Siti Khatijah Md Saad

Porous (001)-faceted Zn-doped anatase TiO2 nanowalls and their heterogeneous photocatalytic characterization

The synthesis of a poriferous and high energy (001) faceted anatase Zn-doped TiO2 nanowall (ZnTNW), vertically grown on an indium tin oxide substrate, is presented. The ZnTNW was prepared using a modified liquid phase deposition method using zinc nitrate (Zn(NO3)2·xH2O) as a fluoride scavenger in the presence of hexamethylenetetramine. In a typical procedure, the ZnTNW nanowall with length and thickness of approximately 2 μm and 60 nm, respectively, can be obtained from the reaction during a 5 h growth process. X-ray diffraction analysis shows that the nanowall has an anatase structure with a dominant high energy (001) basal plane. Meanwhile, the X-ray energy dispersive analysis confirms the presence of Zn in the TiO2 nanowall. High resolution transmission electron microscopy analysis results reveal, surprisingly, that the ZnTNW is single crystalline in nature although it has a highly porous (surface and bulk) structure. Photocatalytic properties of the ZnTNW were examined in the degradation of methylene blue. It was found that the ZnTNW exhibits excellent photocatalytic efficiency with kinetic reaction rate, turnover number and turnover frequency as high as 0.004 min−1, 760 and 11 min−1, respectively. The photocatalytic performance of the ZnTW was found to be higher for about 10% and 50% than the pristine TiO2 nanowalls and (001) faceted poriferous TiO2 microtablet, which reflected the effective effect of the Zn doping. The ZnTNW may find potentially use in photocatalytic heterogeneous applications.

Effect of TiO 2 nanostructure's shape on the DSSCs performance

The effect of morphology of anatase TiO2 nanoparticles as photoanode in dye sensitized solar cells (DSSCs) has been investigated. Two types of TiO2 nanostructures, namely nanograss and nanospherical particles, used in this study have been prepared via liquid phase deposition (LPD) method. Electrochemical impedance spectroscopy (EIS) analysis of DSSCs device with a sandwich structure of ITO/TiO2/dye/electrolyte/ Pt film indicated that the device utilizing TiO2 nanograss exhibited the lower in charge transfer resistance (Rct), of 49.1 Ω. This might be due to the high-porous characteristic of TiO2 nanograss compared to the nanospherical particles that provides facile charge transport and ion diffusion. Power conversion efficiency as high as 0.97% has been recorded from the device utilizing nanograss of TiO2, which was 3 times higher compared to TiO2 nanospherical particles of which its conversion efficiency was only 0.33%.

Synthesis of amorphous platinum nanofibers directly on an ITO substrate and its heterogeneous catalytic hydrogenation characterization

This paper reports a facile, solution-phase approach to synthesizing a one-dimensional amorphous face-centered-cubic (fcc) platinum (a-Pt) nanostructure (nanofibers) directly on an indium-tin oxide (ITO) substrate. The electron microscopy analysis result shows that the a-Pt nanofiber has a diameter and length of approximately 50 nm and 1 μm, respectively, and is grown in high density on the entire surface of the ITO substrate. The X-ray photoelectron spectroscopy analysis result further reveals that the a-Pt nanofibers feature metallic properties with highly reactive surface chemistry, promising novel performance in electrochemistry, catalysis, and sensors. A synergetic interplay between the formic acid reducing agent and the hexamethylenetetramine surfactant in the reduction of Pt ions is assumed as the driving force for the formation of the amorphous phase in the Pt nanostructure. The catalytic properties of a-Pt were examined in the acetone hydrogenation reaction under microwave irradiation. a-Pt shows excellent heterogeneous catalytic properties for converting acetone to isopropyl alcohol with turnover number and frequency as high as 400 and 140 min(-1), respectively. The preparation and formation mechanism of the a-Pt nanofibers will be discussed in detail in this paper.

Scalable Mesoporous Platinum Diselenide Nanosheet Synthesis in Water

Newly discovered two-dimensional (2D) atomic crystals (nanosheet) of platinum diselenide (PtSe2) have progressively attracted attention due to their expected high performance in catalysis, sensing, electronics, and optoelectronics applications. Further extraordinary physicochemical properties are expected if these nanosheets of platinum diselenide can possess mesoporosity as this may enable a high range of molecular adsorption, enhancing their functionalities in catalysis, batteries, supercapacitors, and sensing. Here, we present for the first time a straightforward, aqueous-phase synthetic strategy for the preparation of scalable nanosheets of platinum diselenide with mesoporous structure via a surfactant-templated self-assembly followed by a thermal annealing phase-transformation process. We used hexamethylenetetramine as a hexagonal honeycomb (sp2–sp3 orbital) scaffold for assembling the Pt and Se organic complexes to form the nanosheet structure, which is stable, preserving the 2D structure and mesoporosity during a thermal annealing at 500 °C. Density functional theory analysis then indicated that the mesoporous nanosheets of platinum diselenide exhibit a high free-energy and large density of π electrons crossing the Fermi level, inferring a high-catalytic performance. This effortless strategy is currently being extended to the synthesis of other transition metal dichalcogenides, including the preparation of multi-metal atomic dichalcogenide nanosheets, for a wide variety of scientific and technological applications.

