Khaled M. AbouZeid

Microwave synthesis of graphene sheets supporting metal nanocrystals in aqueous and organic media

We have developed a facile and scalable chemical reduction method assisted by microwave irradiation for the synthesis of chemically converted graphene sheets and metal nanoparticles dispersed on the graphene sheets. The method allows rapid chemical reduction of exfoliated graphite oxide (GO) using a variety of reducing agents in either aqueous or organic media. It also allows the simultaneous reduction of GO and a variety of metal salts thus resulting in the dispersion of metallic and bimetallic nanoparticles supported on the large surface area of the thermally stable 2D graphene sheets.

Growth mechanism of anisotropic gold nanocrystals via microwave synthesis: formation of dioleamide by gold nanocatalysis.

A facile and fast one-pot microwave irradiation method has been developed to prepare different shapes of gold nanoparticles capped with a mixture of oleylamine and oleic acid. The size, shape, and morphology of the nanocrystals could be tailored by varying the ratio of oleylamine to oleic acid, the microwave time, and the concentration of the gold ions. These effects are directly reflected in the surface plasmon resonance properties of the resulting nanocrystals in the visible and near-infrared regions. Pure amine leads to the formation of only spherical particles. Introducing oleic acid increases the growth rate and enhances the formation of anisotropic shapes. Experimental evidence and new insights on the reaction mechanism confirm the formation of dioleamide from the reaction of oleic acid and oleylamine catalyzed by the gold nanocrystals. In the absence of gold nanoparticles, the conventional synthesis of dioleamide requires 12 h of reaction time at 120 degrees C. New insights on the reaction mechanism indicate that excess oleic acid enhances the formation of hexagons and more anisotropic shapes of the gold nanocrystals.

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.

Hybrid Au–CdSe and Ag–CdSe Nanoflowers and Core–Shell Nanocrystals via One‐Pot Heterogeneous Nucleation and Growth

A general approach, based on heterogeneous nucleation and growth of CdSe nanostructures on Au or Ag nanocrystals, for the synthesis of Au-CdSe and Ag-CdSe hybrid nanostructures is developed. The new approach provides a versatile one-pot route for the synthesis of hybrid nanoflowers consisting of a gold or silver core and multipod CdSe rods or an intact CdSe shell with controlled thickness, depending on the nucleation and growth parameters. At lower growth temperatures such as 150 °C, the CdSe clusters are adsorbed on the surface of the metal cores in their surface defects, then multiple arms and branches form, resulting in nanoflower-shaped hybrid structures. Increasing the size of the metal core through the choice of the reducing and capping agents results in an improvement of the interface between the metal and CdSe domains, producing core-shell structures. The growth temperature appears to be the most important factor determining the nature of the interface between the metal and CdSe domains. At relatively high temperatures such as 300 °C, the formation of large, faceted Au cores creates preferential growth sites for the CdSe nanocrystalline shell, thus resulting in well-defined Au-CdSe core-shell structures with large interfaces between the Au and CdSe domains. The present approach is expected to foster systematic studies of the electronic structures and optical properties of the metal-semiconductor hybrid materials for potential applications in photovoltaic and nanoelectronic devices.

Efficient Removal of Heavy Metals from Polluted Water with High Selectivity for Mercury(II) by 2-Imino-4-thiobiuret–Partially Reduced Graphene Oxide (IT-PRGO)

A novel chelating adsorbent, based on the chemical modification of graphene oxide by functionalization amidinothiourea to form 2-imino-4-thiobiuret-partially reduced graphene oxide (IT-PRGO), is used for the effective extraction of the toxic metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) from wastewater. FTIR and Raman spectroscopy, XRD, and XPS confirm the successful incorporation of the amidinothiourea groups within the partially reduced GO nanosheets through nucleophilic substitution reactions with the acyl chloride groups in the chemically modified GO. The IT-PRGO adsorbent shows exceptional selectivity for the extraction of Hg(II) with a capacity of 624 mg/g, placing it among the top of carbon-based materials known for the high capacity of Hg(II) removal from aqueous solutions. The maximum sorption capacities for As(V), Cu(II), Cr(VI), and Pb(II) are 19.0, 37.0, 63.0, and 101.5 mg/g, respectively. The IT-PRGO displays a 100% removal of Hg(II) at concentrations up to 100 ppm with 90%, 95%, and 100% removal within 15, 30, and 90 min, respectively, at 50 ppm concentration. In a mixture of six heavy metal ions containing 10 ppm of each ion, the IT-PRGO shows a removal of 3% Zn(II), 4% Ni(II), 9% Cd(II), 21% Cu(II), 63% Pb(II), and 100% Hg(II). A monolayer adsorption behavior is suggested based on the excellent agreement of the experimental sorption isotherms with the Langmuir model. The sorption kinetics can be fitted well to a pseudo-second-order kinetic model which suggests a chemisorption mechanism via the amidinothiourea groups grafted on the reduced graphene oxide nanosheets. Desorption studies demonstrate that the IT-PRGO is easily regenerated with the desorption of the metal ions Hg(II), Cu(II), Pb(II), Cr(VI), and As(V) reaching 96%, 100%, 100%, 96%, and 100%, respectively, from their maximum sorption capacities using different eluents. The IT-PRGO is proposed as a top performing remediation adsorbent for the extraction of heavy metals from waste and polluted water.

Palladium Nanoparticles Supported on a Metal–Organic Framework‐Partially Reduced Graphene Oxide Hybrid for the Catalytic Hydrodeoxygenation of Vanillin as a Model for Biofuel Upgrade Reactions

In this work we report a new strategy to enhance the catalytic activity and selectivity in heterogeneous catalysis by using a hybrid support that consists of metal–organic framework (MOF) crystals and partially reduced graphene oxide (PRGO) nanosheets to disperse metal nanoparticle catalysts efficiently. We report the development of a Pd nanocatalyst incorporated within a 3 D hierarchical nanocomposite that consists of a Ce‐based MOF wrapped with thin PRGO nanosheets, Pd/PRGO/Ce‐MOF, as a heterogeneous tandem catalyst for the hydrodeoxygenation of vanillin, a common component in lignin‐derived bio‐oil, under mild reaction conditions. Our results demonstrate that the PRGO/Ce‐MOF hybrid scaffold is an excellent support for Pd nanoparticles for the transformation of vanillin into 2‐methoxy‐4‐methyl phenol, an important high‐value phenol compound that can be used directly in the chemical and pharmaceutical industries. The high catalytic performance of the Pd/PRGO/Ce‐MOF catalyst is attributed to the unique characteristics of the incorporation of the PRGO support that leads not only to a stable and uniform dispersion of the Pd nanoparticles but also to the presence of acidic active sites that promote the hydrogenolysis reaction.

Microwave Synthesis of Metal Oxide Nanoparticles

This chapter summarizes microwave irradiation methods for the preparation of metal oxide nanoparticles and their catalytic and sensing properties and applications. Microwave irradiation provides rapid decomposition of metal precursors and can be extended for synthesis of a wide range of metal oxide nanoparticles with various compositions, sizes and shapes. This chapter introduces the microwave method and describes the nucleation and growth process for the formation nanocrystals. We offer a broad overview of metal oxide nanostructures synthesized by microwave irradiation including: ZnO, TiO2, CeO2, other rare earth metal oxides, transitional metal oxides and metal ferrite nanostructures. Finally, we describe the application of metal oxides in the photocatalytic degradation of organic dyes and gas sensing devices.