Sub-nanometric Rh decorated magnetic nanoparticles as reusable catalysts for nitroarene reduction in water

Picolylamine-Ni(ii) complex attached on 1,3,5-triazine-immobilized silica-coated Fe3O4 core/shell magnetic nanoparticles as an environmentally friendly and recyclable catalyst for the one-pot synthesis of substituted pyridine derivatives

In the current study, an environmentally friendly and facile method was proposed for designing and constructing a catalyst with Ni(ii) attached to a picolylamine complex on 1,3,5-triazine-immobilized Fe₃O₄ core-shell magnetic nanoparticles (Ni^II-picolylamine/TCT/APTES@SiO₂@Fe₃O₄) via a stepwise procedure. The as-synthesized nanocatalyst was identified and characterized via Fourier-transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), vibrating-sample magnetometry (VSM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), field-emission scanning electron microscopy (FE-SEM), inductively coupled plasma (ICP), and energy-dispersive X-ray spectrometry (EDX). The obtained results from the BET analysis indicated that the synthesized nanocatalyst had high specific area (53.61 m² g^-1) and mesoporous structure. TEM observations confirmed the particle size distribution was in the range 23-33 nm. Moreover, the binding energy peaks observed at 855.8 and 864.9 eV in the XPS analysis confirmed the successful and stable attachment of Ni(ii) on the surface of the picolylamine/TCT/APTES@SiO₂@Fe₃O₄. The as-fabricated catalyst was used to produce pyridine derivatives by the one-pot pseudo-four component reaction of malononitrile, thiophenol, and a variety of aldehyde derivatives under solvent-free conditions or EG at 80 °C. The highest yield achieved was 97% for compound 4d in EG at 80 °C with a TOF of 823 h^-1 and TON of 107. It was found that the used catalyst was recyclable for eight consecutive cycles. On the basis of ICP analysis, the results indicated that the Ni leaching was approximately 1%.

Multifunctional Core-Shell NiFe2O4 Shield with TiO2/rGO Nanostructures for Biomedical and Environmental Applications

Multifunctional core@shell nanoparticles have been synthesized in this paper through 3 stages: NiFe2O4 nanoparticles by microwave irradiation using Pedalium murex leaf extract as a fuel, core@shell NiFe2O4@TiO2 nanoparticles by sol-gel, and NiFe2O4@TiO2@rGO by sol-gel using preprepared reduced graphene oxide obtained by modified Hummer’s method. XRD analysis confirmed the presence of both cubic NiFe2O4 spinel and tetragonal TiO2 rutile phases, while Raman spectroscopy analysis displays both D and G bands (ID/IG = 1.04) associated with rGO. Morphological observations by HRTEM reveal a core-shell nanostructure formed by NiFe2O4 core as confirmed by SAED with subsequent thin layers of TiO2 and rGO. Magnetic measurements show a ferromagnetic behavior, where the saturation magnetization drops drastically from 45 emu/g for NiFe2O4 to 15 emu/g after TiO2 and rGO nonmagnetic bilayers coating. The as-fabricated multifunctional core@shell nanostructures demonstrate tunable self-heating characteristics: rise of temperature and specific absorption rate in the range of ΔT = 3–10°C and SAR = 3–58 W/g, respectively. This effectiveness is much close to the threshold temperature of hyperthermia (45°C), and the zones of inhibition show the better effective antibacterial activity of NTG against various Gram-positive and Gram-negative bacterial strains besides simultaneous good efficient, stable, and removable sonophotocatalyst toward the TC degradation.

Pillararene-functionalized rhodium nanoparticles for efficient catalytic reduction and photothermal sterilization

Pillar[5]arene-functionalized rhodium nanoparticles are prepared for catalytic reduction of toxic nitrophenols and azo dyes and efficient photothermal sterilization.

