Single Step Synthesis of MoSe2−MoO3 Heterostructure for Highly Sensitive Amperometric Detection of Nitrite in Water Samples of Industrial Areas

The present work reports a simple and single‐step hydrothermal synthesis of MoSe₂?MoO₃ composite for highly sensitive and selective electrochemical oxidation of nitrite. FESEM of the MoSe₂?MoO₃ hybrid revealed the formation of composite as laminated structure of different sizes piled up together as finger‐like MoSe₂ bars whilst other physico‐chemical characterizations (XRD, FTIR, UV‐Vis, XPS) confirmed that co‐existence of MoO₃ as a major by‐product of hydrothermal synthesis. The as‐fabricated MoSe₂?MoO₃ composite based nitrite sensor showed remarkable selectivity and reproducibility with <3s of response time, excellent sensitivity and detection limit of 10.84 A M^?1 cm^?2 (R²=0.996) and 0.1 μM, respectively, in the range of 2.5–80 μM. The obtained sensitivity can be credited to the high surface area obtained from 1T phase MoSe₂ and α phase MoO₃ as the sensing material. The developed sensor was effectively evaluated for electrochemical recognition of nitrite in the water samples (potable and tap water) gathered from an industrial area. This new and efficient MoSe₂?MoO₃ based electrode material offers a new frontier for the progress of a novel composites by simple and single‐step approach which can be used for progress of non‐enzymatic and inexpensive electrochemical sensors for a wide range of analytical applications.     

Detecting lateral interfaces with focus‐engineered coherent anti‐Stokes Raman scattering microscopy

Focus‐engineered coherent anti‐Stokes Raman scattering (FE‐CARS) microscopy is used to highlight the lateral interfaces between chemically distinct media. Interface highlighting is achieved by using a HG10 mode for the Stokes laser beam and a HG00 mode for the pump laser beam in the forward detection scheme. The spectral and the orientation dependence of FE‐CARS are found to be in agreement with theoretical predictions. A brief discussion on the relevance of this technique for imaging third‐order nonlinear susceptibility interfaces in thin samples of biological or chemical importance is presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Study on the device characteristics of FePc and FePcCl organic thin film Schottky diodes: Influence of oxygen and post deposition annealing

Device characteristics of Al/FePc/Au and Al/FePcCl/Au are performed and found to show rectification properties. The basic diode parameters of the device are determined. The electrical conductivity has been measured both after exposure to oxygen for 20 days and after annealing at temperature up to 473 K. Current density-voltage characteristics under forward bias are found to be due to ohmic conduction at lower voltage regions. At higher voltage regions there is space charge limited conductivity (SCLC) controlled by a discrete trapping level above the valance edge. The electrical parameters of oxygen doped and annealed samples in the ohmic and SCLC region are determined. The reverse bias curves are interpreted in terms of a transition from electrode-limited Schottky emission to the bulk-limited the Poole-Frenkel effect. The Schottky barrier parameters of oxygen doped and annealed structures of FePc and FePcCl are determined from the C²-V characteristics.     

Lewis acid metal ion-exchanged MAPO-36 molecular sieve: Characterisation and catalytic activity

Magnesium aluminophosphate-36 (MAPO-36) molecular sieve was synthesised hydrothermally and subjected to wet ion-exchange with Fe³⁺, Zn²⁺, La³⁺ or Ce³⁺. They were characterised by using XRD, SEM, temperature programmed desorption (TPD) of ammonia and thermogravimetric analysis (TGA). The XRD patterns of ion-exchanged MAPO-36 exhibit similar features to that of MAPO-36, which revealed no structural degradation during ion-exchange. TPD (ammonia) showed selective ion-exchange of strong acid sites for Fe³⁺, La³⁺ and Ce³⁺ but not for Zn²⁺. Based on the results of TGA the actual species involved in the ion-exchange is suggested to be M(OH)₂⁺, which upon calcination converted to MO⁺ where M is Fe³⁺, La³⁺ or Ce³⁺. tert-Butylation of phenol was carried out in the vapour phase as a probe reaction to examine the catalytic activity of MAPO-36 and ion-exchanged MAPO-36 molecular sieves. The ion-exchanged catalysts were found to be more active than the parent MAPO-36 and also showed higher selectivity to 4-tert-butylphenol.     

