The synthesis, structure, optical and photocatalytic properties of silica-coated cadmium sulfide nanocomposites of different shapes

The CdS nanostructure undergoes photochemical dissolution, and hence, the photocatalytic activity deteriorates with light irradiation time. A thin layer of silica coating over CdS surface may prevent the photocorrosion and coalescence of quantum size CdS particles. Hence, we synthesized SiO(2)@CdS nanocomposites of different shapes and characterized them by XRD, HRTEM, EDX, SAED, BET surface area measurement and absorption and emission study. The dispersion of spherical CdS (Cd-2.62 at% and S-2.33 at%) nanoparticles of cubic crystal structure into thick amorphous SiO(2) (43.79 at%) matrix is demonstrated here. The fabrication of core (CdS)-shell (SiO(2)) structure (SiO(2)@CdS) consisting of CdS nanorod (Cd-19.79 at% and S-22.90 at%) core (length ~126 nm and width ~6 nm) having characteristic lattice fringes of hexagonal crystals and thin SiO(2) (12.81 at%) shell (thickness=1-1.4 nm) is successfully achieved for the first time. The surface area (21.2m(2)/g) of CdS nanorod (aspect ratio=21) is found to increase (42.3m(2)/g) after SiO(2) coating. The photoluminescence of CdS nanosphere (485 nm) and nanorod (501 nm) is highly quenched after SiO(2) layer formation. The superior photocatalytic activity of SiO(2)@CdS composites for the benzaldehyde oxidation under UV irradiation has been displayed.     

Role of solvation dynamics in excited state proton transfer of 1-naphthol in nanoscopic water clusters formed in a hydrophobic solvent

Excited state proton transfer (ESPT) in biologically relevant organic molecules in aqueous environments following photoexcitation is very crucial as the reorganization of polar solvents (solvation) in the locally excited (LE) state of the organic molecule plays an important role in the overall rate of the ESPT process. A clear evolution of the two photoinduced dynamics in a model ESPT probe 1-naphthol (NpOH) upon ultrafast photoexcitation is the motive of the present study. Herein, the detailed kinetics of the ESPT reaction of NpOH in water clusters formed in hydrophobic solvent are investigated. Distinct values of time constants associated with proton transfer and solvent relaxation have been achieved through picosecond-resolved fluorescence measurements. We have also used a model solvation probe Coumarin 500 (C500) to investigate the dynamics of solvation in the same environmental condition. The temperature dependent picosecond-resolved measurement of ESPT of NpOH and the dynamics of solvation from C500 identify the magnitude of intermolecular hydrogen bonding energy in the water cluster associated with the ultrafast ESPT process.     

Design and synthesis of coumarinyl 1,4-benzodioxanes as potential anti-oxidant

A series of novel coumarinyl 1,4-benzodioxanes were successfully synthesized from electronically diverse 2-[(o-iodophenoxy)methyl]oxiranes and different positional isomers of hydroxycoumarin via one-pot tandem nucleophilic displacement and copper-mediated intramolecular C–O coupling reaction using CuI and 1,10-phenanthroline as the efficient catalytic system. All the compounds were characterized by ¹H, ¹³C NMR, IR, HRMS spectra and a selected set of newly synthesized compounds offered noticeable in vitro free hydroxyl radical scavenging activity in a systematic dose dependent manner which signifies their excellent biological potential.     

Catalysis by zeolite leading to the construction of thiazole ring: an improved synthesis of 4-alkynyl substituted thiazoles

Zeolite H-beta facilitated the reaction of α-chloro acetyl chloride with 1,2-bis-trimethyl silyl acetylene to give 1-chloro-4-(trimethylsilyl)but-3-yn-2-one which on treatment with thioacetamide afforded 2-methyl-4-[(trimethylsilyl)ethynyl]thiazole. l-Proline on the other hand facilitated the coupling reaction of 2-methyl-4-[(trimethylsilyl)ethynyl]thiazole with (hetero)aryl halides (modified Sonogashira reaction) under Pd-Cu catalysis in the presence of aqueous K₂CO₃ affording an improved method for the synthesis of corresponding 4-alkynyl substituted thiazole derivatives.     

Total synthesis of (+)-pericosine B and (+)-pericosine C and their enantiomers by using the Baylis–Hillman reaction and ring-closing metathesis as key steps

A simple and divergent route for the total synthesis of pericosine B and pericosine C and their enantiomers from d-ribose by using the Baylis–Hillman reaction and ring-closing metathesis reactions as key steps has been described.     

