Facile synthesis of PbWO4: Applications in photoluminescence and photocatalytic degradation of organic dyes under visible light

Stolzite polymorph of PbWO4 catalyst was prepared by the facile room temperature precipitation method. Structural parameters were refined by the Rietveld analysis using powder X-ray data. PbWO4 was crystallized in the scheelite-type tetragonal structure with space group I4(1)/a (No. 88). Field emission scanning electron microscopy revealed leaf like morphology. Photoluminescence spectra exhibit broad blue emission (425 nm) under the excitation of 356 nm. The photocatalytic degradation of Methylene blue, Rhodamine B and Methyl orange dyes were measured under visible illumination. The 100% dye degradation was observed for MB and RhB dyes within 60 and 105 min. The rate constant was found to be in the decreasing order of MB > RhB > MO which followed the 1st order kinetic mechanism. Therefore, PbWO4 can be a potential candidate for blue component in white LEDs and also acts as a catalyst for the treatment of toxic and non-biodegradable organic pollutants in water. (C) 2014 Elsevier B.V. All rights reserved.

Modeling of sonochemical decomposition of CCI4 in aqueous solutions

In the context of removal of organic pollutants from wastewater, sonolysis of CCl4 dissolved in water has been widely investigated. These investigations are either completely experimental or correlate data empirically. In this work, a quantitative model is developed to predict the rate of sonolysis of aqueous CCl4. The model considers the isothermal growth and partially adiabatic collapse of cavitation bubbles containing gas and vapor leading to conditions of high temperatures and pressures in them, attainment of thermodynamic equilibrium at the end of collapse, release of bubble contents into the liquid pool, and reactions in the well-mixed pool. The model successfully predicts the extent of degradation of dissolved CCl4, and the influence of various parameters such as initial concentration of CCl4, temperature, and nature of gas atmosphere above the liquid. in particular, it predicts the results of Hua and Hoffmann (Environ. Sci Technol, 1996, 30, 864-871), who found that degradation is first order with CCl4 and that Argon as well as Ar-O-3 atmospheres give the same results. The framework of the model is capable of quantitatively describing the degradation of many dissolved organics by considering all the involved species.

Cyclodextrin functionalized magnetic iron oxide nanocrystals: a host-carrier for magnetic separation of non-polar molecules and arsenic from aqueous media

A single-step magnetic separation procedure that can remove both organic pollutants and arsenic from contaminated water is clearly a desirable goal. Here we show that water dispersible magnetite nanoparticles prepared by anchoring carboxymethyl-beta-cyclodextrin (CMCD) cavities to the surface of magnetic nanoparticles are suitable host carriers for such a process. Monodisperse, 10 nm, spherical magnetite, Fe3O4, nanocrystals were prepared by the thermal decomposition of FeOOH. Trace amounts of antiferromagnet, FeO, present in the particles provides an exchange bias field that results in a high superparamagnetic blocking temperature and appreciable magnetization values that facilitate easy separation of the nanocrystals from aqueous dispersions on application of modest magnetic fields. We show here that small molecules like naphthalene and naphthol can be removed from aqueous media by forming inclusion complexes with the anchored cavities of the CMCD-Fe3O4 nanocrystals followed by separation of the nanocrystals by application of a magnetic field. The adsorption properties of the iron oxide surface towards As ions are unaffected by the CMCD capping so it too can be simultaneously removed in the separation process. The CMCD-Fe3O4 nanocrystals provide a versatile platform for magnetic separation with potential applications in water remediation.

Photoelectrochemical oxidation of p-nitrophenol on an expanded graphite-TiO2 electrode

In the quest for more efficient photoanodes in the photoelectrochemical oxidation processes for organic pollutant degradation and mineralisation in water treatment, we present the synthesis, characterisation and photoelectrochemical application of expanded graphite-TiO2 composite (EG-TiO2) prepared using the sol-gel method with organically modified silicate. The Brunauer-Emmett-Teller surface area analyser, ultraviolet-visible diffuse reflectance, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, Raman spectrometry and X-ray photoelectron spectroscopy were employed for the characterisation of the composites. The applicability of the EG-TiO2 as photoanode material was investigated by the photoelectrochemical degradation of p-nitrophenol as a target pollutant in a 0.1 M Na2SO4 (pH 7) solution at a current density of 5 mA cm(-2). After optimising the TiO2 loading, initial p-nitrophenol concentration, pH and current density, a removal efficiency of 62% with an apparent kinetic rate constant of 10.4 x 10(-3) min(-1) was obtained for the photoelectrochemical process as compared to electrochemical oxidation and photolysis, where removal efficiencies of 6% and 24% were obtained respectively after 90 min. Furthermore, the EG-TiO2 electrode was able to withstand high current density due to its high stability. The EG-TiO2 electrode was also used to degrade 0.3 x 10(-4) M methylene blue and 0.1 x 10(-4) M Eosin Yellowish, leading to 94% and 47% removal efficiency within 120 reaction time. This confirms the suitability of the EG-TiO2 electrode to degrade other organic pollutants.

