Reduction Of Nitroaromatics Research Articles

Synthesis of phytogenically deposed Ag nanospheres on ZnO nanosheets for photocatalytic and catalytic applications

Current study presents the phytogenic deposition of metallic Ag nanospheres on ZnO nanosheets to produce Ag/ZnO nanostructures using Jacobaea Maritima (Silver Ragwort) plant extract and the prepared materials were tested for the photo-mineralization of methylene blue (MB) dye and catalytic reduction of nitroaromatics i.e. 4-nitroaniline (4-NA) and 4-nitrophenol (4-NP) in the presence of NaBH4 solution. The mean grain size and crystallinity of ZnO particles in Ag/ZnO nanostructures were found to be increased while the particle strain and dislocation density decreased with the elevation of Ag level in ZnO, and band gap energy value was reduced that has improved the photodegradation efficiency for MB dye from 45% to 98.60%, however, an excess amount of Ag has suppressed the photo-activity of Ag/ZnO nanostructures due to increase of band gap value and coverage of ZnO nanocrystals by Ag clusters. The catalytic reduction process indicated that the 4-NA and 4-NP were almost decolorized within 8 and 10 min, respectively. The degradation reaction rate of MB dye was enhanced by ∼7 times for Ag/ZnO nanostructures in comparison to pure ZnO nanosheets. The trapping experiments established that the •O2− and •OH radicals were the key active entities engaged in the deprivation of MB dye.

Pd/NHC catalyzed reduction and coupling of nitroaromatics for the synthesis of diarylamines.

Herein, we report a one-pot approach to diarylamines through the reductive homocoupling of nitroaromatics, employing triethylsilane as the reducing agent and Pd/NHC as the catalyst. This method enables nitroaromatics to serve both as electrophilic reagents and as precursors of nucleophilic reagents, allowing for the direct preparation of diarylamines without the need to isolate aromatic primary amines.

Flower-like MoS2 microspheres highly dispersed on CoFe2O4/MIL-101(Fe) metal organic framework: a recoverable magnetic catalyst for the reduction of toxic nitroaromatics in water

In this study, we report on the synthesis and characterization of novel magnetic MoS2/CoFe2O4/MIL101-(Fe) nanocomposite catalysts designed for the efficient reduction of toxic nitroaromatic compounds, such as nitrophenols and nitroanilines,...

Semiconductor-cluster-loaded ionic covalent organic nanosheets with enhanced photocatalytic reduction reactivity of nitroarenes

A composite catalyst, developed by electrostatic self-assembly of anionic semiconductor clusters onto 2D cationic CONs, boosts photocatalytic selective nitroarene reduction through a strong internal electric field and the II-scheme mechanism.

Coupling Fe-Co atomic pair to promote the selective reduction of nitroaromatics under mild conditions

Selectively reducing nitroaromatics into aromatic amines will not only remove nitroaromatic pollutants in waste effluents to reduce environmental risks, but also yield important feedstocks for chemical industrial manufactures. In this study, a FeCo-co-embedded N-doped Carbon (FeCo-N-C) catalyst with Fe-Co atomic pair has been identified with favorable activity, superior selectivity, excellent reusability, as well as outstanding performance in the treatment of real water. The combined results from theoretical study and experimental tests indicate that the improved catalytic performance of FeCo-N-C is owing to the narrowed band gap and electron delocalization caused by the Fe-Co atomic pair which can improve electron transport in its catalytic reaction. The results of isotope experiments and H* quenching experiments confirm that H2O is the source of hydrogen in catalytic reduction of PNP. FeCo-N-C is identified as a superior catalyst to replace multitudinous currently used noble-metal catalysts for the selective catalytic reduction of nitroaromatics in wastewater treatment.

