Hofmann Method Research Articles

Experimental quantum teleportation of a Toffoli gate across three spatially distributed parties in a photonic quantum network

Quantum computers may offer significant computational advantages over classical counterparts, revolutionizing the technology landscape in the near future. When networked together, the advantage of quantum computing may be further amplified, and there may emerge innovative applications. Among various active explorations on distributed quantum computing, multiqubit quantum gates between distant networked quantum computers are of particular interest because they offer operational advantages of efficiency and fidelity. Here we report the first experimental demonstration of quantum teleportation for a Toffoli gate, which is a commonly used multiqubit quantum gate, across three spatially distributed parties within a photonic quantum network. Employing the Hofmann method, we estimate the fidelity of the teleported Toffoli gate to be at least 0.706 ± 0.131. This successful demonstration of the quantum teleportation of a Toffoli gate constitutes a critical step toward the ultimate realization of distributed quantum computation.

Synthesis and Nitrite/Sulfite Electrochemical Response Investigation of Fluorene‐Based, Cross‐Linked Polyisocyanide

AbstractAs compared to the widely studied linear‐type polyisocyanides (PICs), the development of cross‐linked PICs has not attracted much attention, and their applications in electrochemical fields are scarcely reported by far. Herein, a type of novel fluorene‐based isocyanide monomer (BIF), which bears two isocyano (─NC) groups, is successfully synthesized via Hofmann method with 9, 9‐bis (4‐aminophenyl) fluorene as the precursor. Corresponding fluorene‐based, cross‐linked PIC derivative (PBIF) is successfully prepared by Ni2+‐catalyzed polymerization of BIF. Chemical structure, elemental composition, accumulation state, thermal stability, microstructure, porous characteristics, and specific surface area of PBIF are characterized. NO2− and SO32− electrochemical responses of the modified glassy carbon electrode (PBIF/CS/GCE), which is fabricated with PBIF as the active material and chitosan (CS) as adhesive agent, is systematically analyzed here. Experimental results show that PBIF/CS/GCE exhibits strengthened NO2−/SO32− electrochemical response, suggesting that PBIF has a potential application prospect as novel non‐conjugated polymer‐based NO2−/SO32− electrochemical probing material.

Diphenylmethane-based cross-linked polyisocyanide: synthesis and application as nitrite electrochemical probe and N-doped carbon precursor

With 4,4′-diaminodiphenylmethane as the starting material, a compound (M1) containing two functional isocyanide groups was successfully prepared via Hofmann method, and a polyisocyanide derivative (P1), with a cross-linked structure, was successfully prepared via Ni2+-catalyzed polymerization. Electrochemical detection of nitrite was achieved by utilizing P1-modified glassy carbon electrode as the working electrode, and the corresponding detection limit reached ~ 0.51 μM (3σ/k). Subsequently, nitrogen-doped porous carbon material (P1-C) was obtained by direct carbonization of P1. The preliminary study of its electrochemical performance was carried out. Specific capacitance of P1-C reached 152.5 F g−1 at 0.5 A g−1, and high capacitance retention of 94.4% was recorded after 1000 galvanostatic charge–discharge cycles (at 1 A g−1), indicating that P1-C can act as potential energy storage electrode material.

Dichloro-[2,2]-paracyclophane. Methods for Synthesis

Methods for synthesis of dichloro-[2,2]-paracyclophane (dichloroPCP) are discussed. DichloroPCP is a valuable monomer to prepare polymer coats for electronics. This monomer is not produced in Russia. Analysis of available synthetic techniques leads to conclude that the Hofmann method for cleavage of quaternary ammonium salts is the most appropriate for the industrial production. Application of catalytic technologies – alkali catalysis and catalysis by Lewis acids – is the promising way for practical implementation of this four-stage process.

Chemical Approach to Ultrastiff, Strong, and Environmentally Stable Graphene Films.

Reduced graphene oxide (rGO) sheets prepared by a modified Hofmann method (Ho-rGO) have large graphitic domains with few structural defects, facilitating the dense packing between rGO sheets to enhance the mechanical performances of the resultant graphene films. Graphene films are fabricated by the filtration of the aqueous dispersions of Ho-rGO sheets and further treated by thermal annealing. They display high moduli (stiffness) of 54.6 ± 1.4 GPa and high tensile strengths of 521 ± 19 MPa. They also exhibit high toughness and good electrical properties. The intact structure of Ho-rGO sheets narrows the nanochannels in the film matrices, greatly reducing the water infiltration into films and providing the graphene films with excellent environmental stability. These graphene films are attractive for practical applications because of their light weights and ultrastiff and ultrastrong mechanical properties.

