Effect of calcination temperature on performance of ZnO nanoparticles for dye-sensitized solar cells

The photovoltaic performances of ZnO-based dye-sensitized solar cells (DSSCs) were studied using ZnO nanoparticles prepared via the sol–gel method in gelatin medium at different calcination temperatures. The effects of the calcination temperature on the size, surface area, photoluminescence properties, and dye adsorption ability of ZnO nanoparticles were investigated. The results showed that the size of the nanoparticles increased and the surface area decreased with an increase in the calcination temperature. In addition, the oxygen vacancies of the nanoparticles increased with an increase in the calcination temperature. Moreover, although the surface area of the nanoparticles prepared at 600 °C was lower than that of those prepared at 500 °C, their dye adsorption abilities were the same, and both were higher than that of those prepared at 700 °C. Electrochemical impedance spectroscopy and open-circuit voltage decay measurements were carried out to investigate the cell functions. The DSSC based on ZnO nanoparticles calcined at 600 °C exhibited the highest conversion efficiency because of its higher dye adsorption ability and lower recombination rate compared to the others.This work was supported by a High Impact Research Grant from the Ministry of Higher Education of Malaysia. A. Moradi Golsheikh would like to thank Iran Nanotechnology Initiative Council

Time-dependent effect in green synthesis of silver nanoparticles.

The application of "green" chemistry rules to nanoscience and nanotechnology is very important in the preparation of various nanomaterials. In this work, we successfully developed an eco-friendly chemistry method for preparing silver nanoparticles (Ag-NPs) in natural polymeric media. The colloidal Ag-NPs were synthesized in an aqueous solution using silver nitrate, gelatin, and glucose as a silver precursor, stabilizer, and reducing agent, respectively. The properties of synthesized colloidal Ag-NPs were studied at different reaction times. The ultraviolet-visible (UV-vis) spectra were in excellent agreement with the obtained nanostructure studies performed by transmission electron microscopy (TEM) and their size distributions. The prepared samples were also characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM). The use of eco-friendly reagents, such as gelatin and glucose, provides green and economic attributes to this work

Fabrication and Characterization of Gelatin Stabilized Silver Nanoparticles under UV-Light

Silver nanoparticles (Ag-NPs) were successfully synthesized using the UV irradiation of aqueous solutions containing AgNO3 and gelatin as a silver source and stabilizer, respectively. The UV irradiation times influence the particles’ diameter of the Ag-NPs, as evidenced from surface plasmon resonance (SPR) bands and transmission electron microscopy (TEM) images. When the UV irradiation time was increased, the mean size of particles continuously decreased as a result of photoinduced Ag-NPs fragmentation. Based on X-ray diffraction (XRD), the UV-irradiated Ag-NPs were a face-centered cubic (fcc) single crystal without any impurity. This study reveals that the UV irradiation-mediated method is a green chemistry and promising route for the synthesis of stable Ag-NPs for several applications (e.g., medical and surgical devices). The important advantages of this method are that it is cheap, easy, and free of toxic materials

Fabrication and characterization of zinc oxide and lead zirconate titanate nanostructures / Ali Khorsand Zak

Since 1990, research on nanostructures and nanoparticles has attracted the interest of many researchers. Several methods have been developed to fabricate nano-sized materials. The main concern is to establish method that can be used to produce these materials at low cost, which is attractive for industry. Based on this motivation, in this thesis, I attempt to develop and investigate new and modified routes for preparing ZnO and PZT nanostructures and nanoparticles, which are the two materials that have attracted the most interest in in this decade. The aim of this work is to design and modify simple, inexpensive, fast, and safe methods for preparing the nanopowders of these two materials on a large scale and to study the characteristics of the nanostructures, such as structure, morphology, and optical properties by various characterization tools. To date, four different preparation techniques have been used to prepare ZnO nanoparticles, i.e., sol-gel synthesis, sol-combustion synthesis, solvothermal synthesis, and sonochemical synthesis. In addition, the sol-gel synthesis process has been used to prepare PZT nanoparticles. Initially, ZnO nanoparticles were prepared by the sol-gel method in two different media, i.e., gelatin and starch. These two natural materials were used as the polymerization agent. ZnO NPs were also synthesized by the sol-combustion method in which DEA was used as the polymerization agent and stabilizer, and citric and nitric acids were used as fuel. In the second preparation technique, the ZnO nanoparticles and nanostructures were prepared by the solvothermal method. The ethanolamine family, (MEA, DEA, and TEA), was investigated to determine its effect on the morphology of the ZnO nanostructures. The ZnO nanostructures (rods and flowers) were prepared successfully using the third preparation technique, i.e., the sonochemichal method. NaOH and NH3 solutions were used to control the pH of the Zn2+. The sonication process was applied for 5, 15, 30, and 60 min. In the fifth preparation technique, the PZT nanoparticles were prepared by the modified sol-gel method. Polyethylenglycol (PEG) and 2-methoxyethanol (EGME) were used as separate solvents to prepare the PZT nanoparticles. The structures of the ZnO and PZT nanoparticles also were investigated theoretically. Different theoretical models, such as Williamson-Hall and the Size-Strain Plot, were applied to analyze the XRD data of the ZnO and PZT nanoparticles. We also investigated the effect of calcination temperature on the mechanical properties of the nanoparticles. In addition, we investigated the optical properties of PZT nanoparticles prepared in different solvents, i.e., PEG and EGME. The dielectric properties of the PZT nanoparticles (with and without PVDF matrix) were investigated in the frequency range of 100 Hz to 40 MHz. The characterization of the materials using various techniques, such as XRD, TEM, SEM, and UV-vis, proved that good quality (narrow size distribution and uniform morphology) ZnO nanoparticles can be produced by the preparation technique that uses gelatin, while good quality (narrow size distribution and uniform morphology) PZT nanoparticles can be produced by the preparation technique that uses 2-methoxyethanol. These preparation techniques are attractive because they can be used to prepare these nanoparticles in large-scale production facilities, which is suitable for industry. In the future, these preparation methods can also be modified to prepare other metal oxide nanostructures, such as MgO and NiO, which also have various potential applications, such as in the medical field and electronics industries

