Comparative Catalytic Evaluation of Nano-ZrO x

This work reports the zirconia (ZrOx) nanoparticles doped MnCO3 catalysts prepared by facile and simple coprecipitation technique and the synthesis of zirconia-manganese carbonate [X% ZrOx–MnCO3] (where X% = 0–7%) catalyst which upon calcination at 400°C is converted to zirconia-manganese dioxide [1% ZrOx–MnO2] and when calcined at 500°C is converted to zirconia-manganic trioxide [1% ZrOx–Mn2O3]. A comparative catalytic study was performed to investigate the catalytic efficiency between carbonate and oxides for the selective oxidation of 1-phenylethanol by using molecular O2 as a clean oxidant. The influence of several parameters such as w/w% of ZrOx, reaction time, calcination temperature, catalyst amount, and reaction temperature has been thoroughly examined using oxidation of 1-phenylethanol as a model substrate. The 1% ZrOx–MnCO3 precalcined at 300°C exhibited the best catalytic efficiency. It was found that ZrOx nanoparticles also play an essential role in enhancing the effectiveness of the catalytic system for the aerobic oxidation of alcohols. Furthermore, the physical and chemical properties of synthesized catalysts were evaluated by microscopic and spectroscopic techniques. An extremely high specific activity of 40 mmol·g−1·h−1 with a 100% conversion of oxidation product and selectivity of >99% was achieved within extremely short reaction time (6 min)

Comparative structural and optical spectroscopic studies of Nd3+ ion doped LaF3 and their core/shell nanoparticles

LaF3:Nd3+ (core), LaF3:Nd3+@LaF3 (core/shell) and LaF3:Nd3+@LaF3@SiO2 (core/shell/SiO2) nanoparticles (NPs) were designed and synthesized at low temperature. The structure and morphology of the as-prepared nanoproducts were characterized by X-ray diffraction and transmission electron microscopy (TEM) techniques. Thermal analysis and FTIR spectral studies were conducted to examine the surface properties of the nanomaterials. The as-prepared LaF3:Nd3+ NPs exhibited hexagonal structure and were composed of monodispersed irregularly and spherically shaped NPs with average grain size of 21 nm. TEM image showed the successful silica surface coating, which was verified by FTIR spectral analysis. The emission spectra of LaF3:Nd3+ NPs was obtained by monitoring the emission of Nd3+ at 325 nm (Cd laser) where it exhibited the characteristic 4f→4f transitions lines originating from the Nd 4f3 configuration. Under UV light irradiation, the emission spectra revealed various strong emission transitions which were greatly affected by the surrounding silica surface coating. These observed results suggested future applications in biolabeling and light-emitting diode

Effects of Zinc Oxide and Silicon Dioxide Nanoparticles on Physiological, Yield, and Water Use Efficiency Traits of Potato Grown under Water Deficit

Water deficit is a major challenge for sustainable global food security, especially, in arid and semi-arid regions. Nanotechnology is regarded as an effective tool for managing a wide range of environmental stresses by providing novel and practical solutions. A field experiment was conducted to assess the effects of zinc oxide nanoparticles ‘ZnO NPs’ (0, 50, 100 ppm) and silicon dioxide nanoparticles ‘SiO2 NPs’ (0, 25, 50 ppm) as an exogenous application on the physiological indices, total yield and water use efficiency (WUE) of potato under water deficit conditions (50%, 75%, and 100% of crop evapotranspiration (ETc) water requirements). Water deficit significantly decreased most physiological indices and yield traits of potato, but increased proline content and WUE. In contrast, exogenous application of ZnO NPs and SiO2 NPs to plants grown under different water deficit treatments resulted in an increase in leaf gas exchange, leaves relative water contents (LRWC), photosynthetic pigments, and leaf green index. Under different water deficit treatments, the highest total yield and harvest index traits were obtained from plants treated with ZnO-NPs-100 ppm followed by 50 ppm of ZnO and SiO2 NPs, respectively. The highest WUE was recorded when the potato plants were irrigated with 50% ETc and exogenous treated with 100 ppm of ZnO NPs compared with fully irrigated plants. In conclusion, the exogenous application of ZnO NPs (100 ppm) can significantly mitigate the water deficit stress and improve the physiological, yield, and WUE of potato grown in arid regions under water deficit conditions

Ceria doped mixed metal oxide nanoparticles as oxidation catalysts: Synthesis and their characterization

