Mohamed B. Zakaria

Reduced graphene oxide nanosheets decorated with Au, Pd and Au–Pd bimetallic nanoparticles as highly efficient catalysts for electrochemical hydrogen generation

Reduced graphene oxide (rGO) nanosheets decorated with gold nanoparticles (Au NPs/rGO), palladium nanoparticles (Pd NPs/rGO), and gold–palladium bimetallic nanoparticles (Au–Pd NPs)/rGO are synthesized by a simple solution chemistry approach using ascorbic acid as an eco-friendly reducing agent. These materials are characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-angle annular diffraction field-scanning transmission electron microscopy (HAADF-STEM) and thermogravimetric analysis (TGA). The as-prepared nanocomposites are tested as electrocatalysts for efficient hydrogen evolution in deaerated 0.5 M H2SO4 aqueous solution using polarization and impedance measurements. Experimental findings show that the tested catalysts exhibit fast hydrogen evolution kinetics with onset potentials as low as −17, −7.2, and −0.8 mV vs. RHE for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. In addition, Tafel slopes of 39.2, 33.7 and 29.0 mV dec−1 and exchange current densities of 0.09, 0.11, and 0.47 mA cm−2 are measured for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. The tested materials not only maintain their high performance after 5000 sweep cycles, but their activity is simultaneously enhanced after this aging process. These findings reveal that the tested catalysts, particularly Au–Pd NPs/rGO, are promising candidates among other noble metal catalysts for hydrogen evolution, approaching the commercial Pt/C catalyst (onset potential: 0.0 mV, Tafel slope: 31 mV dec−1, and exchange current density: 0.78 mA cm−2). The high hydrogen evolution reaction (HER) activity of such materials is likely due to the abundance of active catalytic sites, the increased electrochemically accessible surface area and significantly improved electrochemical conductivity.

Controlled Synthesis of Nanoporous Nickel Oxide with Two‐Dimensional Shapes through Thermal Decomposition of Metal–Cyanide Hybrid Coordination Polymers

The urgent need for nanoporous metal oxides with highly crystallized frameworks is motivating scientists to try to discover new preparation methods, because of their wide use in practical applications. Recent work has demonstrated that two-dimensional (2D) cyanide-bridged coordination polymers (CPs) are promising materials and appropriate for this purpose (Angew. Chem. Int. Ed.- 2013, 52, 1235). After calcination, 2D CPs can be transformed into nanoporous metal oxides with a highly accessible surface area. Here, this strategy is adopted in order to form 2D nanoporous nickel oxide (NiO) with tunable porosity and crystallinity, using trisodium citrate dihydrate as a controlling agent. The presence of trisodium citrate dihydrate plays a key role in the formation of 2D nanoflakes by controlling the nucleation rate and the crystal growth. The size of the nanoflakes gradually increases by augmenting the amount of trisodium citrate dihydrate in the reaction. After heating the as-prepared CPs in air at different temperatures, nanoporous NiO can be obtained. During this thermal treatment, organic units (carbon and nitrogen) are completely removed and only the metal content remains to take part in the formation of nanoporous NiO. In the case of large-sized 2D CP nanoflakes, the original 2D flake-shapes are almost retained, even after thermal treatment at low temperature, but they are completely destroyed at high temperature because of further crystallization in the framework. Nanoporous NiO with high surface area shows significant efficiency and interesting results for supercapacitor application.

Self-Construction from 2D to 3D: One-Pot Layer-by-Layer Assembly of Graphene Oxide Sheets Held Together by Coordination Polymers.

Deposition of Ni-based cyanide bridged coordination polymer (NiCNNi) flakes onto the surfaces of graphene oxide (GO) sheets, which allows precise control of the resulting lamellar nanoarchitecture by in situ crystallization, is reported. GO sheets are utilized as nucleation sites that promote the optimized crystal growth of NiCNNi flakes. The NiCNNi-coated GO sheets then self-assemble and are stabilized as ordered lamellar nanomaterials. Regulated thermal treatment under nitrogen results in a Ni3 C-GO composite with a similar morphology to the starting material, and the Ni3 C-GO composite exhibits outstanding electrocatalytic activity and excellent durability for the oxygen reduction reaction.

Prussian Blue Derived Nanoporous Iron Oxides as Anticancer Drug Carriers for Magnetic‐Guided Chemotherapy

New nanoporous iron oxide nanoparticles with superparamagnetic behavior were successfully synthesized from Prussian blue (PB) nanocubes through a thermal conversion method and applied to the intracellular drug-delivery systems (DDS) of bladder cancer cells (i.e., T24) with controlled release and magnetic guiding properties. The results of the MTT assay and confocal laser scanning microscopy indicate that the synthesized iron oxide nanoparticles were successfully uptaken by T24 cells with excellent biocompatibility. An anticancer drug, that is, cisplatin, was used as a model drug, and its loading/release behavior was investigated. The intracellular drug delivery efficiency was greatly enhanced for the cisplatin-loaded, PB-derived, magnetic-guided drug-delivery system compared with the non-drug case. The synthesized nanomaterials show great potential as drug vehicles with high biocompatibility, controlled release, and magnetic targeting features for future intracellular DDS.

