TiO2/ZnO core/shell nano-heterostructure arrays as photo-electrodes with enhanced visible light photoelectrochemical performance

The present article reports a facile method for preparing the vertically-aligned 1D arrays of a new type of type II n-n TiO2/ZnO core/shell nano-heterostructures by growing the nano-shell of ZnO on the electrochemically fabricated TiO2 nanotubes core for visible light driven photoelectrochemical applications. The strong interfacial interaction at the type II heterojunction leads to an effective interfacial charge separation and charge transport. The presence of various defects such as surface states, interface states and other defects in the nano-heterostructure enable it for improved visible light photoelectrochemical performance. The presence of such defects has also been confirmed by the UV-vis absorption, cathodoluminescence, and crystallographic studies. The TiO2/ZnO core/shell nano-heterostructures exhibit strong green luminescence due to the defect transitions. The TiO2/ZnO core/shell nano-heterostructures photo-electrode show significant enhancement of visible light absorption and it provides a photocurrent density of 0.7 mA cm(-2) at 1 V vs. Ag/AgCl, which is almost 2.7 times that of the TiO2/ZnO core/shell nano-heterostructures under dark conditions. The electrochemical impedance spectroscopy results demonstrate that the substantially improved photoelectrochemical and photo-switching performance of the nano-heterostructures photo-anode is because of the enhancement of interfacial charge transfer and the increase in the charge carrier density caused by the incorporation of the ZnO nano-shell on TiO2 nanotube core.

Enhancing the photocatalytic efficiency of sprayed ZnO thin films through double doping (Sn plus F) and annealing under different ambiences

Doubly (Sn + F) doped zinc oxide (ZnO:Sn:F) thin films were deposited onto glass substrates using a simplified spray pyrolysis technique. The deposited films were annealed at 400 degrees C under two different ambiences (air and vacuum) for 2 h. The photocatalytic activity of these films was assessed through photocatalytic decolorization kinetics of Methylene Blue (MB) dye and the decolorization efficiency of the annealed films was compared with that of their as-deposited counterpart. The photocatalytic studies reveal that the ZnO:Sn:F films annealed under vacuum environment exhibits better photocatalytic efficiency when compared with both air annealed and as-deposited films. The SEM and TEM images depict that the surface of each of the films has an overlayer comprising of nanobars formed on a bottom layer, having spherical grains. The studies show that the diameter of the nanobars plays crucial role in enhancing the photocatalytic activity of the ZnO:Sn:F films. The structural, optical and electrical studies substantiate the discussions on the photocatalytic ability of the deposited films. (C) 2014 Elsevier B.V. All rights reserved.

Combinatorial Crystal Synthesis: Structural Landscape of Phloroglucinol:1,2-bis(4-pyridyl)ethylene and Phloroglucinol:Phenazine

A large number of crystal forms, polymorphs and pseudopolymorphs, have been isolated in the phloroglucinol-dipyridylethylene (PGL:DPE) and phloroglucinol-phenazine (PGL:PHE) systems. An understanding of the intermolecular interactions and synthon preferences in these binary systems enables one to design a ternary molecular solid that consists of PGL, PHE, and DPE, and also others where DPE is replaced by other heterocycles. Clean isolation of these ternary cocrystals demonstrates synthon amplification during crystallization. These results point to the lesser likelihood of polymorphism in multicomponent crystals compared to single-component crystals. The appearance of several crystal forms during crystallization of a multicomponent system can be viewed as combinatorial crystal synthesis with synthon selection from a solution library. The resulting polymorphs and pseudopolymorphs that are obtained constitute a crystal structure landscape.

ZnO/ITO core/shell nanostructure electrodes for future prototype solar cell devices

The impact of indium tin oxide (ITO) layers over vertically aligned zinc oxide nanorods (ZnO NRs) has been investigated to consider ITO nanolayers as transparent conducting oxide electrodes (TCOE) for hierarchical heteronanostructure solar cell devices that have ZnO nanostructures as branches. ZnO/ITO core/shell nanostructures were prepared in two- steps using vapor-liquid-solid and evaporation processes, and further the structures were annealed at various temperatures. Transmission electron microscopic studies show that the as-grown ZnO/ITO structures consist of an amorphous ITO shell on single crystalline ZnO cores, whereas the structures annealed above 300 degrees C consist of a single crystalline ITO shell. ITO layer deposited ZnO NRs exhibit a small red-shift in ZnO near-band-edge emission as well as optical band gap. The electrical measurements carried out on single ZnO/ITO core/shell NR under dark and UV light showed excellent thermionic transport properties. From these investigations it is emphasized that ITO nanolayers could be used as TCO electrodes for prototype ZnO based hierarchical solar cell devices.

