Extra Oxide Research Articles

MFM-300(V) as an active heterogeneous catalyst for deep desulfurization of fuel oil by aerobic oxidation

Oxidative desulfurization (ODS) is considered as one of the most promising processes for producing clean fuel oil. Generally, such a process was realized by adding extra oxidants. However, it maintains a great challenge to carry out ODS under ambient air atmosphere. In this work, we report that a metal-organic framework MFM-300(V) exhibited efficient ODS performance under ambient air atmosphere. The removal rate of sulfur content in model oil reached 99.6% for dibenzothiophene and 98.1% for 4,6-dimethyldibenzothiophene, respectively. Additionally, it was found that MFM-300(V) was active in the presence of not only hydrogen-donating solvents like decalin but also hydrogen-withdrawing solvents like n-dodecane. Such ODS performance might be attributed to the unique pore structure and active V sites in MFM-300(V) to produce ·OH radicals in situ that could initiate the chain auto-oxidation reaction.

Investigation of the structural and optical properties of copper-titanium oxide thin films produced by changing the amount of copper

We examine how the structural, morphological and optical properties of TiO2 thin films are changed with heavily copper (Cu) content. Variations in characteristic properties of the films with 0, 12.5, 25 and 50 wt% Cu contents, grown by sol-gel dip coating method, are observed by using X-ray diffraction (XRD), Raman scattering, atomic force microscopy, energy dispersive X-ray analysis and optical spectroscopy measurements. The XRD and Raman spectra indicate that pure TiO2 film forms in the anatase structure. At high Cu concentrations, XRD results also reveal the substitution of Ti with Cu and formation of extra compound Copper-Titanium oxide. Raman measurements also show that Cu is incorporated homogeneously into TiO2 matrix up to 12.5 wt% concentration and this uniformity is distorted at higher Cu contents. In addition, optical spectroscopy measurements show that the optical band gap energy decreases from 3.26 eV to 2.05 eV with increasing Cu concentration. Furthermore, it is observed that the refractive index values obtained by means of transmittance spectra at 550 nm wavelength; increases from 2.47 to 3.39 when the Cu concentration increases from 0 to 50 wt%.

Cadmium solubility in paddy soil amended with organic matter, sulfate, and iron oxide in alternative watering conditions.

We successfully accounted for the dynamics of cadmium (Cd) solubility in paddy soil that contained a realistically low total Cd concentration (0.36 mg kg-1) after submergence and redrying by monitoring multiple chemical and microbial soil properties. The addition of rice straw promoted greater microbial iron reduction and induced a greater increase in soil pH after submergence, compared to the control and treatments with added gypsum or hematite. Consequently, dissolved Cd decreased to under the detection limit in one week in the straw-amended treatment but remained high even after eight weeks in the other three treatments. The Cd solubility strongly correlated with soil pH and was unlikely to decrease due to Cd precipitation in secondary iron minerals. After five weeks of redrying, the dissolved Cd content was still the lowest, and the putative iron-reducing bacteria Geobacter remained the most abundant in the straw-amended soil. The results suggest that the addition of organic matter can efficiently immobilize soil Cd at an environmentally realistic concentration by stimulating the microbial reduction of native oxidized soil components after submergence, while adding extra iron oxide or sulfate alone is not effective because it does not eliminate the limitation imposed by electron donors on microbial reduction.

Trends in Reverse-Current Change in Tunnel MIS Diodes with Calcium Fluoride on Si(111) Upon the Formation of an Extra Oxide Layer

The currents flowing in metal–CaF2–n-Si and metal–SiO2–CaF2–n-Si structures with the same (about 1.5 nm) fluoride thickness are compared in the reverse-bias mode. It is revealed that the current in the case of a two-layer dielectric can be notably higher within a certain voltage range. Such unexpected behavior is associated with the coexistence of both electron and hole components of the current as well as with the configuration of the SiO2–CaF2 barrier through which tunneling occurs. The results of measurements and explanatory simulation data are presented.