Palladium Nanoparticles Supported on Cellulosic Paper as Multifunctional Catalyst for Coupling and Hydrogenation Reactions

Hallmark of a successful catalyst is its high efficiency, economic aspects, operational simplicity, extensive reusability, higher environment friendliness, and potential use in multiple industrial applications. Herein, a facile protocol involving a catalyst with Pd nanoparticles supported on cellulose paper (also known as a "dip-catalyst") for the hydrogenation of a series of quinolines, nitroarene, and C-C bond formation reactions in most benign solvents such as water is described. The mere insertion/removal of the "dip-catalyst" strip enables instantaneous start/stop of the reaction, which enhances its reusability and ease of separation of products. Cellulose paper (CP) strips decorated with Pd nanoparticles (Pd/CP) are prepared by the reduction of K₂ PdCl₄ soaked strips using formic acid as reductant. The resulting spherical shaped Pd particles, confirmed by scanning electron microscopy, form stable catalysis centers on the support. XRD signature confirms the crystallinity of the Pd nanoparticles and the TEM images display 15-20 nm size particles uniformly decorating CP. X-ray photoelectron spectroscopy indicates the formation of metallic Pd. The catalyst is tested for the C-C bond formation reactions. Pd/CP catalyzed Suzuki-Miyaura coupling reaction demonstrate >99% conversion with optimum selectivity. On the other hand, Mizoroki-Heck reaction produced 87% conversion with the reaction of 4-methoxycarbonyl phenylboronic acid and iodobenzene in ethanol:water (1 : 1 v/v) using KOH as base. The developed Pd/CP construct produces >99% of the pyridine-ring hydrogenated product on quinoline hydrogenation using tetrahydroxydiboron (THDB) as the hydrogen source. Diverse and highly reducible functional groups were also evaluated for transfer hydrogenation, which demonstrates a high efficiency in terms of both reactivity and selectivity. The used catalysts are recyclable for the multiple cycles.

Heavy Metal Adsorption Using Magnetic Nanoparticles for Water Purification: A Critical Review

Research on contamination of groundwater and drinking water is of major importance. Due to the rapid and significant progress in the last decade in nanotechnology and its potential applications to water purification, such as adsorption of heavy metal ion from contaminated water, a wide number of articles have been published. An evaluating frame of the main findings of recent research on heavy metal removal using magnetic nanoparticles, with emphasis on water quality and method applicability, is presented. A large number of articles have been studied with a focus on the synthesis and characterization procedures for bare and modified magnetic nanoparticles as well as on their adsorption capacity and the corresponding desorption process of the methods are presented. The present review analysis shows that the experimental procedures demonstrate high adsorption capacity for pollutants from aquatic solutions. Moreover, reuse of the employed nanoparticles up to five times leads to an efficiency up to 90%. We must mention also that in some rare occasions, nanoparticles have been reused up to 22 times.

Biogenic Synthesis of Gold Nanoparticles on a Green Support as a Reusable Catalyst for the Hydrogenation of Nitroarene and Quinoline

Direct attachment of gold nanoparticles to a green support without the use of an external reducing agent and using it for removing toxic pollutants from wastewater, i. e., reduction of nitroarene to amine, are described. A novel approach involving the reduction of gold by the jute plant (Corchorus genus) stem-based (JPS) support itself to form nanoparticles (AuNPs) to be used as a catalytic system ('dip-catalyst') and its catalytic activity for the hydrogenation of series of nitroarenes in aqueous media are presented. AuNPs/JPS catalyst was characterized using SEM, UV-Vis, FTIR, TEM, XPS, and ICP-OES. Confined area elemental mapping exhibits uniform and homogeneous distribution of AuNPs on the support surface. TEM shows multi-faceted AuNPs in the range of 20-30 nm. The reactivity of AuNPs/JPS for the transfer hydrogenation of nitroarene as well as hydrogenation of quinoline under molecular H₂ pressure was evaluated. Sodium borohydride, when used as the hydrogen source, demonstrates a high catalytic efficiency in the transfer hydrogenation reduction of 4-nitrophenol (4-NP). Quinoline is quantitatively and chemoselectively hydrogenated to 1,2,3,4-tetrahydroquinoline (py-THQ) using molecular hydrogen. Reusability studies show that AuNPs are stable on the support surface and their selectivity is not affected.

