Showing papers on "Nitrobenzene published in 2014"

Copper Nanoparticles on Graphene Support: An Efficient Photocatalyst for Coupling of Nitroaromatics in Visible Light

Abstract: Copper is a low-cost plasmonic metal. Efficient photocatalysts of copper nanoparticles on graphene support are successfully developed for controllably catalyzing the coupling reactions of aromatic nitro compounds to the corresponding azoxy or azo compounds under visible-light irradiation. The coupling of nitrobenzene produces azoxybenzene with a yield of 90 % at 60 °C, but azobenzene with a yield of 96 % at 90 °C. When irradiated with natural sunlight (mean light intensity of 0.044 W cm−2) at about 35 °C, 70 % of the nitrobenzene is converted and 57 % of the product is azobenzene. The electrons of the copper nanoparticles gain the energy of the incident light through a localized surface plasmon resonance effect and photoexcitation of the bound electrons. The excited energetic electrons at the surface of the copper nanoparticles facilitate the cleavage of the NO bonds in the aromatic nitro compounds. Hence, the catalyzed coupling reaction can proceed under light irradiation and moderate conditions. This study provides a green photocatalytic route for the production of azo compounds and highlights a potential application for graphene.

Coupled systems for selective oxidation of aromatic alcohols to aldehydes and reduction of nitrobenzene into aniline using CdS/g-C3N4 photocatalyst under visible light irradiation

Abstract: A coupled system of selective oxidation of aromatic alcohols to aromatic aldehydes and reduction of nitrobenzene into aniline was realized using CdS/g-C 3 N 4 composite as a photocatalyst under visible light illumination. The CdS/g-C 3 N 4 composite photocatalyst was prepared by hydrothermal method. The photocatalyst was characterized by x-ray powder diffraction (XRD), UV–vis diffuse reflection spectroscopy (DRS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Brunauer–Emmett–Teller (BET) specific surface area. Compared with single g-C 3 N 4 and CdS, the CdS/g-C 3 N 4 photocatalyst exhibits enhanced photocatalytic activity and excellent photostability under visible light illumination. It demonstrates that the selective oxidation of aromatic alcohol into aromatic aldehyde is achieved by direct holes oxidation, and the reduction of nitrobenzene into aniline is reached by direct electrons reduction. The optimum percentage of CdS is 10 wt.%. Under illumination for 4 h, the conversion of benzyl alcohol and the yield of benzaldehyde are about 48.0% and 44.6%, and the conversion of nitrobenzene and the yield of aniline are about 49.2% and 26.0%, respectively. The synergic effect of g-C 3 N 4 and CdS, which can effectively separate and transfer photoexcited carriers, was proposed to be responsible for the enhancement of the photocatalytic activity. This study has a guiding significance for the design of a coupled system which realizes selective oxidation and reduction of organics.

Methylation of amines, nitrobenzenes and aromatic nitriles with carbon dioxide and molecular hydrogen

Abstract: CO2/H2 was successfully employed in alkylation reactions by performing CO2 reduction and amine N-methylation in one-pot. In the presence of a simple CuAlOx catalyst, N-methyl or N,N-dimethyl amines with different structures can be selectively synthesized with up to 96% yields by applying amine, nitrobenzene and nitrile as starting materials.

Luminescent Anionic Metal–Organic Framework with Potential Nitrobenzene Sensing

Abstract: Solvothermal reaction of multidentate organic ligand, 5,5′,5″,5‴,5],5]′-[1,2,3,4,5,6-phenylhexamethoxyl]hexaisophthalic acid (H12L), with Cd(NO3)·4H2O produced an anionic 3D metal–organic framework [(CH3)2NH2]4[Cd3(H2L)] (1), which features a novel cage-to-cage connection. Interestingly, the 1D channel, which is stacked by cages, is divided into uniform segments by molecular-scale bricks. The luminescent properties of compound 1 have been explored, which shows that 1 is a potential luminescent sensory material for nitrobenzene.

Degradation of aniline with zero-valent iron as an activator of persulfate in aqueous solution

Abstract: Zero valent iron (ZVI) can activate persulfate to generate sulfate free radicals which are a strong oxidant to degrade organic pollutants. The oxidative degradation of aniline in aqueous solution by persulfate activated with zero valent iron was studied under laboratory conditions. Batch experiments were conducted to investigate the effects of different parameters such as pH, ZVI concentration, aniline concentration, persulfate concentration and reaction temperature on aniline degradation. The results showed that aniline degradation increased with increasing temperature. The optimum dosage of ZVI was 0.4 g L−1 and 85% aniline degradation was observed. Maximum aniline degradation was observed at pH 4.0, whereas at pH above or below 4.0, aniline degradation efficiency was decreased. In the persulfate-ZVI system, the apparent energy of activation for aniline degradation was 14.85 kJ mol−1. The existence of persulfate radicals and hydroxyl radicals produced during the degradation of aniline were identified with scavenger ethanol and tert-butyl alcohol. The reaction intermediates nitrobenzene, nitroso-benzene and p-benzoquinone were detected by gas chromatography-mass spectrometry and based on these intermediates obtained a probable pathway for aniline degradation has been proposed.

