Increasing Precursor Concentration Research Articles

Green synthesis of copper oxide nanoparticles using gum karaya as a biotemplate and their antibacterial application

BackgroundCopper oxide (CuO) nanoparticles have attracted huge attention due to catalytic, electric, optical, photonic, textile, nanofluid, and antibacterial activity depending on the size, shape, and neighboring medium. In the present paper, we synthesized CuO nanoparticles using gum karaya, a natural nontoxic hydrocolloid, by green technology and explored its potential antibacterial application.MethodsThe CuO nanoparticles were synthesized by a colloid-thermal synthesis process. The mixture contained various concentrations of CuCl2 • 2H2O (1 mM, 2 mM, and 3 mM) and gum karaya (10 mg/mL) and was kept at 75°C at 250 rpm for 1 hour in an orbital shaker. The synthesized CuO was purified and dried to obtain different sizes of the CuO nanoparticles. The well diffusion method was used to study the antibacterial activity of the synthesized CuO nanoparticles. The zone of inhibition, minimum inhibitory concentration, and minimum bactericidal concentration were determined by the broth microdilution method recommended by the Clinical and Laboratory Standards Institute.ResultsScanning electron microscopy analysis showed CuO nanoparticles evenly distributed on the surface of the gum matrix. X-ray diffraction of the synthesized nanoparticles indicates the formation of single-phase CuO with a monoclinic structure. The Fourier transform infrared spectroscopy peak at 525 cm−1 should be a stretching of CuO, which matches up to the B2u mode. The peaks at 525 cm−1 and 580 cm−1 indicated the formation of CuO nanostructure. Transmission electron microscope analyses revealed CuO nanoparticles of 4.8 ± 1.6 nm, 5.5 ± 2.5 nm, and 7.8 ± 2.3 nm sizes were synthesized with various concentrations of CuCl2 • 2H2O (1 mM, 2 mM, and 3 mM). X-ray photoelectron spectroscopy profiles indicated that the O 1s and Cu 2p peak corresponding to the CuO nanoparticles were observed. The antibacterial activity of the synthesized nanoparticles was tested against Gram-negative and positive cultures.ConclusionThe formed CuO nanoparticles are small in size (4.8 ± 1.6 nm), highly stable, and have significant antibacterial action on both the Gram classes of bacteria compared to larger sizes of synthesized CuO (7.8 ± 2.3 nm) nanoparticles. The smaller size of the CuO nanoparticles (4.8 ± 1.6 nm) was found to be yielding a maximum zone of inhibition compared to the larger size of synthesized CuO nanoparticles (7.8 ± 2.3 nm). The results also indicate that increase in precursor concentration enhances an increase in particle size, as well as the morphology of synthesized CuO nanoparticles.

Effects of precursor concentrations on ZnO nano-fibrous thin films grown by using the sol-gel dip-coating method

ZnO thin films were fabricated by using the dip-coating method to deposit solutions with different precursor concentrations on quartz substrates. The structural and the optical properties of the ZnO thin films were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), photoluminescence (PL), and ultraviolet-visible spectroscopy. The average grain size in the ZnO thin films increased from 19.09 to 39.19 nm with increasing precursor concentrations, and nanofibrous structures were observed on the surface when precursor concentrations above 0.4 M were used. The PL spectra, in all cases, showed near-band-edge (NBE) emission and deep-level emission (DLE). When the precursor concentrations were increased, the optical band gap values for the ZnO thin films shifted towards the blue region, and the values of the Urbach energy (EU) gradually decreased from 154 to 65 meV.