Concentration of Nitric Acid Strongly Influences Chemical Composition of Graphite Oxide.

Graphite oxide is the most widely used precursor for the synthesis of graphene through top-down methods. We demonstrate a significant influence of nitric acid concentration on the structure and composition of the graphite oxide prepared by graphite oxidation. In general, two main chlorate-based oxidation methods are currently used for graphite oxide synthesis: the Staudenmaier method using 98 wt % nitric acid, and the Hofmann method with 68 wt % nitric acid. However, a gradual change in nitric acid concentration allows a continuous change in the graphite oxide composition. The prepared samples are thoroughly characterised by microscopic techniques as well as various spectroscopic and analytical methods. Lowering the nitric acid concentration leads to an increase in oxidation degree, and in particular, to the concentration of epoxy and hydroxyl groups. This knowledge is not only useful for the large-scale synthesis of graphite oxide with tuneable size and chemical composition, but the use of nitric acid in lower concentrations can also reduce the overall cost of the synthesis significantly.

Definitive Insight into the Graphite Oxide Reduction Mechanism by Deuterium Labeling.

The reduction of graphite oxide is one of the most important reactions in the production of graphene in gram quantities. The mechanisms of these widely used reactions are poorly understood. The mechanism of the chemical reduction of two different graphite oxides prepared by the chlorate (Hofmann method) and permanganate methods (Hummers method) has been investigated. Three different reduction agents, lithium tetrahydridoaluminate, sodium tetrahydridoborate, and lithium tetrahydridoborate, as well as their deuterated counterparts, were used for the reduction of graphite oxide. Reduced graphite oxides were analyzed by scanning electron microscopy, energy-dispersive spectroscopy, elemental combustion analysis, Raman spectroscopy, high-resolution X-ray photoelectron spectroscopy, and simultaneous thermal analysis. The concentration of boron incorporated into graphene was measured by prompt gamma activation analysis. Rutherford back-scattering spectroscopy and elastic recoil detection analysis were used for the determination of the elemental composition, including deuterium concentration, as evidence of CH bond formation.

Insight into the mechanism of the thermal reduction of graphite oxide: deuterium-labeled graphite oxide is the key.

For the past decade, researchers have been trying to understand the mechanism of the thermal reduction of graphite oxide. Because deuterium is widely used as a marker in various organic reactions, we wondered if deuterium-labeled graphite oxide could be the key to fully understand this mechanism. Graphite oxides were prepared by the Hofmann, Hummers, Staudenmaier, and Brodie methods, and a deuterium-labeled analogue was synthesized by the Hofmann method. All graphite oxides were analyzed not only using the traditional techniques but also by gas chromatography-mass spectrometry (GC-MS) during exfoliation in hydrogen and nitrogen atmospheres. GC-MS enabled us to compare differences between the chemical compositions of the organic exfoliation products formed during the thermal reduction of these graphite oxides. Nuclear analytical methods (Rutherford backscattering spectroscopy, elastic recoil detection analysis) were used to calculate the concentrations of light elements, including the ratio of hydrogen to deuterium. Combining all of these results we were able to determine graphite oxide's thermal reduction mechanism. Carbon dioxide, carbon monoxide, and water are formed from the thermal reduction of graphite oxide. This process is also accompanied by various radical reactions that lead to the formation of a large amount of carcinogenic volatile organic compounds, and this will have major safety implications for the mass production of graphene.

Permanganate-Route-Prepared Electrochemically Reduced Graphene Oxides Exhibit Limited Anodic Potential Window

Graphene-related materials have been of significant interest in the field of electrochemical sensing and biosensing. Four main methods of synthesizing large quantities of graphene from graphite via graphene oxide have been used to date, using either chlorate (Staudenmaier and Hofmann methods) or permanganate (Hummers and Tour methods) oxidants and strong mineral acids to generate graphite oxide with subsequent reduction. In electrochemical applications, electrochemical reduction is often used to prepare reduced graphenes so as to eliminate any electrochemically reducible groups on the surface of graphene oxides which could interfere with the analytical signals. Here, we show that electrochemical reduction of oxygen-containing groups at graphene oxide surfaces indeed results in materials without inherent electrochemistry for chlorate-based graphene oxides; however, permanganate-based electrochemically reduced materials exhibited significant limitation in the anodic region, starting from ∼+0.1 V (vs Ag/AgCl...

