Mahmud Diab

Studying the chemical, optical and catalytic properties of noble metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanostructures grown via a general approach

We studied the chemical, optical and catalytic properties of metal (Pt, Pd, Ag, Au)–Cu2O core–shell nanoparticles grown via a simple and reproducible approach which utilizes aqueous-phase reactions at room temperature. We were able to control the thickness of the Cu2O shell and examine the effect of the cores shape and size on the structure and properties of the hybrid nanocrystals. We also studied the optical properties of the hybrid nanocrystals, in particular the effect of the Cu2O shell thickness on the frequency of the plasmon of gold nanorods. In addition, the catalytic activity of the hybrid nanostructures was examined by testing the reduction reaction of 4-nitrophenol with NaBH4. Finally, the hybrid metal–Cu2O nanostructures were used as templates to form the yolk–shell of metal–Cu2S materials. The interface and the crystalline structures of the four hybrid nanostructures were extensively characterized by high resolution transmission electron microscopy (HRTEM), energy-filtered TEM (EFTRM) and X-ray diffraction (XRD).

A facile one-step approach for the synthesis and assembly of copper and copper-oxide nanocrystals

A simple one-step approach for the formation of close packed films of copper and copper oxide nanoparticles is described. Thermal decomposition of copper cupferrate, a single-source precursor, on silicon produces a well-controlled, assembled film of Cu nanocrystals. Upon oxidation, Cu2O is formed with retention of the assembly. Similarly, the thermal decomposition of manganese cupferrate results in the formation of porous MnO nanowires. Various solvents were used to examine their influence on the composition and assembly of the nanoparticles. This approach enables an easy and reproducible process for the synthesis and assembly of metal oxide nanostructures.

Thermal decomposition approach for the formation of α-Fe2O3 mesoporous photoanodes and an α-Fe2O3/CoO hybrid structure for enhanced water oxidation.

Hematite (α-Fe2O3) is one of most investigated oxides for energy applications and specifically for photocatalysis. Many approaches are used to prepare well-controlled films of hematite with good photocatalytic performance. However, most of these methods suffer from a number of disadvantages, such as the small quantities of the product, and the assembly of the nanostructures is usually a secondary process. Herein, we present a facile and large-scale synthesis of mesoporous hematite structures directly on various substrates at moderate temperature and study their photoelectrochemical (PEC) properties. Our approach is based on thermal decomposition of iron acetate directly on a substrate followed by an annealing process in air to produce a continuous mesoporous film of α-Fe2O3, with good control of the size of the pores. Improving the PEC properties of iron oxide was achieved by deposition of CoO domains, which were formed by thermal decomposition of cobalt acetate directly onto the hematite surface to produce α-Fe2O3/CoO nanostructures. PEC measurements of the hematite film before and after CoO growth were tested. Two methods were used to deposit the cobalt material: (a) thermal decomposition and (b) the most typically used method, adsorption of cobalt salt. The photocurrent of pure hematite was 0.25 mA/cm(2) at 1.23 V versus reversible hydrogen electrode (RHE), while modification of the hematite surface using the thermal decomposition method showed 180% improvement (0.7 mA/cm(2) at 1.23 V vs RHE) and 40% improvement (0.35 mA/cm(2) at 1.23 V vs RHE) via the adsorption method. Moreover, the onset potential was shifted by 130 and 70 mV when the surface of the hematite was modified by the thermal decomposition and adsorption methods, respectively.

Coating and enhanced photocurrent of vertically aligned zinc oxide nanowire arrays with metal sulfide materials.

Hybrid nanostructures combining zinc oxide (ZnO) and a metal sulfide (MS) semiconductor are highly important for energy-related applications. Controlled filling and coating of vertically aligned ZnO nanowire arrays with different MS materials was achieved via the thermal decomposition approach of single-source precursors in the gas phase by using a simple atmospheric-pressure chemical vapor deposition system. Using different precursors allowed us to synthesize multicomponent structures such as nanowires coated with alloy shell or multishell structures. Herein, we present the synthesis and structural characterization of the different structures, as well as an electrochemical characterization and a photovoltaic response of the ZnO-CdS system, in which the resulting photocurrent upon illumination indicates charge separation at the interface.

Selective growth of metal sulfide tips onto cadmium chalcogenide nanostructures

We demonstrate a general approach for growing selectively semiconductor nanocrystals onto the edges of elongated Cd–chalcogenide nanostructures. Our approach utilizes the thermal decomposition of metal bisdiethyldithiocarbamate precursors to achieve selective growth onto cadmium chalcogenide nanostructures.