High Mobility Indium Zinc Oxide Thin Film Field-Effect Transistors by Semiconductor Layer Engineering

Indium zinc oxide thin-film transistors are fabricated via a precursor in solution route on silicon substrates with silicon dioxide gate dielectric. It is found that the extracted mobility rises, peaks, and then decreases with increasing precursor concentration instead of rising and saturating. Investigation with scanning probe techniques reveals full thickness variations within the film which are assumed to adversely affect charge transport. Additional layers are coated, and the extracted mobility is observed to increase up to 19.7 cm(2) V(-1) s(-1). The reasons for this are examined in detail by direct imaging with scanning tunneling microscopy and extracting electron density profiles from X-ray reflection measurements. It is found that the optimal concentration for single layer films is suboptimal when coating multiple layers and in fact using many layers of very low concentrations of precursor in the solution, leading to a dense, defect and void free film, affording the highest mobilities. A consistent qualitative model of layer formation is developed explaining how the morphology of the film develops as the concentration of precursor in the initial solution is varied.

Room Temperature Radiolytic Synthesized Cu@CuAlO2-Al2O3 Nanoparticles

Colloidal Cu@CuAlO2-Al2O3 bimetallic nanoparticles were prepared by a gamma irradiation method in an aqueous system in the presence of polyvinyl pyrrolidone (PVP) and isopropanol respectively as a colloidal stabilizer and scavenger of hydrogen and hydroxyl radicals. The gamma irradiation was carried out in a 60Co gamma source chamber with different doses up to 120 kGy. The formation of Cu@CuAlO2-Al2O3 nanoparticles was observed initially by the change in color of the colloidal samples from colorless to brown. Fourier transform infrared spectroscopy (FTIR) confirmed the presence of bonds between polymer chains and the metal surface at all radiation doses. Results of transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD) showed that Cu@CuAlO2-Al2O3 nanoparticles are in a core-shell structure. By controlling the absorbed dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increased precursor concentration and decreased with increased dose. This is due to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.

Aqueous chemical route deposition of nanocrystalline ZnO thin films as acetone sensor: Effect of molarity

Nanocrystalline ZnO thin films were deposited onto glass substrate using a simple and inexpensive aqueous chemical method at low temperature (90°C). The concentration of precursor solution was varied in order to study its effect on structural, morphological, and gas response properties. Field-emission scanning electron microscopy (FESEM) images indicate the growth of ZnO with hexagonal shaped nanostructure. Further these films were used to explore gas response properties towards acetone, propanol and ethanol vapors. The sensor response was found to be decreased with increase in precursor concentration. The highest sensor response of 92% was observed towards acetone for the film deposited at 0.05M at an operating temperature of 350°C. The higher vapor response towards acetone is attributed to size and surface morphology of the film deposited at 0.05M.

Structural and optical properties of ZnO rods hydrothermally formed on polyethersulfone substrates

Various unique ZnO morphologies, such as cigar-like and belt-like structures and microrod and nanorod structures, were formed on flexible polyethersulfone (PES) substrates by using a low temperature hydrothermal route. The structural properties of ZnO depended highly on the precursor concentration. The effect of a thin ZnO seed layer deposited the on PES substrate by using atomic layer deposition on the structural and the optical properties of ZnO hydrothermally grown on the ZnO seed layer/PES substrates was studied. Field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements were employed to analyze the characteristics of hydrothermally-grown ZnO. The diameter of the ZnO nanorods grown on the ZnO seed layer/PES substrates increased with increasing precursor concentration from 0.025 to 0.125 M due to the Ostwald ripening process. ZnO hydrothermally-grown on the ZnO seed layer/PES substrates at a low precursor concentration showed better structural properties than ZnO formed without a seed layer. Well-formed ZnO nanorods deposited on the ZnO seed layer/PES substrates showed two PL peaks, one in the ultraviolet and the other in the visible region, whereas horizontally positioned ZnO formed on the PES substrate in the absence of a seed layer emitted only one broad PL peak in the violet region. The ZnO grown on PES substrates in this work can be used as high-quality transparent electrodes for solar cells fabricated on flexible substrates.

