Reduction Of Nitroaromatics Research Articles

Rational design, synthesis, and applications of carbon-assisted dispersive Ni-based composites

Herein, we review recent developments in the rational design and engineering of various carbon-assisted dispersive nickel-based composites, and boosted properties for protein adsorption and nitroaromatics reduction.

Phosphate based new organic polymer networks for efficient dye sorption and catalyst loading for chemo-selective reactivity.

Phosphate based organic polymer networks (OPNs) have been synthesized for the first time for dye sorption and heterogeneous catalysis. The OPNs were sythesized by the polycondensation of POCl3 with di- and tri-hydroxy organic linkers e.g., quinol, 4,4'-biphenol, phloroglucinol and 1,3,5-(4-hydroxyphenyl)benzene. These show remarkably selective adsorption of cationic dyes methylene blue and propidium iodide via the electrostatic interaction of the polymers with the dyes. These OPNs also allow the in situ synthesis and stabilization of gold nanoparticles within the polymer networks which demonstrate effective heterogeneous, catalytic reduction of the aromatic nitro to amino group.

Unleashing non-conjugated polymers as charge relay mediators.

The core factors affecting the efficiency of photocatalysis are predominantly centered on controllable modulation of anisotropic spatial charge separation/transfer and regulating vectorial charge transport pathways in photoredox catalysis, yet it still meets with limited success. Herein, we first conceptually demonstrate the rational design of unidirectional cascade charge transfer channels over transition metal chalcogenide nanosheets (TMC NSs: ZnIn2S4, CdS, CdIn2S4, and In2S3), which is synergistically enabled by a solid-state non-conjugated polymer, i.e., poly(diallyldimethyl ammonium chloride) (PDDA), and MXene quantum dots (MQDs). In such elaborately designed photosystems, an ultrathin PDDA layer functions as an intermediate charge transport mediator to relay the directional electron transfer from TMC NSs to MQDs that serve as the ultimate electron traps, resulting in a considerably boosted charge separation/migration efficiency. The suitable energy level alignment between TMC NSs and MQDs, concurrent electron-withdrawing capabilities of the ultrathin PDDA interim layer and MQDs, and the charge transport cascade endow the self-assembled TMC/PDDA/MQD heterostructured photosystems with conspicuously improved photoactivities toward anaerobic selective reduction of nitroaromatics to amino derivatives and photocatalytic hydrogen evolution under visible light irradiation. Furthermore, we ascertain that this concept of constructing a charge transfer cascade in such TMC-insulating polymer-MQD photosystems is universal. Our work would afford novel insights into smart design of spatial vectorial charge transport pathways by precise interface modulation via non-conjugated polymers for solar energy conversion.

Synthesis of Ag/CoFe2O4 magnetic aerogel for catalytic reduction of nitroaromatics

An efficient technique for producing the Ag/CoFe2O4 noble trimetallic aerogel is provided. The advantages of this approach are fast preparation, short gelation time, avoiding the use of surfactants, and preparation at room temperature. The Ag/CoFe2O4 aerogel was characterized by common analysis methods including FESEM, VSM, EDX mapping, TEM, BET, and XRD. The resulting aerogel exhibits outstanding catalytic activity, and durability in reducing different nitroarenes. The reactions were carried out using hydrazine hydrate as a reducing agent, a 0.03 g catalyst, and ethanol as thesolvent atrefluxconditions. Under these conditions, 13 derivatives of nitroarenes were successfully reduced to aniline derivatives in 4 h in 70–95 % yield. This reaction had some advantages such as no use of toxic organic solvents, mild reaction conditions, easy separation of the products without any tedious separation techniques, and a recyclable catalyst. The catalyst showed high recyclability in which only 8 % decrease was observed after five runs.

