Core-shell zirconia-coated magnetic nanoparticles offering a strong option to prepare a novel and magnetized heteropolyacid based heterogeneous nanocatalyst for three- and four-component reactions

Recent advances in the application of magnetic nanocatalysts in multicomponent reactions

Recently, the preparation and applications of magnetic nanostructures have attracted increasing attention in nanocatalysis studies, and magnetic nanoparticle (MNP) functionalized catalysts have been applied in important reactions such as Suzuki-Miyaura and Heck couplings. The modified nanocomposites demonstrate significant catalytic efficiency and excellent benefits in the context of catalyst recovery methods. This review discusses the recent modified magnetic nanocomposites in the field of catalytic applications along with the synthetic processes that are usually employed.

Deposition of Thick SiO2 Coatings to Carbonyl Iron Microparticles for Thermal Stability and Microwave Performance

Thick dielectric SiO₂ shells on the surface of iron particles enhance the thermal and electrodynamic parameters of the iron. A technique to deposit thick, 500-nm, SiO₂ shell to the surface of carbonyl iron (CI) particles was developed. The method consists of repeated deposition of SiO₂ particles with air drying between iterations. This method allows to obtain thick dielectric shells up to 475 nm on individual CI particles. The paper shows that a thick SiO₂ protective layer reduces the permittivity of the 'Fe-SiO₂-paraffin' composite in accordance with the Maxwell Garnett medium theory. The protective shell increases the thermal stability of iron, when heated in air, by shifting the transition temperature to the higher oxide. The particle size, the thickness of the SiO₂ shells, and the elemental analysis of the samples were studied using a scanning electron microscope. A coaxial waveguide and the Nicholson-Ross technique were used to measure microwave permeability and permittivity of the samples. A vibrating-sample magnetometer (VSM) was used to measure the magnetostatic data. A synchronous thermal analysis was applied to measure the thermal stability of the coated iron particles. The developed samples can be applied for electromagnetic compatibility problems, as well as the active material for various types of sensors.

One-step preparation of RGO/Fe3O4-FeVO4 nanocomposites as highly effective photocatalysts under natural sunlight illumination

The study used a one-step hydrothermal method to prepare Fe3O4-FeVO4 and xRGO/Fe3O4-FeVO4 nanocomposites. XRD, TEM, EDS, XPS, DRS, and PL techniques were used to examine the structurally and morphologically properties of the prepared samples. The XRD results appeared that the Fe3O4-FeVO4 has a triclinic crystal structure. Under hydrothermal treatment, (GO) was effectively reduced to (RGO) as illustrated by XRD and XPS results. UV-Vis analysis revealed that the addition of RGO enhanced the absorption in the visible region and narrowed the band gap energy. The photoactivities of the prepared samples were evaluated by degrading methylene blue (MB), phenol and brilliant green under sunlight illumination. As indicated by all the nanocomposites, photocatalytic activity was higher than the pure Fe3O4-FeVO4 photocatalyst, and the highest photodegradation efficiency of MB and phenol was shown by the 10%RGO/Fe3O4-FeVO4. In addition, the study examined the mineralization (TOC), photodegradation process, and photocatalytic reaction kinetics of MB and phenol.

Magnetic nanoparticle-supported sulfonic acid as a green catalyst for the one-pot synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted imidazoles under solvent-free conditions

In this work, magnetic nanoparticle-supported sulfonic acid (γ-Fe2O3-SO3H) is used as an efficient catalyst in the synthesis of 2,4,5-trisubstituted imidazoles and 1,2,4,5-tetrasubstituted imidazoles in a short time (40–70 min for trisubstituted imidazoles and 30–40 min for tetrasubstituted imidazoles) and high-purity products were obtained (92–98% for trisubstituted imidazoles and 94–98% for tetrasubstituted imidazoles) in simple multicomponent reactions. The structure of these products was confirmed via FT-IR and NMR. Green and recyclable catalysts, eco-friendly and solvent-free conditions, high catalytic activity, shorter reaction time, easy recovery by an external magnet, high purity, and excellent yields are some features of these reactions.

Selective N-Alkylation of Amines with DMC over Biogenic Cu-Zr Bimetallic Nanoparticles

Herein, we report the green synthesis of copper-zirconium bimetallic nanoparticles (Cu-Zr BNPs) from aqueous solutions using Azadirachta indica leaf extract as a reducing and stabilizing agent. The CuO, ZrO2 NP, and Cu-Zr BNP samples were characterized by X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy, and the morphologies of the samples were analyzed by high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction analysis (SAED). The synthesized Cu-Zr BNPs have been employed as efficient catalysts for the selective N-methylation of aromatic and aliphatic amines with dimethyl carbonate. The effect of process conditions on the percentage conversion of benzylamine with dimethyl carbonate as a model reaction has been investigated. The Cu-Zr bimetallic nanoparticle catalytic system in a 1:2 molar ratio was able to convert amines into the corresponding N-methylated amines with a selectivity up to 91% at 180 °C in 4 h. The analysis of catalytic reusability confirmed that the reported heterogeneous catalyst can be used for five consecutive cycles without much loss in activity. Thus, the current protocol can be considered as a simpler, reproducible, and environmentally benign approach for N-methylation of amines.

MOF-derived zirconia-supported Keggin heteropoly acid nanoporous hybrids as a reusable catalyst for methyl oleate production

In this study, a series of nanoporous HSiW@ZrO2 hybrids were synthesized using a zirconium metal-organic framework UiO-66 as a precursor towards biodiesel production. The structural and morphological properties of the obtained hybrids were characterized by the wide-angle XRD, FTIR, SEM, TEM, N2 adsorption/desorption, and NH3-TPD methods. Moreover, their catalytic activity in terms of calcination temperature during preparation was investigated, and the HSiW@ZrO2 hybrids calcinated at 300 °C exhibited the highest activity and the oleic acid (OA) conversion of 94.0% owing to the presence of the relatively high surface area, appropriate pore size and strong acidity. It was also revealed that the hybrids maintained as high as 82.0% even after nine cycles. Intriguingly, the nanoporous catalysts were found to exhibit excellent catalytic activity towards the esterification of the high acid value of Jatropha curcas oil.