A high-performance metal-free hydrogen-evolution reaction electrocatalyst from bacterium derived carbon

We report a sustainable approach to obtain carbon materials with nitrogen and phosphorus dual functionalities from a common bacterium strain (S. aureus) as a highly efficient hydrogen-evolution reaction (HER) catalyst. With mesoporous structure introduced by ZnCl2 salt and cathodic activation, it demonstrates an onset overpotential as low as 76 mV, a Tafel slope of 58.4 mV dec(-1) and a large normalized exchange current density of 1.72 x 10(-2) mA cm(-2), which are comparable to those of hitherto best metal-free and well-fabricated metallic HER catalyst

Spectroscopic investigation of polyvinyl chloride photodegradation in blends with basic traps

Ankara : The Department of Chemistry and the Institute of Engineering and Sciences of Bilkent Univ., 1999.Thesis (Master's) -- Bilkent University, 1999.Includes bibliographical references leaves 61-68.Polyvinyl chloride degrades via loss of HCI when it is exposed to heat, energetic particles or photons. The mechanism is known as the zip mechanism and results in conjugated segments, polyenes. Degradation also leads to loss of mechanical properties of PVC. However, from another point of view, PVC is a Bronsted acid source, with controllable emission. Furthermore, the polyenes are small segments of polyacetylene, which itself is a very interesting one-dimensional system. Understanding the building blocks clearly helps to envisage larger systems. This study has two main goals. The first goal is benefiting from the radiation induced in-situ created HCI by incorporating basic traps into the polymer matrix and inducing optical or electrical conductivity changes. The second goal is to tune the wavelength of photodegradation by introducing sensitisers into the polymer matrix to affect the chain length of the polyenes. For the first part of the study, pH indicators, and basic forms of conducting polymers were blended with PVC and the films were irradiated with UV radiation. Optical changes were monitored with UV-Vis-NIR Spectroscopy. Similar to several other dyes tried, Bromcresol Green, and Methyl Violet changed their optical properties when they were exposed to UV radiation in the PVC matrix. However, Methyl Violet, being resistant to UV radiation, proved to be a suitable component for possible dosimetric and lithographic applications. Basic forms of polyaniline and poly-2-chloro aniline were blended with PVC, and upon irradiation of the blend, they were converted to conducting salt forms as a result of doping with in-situ created HCI. The structural changes were monitored with UV-Vis-NIR spectrophotometry as well as FTIR spectroscopy. PVC/2-CI PAN I blends gave better results compared to PVC/PANI blends. For the second part of the study, hydroquinone, anthraquinone, and anthracene were introduced into the PVC matrix. The samples were irradiated with monochromatic UV radiation at the absorption maxima of these sensitisers. It was established that the nature of polyene formation is dependent on the wavelength of irradiation as well as the amount of energy transferred to the PVC chains.Birer, ÖzgürM.S

Dielectric Property-Microstructure Relation in Magnesium Calcium Titanate Ceramics

In this paper, Magnesium Calcium Titanate (MCT) powders were prepared by both conventional solid-state method and the Pechini method. 0.95MgTiO3-0.05CaTiO3 (95MCT) were chosen as the optimum stoichiometry. Microstructure and phase transformation of calcined 95MCT powders have been observed. First, the powders were prepared by conventional solid-state method and calcined at 1000°C, 1100°C and 1200°C. Second, the 95MCT powders were prepared via the Pechini method, then calcined at 900°C and 1000°C. The calcined powders were investigated by X-Ray Diffraction analysis to identify the phases developed during calcination. For both routes, it is observed that MgTiO3 is the main crystalline phase, whereas CaTiO3 and MgTi2O5 are minor phases. However, MgTi2O5 is not desired in the structure because of its negative effect on dielectric properties. Powders produced by the Pechini method were observed to have different microstructures than conventionally produced powders

Discovery of superior Cu-GaOx-HoOy catalysts for the reduction of carbon dioxide to methanol at atmospheric pressure

Catalytic conversion of carbon dioxide to liquid fuels and basic chemicals by using solar-derived hydrogen at, or near, ambient pressure is a highly desirable goal in heterogeneous catalysis. If realized, this technology could lead to a more sustainable society together with decentralized power generation. A novel class of holmium-containing multi-metal oxide Cu catalysts, discovered through the application of high-throughput methods, is reported. In particular, ternary systems of Cu-GaOx-HoOy>Cu-CeOx-HoOy approximate to Cu-LaOx-HoOy supported on -Al2O3 exhibited superior methanol production (10x) with less CO formation than previously reported catalysts at 1atm pressure. Holmium was shown to be highly dispersed as few-atom clusters, suggesting that the formation of trimetallic sites could be the key for the promotion of methanol synthesis by Ho

Aggregation-induced dissociation of HCl(H2O)4 below 1 K: the smallest droplet of acid

Acid dissociation and the subsequent solvation of the charged fragments at ultracold temperatures in nanoenvironments, as distinct from ambient bulk water, are relevant to atmospheric and interstellar chemistry but remain poorly understood. Here we report the experimental observation of a nanoscopic aqueous droplet of acid formed within a superfluid helium cluster at 0.37 kelvin. High-resolution mass-selective infrared laser spectroscopy reveals that successive aggregation of the acid HCl with water molecules, HCl(H2O)n, readily results in the formation of hydronium at n = 4. Accompanying ab initio simulations show that undissociated clusters assemble by stepwise water molecule addition in electrostatic steering arrangements up to n = 3. Adding a fourth water molecule to the ringlike undissociated HCl(H2O)3 then spontaneously yields the compact dissociated H3O+(H2O)3Cl– ion pair. This aggregation mechanism bypasses deep local energy minima on the n = 4 potential energy surface and offers a general paradigm for reactivity at ultracold temperatures

Structural changes in a Schiff base molecular assembly initiated by scanning tunneling microscopy tip

We report the controlled self-organization and switching of newly designed Schiff base (E)-4-((4-(phenylethynyl) benzylidene) amino) benzenethiol (EPBB) molecules on a Au (111) surface at room temperature. Scanning tunneling microscopy and spectroscopy (STM/STS) were used to image and analyze the conformational changes of the EPBB molecules. The conformational change of the molecules was induced by using the STM tip while increasing the tunneling current. The switching of a domain or island of molecules was shown to be induced by the STM tip during scanning. Unambiguous fingerprints of the switching mechanism were observed via STM/STS measurements. Surface-enhanced Raman scattering was employed, to control and identify quantitatively the switching mechanism of molecules in a monolayer. Density functional theory calculations were also performed in order to understand the microscopic details of the switching mechanism. These calculations revealed that the molecular switching behavior stemmed from the strong interaction of the EPBB molecules with the STM tip. Our approach to controlling intermolecular mechanics provides a path towards the bottom-up assembly of more sophisticated molecular machines.TUBITAK (TBAG 112T507); Flemish Science Foundation (FWO-Vl); FWO Pegasus Long Marie Curie Fellowshi