Reduction Of Nitroaromatics Research Articles

Confinement of Quantum Dots in between Monolayered Graphene Nanosheets for Arousing Boosted Multifarious Photoredox Selective Organic Transformation.

Transition metal chalcogenide quantum dots (TMC QDs) represent promising light-harvesting antennas because of their fascinating physicochemical properties including quantum confinement effect and suitable energy band structures. However, TMC QDs generally suffer from poor photoactivities and photostability due to deficiency of active sites and ultrafast recombination rate of photoinduced charge carriers. Here, we demonstrate how to rationally arouse the charge transfer kinetic of TMC QDs by close monolayered graphene (GR) encapsulation via a ligand-dominated layer-by-layer (LbL) assembly utilizing oppositely charged TMC QDs and GR nanosheets as the building blocks. The assembly units were spontaneously and intimately integrated in an alternate integration mode, thereby resulting in the multilayered three-dimensional (3D) TMC QDs/GR ensembles. It was unveiled that multifarious photoactivities of TMC QDs/GR nanocomposites toward versatile photoredox organic catalysis including photocatalytic aromatic alcohols oxidation to aldehydes and nitroaromatics reduction to amino derivatives under visible light irradiation are conspicuously boosted because of spatially multilayered monolayered GR encapsulation which are superior to those of TMC QDs counterparts. The substantially enhanced photoactivities of TMC QDs/GR nanocomposites arise from reasons including improved light absorption and enhanced charge separation efficacy because of GR encapsulation together with unique stacking mode between TMC QDs and GR endowed by LbL assembly. Our work would provide a promising and efficacious route to smartly accelerate the charge transfer kinetic of TMC QDs for solar energy conversion.

Boron nitride-palladium nanostructured catalyst: efficient reduction of nitrobenzene derivatives in water

Boron nitride (BN) supported palladium (Pd) nanostructured catalyst, as an alternative support for heterogeneous reduction of nitrobenzene derivatives, was prepared by a mild reduction of a Pd precursor in water. The structural characteristics and distribution of the synthesized Pd nanoparticles (NPs) on BN support were investigated by transmission electron microscopy, scanning transmission electron microscopy, energy-dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy methods. The potential and efficiency of the BN supported Pd NPs as an active and stable nanostructured catalyst were verified in the reduction of nitroaromatics. Excellent yields of the corresponding aryl amines in water were obtained and due discussion were included about the catalytic activity of the synthesized catalyst. It was also indicated that the nanostructured catalyst can be recycled at least for six consecutive cycles in the reduction of nitrobenzene, without losing significant activity.

A Single‐Source Precursor Route toward Small‐Sized Nickel Particles Embedded into SiO2 Sheet as Magnetic Separable Catalyst

AbstractA single‐source precursor route is presented to prepare small‐sized Ni particles (∼5 nm) uniformly embedded into SiO2 sheet (Ni/SiO2). The synthetic process involved the coordination of APTES (3‐aminopropyltriethoxysilane) with Ni2+ to form Ni−Si precursor in high yield, followed by pyrolysis under NH3 atmosphere. During the heating, the Si component in the Ni−Si precursor was transformed into SiO2, which could restrict the in‐situ generated Ni from aggregation, resulting in the formation of the small‐sized Ni particles. Small size is conducive to promoting the catalytic performance, and meanwhile SiO2 protection plays a vital role in improving stability. During aromatic nitro reduction, Ni/SiO2 shows excellent catalytic performance, which can be separated conveniently by an external magnet after use. The route is indicative of designing other catalysts protected by SiO2 due to the versatile coordination ability of APTES with other metal ions (Fe, Co, Cu, etc).