Transition metal- and oxidant-free sulfonylation of 1-sulfonyl-1H-1,2,3-triazoles to enols for the synthesis of sulfonate derivatives

A novel and convenient protocol for the synthesis of sulfonate derivatives via DABCO-catalyzed direct sulfonylation of 1-sulfonyl-1,2,3-triazoles to different enols has been established. This synthetic route could effectively avoid the use of transition metal catalysts and extra oxidants, and the target products could be obtained in good to excellent yields (75-86%) with wide substrate scope under mild conditions at low-catalyst loadings, which would provide a facile and practical access to enol sulfonates. Furthermore, the use of the resulting enol sulfonates for the C-C bond formation has been demonstrated via Suzuki-Miyaura, Sonogashira, and Heck cross-coupling reaction.

Redox-Neutral ortho Functionalization of Aryl Boroxines via Palladium/Norbornene Cooperative Catalysis

Palladium/norbornene (Pd/NBE) cooperative catalysis, also known as the Catellani reaction, has become an increasingly useful method for site-selective arene functionalization; however, certain constraints still exist due to its intrinsic mechanistic pathway. Herein we report a redox-neutral ortho functionalization of aryl boroxines via Pd/NBE catalysis. An electrophile, such as carboxylic acid anhydrides or O-benzoyl hydroxylamines, is coupled at the boroxine ortho position, and a proton as the second electrophile is introduced at the ipso position. This reaction does not require extra oxidants or reductants, and avoids stoichiometric bases or acids, thereby tolerating a wide range of functional groups. In particular, orthogonal chemoselectivity between aryl iodide and boroxine moieties is demonstrated, which could be used to control reaction sequences. Finally, a deuterium labelling study supports the ipso-protonation pathway. This unique mechanistic feature could inspire the development of a new class of Pd/NBE-catalyzed transformations.

Synthesis of nanodispersed titanium dioxide via pH-controlled polymerization of titanium acid

The possibility of synthesis of highly photoactive nanosized titania employing ion exchange to exert control over polycondensation of titanium acid in aqueous medium has been demonstrated. The resultant spherical TiO2 nanoparticles exhibits extra high light-induced oxidation activity remaining for some time even after termination of UV illumination. The nanodispersed titania readily penetrate into the surface pores and can be used for deposition of photocatalytic coatings by impregnation technique.

Direct dehydrogenative alkyl Heck-couplings of vinylarenes with umpolung aldehydes catalyzed by nickel

Alkenes are fundamental functionalities in nature and highly useful intermediates in organic synthesis, medicinal chemistry and material sciences. Transition-metal-catalyzed Heck couplings with organic halides as electrophiles have been established as a powerful protocol for the synthesis of this valuable building block. However, the requirement of organic halides and the generation of stoichiometric hazardous halide wastes may cause significant sustainable concerns. The halide-free oxidative Heck alkenylations involving organometallics or arenes as the coupling partners provide a facile and alternative pathway. Nonetheless, stoichiometric amounts of extra oxidant are essential in most cases. Herein, we present a direct dehydrogenative alkyl Heck-coupling reaction under oxidant-free conditions, liberating hydrogen, nitrogen and water as the side products. Excellent regioselectivity is achieved via neighboring oxygen atom coordination. Broad substrate scope, great functional group (ketone, ester, phenol, free amine, amide etc) tolerance and modification of pharmaceutical candidates and biological molecules exemplified its generality and practicability.

I2-mediated and direct synthesis of 3-phenoxy imidazo heterocycles

An I2-mediated protocol was proposed for the synthesis of 3-phenoxy imidazo heterocycles from aromatic ketones and 2-aminopyridines or 2-aminobenzothiazole. This direct, efficient and operationally simple method provided a fundamentally novel and rapid approach for the synthesis of 3-phenoxy imidazo heterocycles with good to excellent yields, and it avoided the requirement of any metal, base and extra oxidant.