Synergistic nitroreductase/vanadium catalysis enables chemoselective nitro reductions to anilines in the absence of hydrogen gas

Anilines are valuable synthons in pharmaceuticals and agrochemicals. These compounds are generally produced by chemocatalytic reduction of the corresponding nitrobenzene precursors. However, known synthetic methods often lack sufficient activity or selectivity, which results in low yields or the formation of a variety of undesired side products. We envisaged a biocatalytic approach as a promising general platform for selective and mild nitroarene reduction. Herein, we report using nitroreductases in combination with vanadium salts for the quantitative reduction of nitroaromatics to their corresponding anilines. Substrate scope studies were performed with fourteen nitrobenzene and four nitropyridine compounds. In one example, the reaction was intensified to 27 ​g/L substrate loading at 25 ​mL scale, where chemoselective reduction of the nitro group was obtained with full conversion and more than 93% selectivity toward aniline product (isolated in 82% yield). These conditions demonstrate the first general enzymatic method for the reduction of nitroaromatics to anilines.

Efficient Reusable Gold-Mesoporous Silica Nanocatalysts for Aromatic Nitro Reduction: Role of Phenolic Chelating Ligands on Immobilizing Gold Nanoparticles and Catalytic Activity

Developing heterogeneous metal nanocatalysts is highly desirable since the catalyst can be easily separated and reused for several times. In this manuscript, we have immobilized gold nanoparticles (AuNPs) on the surface of mesoporous silica (SiO[Formula: see text] using simple amino acid-based phenolic chelating molecules and utilized as highly reusable catalyst for nitroarene reduction. The synthesized nanocomposites (Au@SiO2-1 and Au@SiO2-2) have been unambiguously confirmed using powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR), high resolution-transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS). Interestingly, Au@SiO2-1 exhibited highly enhanced 4-nitrophenol reduction that was studied using absorption spectroscopy. Further catalytic activity of Au@SiO2-1 was also explored for 2-nitroaninline and 4-nitroaniline. The reusable studies demonstrated that the catalyst did not show significant change in the activity up to ten cycles. After catalytic reactions studies confirmed the strong attachment of AuNPs on the SiO2 matrix.

MOF-derived NiFe2O4 nanoparticles on molybdenum disulfide: Magnetically reusable nanocatalyst for the reduction of nitroaromatics in aqueous media

Metal organic framework (MOF)-derived nanocatalysts on various nanostructured supports are generally efficient heterogeneous catalysts employable for organic transformations. Herein, nickel Prussian blue (PB) nanoparticles were deployed to form NiFe2O4 nanocatalysts supported on 2D molybdenum disulfide (MoS2) through a facile heat treatment. NiFe2O4 nanocatalysts could be uniformly dispersed on the high-specific-area MoS2 surface, representing a highly efficient, inexpensive, and magnetically recoverable nanocomposite catalyst. The semiconductor property of MoS2 ensures a high electric conductivity, thus enhancing electron transfer between the reductant and the reactant. Furthermore, the strong magnetic characteristics enable its convenient separation from the reaction mixture. NiFe2O4 nanoparticles on MoS2-supported produces multiple electron transfer pathways and overcomes known drawbacks of catalytic methods that use metals alone, endowing long-term cycle stability. Overall, MoS2/NiFe2O4 exhibited an excellent catalytic activity and high yields in the reduction of nitrobenzene in water, maintained even after five cycles.

Self-reductive palladium nanoparticles loaded on polydopamine-modified MXene for highly efficient and quickly catalytic reduction of nitroaromatics and dyes

