Boda, Muzaffar Ahmad; Shah, Mohammad Ashraf; Khan, Matiullah; Çırak, Çagrı

In this study, multi-podal titania nanotube array (anatase) were fabricated via electrochemical anodization technique on employing third generation electrolyte with suitable and sharp optimization of every anodization parameter. In comparison to conventional titania nanotubes, these nanotubes offer sufficient nanotube wall/electrolyte interface and thereby makes the appreciable reduction in electron hole pair recombination rate by immediate involvement of holes and electrons in oxidation and reduction process, respectively. Furthermore, 85 nm diameter variation in these nanotubes from base diameter 263 nm to top diameter 348 nm makes the incoming light to undergo through graded refractive index which in corresponding increases their light harnessing ability. Although morphological advantage of these nanotubes is being efficiently harnessed in the scattering of incident light but the large band gap 3.2 eV still confines their utility to UV region only. To increase their photo-electrochemical potential under visible light as well, these nanotubes were functionalized suitably with Cu2O nano-cubes without disturbing the nanotube morphology. Under the analysis of their photo-electrochemical potential, the photocurrent density recorded for bare and Cu2O functionalized multi-podal titania nanotube array under visible light source 300 W Xenon lamp (1 sun illumination) was 0.27 mAcm− 2 and 0.39 mAcm− 2, respectively. The enhancement of ~45% in photocurrent density under visible light illumination is attributed to suitable band edge positions in Cu2O with respect to the band edge positions in TiO2 which in corresponding leads the formation of effective visible light active band gap in the resulting hybrid structure.

Tuzluca, Fatma Nur; Yesilbag, Yasar Ozkan; Ertugrul, Mehmet

The aim of the present study was to examine the electrochemical performance of boron nanowires (BNWs) grown using the vapor-liquid-solid (VLS) growth mechanism in the chemical vapor deposition (CVD) system at 1200 °C on a silicon wafer in the presence of iron (Fe) catalyst nanodroplets as a supercapacitor electrode material in 1 M Na2SO4 aqueous electrolyte solution. The structure and morphology of BNWs were examined using field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HR-TEM) analyses, while their electrochemical performances were determined by measuring the cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectra (EIS). BNWs showed great cycle stability with an areal capacitance of 30 mF cm−2 and 93.4% of the initial areal capacitance even after a 10,000 GCD cycle at a current density of 0.1 mA cm−2.

Tuzluca, Fatma Nur; Yesilbag, Yasar Ozkan; Ertugrul, Mehmet

In this study performed using a chemical vapor deposition (CVD) system, one-dimensional (1-D) single crystal indium oxide (In 2 O 3 ) nanotowers, nanobouqets, nanocones, and nanowires were investigated as a candidate for a supercapacitor electrode material. These nanostructures were grown via Vapor–Liquid–Solid (VLS) and Vapor–Solid (VS) mechanisms according to temperature differences (1000–600 °C). The morphologies, growth mechanisms and crystal structures of these 1-D single crystal In 2 O 3 nanostructures were defined by Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Microscopy (HR-TEM), X-Ray Diffraction (XRD) and Raman Spectroscopy analyses. The elemental analyses of the nanostructures were carried out by energy dispersive X-Ray Spectroscopy (EDS); they gave photoluminescence (PL) spectra with 3.39, 2.65, and 1.95 eV band gap values, corresponding to 365 nm, 467 nm, and 633 wavelengths, respectively. The electrochemical performances of these 1-D single crystal In 2 O 3 nanostructures in an aqueous electrolyte solution (1 M Na 2 SO 4 ) were determined by Cyclic Voltammetry (CV), Galvanostatic Charge Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS) analyses. According to GCD measurements at 0.04 mA cm −2 current density, areal capacitance values were 10.1 mF cm −2 and 6.7 mF cm −2 for nanotowers, 12.5 mF cm −2 for nanobouquets, 4.9 mF cm −2 for nanocones, and 16.6 mF cm −2 for nanowires. The highest areal capacitance value was observed in In 2 O 3 nanowires, which retained 66.8% of their initial areal capacitance after a 10000 charge-discharge cycle, indicating excellent cycle stability.