Consequences of Bi3+ introduction for Pr3+ in PrAlO3

With the intent to comprehend the structure and hence the property changes in the PrAlO3 system, the substitution of Bi3+ for Pr3+ has been attempted. The samples were synthesized by solution combustion synthesis and characterized extensively. X-ray diffraction studies revealed that the rhombohedral perovskite structure was preserved up to 20 mol% substitution of bismuth, beyond which diffraction peaks of the secondary phase of α-Bi2O3emerged. The structural refinements indicated the increment of both a and c lattice dimensions with an increase in bismuth content. The samples had porous morphology, and a mean pore diameter of 22.4 nm, along with a surface area of 100 m2/g, was deduced from BET measurements for the 20 mol% bismuth-substituted sample. FTIR, Raman spectroscopic and electron microscopic analysis reinforced the perovskite structure adopted by the bismuth-substituted samples. Both Pr and Bi in Pr0.80Bi0.20AlO3 existed in the + 3 oxidation state as established from the XPS analysis. The inclusion of bismuth introduced intermediate energy levels within the bandgap, as suggested by the redshift of the absorption edge for the bismuth-substituted samples. As the optical bandgap values were in the semiconductor regime, the application of bismuth-replaced samples as a catalyst for the photodegradation of crystal violet dye solution was demonstrated. The amount of dye degraded increased with an increase in the amount of bismuth in the sample. Additionally, Pr0.80Bi0.20AlO3 catalyzed the reduction of nitroaromatics promoted possibly by the Bi3+/Bi(0) redox couple.

Reduction of nitroaromatics on cadmium sulfide: further probing the electrochemical model of semiconductor photocatalysis

The photoreduction of nitroarene compounds is a typical multielectron process that is examined here at cadmium sulfide electrodes and particle suspensions. Electrochemistry in the dark and photoluminescence indicate that reduction is mediated by surface states (sulfur vacancies) approximately located at 0.55 eV below the conduction band. In keeping with the known reduction mechanism, phenylhydroxylamine intermediates are detected at both electrodes and in suspensions. A focus of the present work was to use the nitroarenes reduction as a probe reaction to confirm the common bases of photoelectrochemistry and photocatalysis. Superimposition photocurrents (due to oxidation of hole scavengers) and dark currents identifies one potential at which the net observed current is zero and then establishes the operative photocatalytic condition. Rates of reduction on electrodes at open circuit compare very well with currents calculated from the intersection of photocurrent and dark current confirming that the photocatalytic process can be predicted from electrochemical measurements. Analysis of reaction rates in CdS suspensions suggests that a significant portion of reduction occurs on dark sites of the particles.

In Situ Synthesized Silica‐Supported Co@N‐Doped Carbon as Highly Efficient and Reusable Catalysts for Selective Reduction of Halogenated Nitroaromatics

AbstractSilica‐supported Co@N‐doped carbon (Co@CN/SiO2) catalysts were first prepared by a one‐step impregnation with a mixed solution of cobalt nitrate, glucose and urea, followed by in situ carbonization and reduction. The Co@CN/SiO2 catalysts were investigated for the selective reduction of nitro aromatics to the corresponding anilines using hydrazine hydrate. The Co@CN/SiO2‐500 carbonized at 500 °C exhibited the highest catalytic activity and excellent stability without any decay of activity after 6 cycles for the reduction of nitrobenzene. Both metallic Co atoms and Co−N species formed in the Co@CN/SiO2 catalysts were active, but the Co−N species were dominant active sites. The high activities of the Co@CN/SiO2 catalysts were attributed to the synergistic effect between the Co and N atoms, promoting heterolytic cleavage of hydrazine to form H+/H− pairs. Representative examples demonstrated that the Co@CN/SiO2‐500 could completely transform various halogen‐substituted nitro aromatics to the corresponding halogenated anilines with high TOFs and selectivity of >99.5 %.

Hydrogen Atom Transfer Reaction Free Energy as a Predictor of Abiotic Nitroaromatic Reduction Rate Constants: A Comprehensive Analysis.

A linear free energy model is presented that predicts the second-order rate constant for the abiotic reduction of nitroaromatic compounds (NACs). Previously presented models use the one-electron reduction potential of the NAC reaction . If is not available, it has been proposed that be computed directly or estimated from the gas-phase electron affinity (EA). The model proposed uses the Gibbs free energy of the hydrogen atom transfer (HAT) reaction as the parameter in the linear free energy model. Both models employ quantum chemical computations for the required thermodynamic energies. The available and proposed models are compared using experimentally determined second-order rate constants from 5 investigations from the literature in which a variety of NACs were exposed to a variety of reductants. A comprehensive analysis utilizing all the NACs and reductants demonstrate that the HAT energy model and the experimental one-electron reduction potential model have similar root mean square errors and residual error probability distributions. In contrast, the model using the computed EA has a more variable residual error distribution with a significant number of outliers. The results suggest that a linear free energy model utilizing computed HAT reaction free energy produces a more reliable prediction of the NAC abiotic reduction second-order rate constant than previously available methods. The advantages of the proposed HAT energy model and its mechanistic implications are discussed as well. Environ Toxicol Chem 2020;39:1678-1684. © 2020 SETAC.