Palladium nanoparticles (PdNPs) with average particle size of 10 nm were deposited on the surface of Ti3C2 (MXene) using polydopamine (PDA) as the stabilizer by in-situ self-reduction mechanism. A series of characterization methods were used to analyze the morphology and microstructure of the resulting composite catalyst (Ti3C2-PDA@PdNPs). The catalytic performance of the composite catalysts toward 2-nitrophenol (2-NP), 4-nitrophenol (4-NP), methyl orange (MO) and methylene blue (MB) were systematically investigated. The results indicate that Ti3C2-PDA@PdNPs exhibits highly efficient and quickly catalytic reduction activity. Specifically, it takes only 70 s for Ti3C2-PDA1.0 @PdNPs to catalyze the complete conversion for 2-NP. The reaction rate constants of Ti3C2-PDA1.0 @PdNPs for these four pollutants are calculated as k2-NP = 0.1536 s−1, k4-NP = 0.1245 s−1, kMO= 0.2014 s−1, and kMB= 0.0732 s−1. In addition, after 10 recycles of catalytic reduction, the catalytic efficiency of Ti3C2-PDA1.0 @PdNPs can be still maintained above 92%, and the loss of PdNPs in each cycle is not more than 1.2%, indicating that Ti3C2-PDA@PdNPs composite catalyst has high stability and recyclability. This work provides a new, green and simple synthesis idea for MXene nanocomposite catalyst, and provides a good application prospect for the catalytic degradation of nitroaromatic compounds and dyes.

Dual Modification of Carbon Support Enables Robust Anchoring of Ruthenium Nanoclusters for Efficient Hydrogen Evolution and Aromatic Nitroreduction

AbstractGraphite carbons have been widely used as catalyst support due to their low‐cost, tunable porous structure, high electrical conductivity, and good resistance to harsh conditions. To date, various defect engineerings have been adopted to enhance the cohesion between graphite carbons and metallic nanocatalysts. Nevertheless, the modification of carbon basal plane has been less explored. In this work, a dual modification strategy is developed to achieve novel carbon support (denoted as NCf) incorporating both C60 units and trace N‐defects. Benefiting from the dual anchoring modes (Ru–C and Ru–N–C), ultrafine ruthenium (Ru) nanoclusters (average size: 2.26 ± 0.38 nm) can be well‐dispersed and robustly anchored on the NCf support. The optimal Ru0.013@NCf catalyst exhibits decent catalytic activities and long‐term stabilities toward both alkaline hydrogen evolution reaction (HER) and aromatic nitroreduction (ANR), outperforming the individually modified counterparts. Computational studies suggest that introducing both C60 and N‐defects into carbon support leads to electron‐deficient Ru nanocluster, which is critical for not only HER but also ANR. This work thus provides a new guideline for rational design of advanced carbon supported nanocatalysts for multipurpose applications.

Facile fabrication of graphene encapsulating 3d transition metal nanoparticles as highly active and anti-poisoning catalysts for selective hydrogenation of nitroaromatics

Graphene encapsulating 3d transition metal nanoparticles (Ni, Co, Fe@G) are successfully fabricated through pyrolysis of complexes which are simply prepared via “acid-base reactions” between metal hydroxides and carboxylic acid such as citric acid. In particular, the Ni@G catalyst exhibits outstanding catalytic activity and selectivity (>99%) toward the reduction of various nitroaromatics under mild conditions (1 MPa H2, 60 °C), even in the presence of poisons (CO and thiophene etc.). This “acid-base reactions” based method provides a facile and scalable approach to prepare graphene encapsulating 3d transition metals with wide ranges of applications.

Ultrafast catalytic reduction of toxic nitroaromatics and organic colouring dyes by using Au/ZIF-11: Efficient wastewater treatment

