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

Ionothermal synthesis of magnetic N-doped porous carbon to immobilize Pd nanoparticles as an efficient nanocatalyst for the reduction of nitroaromatic compounds

Carbon materials play important roles as catalysts or catalyst supports for reduction reactions owing to their high porosity, large specific surface area, great electron conductivity, and excellent chemical stability. In this paper, a mesoporous N-doped carbon substrate (exhibited as N-C) has been synthesized by ionothermal carbonization of glucose in the presence of histidine. The N-C substrate was modified by Fe3O4 nanoparticles (N-C/Fe3O4), and then Pd nanoparticles were stabilized on the magnetic substrate to synthesize an eco-friendly Pd catalyst with high efficiency, magnetic, reusability, recoverability, and great stability. To characterize the Pd/Fe3O4-N-C nanocatalyst, different microscopic and spectroscopic methods such as FT-IR, XRD, SEM/EDX, and TEM were applied. Moreover, Pd/Fe3O4-N-C showed high catalytic activity in reducing nitroaromatic compounds in water at ambient temperatures when NaBH4 was used as a reducing agent. The provided nanocatalyst's great catalytic durability and power can be attributed to the synergetic interaction among well-dispersed Pd nanoparticles and N-doped carbonaceous support.

High-Rate CO2 Electrolysis to Formic Acid over a Wide Potential Window: An Electrocatalyst Comprised of Indium Nanoparticles on Chitosan-Derived Graphene

Realizing industrial-scale production of HCOOH from the CO2 reduction reaction (CO2 RR) is very important, but the current density as well as the electrochemical potential window are still limited to date. Herein, we achieved this by integration of chemical adsorption and electrocatalytic capabilities for the CO2 RR via anchoring In nanoparticles (NPs) on biomass-derived substrates to create In/X-C (X=N, P, B) bifunctional active centers. The In NPs/chitosan-derived N-doped defective graphene (In/N-dG) catalyst had outstanding performance for the CO2 RR with a nearly 100 % Faradaic efficiency (FE) of HCOOH across a wide potential window. Particularly, at 1.2 A ⋅ cm-2 high current density, the FE of HCOOH was as high as 96.0 %, and the reduction potential was as low as -1.17 V vs RHE. When using a membrane electrode assembly (MEA), a pure HCOOH solution could be obtained at the cathode without further separation and purification. The FE of HCOOH was still up to 93.3 % at 0.52 A ⋅ cm-2 , and the HCOOH production rate could reach 9.051 mmol ⋅ h-1  ⋅ cm-2 . Our results suggested that the defects and multilayer structure in In/N-dG could not only enhance CO2 chemical adsorption capability, but also trigger the formation of an electron-rich catalytic environment around In sites to promote the generation of HCOOH.

Elimination of toxic azo dye using a calcium alginate beads impregnated with NiO/activated carbon: Preparation, characterization and RSM optimization

Nickel oxide nanoparticles supported activated carbon (AC-NiO) was fabricated using thermal activation. Then, AC-NiO composite was immobilized on alginate beads to obtain 3-dimensional network structure ALG@AC-NiO nanocomposite beads for catalytic reduction of Congo red (CR) dye. The resulting nanocomposite beads were identified by various physical techniques. The crystalline nature and dispersion of NiO nanoparticles was defined by the XRD and EDS techniques, respectively. ALG@AC-NiO beads have a Ni element content of 4.65 wt% with an average NiO particle diameter of 23 nm. The statistical approach mathematically describes the catalytic reduction of the CR dye as a function of the NaBH₄ concentration, the catalyst dose and the concentration of the CR dye modeled by a BBD-RSM. According to the statistical modeling and the optimization process, the catalytic optimum conditions were obtained for NaBH₄ concentration of 0.05 M, catalyst dose of 11 mg and CR dye concentration of 80 ppm who permit meet 99.67 % of CR dye conversion. The adjusted coefficient of determination (R² = 0.9957) indicates that the considered model was quite suitable with a good correlation between the experiment and predicted.