Nitro reduction involving PEG200(4)@C@MoSe2@MWCNT driven by UV light

A mild and green nitro-reduction method was developed using PEG200(4)@C@MoSe2@MWCNT driven by UV light. The photocatalytic performance of MoSe2 was enhanced by MWCNTs and polyethylene glycol, and the catalyst was characterized by SEM, TEM, XRD, and TGA. Eleven reduction applications had been accomplished, in which the conversion of 3-nitrobenzonitrile reached up to >99% and the selectivity of 3-aminobenzonitrile reached up to 74%. Although the selectivity of the target products was low, it provided a new approach for the photocatalytic reduction of nitroaromatics and also brought new insights into the photocatalytic application of MoSe2.

Construction of metal-organic frameworks with unsaturated Cu sites for efficient and fast reduction of nitroaromatics: A combined experimental and theoretical study

Metal-organic frameworks (MOFs) functionalized with open metal sites (OMSs) have received widespread attention in various applications due to their fascinating electronic properties and unique interactions with guest molecules. However, rational tailoring of the coordination environment of metal nodes during the synthesis of MOFs remains a great challenge due to their tendency of saturated coordination with linkers. Herein, we reported the construction of three new MOFs featuring unsaturated Cu(II) sites, namely [Cu(HCOO)(pzta)]n (HL-1), {[Cu(PTA)0.5(pzta)(H2O)]·2H2O}n (HL-2) and [Cu(NA)0.5(pzta)]n (HL-3) (Hpzta = 3-pyrazinyl-1,2,4-triazole; PTA = terephthalic acid; NA = 1,4-naphthalene dicarboxylic acid), based on the mixed-linker strategy via specific selection of versatile Hpzta ligand and carboxylate ligands. Remarkably, the obtained MOFs exhibited excellent activity and good recyclability for the catalytic reduction of nitroaromatics under mild conditions (25 °C and 1 atm). In particular, the complete conversion of 4-nitrophenol (4-NP) took only 30 s on HL-2, reaching a record-high TOF value compared with previously reported metal catalysts. The combined experimental and theoretical studies on HL-2 revealed that the open Cu site with positive-charged nature could improve the adsorption and subsequent electron transport between the substrates, and was responsible for the outstanding performance. This work shined lights on the further enhancement of performance for MOFs through rational OMSs construction.

Gemini surfactant‐stabilized Pd nanoparticles: Synthesis, characterization, and catalytic application in the reduction and reductive acetylation in the water solvent

A series of Gemini surfactants (GSs) were prepared by reacting alkyl bromides with N,N,N′,N′‐tetramethyl ethylenediamine. Various alkyl bromides used in for the preparation of GSs are 1,3‐dibromo ethane, 1,3‐dibromoethane, 1‐Bromohexane, 1‐Bromooctane, 1‐Bromooctadecane and 1‐Bromooctadodecane. Different solvents and temperatures were investigated for the formation of gels of prepared GSs. Among all, 1‐Bromooctane, 1‐Bromooctadecane‐derived GSs formed organogels. Thus, synthesized long‐chain organogels have been used to stabilize Pd NPs. The Pd NPs formation initially confirmed through Ultraviolet‐visible, Scanning Electron Microscopy, and Atomic Force Micrograph studies. Later Fourier Tansform Infra Red, Thermo Gravimetric Analysis, and Zeta potential studies were also carried out to understand their properties extensively. The Pd NPs stabilized by GSs have been identified as a potential catalyst in the reductive N‐acetylation of nitroaromatics at room temperature. The N‐acetylated products were obtained in good yields in an aqueous medium. In addition, the potentiality of our catalyst has been also evaluated in the reduction of nitroaromatics in an aqueous medium, which is a green protocol. Further, the semi‐empirical geometry optimizations of active GS gel confirmed the dihedral angle of 59° in between the two octyl moieties calculated from computational studies. The rheological properties such as amplitude sweeping, viscosity shear profile of the gel have also been studied.