Single‐Crystal‐like Nanoporous Spinel Oxides: A Strategy for Synthesis of Nanoporous Metal Oxides Utilizing Metal‐Cyanide Hybrid Coordination Polymers

Development of a new method to synthesize nanoporous metal oxides with highly crystallized frameworks is of great interest because of their wide use in practical applications. Here we demonstrate a thermal decomposition of metal-cyanide hybrid coordination polymers (CPs) to prepare nanoporous metal oxides. During the thermal treatment, the organic units (carbon and nitrogen) are completely removed, and only metal contents are retained to prepare nanoporous metal oxides. The original nanocube shapes are well-retained even after the thermal treatment. When both Fe and Co atoms are contained in the precursors, nanoporous Fe-Co oxide with a highly oriented crystalline framework is obtained. On the other hand, when nanoporous Co oxide and Fe oxide are obtained from Co- and Fe-contacting precursors, their frameworks are amorphous and/or poorly crystallized. Single-crystal-like nanoporous Fe-Co oxide shows a stable magnetic property at room temperature compared to poly-crystalline metal oxides. We further extend this concept to prepare nanoporous metal oxides with hollow interiors. Core-shell heterostructures consisting of different metal-cyanide hybrid CPs are prepared first. Then the cores are dissolved by chemical etching using a hydrochloric acid solution (i.e., the cores are used as sacrificial templates), leading to the formation of hollow interiors in the nanocubes. These hollow nanocubes are also successfully converted to nanoporous metal oxides with hollow interiors by thermal treatment. The present approach is entirely different from the surfactant-templating approaches that traditionally have been utilized for the preparation of mesoporous metal oxides. We believe the present work proves a new way to synthesize nanoporous metal oxides with controlled crystalline frameworks and architectures.

Novel block copolymer templates for tuning mesopore connectivity in cage-type mesoporous silica films

Mesoporous silica films with large spherical mesopores are synthesized using new laboratory-made polystyrene-block-polybutadiene-block-polystyrene based triblock copolymers in which the polystyrene block is functionalized with hydrophilic sulfonic groups. When the relative weight of the copolymer to silica source is in the range from 10 to 70 mass%, spherical mesopores with uniform sizes can be formed in the films. In addition, when the ratio is lower than 20 mass%, spherical mesopores are separated by thick silica walls in the films. Nevertheless, owing to the presence of small-sized mesopores in the silica walls, all the spherical mesopores are accessible from the outside. With the gradual increase of the chosen copolymer/silica ratios, the distance between neighboring mesopores is reduced without a significant change of the original mesopore size, which has not been observed in previous reports using other block copolymers as templates.

Synthesis of Highly Strained Mesostructured SrTiO 3 /BaTiO 3 Composite Films with Robust Ferroelectricity

A new class of highly stable ferroelectric material, that is, a mesostructured SrTiO(3)/BaTiO(3) composite film, obtained by a surfactant-templated sol-gel method is reported. Due to the concave surface geometry and abundant hetero-interface between SrTiO(3) (ST) and BaTiO(3) (BT) phases, a large number of strains can be created in the composite film, thereby leading to dramatic enhancement of ferroelectric property (see scheme).

Synthesis of Nanoporous Ni-Co Mixed Oxides by Thermal Decomposition of Metal-Cyanide Coordination Polymers

A straightforward strategy to prepare nanoporous metal oxides with well-defined shapes is highly desirable. Through thermal treatment and a proper selection of metal-cyanide coordination polymers, nanoporous nickel-cobalt mixed oxides with different shapes (i.e., flakes and cubes) can be easily prepared. Our nanoporous materials demonstrate high electrocatalytic activity for oxygen evolution reaction.

Controlled Crystallization of Cyano-Bridged Cu–Pt Coordination Polymers with Two-Dimensional Morphology

Two-dimensional (2D) coordination polymers (CPs) have a highly accessible surface area that permits guest molecules to effectively access the micropores in the CPs. Here we report a bottom-up synthesis of 2D cyano-bridged Cu-Pt CP nanoflakes using trisodium citrate as a chelating agent, which controls the nucleation rate and the crystal growth. The lateral sizes of the CP nanoflakes are controlled by changing the amount of trisodium citrate used. We strongly believe that our method will be useful for the preparation of other types of 2D CP nanoflakes. The 2D CPs have many active sites for catalytic and electrochemical reactions, and furthermore the assembled CPs can be used as membrane filters.

Prussian blue derived iron oxide nanoparticles wrapped in graphene oxide sheets for electrochemical supercapacitors

Hybrid materials have shown promising potential for energy storage applications, such as supercapacitors due to the combined properties or advantages of two (or more) individual constituents. In this work, we report the fabrication of a new composite which combines graphene oxide (GO) sheets with Prussian blue (PB) nanoparticles, which act as a precursor for iron oxide (IO). The GO/PB composite precursors with different GO : PB ratios can be successfully converted into nanoporous GO/IO hybrid composites through a thermal treatment in air at 400 °C. In the resulting GO/IO composites, the GO sheets are efficiently spaced due to the insertion of IO layers. Interestingly, the GO/IO hybrid (GO : PB ratio = 25 : 75) exhibits a higher surface area of 120 m2 g−1 compared to pure GO (34.9 m2 g−1) and IO (93.1 m2 g−1) samples. When employed as a supercapacitor electrode, the GO/IO hybrid (prepared from GO : PB = 75 : 25) showed a higher specific capacitance of 91 F g−1 at a scan rate of 20 mV s−1, compared to pure GO (81 F g−1) and pure IO (47 F g−1). The enhanced electrochemical performance of the GO/IO hybrid electrode may be attributed to the insertion of IO nanoparticles in between the GO layers which creates a well-spaced electrical transportation path for electrolytes and ions, whilst also enabling easy access for the electrolytes to the whole electrode surface. Furthermore, the presence of GO in the GO/IO hybrid composite helps to lower the resistivity of IO and increase the specific capacitance value of the hybrid, as a result of the improved conductivity.