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.

Deposition of Au/TiO2 nanocomposite on ITO surface by seed-mediated liquid phase deposition method

An efficient, simple and new procedure has been performed to synthesis Au/TiO2 nanocomposite thin film on solid surface of ITO by seed-mediated of liquid phase deposition (LPD) method. The deposition of Au seed was applied by our previously reported seed-mediated growth procedure. The solution was prepared by mixing HAuCl4 and (NH4)2TiF6 successfully deposited on to ITO substrate containing Au seed. After one hour well adhered film was obtained by mentioned approach of synthesis and nonocomposite with spherical rod like networks has been successfully grown. The resulting nanocomposites were confirmed by ultraviolet-visible (Uv-Vis) absorption spectroscopy. Further characterization and morphology was checked by field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD).

Carbon/Carbon Nanotubes (CNTs) Composites from Green Pellets Contain CNTs and Self‐adhesive Carbon Grains from Fibres of Oil Palm Empty Fruit Bunch

Nano composites green pellets (GPs) were prepared from the mixtures of carbon nanotubes (CNTs) at varying percentage (0, 2, 4, 6, 8 and 10%) and self‐adhesive carbon grains (SACG) from fibres of oil palm empty fruit bunch. These GPs were carbonized and CO2 activated to produce activated carbon/CNTs composites in the form of pellets (ACPs). It was found that the density (ρ) and electrical conductivity (σ) of the ACPs varied nonlinearly with CNTs content; as for the CNTs content of 3–5%, we observed the peak values of ρ and σ at 1.3781 gcm−3 and 3.4146 (Ωcm)−1 respectively. The presence of the agglomerated and individual particles of CNTs in the pores of the ACPs was clearly shown by the micrograph of the Field Emission Scanning Electron Microscope (FESEM). The nitrogen adsorption isotherm data showed the decrease in surface area, volume and diameter of pores due to the effect of CNTs. The effect of CNTs on the electrochemical behavior of the ACPs were investigated from the supercapacitor cells fabricated u...

Performance of dye-sensitized solar cell utilizing Ga-ZnO nanorods: Effect of Ga concentration

Ga-doped ZnO nanorods with various Ga concentration have been successfully grown on the surface of the FTO (Fluorine Tin Oxide) substrate using hydrothermal method that was achieved by varying the gallium nitrate hydrate precursor concentration during the growth reaction containing zinc nitrate hexahydrate (ZNH) and hexamethylenetetramine (HMTGallium nitrate hydrate (GNH) concentration used were 2, 3, 5, 6 and 10% of the ZnO precursor solution. The FESEM analysis on the sample indicated that the nanostructures were vertically oriented nanorods. While XRD analysis confirmed that the Ga-ZnO was successfully prepared using the present approach and the Ga content in the GaZnO nanorods can be simply varied by suing different concetration of Ga precursor during the growth process. Current-voltage analysis on the dye sensitized solar cell (DSSCs) containing Ga-doped ZnO nanorods as photoanode with structure of FTO/Ga-doped ZnO/Dye/Electrolyte/Platinum indicated that the performance of the device increased with the increasing of Ga concentration in the ZnO nanorods and optimum if using Ga precursor concentrration of 5%. At this condition the efficiecy was as high as 0.362%. It is nearly three times higher compared to device utilizing pure ZnO nanorods (0.132%). The performance decreased when the Ga concentration further increased in the nanorods. Enhancement of the device performance upon doped with the Ga is associated with the decreasing of carrierrecombination as judged from the dark current analysis results.

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.

The Optical Properties of Ammonia Treated TiO2 Nanostructure Prepared by Liquid Phase Deposition Method

. TiO2 was known for its potential in solar cell and photocatalyst application. However the usage of anatase TiO2 in solar cell application has its own disadvantage as TiO2 spectrum was limited to ultraviolet (UV) light limiting its application. It was found that the broader optical absorption of TiO2 can be obtained by nitrogen doping. This paper report the optical properties study of ammonia treated TiO2 nanostructures with various percentage concentration of ammonia. The TiO2 nanostructures was prepared by liquid phase deposition (LPD) method using on ITO substrate and annealed at 450 °C for 1h. The TiO2 nanostructures were characterized with rod-like morphology with length and diameter of ca. 100 nm and ca. 100 nm respectively that vertically oriented on the surface. The optical properties of the samples exhibit strong band near the UV region. The optical properties drastically changed if the samples treated with ammonia, of which exhibit the present of broader absorption band in the visible region. The TiO2 treated ammonia should be find used in photoelectrochemical (PEC) solar cell application.