Multi-walled carbon nanotube/zinc oxide (MWCNT/ZnO) composites were synthesized by thermal hydrolysis method. The composites were prepared using multi-walled carbon nanotubes (MWCNTs) as a starting ...material, and zinc nitrate as a precursor. For characterization and morphological studies, different techniques such as FE-SEM, HRTEM, XRD, UV and FT-IR were applied. The photo catalytic activity of the prepared composite was evaluated by measuring the degradation of acetaldehyde in aqueous solution under UV laser irradiation. Almost 50% enhancement in photocatalytic activity for removal of acetaldehyde was recorded by embedding ZnO nanoparticles on the surface of MWCNTs.
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•Modifying the surface of c-axis oriented ZnO thin film prepared by DC reactive sputtering with gold nanostructures by post annealing of thin layer of gold on ZnO.•The structural, ...optical and compositional were studied.•The gas sensing properties of the prepared sample toward hydrogen at different temperatures and concentrations were investigated and compared with as deposited and heated ZnO thin films.•Au@ZnO thin film showed high response compared with as deposited and heated ZnO.•A plausible mechanism for the observed enhancement is proposed.
Hydrogen present in concentration up to 4 vol.% forms an explosive mixture with air. Its propensity to escape in the event of leak, could lead to quick build-up and formation of an explosive mixture with air in confined spaces, such as an automobile. This necessitates its detection at very low concentration. Zinc oxide (ZnO) is a well-known wide band gap (∼3.37eV) semiconducting oxide that has been widely used for gas sensing applications. This work reports on the fabrication, characterization and gas sensing performance of nanogold decorated ZnO thin films made by DC reactive sputtering. The sensor films were fabricated by depositing a very thin layer of gold on the sputtered ZnO thin film. The as deposited Au@ZnO films were converted into highly crystalline ZnO film covered with gold nanostructures (AuNs@ZnO) by mild heat treatment. The structural and morphological as well as the compositional homogeneity of the as-deposited and heat-treated ZnO, Au@ZnO and AuNs@ZnO thin films were ascertained. The gas sensing behavior of the AuNs@ZnO thin films towards hydrogen as a function of temperature at different H2 concentrations was investigated and compared with that of pure and heat-treated ZnO films. The effect of the presence of gold nanoparticles on imparting improvement (in terms of higher response signal, high reproducibility and complete reversibility) was established; the optimal operating temperature was about 400°C. A plausible mechanism for the observed enhancement in the sensing behavior of AuNs@ZnO films towards H2 is proposed.
The photocatalytic degradation of Safranin-O (known as Basic Red 2) in water using locally synthesized nanocrystalline WO3 as a photocatalyst was investigated under UV laser irradiation. The ...photo-oxidation removal of the dye was monitored by UV–vis spectrophotometer. The blank experiments for either laser irradiated only Safranin-O solution or the suspension containing WO3 and Safranin-O in the dark showed that both laser illumination and the photocatalyst were essential for the removal of Safranin-O. The effect of experimental parameters including laser energy, catalyst loading, solution pH and the initial dye concentration on photocatalytic degradation of Basic Red 2 were also investigated. Results indicate that the rate of reaction is strongly influenced by the adsorption of an azo dye into the surface of the photocatalyst materials and suggests an optimum catalyst loading and dye concentration for the degradation reaction. It was investigated that the adsorption of the dye decreases at higher alkaline pH because both catalyst and substrate are negatively charged, developing repulsive forces between them. Kinetic data obtained reveals that the rate of the reaction obeys the first-order kinetics.
In the present work, pure and SnO2 modified ZSM-5 zeolites were successfully prepared using hydrothermal method. Structural, morphological, surface compositions and vibrational properties of the ...synthesized samples were characterized by XRD, HRTEM, FE-SEM, EDS, XPS, and FT-IR. HRTEM analysis through SAED patterns showed that pure and SnO2 modified ZSM-5 have well-defined nanocrystalline structure. SnO2 nanoparticles, approximately 5 nm in size, were highly dispersed and homogenously distributed throughout the ZSM-5 zeolite. XPS surface composition analysis confirmed Sn in its +4 oxidation state, indicating that ZSM-5 successfully incorporated the SnO2 nanoparticles. The SnO2 modified ZSM-5 zeolite chemiresistive sensitivity towards different concentrations of H2 gas (500–10,000 ppm) was investigated. The sensor exhibited reasonable performance with excellent stability and repeatability. Moreover, the transient and steady state characteristics of the sensor's experimental response to hydrogen was found to be consistent with the Langmuir adsorption model in evaluating the adsorption/desorption behavior of analytes (i.e., H2 adsorbate) on the sensor's active layer, under different concentrations.
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•SnO2-modified ZSM-5 zeolite was synthesized using hydrothermal method.•SnO2 modification of ZSM-5 was confirmed using HR-TEM and XPS analyses.•SnO2 nanoparticles with size of ~5 nm were observed to be highly dispersed on ZSM-5 structure.•SnO2-modified ZSM-5 showed reasonable chemiresistive sensing response towards H2 at different concentrations.•The sensing characteristics were explained by the Langmuir adsorption model.