Cyclodextrin-functionalized Fe3O4@TiO2: reusable, magnetic nanoparticles for photocatalytic degradation of endocrine-disrupting chemicals in water supplies

Water-dispersible, photocatalytic Fe3O4@TiO2 core shell magnetic nanoparticles have been prepared by anchoring cyclodextrin cavities to the TiO2 shell, and their ability to capture and photocatalytically destroy endocrine-disrupting chemicals, bisphenol A and dibutyl phthalate, present in water, has been demonstrated. The functionalized nanoparticles can be magnetically separated from the dispersion after photocatalysis and hence reused. Each component of the cyclodextrin-functionalized Fe3O4@TiO2 core shell nanoparticle has a crucial role in its functioning. The tethered cyclodextrins are responsible for the aqueous dispersibility of the nanoparticles and their hydrophobic cavities for the capture of the organic pollutants that may be present in water samples. The amorphous TiO2 shell is the photocatalyst for the degradation and mineralization of the organics, bisphenol A and dibutyl phthalate, under UV illumination, and the magnetism associated with the 9 nm crystalline Fe3O4 core allows for the magnetic separation from the dispersion once photocatalytic degradation is complete. An attractive feature of these ``capture and destroy'' nanomaterials is that they may be completely removed from the dispersion and reused with little or no loss of catalytic activity.

Renewable Energy via Photocatalysis

The generation of renewable energy through photocatalysis is an attractive option to utilize the abundantly available solar radiation for a sustainable future. Photocatalysis refers to charge-carrier, i.e. electron and hole, mediated reactions occurring on a semiconductor surface in presence of ultraviolet or visible light radiation. Photocatalysis is a well established advanced oxidation technique for the decontamination of toxic organic pollutants to CO2 and H2O. However, the generation of energy in the form of hydrogen, hydrocarbon fuels and electricity via photocatalysis is an upcoming field with great many technical challenges towards practical implementation. This review will describe the fundamental reaction mechanism of (i) photocatalytic water splitting, (ii) photocatalytic H-2 generation in presence of different sacrificial agents, (iii) H-2 and electricity generation in a photofuel cell, (iv) photocatalytic reduction of CO2 to hydrocarbons and useful chemicals, and (v) photocatalytic water-gas shift reaction. A historic and recent perspective of the above conversion techniques, especially with regard to the development of TiO2-based and non-TiO2 materials is provided. The activity of different materials for the above reactions based on quantifiers like reaction rate, quantum yield and incident-photon-to-current efficiency is compared, and key design considerations of the ``best'' photocatalyst or photoelectrode is outlined. An overall assessment of the research area indicates that the presently achieved quantum efficiencies for the above reactions are rather moderate in the visible region, and the goal is to develop a catalyst that absorbs visible radiation, provides good charge-carrier separation, and exhibits high stability for long periods of usage.

Photoluminescence, photocatalysis and Judd-Ofelt analysis of Eu3+-activated layered BiOCl phosphors