Surfactant-free synthesis of Ag@TiO2 and CuO@TiO2 photocatalyst: a comparative study of their photocatalytic activity for reduction of nitroaromatics in water

The reduction of harmful nitroaromatics to useful amino-aromatics have significant opportunities in synthetic chemistry. Here a visible-light-driven eco-friendly method for the selective reduction of aromatic nitro compounds to their corresponding amines in aqueous solution by using Ag@TiO2 and CuO@TiO2 is described. It was observed that both Ag@TiO2 and CuO@TiO2 are photo-catalytically more efficient compared to bare TiO2 and CuO@TiO2 has higher activity over Ag@TiO2 for the said conversion. The structural and morphological characterization of the as-synthesized catalysts has been done with SEM-EDX, TEM, powder XRD, ICP-AES, XPS, Photoluminescence, and UV-vis spectroscopic techniques. The nanocomposites Ag@TiO2 and CuO@TiO2 exhibit pure anatase phase with average crystallite size of 5.89 nm and 5.87 nm respectively as calculated from the Debye-Scherrer equation depending on the (101) plane. UV-visible results inferred enhanced optical properties of both the synthesized catalysts and revealed a reduced band gap (3.07 eV for Ag@ TiO2 and 2.5 eV for CuO@ TiO2) as compared to neat TiO2 (3.36 eV). Various nitro compounds were tolerated under 150 W LED as a light source (13.9 lumens for an area of 0.2 ft2) in an aqueous medium at room temperature (30 °C) using NaBH4 as a reducing agent to access corresponding amines in satisfying yields (78%–99%). The catalyst can be separated from the reaction mixture by simple centrifugal precipitation and reused for up to six consecutive cycles without apparent loss of its catalytic activity. The products were characterized by 1H-NMR spectroscopic techniques and compared with authentic samples.

Amino-functionalized CuFe2O4 supported Pd nanoparticles as magnetically catalyst for H2 production from methanolysis of ammonia borane and hydrogenation of nitro aromatics

Small and equally distributed Pd nanoparticles (NPs) are tightly anchored on the surface of magnetic and amino (–NH2) functionalized CuFe2O4 to obtain magnetically separable CuFe2O4–NH2@Pd catalyst with core-shell structure. Compared to the inherent catalytic activity of CuFe2O4, the catalytic performance of CuFe2O4–NH2@Pd for dehydrogenation of ammonia-borane (AB) and concurrent hydrogenation of different nitro aromatics by H2 generated from AB methanolysis can be boosted more effectively than that of CuFe2O4@Pd, which is the control catalyst and is prepared by loading Pd NPs on pristine CuFe2O4. As electron donating groups, the –NH2 groups covalently bonded to the surface of CuFe2O4 play vital roles in stabilizing Pd NPs, providing strong metal-support interaction and rendering enhanced catalytic activity. However, we find that the catalytic performance of CuFe2O4, CuFe2O4@Pd and CuFe2O4–NH2@Pd for the hydrogenation reduction of mercapto-substituted nitro aromatics (p-nitrothiophenol, p-NTP) is far inferior to that for the reduction of nitroarenes that do not contain a sulfur substituent. Therefore, it is quite essential to research and develop the new-type catalysts with more excellent catalytic performance.

Solution Combustion Synthesis of NiS‐NiS2 Nanoparticles for Catalytic Reduction of Nitro Aromatics

AbstractExploring an efficient and economic reductant for nitro aromatics is of great significance for environmental remediation. In this work, nickel sulfide catalysts have been prepared by simple solution combustion method from a mixture of nickel(II) nitrate hexahydrate as oxidant (O) and thiourea as fuel (F) in different ratios. The phase and crystallinity, composition and morphology of synthesized samples were obtained by X‐ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy and Fourier transform infrared (FTIR) techniques. The catalytic efficiency of as synthesized nickel sulfide nanoparticles towards reduction of 4‐nitrophenol (4‐NP) as a model compound using sodium borohydride as the reducing agent was explored. The catalyst prepared with 1 : 3 O/F ratio that composed of NiS and NiS2 phases exhibited highest efficiency towards catalytic reduction of 4‐NP and the rate constant was found to be 0.429 min−1. Further, the catalyst could effectively reduce the nitro group in 2‐nitroaniline, 4‐nitroaniline and picric acid also. Reduced products of 2‐nitroaniline and 4‐nitrophenol were employed for the synthesis of benzimidazole and paracetamol successfully.

Cu-Based Catalysts Supported on H3PO4-Activated Coffee Biochar for Selective Reduction of Nitroaromatics.