Mn-doped CeO2 Nanorod Supported Au Catalysts for Dehydrogenation of Ethane with CO2

Dehydrogenation of ethane to ethylene was investigated in the presence of CO2 over Au catalyst supported on an Mn-doped ceria nanorod. The activity can be greatly enhanced by proper Mn doping. Mn was found to preferentially occupy defect sites or surface sites of ceria, resulting in the formation of extra oxide ions. Characterization results indicated that the reducible oxygen species related to ceria might play a vital role in the dehydrogenation. The addition of CO2 improved the stability of the catalysts remarkably, since CO2 can sustainably replenish the reducible oxygen species and eliminate the coke on the surface of the catalysts, which was proved by the H2-TPR and Raman analysis of spent catalysts. An ethane conversion of 17.4% with an ethylene selectivity of 97.5% can be obtained after 44 h of reaction.

Effect of Various Copper Salt Precursors on Metal-Assisted Chemical Etching of Silicon

Metal-assisted chemical etching (MACE) of Si with unstable metals like Cu can be described with reference to the oxidation effect of aqueous Cu2+ metal cations, in combination with the dissolution of Si species by HF. For 1-step MACE, salt precursors introduce possibly oxidizing additional anionic species, such as NO3− ions from Cu(NO3)2, that cannot be ignored when explaining MACE. This study for the first time unites Cu(NO3)2-MACE with isotropic hydrofluoric/nitric/acetic acid (HNA) Si etching, by purposely avoiding extra oxidants like H2O2, and contrasting the etching characteristics with etchants containing CuSO4, Cu(OAc)2, or CuCl2 precursors. A new model involving Cu2+-promoted autocatalysis of reactive nitrogen species (RNSs) is discussed, which explains the high etch rates, the NO3− anion concentration dependence, and the induction period specific to Cu(NO3)2 etchants. These results highlight the importance of Cu salt precursor selection when rationally designing new Cu-containing wet chemical etchants for key applications like MEMS and black silicon.

Combustion and Emission Performance of an HCCI Engine Fuelled by n-Heptane/Toluene Blends at a Low-Load Operating Condition

Homogeneous charge compression ignition (HCCI) engine technology offers high fuel efficiency and extra low nitrogen oxide (NOx) and particulate matter (PM) emissions, which makes it a potential alternative combustion mode to conventional diesel engines. A diesel fuel is usually composed of many classes of hydrocarbons among which aromatic compounds have attracted special attention due to their specific combustion characteristics. Understanding the combustion and emission characteristics of different classes of hydrocarbons is crucial for identifying appropriate diesel fuels suitable for HCCI combustion. Toluene is a typical aromatic compound in a diesel fuel. A study of toluene content may provide implications of the effect of aromatic in a diesel fuel on HCCI combustion. In this paper, the combustion and emission performance of an HCCI engine fuelled by n-heptane/toluene blends at a low load operating condition was investigated by experiment and numerical simulation. A modified Cooperative Fuel Research (CFR) engine and a in-house-developed multi-zone model were employed. The engine was operated at the condition of engine speed of 900 rpm, relative air/fuel ratio of 3.5 and without external exhaust gas recirculation. The investigated fuel blends covered a range from pure n-heptane to 70% toluene by volume. Both experimental and numerical results showed that an increase in toluene fraction in the fuel blend retarded combustion phasing. As a result, the optimal compression ratio, at which thermal efficiency reached its maximum for a fuel blend, increased with increasing toluene fraction. The maximum thermal efficiency increased as the toluene fraction increased from 0 to 50%, but then decreased with further increasing toluene fraction to higher values. The peak pressure rise rate also increased with increasing toluene fraction at a constant combustion phasing. An increase in toluene fraction resulted in an increase in unburned hydrocarbon emissions but had little effect on NOx emissions.

Fluorescein and its derivatives: New coreactants for luminol chemiluminescence reaction and its application for sensitive detection of cobalt ion