Vacuum-assisted microwave reduction/exfoliation of graphite oxide and the influence of precursor graphite oxide

One-step synthesis of high quality graphene at gram-scale quantities is important for industrial applications, e.g. in electrochemistry for sensing and energy storage. Currently, thermal reduction/exfoliation of graphite oxide (GO) is a typical method of choice. However, it has the drawback of requiring specialized equipment for rapid thermal shock. A recent alternative method, microwave-assisted exfoliation, usually suffers from poor reduction of graphite oxide and thus low C/O ratios. Herein we show that vacuum-assisted microwave reduction/exfoliation of graphite oxide in a closed system leads to high C/O ratios and partial hydrogenation of graphene (2.6at.% of H). Microwave irradiation of graphite oxide in vacuum leads to outgassing from GO and the creation of plasma which aids temperature distribution and hydrogenation. This plasma is quickly extinguished by further dramatic evolution of gases from GO and consequent pressure increase. We assess the influence of precursor graphite oxide, prepared by Hummers, Staudenmaier, and Hofmann methods, upon the materials properties of microwave exfoliated graphene. We show that microwave-exfoliated graphenes prepared from different graphite oxides show very fast heterogeneous electron transfer rates, with similar electrochemical behaviour to thermally reduced graphene oxide.

Towards highly electrically conductive and thermally insulating graphene nanocomposites: Al2O3–graphene

Highly electrically conductive materials with low heat transfer rates are of very high importance for high temperature fuel cell technologies and the refractory material industry. We aim to develop such materials with high electrical conductivities/high thermal resistivities by creating composite materials of graphene and Al2O3. Here we describe a novel and facile method for the synthesis of Al2O3–graphene composites. Graphite oxide, which was prepared by the Hofmann method, was reduced by active hydrogen generated by the reaction of aluminum with a solution of sodium hydroxide. This reaction led to the formation of a nanocrystalline composite of graphene and aluminum hydroxide. The Al(OH)3–graphene composite was then calcined and pressed into pellets. Sintering of the pellets yielded a nanostructured Al2O3–graphene composite. We characterized the properties of the Al(OH)3–graphene and Al2O3–graphene composite materials in all steps to get an understanding of the process of the nanocomposite formation. The materials were analyzed by XRD, high resolution XPS, Raman spectroscopy, SEM, SEM-EDS, STEM, STA and AFM. The resistivity and thermal conductivity of the final Al2O3–graphene composite were measured. The Al2O3–graphene nanocomposite is a promising conductive material for high-temperature applications.

Graphenes Prepared by Hummers, Staudenmaier and Hofmann Methods for Analysis of TNT‐Based Nitroaromatic Explosives in Seawater

AbstractThe detection of TNT and related nitroaromatic compounds in seawater is of great interest. Electrochemical techniques can be applied for detection purposes since nitroaromatic compounds contain easily reducible nitro groups. In this study, we investigate the performance of thermally reduced graphenes prepared by three different oxidative methods: Hummers, Staudenmaier and Hofmann methods with consequent thermal exfoliation. The Hofmann method‐based graphene was found to exhibit the highest sensitivity in detecting TNT electrochemically. Extended study on the detection of TNT in seawater using the graphene material provided significant improvements in the detection sensitivity. These findings will have profound impacts on the detection of nitroaromatic explosives in seawater.

Graphite Oxides: Effects of Permanganate and Chlorate Oxidants on the Oxygen Composition

Research on graphene materials has refocused on graphite oxides (GOs) in recent years. The fabrication of GO is commonly accomplished by using concentrated sulfuric acid in conjunction with: a) fuming nitric acid and KClO(3) oxidant (Staudenmaier); b) concentrated nitric acid and KClO(3) oxidant (Hofmann); c) sodium nitrate for in situ production of nitric acid in the presence of KMnO(4) (Hummers); or d) concentrated phosphoric acid with KMnO(4) (Tour). These methods have been used interchangeably in the graphene community, since the properties of GOs produced by these different methods were assumed as almost similar. In light of the wide applicability of GOs in nanotechnology applications, in which presence of certain oxygen functional groups are specifically important, the qualities and functionalities of the GOs produced by using these four different methods, side-by-side, was investigated. The structural characterizations of the GOs would be probed by using high resolution X-ray photoelectron spectroscopy, nuclear magnetic resonance, Fourier transform infrared spectroscopy, and Raman spectroscopy. Further electrochemical applicability would be evaluated by using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Our analyses highlighted that the oxidation methods based on permanganate oxidant (Hummers and Tour methods) gave GOs with lower heterogeneous electron-transfer rates and a higher amount of carbonyl and carboxyl functionalities compared with when using chlorate oxidant (Staudenmaier and Hofmann methods). These observations indicated large disparities between the GOs obtained from different oxidation methods. Such insights would provide fundamental knowledge for fine tuning GO for future applications.