Chitosan-supported metal nanocatalysts for the reduction of nitroaromatics

The second most abundant natural polymer in the earth's crust is chitosan (CS). The unique physical, chemical, structural, and mechanical features of this natural polymer have led to its increased application in a variety of fields such as medicine, catalysis, removal of pollutants, etc. To eliminate various pollutants, it is preferable to employ natural compounds as their use aids the removal of contaminants from the environment. Consequently, employing CS to eliminate contaminants is a viable choice. For this aim, CS can be applied as a template and support for metal nanoparticles (MNPs) and prevent the accumulation of MNPs as well as a reducing and stabilizing agent for the fabrication of MNPs. Among the pollutants present in nature, nitro compounds are an important and wide category of biological pollutants. 4-Nitrophenol (4-NP) is one of the nitro pollutants. There are different ways for the removal of 4-NP, but the best and most effective method for this purpose is the application of a metallic catalyst and a reducing agent. In this review, we report the recent developments regarding CS-supported metallic (nano)catalysts for the reduction of nitroaromatics such as nitrophenols, nitroaniline compounds, nitrobenzene, etc. in the presence of reducing agents. The metals investigated in this study include Ag, Au, Ni, Cu, Ru, Pt, Pd, etc.

Magnetic bentonite decorated with Pd nanoparticles and cross-linked polyvinyl pyridine as an efficient nanocatalyst for Suzuki coupling and 4-Nitrophenol reduction reactions

This study reports the preparation of a novel type of support based on magnetically recyclable bentonite functionalized with divinylbenzene-polyvinyl pyridine (PVP-DVB) for Pd (II) nanocatalyst by a simple cost-effective method. Firstly, the conventional co-precipitation method synthesized Fe₃O₄ nanoparticles (NPs) onto bentonite sheets. Then the prepared magnetic support surface was functionalized by divinylbenzene-polyvinyl pyridine (PVP-DVB) to create a cross-linked polymer with a high coordination ability with palladium. Repeated nitrogen units in the PVP-DVB polymer chain increase the number of Pd bonds and thus lead to higher performance of the nanocatalyst. Finally, the palladium NPs were simultaneously synthesized and immobilized under mild conditions. The synthesized nanocatalyst was characterized by several methods such as scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, vibrating sample magnetometer, inductively coupled plasma mass spectrometry and thermogravimetric analysis. The efficiency of synthesized heterogeneous nanocatalyst was investigated in Suzuki-Miyaura cross-coupling reactions between a range of aryl halides (X = Cl, Br, I) with phenylboronic acid and in the reduction of 4-nitrophenol (4-NP). Moreover, the synthesized nanocatalyst could be easily recovered and reused several times with an efficiency greater than 90%.

Heteropolyacid coupled with cyanoguanidine decorated magnetic chitosan as an efficient catalyst for the synthesis of pyranochromene derivatives

In this study, a novel nanocatalyst was successfully prepared by heteropolyacid immobilization of magnetic chitosan-cyanoguanidine composite and fully characterized by different analysis methods, including FTIR, XRD, TGA, SEM, and EDS. The catalytic activity of fabricated composite was examined in a one-pot three-component reaction, involving the diverse active methylene compounds, various aryl aldehydes, and malononitrile in water. The results revealed the efficient catalytic performance of composite, while all reactions proceeded smoothly and led to the formation of the corresponding pyranochromene derivatives in high to excellent yields.

Very rapid synthesis of highly efficient and biocompatible Ag2Se QD phytocatalysts using ultrasonic irradiation for aqueous/sustainable reduction of toxic nitroarenes to anilines with excellent yield/selectivity at room temperature

