Marjoni Imamora Ali Umar

Characterization of multilayer graphene prepared from short-time processed graphite oxide flake

Multilayer graphene has been prepared by thermal reduction of graphene oxide film. The graphite oxide flake was first synthesized by using modified Hummers method with a relatively small amount of oxidizing agent and short-time processing at ambient temperature. The graphite oxide flake was dispersed in deionized water and deposited on quartz substrates to form graphene oxide film. The red shift of absorption peak and decrease of interlayer distance as interpreted from the X-ray diffraction spectrum indicate the formation of multilayer graphene. The resultant multilayer graphene has been successfully used as counter electrode in FTO/ZnO nanorods/electrolyte/multilayer graphene dye sensitized solar cell.

Two-Dimensional, Hierarchical Ag-Doped TiO2 Nanocatalysts: Effect of the Metal Oxidation State on the Photocatalytic Properties

This paper reports the synthesis of two-dimensional, hierarchical, porous, and (001)-faceted metal (Ag, Zn, and Al)-doped TiO2 nanostructures (TNSs) and the study of their photocatalytic activity. Two-dimensional metal-doped TNSs were synthesized using the hydrolysis of ammonium hexafluorotitanate in the presence of hexamethylenetetramine and metal precursors. Typical morphology of metal-doped TNSs is a hierarchical nanosheet that is composed of randomly stacked nanocubes (dimensions of up to 5 μm and 200 nm in edge length and thickness, respectively) and has dominant (001) facets exposed. Raman analysis and X-ray photoelectron spectroscopy results indicated that the Ag doping, compared to Zn and Al, much improves the crystallinity degree and at the same time dramatically lowers the valence state binding energy of the TNS and provides an additional dopant oxidation state into the system for an enhanced electron-transfer process and surface reaction. These are assumed to enhance the photocatalytic of the TNS. In a model of photocatalytic reaction, that is, rhodamine B degradation, the AgTNS demonstrates a high photocatalytic activity by converting approximately 91% of rhodamine B within only 120 min, equivalent to a rate constant of 0.018 m–1 and ToN and ToF of 94 and 1.57 min–1, respectively, or 91.1 mmol mg–1 W–1 degradation when normalized to used light source intensity, which is approximately 2 times higher than the pristine TNS and several order higher when compared to Zn- and Al-doped TNSs. Improvement of the crystallinity degree, decrease in the defect density and the photogenerated electron and hole recombination, and increase of the oxygen vacancy in the AgTNS are found to be the key factors for the enhancement of the photocatalytic properties. This work provides a straightforward strategy for the preparation of high-energy (001) faceted, two-dimensional, hierarchical, and porous Ag-doped TNSs for potential use in photocatalysis and photoelectrochemical application.

Effect of graphite oxide solution concentration on the properties of multilayer graphene

This paper reports the influence of graphite oxide (GO) solution concentration on the optical and electrical properties of multilayer graphene (MLG) films. Graphene oxide (GrO) films were deposited on the glass substrates by spin coating aqueous solutions of GO with different concentrations (7, 8, 9, 10 and 11 mg/ml). The GrO films were then thermally reduced at temperature of 500°C in argon flow for half an hour to form MLG films. Both the transmittance and sheet resistance decreased with the GO concentration from 8 mg/ml to 9 mg/ml, possibly due to thicker and uniform coverage of MLG over the substrate. However, the transmittance and sheet resistance increased rapidly as the GO concentration reached 11 mg/ml, which can be attributed to poor film quality. The MLG film obtained at concentration of 10 mg/ml showed the highest transmittance/sheet resistance ratio with 69 % transmittance and sheet resistance of 292 ± 63 kΩ/sq. The optimum MLG film was utilized as counter electrode in dye sensitized solar cells based on ZnO nanorods.

Preparation of patterned graphene-ZnO hybrid nanoflower and nanorods on ITO surface

Hybrid ZnO nanostructure with controlled morphology have been proved to enhance the physical and chemical properties of the material and used as photodiode and sensor. In this paper, hybrid graphene-ZnO nanoflower and nanorods have been successfully synthesized via a seed mediated method with micropatterned ZnO nanoseed treated with multilayer graphene (MLG) in a hydrothermal process. In typical process, the ZnO nanoseeds with and without resists were spin coated with a multilayer graphene prior to the growth process. The treated seed was then used to grow the ZnO nanostructures in the growth solution that contained equimolar (0.04 M) of zinc nitrate hexahydrate and hexamethylenetetramine. The growth process was carried out inside an autoclave at temperature 70 °C. The growth time was 4 h. It was proved that the MLG treatment on micropatterning substrate may induce new morphology formation of ZnO nanostructure. It is expected that the heteroepitaxy reaction occurred between the MLG and ZnO interface. This presence method can be used as an alternative approach to control the morphology of hybrid ZnO nanostructure growth.

Preparation and Characterization of TiO2 Nanowire - Cu2O Nanocube Composite Thin Film

Composite of TiO2 nanowire and Cu2O nanocube has been prepared. TiO2 nanowire with ~240nm in thickness and 20 nm in length were synthesized by using liquid phase deposition(LPD) method at 50°C for 4h on ITO substrate. The anatase phase of TiO2 nanowire was obtained by annealing the samples at 400°C for 1hin air. The Cu2O nanocubes were prepared by the reduction of Cu2+ions with ascorbic acid in the present of trisodium citrate and sodium dodecilsulfat (SDS) surfactant under an alkaline condition. The SDS addition was added with various concentrations namely 10 mM, 18 mM, and 26 mM during the Cu2O preparation for spin-coated onto TiO2 nanowire at 3000 rpm for 30s. An optical property of TiO2 Nanowire - Cu2O Nanocube has been characterized by UV-Vis spectroscopy.The original TiO2 nanowire has single absorption peak at 318 nm, but it was shifted to 321 nm as Cu2O/SDS addition. A new peak at 440 nm was as the Cu2O nanocube absorption spectra. The Cu2O nanocube addition to the TiO2 nanostructure film caused increase in the optical absorption of the system in the region 400 – 800 nm. We also studied the absorption properties of the hybrid system when Cu2O nanocube preparation under SDS condition. It was that found the increase in the SDS concentration has caused the optical absorption of the hybrid in this region decreased. This is believed due to the decrease of Cu2O nanocube size as the SDS concentration increase. This could be due to change in the TiO2 nanowire-Cu2O nanocube hybrid-structure. This cooperate may find use in photoelectrochemical application.