Assignment of the C-13 NMR spectrum by correlation to dipolar coupled proton-pairs and estimation of order parameters of a thiophene based liquid crystal

Materials with widely varying molecular topologies and exhibiting liquid crystalline properties have attracted considerable attention in recent years. C-13 NMR spectroscopy is a convenient method for studying such novel systems. In this approach the assignment of the spectrum is the first step which is a non-trivial problem. Towards this end, we propose here a method that enables the carbon skeleton of the different sub-units of the molecule to be traced unambiguously. The proposed method uses a heteronuclear correlation experiment to detect pairs of nearby carbons with attached protons in the liquid crystalline core through correlation of the carbon chemical shifts to the double-quantum coherences of protons generated through the dipolar coupling between them. Supplemented by experiments that identify non-protonated carbons, the method leads to a complete assignment of the spectrum. We initially apply this method for assigning the C-13 spectrum of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl oriented in the magnetic field. We then utilize the method to assign the aromatic carbon signals of a thiophene based liquid crystal thereby enabling the local order-parameters of the molecule to be estimated and the mutual orientation of the different sub-units to be obtained.

Zinc oxide based photocatalysis: tailoring surface-bulk structure and related interfacial charge carrier dynamics for better environmental applications

As an alternative to the gold standard TiO2 photocatalyst, the use of zinc oxide (ZnO) as a robust candidate for wastewater treatment is widespread due to its similarity in charge carrier dynamics upon bandgap excitation and the generation of reactive oxygen species in aqueous suspensions with TiO2. However, the large bandgap of ZnO, the massive charge carrier recombination, and the photoinduced corrosion-dissolution at extreme pH conditions, together with the formation of inert Zn(OH)(2) during photocatalytic reactions act as barriers for its extensive applicability. To this end, research has been intensified to improve the performance of ZnO by tailoring its surface-bulk structure and by altering its photogenerated charge transfer pathways with an intention to inhibit the surface-bulk charge carrier recombination. For the first time, the several strategies, such as tailoring the intrinsic defects, surface modification with organic compounds, doping with foreign ions, noble metal deposition, heterostructuring with other semiconductors and modification with carbon nanostructures, which have been successfully employed to improve the photoactivity and stability of ZnO are critically reviewed. Such modifications enhance the charge separation and facilitate the generation of reactive oxygenated free radicals, and also the interaction with the pollutant molecules. The synthetic route to obtain hierarchical nanostructured morphologies and study their impact on the photocatalytic performance is explained by considering the morphological influence and the defect-rich chemistry of ZnO. Finally, the crystal facet engineering of polar and non-polar facets and their relevance in photocatalysis is outlined. It is with this intention that the present review directs the further design, tailoring and tuning of the physico-chemical and optoelectronic properties of ZnO for better applications, ranging from photocatalysis to photovoltaics.

Synthesis and crystal structure of copper (II) uracil ternary polymeric complex with 1,10-phenanthroline along with the Hirshfeld surface analysis of the metal binding sites for the uracil ligand

The study of models for ``metal-enzyme-substrate'' interaction has been a proactive area of research owing to its biological and pharmacological importance. In this regard the ternary copper uracil complex with 1,10-phenanthroline represents metal-enzyme-substrate system for DNA binding enzymes. The synthesis of the complex, followed by slow evaporation of the reaction mixture forms two concomitant solvatomorph crystals viz., {Cu(phen)(mu-ura)(H2O)](n)center dot H2O (1a)} and {Cu(phen)(mu-ura)(H2O)](n)center dot CH3OH (1b)}. Both complexes are structurally characterized, while elemental analysis, IR and EPR spectra were recorded for 1b (major product). In both complexes, uracil coordinates uniquely via N1 and N3 nitrogen atom acting as a bidentate bridging ligand forming a 1-D polymer. The two solvatomorphs were quantitatively analyzed for the differences with the aid of Hirshfeld surface analysis. (C) 2014 Elsevier B.V. All rights reserved.

