Niobium metal doped ZnO nanorods were fabricated on a glass substrate using an ultrasonic spray pyrolysis system in two steps. The structural, morphological, and optical properties of the produced ...samples were investigated via an x-ray diffractometer (XRD), a field emission scanning electron microscopy (FE-SEM) combined with energy dispersive x-ray spectroscopy (EDX), and a spectrophotometer, respectively. The XRD patterns were indexed in the hexagonal (wurtzite) unit cell type for all the ZnO samples. In addition, according to the XRD peaks, the crystals grew in the c-axis (002) direction. The morphological features of the obtained thin films were examined. From the SEM micrographs, it was observed that ZnO thin films doped with Nb had a nanorod structure in the c-axis direction. The presence of Nb ions in the samples was proved via EDX analysis. The electrical conductivity values of the pristine and 10 % mol Nb-doped ZnO samples were 3.16 x 10−9 and 3.98 x 10−7 (ohm−1.cm−1) at 25 °C; and 7.08 x 10−7 and 5.01 x 10−5 (ohm−1.cm−1) at 300 °C, respectively. The optical transmittances of the samples were measured at wavelengths of 350–1000 nm. It was observed that the produced films had high optical transparency. The average optical transmittance value of the samples was 90 %.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A multistep synthesis procedure for the homogeneous coating of a complex porous conductive oxide with small Ir nanoparticles is introduced to obtain a highly active electrocatalyst for water ...oxidation. At first, inverse opal macroporous Sb doped SnO2 (ATO) microparticles with defined pore size, composition, and open‐porous morphology are synthesized that reach a conductivity of ≈3.6 S cm−1 and are further used as catalyst support. ATO‐supported iridium catalysts with a controlled amount of active material are prepared by solvothermal reduction of an IrOx colloid in the presence of the porous ATO particles, whereby homogeneous coating of the complete outer and inner surface of the particles with nanodispersed metallic Ir is achieved. Thermal oxidation leads to the formation of ATO‐supported IrO2 nanoparticles with a void volume fraction of ≈89% calculated for catalyst thin films based on scanning transmission electron microscope tomography data and microparticle size distribution. A remarkably low Ir bulk density of ≈0.08 g cm−3 for this supported oxide catalyst architecture with 25 wt% Ir is determined. This highly efficient oxygen evolution reaction catalyst reaches a current density of 63 A gIr−1 at an overpotential of 300 mV versus reversible hydrogen electrode, significantly exceeding a commercial TiO2‐supported IrO2 reference catalyst under the same measurement conditions.
Illustration of the solvothermal loading of open porous antimony doped tin oxide microparticles employed as a catalyst support with a thin layer of catalytic highly active IrO2 nanoparticles is shown. Independent control of the microparticle porosity, doping level, as well as of the IrOx precursor‐to‐support ratio allows for the synthesis of an optimized supported oxygen evolution reaction (OER) catalyst with high catalytic activity for the OER.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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•Simple and precise synthesis method for homogenous ZnO nanorods and nanowires growth.•Preferred CO2 surface adsorptions at monodentate and bidentate sites on ZnO structures.•Stable, ...repetitive and high CO2 sensing response ∼80 %.
