature, and electrochemical deposition conditions on the deposition rate, growth process and morphology of the films has been investigated. Several electrochemical, microscopic and quantitative analysis revealed that the metallic films have been successfully deposited at the cathode-polyelectrolyte interface through ion exchange reaction in the polyelectrolyte layers, the deposition rate of which are determined by ion exchange rate of cations. This strategy offers an opportunity to translate solution-phase electrochemical deposition into a high-throughput, cost-effective, environmentally-friendly process for the fabrication of metal thin films on substrates. 1) Matsumura, Y. Enomoto, T. Tsuruoka, K. Akamatsu, H. Nawafune, Langmuir, 26, 12448-12454 (2010). 2) S. Ikeda, H. Yanagimoto, K. Akamatsu, H. Nawafune, Adv. Funct. Mater., 17, 889-897 (2007). 3) K. Akamatsu, Y. Fukumoto, T. Taniyama, T. Tsuruoka, H. Yanagimoto, H. Nawafune, Langmuir, 27, 11761-11766 (2011). Figure 1

A multi-stacked hyperporous silicon flake for highly active solar hydrogen production.

3D multi-stacked hyperporous silicon flakes (MHSFs) are prepared via a selective chemical reduction of natural clay minerals bearing MgO negative catalyst layers. The resultant MHSFs are used as a photocatalyst for solar-driven hydrogen evolution and exhibit the highest photocatalytic acitivty (1031 μmol H2 h(-1) g(-1) Si) coupled with a Pt cocatalyst.

Selective chemical reduction of carbon dioxide to formate using microwave irradiation

Selective chemical reduction of carbon dioxide to formate anion under microwave irradiation is reported. No formaldehyde or methanol was generated as by products of the CO2 reduction making the process highly selective. (NH4)2CO3 or dry ice was employed as CO2 source. NaBH4 is used as reducing agent. Aqueous solutions of (NH4)2CO3 or dry ice and NaBH4 were subjected to microwave irradiation for a short duration of 5min. The formation of formate is unequivocally established from the 1H, 13C and DEPT-135 NMR spectroscopic studies. FT-IR and UV–vis have been employed as auxiliary tools to observe the presence of formate ions. The obtained formate has the potential to be used as fuel in fuel cells or in turn can be converted to alkanes or can be used as a precursor for the production of hydrogen. Thus the current process is highly significant for the energy sector and to the chemical industry as well.

Quantitative sequencing of 5-formylcytosine in DNA at single-base resolution.

Recently, the cytosine modifications 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) were found to exist in the genomic deoxyribonucleic acid (DNA) of a wide range of mammalian cell types. It is now important to understand their role in normal biological function and disease. Here we introduce reduced bisulfite sequencing (redBS-Seq), a quantitative method to decode 5fC in DNA at single-base resolution, based on a selective chemical reduction of 5fC to 5hmC followed by bisulfite treatment. After extensive validation on synthetic and genomic DNA, we combined redBS-Seq and oxidative bisulfite sequencing (oxBS-Seq) to generate the first combined genomic map of 5-methylcytosine, 5hmC and 5fC in mouse embryonic stem cells. Our experiments revealed that in certain genomic locations 5fC is present at comparable levels to 5hmC and 5mC. The combination of these chemical methods can quantify and precisely map these three cytosine derivatives in the genome and will help provide insights into their function.

Shape-Controlled Catalysis by Cetyltrimethylammonium Bromide Terminated Gold Nanospheres, Nanorods, and Nanoprisms

Shape-controlled Au nanospheres, nanorods, and nanoprisms have been utilized for the first time for selective chemical reduction of different aromatic nitro compounds to the corresponding amino derivatives at room temperature. Careful observation reveals that the reaction was fastest with nanospheres and slowest with nanorods, whereas the rate was intermediate with nanoprisms when keeping the numbers of particles approximately the same. Controlled experiments revealed that our reaction followed the nitroso and hydroxylamine pathway. The yield of the product was very high, and the method should be applicable for very fast catalysis reaction of other nitro compounds.