There are many problems associated with the synthesis of nanocatalysts and catalytic reduction of nitroarenes - e.g., high temperatures, costs, long reaction/synthesis process times, the toxicity of chemicals/solvents, undesirable byproducts, the toxic/harmful wastes, low efficiency/selectivity, etc. This study represents an attempt to overcome these challenges. To this purpose, biocompatible and highly efficient Ag₂Se quantum dots (QDs) catalysts with antibacterial activity were synthesized in a very rapid (30 sec, rt), simple, inexpensive, sustainable/green, and one-pot strategy in water using ultrasonic irradiation. Characterization of the QDs was performed using different techniques. UV-Vis absorption and fluorescence spectroscopic studies showed an absorption peak at 480-550 nm and a maximum emission peak around 675 nm, which confirmed the successful synthesis of Ag₂Se QDs via the applied biosynthetic method. Subsequently, catalytic reduction of nitroarenes by them was carried out under safe conditions (H₂O, rt, air atmosphere) in ∼ 60 min with excellent yield and selectivity (>99%). Their catalytic activity in the reduction of various toxic nitroarenes to aminoarenes under green conditions was investigated. Thus, a rapid and safe ultrasound-based method was employed to prepare stable and green Ag₂Se QDs phyto-catalysts with unique properties, including exquisite monodispersity in shape (orthorhombic) and size (∼7 nm), air-stability, and good purity and crystallinity. Importantly, instead of various toxic chemicals, the plant extract obtained by rapid ultrasonic method (10 min, rt) was used as natural reducing, capping, and stabilizing agents. Moreover, antibacterial assays results showed that Ag₂Se-QDs catalysts at low concentrations (ppm) have high activity against all tested bacteria, especially E. coli (MIC:31.25 ppm, MBC:125 ppm) which were significantly different from those of Fig extract (MIC = MBC:500 ppm). The data reflect the role of these bio-synthesized Ag₂Se-QDs catalysts in the development of versatile and very safe catalysts with biomedical properties.

Catalytic nanoparticles and magnetic nanocatalysts in organic reactions: A mini review

Nanocatalysts, as a part of nanotechnology, have been seen very useful for various fileds of applications capturing a large contribution of the world market. Indeed, several unsolved issues of catalysts have been reconsidered by employing the new nanocatalysts including single core metal atoms and ions with surrounding holes. Moreover, it was expected that the future of catalytic reactions, especially those organic ones, will deal with the nanocatalyst applications. To this aim, the features of catalytic nanoparticles and magnetic nanocatalysts regarding evaluation of their advantages and applications in organic reactions were investigated in this work. Developments of catalytic nanoparticles and magnetic nanocatalysts were discussed in this work regarding the novel applications of such materials at the nanoscale for approaching advantageous features. Increased availability, activity, and stability are very important for applications of the catalysts in various organic reactions. Therefore, it is a must to discuss features of such nanocatalytic systems to provide more information about their advantages and even disadvantages of their applications.

1T-MoS2 catalysed reduction of nitroarenes and a one-pot synthesis of imines

An expedient synthesis of aromatic amines and imines via the reduction of nitroaromatics using 1T-MoS2 as a heterogeneous catalyst.

Antibacterial Films of Alginate-CoNi-Coated Cellulose Paper Stabilized Co NPs for Dyes and Nitrophenol Degradation

The development of a solid substrate for the support and stabilization of zero-valent metal nanoparticles (NPs) is the heart of the catalyst system. In the current embodiment, we have prepared solid support comprise of alginate-coated cellulose filter paper (Alg/FP) for the synthesis and stabilization of Co nanoparticles (NPs) named as Alg/FP@Co NPs. Furthermore, Alginate polymer was blended with 1 and 2 weight percent of CoNi NPs to make Alg-CoNi1/FP and Alg-CoNi2/FP, respectively. All these stabilizing matrixes were used as dip-catalyst for the degradation of azo dyes and reduction of 4-nitrophenol (4NP). The effect of initial dye concentration, amount of NaBH4, and catalyst dosage was assessed for the degradation of Congo red (CR) dye by using Alg-CoNi2/FP@Co NPs. Results indicated that the highest kapp value (3.63 × 10-1 min-1) was exhibited by Alg-CoNi2/FP@Co NPs and lowest by Alg/FP@Co NPs against the discoloration of CR dye. Furthermore, it was concluded that Alg-CoNi2/FP@Co NPs exhibited strong catalyst activity against CR, and methyl orange dye (MO) degradation as well as 4NP reduction. Antibacterial activity of the prepared composites was also investigated and the highest l activity was shown by Alg-CoNi2/FP@Co NPs, which inhibit 2.5 cm zone of bacteria compared to other catalysts.