Interaction of Cobalt Nanoparticles with Oxygen- and Nitrogen-Functionalized Carbon Nanotubes and Impact on Nitrobenzene Hydrogenation Catalysis

Abstract: The type and the amount of functional groups on the surface of carbon nanotubes (CNTs) were tuned to improve the activity of supported Co nanoparticles in hydrogenation catalysis. Surface nitrogen species on CNTs significantly promoted the decomposition of the cobalt precursor and the reduction of cobalt oxide, and improved the resistance of metallic Co against oxidation in ambient atmosphere. In the selective hydrogenation of nitrobenzene in the gas phase, Co supported on CNTs with the highest surface nitrogen content showed the highest activity, which is ascribed to the higher reducibility and the lower oxidation state of the Co nanoparticles under reaction conditions. For Co nanoparticles supported on CNTs with a smaller amount of surface nitrogen groups, a repeated reduction at 350 °C was essential to achieve a comparable high catalytic activity reaching 90% conversion at 250 °C, pointing to the importance of nitrogen species for the supported Co nanoparticles in nitrobenzene hydrogenation.

Direct vs. indirect pathway for nitrobenzene reduction reaction on a Ni catalyst surface: a density functional study.

Abstract: Density functional theory (DFT) calculations are performed to understand and address the previous experimental results that showed the reduction of nitrobenzene to aniline prefers direct over indirect reaction pathways irrespective of the catalyst surface. Nitrobenzene to aniline conversion occurs via the hydroxyl amine intermediate (direct pathway) or via the azoxybenzene intermediate (indirect pathway). Through our computational study we calculated the spin polarized and dispersion corrected reaction energies and activation barriers corresponding to various reaction pathways for the reduction of nitrobenzene to aniline over a Ni catalyst surface. The adsorption behaviour of the substrate, nitrobenzene, on the catalyst surface was also considered and the energetically most preferable structural orientation was elucidated. Our study indicates that the parallel adsorption behaviour of the molecules over a catalyst surface is preferable over vertical adsorption behaviour. Based on the reaction energies and activation barrier of the various elementary steps involved in direct or indirect reaction pathways, we find that the direct reduction pathway of nitrobenzene over the Ni(111) catalyst surface is more favourable than the indirect reaction pathway.

A luminescent 3D interpenetrating metal–organic framework for highly selective sensing of nitrobenzene

Abstract: A three-dimensional (3D), luminescent, 5-fold interpenetrating metal-organic framework (MOF), [Zn2(fdc)2(bpee)2(H2O)]n·2H2O (1) exhibiting highly selective sensing of nitrobenzene (NB) via a fluorescence quenching mechanism has been demonstrated.

Size-Dependent Halogenated Nitrobenzene Hydrogenation Selectivity of Pd Nanoparticles

Abstract: The selective hydrogenation of halogenated nitrobenzene (HNB) has been a great important chemical reaction in the fine chemical productions. In this study, the effect of metal particle size on the selective hydrogenation of HNB over Pd/C catalysts has been extensively investigated through the combination of theoretical (density functional theory calculations, DFT) and experimental methods. DFT calculations showed that the reaction barriers for dechlorination strongly depend on the type of reaction sites (terrace or edge), while the hydrogenation reaction barriers are nearly the same on different sites, which indicates that Pd nanoparticle size significantly affects the catalyst selectivity. Moreover, Pd nanoparticles with different sizes (from 2.1 to 30 nm) supported on activated carbon were synthesized using the methods developed by our group. In a 500 mL reactor, the selectivity is over 99.90% when the Pd nanoparticles are bigger than 25 nm. Finally, the industrial applications of the proposed catalyst ...

A Stable Porous Anionic Metal–Organic Framework for Luminescence Sensing of Ln3+ Ions and Detection of Nitrobenzene

Abstract: A hexagonal channel-based porous anionic metal-organic framework was successfully constructed. IFMC-3 is stable in air and acidic/basic aqueous solutions at room temperature, and constitutes a selective luminescent sensing material for Ln(3+) ions and a recyclable probe for the sensitive detection of nitrobenzene.

