Sherif Moussa

Ultrasmall Gold Nanoparticles Anchored to Graphene and Enhanced Photothermal Effects by Laser Irradiation of Gold Nanostructures in Graphene Oxide Solutions

In this work we demonstrate the coupling of the photothermal effects of gold nanostructures of controlled size and shape with graphene oxide nanosheets dispersed in water. The enhanced photothermal effects can be tuned by controlling the shape and size of the gold nanostructures, which result in a remarkable increase in the heating efficiency of the laser-induced size reduction of gold nanostructures. The Raman spectra of the Au-graphene nanosheets provide direct evidence for the presence of more structural defects in the graphene lattice induced by laser irradiation of graphene oxide nanosheets in the presence of Au nanostructures. The large surface areas of the laser-reduced graphene oxide nanosheets with multiple defect sites and vacancies provide efficient nucleation sites for the ultrasmall gold nanoparticles with diameters of 2-4 nm to be anchored to the graphene surface. This defect filling mechanism decreases the mobility of the ultrasmall gold nanoparticles and, thus, stabilizes the particles against the Ostwald ripening process, which leads to a broad size distribution of the laser-size-reduced gold nanoparticles. The Au nanostructures/graphene oxide solutions and the ultrasmall gold-graphene nanocomposites are proposed as promising materials for photothermal therapy and for the efficient conversion of solar energy into usable heat for a variety of thermal, thermochemical, and thermomechanical applications.

Highly efficient electron field emission from graphene oxide sheets supported by nickel nanotip arrays.

Electron field emission is a quantum tunneling phenomenon whereby electrons are emitted from a solid surface due to a strong electric field. Graphene and its derivatives are expected to be efficient field emitters due to their unique geometry and electrical properties. So far, electron field emission has only been achieved from the edges of graphene and graphene oxide sheets. We have supported graphene oxide sheets on nickel nanotip arrays to produce a high density of sharp protrusions within the sheets and then applied electric fields perpendicular to the sheets. Highly efficient and stable field emission with low turn-on fields was observed for these graphene oxide sheets, because the protrusions appear to locally enhance the electric field and dramatically increase field emission. Our simple and robust approach provides prospects for the development of practical electron sources and advanced devices based on graphene and graphene oxide field emitters.

Laser assisted photocatalytic reduction of metal ions by graphene oxide

This work provides a new approach for the solution processable synthesis of metal–graphene oxide nanocomposites in aqueous solutions at ambient conditions. Using 532 nm laser or tungsten lamp irradiation of a mixture of graphene oxide (GO) and metal ions derived from HAuCl4 or AgNO3 we report the photocatalytic reduction of the metal ions simultaneously with partial reduction of GO, and the synthesis of metal–graphene nanocomposites. The gold and silver ions are reduced following the laser or the tungsten lamp irradiation of GO for a few minutes in water–ethanol, water–polyethylene glycol (PEG) or pure water solvents. The reduction of GO in the presence of ethanol or PEG is much faster than in pure water under identical experimental conditions. This is attributed to the role of ethanol or PEG in scavenging the holes generated by the irradiation of GO thus leaving the photogenerated electrons to reduce GO. In pure water in the presence of gold ions, partial reduction of GO occurs due to the efficient capturing of the photogenerated electrons in GO by the gold ions and the strong absorption of the 532 nm photons by the newly formed Au nanoparticles. Strong photothermal effects are observed leading to a significant increase in the temperature of the solution and suggesting that metal–graphene nanocomposites could be promising materials for the efficient conversion of solar energy into usable heat for a variety of thermal, thermochemical and thermomechanical applications.

