Alp Yürüm

Significant improvement in the hydrogen storage capacity of a reduced graphene oxide/TiO2 nanocomposite by chemical bonding of Ti–O–C

A series of graphene-based nanocomposites with different TiO2 contents have been prepared via a facile chemical method. All nanocomposites were employed as hydrogen gas adsorption materials at room temperature and pressures up to 10 bar. The effect of dispersion state and size of the particles on the hydrogen storage capacity of nanocomposites was studied. The highest hydrogen uptake of 0.39 wt% was obtained among prepared nanocomposites and it is 125% higher than the hydrogen adsorption of the parent graphene material. This improvement can account for the presence of a high number of active sites needed for hydrogen molecules and the strong interaction between nanoparticles and graphene sheets.

SYNTHESIS OF MESOPOROUS MCM-41 MATERIALS WITH LOW-POWER MICROWAVE HEATING

Crystalline, high-surface-area, hexagonal mesoporous MCM-41 having uniform pore sizes and good thermal stability was successfully synthesized at 90°–120°C in 30 min using low-power microwave irradiation. This appears to be the first comprehensive and quantitative investigation of the comparatively rapid synthesis of mesoporous MCM-41 using low-power microwave heating of 80 W (90°C) and 120 W (120°C). The influence of reaction temperature and the duration of heating were carefully investigated, and the calcined MCM-41 materials were characterized by XRD, SEM, TEM, nitrogen adsorption, TGA, and FT-IR. The mesoporous MCM-41 product synthesized in 30 min at 120 W and calcined at 550°C had a very high surface area of 1438 m2/g and was highly ordered, containing uniform pores with diameters in the range of 3.5–4.5 nm. The wall thickness of the materials highly depended on the power of the microwave energy used during synthesis. Synthesis of the mesoporous MCM-41 products at 120°C resulted in a structure with thinner walls. The mesoporous MCM-41 materials synthesized in the present work had good thermal stability.

The effect of pH on the interlayer distances of elongated titanate nanotubes and their use as a Li-ion battery anode

Titanate nanotubes are promising materials for Li-ion battery anodes because of their special morphology and high specific surface areas. These titanates provide high rate capability and low volume expansion upon lithiation. More importantly, their tubular structure helps the transport of ions through the crystal. In this study, we synthesized elongated titanate nanotubes and modified their interlayer distances by changing the pH (2-13). For the structural characterization XRD, BET, SEM and TEM techniques were used. In addition, the effect of interlayer distance on energy capacity and rate capability was investigated. The highest interlayer distance was obtained at pH 10 and with decreasing pH, the interlayer distance dropped until reaching a pH value of 4. Conversely, the specific surface area reached its maximum value of 204 m(2) g(-1) at a pH of 4. Different from anatase (TiO2), titanate nanotubes had broad peaks in cyclic voltammograms suggesting a pseudocapacitive behavior. The sloping profiles of potential-capacity results also supported the pseudocapacitive property. For the titanate nanotubes obtained at pH 10, an initial discharge capacity of 980 mAh g(-1) was achieved. More importantly, titanate nanotubes showed exceptional rate capabilities and the capacities stayed almost constant at high current rates because of their elongated structure. It was found that the interlayer distance and the elongated structure play an important role in the electrochemical performance of the material.

Homogeneous growth of TiO2-based nanotubes on nitrogen-doped reduced graphene oxide and its enhanced performance as a Li-ion battery anode

The pursuit of a promising replacement candidate for graphite as a Li-ion battery anode, which can satisfy both engineering criteria and market needs has been the target of researchers for more than two decades. In this work, we have investigated the synergistic effect of nitrogen-doped reduced graphene oxide (NrGO) and nanotubular TiO2 to achieve high rate capabilities with high discharge capacities through a simple, one-step and scalable method. First, nanotubes of hydrogen titanate were hydrothermally grown on the surface of NrGO sheets, and then converted to a mixed phase of TiO2-B and anatase (TB) by thermal annealing. Specific surface area, thermal gravimetric, structural and morphological characterizations were performed on the synthesized product. Electrochemical properties were investigated by cyclic voltammetry and cyclic charge/discharge tests. The prepared anode showed high discharge capacity of 150 mAh g-1 at 1 C current rate after 50 cycles. The promising capacity of synthesized NrGO-TB was attributed to the unique and novel microstructure of NrGO-TB in which long nanotubes of TiO2 have been grown on the surface of NrGO sheets. Such architecture synergistically reduces the solid-state diffusion distance of Li+ and increases the electronic conductivity of the anode.

An Improved Technique for the Exfoliation of Graphene Nanosheets and Utilization of their Nanocomposites as Fuel Cell Electrodes

Graphene is a flat monolayer of carbon atoms tightly packed into a two-dimensional 2D honeycomb lattice. The graphene sheets in graphite interact with each other through van der Waals forces to form layered structure. The first graphene sheets were obtained by extracting monolayer sheets from the three-dimensional graphite using a technique called micromechanical cleavage in 2004 [. There are numerous attempts in the literature to produce monolayer graphene sheets by the treatment of graphite. The first work was conducted by Brodie in 1859 and GO was prepared by repeated treatment of Ceylon graphite with an oxidation mixture consisting of potassium chlorate and fuming nitric acid [. Then, in 1898, Staudenmaier produced graphite oxide (GO) by the oxidation of graphite in concentrated sulfuric acid and nitric acid with potassium chlorate [. However, this method was time consuming and hazardous. Hummers and Offeman found a rapid and safer method for the preparation of GO and in this method graphite was oxidized in water free mixture of sulfuric acid, sodium nitrate and potassium permanganate [.