Eu3+-activated layered BiOCl phosphors were synthesized by the conventional solid-state method at relatively low temperature and shorter duration (400 degrees C for 1 h). All the samples were crystallized in the tetragonal structure with the space group P4/nmm (no. 129). Field emission scanning electron microscopy (FE-SEM) studies confirmed the plate-like morphology. Photoluminescence spectra exhibit characteristic luminescent D-5(0) -> F-7(J) (J = 0-4) intra-4f shell Eu3+ ion transitions. The electric dipole transition located at 620 nm (D-5(0) -> F-7(2)) was stronger than the magnetic dipole transition located at 594 nm (D-5(0) -> F-7(1)). The evaluated Commission International de l'Eclairage (CIE) color coordinates of Eu3+-activated BiOCl phosphors were close to the commercial Y2O3:Eu3+ and Y2O2S:Eu3+ red phosphors. Intensity parameters (Omega(2), Omega(4)) and various radiative properties such as transition probability (A(tot)), radiative lifetime (tau(rad)), stimulated emission cross-section (sigma(e)), gain bandwidth (sigma(e) x Delta lambda(eff)) and optical gain (sigma(e) x tau(rad)) were calculated using the Judd-Ofelt theory. The experimental decay curves of the D-5(0) level in Eu3+-activated BiOCl have a single exponential profile. In comparison with other Eu3+ doped materials, Eu3+-activated BiOCl phosphors have a long lifetime (tau(exp)), low non-radiative relaxation rate (W-NR), high quantum efficiency (eta) and better optical gain (sigma(e) x tau(rad)). The determined radiative properties revealed the usefulness of Eu3+-activated BiOCl in developing red lasers as well as optical display devices. Further, these samples showed efficient photocatalytic activity for the degradation of rhodamine B (RhB) dye under visible light irradiation. These photocatalysts are useful for the removal of toxic and non-biodegradable organic pollutants in water.

Fabrication of novel Ag3PO4/BiOBr heterojunction with high stability and enhanced visible-light-driven photocatalytic activity

Herein, we report a facile and effective method to enhance the photocatalytic activity of bismuth oxybromide (BiOBr) semiconductor through the fabrication of heterojunction with Ag3PO4. The as synthesized Ag3PO4/BiOBr microspheres were characterized with transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) and UV-vis diffuse reflectance spectroscopy (DRS). The new Ag3PO4/BiOBr heterojunctions exhibited wide absorption in the visible-light region and compared to pure BiOBr and Ag3PO4 samples displayed exceptionally high photocatalytic activity for the degradation of typical organic pollutants such as Rhodamine B (RhB) and phenol. The optimal Ag/Bi weight ratio in Ag3PO4/BiOBr microsphere (AB7) was found to be 0.7. The enhanced photocatalytic activity was related to the efficient separation of electron-hole pairs derived from matching band potentials between BiOBr and Ag3PO4 which results into the generation of natural energy bias at heterojunction and subsequent transfer of photoinduced charge carriers. Moreover, the synthesized samples exhibited almost no loss of activity even after 6 recycling runs indicating their high photocatalytic stability. Considering the facile and environment friendly route for the synthesis of Ag3PO4/BiOBr hybrids with enhanced visible-light induced photocatalytic activity, it is possible to widely apply these hybrids in various fields such as waste water treatment. (C) 2015 Elsevier B.V. All rights reserved.

High photoconductive combustion synthesized TiO2 derived nanobelts for photocatalytic water purification under solar irradiation

Drinking water scarcity is a major issue that needs to be addressed seriously. Water needs to be purified from organic pollutants and bacterial contamination. In this study, sunlight driven photocatalysis for the degradation of dyes and bacterial inactivation has been conducted over TiO2 nanoparticles (CST) and TiO2 nanobelts (CSTNB). TiO2 nanoparticles were synthesized by a solution combustion process using ascorbic acid as a fuel. Acid etched TiO2 nanobelts (CSTNB) were synthesized using combustion synthesized TiO2 as a novel precursor. The mechanism of formation of TiO2 nanobelts was hypothesized. The antibacterial activity of combustion synthesized TiO2 and acid etched TiO2 nanobelts were evaluated against Escherichia coli and compared against commercial TiO2. Various characterization studies like X-ray diffraction analysis, BET surface area analysis, diffused reflectance measurements were performed. Microscopic structures and high resolution images were analyzed using scanning electron microscopy, transmission electron microscopy. The extent of photo-stability and reusability of the catalyst was evaluated by conducting repeated cycles of photo degradation experiments and was compared to the commercial grade TiO2. The reactive radical species responsible for high photocatalytic and antibacterial activity has been determined by performing multiple scavenger reactions. The excellent charge transfer mechanism, high generation of hydroxyl and hole radicals resulted in enhanced photocatalytic activity of the acid etched TiO2 nanobelts compared to commercial TiO2 and nanobelts made from commercial TiO2.