Fluorescein and its derivatives, including 4′,5′–dibromofluorescein, 2′,7′–dichlorofluorescein and 2′,4′,5′,7′–tetrabromofluorescein can be employed as efficient coreactants for luminol reaction. Under an alkaline condition they reacted with luminol to produce measureable chemiluminescence (CL) in the absence of any extra–oxidant. Cobalt ion (Co2+) significantly enhanced the CL emission of the reaction. The CL emission was strongly dependent on the concentration of carbonate buffer used; higher concentration of carbonate buffer provided more intense CL emission. The system had two emission peaks locating at 425 nm and 535 nm, respectively. With 4′,5′–dibromofluorescein as the coreactant for luminol reaction, a new CL method was developed for the detection of Co2+. The procedure allowed the linear detection of Co2+ in the range of 5–1000 nmol/L. The limit of detection (LOD) and limit of quantitation (LOQ) were 1.8 nmol/L and 5.0 nmol/L, respectively. The intra–day precision (n = 11) and inter–day precision (n = 3) was 3.2% and 4.7% for replicated measurements of 0.2 μmol/L Co2+ solution. The method was successfully applied to the determination of Co2+ in blue silica gel samples.

Pd0-PyPPh2@porous organic polymer: Efficient heterogeneous nanoparticle catalyst for dehydrogenation of 3-methyl-2-cyclohexen-1-one without extra oxidants and hydrogen acceptors

In this contribution, we have developed an efficient and recyclable porous organic polymer (POP) supported Pd nanoparticle catalyst (Pd°-PyPPh2@POP) for dehydrogenation of 3-methyl-2-cyclohexen-1-one. This heterogeneous catalytic system represents a totally clean process without using any extra oxidant and hydrogen acceptors. The SEM-EDS mapping images of the Pd°-PyPPh2@POP catalyst reveal the highly uniformly dispersed character of C, Pd, P and N elements. The coordination bonds between Pd nanoparticle and exposed P atom as well as N atom on the surface of PyPPh2@POP polymer are confirmed by means of solid-state 31P NMR and XPS. Importantly, both P atom and pyridyl ring on the PyPPh2@POP polymer are themselves used as solid base over the Pd°-PyPPh2@POP catalyst, leading to a catalytic conversion of 88.2% even without the employment of inorganic base additives (K2CO3). Our results have provided a strategy for designing highly active bifunctional POP supported nanoparticle catalysts.

Facile photochemical synthesis of α-ketoamides and quinoxalines from amines and benzoylacetonitrile under mild conditions

A selective protocol for the synthesis of either α-ketoamides or quinoxaline derivatives under the same reaction conditions has been achieved simply by varying substitution number of amino-groups. The method features metal-free, room temperature and broad substrate scopes as well as no extra oxidant. This process applies to various substituent groups and gives products in moderate to good yield. Finally, a rational mechanism was proposed.

Interfacial Constructing Flexible V2O5@Polypyrrole Core-Shell Nanowire Membrane with Superior Supercapacitive Performance.

Flexible membrane consisting of ultralong V2O5@conducting polypyrrole (V2O5@PPy) core-shell nanowires is prepared by a facile in situ interfacial synthesis approach. The V2O5 is for the first time demonstrated to show versatile function of reactive template to initiate the uniform and conformal polymerization of PPy nanocoating without the need for extra oxidants. The freestanding PPy-encapsulated V2O5 nanowire membrane is of great benefit in achieving strong electrochemical harvest by increasing electrical conductivity, shortening ion/electron transport distance, and enlarging electrode/electrolyte contact area. When evaluated as binder- and additive-free supercapacitor electrodes, the V2O5@PPy core-shell hybrid delivers a significantly enhanced specific capacitance of 334 F g-1 along with superior rate capability and improved cycling stability. The present work would provide a simple yet powerful interfacial strategy for elaborate constructing V2O5/conducting polymers toward various energy-storage technologies.

Degradation of surface film on LiCoO2 electrode by hydrogen fluoride attack at moderately elevated temperature