Highly luminescent CuGaxIn1−xSySe2−y nanocrystals from organometallic single-source precursors

The solution-based thermolysis of the organometallic single-source precursors [(iPr3PCu)4(MeGa)4S6] (1) and [(iPr3PCu)4(MeIn)4Se6] (2) is investigated. Multinary semiconductor nanocrystals with sizes in the range of 3–10 nm are obtained by a simple heating-up process in a solvent mixture of long-chain alkyl thiols and amines. The thiols also serve as a sulfur source and capping ligand for the nanoparticles. By mixing 1 and 2, nanocrystal compositions in the range from CuGaS2 to CuInSSe are accessible. Surface passivation of the nanocrystals with ZnS results in high stability and bright photoluminescence (PL). PL maxima are observed in the spectral range between 600 and 800 nm, depending on the size and composition of the nanocrystals. The highest PL quantum yields exceed 50% and are observed for a gallium to indium ratio of 1 : 5.

Electrophoretic deposition of single-source precursors as a general approach for the formation of hybrid nanorod array heterostructures

HYPOTHESIS Subjecting colloids to electric fields often results in (electrophoretic) deposition on conductive substrates. Dispersing a single-source precursor (SSP) of choice in an appropriate solvent, should allow its deposition on different substrates. The SSP-solvent interaction might play a role in the deposition (e.g., direction, rate, coverage). After thermal decomposition, the SSPs convert to the designed material, thus allowing formation of thin films or hybrid nanostructures. EXPERIMENTS Electrophoretic deposition (EPD) was applied on two representative SSPs in different solvents. These SSPs were deposited onto substrates covered with vertically-aligned ZnO nanorod (NR) arrays. After thermal decomposition, hybrid nanostructures were obtained and their morphology and interfaces were characterized by electron microscopy, X-ray diffraction, UV-vis, and electrochemistry. FINDINGS Tuning the organic dispersant-SSP interaction allows control over the final film morphology, which can result in coating and filling of NRs with metal-sulfides or metal-oxides after thermal decomposition of the SSP. These findings introduce a new facile method for a fast and large-scale uniform deposition of different (nanostructured) thin film semiconductors on a variety of substrates. We discuss the influence of the dispersant medium on the deposition of metallo-organic SSPs. As an example, the formed ZnO-CdS interface supports charge transfer upon illumination.

Bioinspired Hierarchical Porous Structures for Engineering Advanced Functional Inorganic Materials

Tremendous efforts have been directed at designing functional and well-defined 3D structures in recent decades. Many approaches have been devised and are currently used to create 3D structures, including lithography, 3D printing, assembly, and template-mediated (natural or synthetic) methods. Natural scaffolds offer some unique traits, as compared to their artificial counterparts, presenting highly ordered, porous, identical, abundant, and diverse structures. Various organisms, such as viruses, bacteria, diatoms, foraminifera, and others, are used as templates to form 3D structures. Herein, advancements made in using the shell of marine microorganisms, diatoms, and foraminifera, as scaffolds for designing functional 3D structures are reported. Furthermore, a succinct overview of various synthetic methods used to coat these scaffolds with inorganic materials (i.e., metals, metal oxides, and metal sulfides) is provided. Finally, the use of such fabricated functional 3D structures in a wide range of applications, such as catalysis, sensing, drug delivery, photo-electrochemical uses, batteries, and others, is considered.

Organic phase synthesis of noble metal-zinc chalcogenide core-shell nanostructures

Multi-component nanostructures have been attracting tremendous attention due to their ability to form novel materials with unique chemical, optical and physical properties. Development of hybrid nanostructures that are composed of metal-semiconductor components using a simple approach is of interest. Herein, we report a robust and general organic phase synthesis of metal (Au or Ag)-Zinc chalcogenide (ZnS or ZnSe) core-shell nanostructures. This synthetic protocol also enabled the growth of more compositionally complex nanostructures of Au-ZnSxSe1-x alloys and Au-ZnS-ZnSe core-shell-shell. The optical and structural properties of these hybrid nanostructures are also presented.

Insight into the formation mechanism of PtCu alloy nanoparticles

Different compositions of PtCu alloy nanoparticles were formed using one-pot synthesis. The effects of different reaction parameters (precursor type, precursor ratio, stabilizing agent concentration, and temperature) were studied. To achieve an insight into the formation mechanism, a kinetic study of time-evolution of the system was conducted, followed by a study of the influence of the precursor addition step. Studying the formation mechanism of alloy nanoparticles enables a better design of next-generation hybrid metal nano-catalysts.