Influence of dose and ion concentration on formation of binary Al–Ni alloy nanoclusters

Colloidal Al–Ni nanoclusters were prepared in an aqueous polyvinyl alcohol solution containing aluminum chloride and nickel chloride as metal precursors, polyvinyl alcohol as a capping agent, isopropanol as a scavenger of hydroxyl radicals, and distilled water as a solvent. Gamma irradiations were carried out in a 60Co gamma source chamber at doses up to 100kGy. The nanocluster properties were characterized by transmission electron microscopy (TEM), UV–visible spectrophotometry, and X-ray diffraction (XRD). By controlling the dose and precursor concentration, nanoclusters with different particle sizes were obtained. The average particle diameter increased with increase of precursor concentration and decreased with increase of dose. This is owing to the competition between nucleation, growth, and aggregation processes in the formation of nanoclusters during irradiation.

Characteristics of ZnO Nanorod/ZnO/Si(100) Grown by Hydrothermal Method

Nanostructures of ZnO, such as nanowires, nanorods, nanorings, and nanobelts have been actively studied and applied in electronic or optical devices owing to the increased surface to volume ratio and quantum confinement that they provide. ZnO seed layer (about 40 nm thick) was deposited on Si(100) substrate by RF magnetron sputtering with power of 60 W for 5 min. ZnO nanorods were grown on ZnO seed layer/Si(100) substrate at <TEX>$95^{\circ}C$</TEX> for 5 hr by hydrothermal method with concentrations of <TEX>$Zn(NO_3)_2{\cdot}6H_2O$</TEX> [ZNH] and <TEX>$(CH_2)_6N_4$</TEX> [HMT] precursors ranging from 0.02M to 0.1M. We observed the microstructure, crystal structure, and photoluminescence of the nanorods. The ZnO nanorods grew with hexahedron shape to the c-axis at (002), and increased their diameter and length with the increase of precursor concentration. In 0.06 M and 0.08 M precursors, the mean aspect ratio values of ZnO nanorods were 6.8 and 6.5; also, ZnO nanorods had good crystal quality. Near band edge emission (NBE) and a deep level emission (DLE) were observed in all ZnO nanorod samples. The highest peak of NBE and the lower DLE appeared in 0.06 M precursor; however, the highest peak of DLE and the lower peak of NBE appeared in the 0.02 M precursor. It is possible to explain these phenomena as results of the better crystal quality and homogeneous shape of the nanorods in the precursor solution of 0.06 M, and as resulting from the bed crystal quality and the formation of Zn vacancies in the nanorods due to the lack of <TEX>$Zn^{++}$</TEX> in the 0.02 M precursor.

Size and shape effects on magnetic properties of Ni nanoparticles

Pure Ni nanoparticles ranging in size from 24 to 200nm are prepared via thermal decomposition of nickel acetylacetonate in oleylamine. The as-prepared Ni particles change from spherical to dendritic or starlike with increasing precursor concentration. The particles are stable because the organic coating occurs in situ. Magnetic measurement reveals that all the Ni nanoparticles are ferromagnetic and show ferromagnetic–paramagnetic transitions at their Curie points. The saturation magnetization Ms is size-dependent, with a maximum value of 52.01 and 82.31emu/g at room temperature and 5K, respectively. The coercivity decreases at first and then increases with increasing particle size, which is attributed to the competition between size effect and shape anisotropy. The Curie temperature Tc is 593, 612, 622, 626 and 627K for the 24, 50, 96, 165 and 200nm Ni nanoparticles, respectively. A theoretical model is proposed to explain the size-dependence of Ni nanoparticle Curie temperature.

Annealing effect on physical properties of spin coated ZnO films

ZnO thin films were deposited onto glass substrates using sol–gel spin coating technique from starting solutions having different precursor concentrations (0·1, 0·3 and 0·5M). The effects of precursor concentration and annealing temperature on the physical properties of the films were investigated. The X-ray diffraction studies confirm that all the films have preferential orientation along the (002) plane with hexagonal wurtzite structure. The optical transparency gradually decreases (from 95 to 80%) as the precursor concentration increases. The optical energy gap is in the range of 3·18–3·32 eV. The systematic study shows that the post-annealing process has significant impact on the quality of the films. The SEM images depict that the grain size decreases as the precursor concentration increases, and the AFM images show that the film annealed at 550°C has well defined uniform grains. The lowest dislocation density is observed for 0·3M annealed at 550°C.