An ultrafast catalytic method to reduce various toxic nitrophenols, nitroaniline and organic dyes by using gold nanoparticles decorated-ZIF-11 (Au/ZIF-11) composite for wastewater treatment has been described. Three new Au/ZIF-11 composites (abbreviated as Au0.1Z, Au0.2Z and Au0.3Z) have been synthesized via direct reduction of HAuCl4 (0.1 to 0.3 mM) using sodium borohydride (NaBH4) in the suspension of pre-synthesized ZIF-11 and characterized by various spectroscopic and morphological/surface techniques. TEM images confirmed the formation of spherical and uniformly distributed gold NPs, having average particle size of 7.35 ± 0.95 nm, on the surface of ZIF-11 microcrystals. Au0.2Z displayed exceptionally high catalytic efficiency towards the reduction of nitrophenols (2-NPhenol, 3-NPhenol and 4-NPhenol), 4-nitroaniline (4-NANI) and 2,4,6-triNPhenol at substrate's concentration: 1.58 × 10−4 M in the presence of NaBH4 (0.04 M) at ambient condition. k̅app, (apparent rate constant) was (4.64/3.24/1.90) × 10−2 s−1 having activity coefficient k′ (k′ = k̅app/M) value of 928.83, 647.59 and 380.61 s−1 g−1 for 3-NPhenol, 4-NPhenol and 2-NPhenol, respectively, using Au0.2Z ([catalyst] = 15.87 μg/mL). Further, Au0.2Z can be re-used up to 5 cycles with more than 90% conversion efficiency. Moreover, Au0.2Z also reduced organic colouring dyes (methylene blue (MB), rhodamine B (RhB), congo red (CR) and methyl orange (MO)) in the presence of NaBH4 and the corresponding k̅app was 7.88 × 10−3–9.22 × 10−4 s−1 with k′ value of 157.71–9.22 s−1 g−1. The probable mechanism involving Langmuir-Hinshelwood apparent first-order kinetics model described that Au nanoparticles immobilized onto ZIF-11 may serve as antenna to transfer electrons and hydrogen from borohydride (BH4−) ions to the acceptor (nitro group/organic dye). Therefore, Au0.2Z can effectively be used for environmental remediation application to remove organic pollutants from the industrial wastewater.

Cu nanoparticles embedded in the porous organic polymer as highly effective catalysts for nitroaromatics reduction

The improvement of effective catalytic systems relies on the synthesis of catalytically active composites including metal nanocatalysts and porous supports. In particular, it is essential to develop porous composites comprising cheaper metal nanocatalysts rather than expensive noble metals. This study reports the preparation of covalent organic polymer (COP) as a support in the immobilization of Cu nanoparticles (NPs). Cu(II) species were successfully chelated to nitrogen and oxygen atoms in the COP by mixing with a copper (II) acetate solution. The as-prepared catalysts were distinguished using various methods, including XRD, FE-SEM, FT-IR, BET, EDX, and ICP-AES. The findings indicated that uniform Cu NPs were homogeneously and firmly embedded into the surface of COP. The final Cu–COP sample demonstrated efficient catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP). The activity factor (k') and rate constant (K app ) of Cu–COP were respectively 9.65 s −1 and 0.0193 s −1 g −1 for 4-NP reduction and could completely transform 4-NP to 4-AP within 3 min. Furthermore, the conversion rate of the supported nanoparticles was 97.1% in 4-NP reduction up to five cycles with no decreased reactivity. • Covalent organic polymer‏ ‏(COP) as support in the immobilization of Cu nanoparticles (NPs) is reported. • Findings indicates the embedding of uniform Cu NPs into the surface of COP. • Cu–COP catalyst show efficient catalytic activity in the reduction of 4-nitrophenol. • The activity factor and rate constant of Cu–COP is 9.65 s −1 and 0.0193 s −1 g −1 for 4-NP reduction within 3 min.

Modification of cellulose filter paper with bimetal nanoparticles for catalytic reduction of nitroaromatics in water

Modification of cellulose filter paper with bimetal nanoparticles for catalytic reduction of nitroaromatics in water

Encapsulating nitroreductase into metal-organic framework: Boosting industrial performance for the reduction of nitro-aromatics

Traditional chemical methods for nitro reduction are typically conducted under harsh conditions and are readily explosive, such as hydrogen pressurization and zinc powder reduction. Nitroreductase (NTR) as a biocatalyst may represent a promising strategy to solve this synthetic challenging. Unfortunately, due to the availability of this enzyme, the lack of long-term stability as well as challenging recovery process, very limited work was reported about its applicability for the reduction of nitro groups. Here, based on the highly efficient expression of NTR in our lab, we firstly reported the encapsulation of NTR into ZIF-8 to form NTR@ZIF-8. The resulting framework composite demonstrated an excellent protective capability of enzyme against harsh environment and could also simplify the complex downstream separation and recovery operations. Moreover, after five successive cycles of reuse to reduce 4-NP, the residual NTR@ZIF-8 still reserved a certain activity, which can significantly reduce the processing cost and might be applicable in the industries in the future.

