Synthesis,characterisation and photocatalytic activity of Ag<Superscript>+</Superscript>- and Sn<Superscript>2+</Superscript>-substituted KSbTeO<Subscript>6</Subscript>

Ag⁺- and Sn²⁺-substituted KSbTeO₆ were prepared by a facile ion-exchange method at ambient temperature. All the samples were characterised by scanning electron microscopy, energy-dispersive spectra, thermogravimetric analysis, powder X-ray diffraction, Raman spectra and UV-VIS diffuse reflectance spectra. Both Sn²⁺- and Ag⁺-substituted KSbTeO₆ were crystallised in a cubic lattice with the \(Fd\bar 3m\) space group. The band-gap energy of all the samples was deduced from their UV-VIS diffuse reflectance spectral profiles. The visible light-induced photocatalytic oxidation of the methylene blue (MB) dye was examined in the presence of all the as-prepared materials. The Ag⁺- and Sn²⁺-substituted KSbTeO₆ exhibited a higher photocatalytic activity than the parent KSbTeO₆ in degradation of the MB dye under visible light irradiation.     

Facile ion-exchange synthesis of Gd-doped K2Ta2O6 photocatalysts with enhanced visible light activity

One of the well-known ways of increasing the visible light absorption capability of semiconducting materials is cation doping. This study aims to use Gd doping to tailor the bandgap energy of K₂Ta₂O₆ (KTO) for photocatalytic degradation of organic pollutants under visible light irradiation. Accordingly, the parent KTO and Gd-doped KTO with different Gd concentrations (K_2-3xGd_xTa₂O₆; x = 0.025, 0.05, 0.075 and 0.1 mol%) were synthesized by hydrothermal and facile ion-exchange methods, respectively. The powder XRD, FT-IR, SEM-EDS, TEM-SAED, N₂ adsorption-desorption, XPS, UV–Vis DRS, PL and ESR techniques were used to investigate the effect of Gd dopant concentration on the structural and photocatalytic properties of KTO. The photocatalytic activity of these samples was investigated for the photocatalytic degradation of methylene blue (MB) dye in an aqueous solution at room temperature under visible light irradiation. The experimental results show that all Gd-doped KTO samples exhibit enhanced photocatalytic activity compared with parent KTO toward MB degradation. In particular, Gd-KTO obtained by doping of 0.075 mol% shows the highest photocatalytic activity among the Gd-doped samples and the degradation efficiency of MB was 79% after 180 min of visible light irradiation, which is approximately 1.5 times as high as that by parent KTO (53%). In addition, trapping experiments and electron spin resonance (ESR) analysis demonstrated that the hydroxyl radicals (^?OH) have played a crucial role in the photocatalytic degradation of MB. The reusability and stability of Gd doped-KTO with a Gd content of 0.075 mol% against MB degradation were examined for five cycles. Based on the present study results, a visible light induced photocatalytic mechanism has been proposed for Gd0075-KTO sample.     

Enhancement of Photocatalytic Activity of Sodium Bismuth Titanate by Doping with Copper,Silver, and Tin Ions

Perovskite type oxides, sodium bismuth titanate (Na_0.5Bi_0.5TiO₃), and Ag⁺, Cu²⁺, and Sn²⁺ doped Na_0.5Bi_0.5TiO₃ were prepared by pechini and ion exchange methods, respectively. Photocatalytic activities of these catalysts were tested by decomposition of methylene blue (MB) under visible light irradiation. Results showed that the photocatalytic activity of metal ion doped Na_0.5Bi_0.5TiO₃ was higher than undoped Na_0.5Bi_0.5TiO₃. Relatively high photocatalytic performance of Ag⁺‐doped Na_0.5Bi_0.5TiO₃ is mainly ascribed to the efficient separation of electron‐hole (e^–, h⁺) pairs, lower bandgap energy and the creation of active hydroxyl radicals ( ^? OH). Further, the Ag⁺‐doped Na_0.5Bi_0.5TiO₃ catalyst showed good reusability up to four cycles. A possible mechanism for the enhanced photocatalytic performance was proposed. The synthesized photocatalysts were characterized by XRD, SEM, EDS, XPS, FT‐IR, and UV/Vis DRS techniques.     