Growth and characterization of seed layer-free ZnO thin films deposited on porous silicon by hydrothermal method

Catalyst- and seed layer-free zinc oxide (ZnO) thin films were grown on porous silicon (PS) by a hydrothermal method. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, and photoluminescence (PL) were carried out to investigate the structural and optical properties of the PS and the ZnO thin films. The ZnO thin films have an extraordinary tendency to grow along the a-axis with a hexagonal wurtzite structure. The growth rate of the ZnO thin films was increased with the increase in the precursor concentration. The crystal quality of the ZnO thin films was improved, and the residual stress was decreased as their thickness increased. Monochromatic indigo and red light emission peaks were observed from the ZnO thin films and the PS, respectively. At an excessively high precursor concentration, a green light emission peak was also observed in the ZnO thin films. The luminescent efficiency of the indigo light emission peak was enhanced with the increase in the precursor concentration.

Synthesis and Photocatalytic Property of ZnO nanoparticles Prepared by Spray-Pyrolysis Method

In this research, ZnO nanoparticles were synthesized by spray-pyrolysis method using the zinc acetate dihydrate as starting material at synthesis temperature of 900°C with various concentrations (0.01, 0.1, 1.0 M, respectively). The physico-chemical property of synthesized ZnO nanoparticles was characterized by XRD, SEM, FT-IR, and UV-vis spectroscopy. The synthesized ZnO nanoparticles indicated particle size with two-type shape. With increased precursor concentration, the ZnO nanoparticles were shown not only increasing from 0.8 to 1.5 μm at primary particles but also similar tendency (15 to 35 nm) at secondary particles. Also, the photocatalytic activities of ZnO synthesized in different precursor concentration was evaluated by removal rate of methyleneblue (MB) under UV irradiation (365 nm) at room temperature. The results showed that the photocatalytic efficiency of ZnO nanoparticles was enhanced by increased precursor concentration.

Optimizing the Hydrothermal Synthesis of Micro-Sized Olivine LiFePO&lt;sub&gt;4&lt;/sub&gt;

The low tap density of LiFePO4 is hindering the energy and power density of lithium-ion batteries in portable electronics, electric vehicles, and stationary electricity storage applications. As part of our work to investigate the pathological mechanism of performance degradation in large particle LiFePO4, micro-sized pristine LiFePO4 without modifications, such as surface coating or bulk doping, was first prepared hydrothermally by optimizing the synthesis parameters in this work. The influences of precursor concentration, solution pH, hydrothermal temperature, and heating time on the phase structure, particle size, and morphology of the products were systematically investigated. It was found that the particle size of LiFePO4 increases with decreasing pH value, increasing precursor concentration, increasing hydrothermal temperature, and increasing heating time during hydrothermal synthesis. The performance degradation of large particle LiFePO4 was demonstrated by these intrinsic samples. The specific discharge capacity decreased from 152 to 80 mAh·g-1 at 0.1C rate when the particle size was increased from 0.7 to 16.5 μm. Moreover, less capacities were retained after 100 cycles at 1C rate for larger particle materials. Finally, the optimized LiFePO4 with a distorted diamond shape was prepared for later investigation of the plausible mechanism of performance degradation in large particle LiFePO4. Its electrochemical performance was preliminarily discussed, and will need to be improved in future to obtain practical high energy/power density LiFePO4 cathodes for lithium-ion batteries. [Article] doi: 10.3866/PKU.WHXB201209271 www.whxb.pku.edu.cn 物理化学学报(Wuli Huaxue Xuebao) Acta Phys. -Chim. Sin. 2012, 28 (12), 2885-2892 December Received: July 3, 2012; Revised: September 7, 2012; Published on Web: September 27, 2012. ∗Corresponding author. Email: ylxu@mail.xjtu.edu.cn; Tel: +86-29-82665161 C Editorial office of Acta Physico-Chimica Sinica 2885 Acta Phys. -Chim. Sin. 2012 Vol.28