Sub-nanometric Manganous Oxide Clusters in Nitrogen Doped Mesoporous Carbon Nanosheets for High-Performance Lithium-Sulfur Batteries

The greatest challenge for lithium-sulfur (Li-S) batteries application is the development of cathode hosts to address the low conductivity, huge volume change, and shuttling effect of sulfur or lithium polysulfides (LiPs). Herein, we demonstrate a composite host to circumvent these problems by confining sub-nanometric manganous oxide clusters (MOCs) in nitrogen doped mesoporous carbon nanosheets. The atomic structure of MOCs is well-characterized and optimized via the extended X-ray absorption fine structure analysis and density functional theory (DFT) calculations. Benefiting from the unique design, the assembled Li-S battery displays remarkable electrochemical performances including a high reversible capacity (990 mAh g^-1 after 100 cycles at 0.2 A g^-1) and a superior cycle life (60% retention over 250 cycles at 2 A g^-1). Both the experimental results and DFT calculations demonstrate that the well-dispersed MOCs could significantly promote the chemisorption of LiPs, thus greatly improving the capacity and rate performance.

Catalytic activity of maghemite supported palladium catalyst in nitrobenzene hydrogenation

A maghemite supported palladium catalyst was prepared and tested in nitrobenzene hydrogenation. The catalyst support was made by a newly developed combined technique, where sonochemical treatment and combustion have been used. As a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated in polyethylene glycol by high-intensity ultrasound cavitation to get a homogeneous dispersion, then the product was combusted. The produced powder contained maghemite nanoparticles with 21.8 nm average particle size. In the second step of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+ ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active palladium was formed. The prepared maghemite supported Pd catalyst have been tested in nitrobenzene hydrogenation at three different temperatures (283 K, 293 K and 303 K) and constant pressure (20 bar). At 293 K and 303 K, the conversion and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the selectivity was only 73% at 273 K because the intermediate species (azoxybenzene and nitrosobenzene) have not been transformed to aniline. All in all, the prepared catalyst is successfully applied in nitrobenzene hydrogenation and easily separable from the reaction media.

Pd nanoparticles on green support as dip-catalyst: a facile transfer hydrogenation of olefins and N-heteroarenes in water

Chemo- and regioselective hydrogenation methods using highly green sources, particularly from metal nanoparticles on plant stem as support and water, is an intensive research area, which is highly relevant to the development of green chemistry and technology in the 21^st century. Here, the synthesis and activity of a heterogeneous catalytic system (called “dip-catalyst”) for the transfer hydrogenation of a series of styrenyl, unfunctionalized olefins, quinoline and other N-heteroarenes, are presented. It consists of Pd nanoparticles (15–20 nm) anchored on bio-processed jute plant (Corchorus genus) stem as the support. Pd nanoparticles were decorated on the green support (GS) jute stem by the in situ reduction of K₂PdCl₄ in aqueous medium at 70 °C, using formic acid as the reductant. The Pd@GS was characterized using SEM, EDS, XRD, FTIR, XPS and TEM. Elemental mapping revealed uniform distribution of Pd on the cellulose matrix of the jute stem. The catalyst was successfully applied to the chemoselective transfer hydrogenation of numerous styrenyl, unfunctionalized olefins. Its high functional group tolerance was investigated during the olefins hydrogenation in water. Furthermore, Pd@GS was capable of quantitative hydrogenation to selectively produce 1,2,3,4-tetrahydroquinoline (THQ) in water using stoichiometric amounts of tetrahydroxydiboron (THDB) at 60 °C with turn over frequency (TOF) 4938 h⁻¹. This system is stable in water and displays excellent recyclability; it could be used for 32 consecutive cycles, without losing its original crystallinity or requiring replenishment.

A dip catalyst consisting of Pd nanoparticles immobilized on the surface of thin slices of jute-stem was fabricated. Its versatility as a hydrogen transfer agent for styrenyl, cyclic and unfunctionalized olefins and N-heterocycles was investigated.