Mixed metal nanoparticles (NPs) have attracted significant attention as catalysts for various organic transformations. In this study, we have demonstrated the preparation of nickel–manganese mixed metal oxide NPs doped with X% nano cerium oxide (X = 1, 3, 5 mol%) by a facile co-precipitation technique using surfactant and surfactant free methodologies. The as-synthesized materials were calcined at different temperatures (300 °C, 400 °C, and 500 °C), and were characterized using various spectroscopic techniques, including, FTIR and XRD. SEM analysis, TEM analysis and TGA were employed to evaluate the structural properties of the as-prepared catalyst. These were evaluated for their catalytic behaviour towards the conversion of benzyl alcohol to benzaldehyde, which was used as a model reaction with molecular oxygen as oxidant. Furthermore, the effect of the variation of the percentage of nano ceria doping and the calcination temperature on the performance of as-prepared mixed metal catalysts was also evaluated. The kinetic studies of the reactions performed employing gas chromatographic technique have revealed that the mixed metal oxide catalyst doped with 5% nano ceria displayed excellent catalytc activity, among various catalysts synthesized

SrZnO nanostructures grown on templated <0001> Al2O3 substrates by pulsed laser deposition

The parameters of pulsed laser deposition (PLD) have been optimized to design different nanostructures of Strontium-alloyed zinc oxide (SrZnO). In this work, SrZnO nanostructures are grown on Al2O3 substrates via two-step templating/seeding approach. In the temperature range between 300 - 750 oC and O2 background pressures between 0.01 and 10 Torr, the growth conditions have been tailored to grow unique pointed leaf-like- and pitted olive-like nanostructures. Prior to the growth of the nanostructures, a thin SrZnO layer that serves as seed layer/template is first deposited on the Al2O3 substrates at ∼300oC and background oxygen pressure of 10 mTorr. The optical properties of the nanostructures were examined by UV/Vis spectroscopy and photoluminescence (PL), while the structures/morphologies were examined by SEM, TEM, and XRD. The alloyed SrZnO nanostructures, grown by ablating ZnO targets with 5, 10, 25% SrO contents, have in common a single-crystal hexagonal nanostructure with (0002) preferential orientation and have shown remarkable changes in the morphological and optical properties of the materials. To date, this is the only reported work on optimization of laser ablation parameters to design novel SrZnO nanostructures in the 5-25% alloying range, as most related Sr-doped ZnO studies were done below 7% doping. Although the physical properties of ZnO are modified via Sr doping, the mechanism remains unclear. The PLD-grown SrZnO nanostructures were directly grown onto the Al2O3 substrates; thus making these nanomaterials very promising for potential applications in biosensors, love-wave filters, solar cells, and ultrasonic oscillators

Laser induced photocurrent and photovoltage transient measurements of dye-sensitized solar cells based on TiO2 nanosheets and TiO2 nanoparticles

Dye-sensitized solar cells (DSSCs) based on TiO2 nanoparticles and TiO2 nanosheets with exposed {001} facets are investigated using laser-induced photovoltage and photocurrent transient decay (LIPVCD) measurements. We adopted a simplified version of LIPVCD technique, in which a single illumination light source and a laboratory oscilloscope could be conveniently used for the measurements. Although the {001} surface of TiO2 nanosheets allowed a noticeably slower recombination with the electrolyte, this was counterpoised by a slower electron transport probably due to its planar morphology, resulting in a shorter diffusion length in TiO2 nanosheets. The nanosheet morphology also resulted in less surface area and therefore reduced short circuit current density in the fabricated devices. Ourwork highlights the fact that the morphological parameters of TiO2 nanosheets finally resulting after electrode film deposition is of no less importance than the reported efficient dye adsorption and slow electron recombination at the surface of individual nanosheets. (C) 2016 Elsevier Ltd. All rights reserved

Fabrication of Fe₃O₄ core-TiO₂/mesoSiO₂ and Fe₃O₄ core-mesoSiO₂/TiO₂ Double Shell Nanoparticles for Methylene Blue Adsorption: Kinetic, Isotherms and Thermodynamic Characterization

Herein, Fe3O4 core-TiO2/mesoSiO2 and Fe3O4 core-mesoSiO2/TiO2 double shell nanoparticles were prepared by first (R1) and second (R2) routes and applied for the removal of methylene blue. The reported adsorption capacities for R1-0.2, R1-0.4 and R2 samples were 128, 118 and 133 mg.g−1, respectively, which were obtained after 80 min as equilibrium contact time, and pH of 6 using a methylene blue concentration of 200 ppm. The adsorption of methylene blue using the prepared Fe3O4 core-meso SiO2/TiO2 double shell was analyzed by kinetic and isotherms models. In addition, thermodynamic investigations were applied to assess the spontaneous nature of the process. The obtained results confirmed that the pseudo-second order model is well fitted with the adsorption data and the Freundlich-isotherm assumption suggested a multilayer adsorption mechanism. In addition, results of the thermodynamic investigation indicated that ΔG° was in the range of −2.3 to −6.8 kJ/mol for R1-0.2, −2.8 to −6.3 kJ/mol for R1-0.4 and −2.0 to −5.2 kJ/mol for R2. In addition, the ΔH° and ΔS° values were found in the range of 26.4 to 36.19 kJ.mol−1 and 94.9 to 126.3 Jmol−1 K−1, respectively. These results confirm that the surfaces of Fe3O4 core-mesoSiO2/TiO2 and Fe3O4 core-TiO2/mesoSiO2 double shell exhibit a spontaneous tendency to adsorb methylene blue from the aqueous solutions. The achieved performance of Fe3O4 core-meso SiO2/TiO2 and Fe3O4 core-TiO2/meso SiO2 double shell as adsorbent for methylene blue removal will encourage future research investigations on the removal of a broad range of contaminants from wastewater

