Ni Nanoparticles on the Reduced Graphene Oxide Surface Synthesized in Supercritical Isopropanol

Nanocomposites based on ferromagnetic nickel nanoparticles and graphene-related materials are actively used in various practical applications such as catalysis, sensors, sorption, etc. Therefore, maintaining their dispersity and homogeneity during deposition onto the reduced graphene oxide substrate surface is of crucial importance to provide the required product characteristics. This paper demonstrates a new, reproducible method for preparing a tailored composite based on nickel nanoparticles on the reduced graphene oxide surface using supercritical isopropanol treatment. It has been shown that when a graphene oxide film with previously incorporated Ni2+ salt is treated with isopropanol at supercritical conditions, nickel (2+) is reduced to Ni (0), with simultaneous deoxygenation of the graphene oxide substrate. The resulting composite is a solid film exhibiting magnetic properties. XRD, FTIR, Raman, TEM, and HRTEM methods were used to study all the obtained materials. It was shown that nickel nanoparticles on the surface of the reduced graphene oxide had an average diameter of 27 nm and were gradually distributed on the surface of reduced graphene oxide sheets. The data obtained allowed us to conduct a reconnaissance discussion of the mechanism of composite fabrication in supercritical isopropanol.

Magnetically separable nickel ferrite supported palladium nanoparticles: Highly reusable catalyst in Sonogashira cross-coupling reaction

There is an increasing attention in developing highly efficient and reusable palladium-based catalysts used for the coupling reactions due to the high cost of palladium metal salts. Magnetically separable palladium nanoparticles have a high potential to be used as catalysts in numerous organic reactions due to their facile separation from the reaction medium by an external magnet. Herein, NiFe₂O₄ supported palladium nanoparticles (Pd/NiFe₂O₄) were successfully prepared by impregnation and reduction method in water and used as catalysts for Sonogashira cross-coupling reactions. Magnetically separable Pd/NiFe₂O₄ catalysts were found to be highly active and reusable in this reaction. Pd/NiFe₂O₄ provided an outstanding turnover frequency value (106.4 h^-1) in the reaction between phenylacetylene and iodobenzene in ethanol at 70 °C and it was also found to be highly active in the water. Magnetically separable Pd/NiFe₂O₄ exhibited high catalytic performance even after the tenth use in this reaction.

Study of Barium Adsorption from Aqueous Solutions Using Copper Ferrite and Copper Ferrite/rGO Magnetic Adsorbents

The development of advanced materials for the removal of heavy metal ions is a never-ending quest of environmental remediation. In this study, a facile and cost-effective approach was employed to synthesize copper ferrite (CF) and copper ferrite/reduced graphene oxide (CG) by microwave assisted combustion method for potential removal of barium ions from aqueous medium. The physiochemical characterizations indicated the formation of magnetic nanocomposite with an average crystallite size of CF and CG is 32.4 and 30.3 nm and with specific surface area of 0.66 and 5.74 m2/g. The magnetic results possess multidomain microstructures with saturation magnetization of 37.11 and 33.84 emu/g for CF and CG. The adsorption studies prove that upon addition of rGO on the spherical spinel ferrite, the adsorption performance was greatly improved for CG nanocomposite when compared with the bare CF nanoparticles. The proposed magnetic adsorbent demonstrated a relatively high Ba2+ adsorption capacity of 161.6 mg·g-1 for CG nanocomposite when compared to 86.6 mg·g-1 for CF nanoparticles under optimum conditions ( $\text{pH}=7;T={25}^{°}\text{C}$ ). The pseudo-first-order (PFO), pseudo-second-order (PSO), and Elovich models were fitted to the kinetic data, the yielded $R^2$ value of 0.9993 (PSO) for CF and 0.9994 (PSO) for CG which is greater than the other two models, which signify that the adsorption process is chemisorption. Thermodynamic studies show that barium adsorption using CF and CG adsorbents is endothermic. The as-fabricated CuFe2O4/rGO nanocomposite represents a propitious candidate for the removal of heavy metal ions from aqueous solutions.