Silicate sol–gel stabilized silver nanoparticles for sensor applications toward mercuric ions, hydrogen peroxide and nitrobenzene

Abstract: Here, we developed a silver nanoparticles (Ag NPs) based sensor for the detection of mercuric ions (Hg(II)), hydrogen peroxide (H2O2) and nitrobenzene. The silicate sol–gel (SSG) stabilized Ag NPs were synthesized via one-pot synthetic route using the mixture of hydrazine, ammonium chloride and nitric acid as reduction solution. The Ag NPs were further characterized by absorption spectra, XRD, SEM, TEM, EDX and SAED analyses. The spectral and colorimetric methods revealed the efficiency of Ag NPs to detect Hg(II) ions and the lowest detection limit was found to be 5 μM. Also, Ag NPs exhibited selectivity toward Hg(II) ions in the presence of other environmentally relevant heavy metal ions. For the detection of H2O2, an enzymeless electrochemical sensor was prepared by modifying glassy carbon electrode with SSG stabilized Ag NPs. Using the linear sweep voltammetry (LSV) and differential pulse voltammetry (DPV) techniques, the lowest experimental detection limits for H2O2 sensing were found to be 0.5 and 0.1 μM, respectively. Similarly, the electrochemical sensing of nitrobenzene using the modified electrode was identified to have the lowest experimental detection limit of 1 μM by square wave voltammetry (SWV).

CNT–PVDF composite flow-through electrode for single-pass sequential reduction–oxidation

Abstract: In this study, a five-layer electrochemical CNT–PVDF filter that is thin, flexible, and stable is demonstrated to be effective and efficient for single-pass nitrobenzene mineralization by sequential reduction–oxidation Key to the technology is development of a CNT–PVDF membrane that is mechanically stable, electrically conductive, and non-Faradaic, which is used to prevent CNT release from and electrochemical degradation of the Faradaic CNT electrodes A five-layer electrochemical filter: (1) conductive & protective CNT–PVDF, (2) Faradaic CNT electrode, (3) insulating PVDF separator, (4) Faradaic CNT electrode, and (5) conductive & protective CNT–PVDF is formed by mechanical press At a total cell potential of 4 V, the sequential electrochemical reduction–oxidation process is able to reduce >99% of the influent nitrobenzene to aniline then oxidize >80% of the aniline to non-aromatic products (mostly carbon dioxide) in a single-pass (∼5 s hydraulic residence time) The mineralization current efficiency is ∼20%, total cell potential is completely (>99%) distributed to the two electrodes, and the energy requirement is ∼36000 kJ per mole of nitrobenzene degraded

Ultrasound-assisted magnetic solid-phase extraction based ionic liquid-coated Fe3O4@graphene for the determination of nitrobenzene compounds in environmental water samples

Abstract: An ultrasound-assisted magnetic solid-phase extraction procedure with the [C7MIM][PF6] ionic liquid-coated Fe3O4-grafted graphene nanocomposite as the magnetic adsorbent has been developed for the determination of five nitrobenzene compounds (NBs) in environmental water samples, in combination with high performance liquid chromatography-photodiode array detector (HPLC-PDA). Several significant factors that affect the extraction efficiency, such as the types of magnetic nanoparticle and ionic liquid, the volume of ionic liquid and the amount of magnetic nanoparticles, extraction time, ionic strength, and solution pH, were investigated. With the assistance of ultrasound, adsorbing nitrobenzene compounds by ionic liquid and self-aggregating ionic liquid onto the surface of the Fe3O4-grafted graphene proceeded synchronously, which made the extraction achieved the maximum within 20 min using only 144 μL [C7MIM][PF6] and 3 mg Fe3O4-grafted graphene. Under the optimized conditions, satisfactory linearities were obtained for all NBs with correlation coefficients larger than 0.9990. The mean recoveries at two spiked levels ranged from 80.35 to 102.77%. Attributed to the convenient magnetic separation, the Fe3O4-grafted graphene could be recycled many times. The proposed method was demonstrated to be feasible, simple, solvent-saving and easy to operate for the trace analysis of NBs in environmental water samples.

