Spectral features and antibacterial properties of Cu-doped ZnO nanoparticles prepared by sol-gel method

Zn_(1-x)Cu_x O(x=0.00, 0.01, 0.03, and 0.05) nanoparticles are synthesized via the sol-gel technique using gelatin and nitrate precursors. The impact of copper concentration on the structural, optical, and antibacterial properties of these nanoparticles is demonstrated. Powder x-ray diffraction investigations have illustrated the organized Cu doping into ZnO nanoparticles up to Cu concentration of 5%(x = 0.05). However, the peak corresponding to CuO for x= 0.01 is not distinguishable. The images of field emission scanning electron microscopy demonstrate the existence of a nearly spherical shape with a size in the range of 30–52 nm. Doping Cu creates the Cu–O–Zn on the surface and results in a decrease in the crystallite size. Photoluminescence and absorption spectra display that doping Cu causes an increment in the energy band gap. The antibacterial activities of the nanoparticles are examined against Escherichia coli(Gram negative bacteria)cultures using optical density at 600 nm and a comparison of the size of inhibition zone diameter. It is found that both pure and doped ZnO nanoparticles indicate appropriate antibacterial activity which rises with Cu doping.     

A novel polyol method to synthesize colloidal silver nanoparticles by ultrasonic irradiation

A polyol synthesis of silver nanoparticles in the presence of ultrasonic irradiation was compared with other configurations (at ambient temperature, 120 °C, and 120 °C with injected solutions) in the absence of ultrasonic irradiation in order to obtain systematic results for morphology and size distribution. For applying ultrasonic irradiation, rather fine and uniform spherical silver particles (21 ± 3.7 nm) were obtained in a simple (at ambient temperature without mechanical stirring) and fast (within 4 min, 3.61 × 10⁻³ mol min⁻¹) manner than other cases (at ambient temperature (for 8 h, 0.03 × 10⁻³ mol min⁻¹): 86 ± 16.8 nm, 120 °C (for 12 min, 1.16 × 10⁻³ mol min⁻¹): 64 ± 14.9 nm, and 120 °C with injected solutions (during 12 min): 35 ± 6.8 nm; all other cases contained anisotropic shaped particles). Even though the temperature of polyol reaction reached only at 80 °C (<120 °C) in the presence of ultrasonic irradiation, a uniform mixing (i.e. enhanced collision between silver particle and surrounding components) by ultrasonic irradiation might induce a better formation kinetics and morphological uniformity.     

Ultrasonic irradiation effects on electrochemical synthesis of ZnO nanostructures

In the present article, electrochemical synthesis of ZnO nanostructures in presence of ultrasonic irradiation is investigated. The ultrasonic bath use for synthesis is calibrated using hydrophone method so that its frequency and acoustic power were obtained. From the results of the experimentation the role of ultrasonic irradiation in synthesis of ZnO nanoparticles is discussed. Diameter of the ZnO nanoparticles produced in the electrolyte was compared and investigated in absence and presence of the ultrasonic irradiation utilizing UV–visible photo-spectrometer. Then electrodeposited ZnO layer on the ITO glass as cathode’s surface in absence and presence of the ultrasonic irradiation were studied by UV–visible photo-spectrometer and field emission scanning electron microscopy (FE-SEM) and the results were compared. FE-SEM micrographs show, higher growth of nanosheets on the cathode electrode in presence of ultrasonic irradiation. Experiment shows synthesis of ZnO nanoparticles in presence of the ultrasonic irradiation happen 10 times faster.     

The influence of annealing temperature on the structure,morphologies and optical properties of ZnO nanoparticles

ZnO nanoparticles (NPs) have been successfully synthesized by the simple solution method at low temperature. The effects of annealing temperature on the structure and optical properties of ZnO NPs were investigated in detail by X-ray diffraction, transmission electron microscopy (TEM), ultraviolet–visible (UV–vis) spectroscopy and photoluminescence (PL) measurements. As the annealing temperature was increased above 180 ^°C the particles morphology evolved from spherical to hexagonal shape, indicating that the average particle size increased from 11 nm to 87 nm. The UV-vis and PL spectra showed a red-shift from 3.62 to 3.33 eV when the annealing temperature was increased.     

The structure and magnetic properties of Cu-doped ZnO prepared by sol-gel method

The Cu-doped ZnO and pure ZnO powders were synthesized by sol-gel method. The structural properties of the samples were investigated by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. All the results confirmed that copper ions were well incorporated into the ZnO lattices by substituting Zn sites without changing the wurtzite structure and no secondary phase existed in Cu-doped ZnO nanoparticles. The Zn_0.97Cu_0.03O nanoparticles exhibited ferromagnetism at room temperature, as established by the vibrating sample magnetometer analysis.     

Microstructural, optical and electrical studies on sol gel derived ZnO and ZnO:Al films

ZnO and ZnO:Al films were deposited onto glass substrates by the sol gel method using spin coating technique. The effects of aluminum dopant on the crystalline structure and orientation of the ZnO films have been investigated by X-ray diffraction (XRD) study. Surface morphology of the films has also been analyzed by a field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The average optical transmittance values of all the films is over >83% in the visible region. The optical band gap and Urbach energy values of these films were determined. The absorption edge shifted to the lower energy depending on the Al doping level. The shift of absorption edge is associated with shrinkage effect. The electrical conductivity of the ZnO film enhanced with the Al dopant. From the temperature dependence of conductivity measurements, the activation energy of the films was also calculated.     

Sol-gel preparation and enhanced photocatalytic performance of Cu-doped ZnO nanoparticles

Cu-doped ZnO nanoparticles were prepared by a sol-gel method for the first time. XRD, XPS, UV-vis and FS techniques were used to characterize the Cu-doped ZnO samples. The photocatalytic activity was tested for methyl orange degradation under UV irradiation. The results show that the crystal sizes of ZnO and 0.5% Cu/ZnO nanoparticles with wurtzite phase are 32.0 and 28.5 nm, indicating that Cu-doping hinder the growth of crystal grains. The doped Cu element existed as Cu²⁺. The optimal Cu doping concentration in ZnO is 0.5%. The optimal calcination condition is at 350 °C for 3 h. The MO degradation rate of 0.5% Cu/ZnO reaches 88.0% when initial concentration of MO is 20 mg/L, exceeding that of undoped ZnO. The enhanced charge carrier separation and increased surface hydroxyl groups due to Cu-doping contributed to the enhanced photocatalytic activity of 0.5% Cu/ZnO.     

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.     

Effect of sol concentration on the properties of ZnO thin films prepared by sol-gel technique

ZnO thin films are deposited on the glass substrates by sol-gel drain coating technique by varying the concentration of the sol. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis were used to investigate the effect of sol concentration on the crystallinity and surface morphology of the films. The results show that with increase in sol concentration, the value of full width at half maximum (FWHM) of (0 0 2) peak decreases while the strain first increases and then decreases. The sol with higher concentration results in the increase in the grain size. The studies on the optical properties show that the band gap value increases from 3.27 to 3.3 eV when the sol concentration changes from 0.03 to 0.1 M. The photoconductivity studies reveal that the film for 0.05 M sol shows the maximum photoresponse for ultraviolet (UV) wavelength (<400 nm) which is co-related with the deep-level defects. The growth and decay of the photocurrent is found to be slowest for the same film.     

Effect of annealing temperature on photocatalytic activity of ZnO thin films prepared by sol-gel method

Zinc oxide thin films are deposited on Si and quartz substrates using the sol-gel method. The thin films, annealed at 400, 600 and 800 °C respectively, are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), ultraviolet-visible spectrophotometer (UV-Vis), fluorescence spectrometer (FL) and the photocatalytic activity is tested by the decomposition of methyl orange dye under UV illumination. The results show that the mean grain size, surface-to-volume ratio, rms roughness and degradation efficiency of the thin films increases with increasing annealing temperature. In particular, ZnO thin film annealed at 800 °C exhibits the highest photocatalytic activity, degrading methyl orange by almost 88% in 180 min. Photocatalytic reaction mechanism of the ZnO thin films is discussed in detail, and the oxygen defects are proposed to be the active sites of the ZnO photocatalyst.     

The modification of the characteristics of nanocrystalline ZnO thin films by variation of Ta doping content

Thin films of Ta-doped ZnO were synthesised via sol–gel spin coating route. The structural and optical properties of the films were evaluated to find out the effect of Ta dopant content. X-ray diffraction results indicated that all samples have hexagonal wurtzite crystal structure with polycrystalline nature. (0 0 2) peak is the most intense peak observed in all samples as well as the highest textured coefficient. Standard deviation results have shown that the kind of nucleation varies from heterogeneous to homogenous with Ta doping content. Additionally, Ta-incorporated ZnO films revealed not only a decreased surface roughness, but also an increased optical transmittance. Direct optical band gap values increased from 3.14 to 3.28 eV, and Urbach energy values decreased from 217 to 147 meV with increasing Ta doping. Refractive index and dielectric constant values were determined by means of two different functions and a significant consistency was found among them. Moreover, the correlation between the optical and structural properties showed that there is a relationship between refractive index and lattice constants of Ta-doped ZnO films.     

ZnO nanoparticles obtained by mechanochemical technique and the optical properties

Crystalline ZnO nanoparticles were synthesized by mechanochemical method. Mechanochemical processing involves the mechanical activation of solid-state displacement reactions at low temperatures in a ball mill. Statistical design was used to investigate the effect of main parameters (i.e. time, milling rate and calcination temperature) on ZnO crystallite size and morphology. After annealing at 400 °C in air, zinc oxide (ZnO) nanoparticles were obtained. The milled powders are analyzed by X-ray diffraction (XRD), TG/DTA and transmission electron microscope (TEM).The crystallite size of ZnO samples calculated from XRD is consistent with the TEM images and estimated to be less than 20 nm. The optical properties of the samples were studied by UV-vis spectrophotometer.     

Facile,high yield ultrasound mediated protocol for ZnO hierarchical structures synthesis: Formation mechanism,optical and photocatalytic properties

Hierarchical flowers-like zinc oxide structures have been successfully obtained by a simple and fast ultrasound-assisted method performed in a ordinary ultrasonic bath using an ammonia solution and zinc acetate, in the absence of any surfactant or template. The composition, structure, crystallinity, morphology and optical properties of the materials obtained at different ultrasound irradiation times were characterized by infrared, UV–Vis and photoluminescence spectroscopy, X-ray diffraction, scanning and transmission electron microscopy investigations. It was proved that the ultrasound irradiation time manipulates both the defect content (implicit the photoluminescent properties) and morphology of the ZnO materials: shorter irradiation times leads to the synthesis of high-defected ZnO structures of flower morphology with triangular-shaped petals, while higher irradiation times favours the formation of low-defected ZnO structures with tipped rod-like petals. A plausible growth mechanism of the architectures that implies aggregation via oriented attachment followed by an Ostwald ripening is advanced based on these results. The ZnO flower-like structures present high photocatalytic activities, a total phenol mineralization being registered in the case of visible light experiments. Electron-spin resonance measurements demonstrate the generation of reactive oxygen species, namely hydroxyl radicals but also C centred radicals adducts derived most probable from the residual acetate adsorbed on ZnO surface.     

Sonocatalytic degradation of acid red B and rhodamine B catalyzed by nano-sized ZnO powder under ultrasonic irradiation

Nano-sized ZnO powder was introduced to act as the sonocatalyst after the treatment of high-temperature activation, and the ultrasound of low power was used as an irradiation source to induce nano-sized ZnO powder performing sonocatalytic degradation of acid red B and rhodamine B. At the same time, the effects of operational parameters such as solution pH value, initial concentration of dyestuff and addition amount of nano-sized ZnO powder have been examined in this paper. We found that the degradation ratios of acid red B and rhodamine B in the presence of nano-sized ZnO powder were much higher than that with only ultrasonic irradiation. However, the degradation ratio of acid red B was about two times higher than that of rhodamine B for the initial concentration of 10.0 mg/L, addition amount of 1.0 g/L nano-sized ZnO powder, solution acidity of pH 7.0 and 60 min irradiation experimental condition. The difference of the degradation ratios can be illustrated by the difference of chemical forms of acid red B and rhodamine B in aqueous solution and the surface properties of nano-sized ZnO particles. In addition, the researches on the kinetics of sonocatalytic reactions of acid red B and rhodamine B have also been performed and found to the follow pseudo first-order kinetics. All the experiments indicated that the sonocatalytic method in the presence of nano-sized ZnO powder was an advisable choice for the treatments of non- or low-transparent organic wastewaters in future.     

One-step synthesis of black TiO2-x microspheres by ultrasonic spray pyrolysis process and their visible-light-driven photocatalytic activities

Black TiO_2-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 TiO_2-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 TiO_2-x microspheres were obtained at 900 °C. The synthesized black TiO_2-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.     

Quantum confinement effect in ZnO nanoparticles synthesized by co-precipitate method

Quantum mechanical effects such as an increased bandgap of semiconductors with reduction of size are viewed as having strong potential for future applications. In the present work, zinc oxide (ZnO) nanoparticles (NPs) were synthesized via the co-precipitate method. Very narrow particle size distribution of the ZnO nanoparticles was achieved through careful control of the synthesis conditions. The structural, morphological, and optical characterization was carried out using X-ray diffraction, atomic force microscopy, and UV–vis reflectance techniques, respectively. The results indicated that increasing the temperature from 60 to 65 °C caused a subsequent increase in particle size from 4 to 12 nm. An associated increase in bandgap with decrease in particle size was also noticed which is a strong indication of the quantum confinement effect.     

Microstructures, optical and electrical properties of In-doped ZnO thin films prepared by sol-gel method

ZnO and indium-doped ZnO (I_xZO) thin films were prepared on silica-glass substrates by the sol-gel method. The thin films were crystallized at 600 °C and 700 °C for 1 h in 6.9 × 10⁻¹ Torr under pure O₂ atmosphere. The analyzed results were compared to investigate the structural characteristics and optical properties. The surface morphology of the I_xZO films was different from that of the ZnO films, and showed a thin overlay structure. In addition, the crystallization of I_xZO film was depleted at higher crystallized temperatures. From XRD analysis, the ZnO and I_xZO thin films possessed hexagonal structures. Notably, micro-In₂O₃ phases were observed in the I_xZO thin films using EDS. Both of In₂O₃ phases and the crystallization mechanism not only improved the peeling of structure, but also improved the electrical conductivity of I_xZO thin films. For the PL spectrum, the optical property of the I_xZO film was raised at a higher crystallization temperature. Although the In₂O₃ phases reduced the structural defects of I_xZO thin film, the optical effect of the residual In³⁺ was not enhanced completely at higher crystallized temperatures.     

White-light emission of ZnO nanoparticles prepared by sol-gel method

In:ZnO nanoparticles are prepared by the sol-gel process. The ratios of In/(Zn+In) are 0%, 5%, 8%, 10%, and 15%, respectively. Crystal phase structures and optoelectronic properties of these samples are characterized and the chromaticity coordinates of different samples are also calculated in CIE-XYZ colour system. The results show that preferred growth direction of ZnO changes from (002) plane to (001) plane and interplanar distance becomes shorter. When the doping amount of In is 5%, Zn atoms are completely replaced by In atoms. The resistivities of the samples first decrease, then increase afterwards with the increase of the amount of In. With the increase of In, the ultraviolet emission is redshifted and new peaks occur at 465 nm, 535 nm, and 630 nm. The sample with 10% indium has white-light emission. The band structures of samples with 0% and 12.5% indium are investigated by the first principle method. The mechanism of white emission is discussed from the viewpoint of additional energy levels.     

Determining the thermophysical properties of Al-doped ZnO nanoparticles by the photoacoustic technique

The thermal conductivity and specific heat capacity of undoped and Al-doped (1-10 at.%) ZnO nanoparticles prepared using the solvent thermal method are determined by measuring both thermal diffusivity and thermal effusivity of a pressed powder compact of the prepared nanoparticles by using the laser-induced photoacoustic technique. The impact of Al doping versus the microstructure of the samples on such thermal parameters has been investigated. The results reveal an obvious enhancement in the specific heat capacity when decreasing the particle size, while the effect of Al doping on the specific heat capacity is minor. The measured thermal conductivities are about one order of magnitude smaller than that of the bulk ZnO due to several nested reducing heat transfer mechanisms. The results also show that Al doping significantly influences the thermal resistance. Using a simple thermal impedance model, the added thermal resistance due to Al dopant has been estimated.