Magnetic nickel nanostructure as cellulase immobilization surface for the hydrolysis of lignocellulosic biomass

In this research, a magnetic reusable nickel nanoparticle (NiNPs) supporting materials were prepared for cellulase enzyme immobilization. The immobilized cellulase showed high activity recovery, large & fast immobilization capacity and improved pH & temperature tolerance. The excellent stability and reusability enabled the immobilized cellulase to retain 84% of its initial activity after ten cycles. At 2 mg/mL enzyme concentration, highest 93% immobilization efficiency was achieved within two hours of immobilization. When the treatment temperature reached 40 °C and pH 5, the immobilized cellulase exhibited highest residual activity. The immobilized cellulase could be separated from the solution by a magnetic force. This study introduced a novel supporting material for cellulase immobilization, and the immobilized cellulase poses a great potential in the hydrolysis of lignocellulosic biomass which can used as an easily applicable and sustainable pre-treatment step for advanced biofuel production.

Cucurbit[6]uril supported β-Ni(OH)2 nanoparticles as a heterogeneous catalyst for the synthesis of quinazolines via acceptorless dehydrogenative coupling of alcohols with nitriles

Synthesis of a series of quinazolines using β-Ni(OH)2-CB[6] as a heterogeneous nanocatalyst.

Insights into Cascade and Sequential one pot pathways for reductive amination of aldehydes paired with bio-derived levulinic acid to N-substituted pyrrolidones using molecular hydrogen

This work aims to explore cascade and sequential one pot syntheses pathways for N-substituted pyrrolidones from aryl aldehydes and bio-derived levulinic acid (LA) using molecular hydrogen and ammonia. This process...

Magnetic Nanoparticle Composites: Synergistic Effects and Applications

Composite materials are made from two or more constituent materials with distinct physical or chemical properties that, when combined, produce a material with characteristics which are at least to some degree different from its individual components. Nanocomposite materials are composed of different materials of which at least one has nanoscale dimensions. Common types of nanocomposites consist of a combination of two different elements, with a nanoparticle that is linked to, or surrounded by, another organic or inorganic material, for example in a core-shell or heterostructure configuration. A general family of nanoparticle composites concerns the coating of a nanoscale material by a polymer, SiO2 or carbon. Other materials, such as graphene or graphene oxide (GO), are used as supports forming composites when nanoscale materials are deposited onto them. In this Review we focus on magnetic nanocomposites, describing their synthetic methods, physical properties and applications. Several types of nanocomposites are presented, according to their composition, morphology or surface functionalization. Their applications are largely due to the synergistic effects that appear thanks to the co-existence of two different materials and to their interface, resulting in properties often better than those of their single-phase components. Applications discussed concern magnetically separable catalysts, water treatment, diagnostics-sensing and biomedicine.

Nickel catalysts in Sonogashira coupling reactions

Nickel has emerged as a desirable substitute for palladium in Sonogashira coupling reactions due to its abundance, less toxicity and high catalytic activity. Ni complexes have been developed to catalyse C(sp)-C(sp2) and C(sp)-C(sp3) Sonogashira couplings that find applications in the synthesis and modifications of biologically relevant molecules. This review focuses on the catalytic potential and mechanistic details of various Ni complexes employed in the Sonogashira coupling. These include homogeneous catalytic systems with Ni-phosphorus and Ni-nitrogen catalysts, ligand-free catalysts, and carbonylative coupling strategies. Various heterogeneous catalytic systems using supported Ni complexes, Ni nanoparticles and Pd-Ni bimetallic catalysts have also been discussed. This is the first review reported so far dealing exclusively with Ni-catalysed Sonogashira coupling reactions. This review illustrates the current strategies and potential of Ni-catalysed Sonogashira coupling reactions in both homogeneous and heterogeneous systems, and covers the literature up to 2020.