Optical properties of ZnO/BaCO3 nanocomposites in UV and visible regions

Pure zinc oxide and zinc oxide/barium carbonate nanoparticles (ZnO-NPs and ZB-NPs) were synthesized by the sol-gel method. The prepared powders were characterized by X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), Auger spectroscopy, and transmission electron microscopy (TEM). The XRD result showed that the ZnO and BaCO3 nanocrystals grow independently. The Auger spectroscopy proved the existence of carbon in the composites besides the Zn, Ba, and O elements. The UV-Vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is redshifted by adding barium carbonate. In addition, the optical parameters including the refractive index and permittivity of the prepared samples were calculated using the UV-Vis spectra. PACS: 81.05.Dz; 78.40.Tv; 42.70.-

Sol–gel Grown Fe-doped ZnO Nanoparticles: Antibacterial and Structural Behaviors

Iron (Fe) doped Zinc-oxide (ZnO) nanoparticles (NPs) with composition Zn1-xFexO, where x = 0.0, 0.01, 0.03, and 0.05 are synthesized by sol–gel method from nitrate precursors and gelatin at fixed calcination temperature of 650 °C maintained for 2 h. The effects of Fe contents on the antibacterial and structural features of these NPs are inspected. Prepared NPs are characterized via X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD patterns display the single crystalline nature of samples that exists in hexagonal wurtzite phase. SEM images reveal the existence of nearly spherical shaped single-crystalline NPs. A quantitative analysis of the size dependent strain effects is performed through Williamson-Hall and size-strain plot and its impact of strain on peak broadening is demonstrated. The values of strain, stress, and energy density are calculated. The estimated NPs mean size from FESEM and size-strain plot (SSP) is found to be in close agreement. ZnO NPs in the presence of Fe show great inhibition towards E. coli bacterial growth. It is asserted that, Fe acting as impurity in the ZnO nanostructure enhances the power oxidation of ZnO which results an augmentation of antimicrobial activity. Keywords: ZnO, lattice strain, crystallite size, antibacterial activity, E. col

Synthesis of ZnO/Cu micro and nanostructures via a vapor phase transport method using different tube systems

ZnO micro and nanostructures were grown on copper coated silicon substrates using two different systems: an opened system (both ends opened tube) and a closed system (one closed end tube). The thermodynamic conditions of the systems made a significant difference in boundary layer and super-saturation between the systems. The results indicate that diffusion of the gaseous species through the boundary layers at low and high pressures controls the final formation of the morphologies. The ZnO nanostructures which have been grown in a restricted place have larger diameters and lengths. The structure of the products was analyzed by X-ray diffractometer (XRD) and it was found that the good crystalline quality of the samples was obtained in a closed system. To study the optical properties, photoluminescence (PL) and ultra violet–visible (UV–vis) spectroscopy were employed. It was observed that a decrease in the growth temperature of the opened system caused a broad and dominant visible emission covering the blue and green emission in the PL spectra

Sol-gel combustion synthesis of Zr-doped BaTiO3 nanopowders and ceramics: Dielectric and ferroelectric studies

The dielectric and ferroelectric properties of the ceramic system, Ba(Ti1-x,Zrx)O3, were investigated for compositions 0 ≤ x ≤ 0.2. The primary nanopowders were synthesized using a sol-gel combustion route to obtain the homogenous compounds. X-ray diffraction patterns demonstrated that there was a cubic structure for the prepared nanopowders. The nanopowders were pressed into pellet form and sintered at 1250, 1300, and 1350 °C. The results revealed a significant increase in the permittivity of the Zr-doped samples. The sample showed the best dielectric properties and a ferroelectric behavior for the value of x=0.05

Preparation of gelatinous gold nanoparticles by pulsed laser ablation

Colloidal gold nanoparticles (Au-NPs) were successfully prepared using a nanosecond-pulsed Nd:YAG laser, k = 1,064 nm, with laser fluence of approximately about 360 mJ/pulse, in an aqueous gelatin solution. In this work, gelatin was used as a stabilizer, and the size and optical absorption properties of samples were studied as a function of the laser ablation times. The results from the UV–Vis spectroscopy demonstrated that the mean diameter of Au-NPs decrease as the laser ablation time increases. The Au-NPs have mean diameters ranging from approximately 19 to 7 nm. Compared with other preparation methods, this work is clean, rapid, and simple to use