Sustainable and recyclable palladium nanoparticles–catalyzed reduction of nitroaromatics in water/glycerol at room temperature

Palladium nanoparticles with unique catalytic activity and high stability are synthesized. These nanoparticles exhibit excellent catalytic reduction activity for nitroaromatics in green solvents in the presence of H2 at ambient pressure and temperature. The prominent advantages of this nanotechnology include low consumption of catalyst, excellent chemoselectivity, high reusability of the catalyst, and environmentally green solvents.

Employable metal (Ag & Pd)@MIL-125-NH2@cellulose acetate film for visible-light driven photocatalysis for reduction of nitro-aromatics

The effective and reusable photocatalyst film based on metal @metal organic framework@cellulose acetate [metal (Ag & Pd)@MIL-125-NH2@CA] was systematically studied. Nano-silver was grown over the crystalline disc of MIL-125-NH2 within CA film, while, self-assembly of crystalline trees like the structure of Pd)@MIL-125-NH2 was observed inside CA matrix. The calculated band gap was diminished from 2.53 eV to 2.38–1.99 eV after doping of metal (Ag & Pd) within MIL-125-NH2@CA film. Compared to MIL-125-NH2@CA; metal (Ag & Pd)@MIL-125-NH2@CA film showed a considerably higher photocatalytic reduction of nitro-aromatics in visible light. After 60 min, 80.6–93.5 % of 2-nitrophenol was photoreduced when metal (Ag & Pd)@MIL-125-NH2@CA film was used. After 5 recycles, the photoreduction percentage of 2-nitrophenol was lowered to 54.4–62.0. The produced metal@MIL-125-NH2@CA films showed an effective photocatalytic reduction of nitro-aromatics in the visible light, reflecting their promising performance in preparation of intermediates useful in many industrial products.

Graphene-TiO2-polyaniline nanocomposite: A new green and efficient catalyst as a alternative for noble metal and NaBH4 induced the reduction of 4-nitro phenol

Graphene-TiO2-polyaniline (GP-TiO2-PANI) nanocomposites have been prepared via sol gel method. A reduction of nitro aromatic organic compounds using synthesized GP-TiO2-PANI nanocomposite photocatalyst under visible light in aqueous phase was reported. Photo irradiation (λ > 420 nm) of GP-TiO2-PANI photocatalysts reduces nitro aromatics in absence of NaBH4 with high yields. Graphene acts as electron carrier and adsorbent which is essential for visible light motivated photocatalytic reduction of nitro aromatics over GP-TiO2-PANI disclosed by control experiments. The current work can broaden its applications of photocatalyst for various organic transformations which are economically viable. The reduction of nitro group of nitro aromatics by GP-TiO2-PANI is a green and selective reaction.

Pd modified prussian blue frameworks: Multiple electron transfer pathways for improving catalytic activity toward hydrogenation of nitroaromatics

Prussian blue analogs (PBAs) exhibit potential as low-cost and eco-friendly nanocatalysts that can be fabricated with ease. However, the PBA framework structure suffers from poor electronic conductivity, which limits the catalytic efficiency for this class of materials. Noble metals represent an alternative class of materials that display inherent catalytic activity but suffer from aggregation, ultimately reducing the amount of accessible catalytic sites. Herein, we demonstrate a combinatory approach that circumvents the known disadvantages with these classes of catalytic materials in which PBA-supported nanocatalysts were synthesized. These composite materials exhibit excellent catalytic activity for the reduction of nitroaromatics to aminoaromatics while displaying long-term cycling stability, which is attributed to the availability of multiple electron transfer pathways. Overall, this work opens the study on the assembly of PBA-supported heterogeneous nanocatalysts and potentially paves the way toward future applications.