Salts of hexamethylenetetramine with organic acids: Enhanced anomeric interactions with a lowering of molecular symmetry revealed by crystal structures

The hexamethylenetetramine (HMT) framework displays interesting stereoelectronic interactions of the anomeric type. In the highly symmetrical parent system, the nitrogen centres act as both donors and acceptors. Protonation lowers symmetry and also leads to an enhancement of the anomeric interaction around the protonated centre. X-ray diffraction crystal structures of four derivatives of HMT - with succinic, (DL)-malic, phthalic and 4-hydroxybenzoic acids - reveal significant trends. (The first three form well-defined salts, 4-hydroxybenzoic acid forming a co-crystalline compound.) Each molecular structure is essentially characterised by a major anomeric interaction involving the protonated centre as acceptor. In two cases (succinic and 4-hydroxybenzoic), secondary protonation leads to a weaker anomeric interaction site that apparently competes with the dominant one. Bond length changes indicate that the anomeric interaction decreases as malic > phthalic > succinic > 4-hydroxybenzoic, which correlates with the degree of proton transfer to the nitrogen centre. Along with other bond length and angle changes, the results offer insight into the applicability of the antiperiplanar lone pair hypothesis (ALPH) in a rigid system. (C) 2014 Elsevier B.V. All rights reserved.

Salts of hexamethylenetetramine with organic acids: Enhanced anomeric interactions with a lowering of molecular symmetry revealed by crystal structures

The hexamethylenetetramine (HMT) framework displays interesting stereoelectronic interactions of the anomeric type. In the highly symmetrical parent system, the nitrogen centres act as both donors and acceptors. Protonation lowers symmetry and also leads to an enhancement of the anomeric interaction around the protonated centre. X-ray diffraction crystal structures of four derivatives of HMT - with succinic, (DL)-malic, phthalic and 4-hydroxybenzoic acids - reveal significant trends. (The first three form well-defined salts, 4-hydroxybenzoic acid forming a co-crystalline compound.) Each molecular structure is essentially characterised by a major anomeric interaction involving the protonated centre as acceptor. In two cases (succinic and 4-hydroxybenzoic), secondary protonation leads to a weaker anomeric interaction site that apparently competes with the dominant one. Bond length changes indicate that the anomeric interaction decreases as malic > phthalic > succinic > 4-hydroxybenzoic, which correlates with the degree of proton transfer to the nitrogen centre. Along with other bond length and angle changes, the results offer insight into the applicability of the antiperiplanar lone pair hypothesis (ALPH) in a rigid system. (C) 2014 Elsevier B.V. All rights reserved.

Exploring the Crystal Structure Landscape with a Heterosynthon Module: Fluorobenzoic Acid:1,2-Bis(4-pyridyl)ethylene 2:1 Cocrystals

The crystal structure landscape of the 2:1 benzoic acid:dipyridylethylene cocrystal (BA:DPE-I) is explored experimentally with fluoro-substituted benzoic acids and extended with studies employing the Cambridge Structural Database (CSD). The interpretation of the cocrystal landscape is facilitated by considering the kinetically favored and robust acidpyridine heterosynthon as a modular unit. Information based on high-throughput crystallography shows that polymorphs and pseudopolymorphs may belong to the same landscape but arise from different crystallization pathways because of complex and different kinetic features, and secondary synthon preferences. Using the CSD as a guide, the coformer was changed from 1,2-bis(4-pyridyl)ethylene (DPE-I) to 1,2-bis(4-pyridyl)ethane (DPE-II) and this provides an extended interpretation of the BA:DPE-I cocrystal landscape, also highlighting the complexity of the kineticthermodynamic dichotomy during the molecule-to-crystal progression.

Simple chemical aqueous synthesis of dahlia nanoflower consisting of finger-like ZnO nanorods and observation of stable ultraviolet photoluminescence emission

In this work, we have reported the synthesis of dahlia flower-like ZnO nanostructures consisting of human finger-like nanorods by the hydrothermal method at 120 degrees C and without using any capping agent. Optical properties of the samples, including UV-vis absorption and photoluminescence (PL) emission characteristics are determined by dispersing the samples in water as well as in ethanol media. The quenching of PL emission intensity along-with the red shifting of the PL emission peak are observed when the samples are dispersed in water in comparison to those obtained after dispersing the samples in ethanol. It has been found that PL emission characteristic, particularly the spectral nature of PL emission, of the samples remains almost unaltered (except some improvement in UV PL emission) even after thermally annealing it for 2 h at the temperature of 300 degrees C. Also the synthesized powder samples, kept in a plastic container, showed a very stable PL emission even after 15 months of synthesis. Therefore, the synthesized samples might be useful for their applications in future optoelectronics devices. (C) 2014 Elsevier Ltd. All rights reserved.