Multifunctional White-Light-Emitting Metal–Organic Gels with a Sensing Ability of Nitrobenzene

Abstract: In this study, three novel luminescent nanofibrous metal–organic gels (MOGs) have been synthesized by the reaction of 1,3,5-tris(3-pyridylmethoxyl)benzene (L) with chloride salts of Cd(II), Hg(II), and Cu(II). The metal–ligand coordination, intermolecular π–π stacking and several other weak interactions found to play an important role in the formation of nanofibrous materials. The gel materials are characterized by rheology, diffuse reflectance spectra and various microscopic techniques such as TEM, FESEM, and AFM. The gels MOG-1 and MOG-2 were found to exhibit significant white photoluminescence, whereas the MOG-3 exhbits green emission upon excitation at 325 nm. Furthermore, the MOG-1 has shown its application as a chemosensor for the remarkable detection of nitroaromatics such as nitrobenzene (NB), 2,4-dinitrophenol (DNP). The significant quenching response for NB and DNP is attributed to the strong charge-transfer interactions between the electron-deficient aromatic ring of NB and the electron rich ar...

Enhanced Photocatalytic Degradation of Aqueous Nitrobenzene Using Graphitic Carbon–TiO2 Composites

Abstract: Graphitic carbon–TiO2 nanocomposites with different carbon loadings were synthesized by a one-pot hydrothermal method. The prepared catalysts were characterized by X-ray diffractometry (XRD), scanning electron microscopy, UV–vis diffuse reflectance spectrophotometry, and Brunauer–Emmett–Teller surface area analysis. The XRD results confirmed the presence of graphite in the composite without alteration of the TiO2 structure. The photocatalytic efficiencies of the synthesized composites were determined by the degradation of aqueous nitrobenzene (NB) under UV irradiation. Because of the presence of graphitic carbon in the composite, there was an increase in the adsorption of NB (24%) on the composite surface, which led to a higher photocatalytic yield (up to 96% in 4 h at a graphitic carbon content of 1%). NB degradation was corroborated by chemical oxygen demand determinations.

Model Molecules with Oxygenated Groups Catalyze the Reduction of Nitrobenzene: Insight into Carbocatalysis

Abstract: The role of different oxygen functional groups on a carbon catalyst was studied in the reduction of nitrobenzene by using a series of model molecules. The carbonyl and hydroxyl groups played important roles, which may be ascribed to their ability to activate hydrazine. In comparison, the ester, ether, and lactone groups seemed to be inactive, whereas the carboxylic group had a negative effect. The reaction occurred most likely through a direct route, during which nitrosobenzene may be converted directly into aniline.

Nitrogen and oxygen-doped metal-free carbon catalysts for chemoselective transfer hydrogenation of nitrobenzene, styrene, and 3-nitrostyrene with hydrazine

Abstract: An activated carbon (AC) was treated by hydrogen peroxide and ammonia to dope oxygen and nitrogen on its surface. The surface-functionalized AC catalysts were used for the transfer reduction of nitrobenzene, styrene, and 3-nitrostyrene by hydrazine hydrate. The reduction of nitrobenzene and 3-nitrostyrene was promoted over the oxygen- and nitrogen-doped catalysts compared to the parent AC catalyst. Those were less active for the reduction of styrene but active for the reduction of vinyl group of 3-nitrostyrene. However, the nitrogen dopant suppressed the reduction of vinyl group of 3-vinylaniline. The functionalized AC catalysts are likely to facilitate the adsorption and activation of nitro group of the nitro substrates through interactions with polarized surface induced by the oxygen and nitrogen hetero dopants. This should make it possible to reduce the vinyl group of 3-nitrostyrene on the surface. The nitrogen dopant hindered the reduction of the vinyl group of 3-vinylaniline because the adsorption through its amino group should become difficult on the surface of basic nature induced by the nitrogen doping. The AC serves as an electrical conductor and its performance should be enhanced by the surface functionalization and this would contribute to the formation of reducing species such as diimide and proton from hydrazine on the surface. The present results show that oxygen- and/or nitrogen-doped, functionalized carbon materials could be promising as metal-free multi-task catalysts.

Bimetallic Au/Ag nanorods embedded in functionalized silicate sol–gel matrix as an efficient catalyst for nitrobenzene reduction

Abstract: A simple method for the preparation of bimetallic gold/silver nanorods embedded in amine functionalized silicate sol–gel matrix (Au/Ag–TPDT NRs) in aqueous medium and their application towards the catalytic reduction of nitrobenzene is reported. The Au/Ag–TPDT NRs are prepared by using N 1 -[3-trimethoxysilyl)propyl]diethylene triamine (TPDT) as a reducing as well as stabilizing agent. The catalytic activity of the Au/Ag–TPDT NRs is evaluated by studying the catalytic reduction of nitrobenzene to aniline upon the addition of NaBH 4 in an aqueous solution. The Au/Ag–TPDT NRs was found to be a good catalyst when compared to the Au–TPDT NRs and Au NRs for the reduction of nitrobenzene to aniline at room temperature. The enhanced catalytic activity of Au/Ag–TPDT NRs is due to the synergistic effect of Au and Ag present in the bimetallic Au/Ag–TPDT NRs. The reaction rate constants ( k ) are estimated to be 0.4050, 0.2515 and 0.1235 min −1 for Au/Ag–TPDT NRs, Au–TPDT NRs and Au NRs, respectively. The electrocatalytic reduction of nitrobenzene at pH 7 using the Au/Ag–TPDT NRs modified electrode is also investigated and compared with the Au–TPDT NRs. The higher electrocatalytic activity of Au/Ag–TPDT NRs is due to the synergistic effect of Au and Ag present in the bimetallic Au/Ag–TPDT NRs. The results of the study demonstrate that the Au/Ag–TPDT NRs are efficient catalyst for the catalytic reduction of nitrobenzene.