Microwave-assisted synthesis of Pd nanoparticles supported on Fe3O4, Co3O4, and Ni(OH)2 nanoplates and catalysis application for CO oxidation

AbstractIn this paper, we report a simple, versatile, and rapid method for the synthesis of Pd nanoparticle catalysts supported on Fe3O4, Co3O4, and Ni(OH)2 nanoplates via microwave irradiation. The important advantage of microwave dielectric heating over convective heating is that the reactants can be added at room temperature (or slightly higher temperatures) without the need for high-temperature injection. Furthermore, the method can be used to synthesize metal nanoparticle catalysts supported on metal oxide nanoparticles in one step. We also demonstrate that the catalyst-support interaction plays an important role in the low temperature oxidation of CO. The current results reveal that the Pd/Co3O4 catalyst has particularly high activity for CO oxidation as a result of the strong interaction between the Pd nanoparticles and the Co3O4 nanoplates. Optimizations of the size, composition, and shape of these catalysts could provide a new family of efficient nanocatalysts for the low temperature oxidation of CO.

The Effect of Graphene on Catalytic Performance of Palladium Nanoparticles Decorated with Fe3O4, Co3O4, and Ni (OH)2: Potential Efficient Catalysts Used for Suzuki Cross—Coupling

In this research, we report a scientific investigation of an efficient method used for the synthesis of highly active Palladium Nanoparticles decorated with Fe3O4, Co3O4, and Ni (OH)2 Supported on Graphene as Potential Efficient Catalysts for Suzuki Cross—Coupling. Pd/Fe3O4 nanoparticles supported on graphene nanosheets (Pd/Fe3O4/G) showed an excellent catalytic activity for Suzuki coupling reactions and recycled for up to four times without loss of catalytic activity. An efficient magnetic catalyst has been successfully synthesized using a simple, reproducible fast and reliable method using microwave irradiation conditions. The prepared catalysts are magnetic as in case of iron and cobalt oxides which is an advantage in the separation process of catalyst from the reaction medium via applying a strong external magnetic field. The synthesis approach is based on the Microwave (MW)-assisted simultaneous reduction of palladium and ferric nitrates in the presence of graphene oxide (GO) nanosheets using hydrazine hydrate as the reducing agent. The results provide a fundamental understanding of the system variables by comparing the catalytic activity and recyclability of different catalysts with different properties. The most active and recyclable catalyst was Pd–Fe3O4—supported on graphene which offers several added advantages including recyclability of up to seven times, mild reaction conditions, and short reaction times in an environmentally benign solvent system. Furthermore, the magnetic properties imparted by the Fe3O4 component of the catalyst enables the catalyst to be easily isolated and recycled, thus greatly simplifying the ability to purify the reaction products and increasing the economic value of the catalyst. The utility of these magnetic catalysts towards Suzuki cross coupling reaction was also demonstrated. The high activity and recyclability of these catalysts are attributed to a strong catalyst-support interaction where the defect sites in the reduced GO nanosheets act as nucleation centers for anchoring the Pd and Fe3O4 nanoparticles thus minimizing the potential of their agglomeration and the subsequent decrease in the catalytic activity.Graphical Abstract

The continuous synthesis of Pd supported on Fe3O4 nanoparticles: a highly effective and magnetic catalyst for CO oxidation

Abstract We report a facile approach used for the simultaneous reduction and synthesis of a well dispersed magnetically separable palladium nanoparticle supported on magnetite (Pd/Fe3O4 nanoparticles) via continuous flow synthesis under microwave irradiation conditions, using a Wave Craft’s microwave flow reactor commercially known as ArrheniusOne, which can act as a unique process for the synthesis of highly active catalysts for carbon monoxide (CO) oxidation catalysis. The prepared catalysts are magnetic, which is an advantage in the separation process of the catalyst from the reaction medium. The separation process is achieved by applying a strong external magnetic field which makes the separation process easy, reliable, and environmentally friendly. Hydrazine hydrate was used as the reducing agent under continuous flow reaction conditions. The investigated catalysis data revealed that palladium supported on iron oxide catalyst synthesized by continuous flow microwave irradiation conditions showed remarkable high catalytic activity towards CO oxidation compared to the ones that were prepared by batch reaction conditions under the same experimental conditions. This could be attributed to the high degree of dispersion and concentration ratio of the Pd nanoparticles dispersed on the surface of magnetite (Fe3O4) with a small particle size of 5–8 nm due to the effective microwave-assisted reduction method under continuous flow conditions. These nanoparticles were further characterized by a variety of spectroscopic techniques including X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM).