Improved electroluminescence performance of ZnS:Cu,Cl phosphors by ultrasonic treatment

ZnS:Cu,Cl electroluminescence (EL) phosphors were prepared by high-temperature (1150 °C) solid-state reaction, subsequent ultrasonic treatment (t=0-60 min) and final low-temperature annealing process at 750 °C. The as-synthesized phosphors were characterized by X-ray powder diffraction (XRD), UV-vis absorbance spectra, electron probe microanalyzer (EPMA) and photoluminescence (PL) spectra. EL performance was investigated on an EL lamp fabricated by screen-printing at 100 V and 400 Hz. Ultrasound irradiation leads to intensity reductions and width increases of some XRD diffraction peaks, and results in a slight red-shift of UV-vis absorption edge. It also exhibits strong influences on PL and EL properties of the phosphors. Generally, PL performance monotonically declines with the increase of ultrasonic time, while EL performance benefits from the ultrasonic treatment and is superior to that of the commercial ones. The defects in the microstructure induced by the ultrasonic treatment are the fundamental reason for the change of PL and EL performances.     

Comparative study of lignins isolated by alkali and ultrasound-assisted alkali extractions from wheat straw.

Treatment of the dewaxed wheat straw with 0.5 M KOH at 35 degrees C for 2.5 h without ultrasonic irradiation and with ultrasound assistance for 5, 10, 15, 20, 25, 30, and 35 min resulted in a dissolution of 43.9%, 43.9%, 43.9%, 44.4%, 44.4%, 45.6%, 46.8%, and 49.1% of the original lignin, respectively. Much better results were achieved under the ultrasonic irradiation time for 35 min where nearly 50% of the original lignin was solubilized at 35 degrees C for 2.5 h. The purity of the lignin preparations isolated by alkali with ultrasound assistance was higher than that of the lignin fraction obtained by alkali without ultrasonic irradiation, and their purity increased with an increment of irradiation time between 5 and 35 min, in which the content of associated polysaccharides in the former lignin preparations (0.87-1.06%) was lower than that of the latter lignin fraction (1.16%). In addition, the lignins isolated by alkali with ultrasonic irradiation time between 5 and 30 min showed a slightly higher molecular weight and thermal stability than the lignin obtained by alkali without ultrasound assistance. No substantial differences in the main structure features between the lignin preparations isolated by alkali and ultrasound-assisted alkali extractions were found.     

Study of nanodispersed aluminum and iron alcosols by photoacoustic spectroscopy

Nanodispersed aluminum and iron alcosols were prepared by ultrasonic dispersion of nanodispersed aluminum and iron powders in absolute ethanol. The photoacoustic signal (PAS) produced in modulated CO₂ laser irradiation (1.026 and 1.096 kHz) of alcosols depends on the nature and method of nanoparticle fabrication and does not depend on their concentration in ethanol (within 1-5 g/l). Chemical interaction between metal nanoparticles and ethanol activated by laser irradiation or/and ultrasound is considered as the cause of the PAS.     

A comparative study on structural and optical properties of ZnO and Al-doped ZnO thin films obtained by ultrasonic spray method using different solvents

Transparent conducting ZnO and Al doped ZnO thin films were deposited on glass substrate by ultrasonic spray method. The thin films with concentration of 0.1 M were deposited at 350 °C with 2 min of deposition time. The effects of ethanol and methanol solution before and after doping on the structural, optical and electrical properties were examined. The DRX analyses indicated that ZnO films have nanocrystalline nature and hexagonal wurtzite structure with (1 0 0) and (0 0 2) preferential orientation corresponding to ZnO films resulting from methanol and ethanol solution, respectively. The crystallinity of the thin films improved with methanol solution after doping to (0 0 2) oriented. All films exhibit an average optical transparency about 90%, in the visible range. The band gaps values of ZnO thin films are increased after doping from 3.10 to 3.26 eV and 3.27 to 3.30 eV upon Al doping obtained by ethanol and methanol solution, respectively. The electrical conductivity increase from 7.5 to 15.2 (Ω cm)⁻¹ of undoped to Al doped ZnO thin films prepared by using ethanol solution. However, for the methanol solution; the electrical conductivity of the film is stabilized after doping.     

Ultrasound-assisted lipase-catalyzed transesterification of soybean oil in organic solvent system

This work reports the transesterification of soybean oil with ethanol using two commercial immobilized lipases under the influence of ultrasound irradiation. The experiments were performed in an ultrasonic water bath, following a sequence of experimental designs to assess the effects of temperature, enzyme and water concentrations, oil to ethanol molar ratio and output irradiation power on the reaction yield. Results show that ultrasound-assisted lipase-catalyzed transesterification of soybean oil with ethanol might be a potential alternative route to conventional alkali-catalyzed method, as high reaction yields (∼90 wt.%) were obtained at mild irradiation power supply (∼100 W), and temperature (60 °C) in a relatively short reaction time, 4 h, using Lipozyme RM IM as catalyst. The repeated use of the catalyst under the optimum experimental condition resulted in a decay in both enzyme activity and product conversion after two cycles. The use of Novozym 435 led to lower conversions (about 57%) but the enzyme activity was stable after eight cycles of use, showing, however, a reduction in product conversion after the forth cycle.     

Sonochemical growth of antimony selenoiodide in multiwalled carbon nanotube

This paper presents, for the first time, the nanocrystalline, semiconducting antimony selenoiodide (SbSeI) grown in multi-walled carbon nanotubes (CNTs). It was prepared sonochemically using elemental Sb, Se, and I in the presence of ethanol under ultrasonic irradiation (35 kHz, 2.6 W/cm²) at 323 K for 3 h. The CNTs filled with SbSeI were characterized by using techniques such as powder X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, high-resolution transmission electron microscopy, selected area electron diffraction, and optical diffuse reflection spectroscopy. These investigations exhibit that the SbSeI filling the CNTs is single crystalline in nature and in the form of nanowires. It has indirect allowed energy band gap E_gIf = 1.61(6) eV.     

Spectroscopic studies on the interaction and sonodynamic damage of neutral red (NR) to bovine serum albumin (BSA)

In this paper, the interaction of neutral red (NR) with bovine serum albumin (BSA) and the sonodynamic damage to BSA under ultrasonic irradiation was studied by means of ultraviolet-visible (UV-vis) and fluorescence spectra. The quenching constant (K_SV=5.749×10⁴ L/mol), binding constant (K_A=3.19×10⁴ L/mol) and binding site number (n=0.9462) were measured. The binding distance (r=2.47 nm) between NR and BSA was obtained according to Föster’s non-radiative energy transfer theory. The damage process of BSA molecules was detected by the hyperchromic effect of UV-vis spectra and quenching of intrinsic fluorescence spectra. In addition, the influencing factors such as ultrasonic irradiation time and NR concentration on the damage to BSA molecules were also considered. The results showed that the damage degree is enhanced with the increase of ultrasonic irradiation time and NR concentration. The possible mechanism of sonodynamic damage to BSA molecules was mainly mediated by singlet oxygen (¹O₂). Otherwise, the binding and damaging sites to BSA molecules were also estimated by synchronous fluorescence. The results indicated that the NR is more vicinal to tryptophan (Trp) residue than to tyrosine (Tyr) residue and the damage site is also mainly at Trp residues. The research result will bring a certain significance to use sonosensitive drugs in the fields of tumor treatment.     

Luminescence and structure of ZnO-ZnS thin films prepared by oxidation of ZnS films in air and water vapor

Effect of water vapor quantity at oxidation of undoped ZnS films on structural and luminescent properties of the obtained films was investigated. The films were deposited onto glass substrates by electron beam evaporation. ZnO-ZnS layers were prepared by thermal oxidization of ZnS films at 600 °C in dry or wet atmospheres. The films were characterized by X-ray diffraction, atomic force microscopy and photoluminescence spectroscopy. As-deposited ZnS films were sphalerite crystal structure. The “dry annealing” led to the ZnS phase transition from sphalerite to wurtzite structure and from ZnS to ZnO for a small fraction of the film. After the “wet annealing” the amount of ZnO phase with wurtzite structure growing along the 〈0 0 0 2〉 direction varied from 25% to 95% in dependence on the water vapor quantity. Photoluminescent spectrum at room temperature exhibits green emission with maximum at 2.4 eV. A strong influence of the water vapor on shape and intensity of the emission was observed. Photoluminescent spectra at 22 K consisted of two bands—high-energy band at 2.1-2.4 eV and low energy band at 1.7-1.8 eV. Location and intensity ratio depended on the preparation conditions.     

Template-free preparation and characterization of nanocrystalline ZnO in aqueous solution of [EMIM][EtSO4] as a low-cost ionic liquid using ultrasonic irradiation and photocatalytic activity

A fast, template-free, and environmentally benign green route for the preparation of nanocrystalline ZnO in aqueous solution of 1-ethyl-3-methylimidazolium ethyl sulfate, [EMIM][EtSO₄], room-temperature ionic liquid (RTIL), via ultrasonic irradiation is proposed. The X-ray diffraction (XRD) studies display that the products are excellently crystallized in the form of wurtzite hexagonal. Energy-dispersive X-ray spectroscopy (EDX) investigations reveal the products are extremely pure. The morphology of as-prepared nanocrystalline ZnO was characterized by scanning electron microscopy (SEM). Diffuse reflectance spectra (DRS) of the products with absorption maxima at 359 nm show blue shift relative to the bulk ZnO with absorption at 384 nm that can be attributed to quantum confinement effect of nanocrystalline ZnO. A possible formation mechanism of the nanocrystalline ZnO using ultrasonic irradiation in aqueous solution of the RTIL is presented. The results demonstrate that photocatalytic activity of the nanocrystalline ZnO prepared in the presence of the RTIL is higher than the prepared sample in water.     

Luminescence of copper nanoparticles

Copper nanoparticles have been prepared through the chemical reduction of cuprous ions by ethanol. Freshly prepared colloidal solution shows an absorption band at about 296 nm. The particle size using Scherrer's equation is calculated to be about 12 nm. TEM showed nearly uniform distribution of the particles with an average size of 11 nm. Photoluminescence spectra of copper nanoparticles have also been analysed, which show an emission peak at 530 nm when illuminated at 350 nm. Electroluminescence spectra also give maximum emission at 550 nm.     

The effects of solvent nature on spray-deposited ZnO thin film prepared from Zn (CH3COO)2, 2H2O

Transparent conducting zinc oxide was deposited on glass substrate by ultrasonic spray method. The ZnO samples with concentration of 0.1 M were deposited at 300, 350 and 400 °C with 2 min of deposition time. The effects of substrate temperature, ethanol and methanol solution on the structural, electrical and optical properties were examined. The DRX analyses indicated that ZnO films have polycrystalline nature and hexagonal wurtzite structure with (1 0 0) and (0 0 2) preferential orientation corresponding to ZnO films resulting from methanol and ethanol, respectively. The crystallinity of the thin films improved with ethanol solution. All films exhibit an average optical transparency about 80%, in the visible range. The band gap energy of ZnO films obtained with methanol solution higher than of ethanol solution for all the films. The electrical resistivity decrease with ZnO obtained from ethanol indicated; due to the maximum crystallite size retched at this point.     

Ultrasonic characterization of thermally grown oxide in thermal barrier coating by reflection coefficient amplitude spectrum

The thermally grown oxide (TGO) growth at the interface of ceramic coating/bond coating in thermal barrier coatings (TBCs) was evaluated by ultrasonic reflection coefficient amplitude spectrum (URCAS). A theoretical analysis was performed about the influence of acoustic impedance match relationship between the ceramic coating and its adjacent media on URCAS. The immersion ultrasonic narrow pulse echo method was carried out on the TBC specimen before and after oxidation under 1050 °C × 1 h for 15 cycles. The resonant peaks of URCAS obtained before and after oxidation showed that TGO which generated between the ceramic coating and bond coating due to the oxidation, changed the acoustic impedance match between the ceramic coating and its adjacent media. This method is able to nondestructively characterize the generation of TGO in TBCs, and is important to practical engineering application.     

Comparative study of ethanol sensor based on gold nanoparticles: ZnO nanostructure and gold: ZnO nanostructure

Gold colloid:ZnO nanostructures were prepared from Zn powder by using thermal oxidation technique on alumina substrates, then it was impregnated by gold colloid for comparative study. The gold colloid is the solution prepared by chemical reduction technique; it appeared red color for gold nanoparticle solution and yellow color for gold solution. The heating temperature and sintering time of thermal oxidation were 700 °C and 24 h, respectively under oxygen atmosphere. The structural characteristics of gold colloid:ZnO nanostructures and pure ZnO nanostructures were studied using filed emission scanning electron microscope (FE-SEM). From FE-SEM images, the diameter and length of gold colloid:ZnO nanostructures and ZnO nanostructures were in the ranges of 100-500 nm and 2.0-7.0 μm, respectively. The ethanol sensing characteristics of gold colloid:ZnO nanostructures and ZnO nanostructures were observed from the resistance alteration under ethanol vapor atmosphere at concentrations of 50, 100, 200, 500, and 1000 ppm with the operating temperature of 260-360 °C. It was found that the sensitivity of sensor depends on the operating temperature and ethanol vapor concentrations. The sensitivity of gold colloid:ZnO nanostructures were improved with comparative pure ZnO nanostructures, while the optimum operating temperature was 300 °C. The mechanism analysis of sensor revealed that the oxygen species on the surface was O²⁻.     

Photocatalytic performance of ZnO:Fe array films under sunlight irradiation

ZnO:Fe array thin films were prepared by the hydrothermal method using the sol-gel grown film as a seed layer. The samples were characterized by X-ray diffraction (XRD), ultraviolet/visible absorption spectra (UV-vis) and scanning electron microscopy (SEM). The photocatalytic activities of the prepared samples were investigated for the photodegradation of methylene blue (MB) under sunlight irradiation. The results show that the lattice constant a and the cell volume of ZnO:Fe film increase due to the substitution of Fe for Zn. The absorption edge of Fe-doped ZnO displays a red shift with a significant absorption between 600 and 700 nm. The ZnO:Fe array film is composed of disk particles with uniformity and compactness. Doping Fe ions enhances the photodegradation rate of ZnO array film for MB. 1.5% Fe doped ZnO sample exhibits the highest activity under irradiation time of 4 h. Its degradation rate increases about 1.6 times compared to the undoped ZnO.     

Dual-frequency (20/40 kHz) ultrasonic assisted photocatalysis for degradation of methylene blue effluent: synergistic effect and kinetic study

Dual-frequency ultrasonic assisted photocatalysis (DUAP) was proposed to enhance the degradation efficiency of methylene blue (MB) solution. The influence of operational parameters, i.e., irradiation time, ultrasonic arrangement, TiO₂ concentration and power density, was studied. The results implied that the rapid degradation of MB solution was achieved in 18 min under DUAP with the dual frequencies of 20/40 kHz. Kinetic investigation of MB degradation for the DUAP process was conducted on the basis of first-order kinetic equation and the synergistic effect was assessed by examination of the apparent rate constant. The effect of ultrasonic arrangement was analyzed by comparison of the pressure amplitude of ultrasonic superposition field. The evolvement of intermediate products and the role of active species during DUAP were distinguished by UV-Vis spectra and the free radical scavenging experiment.     

Photochemical welding of silica microspheres to silicone rubber by ArF excimer laser

Transparent fused silica (SiO₂) microspheres 2.5 μm in diameter were photochemically welded to transparent, flexible silicone rubber ([SiO(CH₃)₂]_n) substrate by 193 nm ArF excimer laser induced photochemical modification of silicone into silicon oxide. Single layer of silica microspheres was easily formed on an adhesive silicone rubber before laser irradiation after dropping of silica microspheres dispersed in ethanol and subsequent tape peeling. The welding rate, the percentage of welded microspheres tested by ultrasonic cleaning with ethanol, was examined by varying the single pulse fluence and irradiation time of ArF excimer laser. The welding layer underneath microsphere, silicon oxide, was also found to emit white light of strong intensity under UV light illumination.     

The ex-situ and in-situ ultrasonic assisted oxidation of corn starch: A comparative study

The objective of this study was to evaluate the differences in ex-situ (starch treated by ultrasonication and oxidation sequentially, U-OS) and in-situ (starch treated by ultrasonication and oxidation simultaneously, UOS) ultrasonic assisted oxidation process of corn starch, which were studied in contrast to the traditional oxidized starches (OS). Fourier-transform infrared spectra confirmed the successful oxidation of all modified starches samples. In comparison to the OS, the carboxyl contents of U-OS and UOS increased by 56% and 112%, respectively. The same increase trend was also found for the carbonyl contents. The significance raise was attributed to the great increase of pores and specific surface areas in the starch granule after ultrasonic irradiation which promoted the penetration of the sodium hypochlorite into the starch granules with higher chances for chemical reactions. SEM and pore size distribution characterizations further verified this result. However, the method of in-situ ultrasonic assisted oxidation can simultaneously accelerate the increase of pores and the penetration process. Consequently, the starches with higher oxidation degree can be more efficiently prepared by the strategy of in-situ ultrasonic assisted oxidation.     

A novel approach for the synthesis of superparamagnetic Mn3O4 nanocrystals by ultrasonic bath

In this study, the synthesis of Mn₃O₄ (husmannite) nanoparticles was carried out in two different alkali media under sonication by ultrasonic bath and conventional method. Manganese acetate was used as precursor, sodium hydroxide and hexamethylenetetramine (HMT) as basic reagents in this synthesis. An ultrasonic bath with low intensity was used for the preparation of nanomaterials. The as prepared samples were characterized with X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (HRTEM, TEM), energy-dispersive spectrum (EDS), and superconducting quantum interference device (SQUID) analysis. The XRD patterns exhibit the nanocrystals are in pure tetragonal phase. The chemical composition was obtained by EDS analysis and confirmed the presence of Mn and O in the sample. According to the TEM and HRTEM results, both nanorods and nanoparticles of Mn₃O₄ were obtained in the presence of ultrasonic irradiation. The average size of nanoparticles was 10 nm, and the size of nanorods was 12 nm in diameter and 100-900 nm in length for the samples prepared in basic medium with sodium hydroxide. In the conventional method with the same basic medium, the nanorod was not observed and the nearly cubic nanoparticles was appeared with an average size of 2.5 nm. The selected area electron diffraction (SAED) patterns revealed that the nanocrystals are polycrystalline in nature. When HMT was used as a basic reagent in the presence of ultrasonic irradiation, it was led to a higher size of nanoparticles and nanorods than when sodium hydroxide was used as a basic reagent. The average size of nanoparticles was about 15 nm and its shape was nearly cubic. The diameter for nanorods was 50 nm and the length was about a few micrometers.The magnetic measurements were carried out on the sample prepared in sodium hydroxide under ultrasonic irradiation. These measurements as a function of temperature and field strength showed a reduction in ferrimagnetic temperature (T_c = 40 K) as compared to those reported for the bulk (T_c = 43 K). The superparamagnetic behavior was observed at room temperature with no saturation magnetization and hysteresis in the region of measured field strength.     

Measurement of tortuosity in aluminum foams using airborne ultrasound

The slow compressional wave in air-saturated aluminum foams was studied by means of ultrasonic transverse transmission method over a frequency range from 0.2 MHz to 0.8 MHz. The samples investigated have three different cell sizes or pores per inch (5, 10 and 20 ppi) and each size has three aluminum volume fractions (5%, 8% and 12% AVF). Phase velocities show minor dispersion at low frequencies but remain constant after 0.7 MHz. Pulse broadening and amplitude attenuation are obvious and increase with increasing ppi. Attenuation increases considerably with AVF for 20 ppi foams. Tortuosity ranges from 1.003 to 1.032 and increases with AVF and ppi. However, the increase of tortuosity with AVF is very small for 10 and 20 ppi samples.     

Application of ultrasound as pretreatment for extraction of podophyllotoxin from rhizomes of Podophyllum peltatum

The effect of high-power ultrasound pretreatment on the extraction of podophyllotoxin from Podophyllum peltatum was investigated. Direct sonication by an ultrasound probe horn was applied at 24 kHz and a number of factors were investigated: particle size (0.18-0.6 mm), type of solvent (0-100% aqueous ethanol), ultrasonic treatment time (2-40 min), and power of ultrasound (0-100% power intensity, maximum power: 78 W). The optimal condition of ultrasound was achieved with 0.425-0.6 mm particle size, 10 min sonication time, 35 W ultrasound power, and water as the medium. There was no obvious degradation of podophyllotoxin with ultrasound under the applied conditions, and an improvement in extractability was observed. The SEM microscopic structure change of treated samples disclosed the effect of ultrasound on the tissue cells. The increased pore volume and surface area after ultrasonic treatment also confirmed the positive effect of ultrasound pretreatment on the extraction yield of podophyllotoxin from the plant cells.