Graphenes prepared by Staudenmaier, Hofmann and Hummers methods with consequent thermal exfoliation exhibit very different electrochemical properties

Large-scale fabrication of graphene is highly important for industrial and academic applications of this material. The most common large-scale preparation method is the oxidation of graphite to graphite oxide using concentrated acids in the presence of strong oxidants and consequent thermal exfoliation and reduction by thermal shock to produce reduced graphene. These oxidation methods typically use concentrated sulfuric acid (a) in combination with fuming nitric acid and KClO(3) (Staudenmaier method), (b) in combination with concentrated nitric acid and KClO(3) (Hofmann method) or (c) in the absence of nitric acid but in the presence of NaNO(3) and KMnO(4) (Hummers method). The evaluation of quality and applicability of the graphenes produced by these various methods is of high importance and is attempted side-by-side for the first time in this paper. Full-scale characterization of thermally reduced graphenes prepared by these standard methods was performed with techniques such as transmission and scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. Their applicability for electrochemical devices was further evaluated by means of cyclic voltammetry techniques. We showed that while Staudenmaier and Hofmann methods (methods that do not use potassium permanganate as oxidant) generated thermally reduced graphenes with comparable electrochemical properties, the graphene prepared by the Hummers method which uses permanganate as oxidant showed higher heterogeneous electron transfer rates and lower overpotentials as compared to graphenes prepared by the Staudenmaier or Hofmann methods. This clearly shows that the methods of preparations have dramatic influences on the materials properties and, thus, such findings are of eminent importance for practical applications as well as for academic research.

Thermally stimulated currents in disordered solids at fractional heating

Thermally stimulated currents (TSCs) in disordered solids, registered at fractional sample heating, are investigated theoretically. The Gobrecht–Hofmann method of determining trap distribution in energy gap is extended to the case of significant carrier retrapping. Two specific cases, when the TSCs are limited either by carrier recombination or by carrier neutralization on collecting electrode, are considered. The accuracy of proposed method is estimated from the analysis of TSC curves, calculated numerically for exponential and Gaussian trap distributions.

Enantioselective formal synthesis of tridemethylisovelleral

A simple and efficient synthetic route to the bicyclic α,β-unsaturated β-keto ester methyl (3a S,7a S)-6-oxo-2,3,3a,6,7,7a-hexahydro-1 H-indene-5-carboxylate, a versatile intermediate in the synthesis of biologically active unsaturated 1,4-dialdehydes, is described. The synthesis includes a chirality introducing nonenzymatic asymmetric desymmetrization (ADS) reaction of a cyclic meso-anhydride 4 and a modified Hofmann method for preparing exocyclic dienes. The ester was synthesized in a moderate overall yield (19%) from 6 and with an excellent enantioselectivity (>90%).

Über aldose-2,-4 dinitro- und 4-nitro-phenyl- hydrazone

The writer and his collaborators have the structure of 2,4-dinitro- and 4-nitro-phenyl hydrazones of d-glucose, d-xylose, d-mannose, d-arabinose, and d-galactose investigated. With the purpose of determination of the structure the hydrazones have been—following Hofmann's method— at about 0° acetylated and on this way two types of O-acetyl hydrazones have been produced. The 2,4-dinitro-phenyl hydrazones of d-glucose, d-xylose, d-mannose and the 4-nitro-phenyl hydrazone of d-glucose resulted O-acetyl hydrazones of ring-structure. These hydrazones could be transformed in open-chain ones by acetylation at about 100°. The structure of the latter compounds has been proved by synthesis. The U.V. absorption of the two types of hydrazones differs at about 260 mμ. The relative stability of the pyranose ring of O-acetyl- d-glycose-, - d-xylose- and - d-mannose-2,4- dinitro-phenyl hydrazone has been also quantitatively determined. As a result of the investigations on the reactions of aldose hydrazones it has been stated that into derivatives of tetrahydro-furfural hydrazone could be transformed the following compounds: 2-oxy-3-chloro-tetrahydropyran, 2,5- dioxyvaleraldehyd-4′-nitro-phenyl hydrazone and 2-desoxy-2-bromo-3,4-diacetyl d-xylose.

Diphenyl Etherを基核とするAcid Hydrazide誘導体の合成研究 (第10報)

Mononitrodiphenyl ether-monocarboxylic acids, possessing a nitro and a carboxyl groups in each benzene ring, were submitted to the Curtius and Hofmann reactions, as indicated in Chart 1, and a series of corresponding nitro-aminodiphenyl ethers were prepared. In general, the Curtius reaction gave a comparatively better yield than the Hofmann method.