Novel magnetic lignosulfonate-supported Pd complex as an efficient nanocatalyst for N-arylation of 4-methylbenzenesulfonamide

This study presents a novel, economical, and environmentally technique for synthesizing magnetic palladium complex conjugated to activated calcium lignosulfonate with triethylenetetramine (Fe₃O₄@lignosulfonate@triethylenetetramine@Pd complex (FLT-Pd complex)) as a practical and air-stable catalyst. FLT-Pd complex is used as a catalyst for the fabrication of 4-methyl-N-phenyl-benzenesulfonamide derivatives via N-arylation of 4-methylbenzenesulfonamide in good yields. Furthermore, because of the complex magnetic reparability and high stability, it could be removed easily from the reaction media using a magnet and reused 5 cycles without a remarkable loss of catalytic prowess.

Green synthesis of graphene oxide (GO)-anchored Pd/Cu bimetallic nanoparticles using Ocimum sanctum as bio-reductant: an efficient heterogeneous catalyst for the Sonogashira cross-coupling reaction

Here we report the synthesis and characterization of graphene oxide anchored Pd–Cu bimetallic nanoparticles by bio reduction method and its application in Sonogashira cross-coupling reaction.

Ni nanoparticle supported reduced graphene oxide as a highly active and durable heterogeneous material for coupling reactions

We report the loading of highly air stable Ni(0) nanoparticles (average particle size = 11 nm) on the surface of a reduced graphene oxide (RGO) material. The material was characterized using different techniques, including Raman spectroscopy, XRD, TEM, SEM, and HRTEM analysis. The Ni(0)@RGO catalyst showed superb efficiency towards Kumada-Corriu C-C cross-coupling reactions, with 92% yield of 4-methoxybiphenyl at 60 °C. The recycled material can be reused up to the 5^th cycle after regeneration by calcination, without loss of activity.

Ni nanoparticles on RGO as reusable heterogeneous catalyst: effect of Ni particle size and intermediate composite structures in C-S cross-coupling reaction

The present work demonstrates the C–S cross-coupling reaction between aryl halides and thiols using nickel nanoparticles (Ni NPs) supported on reduced graphene oxide (Ni/RGO) as a heterogeneous catalyst. It is observed that the uniformly dispersed Ni NPs supported on RGO could exhibit excellent catalytic activity in C–S cross-coupling reactions and the catalytic application is generalized with diverse coupling partners. Although the electron-rich planar RGO surface helps in stabilizing the agglomeration-free Ni NPs, the catalytic process is found to occur involving Ni(II) species and the recovered catalyst containing both Ni(0)/Ni(II) species is equally efficient in recycle runs. A correlation of loading of Ni species, size of NPs and the intermediate Ni-related heterostructures formed during the catalytic process has been established for the first time, and found to be best in the C–S cross-coupling reaction for Ni(0) and Ni(II) NPs of the average sizes 11–12 nm and 4 nm, respectively.

Cu nanoparticles immobilized on montmorillonite by biquaternary ammonium salts: a highly active and stable heterogeneous catalyst for cascade sequence to indole-2-carboxylic esters

Cu-Q-MMT catalyst was prepared by immobilizing Cu nanoparticals on the biquaternary ammonium salts modified montmorillonite and exhibited high activity for cascade sequence to indole-2-carboxylic esters.

Ni Nanoparticles Supported on Cage-Type Mesoporous Silica for CO2 Hydrogenation with High CH4 Selectivity

Ni nanoparticles (around 4 nm diameter) were successfully supported on cage-type mesoporous silica SBA-16 (denoted as Ni@SBA-16) via wet impregnation at pH 9, followed by the calcination-reduction process. The Ni@SBA-16 catalyst with a very high Ni loading amount (22.9 wt %) exhibited exceptionally high CH4 selectivity for CO2 hydrogenation. At a nearly identical loading amount, the Ni@SBA-16 catalysts with smaller particle size of Ni NPs surprisingly exhibited a higher catalytic activity of CO2 hydrogenation and also led to a higher selectivity on CH4 formation than the Ni@SiO2 catalysts. This enhanced activity of the Ni@SBA-16 catalyst is suggested to be an accumulative result of the advantageous structural properties of the support SBA-16 and the well confined Ni NPs within the support; both induced a favorable reaction pathway for high selectivity of CH4 in CO2 hydrogenation.