Abstract
The inelastic neutron scattering spectra recorded in this study and elsewhere provide a useful set of crystal-field (CF) energy levels for the ground
J
= 6 term of Ho
3+
in HoFeO
3
. The ...resolution of the low-energy, temperature-dependent pseudo-quadrupole ground state splitting and magnon peaks is consistent with the self-ordering of the Ho
3+
sublattice at
T
Ho
∼ 8–10 K and supports earlier electron spin resonance investigations of the Ho
3+
magnon behaviour. Systematic analysis of the grouped singlet CF levels of Ho
3
: HoFeO
3
, in conjunction with the CF Kramers doublet levels of the neighbouring Er
3+
: ErFeO
3
, has yielded possible sets of CF parameters for the two systems.
Zinc oxide (ZnO) nanoflowers have huge potential for various applications. However, the growth mechanism of ZnO nanoflowers is still under debate despite various growth mechanisms having been ...proposed. The aim of this study is to investigate the growth mechanism of different morphologies in a single sample; hopefully, this might help to understand the exact growth mechanism of ZnO nanoflowers. Herein, two models are proposed: (I) the growth mechanism of different morphologies (shapes) in a single sample; and (II) the growth mechanism of different sized ZnO flowers in a single sample. The present work also investigates the mechanism for how morphology assists in tuning the properties of nanomaterials, which is still unclear to date. New insight into the relationship between morphology and native defects has been introduced in this work. XPS, photoluminescence, and FT-IR analyses reveal the presence of oxygen vacancy defects in the structures of the materials prepared, with respect to their morphology. These defects act as self-dopants. Therefore, a change in their concentration results in tuning the band gap and thereby the photocatalytic activity.
Study of various binding materials like potassium bromide, poly(vinyl alcohol), starch, silver and aluminum has been carried out using laser-induced breakdown spectroscopy (LIBS). The role of matrix ...effects using these five binders on LIBS signal intensity was investigated for better performance of LIBS technique as a quantitative analytical tool. For comparative study of different binders, the signal intensity of different Mg lines at 518.3, 517.2, 383.8 and 279.5
nm wavelengths were recorded for pellets prepared with known concentrations of Mg in these binders. The influence of laser energy on ablated mass under different binding materials and its correlation with LIBS signal intensity has been explored. Optical scanning microscopy images of the ablated crater were studied to understand the laser ablation process. The study revealed that the binding material plays an important role in the generation of LIBS signal. The relative signal intensity measured for a standard Mg line (at 518.3
nm) were 735, 538, 387, 227 and 130 for potassium bromide, starch, poly(vinyl alcohol), silver and aluminum as binders, respectively. This indicates clearly that potassium bromide is better as a binder for LIBS studies of powder samples.
The present study demonstrates the complete removal of Cr(VI) in aqueous suspensions of zinc oxide nanoparticles using a novel laser-induced photocatalytic process without the use of any additive. ...The study showed that ∼95% Cr(VI) was removed within short time (60min) of laser exposure in the presence of ZnO. However, the removal of chromium using conventional setup under identical conditions was found to be negligible. Effect of critical parameters, such as laser energy, catalyst concentration, chromium concentration, and added electron donor and acceptor on the photocatalytic reduction process was also investigated. The data regarding temporal behavior of metal removal was fitted to first-order kinetic and reaction rate was computed.
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•Au decorated ZnO/Ag core-shell films (Au/ZnO/Ag) are synthesized via a DC sputtering followed by post annealing treatment.•The Au/ZnO/Ag showed enhanced acetone response as compared ...to ZnO/Ag and pure ZnO.•The Au/ZnO/Ag core-shell film exhibits excellent gas sensing properties to 0.5–10 ppm acetone at 150 °C.•The gas sensing enhancement mechanism of the Au/ZnO/Ag is discussed.
Understanding the role of depletion region, charge transport behaviour, and energy band modulations are essential to improve the performance of different sensors including the accurate acetone sensor for the diagnosis of diabetes via the exhaled breath. Herein, we report a new approach to amplify the performance of the acetone gas sensor by engineering the depletion layer. A novel Au decorated ZnO/Ag core-shell films (Au/ZnO/Ag) with different contents of Au, ZnO, and Ag are successfully fabricated via a sequential DC sputtering and post-heat treatment for the detection of acetone in low concentration. The optimum thickness of Ag, ZnO, and Au, to achieve the highest acetone response, are determined to be 11, 13, and 12 nm, respectively. The acetone sensing performance of the Au/ZnO/Ag is four and two times higher than that of ZnO and ZnO/Ag core-shell films. In addition, the Au/ZnO/Ag core-shell sensor exhibits excellent repeatability, high selectivity, and quick response at 150 °C operating temperature. The high performance of the developed sensor is attributed to the formation of a thick depletion layer, and the homogeneous distribution of Au and Ag nanoparticles. The findings demonstrate that the controlled engineering of the depletion layer is an efficacious approach for designing high-performance metal oxide-based gas sensors.
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