Solar irradiated selective nitroaromatics reduction over plasmonic Ag-TiO2: Deposition time dependent size growth and oxidation state of co-catalyst

Solar irradiated plasmonic Ag-TiO2 (P25) nanocomposites have proficiently harvested solar energy towards nitroaromatics reduction comparatively to almost irresponsive bare TiO2. p-Nitrotoulene (p-NT) and p-nitrobenzaldehyde (p-NBAL) were potentially reduced to p-aminotoulene (p-AT, 87% and 50%) and p-aminobenzaldehyde (p-ABAL, 70% and 38%) with Ag5-P25 (5 min photodeposition time (PDT)) and Ag30-P25 (30 min PDT) respectively. The focus of this study was mainly on the role of PDT (3–30 min) which was found to be directly co-related with size, distribution and oxidation state of deposited Ag nanoparticles (NPs) over titania surface, responsible for superior photocatalytic activity. HR-TEM images confirmed the average size of Ag nanoparticles to be ∼1–2 nm and ∼7–8 nm for Ag5-P25 and Ag30-P25 respectively. Further, XPS analysis suggested the formation of ternary hybrid (Ag2O/Ag-P25) in case of 5 min PDT whereas only metallic Ag was found to be photodeposited as the times was increased to 30 min.

MXene-motivated accelerated charge transfer over TMCs quantum dots for solar-powered photoreduction catalysis

Transition metal chalcogenides quantum dots (TMCs QDs) demonstrate emerging potential in solar energy conversion owing to marvelous physicochemical properties, such as quantum size effect, large extinction coefficient, and multiple excitons generation. Nevertheless, TMCs QDs as photosensitizers are unstable owing to high surface energy, and moreover, substantial trap states of TMCs QDs annihilate the photo-induced charge carriers, thus resulting in ultra-short charge lifetime and inferior photoactivities. Herein, 0D/2D TMCs QDs/MXene heterostructures were designed by a ligand-initiated electrostatic self-assembly strategy, wherein positively charged TMCs QDs were anchored on the negatively charged ultrathin Ti3C2Tx nanosheets (NSs) framework, which promotes the anisotropic unidirectional electron transport from TMCs QDs to MXene NSs. MXene functions as an effective charge mediator to decrease the charge recombination and prolong the charge lifetime for photocatalytic hydrogen generation and anaerobic reduction of nitroaromatics to amino compounds under visible light irradiation. Our work would shed new insights on the role of MXene in tuning the directional charge transport for solar energy conversion.

Galactose Grafted Two-Dimensional Nanosheets as a Scaffold for the In Situ Synthesis of Silver Nanoparticles: A Potential Catalyst for the Reduction of Nitroaromatics.

Two major hurdles in NP-based catalysis are the aggregation of the NPs and their recycling. Immobilization of NPs onto a 2D support is the most promising strategy to overcome these difficulties. Herein, amphiphilicity-driven self-assembly of galactose-hexaphenylbenzene-based amphiphiles into galactose-decorated 2D nanosheet is reported. The extremely dense decoration of reducing sugar on the surface of the sheets is used for the in situ synthesis and immobilization of ultrafine catalytically active AgNPs by using Tollens' reaction. The potential of the system as a catalyst for the reduction of various nitroaromatics is demonstrated. Enhanced catalytic activity is observed for the immobilized AgNPs when compared to the corresponding discrete AgNPs. Recovery of the catalytic system from the reaction mixture by ultrafiltration and its subsequent recycling for several cycles without dropping its activity is shown. This is the first report demonstrating the in situ synthesis and immobilization of ultrafine AgNPs onto a 2D nanosheet that exhibits excellent catalytic performance for the reduction of nitroaromatics.