Modification of poly (ethylene glycol) with a multifunctional silane ligand, stabilization of Ag nanoparticles and its catalytic activity toward nitro-aromatics reduction

The modification of poly (ethylene glycol) (PEG) with (3, 3′-bis-(3-triethoxysilylpropyl)-2, 2′-dithioxo [5, 5′] bithiazolidinylidene-4, 4′-dione) ligand was performed in the presence of Et3N in toluene (MPEG). With the addition of AgNO3, MPEG with obtained spherical nanoparticles on the surface could interact with Ag + under ultrasonic. Finally, the MPEG-Ag + complex were reduced with hydrazine under reflux to obtain MPEG-Ag nanocomposite. The structure of MPEG-Ag nanocomposite was characterized by different techniques. The nanocomposite was used as an efficient catalyst for the reduction of nitro-aromatic compounds using NaBH4 in the water at room temperature. The catalyst was recovered, and applied for subsequent reactions without any substantial loss of efficiency for five runs.

One-pot synthesis of an anionic cyclodextrin-stabilized bifunctional gold nanoparticles for visual chiral sensing and catalytic reduction

A facile one-pot synthetic method for preparing gold nanoparticles by employing sugammadex (SUG), a carboxylic acid functionalized γ-cyclodextrin derivative, as reducing-cum-stabilizing agent herein was reported for the first time. The SUG protected gold nanoparticles (SUG-AuNPs) can work as a colorimetric sensor for visual chiral recognition of α-amino acids enantiomers, especially for lysine (Lys) and asparagine (Asn) enantiomers. The chiral recognition assay was successfully applied to determining the enantiometric excess of L-Lys and L-Asn ranging from −100 % to 100 % respectively. Moreover, the prepared SUG-AuNPs was found to exhibit efficient catalytic activity towards the reduction of toxic 4-nitrophenol by NaBH4 and the efficiency of the system was further demonstrated through the reduction of other typical nitroaromatics under mild condition. The as-synthesized SUG-AuNPs shows good performance for both chiral sensing and reduction activity and thus may facilitate the practical application in the area of both chiral discrimination and catalysis.

Covalent organic frameworks bearing pillar[6]arene-reduced Au nanoparticles for the catalytic reduction of nitroaromatics

While tremendous advancements in 2D materials anchoring Au nanoparticles have been made, it is an urgent challenge to explore a green and facile approach for obtaining small-size Au nanoparticles. The rise of 2D covalent organic framework (COF) presents more-promising candidates for constructing excellent sites for loading metal nanoparticles. In this study, a novel 2D heterogeneous hybrid nanomaterial (P6-Au-COF) based on COF and pillar[6]arene (P6) reduced Au nanoparticles (P6-Au) is prepared by a simple and green procedure. The Au nanoparticles with an average small diameter of 2–3 nm are homogeneously dispersed on the surface of the COF. The P6-Au-COF hybrid material shows highly catalytic performance for the reduction of nitrophenol isomers when compared with commercial Pd/C catalyst and other reported materials. The P6-Au-COF hybrid material exhibits durable recyclablility and stability during the catalytic reaction. Considering the outstanding merits of the heterogeneous 2D catalyst of P6-Au-COF as well as the simple and green preparation, this research might not only present enormous opportunities for stabilized, high-performance and sustainable catalysts, but be applied in other frontier study of sustainable functionalized nanocomposites and advanced materials.

A “competitive occupancy” strategy toward Co–N4 single-atom catalysts embedded in 2D TiN/rGO sheets for highly efficient and stable aromatic nitroreduction

Single-atom M–N-based catalysts have been synthesized based on the “competitive occupancy” of Ti species and Co2+ (Ni2+etc.) on GO, and can be used as a highly active and stable hydrogenation catalyst.

Catalytic Efficiency of Biosynthesized Silver Nanoparticles in Synthesis of Chromones and Reduction of Nitro Aromatics

AbstractSilver nanoparticles (AgNps) were biosynthesized and characterized by transmission electron microscopy (TEM), X‐ray diffraction (XRD), UV‐visible absorption (UV‐vis) and photoluminescence spectroscopy. The average size of the nanoparticles was found to be around 20 nm from TEM and surface plasmon band appeared at 420 nm. The nanoparticles are highly crystalline and possess face‐centered cubic (fcc) structures. These nanoparticles were used for the synthesis of chromones by a simple, mild and efficient method using microwave irradiation. Good yield upto 82% has been achieved for the synthesis of chromones. Further, the AgNps were used in reduction of aromatic nitro compounds to corresponding anilines with high yield. All reactions were studied under benign reaction conditions without using any hazardous organic solvents, expensive ligand or activator.

Ionic Liquid-Modulated Synthesis of Porous Worm-Like Gold with Strong SERS Response and Superior Catalytic Activities.