Antimicrobial Properties of Titanium Nanoparticles

In the present study, nanostructured titania particles were synthesized using hydrothermal processing and their photocatalytic antimicrobial activities were characterized. Sol-gel synthesized TiO2 samples were treated with a two step hydrothermal treatment. The first stage treatment was the alkaline treatment with 10 M of NaOH for 48 h at 130°C, followed with the second step which applied with distilled water for 48 h at 200°C. Scanning Electron Microscope (SEM) images showed that alkaline treatment yields lamellar structure particles from the sol-gel synthesized anatase. Further treatment of nanoplates with distilled water results in crystal growth and the formation of nano structured thorn like particles. The photocatalytic antimicrobial activities of samples were determined against Escherichia coli under solar irradiation for 4 h. It was observed that the samples treated under alkaline conditions have higher antimicrobial activity than the untreated samples.

Development of Efficient Copper-Based MOF-Derived Catalysts for the Reduction of Aromatic Nitro Compounds: Development of Efficient Copper-Based MOF-Derived Catalysts for the Reduction of Aromatic Nitro Compounds

Two Copper-based Cu3(btc)2 and Cu(Im)2 metal organic frameworks were synthesized and annealed to form nanoporous Cu/Cu2O@C and Cu@N-C nanoparticles for utilization as catalysts in the reduction reaction of aromatic nitro compounds to aromatic amines. All synthesized MOF compounds and MOF-derived nanoparticles were characterized using XRD, Raman, TGA, SEM-EDX and XPS methods. Also, the pore size distribution and surface area of the MOF-derived Cu/Cu2O@C and Cu@N-C nanoparticles were characterized by BJH and BET methods. After characterization, the catalysts Cu/Cu2O@C and Cu@N-C were catalytically tested for the reduction reactions of various aromatic nitro compounds chemically by monitoring via a UV-vis spectrometer. Both catalysts exhibited remarkable results compared with those in the literature. Also, the Cu/Cu2O@C catalyst showed better results than the Cu@N-C catalyst.

On the spillover effect of the solid H2 intercalation into GNF's

Yu. S. Nechaev, V. P. Filippova, A. A. Tomchuk, A. Yurum, Yu. Yurum, T. N. Veziroglu Kurdjumov Institute of Metals Science and Physics, Bardin Institute for Ferrous Metallurgy, Moscow, Russia Nanoechnology Research and Application Centre, Sabanci University, Istanbul, Turkey Falulty of Engineering and Natural Sciences, Sabanci University, Istanbul, Turkey International Association for Hydrogen Energy, Miami, FL 33155, USA yuri1939@inbox.ru, varia.filippova@yandex.ru, tomchuk-a@yandex.ru, ayurum@sabanciuniv.edu, yyurum@sabanciuniv.edu, tnveziroglu@gmail.com

Non-isothermal kinetics of pyrolysis of Turkish petroleum pitches

ABSTRACT Non-isothermal thermogravimetric data of two Turkish petroleum pitches were used to evaluate kinetic parameters of pyrolysis reactions. The article reports the application of Ozawa–Flynn–Wall model to deal with non-isothermal TG data for the evaluation of the activation energy corresponding to the pyrolysis of two different petroleum pitches. Non-isothermal kinetic studies of pyrolysis of the pitches based on the TGA measurements at different heating rates resulted that average activation energy of pyrolysis of pitch B (213 kJ/mol) was higher than that of average activation energy of pitch A (186 kJ/mol). Reaction orders of pitch A and pitch B were calculated as 0.6 and 0.9, respectively.

Size and Dispersion Control of Pt Nanoparticles Grown Upon Graphite-Derived Nanosheets

Graphite oxide (GO) nanosheets, graphene nanosheets (GNS), and nanocomposites comprising of GO or GNS coated with polypyrrole (PPy) were prepared and assessed for their ability to influence the surface deposition and growth of Pt nanoparticles. GO was obtained from graphite via oxidation and exfoliation, and GNS was obtained from GO in a subsequent reduction. Both GO and GNS were coated with PPy via in situ polymerization of pyrrole (Py), forming surface-enhanced materials. Scanning electron microscope, energy-dispersive x-ray, transmission electron microscopy, electron energy loss spectroscopy, Raman, and atomic force microscope findings showed that the Pt nanoparticle loading, agglomeration size, aggregate morphology, and surface dispersion varied according to the nanosheet surface, nanocomposite type, and Py/nanosheet feed ratio. Surface oxygen functionalization along GO, GNS, and their nanocomposites influenced the loading, dispersivity, and morphology of nanoparticle agglomerates. PPy/GO nanocomposites yielded an improved nanoagglomerate surface dispersion and loading compared to samples. The PPy-coated substrates offered a greater intrinsic propensity for redox processes, resulting in higher Pt loadings. Additionally, these nanocomposites provided more surface reduction sites compared to bare nanosheets, and the additional sites contributed toward forming smaller, more homogeneously dispersed Pt nanoparticle agglomerates. Bringing together the electrical properties of PPy and physicomechanical traits of carbon nanosheets, it follows to reason that the nanocomposites produced, particularly GO-based nanocomposites, offer promise as a nanoparticle support material for use in catalysis, electrocatalysis, and hydrogen storage.