Ag nanoparticles immobilized on new magnetic alginate halloysite as a recoverable catalyst for reduction of nitroaromatics in aqueous media

Amines can be applied in the synthesis of various important compounds such as dyes, drugs, polymers, pharmaceutical products, and biologically active materials. The significant subject in the preparation of amines is the selection of the most effective heterogeneous catalyst to get the best catalytic efficiency, stability, recoverability, and reusability. For this target, we prepared new alginate magnetically recoverable nanocatalyst by stabilization of Ag nanoparticles on the surface of the halloysite (HS) [HS-Alginate-Ag/Fe3O4]. Several detection methods confirmed the production of HS-Alginate-Ag/Fe3O4 nanocatalyst and the results obtained were well explained in the context. HS-Alginate-Ag/Fe3O4 presented good catalytic performance for the hydrogenation of nitro compounds using NaBH4 as the reducing agent and hydrogen donor. The good activity and durability of this catalyst can be attributed to the good dispersion and nano-sized particle of silver nanoparticles.

Photocatalytic reduction of nitroaromatics into anilines using CeO2-TiO2 nanocomposite

The reduction of nitro compounds into amines is an important approach for synthetic and pharmaceutical chemistry. The reduced compounds are used as synthetic intermediates in the synthesis of therapeutic molecules. In the present work, we have fabricated cerium dioxide decorated TiO2 nanoparticles using a sol-gel-hydrothermal method. The synthesized nanocomposite was effectively reduced various nitro-compounds, specifically aromatic nitro compounds, into amines in visible light. All the nitro compounds screened in the photoreduction reaction showed >90% conversion with >96% selectivity. Chromatographic techniques confirmed the products obtained. The nanocomposite photocatalyst has excellent stability under the experimental condition and exhibited up to five cycles with no loss of metal content. The nanomaterials were characterized using various spectroscopic techniques.

Synthesis and characterization of the ternary graphene oxide, MnFe2O4 nanoparticles, and Polyamidoamine dendrons nanocomposite decorated with palladium as a heterogeneous catalyst for nitroaromatics reduction

In this study, the divergent and magnetic separation method is employed to prepare polyamidoamine (PAMAM) dendrons functionalized magnetic graphene oxide (MGG3) using graphene oxide supported MnFe2O4 nanoparticles as the support (MG), and ethylenediamine (EDA) and methylacrylate (MA) as the precursors of PAMAM dendron. Finally, palladium ions as active catalytic sites are immobilized on the support (MGG3‐Pd). The morphology and structure of the MGG3‐Pd nanocomposite thus produced are characterized by elemental analysis, Fourier transform infrared (FT‐IR), powder X‐ray diffraction (XRD) analysis, thermogravimetric analysis (TGA), field emission scanning electron microscopy (FE‐SEM), transmission electron microscopy (TEM), energy dispersive X‐ray spectroscopy (EDS), inductively coupled plasma atomic emission spectroscopy (ICP‐AES), X‐ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM), and Zeta potential analysis. Subsequently, the catalytic activity of the MGG3‐Pd nanocomposite is studied in the reaction of 4‐nitrophenol (4‐NP) with sodium borohydride as the reducing agent at room temperature. The MGG3‐Pd catalyst is found to exhibit an excellent catalytic activity in the reduction of 4‐NP with a high yield over a short reaction time and at a rate constant (k) of 16.82 × 10−3 s−1. Furthermore, the MGG3‐Pd catalyst thus produced can be recycled at least after 10 runs of 4‐NP reduction without any considerable loss of Pd content. The reduction of other nitroaromatic compounds is also investigated under optimal conditions to illustrate the catalyst's versatility.