PMD tolerance in Stokes space based polarization de-multiplexing algorithms

We numerically investigate the polarization-mode dispersion (PMD) tolerance of Stokes space based polarization-demultiplexing (SSPolDemux) algorithms in optical transmission supported by coherent detection and digital signal processing. The PMD tolerance is evaluated as function of the ratio differential group delay over symbol period, allowing to identify a regime where SSPolDemux is performed practically without penalty (smaller than 1 dB), a regime where SSPolDemux is achievable but induces large penalties, and a third regime where SSPolDemux cannot be accomplished. Results show that coherent access/metro networks are the most evident and potentiating application scenarios for SSPolDemux techniques.     

Resonance expansions in quantum mechanics

The goal of this contribution is to discuss various resonance expansions that have been proposed in the literature. Presented at the 3rd International Workshop “Pseudo-Hermitian Hamiltonians in Quantum Physics”, Istanbul, Turkey, June 20–22, 2005.     

Synthesis,Characterization and Photocatalytic Activity of Ag+‐ and Sn2+‐Doped KTi0.5Te1.5O6

In this study, the photocatalytic dye degradation efficiency of KTi_0.5Te_1.5O₆ synthesized through solid‐state method was enhanced by cation (Ag⁺/Sn⁺²) doping at potassium site via ion exchange method. As prepared materials were characterized by XRD, SEM‐EDS, IR, TGA and UV–Vis Diffuse reflectance spectroscopic (DRS) techniques. All the compounds were crystallized in cubic lattice with space group. The bandgap energies of parent, Ag⁺‐ and Sn⁺²‐doped KTi_0.5Te_1.5O₆ materials obtained from DRS profiles were found to be 2.96, 2.55 and 2.40 eV, respectively. Photocatalytic efficiency of parent, Ag⁺‐ and Sn⁺²‐doped materials was evaluated against the degradation of methylene blue (MB) and methyl violet (MV) dyes under visible light irradiation. The Sn⁺²‐doped KTi_0.5Te_1.5O₆ showed higher activity toward the degradation of both MB and MV dyes and its higher activity is ascribed to the lower bandgap energy compared to the parent and Ag⁺‐doped KTi_0.5Te_1.5O₆. The mechanistic degradation pathway of methylene blue (MB) was studied in the presence of Sn²⁺‐doped KTi_0.5Te_1.5O₆. Quenching experiments were performed to know the participation of holes, super oxide and hydroxyl radicals in the dye degradation process. The stability and reusability of the catalysts were studied.     

Enhanced photoactivity of antimony phosphates by substitution of H+, Cu2+ and N3− in the K3Sb3P2O14·xH2O crystal lattice

Research on Chemical Intermediates - Substitutional doping of framework heteroatoms in photocatalysis is one of the approaches for harvesting visible light. Tunnel structure potassium antimony...     

Preparation of (Z)-1-fluoro-1-alkenyl carboxylates,carbonates and carbamates through chromium mediated transformation of dibromofluoromethylcarbinyl esters and the reactivity as double acyl group donors

CrCl₂/Mn-mediated transformation of various dibromofluoromethylcarbinyl esters including carboxylates, carbonates and carbamates provided 1-fluoro-1-alkenyl esters via [2,3]-sigmatropic rearrangement of ester group. Reaction proceeded by using CrCl₂/Mn system under mild conditions (in THF at room temperature) to give 1-fluoro-1-alkenyl esters in good yield with an excellent Z selective manner. 1-Fluoro-1-alkenyl ester thus obtained acts as a double acyl donor in the reaction with necleophiles such as amine, thiol, alcohol as well as bifunctional necleophiles such as ethylene diamine derivative.