Influence of preparation method and palladium content on Pd/C catalysts activity in the liquid phase hydrogenation of nitrobenzene to aniline

Abstract: Two sets of Pd/C catalysts with 1–10 wt.% Pd content supported on active carbon were prepared by a conventional formaldehyde method. One set was prepared using H2[PdCl4] complex and other one with Na2[PdCl4]. In spite of different metal loadings, average crystallite size of palladium particles estimated by XRD and TEM analyses was virtually the same in all the cases, from 3 to 5 nm. Catalysts were tested for nitrobenzene hydrogenation in a stirred autoclave with the presence of methanol as a solvent, at 5 MPa and 50 °C. Ratio of Pd to nitrobenzene substrate was in every reaction mixture the same: 15.4 mg of palladium per mol of nitrobenzene. Specific initial catalyst activity (initial reaction rate) for catalysts with 1–4 wt.% Pd content for both sets of catalysts was comparable. It means that palladium complex used for the preparation had no-effect on catalyst activity. With palladium content higher than 4 wt.% a significant drop in the catalytic activity and increase in amount of the leached palladium were observed, which should be prescribed for the formation of agglomerates of palladium crystallites (revealed by TEM) and consequent decrease in concentration of catalytic sites. Because of a decrease in catalytic activity, the reaction times were longer, which caused a higher metal leaching.

Cu/CuxO and Pt nanoparticles supported on multi-walled carbon nanotubes as electrocatalysts for the reduction of nitrobenzene

Abstract: Cu/CuxO and Pt nanoparticles supported on multi-walled carbon nanotubes (MWCNTs) were studied as electrocatalysts for the reduction of nitrobenzene in a half-cell set-up. This reaction not only produces valuable chemicals, but has the potential to generate electricity if applied in a fuel cell device. MWCNTs with and without functional groups were investigated as supports for the nanoparticles, employing either ethylene glycol (EG) or H2 gas as reductant. Cu/CuxO nanoparticles supported on pristine multi-walled carbon nanotubes prepared using H2 as reductant (Cu/MWCNT-H2) were identified as the best electrocatalyst for the reduction of nitrobenzene on the basis of its onset potential and of the number of electrons transferred per nitrobenzene molecule. This material consists of well-dispersed Cu/CuxO nanoparticles with an average size of 8 nm. The stability of Cu/MWCNT-H2 was tested by cyclic voltammetry (CV) for 1000 cycles, showing that the activity of this electrocatalyst does not deteriorate over time. The electrochemical reduction of nitrobenzene over Cu/MWCNT-H2 in acidic ethanolic medium at −0.62 V vs. Fc/Fc+ led to 44% conversion with an overall selectivity toward azoxybenzene (AOB) of 82%.

Enhanced Photocatalytic Activity of TiO2 Nanosheets by Doping with Cu for Chlorinated Solvent Pollutants Degradation

Abstract: Photocatalytic of Cu-TiO2 was tested for the degradation of 1.1.1-trichloroethane, tetrachloroethene, and trichloroethene in aqueous phase under UV illumination. Results indicated fast degradation rate of pollutants over TiO2 doped with 0.5 wt % of Cu compared to undoped TiO2 and Degussa P25. Fast degradation of nitrobenzene, a probe of hydroxyl radicals (•OH), over Cu-TiO2 suggested high concentration of •OH generated in UV/Cu-TiO2 system. Cu-TiO2, synthesized by simply hydrothermal solution containing tetrabutyl-titanate, hydrofluoric acid, and cupric nitrate, was characterized by X-ray diffraction, Brunauer–Emmett–Teller, transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). Results showed that Cu-TiO2 was in anatase form and consisted of well-defined sheet-shaped structures having a rectangular outline. XPS analysis showed that surface state of the synthesized products was not modified by Cu doping and Cu was in Cu+ oxidation state. Moreover, Cu-TiO2 product showed good stabili...