One dimensional Ag/Au/AgCl nanocomposites stemmed from Ag nanowires for electrocatalysis of oxygen reduction

This paper reports the synthesis and characterization of one dimensional nanocomposites composed of Ag, Au, and AgCl (denoted as Ag/Au/AgCl). The Ag/Au/AgCl composites with different compositional ratios are prepared by the galvanic replacement reaction between a Ag nanowire template and Au precursor at various concentrations (1, 10, 100 mM HAuCl4). As the Au precursor concentration increases, the structure of the resulting Ag/Au/AgCl changes from a core–shell solid wire to a porous hollow wire with a decrease in the Ag and AgCl contents and increase in the Au content. The catalytic activity of Ag/Au/AgCl for the oxygen reduction reaction (ORR) is investigated in 0.1 M NaOH solution. The nanocomposite with a Ag : Au : AgCl compositional ratio of 4 : 86 : 10 shows reasonable ORR activity (high ORR current, positive onset potential) along with sufficient stability and ethanol tolerance in alkaline media, suggesting that it could be used as a substitute for Pt-based cathode catalysts in fuel cells.

Direct synthesis of nanostructured TiO 2 films with controlled morphologies by stagnation swirl flames

A novel premixed swirl flame in stagnation point geometry is used to synthesize uniform, high-quality nanostructured TiO 2 films at growth rates of 20–200 nm/s in a single step. The roles of precursor concentration and substrate temperature in controlling film morphology and characteristics are investigated. Increasing precursor concentration, for a given substrate temperature, significantly increases the packing density of the nanoporous film. The specific surface area of the film is mainly dependent on substrate temperature, where two distinct regimes, i.e. in-flame-agglomeration at low temperature and on-substrate-sintering at high temperature, specify film properties. A simplified deposition model for the formation of the nanoporous film structure is proposed, correlating penetration distance of thermophoretically-driven Brownian particles into the film with the resultant morphology. The model predicts the packing density in excellent agreement with experiments, thereby clarifying the complex roles of precursor concentration and substrate temperature. Finally, increasing substrate temperature, at fixed precursor concentration, changes the packing density little, but considerably decreases specific surface area, as sintering becomes dominant among controlling mechanisms.

Effect of precursor concentration on the growth of zinc oxide nanorod arrays on pre-treated substrates

Well aligned zinc oxide nanorod arrays (ZNAs) synthesized by a simple chemical bath deposition method were fabricated on pre-treated Si substrates. By keeping the molar VI/II ratio constant, the effect of precursor concentration on the growth and optical quality of the ZNAs was investigated. The as-synthesized ZNAs were characterized by field emission scanning electron microscopy (FESEM), x-ray diffraction (XRD) and photoluminescence spectroscopy (PL). FESEM images show that both the diameter and aspect ratio of the ZNAs increase dramatically as the precursor concentration increases. The XRD analysis indicates that all the as-grown ZNAs are crystalline and are preferentially oriented along the c-axis. The high intensity ratio of the UV emission to visible emission in the room temperature PL spectra illustrate that high optical quality ZNAs were produced.