Characterisation of the backbone structures of several fulvic acids using a novel selective chemical reduction method

Fulvic acid ‘backbone’ structures were studied by subjecting fulvic acids isolated from Elliott soil, Suwannee River and Waskish peat to a selective reduction method. The products were subsequently analysed using gas chromatography and gas chromatography-mass spectrometry. The reducing agent was n-butylsilane in the presence of tris(pentafluorophenyl)borane, the latter serving as a Lewis acid catalyst. The method is the first chemical degradation method able to reduce the polar groups of fulvic acids without destroying any ‘core’ structural information. The degradation method also enables reduction of polycarboxylic acids, alcohols, aldehydes, ketones and methyl esters to alkanes, with phenols being converted to silyl ethers. Ester linkages are reduced to ethers and ethers are unaffected.

Gas-phase and On-surface Chemical Reduction of CO2 to HCHO and CO under Dielectric Barrier Discharge

Selective chemical reduction of CO2(g) (with carrier Ar) in presence of organic compounds, either mixed in the gas-phase or present as a contact surface, under Dielectric Barrier Discharge is presented in this study. Along with gas-phase CO generation, added hydrocarbons (C n H 2n+x ; n = 6–12; x = 0 or 2) resulted in HCHO production with the maximum H-atom utilization efficiency being ∼15% of the total present. Product CO and HCHO were estimated separately by pre-concentration in specific absorber solutions followed by their discrete colorimetric measurements. On the other hand, in presence of various types of organic surfaces (e.g. wax, plastics and polymers, also acting simultaneously as a dielectric barrier), it was found that while CO could be estimated as above, in the ensuing chemical conversion, product HCHO was retained on these surfaces. On leaching the HCHO into the absorber solution, its production efficiency was estimated to be ∼5% of CO2.

Interfacial Fracture Phenomena in Ceramic Composite Directionally Solidified Eutectics with a Ductile Interphase

Interphase interfaces in NixCo1−xO/ZrO2(CaO) directionally solidified eutectics (DSEs) are modified by selective chemical reduction of the NixCo1−xO oxide phase. Scanning electron microscopy studies of such NixCo1−xO/ZrO2(CaO) DSEs show formation of a thin layer of metallic Ni(Co) interphase (∼100 nm) and interfacial porosity upon reduction at high temperatures. A significant change is observed in the mechanical behavior of the reduced NixCo1−xO/ZrO2(CaO) DSEs compared with its pristine counterpart, which is largely attributed to the formation of metallic Ni(Co) interphases. Indentation fracture studies indicate that the presence of metallic interphases in the DSEs enhance the stress energy release mechanism through plastic deformation, interfacial delamination, crack arrest, and crack bridging across the metallic interphase after reduction.

O2 Evolution from the Manganese−Oxo Cubane Core Mn4O46+: A Molecular Mimic of the Photosynthetic Water Oxidation Enzyme?