In the present research, hybrid Au-ZnO one-dimensional (1-D) nanostructures were grown on silicon substrates with an Al-doped ZnO (AZO) seed layer (Ultrasonic Spray Pyrolysis: USP grown) and no seed layer (NSL) using two different catalytic gold films of 2 nm and 4 nm, respectively. Consequently, such 1-D nanostructures growth was associated with the vapor-liquid-solid (VLS) and vapor-solid (VS) processes. Scanning electron microscopy (SEM) imaging analysis confirms that heat treatment triggered Au nanoparticles nucleation with varying diameters. The Au nanoparticles size and underneath seed layer texture strongly affect the morphology and aspect ratio of 1-D ZnO nanostructures. The seed layer (1-D USP) sample resulted in the growth of longer nanowires (NWs) with a high aspect ratio. The NSL sample showed the formation of nanorods (NRs) with a low aspect ratio mainly via VS growth process. X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and photoluminescence (PL) analysis also revealed the differences in the NWs and NRs properties and confirmed VLS and VS growth mechanisms. CO2 gas sensing performance at different concentrations was demonstrated, and NWs with seed layer showed a relatively higher sensing response. In contrast, NSL samples (NRs) exhibited two times faster response. A detailed gas sensing mechanism with different CO2 adsorption modes based on properties of 1-D nanostructures has been discussed. Currently, CO2 sensing and capturing are critical topics in the green transition framework. The present work would be of high significance to the scientific field of NW growth and fulfill the urgent need for CO2 gas sensing.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this study, TiO2 thin films were deposited by ultrasonic spray pyrolysis from solutions with concentrations of 0.1 and 0.2 M. The deposition temperature was adjusted at 350 °C and all samples were ...annealed at 500 °C for 1 h in air. The thickness of TiO2 films was changed in the range of 50 to ca. 800 nm by varying the number of spray cycles from 1 to 21 and the solution concentration. The results showed that the mean crystallite size of the anatase structure, the surface roughness, and light absorption increased with the film thickness. The effect of film thickness on the photocatalytic activity was investigated with the photodegradation of stearic acid under UV-A irradiation. The optimal thickness of TiO2 films fabricated by ultrasonic spray pyrolysis for photocatalytic self-cleaning applications was in the range of 170–230 nm, indicating a ca. 2.6 times-higher photocatalytic self-cleaning activity compared to the reference sample, Pilkington ActivTM. The photocatalytic results showed that the 190 nm-thick TiO2 film deposited from the 0.1 M solution applying seven spray cycles exhibited the finest grain structure and maximum photocatalytic activity, leading to 94% of stearic acid degradation in 180 min under UV-A light with the reaction rate constant k = 0.01648 min−1.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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•A simple and versatile one-step process for black TiO2-x microspheres is demonstrated.•The process is based on an ultrasonic spray pyrolysis under oxygen-deficient environment.•The ...existence of Ti3+ and oxygen vacancies in the microsphere is confirmed.•The microsphere shows distinct absorption in the visible region.•The black TiO2-x microspheres show a higher photocatalytic activity than its white form.
Black TiO2-x has recently emerged as one of the most promising visible-light-driven photocatalysts, but current synthesis routes that require a reduction step are not compatible with cost-effective mass production and a relatively large particle such as microspheres. Herein, we demonstrate a simple, fast, cost-effective and scalable one-step process based on an ultrasonic spray pyrolysis for the synthesis of black TiO2-x microspheres. The process utilizes an oxygen-deficient environment during the pyrolysis of titanium precursors to directly introduce oxygen vacancies into synthesized TiO2 products, and thus a reduction step is not required. Droplets of a titanium precursor solution were generated by ultrasound energy and dragged with continuous N2 flow into a furnace for the decomposition of the precursor and crystallization to TiO2 and through such a process spherical black TiO2-x microspheres were obtained at 900 °C. The synthesized black TiO2-x microsphere with trivalent titanium/oxygen vacancy clearly showed the variation of physicochemical properties compared with those of white TiO2. In addition, the synthesized microspheres presented the superior photocatalytic activity for degradation of methylene blue under visible light irradiation. This work presents a new methodology for a simple one-step synthesis of black metal oxides microspheres with oxygen vacancies for visible-light-driven photocatalysts with a higher efficiency.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high ...intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid‐solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid‐gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase‐separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation‐induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of ∼5000 K, pressures of ∼1000 bar, heating and cooling rates of >1010 K s−1; these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis.