Selective reduction of nitroaromatics to the corresponding aromatic amines is extremely an attractive chemical process for both fundamental research and potential commercial applications. Herewith, we report that a highly dispersed Cu catalyst supported on H3PO4-activated coffee biochar and the resulting Cu/PBCR-600 catalyst show complete conversion of the nitroaromatics and >97.0% selectivity for the corresponding aromatic amines. The TOF of catalyzing the reduction of nitroaromatics (1.55-460.74 min-1) is approximately 2 to 15 times higher than those of previously reported non-noble and even noble metal catalysts. Additionally, Cu/PBCR-600 also shows high stability in catalytic recycles. Furthermore, it exhibits long-term catalytic stability (660 min) for practical application in a continuous-flow reactor. The characterizations and activity tests reveal that Cu0 existing in Cu/PBCR-600 acts as an active site in nitroaromatics reduction. Also, the further characterization by FTIR and UV-vis demonstrates that N, P co-doped coffee biochar could selectively adsorb and activate the nitro group of nitroaromatics.

Reduction of Nitroaromatics by Gold Nanoparticles on Porous Silicon Fabricated Using Metal-Assisted Chemical Etching.

In this study, we investigated the use of porous silicon (PSi) fabricated using metal-assisted chemical etching (MACE) as a substrate for the deposition of Au nanoparticles (NPs) for the reduction of nitroaromatic compounds. PSi provides a high surface area for the deposition of Au NPs, and MACE allows for the fabrication of a well-defined porous structure in a single step. We used the reduction of p-nitroaniline as a model reaction to evaluate the catalytic activity of Au NPs on PSi. The results indicate that the Au NPs on the PSi exhibited excellent catalytic activity, which was affected by the etching time. Overall, our results highlighted the potential of PSi fabricated using MACE as a substrate for the deposition of metal NPs for catalytic applications.

Realizing the Continuous Chemoenzymatic Synthesis of Anilines Using an Immobilized Nitroreductase.

The use of biocatalysis for classically synthetic transformations has seen an increase in recent years, driven by the sustainability credentials bio-based approaches can offer the chemical industry. Despite this, the biocatalytic reduction of aromatic nitro compounds using nitroreductase biocatalysts has not received significant attention in the context of synthetic chemistry. Herein, a nitroreductase (NR-55) is demonstrated to complete aromatic nitro reduction in a continuous packed-bed reactor for the first time. Immobilization on an amino-functionalized resin with a glucose dehydrogenase (GDH-101) permits extended reuse of the immobilized system, all operating at room temperature and pressure in aqueous buffer. By transferring into flow, a continuous extraction module is incorporated, allowing the reaction and workup to be continuously undertaken in a single operation. This is extended to showcase a closed-loop aqueous phase, permitting reuse of the contained cofactors, with a productivity of >10 gproduct gNR-55-1 and milligram isolated yields >50% for the product anilines. This facile method removes the need for high-pressure hydrogen gas and precious-metal catalysts and proceeds with high chemoselectivity in the presence of hydrogenation-labile halides. Application of this continuous biocatalytic methodology to panels of aryl nitro compounds could offer a sustainable approach to its energy and resource-intensive precious-metal-catalyzed counterpart.

Magnetic gold catalysts obtained by sequential preparation for highly efficient catalytic reduction of nitroaromatics

Noble metal catalysts have received considerable interests owing to their glamorous properties and applications in heterogeneous catalysis. In this work, the magnetic Au nanoparticles catalysts were successful fabricated via sequential preparation strategy at room temperature. 4-nitrophenol was chosen as the model molecule to evaluate the catalytic reduction activity for the preparation of amines from their corresponding nitroaromatics. The results showed that the catalytic reaction related with 4-nitrophenol could be achieved in 3 min, and the catalyst could be easily reused at least 15 cycles without significant reduction in activity when the as-prepared Fe3O4@CB6@Au0.4% nanoparticles acted as the catalyst. It revealed that the as-prepared catalyst exhibited outstanding catalytic performance and cycling stability. The SEM and TEM images demonstrated that the Au species presented in composite system in the form of highly dispersed Au0 nanoparticles, playing a crucial role in the catalytic process. Therefore, the Au nanoparticles combined with Fe3O4@CB6 prepared by the sequential preparation strategy had excellent catalytic reduction properties for nitroaromatics, and the method could open a new way for the design of other highly dispersed nanometallic materials.