Emerging trends at the interface of chemistry and biology: Applications to the design of human therapeutics

This article describes recent developments in the design and implementation of various strategies towards the development of novel therapeutics using first principles from biology and chemistry. Strategies for multi-target therapeutics and network analysis with a focus on cancer and HIV are discussed. Methods for gene and siRNA delivery are presented along with challenges and opportunities for siRNA therapeutics. Advances in protein design methodology and screening are described, with a focus on their application to the design of antibody based therapeutics. Future advances in this area relevant to vaccine design are also mentioned.

Organic device electrode fabricated by aluminum in nanopowder and bulk form and effect on device properties

Schottky barrier devices of metal/semiconductor/metal structure were fabricated using organic semiconductor polyaniline (PANI) and aluminium thin film cathode. Aluminium contacts were made by thermal evaporation technique using two different forms of metals (bulk and nanopowder). The structure and surface morphology of these films were investigated by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. Grain size of the as-deposited films obtained by Scherrer's method, modified Williamson-Hall method, and SEM were found to be different. Current-voltage (I-V) characteristic of Schottky barrier device structure indicates that the calculated current density (J) for device fabricated from aluminium nanopowder is more than that from aluminium in bulk form.

Catalytic Enantioselective Halocyclizations beyond Lactones: Emerging Routes to Enantioenriched Nitrogenous Heterocycles

Electrophilic halogen-induced reactions of unactivated olefins are an important class of transformations, whose catalytic enantioselective variants have surfaced during the past few years as effective means of olefin heterodifunctionalization. This article covers important developments in the area of enantioselective halocyclizations, specifically in the context of the synthesis of nitrogenous heterocycles.

Design and synthesis of new low band gap organic semiconductors for photovoltaic applications

Donor-acceptor (D-A) conjugated polymers have attracted a good deal of attention in recent years. In D-A systems, the introduction of electron withdrawing groups reduces E-g by lowering the LUMO levels whereas, the introduction of electron donating groups reduces E-g by raising the HOMO levels. Also, conjugated polymers with desired HOMO and LUMO energy levels could be obtained by the proper selection of donor and acceptor units. Because of this reason, D-A conjugated polymers are emerging as promising materials particularly for polymer light emitting diodes (PLEDs) and polymer solar cells (PSCs). We report the design and synthesis of four new narrow band gap donor-acceptor (D-A) conjugated polymers, PTCNN, PTCNF, PTCNV and PTCNO, containing electron donating 3,4-didodecyloxythiophene and electron accepting cyanovinylene units. The effects of further addition of electron donating and electron withdrawing groups to the repeating unit of a D-A conjugated polymer (PTCNN) on its optical and electrochemical properties are discussed. The studies revealed that the nature of D and A units as well as the extent of alternate D-A structure influences the optical and the electrochemical properties of the polymers. All the polymers are thermally stable up to a temperature of 300 degrees C under nitrogen atmosphere. The electrochemical studies revealed that the polymers possess low-lying HOMO energy levels and low-lying LUMO energy levels. In the UV-Vis absorption study, the polymer films displayed broad absorption in the wavelength region of 400-700 nm. The polymers exhibited low optical band gaps in the range 1.70 - 1.77 eV.

Multifarious facets of sugar-derived molecular gels: molecular features, mechanisms of self-assembly and emerging applications

The remarkable capability of nature to design and create excellent self-assembled nano-structures, especially in the biological world, has motivated chemists to mimic such systems with synthetic molecular and supramolecular systems. The hierarchically organized self-assembly of low molecular weight gelators (LMWGs) based on non-covalent interactions has been proven to be a useful tool in the development of well-defined nanostructures. Among these, the self-assembly of sugar-derived LMWGs has received immense attention because of their propensity to furnish biocompatible, hierarchical, supramolecular architectures that are macroscopically expressed in gel formation. This review sheds light on various aspects of sugar-derived LMWGs, uncovering their mechanisms of gelation, structural analysis, and tailorable properties, and their diverse applications such as stimuli-responsiveness, sensing, self-healing, environmental problems, and nano and biomaterials synthesis.

Electron spin resonance absorption in organic metal polyaniline and its blend with PMMA

The electron spin resonance absorption in the synthetic metal polyaniline (PANI) doped with PTSA and its blend with poly(methylmethacrylate) (PMMA) is investigated in the temperature range between 4.2 and 300 K. The observed line shape follows Dyson's theory for a thick metallic plate with slowly diffusing magnetic dipoles. At low temperatures the line shape become symmetric and Lorentzian when the sample dimensions are small in comparison with the skin depth. The temperature dependence of electron spin relaxation time is discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.