Porous gold with well-defined shape and size have aroused extensive research enthusiasm due to their prominent properties in various applications. However, it is still a great challenge to explore a simple, green, and low-cost route to fabricate porous gold with a “clean” surface. In this work, porous worm-like Au has been easily synthesized in a one-step procedure from aqueous solution at room temperature under the action of ionic liquid tetrapropylammonium glycine ([N3333][Gly]). It is shown that the as-prepared porous worm-like Au has the length from 0.3 to 0.6 μm and the width of approximately 100–150 nm, and it is composed of lots of small nanoparticles about 6–12 nm in diameter. With rhodamine 6G (R6G) as a probe molecule, porous worm-like Au displays remarkable surface enhanced Raman scattering (SERS) sensitivity (detection limit is lower than 10−13 M), and extremely high reproducibility (average relative standard deviations is less than 2%). At the same time, owing to significantly high specific surface area, various pore sizes and plenty of crystal defects, porous worm-like Au also exhibits excellent catalytic performance in the reduction of nitroaromatics, such as p-nitrophenol and p-nitroaniline, which can be completely converted within only 100 s and 150 s, respectively. It is expected that the as-prepared porous worm-like Au with porous and self-supported structures will also present the encouraging advances in electrocatalysis, sensing, and many others.

Template-Oriented Synthesis of Fe–N-Codoped Graphene Nanoshells Derived from Petroleum Pitch for Efficient Nitroaromatics Reduction

In this study, we demonstrate noble metal-free Fe–N-codoped graphene nanoshells (Fe–N/GNS) derived from petroleum pitch as highly efficient and cost-effective catalysts for nitroaromatics reduction...

Synthesis of magnetic silver cyclodextrin nanocomposite as catalyst for reduction of nitro aromatics and organic dyes

Nanocomposites decorated with metallic nanoparticles in their matrix are important class of heterogeneous catalyst with high catalytic activity. Functionalized polymers are low cost materials which offer excellent supports for catalysts to render stability to metallic nanoparticles. Herein we report synthesis of Silver nanocomposite using β-cyclodextrin (b-CD) maleic anhydride crosslinked polymer anchored on the surface of magnetic nanoparticles. The nanocomposite was characterized using sophisticated analytical techniques and its role as a catalyst for reduction of nitroaromatics and organic dyes was investigated. This catalytic system exhibited comparatively lower Ea value of 18 kJ mol−1 and followed pseudo first order kinetics. Simultaneous reduction of 4-Nitrophenol and Methylene Blue could be achieved in a time interval of 7 minutes. Being magnetically separable, the catalyst exhibited high recycling efficiency (up to 5 cycles) and ease of operation under mild conditions.

A model for kinetic isotope fractionation during redox reactions

Stable isotopes are used to track redox reactions in both ancient and modern geochemical systems. However, because the magnitude and even the direction of fractionation depend on the reaction pathway, extracting information about redox conditions from isotopic signatures is difficult. Quantitative understanding of the fundamental thermodynamic controls on redox-driven fractionation may improve the reliability of fractionation models in natural systems. Here we develop a mechanistic framework based on Marcus electron transfer theory to model redox-driven kinetic isotope fractionation as a function of the corresponding equilibrium fractionation and thermodynamic parameters. The framework predicts that for related reactions, (1) kinetic fractionation during electron transfer should be proportional to and in the same direction as equilibrium fractionation and (2) the magnitude of kinetic fractionation should decrease linearly as the standard free energy of the reaction decreases and the reaction becomes more thermodynamically favorable. Furthermore, kinetic fractionation should be log-linearly correlated with the rate constant of electron transfer, such that a faster redox reaction induces less kinetic fractionation. To illustrate the application of the model to stable isotope systems, we discuss examples of kinetic isotope fractionation during reduction of chromium (VI) and nitroaromatics by aqueous and solid-phase reductants respectively. For both these systems, altering the standard reduction potential of the reductant to vary the standard free energy of the redox reaction produces large changes in the magnitude of kinetic fractionation, which can be quantitatively predicted with our model. The proposed framework thus may be valuable for modeling redox-driven kinetic isotope fractionation in a broad range of geochemically relevant systems for both traditional light stable isotopes (e.g., nitrogen) and nontraditional metal isotopes (e.g., chromium).