Synthesis, characterization and relative catalytic study of ZrO_x-MnCO₃, – MnO₂or -Mn₂O₃deposited on highly reduced graphene oxide nanocomposites for aerobic oxidation of secondary alcohols

189-204Zirconia nanoparticles doped MnCO3 have been successfully immobilized on various percentages of highly reduced graphene oxide (HRG)[(X%)HRG/MnCO3–(1%)ZrOx](where, X=0–7)],via a facile and straight forward co-precipitation method. Upon calcination, the as-obtained materials have yielded different types of HRG/manganese oxide nanocomposites at different temperatures i.e.[(X%)HRG/MnO2–(1%)ZrOx] and [(X%)HRG/Mn2O3–(1%)ZrOx]. A detail investigation was carried out to compare the catalytic performance of carbonates and oxides based nanocomposites for the selective oxidation of secondary alcohols.  For this purpose, molecular oxygen was employed as an environmentally benign oxidant under base-free conditions. The reaction conditions were optimized with different weight percentages of HRG, reaction times, calcination temperatures, catalyst dosages, and reaction temperatures using 1-phenylethanol as a substrate model. The catalytic performance of the nanocomposites was enhanced significantly due to the presence of HRG as a support material. The catalyst with (1%)HRG/MnCO3–(1%)ZrOx exhibited outstanding performance as well as excellent selectivity in the aerobic oxidation of 1-phenylethanol. In this case, 100% conversion in 4 min with more than 99% selectivity was achieved with excellent specific activity of 60.0 mmol.g−1.h−1. Moreover, catalyst can be efficiently reused 5 times without discernible decrease in its activity and selectivity. Apart from this, various other alcohols were also selectively oxidized to their corresponding carbonyls with complete conversion in short reaction times under optimal conditions without over-oxidation to the carboxylic acids

Pulsed laser deposition growth of 3D ZnO nanowall network in nest-like structures by two-step approach

The mechanism for the growth of 3D ZnO nanowall networks in nest-like structure by a pulsed laser deposition (PLD) technique have been investigated for dye sensitized solar cells (DSSCs) and biosensor applications. As complex oxides shift towards large volume productions and practical applications, PLD offers a good advantage over other techniques due to the scalability of the produced film/structures, good adhesion between nanostructures and substrates, and preservation of stoichiometric ratio of the target material. In this study, a two-step temperature-pressure approach has been used to grow ZnO nanostructures on Si(100) using PLD. Optimizing this technique, we have structured a 3D ZnO nanowall networks with nest-like feature without any catalyst. Investigating the effect of substrate temperature from 300 degrees C to 750 degrees C and O-2 background from 10 mTorr to 10 Torr, we have grown the nanowall structures by first depositing a thin ZnO seed layer on Si(100) at a substrate temperature of similar to 300 degrees C and a background oxygen pressure of 10 mTorr, subsequently growing the nanowalls at similar to 550 degrees C and 500 mTorr background. The relationship of the PLD parameters and the morphology of the grown nanowalls were examined by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray Diffraction (XRD), Atomic Force Microscope (AFM), Photoluminescence (PL) and X-ray Photoemission Spectroscopy (XPS). The grown ZnO nanowall networks are single-crystals and highly-oriented on the c-axis. The nest-like structures initially grow on the thermodynamically active sites along the grain boundaries of randomly oriented Zn-rich ZnO (01 (1) over bar0) plane, which undergoes self-nucleation on the amorphous layer of the Si (100) substrates. The growth mechanisms for the synthesis of the ZnO nanowalls network can be explained by the vapor-solid (VS) model. The PLD-grown 3D ZnO nanowall network has a very high surface-to-volume ratio and appears to be denser than the previously reported ZnO nanowall structures grown by other techniques. This makes the PLD-grown ZnO nanowall a very promising material as photoanodes in DSSCs and an excellent matrix for biomolecule binding for potential applications in biosensors. (C) 2015 Elsevier B.V. All rights reserved