Ag2O-adorned ZnO nanostructures: cooperative and sustainable nanomaterial system for effective reduction and mineralization of hazardous water pollutants

Organic water pollutants like nitroaromatics and synthetic dyes are causing serious threats to water. Ever-growing urban and industrial activities along with population explosion are rapidly contributing severe level of water contamination. Semiconducting nanomaterial-based photocatalysis has been proven to be an effective process for degradation of organic water pollutants. In the current study, visible light active Ag2O-adorned ZnO nanostructures were fabricated by a simple two-step hydrothermal method and the prepared nanostructures were utilized for the photocatalytic mineralization of rhodamine B (RhB) dye with visible light radiation. The catalytic potential of as-synthesized nanostructures was also investigated for the reduction of nitroaromatics (4-NP and 4-NA) and RhB dye in the presence of NaBH4. The Ag2O-adorned ZnO nanostructures prepared with 5% of silver nitrate denoted as ZnO/Ag2O (5%) demonstrated stupendous photomineralization activity against RhB dye as almost 100% degradation of RhB dye was achieved within 100min of reaction time at pH = 6. The kinetic study revealed that the degradation reaction followed the pseudo-first-order kinetics and the kinetic rate constant (k) of photodecolorization reaction for optimal catalyst was calculated to be 61.4 × 10-3min-1. The nanostructures revealed excellent recyclability and photostability as 95% activity of the catalyst was preserved even after the fifth cyclic run. The catalytic reduction of the 4-NP, 4-NA, and RhB dye was completed in 21, 12, and 40min, respectively, in the presence of ZnO/Ag2O (5%) and NaBH4 solution. The kinetic rate constant values for the reduction reactions were determined to be 229.6 × 10-3, 454.2 × 10-3, and 105.5 × 10-3min-1 for 4-NP, 4-NA, and RhB dye, respectively. Thus, the obtained results suggest that the components of the prepared nanosystem help in mutually strengthening the catalytic and photocatalytic abilities of each other, indicating the development of a cooperative and sustainable nanomaterial system in the current study.

A Phosphate‐based Organic Polymer Nanocontainer Efficiently Hosts Ag/Ru Nanoparticles for Heterogeneous Catalytic Reduction of Nitroaromatics and Oxidation of Benzyl Alcohols

AbstractOrganic polymer networks (OPNs) are an interesting class of materials showing immense potential for supporting various metal nanoparticles for their heterogeneous catalytic applications. Herein, we delineate a protocol for generating metal‐based nanoparticles including silver nanoparticles (AgNPs) and ruthenium nanoparticles (RuNPs) within a phosphate‐based OPN (OPN‐4) prepared by the copolymerization of phosphoryl chloride and 1,3,5‐(4‐hydroxyphenyl)benzene in order to generate the heterogeneous catalysts, M@OPN‐4 (M=Ag/Ru). OPN‐4 emerged as an excellent host for the loading of these nanoparticles. These nanoparticles loaded OPN‐4 were characterized by several techniques including scanning and transmission electron microscopy (SEM, TEM), thermogravimetric analysis (TGA), X‐ray photoelectron spectroscopy (XPS), powder X‐ray diffraction (PXRD), and FTIR studies. M@OPN‐4 acted as the heterogeneous catalysts towards various organic reactions including reduction of nitroaromatics (Ag@OPN‐4) and oxidation of benzyl alcohols (Ru@OPN‐4) furnishing desired products from moderate to excellent yield with high selectivity over a broad range of substrates. They also exhibited easy recovery via filtration and reuse for up to five cycles without losing their catalytic activity significantly. Above all, the as synthesized catalysts were found to possess air and moisture endurance, high cost‐effectiveness and robust behavior. Thus, the OPN‐4 nanocontainer could establish itself as a versatile host towards different metal nanoparticles attributed to electron donating phosphate moiety.