Effect of precursor concentration on structural and optical properties of ZnO microrods by spray pyrolysis

ZnO films have been prepared by spray pyrolysis technique on glass substrate at 500 °C. Zinc Chloride has been used as a precursor. Effect of precursor concentration on structural and optical properties has been investigated. Homogenous films are obtained with precursor concentration rating between 0.1 M and 0.4 M. X-ray diffraction patterns show that ZnO films are polycrystalline with (002) plane as preferential orientation. Field emission scanning electron microscopy images show that ZnO films consist of microrods that their length increases with increasing precursor concentration and tallest microrods obtain by spraying precursor with 0.3 M concentration. The optical transmittance spectrum shows that transmittance increases with decreasing of the concentration and transmittance reaches to a maximum value of about 80% for the visible region ZnO films prepared with 0.1 M. Photoluminescence spectra at room temperature show an ultraviolet emission at 3.21 eV that can be related to band gap and two visible emissions at 2.88 eV and 2.38 eV.

Growth and physical properties of three-dimensional flower-like zinc oxide microcrystals

This study reports the synthesis of ZnO flower-like structures of different sizes on polycrystalline zinc foils by cathodic electrodeposition. X-ray diffraction results indicate that the obtained flower-like ZnO microcrystals had a wurtzite structure. Scanning electron microscopy images reveal that the flower-like ZnO microcrystals consisted of taper petals. The precursor concentration and electrodepositing potential had significant effects on the size of the flower-like ZnO microcrystals. An increase in precursor concentration and electrodepositing potential caused an increase in the size of the ZnO flower-like structures. The flower-like ZnO microcrystals, with an approximate petal length of 0.8–1.6 μm, exhibited a strong UV emission at room temperature, while those with a petal length of 3.0–4.2 μm produced noticeably yellow emissions.

Comparative study of the viscoelastic mechanical behavior of agarose and poly(ethylene glycol) hydrogels

This study presents a comparative investigation into differences in the mechanical properties between two hydrogels commonly used in cartilage tissue engineering [agarose vs. poly(ethylene glycol) (PEG)], but which are formed through distinctly different crosslinking mechanisms (physical vs. covalent, respectively). The effects of hydrogel chemistry, precursor concentration, platen type (nonporous vs. porous) used in compression bioreactors, and degradation (for PEG) on the swelling properties and static and dynamic mechanical properties were examined. An increase in precursor concentration resulted in decreased equilibrium mass swelling ratios but increased equilibrium moduli and storage moduli for both hydrogels (p < 0.05). Agarose displayed large stress relaxations and a frequency dependence indicating its viscoelastic properties. Contrarily, PEG hydrogels displayed largely elastic behavior with minimal stress relaxation and frequency dependence. In biodegradable PEG hydrogels, the largely elastic behavior was retained during degradation. The type of platen did not affect static mechanical properties, but porous platens led to a reduced storage modulus for both hydrogels implicating fluid flow. In summary, agarose and PEG exhibit vastly different mechanical behaviors; a finding largely attributed to differences in their chemistries and fluid movement. Taken together, these design choices (hydrogel chemistry/structure, loading conditions) will likely have a profound effect on the tissue engineering outcome.

Influence of precursor concentration on structural, morphological and electrical properties of spray deposited ZnO thin films

AbstractNanostructured ZnO thin films were coated on glass substrate by spray pyrolysis using Zinc acetate dihydrate as precursor. Effect of precursor concentration on structural, morphological, optical and electrical properties of the films was investigated. The crystal structure and orientation of the ZnO thin films prepared with four different precursor solution concentrations were studied and it was observed that, the prepared films are polycrystalline in nature with hexagonal wurzite structure. The peaks are indexed to (100), (002), (101), (102) and (110) planes. Grain size and texture coefficient (TC) were calculated and the grain size found to increase with an increase in precursor concentration. Presence of Zn and O elements was confirmed with EDAX spectra. Optical absorption measurements were carried out in the wavelength region of 380 to 800 nm and the band gap decreases as precursor concentration increases. The current‐voltage characteristics were observed at room temperature and in dark. It was found that for the films deposited at four different precursor concentrations, the conductivity improves as precursor concentration increases. As trimethyl amine TMA is a good marker for food quality discrimination, sensing behavior of the films at an optimized operating temperature of 373 K, towards various concentrations of (TMA) was observed and reported. (© 2011 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)