Cubuk, Osman; Caglar, Bulent; Topcu, Cihan; Coldur, Fatih; Sarp, Gokhan; Tabak, Ahmet; Sahin, Erdal

Organosmectites were prepared by the intercalation of hexadecyltrimethylammonium cations at various ratios into interlayer of Unye smectite. Structural, thermal, morphological and textural properties of the synthesized organosmectites were characterized. Afterwards, a novel potentiometric PVC-membrane thiocyanate selective electrode was prepared based on the obtained hexadecyltrimethylammonium modified smectites as electroactive material. The basal spacing values of organosmectites were observed in the range of 15.61 and 35.50 Å. Powder X-ray diffraction data show that the surfactant cations penetrated into the smectite layers with different molecular arrangements. Modification of smectite with hexadecyltrimethylammonium led to appreciable decreases in the intensities of the FTIR bands at 3402 and 1635 cm -1 and the new characteristic vibrational bands at 2927, 2850, 1472 and 722 cm -1 originating from the surfactant molecules appeared. The thermal analysis data showed that the decomposition of surfactant species occurred in the temperature range of 170-720 °C and the amount of dehydrated water gradually decreased with the increase in surfactant amount. The intercalation of surfactant species within the gallery spacing led gradually to smaller surface areas. In addition, the electrophoretic mobility values indicate that excess surfactant loadings also generate positive charges on the organosmectite surfaces. The most convenient membrane composition resulting in the best potentiometric performance was investigated. The optimum membrane composition was determined to have 20.0% (w/w) 2.5CEC.HDTMA-smectite, 26.0% (w/w) PVC, 54.0% (w/w) DBP The fabricated electrode exhibited a linear response over the thiocyanate concentration range of 1.0 × 10 -4 -1.0 × 10 -1 M (R 2 = 0.9996) with a slope of -48.6 mV/decade. The detection limit, response time and pH working range were determined as 4.3 × 10 -5 M, ∼10 s and 4-8, respectively. The proposed electrode exhibited selective potentiometric response to thiocyanate comparable to most of the common anions.

Doʇar, Çetin; Gürses, Ahmet; Karaca, Semra; Köktepe, Sevda; Mindivan, Ferda; Güneş, Kübra

This study aims to investigate the thermal properties of phenol-urea-formaldehyde (PUF)/organoclay nanocomposites synthesized at various organoclay ratios by using their DSC thermograms, FT-IR spectra, and HRTEM images. From these analyses, it has been concluded that at low organoclay ratios, the platelets exfoliated of organoclay, which dispersed homogenously in the polymer matrix, created a positive effect in conformational arrangement as suitable to crystallization of PUF chains. DSC analyses revealed that two endotherms in all thermograms imply the presence of linear UF, PF, and PUF chains together. Low organoclay content may also lead to a cross-linked lattice, being more predominant than the linear chain arrangement.

Gürses, Ahmet; Güneş, Kübra; Mindivan, Ferda; Korucu, Mehtap Ejder; Açikyildiz, Metin; Doʇar, Çetin

In this study, the interactions between clay platelets and CTA + ions in aqueous dispersions of Na-montmorillonite (Na-MMT) were examined in detail by using electro kinetic parameters such as electrical conductivity and zeta potential and by considering XRD patterns and d-spacing values of the organoclay samples as a function of both surfactant concentration (CTAB, cetyltrimethylammonium bromide) and clay amount. The amounts adsorbed and zeta potentials of the particles increased with an increase in the initial concentration of CTAB in parallel with the electrical conductivity values. The adsorption mechanisms which predominate at certain ranges of CTAB concentration were proposed and schematized by considering the d-spacing values calculated and the zeta potential values of particles. For the different solid/liquid ratios, the initial concentrations of CTAB, in which appeared significant increases in the d-spacing values were found as 200, 280 and 300 mg/L, respectively. The d-spacing values which correspond to these concentrations are, respectively 1.82, 1.82 and 1.68 nm. It is remarkable that at first three solid/liquid ratios, a "stress region" to be related with hydrophobic binding appeared. Thermodynamic parameters such as Gibbs free energy (ΔG o ), isosteric enthalpy (ΔH o ads ) q , and isosteric entropy (ΔS o ads ) q were also calculated by using experimental data. These parameters indicate that adsorption of CTAB onto Na-montmorillonite is spontaneous and exothermic in the temperature range studied. The ((ΔS o ads ) q , (ΔH o ads ) q and (ΔG o )) values calculated are highly negative. This reveals that the adsorption of CTA + ions at the interlayer region of clay carried out with more order stacking of CTA + ions.