Designing versatile nanocatalysts based on PdNPs decorated on metal oxides for selective hydrogenolysis of biomass derived γ-valerolactone and reduction of nitro aromatics

Designing versatile nanocatalysts based on PdNPs decorated on metal oxides for selective hydrogenolysis of biomass derived γ-valerolactone and reduction of nitro aromatics

One-step Redox-induced Confined Pt Nanoparticles for Reduction of Nitroaromatics

The noble metal nanoparticles sandwiched between the stable inorganic core and the thin polymer shell could not only enhance their stability, but also cut short the diffusion route of the outside reactants through polymer shell toward encapsulated noble metal nanoparticles, which has drawn great attention. However, weak compatibility among inorganic core, polymer shell, and noble metal nanoparticles makes the preparation of noble metal-confined hybrid catalysts complicated, which limits the popular application of these noble metal-based catalysts. A facile method has developed to fabricate core-shell Fe2O3@PEDOT/Pt nanocatalyst with tiny Pt nanoparticles highly dispersed in the polymer shell by one-step simultaneous redox deposition strategy. The confinement effect and strong coordination ability of the thin sulfur-enriched polymer shell prevents the migration and agglomeration of Pt nanoparticles during the catalytic process and improves the stability of the catalyst. The catalyst shows outstanding catalytic activity and relatively good stability towards the reduction of nitroaromatic compounds. The simple method solves the problem of poor compatibility between the inorganic core, the polymer shell, and the noble metal nanoparticles confined in the shell material to some extent. Furthermore, our strategy could be extended to one-step preparation of Fe2O3@Polymer@Pt hybrid materials with core-shell structure.

Sustainable magnetically recoverable Iridium-coated Fe3O4 nanoparticles for enhanced catalytic reduction of organic pollutants in water.

The reduction of nitroarenes to aromatic amines is one of the potential pathways to remediate the hazardous impact of toxic nitroarenes on the aquatic environment. Aromatic amines obtained from the reduction of nitroaromatics are not only less toxic than nitroaromatics but also act as important intermediates in the synthesis of dyes, drugs, pigments, herbicides, and polymers. There is a huge demand for the development of cost-effective, and eco-friendly catalysts for the efficient reduction of nitroarenes. In the present study, Fe3O4@trp@Ir nanoparticles were explored as efficient catalysts for the reduction of nitroarenes. Fe3O4@trp@Ir magnetic nanoparticles were fabricated by surface coating of Fe3O4 with tryptophan and iridium by co-precipitation method. As-prepared Fe3O4@trp@Ir nanoparticles are environmentally benign efficient catalysts for reducing organic pollutants such as 4-nitrophenol (4-NP), 4-nitroaniline (4-NA), and 1-bromo-4-nitrobenzene (1-B-4-NB). The key parameters that affect the catalytic activity like temperature, catalyst loading, and the concentration of reducing agent NaBH4 were optimized. The obtained results proved that Fe3O4@trp@Ir is an efficient catalyst for reducing nitroaromatics at ambient temperature with a minimal catalyst loading of 0.0025%. The complete conversion of 4-nitrophenol to 4-aminophenol took only 20s with a minimal catalyst loading of 0.0025% and a rate constant of 0.0522s-1. The high catalytic activity factor (1.040s-1mg-1) and high turnover frequency (9min-1) obtained for Fe3O4@trp@Ir nanocatalyst highlight the possible synergistic effect of the two metals (Fe and Ir). The visible-light photocatalytic degradation of 4-NP was also investigated in the presence of Fe3O4@trp@Ir. The photocatalytic degradation of 4-NP by Fe3O4@trp@Ir is completed in 20min with 95.15% efficiency, and the rate of photodegradation of 4-NP (0.1507min-1) is about twice the degradation rate of 4-NP in the dark (0.0755min-1). The catalyst was recycled and reused for five cycles without significant reduction in the conversion efficiency of the catalyst.