Ultrasound is a versatile tool for the synthesis of nanostructured materials. For both sonochemistry and ultrasonic spray pyrolysis (USP), the reaction sites are isolated nanoscale reactors: for sonochemistry, the hot spot inside a collapsing cavitation bubble, whereas for USP, a heated liquid droplet. In each case, unique reaction conditions are created: e.g., acoustic cavitation produces transient temperatures of >5000 K, pressures of ∼1000 bar, and cooling rates of >1010 K s−1.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Pure and nickel doped copper oxide thin films were successfully grown on a soda lime glass substrates including various amounts (1, 2, 4, and 8%) of nickel dopants via ultrasonic spray pyrolysis ...method. The effects of the different impurity doping concentrations on the structural, morphological, optical, and H2 gas sensing properties of the prepared samples were assessed by performing X-ray Diffraction, scanning electron microscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy, gas sensing measurements, and X-ray photoelectron spectroscopy. The structural observations revealed that the grown films have polycrystalline nature with monoclinic cubic crystal structure of copper oxide with no secondary phases present, and grain sizes increased in general as the doping percentage increased except for the 4% nickel doped sample. The morphological analysis showed that the impurities clearly led to modifications in the shapes of the grown copper oxide nanocrystals. In the optical measurements, it was uncovered that the ideal impurity level can enhance the absorbance features of the copper oxide material, and a slight increase in bandgap occurred due to the first level of impurity doping, but then the bandgap decreased as the impurity contents increased. A gradual decrease in the intensity of luminescent emissions was observed in the photoluminescence spectra as the doping concentration increased, which may be associated with the defects caused by the added nickel ions into the copper oxide lattices. Gas sensor measurements disclosed that the produced films were responsive when exposed to H2 gas, and enhanced responsivity was realized by the nickel doping compared to that of pure copper oxide sample. X-ray photoelectron spectroscopy confirmed the presence of aimed chemical compositions in the prepared thin films.
•Ni doped CuO nanostructures grown by USP technique to assess their physical and H2 gas sensing features for the first time.•The effects of varied impurity content found to lead modifications in structural parameters of CuO nanostructures.•Bandgap of CuO samples changed between 1.82 and 1.70 eV as Ni doping altered.•The intensity of luminescence peaks, appeared at 472 nm, and 800 nm, decreased as the impurity concentration increased.•The H2 gas sensor responsivity of CuO films found to increase due to the presence of added Ni ions.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Safety is an essential consideration in the utilization of hydrogen energy due to its potential risk of explosion. Thereby, the synthesis of hydrogen sensors with highly sensitive properties is ...required for the early detection of hydrogen leaks. Here, a low-cost process was applied to fabricate PdO-decorated NiO H2 sensors capable of detecting sub-ppm H2 concentration. Unlike the previous two-step noble metal modification strategy, in situ ultrasonic spray pyrolysis was used in this work to directly obtain the needle-like PdO decorated NiO structure. The doped PdO tends to segregate at grain boundaries of NiO in needlelike form and can inhibit crystal growth. The gas-sensing performance was investigated by the means of dynamic gas distribution. The results show that the gas response towards H2 could be enhanced significantly by PdO doping. Especially, the sprayed 2 at% PdO-decorated NiO film sensor shows the highest response and the lowest detection limit at 250 °C, with a response value of 82% to 50 ppm H2 and a detection limit of 500 ppb. It can be speculated that the surface state of NiO film could be heavily affected by PdO doping, which leads to the high performance of PdO-decorated NiO sensors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The photocatalytic process is used to remove organic contaminants, dyes, industrial sewage from wastewater before reusing it for human consumption again. Here a simple cost-effective ultrasonic spray ...pyrolysis (USP) technique is used to deposit ZnO microflower on glass and stainless steel (SS) mesh in a single step. X-Ray Diffraction (XRD) and Raman spectroscopy indicate the polycrystalline wurtzite nature of ZnO. Field emission scanning electron microscope (FESEM) shows the ZnO microflower structure. PL and XPS studies show the oxygen defect in the films. Photocatalytic degradation results show that methylene blue (MB) dye with 1 × 10−5 M concentration can be degraded around 97.94% and 85% in 120min and 210 min with a degradation rate of 0.03035 min−1 and 0.00917 min−1 respectively using ZnO deposited on SS mesh and glass substrate in both UV–Vis and sunlight condition. ZnO deposited on SS mesh shows high repeatability performance to degrade the MB and it can degrade 96% of MB at 10th cycle. Degradation rate at base medium is higher than acidic medium. A plausible photocatalysis mechanism is also explained.
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•A simple single step deposition of ZnO microflower on stainless steel (SS) mesh.•Degradation rate of MB for ZnO on SS mesh is more than thin film.•Highly repeatable performance over 10th cycle with 96% degradation for SS mesh ZnO.•Degradation rate at base medium is higher than acidic medium.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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