Amberlyst-15 mediated synthesis of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones and their crystal structure analysis

An efficient and clean method has been developed for the synthesis of 2-substituted 2,3-dihydroquinazolin-4(1H)-ones using Amberlyst-15 as a recyclable catalyst. A variety of dihydroquinazolinones were prepared from 2-aminobenzamide and aldehydes under mild conditions in excellent yields. Further structure elaboration of one compound and the crystal structure analysis and hydrogen bonding patterns of the two compounds prepared by using this methodology is presented.     

Studies on sorption of plutonium from carbonate medium on polyacrylhydroxamic acid resin

Polyacrylhydroxamic acid resin synthesized by functionalization of polyacrylamide with hydroxylamine has been investigated for the sorption of plutonium(IV) from carbonate medium, aiming at its application for the removal of plutonium from alkali wash effluent generated during purification of TBP in PUREX process. Batch experiments have been carried out to determine distribution coefficient of plutonium(IV) between this exchanger and various compositions of carbonate medium. Effect of the concentration of sodium carbonate, sodium bicarbonate and pH of the solution on the distribution coefficient have been studied to optimize the conditions for the uptake of Pu(IV) by this exchanger. Column experiments were carried out to determine the practical capacity of the exchanger for plutonium. Elution studies were also carried out to recover the loaded plutonium from the ion exchange column The exchanger displayed good exchange capacity for Pu(IV) from feed solution simulating the conditions of carbonate wash effluent generated in PUREX process. The exchanger also exhibited fast elution of Pu, suggesting the feasibility of using it for the recovery of Pu from carbonate based wash effluent.     

Effect of sacrificial electron donors on hydrogen generation over visible light–irradiated nonmetal-doped TiO2 photocatalysts

Hydrogen generation over carbon-, nitrogen- and sulfur-doped TiO₂ semiconductor photocatalysts (represented as C–TiO₂, N–TiO₂ and S–TiO₂, respectively) under visible light irradiation has been achieved using various sacrificial electron donors, namely triethanolamine, diethanolamine, monoethanolamine, triethylamine, MeOH, EtOH, EDTA, l-ascorbic acid and phenol. The highest initial rate of H₂ production was found to be in the range 1,000–2,200 μmol/g/h at ambient conditions when triethanolamine was used as sacrificial electron donor. The efficacy of hydrogen production over these photocatalysts depends strongly on the nature of the sacrificial electron donor and decreases in the following order: C–TiO₂ > S–TiO₂ > N–TiO₂. The results of the present studies suggest that the rate of H₂ production is not simply governed by the reduction potential of the sacrificial electron donor but also by the kinetic barrier of the electron transfer process.     

Structures and optical properties of Zn1?x Ni x O nanoparticles by coprecipitation method

Nanocrystals of undoped and nickel-doped zinc oxide (Zn_1?x Ni _x O, where x?=?0.00?C0.05) were synthesized by the coprecipitation method. Crystalline size, morphology, and optical absorption of prepared samples were determined by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), and UV?Cvisible spectrometer. XRD and SEM studies revealed that Ni-doped ZnO crystallized in hexagonal wurtzite structure. Doping of ZnO with Ni²⁺ was intended to enhance the surface defects of ZnO. The incorporation of Ni²⁺ in place of Zn²⁺ provoked an increase in the size of nanocrystals as compared to undoped ZnO. Crystalline size of nanocrystals varied from 10 to 40?nm as the calcination temperature increased. Enhancement in the optical absorption of Ni-doped ZnO indicated that it can be used as an efficient photocatalyst under visible light irradiation. Optical absorption measurements indicated a red shift in the absorption band edge upon Ni doping. The band gap value of prepared undoped and Ni-doped ZnO nanoparticles decreased as annealing temperature was increased up to 800?°C.     

Photocatalytic studies of silver doped ZnO nanoparticles synthesized by chemical precipitation method

Ag-doped ZnO nanoparticles (Zn_1?xAg_xO; where x = 0.00–0.05) were synthesized by chemical precipitation method. The synthesized products were characterized by X-ray diffraction, scanning electron microscope (SEM), transmission electron microscope (TEM) and UV–Vis spectrometer. The SEM and TEM micrographs revealed the agglomerated spherical-like morphology and the measurements show that the size of crystallites is in the range of 10–40 nm. Optical measurements indicated a red shift in the absorption band edge after Ag doping. The band gap values of as prepared undoped and doped with silver samples were found to decrease with increase in temperature from 300 to 800 °C. Photocatalytic activities of ZnO and Ag doped ZnO were evaluated by irradiating the sample solution to ultraviolet light by taking methylene blue as organic dye. The experiment demonstrated that the photo-degradation efficiency of 1 mol% Ag-doped ZnO was significantly higher than that of undoped and 2–5 mol% Ag doped ZnO under ultraviolet light irradiation.