The failure mechanism of LiCoO2 electrode at moderately elevated temperature (70 °C) is examined. To this end, a Li/LiCoO2 cell is cycled 10 times within 3.0–4.3 V (vs. Li/Li+) to deposit a surface film on the LiCoO2 electrode, followed by storage at 70 °C for 10 h. The charge/discharge cycling data obtained at 25 °C after the storage reveal that the cell is damaged by the storage. The Coulombic efficiency decreases because the charging capacity is larger than that observed before the storage. The increased charging capacity is due to electrolyte oxidation. The postmortem analyses of the stored electrodes show that the surface film on the LiCoO2 electrode becomes thinner after storage and with a notable compositional change compared to before storage. The increased charging capacity after the storage can be attributed to the extra electrolyte oxidation on the damaged (thinned) LiCoO2 electrode surface. The loss of passivating ability due to surface film damage is responsible for the extra electrolyte oxidation and poorer Coulombic efficiency. Meanwhile, the chemical composition of the damaged film is very similar to that of the surface film stored with added hydrogen fluoride (HF, 400 ppm) in the electrolyte. It is thus suggested that the surface film is damaged by attack of HF generated from LiPF6 during the high-temperature storage. Evidently, a decrease of LiPF6 concentration in the electrolyte mitigates the film damage and the associated electrode degradation.

High oxidase-mimic activity of Fe nanoparticles embedded in an N-rich porous carbon and their application for sensing of dopamine

The N-doped porous carbon (NC) has been regarded as one of the promising support materials for nanoparticles (NPs) catalyst due to its inherent virtues such as porosity, large surface areas, and heteroatom incorporation. In this work, Fe/NC-800 hybrid was facilely prepared by uniform dispersion of in situ formed FeNPs onto NC-800 from carbonization of ZIF-8 at 800 °C for the first time. The optimized Fe/NC-800 catalyst was characterized by TEM, XPS and XRD. Compared with sole FeNPs and NC-800, the Fe/NC-800 catalyst exhibited an enhanced oxidase-like activity that could oxidize the colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to the heavy blue without extra oxidants such as H2O2. The possible reason for the enhanced oxidase-like activity of the Fe/NC-800 was discussed on the basis of the experiments of radical scavengers, indicating the importance of superoxide (O2•-) and singlet (1O2) in colorimetric reaction between TMB and Fe/NC-800 hybrid. Furthermore, the oxidase-like activity of Fe/NC-800 was significantly inhibited by dopamine (DA), leading to blue color fading. On this basis, a sensitive and selective colorimetric sensor was fabricated for the quantitative analysis of DA with a linear range of 0.01–40 μM and a low detection limit of 10 nM. The proposed colorimetric method was successfully applied to determine DA in human serum and injection samples, suggesting a promising application in biological analysis.

I2‐Triggered Reductive Generation of N‐Centered Iminyl Radicals: An Isatin‐to‐Quinoline Strategy for the Introduction of Primary Amides

AbstractAn efficient and alternative isatin‐to‐quinoline strategy illustrates the metal‐like behavior of molecular iodine in the N−O reduction of ketoxime acetates. This process involves N−O/C−N bond cleavages and C−C/C−N bond formation to furnish pharmacologically significant quinoline‐4‐carboxamide derivatives. In this process, metal catalysts and extra oxidants are unnecessary. Mechanistic studies confirm the crucial role of molecular iodine in the iminyl radical generation process, in that molecular iodine can catalyze single‐electron reduction coupling reactions in a manner similar to transition metals.magnified image

Synthesis of near-infrared fluorescent rhodamines via an SNArH reaction and their biological applications.

Near-infrared (NIR) dyes are of great interest in biomedicine due to diminished interfering absorption and fluorescence from biological samples, reduced scattering, and enhanced tissue penetration depth. In this context, we report the synthesis of rectilinearly π-extended rhodamine dyes using a unique intramolecular nucleophilic substitution of aromatic hydrogen (SNArH) strategy. The strategy makes use of an SNArH reaction between a preorganized aromatic amino nitrogen and an electron-deficient carbon in the xanthylium ion. The SNArH reaction presented herein can be performed under mild conditions without a transition metal catalyst and can be expected to enable the preparation of a wide variety of π-extended near-infrared fluorescent rhodamine dyes. Using this strategy, seven rectilinearly π-extended rhodamines (RE1-RE7) that had fluorescence emission wavelengths in the near-infrared region were synthesized. RE1, RE3, and RE4 were lysosome targetable and showed good photostabilities. In addition, using dye RE1 as a precursor, we constructed a novel NIR fluorescent turn-on probe (RE1-Cu), which can be used for detecting Cu2+ in living cells, demonstrating the value of our NIR functional fluorescent dyes.