Ionic liquid [Hmim]HSO4-promoted one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts

The first example of the one-pot oxidative conjugate addition of sulfur-centred nucleophiles to Baylis-Hillman adducts is reported. The reaction involves oxidation of Baylis-Hillman adducts with NaNO₃ in the Brønsted acidic ionic liquid [Hmim]HSO₄ to give [E]-α-cyanocinnamaldehydes followed by conjugate hydrothiocyanation/hydrosulfenylation with NH₄SCN/PhSH to afford the corresponding β-thiocyanato (or β-phenylsulfenyl)-α-cyanohydrocinnamaldehydes diastereoselectively in 76-89% yields in a one-pot procedure. After isolation of the product, the ionic liquid [Hmim]HSO₄ could be easily recycled for further use.     

A substituent directed regioselective synthesis of aryl/pyronyl pendant unusual adipate and tetrahydronaphthalene

An efficient regioselective synthesis of pyronyl pendant ethyl methylthiocarbonylalkanoates 5 has been delineated from the base catalyzed reaction of suitably functionalized 2-pyranone 1 and 2-carbethoxycycloalkanones 2, 6 through successive substitution and regioselective ring opening by in situ generated mercaptide ion. To assess the effect of C-4 substituent on regioselectivity, reactions of 6-aryl-3-cyano-4-(piperidin-1-yl)-2-oxopyran 8 with 2-carbethoxycyclohexanone 6a and 2-carbethoxy-2-methylcyclohexanone 6b were carried out separately under analogous reaction conditions but the compounds isolated were identical and characterized as 4-aryl-8-methyl-2-piperidin-1-yl-5,6,7,8-tetrahydronaphthalene-1-carbonitriles 9. Ethyl 2-(5-amino-4′-bromo-4,6-dicyanobiphenyl-3-yl)-5-methylsulfanylcarbonylpentanoate 10 has also been prepared through base catalyzed ring transformation of ethyl 2-[6-(4-bromophenyl)-3-cyano-2-oxo-2H-pyran-4-yl]-5-methylsulfanylcarbonylpentanoate 5d by malononitrile in DMF.     

Solution decomposition of the layered double hydroxide of Co with Fe: phase segregation of normal and inverse spinels

The nitrate-intercalated layered double hydroxide of Co with Fe decomposes on hydrothermal treatment to yield an oxide residue at a temperature as low as 180 degrees C. The oxide product is phase segregated into a Co(3)O(4)-type normal spinel and a CoFe(2)O(4)-type inverse spinel. Phase segregation is facilitated as decomposition in a solution medium takes place by dissolution of the precursor hydroxide followed by reprecipitation of the oxide phases. In contrast, thermal decomposition takes place at 400 degrees C. This temperature is inadequate to induce diffusion in the solid state whereby phase segregation into the thermodynamically stable individual spinels is suppressed. The result is a single-phase metastable mixed spinel oxide. This is rather uncommon in that a hydrothermal treatment yields thermodynamically stable products where as thermal decomposition yields a metastable product.     

Consequences of spin contamination in unrestricted calculations on open-shell species: effect of Hartree-Fock and Møller-Plesset contributions in hybrid and double-hybrid density functional theory approaches

The extent of spin contamination in unrestricted versions of pure, hybrid and double-hybrid density functional theory (DFT) methods, and its consequences, as manifested in the difference between unrestricted and restricted energies (U - R), has been investigated for 22 homolytic bond dissociation reactions. In accordance with previous studies, increasing the amount of Hartree-Fock (HF) exchange in unrestricted hybrid DFT procedures leads to an increase in the extent of spin contamination. However, in unrestricted double-hybrid DFT procedures, which include both a proportion of HF exchange and a perturbative correlation contribution (MP2), the opposing behavior of UHF and UMP2 with respect to spin contamination leads to smaller differences between the energies predicted by unrestricted and restricted variants. For example, for the most spin-contaminated radicals, a 30-100 kJ mol(-1) |U - R| difference at the HF and MP2 levels is reduced to just 0-5 kJ mol(-1) with the double-hybrid functionals. The double-hybrid UDFT procedures can thus benefit from the inclusion of UHF and UMP2 contributions without incurring to the same extent the problems associated with spin contamination.