Photosynthesis produces molecular oxygen from water catalyzed by an enzyme whose active site contains a tetramanganese−oxo core of incompletely established structure. The first functional mimic of this core has been synthesized containing a cubical [Mn4O4]n+ core, surrounded by six facially bridging bidentate chelates to the manganese ions ((dpp)6Mn4O4 (1); dpp- = diphenylphosphinate anion). Bond enthalpy data predict that the Mn4O46+ core is thermodynamically capable of releasing molecular O2, but is kinetically prevented from doing so by an activation barrier. UV light absorption into a Mn−O charge-transfer excited state (but not excitation of a Mn ligand-field excited state) efficiently releases an O2 molecule if performed in the gas phase and concomitantly releases a bridging dpp- anion and the cationic species (dpp)5Mn4O2+ (presumed Mn4O2-butterfly core type). All species were identified by high resolution mass spectrometry. This reaction proceeds with high quantum efficiency (>50%) and is the only observable reaction channel. The O2 product derived exclusively from the corner oxo's of the cube based on photochemistry of the 18O-isotopomer, ((dpp)6Mn4(18O)4. Neither O2 release nor dpp- dissociation are observed individually to occur in the excited state, indicating that O−O bond formation and O2 release require dissociation of one of the six dpp- chelates (“Jack-in-the-Box” mechanism for O2 formation). By contrast, neither O2 production nor chelate photodissociation are observed in condensed phases, presumably due to either quenching of the photoexcited state or rapid recombination of dpp- and (dpp)5Mn4O4+ in the solvent cage. Previous results show that chemical reduction of (1) in solution using hydrogen atom donors produces the deoxygenated (dpp)6Mn4O2 core and releases two water molecules as the only products. Thus the [Mn4O4]n+ cubane core is an intrinsically reactive core topology that facilitates both the selective chemical reduction of two of the four oxygen atom bridges to water molecules and their photorearrangement to an O2 molecule under the control of chelation of the manganese ions by dpp-. These results may offer insight into the possible nature of the photosynthetic O2-evolving mechanism.

Hepatotoxicity of germander (Teucrium chamaedrys L.) and one of its constituent neoclerodane diterpenes teucrin A in the mouse.

The hepatotoxicity of the herbal plant germander and that of one of its major furanoneoclerodane diterpenes, teucrin A, were investigated in mice. Teucrin A was found to cause the same midzonal hepatic necrosis as observed with extracts of the powedered plant material. Evidence that bioactivation of teucrin A by cytochromes P450 (P450) to a reactive metabolite(s) is required for initiation of the hepatocellular damage is provided by results of experiments on the induction and inhibition of P450 and from studies on the effects of glutathione depletion. Pretreatment of mice with the P450 inducer phenobarbital enhanced the hepatotoxic response, as indicated by an increase in plasma alanine aminotransferase (ALT) levels and hepatic necrosis, while pretreatment with the P450 inhibitor piperonyl butoxide markedly attenuated the toxic response. Hepatotoxicity of teucrin A also was increased following pretreatment with the inhibitor of glutathione synthesis buthionine sulfoximine. Most importantly, the tetrahydrofuran analog of teucrin A, obtained by selective chemical reduction of the furan ring, was not hepatotoxic, a result that provides strong evidence that oxidation of the furan ring moiety of the neoclerodane diterpenes is involved in the initiation of hepatocellular injury caused by germander.

A rapid method for the determination of nitrate and nitrite by chemiluminescence.

Nitrite and nitrate + nitrite can be determined by selective chemical reduction to nitric oxide which is measured using a chemiluminescence analyser. The reducing agents are sodium iodide in acetic acid for nitrite and ferrous ammonium sulphate-ammonium molybdate for nitrate + nitrite. The concentrations of the reducing agents have been optimized to obtain the maximum yield of nitric oxide and the minimum coefficient of variation. Under these conditions, it is possible to inject repeated samples into the refluxing reducing agents and to obtain rapid evolutions of nitric oxide from which the determinations can be made. Nitric oxide has also been produced using the nitrite reagents from organic nitrites, a S-nitrosothiol, a pseudonitrole and N-nitrosamines. Similarly, an organic nitrate and some C-nitroso compounds respond to the method for nitrate but only to the extent of a yield of nitric oxide of about 10% of the theoretical. Very low or zero responses were evident from aliphatic and aromatic C-nitro compounds but not omega-N-nitroarginine which gave a large yield of nitric oxide using the reagents for nitrate. In general, however, concentrations of nitrate will be in considerable excess of those of related compounds which would interfere with the determinations. Nitrate can be determined either by difference in its mixtures with nitrite or by prior removal of the nitrite using ascorbic acid provided oxygen and nitric oxide are removed by degassing with nitrogen.