Synthesis, crystal structure and spectroscopic and electrochemical properties of bridged trisbenzoato copper-zinc heterobinuclear complex of 2,2 `-bipyridine

The synthesis of the heterobinuclear copper-zinc complex CuZn(bz)(3)(bpy)(2)]ClO4 (bz = benzoate) from benzoic acid and bipyridine is described. Single crystal X-ray diffraction studies of the heterobinuclear complex reveals the geometry of the benzoato bridged Cu(II)-Zn(II) centre. The copper or zinc atom is pentacoordinate, with two oxygen atoms from bridging benzoato groups and two nitrogen atoms from one bipyridine forming an approximate plane and a bridging oxygen atom from a monodentate benzoate group. The Cu-Zn distance is 3.345 angstrom. The complex is normal paramagnetic having mu(eff) value equal to 1.75 BM, ruling out the possibility of Cu-Cu interaction in the structural unit. The ESR spectrum of the complex in CH3CN at RT exhibit an isotropic four line spectrum centred at g = 2.142 and hyperfine coupling constants A(av) = 63 x 10(-4) cm(-1), characteristic of a mononuclear square-pyramidal copper(II) complexes. At LNT, the complex shows an isotropic spectrum with g(parallel to) = 2.254 and g(perpendicular to) =2.071 and A(parallel to) = 160 x 10(-4) cm(-1). The Hamiltonian parameters are characteristic of distorted square pyramidal geometry. Cyclic voltammetric studies of the complex have indicated quasi-reversible behaviour in acetonitrile solution. (C) 2014 Elsevier B.V. All rights reserved.

An encaged sigma* orbital in 3-methoxy-2,4,10-trioxaadamantane. Preferred exo-anomeric effect as revealed by the crystal structure

In the titled tricyclic orthocarbonate derivative, the three endocyclic C-O bonds are longer than the exo-cyclic C-O bond (similar to 4.40 angstrom vs. similar to 1.37 angstrom). This indicates an anomeric-type interaction between the two electron lone pairs on the exocyclic oxygen atom and the antibonding orbitals of the two antiperiplanar endocyclic C-O bonds. The remaining endocyclic C-O bond - marginally shorter than the other two apparently adds to this effect. Intriguingly, the antibonding orbital of the exocyclic C-O bond extends into the interior of the adamantyl cage, and is stereoelectronically prevented from overlapping with any of the six adjacent lone pairs. The results also seem to indicate a preference for interaction between a single donor oxygen atom and multiple acceptor antibonding orbitals rather than vice versa. The results add insightfully to the substantial body of evidence favouring the antiperiplanar lone pair hypothesis (ALPH). (C) 2014 Elsevier B.V. All rights reserved.

Enhanced photocatalytic efficiency of AuPd nanoalloy decorated ZnO-reduced graphene oxide nanocomposites

Inhibition of electron-hole pair recombination is the most desirable solution for stimulating photocatalytic activity in semiconductor nanostructures. To implement this, herein we study the photocatalytic efficiency of elemental Au, Pd and bimetallic AuPd nanoalloy decorated pristine and reduced graphene oxide (RGO) hybridized ZnO nanorods for degrading rhodamine 6G (R6G) dye. Fabrication of Au, Pd and AuPd nanoalloy on pristine and RGO modified ZnO nanorods is simple and more importantly surfactant or polymer free. AuPd nanoalloyed ZnO-RGO nanocomposites exhibit higher photocatalytic activity for degrading dye than both Au and Pd hybridized ones, indicating the promising potential of bimetallic nanoalloys over elemental components. A non-monotonic dependence on the composite composition was found by analyzing photodegradation efficiency of a series of ZnO-RGO-AuPd hybrid nanostructures with different weight percentages of RGO. The hybrid nanostructure ZnO-RGO (5 wt%)-AuPd (1 wt%) exhibits highest photodegradation efficiency (similar to 100% degradation in 20 min) with an improvement in rate constant (k) by a factor of 10 compared to that of the ZnO-RGO nanocomposite. The enhancement of the photocatalytic activity is attributed to the better separation of photogenerated charge carriers in photocatalysts thereby suggesting possible usefulness in a broad range of applications, such as sensing, photocatalysis and solar energy conversion.

Highly efficient WO3-ZnO mixed oxides for photocatalysis

Monoclinic nanocuboid WO3 enhanced the photocatalyst efficiency of quasi nanobelt zinc oxide for dye degradation in the presence of visible light radiation. Combustion synthesized ZnO resulted in a belt-like morphology through in situ cluster formation of near spherical particles but homogenously disperses and strongly adheres to nanocuboid WO3 during physical mixing. Cationic methylene blue (MB) and anionic orange G (OG) undergo degradation through a charge transfer mechanism in the presence of WO3-ZnO (1 : 9 weight percentage ratio) mixture. The photocatalytic reaction was enhanced due to the reduction in the recombination of photogenerated electron-holes. The high degree of 90% degradation of both dyes is due to the activity of the mixed oxides, which is much higher than that obtained either with WO3 or ZnO individually.