Abnormality of phospholipid transverse diffusion in sickle erythrocytes.

We have used spin-labeled analogues of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine to compare the transverse diffusion rates of lipids in normal and sickle erythrocytes. The beta-chain of the spin-labeled lipids was a short chain (five carbons) providing the spin labels with a relative water solubility, and hence permitting their rapid incorporation into cell membranes. The orientation of the labeled lipids in the membranes was assayed by selective chemical reduction of the nitroxide labels embedded in the outer leaflet. We have found that all three spin-labeled phospholipids are initially incorporated in the outer leaflet. Upon incubation at 4 degrees C the aminophospholipids, not the phosphatidylcholine, diffuse toward the inner leaflet within 3 h. The transverse diffusion rate of aminophospholipids is reduced by 41% (phosphatidylserine) and 14% (phosphatidylethanolamine) in homozygote sickle cells (SS) when compared with normal cells (AA) or heterozygote cells (AS or SC). At equilibrium the asymmetric distribution of spin-labeled phospholipids resulting from this selective diffusion is also reduced in SS cells when compared with AA, SC, or AS cells. This reduced asymmetry was not found in a reticulocyte-rich blood sample (hemoglobin A), indicating that the age of the cell cannot be responsible for this phenomenon. Moreover, because at low temperatures the sickling process does not occur, the observed perturbations in phospholipid organization reflect preexisting membrane abnormalities in sickle cells. Ghosts loaded with ATP give the same results. Varying the concentration of intracellular calcium had no effect on lipid diffusion, except at very high free calcium concentrations (3 microM) when diffusion was practically abolished. We suggest that membrane protein alterations may be part of the explanation of the observed abnormalities.

Solid Phase Derivatization Reactions in HPLC Polymeric Reductions for Carbonyl Compounds

Abstract Polymeric reducing agents, such as polymeric borohydride resins, can be successfully utilized in both the pre-and post-column modes, online, at ambient temperatures, in real-time, for the selective chemical reduction of a large number of aldehydes. Other classes of carbonyl derivatives, such as ketones, esters, amides, etc., are totally unreactive under these same polymeric reduction conditions. This particular reducing agent is fully compatible with conventional reversed phase HPLC columns and mobile phases, such as methanol/water, ethanol/water, and acetonitrile/water, in varying proportions. The approach to selective detection in HPLC described here utilizes conventional UV-VIS detection following pre-or post-column reductions that occur on-line. Alternative detection methods could just as readily be utilized. Overall reactions are rapid, quantitative, reproducible, and highly selective. In certain cases, it is possible to realize improved detection limits as a result of aldehyde reductions. D...

Engineering Development of the MSBR Fuel Recycle

The molten-salt breeder reactor being developed at Oak Ridge National Laboratory (ORNL) requires continuous chemical processing of the fuel salt, 7LiF-BeF2-ThF4 (72-16-12 mole%) containing ~0.3 mole% 233UF4. The reactor and the processing plant are planned as an integral system. The main functions of the processing plant will be to isolate 233Pa from the neutron flux and to remove the rare-earth fission products. The processing method being developed involves the selective chemical reduction of the various components into liquid bismuth solutions at ~600°C, utilizing multistage counter-current extraction. Protactinium, which is easily separated from uranium, thorium, and the rare earths, would be trapped in the salt phase in a storage tank located between two extraction contactors and allowed to decay to 233U. Rare earths would be separated from thorium by a similar reductive extraction method; however, this operation will not be as simple as the protactinium isolation step because the rare-earth-thorium separation factors are only 1.3 to 3.5. The proposed process would employ electrolytic cells to simultaneously introduce reductant into the bismuth phase at the cathode and to return extracted materials to the salt phase at the anode. The practicability of the reductive extraction process depends on the successful development of salt-metal contactors, electrolytic cells, and suitable materials of construction.