Nanocrystalline ZnO Particles Research Articles

Ionic Liquids as an Efficient Reaction Medium in the Robust Synthesis of ZnO Nanoparticles

Aim:: Ionic liquids belong to the class of green solvents and are distinguished by their simple yet distinctive physical properties that are related to their structure. These properties include their remarkable thermal stability, exceptional thermal conductivity, and negligible vapor pressure. Additionally, they are suitable and inert for a wide range of catalytic applications. Zinc Oxide Nanoparticles (ZnO-NPs) have been considered a cost-effective choice that requires modest reaction conditions to provide a high yield of the required products with remarkable selectivity in a short amount of time. Consequently, an investigation into the synthesis of ZnO-NPs in an ionic liquid medium has been attempted in the current work. Background:: The synthesis of metal nanoparticles using highly tunable ionic liquids is being investigated for many pharmacological applications and their usage in catalysis. Objectives:: In this context, the current work has used the co-precipitation approach to synthesize ZnO-NPs. The production of ZnO nanoparticles with a range of morphologies utilizing an imidazolium ionic liquid system has been the main topic of discussion. Methods:: The co-precipitation method has successfully been administered for the synthesis of morphologically diverse nano-crystalline ZnO particles using different ionic liquids, such as 1-propyl- 3-methylimidazolium bromide (pmim)(Br), 1-butyl-3-methylimidazolium bromide ([bmim][Br]), and 1-hexyl-3-methylimidazolium bromide (hmim)(Br) as an additive Results:: Modern analytical tools, including X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and FT-IR absorption spectroscopy have been employed to confirm the structure of these ZnO nanoparticles. The IR absorption peak below 480 cm-1 and the XRD pattern showed all the peaks in the diffraction diagram, revealing the formation of ZnO-NPs. FE-SEM images showed various morphologies of ZnO-NPs and they have been found to be separated from the agglomerated clusters. Conclusion:: The characteristic results have revealed ionic liquids to have substantial effects on the size of the zinc nano-species as well as provide the appropriate environment for the growth of the nanoparticles.

Impact of Cr doping on the structure, optical and magnetic properties of nanocrystalline ZnO particles

The doping of Cr ions on the structure, optical and magnetic properties of ZnO have been investigated. Zn1−xCrxO (0 ≤ x ≤ 0.05) samples were prepared by the solution combustion method. Rietveld refined x-ray diffraction results reveal that all the samples are in a hexagonal structure. Transmission electron microscopy (TEM) revealed that the particle size was 48.2 ±2.1 nm, 29.4 ± 2.2 nm and 25.3 ± 2.1 nm for the Zn1−xCrxO with x = 0, 0.03 and 0.05, respectively. The band-gap decreases slightly from 3.308 ± 0.003 eV to 3.291 ± 0.003 eV with increase of Cr content from x = 0 to 0.05, respectively. The field-dependent magnetization M(μοH) measurements of ZnO and Cr-doped ZnO exhibit room temperature ferromagnetism (RTFM). Photoluminescence and electron paramagnetic resonance exhibits negatively charged zinc vacancies (VZn−) and singly ionized oxygen vacancies (Vo+) in ZnO and these defects are responsible for RTFM. And the VZn− accountable for RTFM in Cr-doped ZnO. EPR results confirmed that Cr3+ ions replaces the Zn2+ sites in the hexagonal ZnO. The observed long-range ferromagnetism ordering is explained based on the bound magnetic polaron (BMP) mechanism. This work elucidates the origin of RTFM in synthesized ZnO and Cr-doped ZnO.

Photoluminescence quenching of green synthesized manganese doped zinc oxide by sodium iodide doped Polypyrrole polymer

Nanocrystalline ZnO particles doped with Manganese(Mn) were prepared by a green synthesis method using cucum sativa fruit pulp extract as biosolvent. Different concentration of Mn(II) was incorporated in ZnO to study the dopant effect in ZnO. The X-ray diffraction pattern data shows a decrease in grain size for Mn-ZnO from 46 nm to 31 nm with the increase in Mn concentration. Scanning electron microscopy reveals spherical morphology with a decrease in particle size while increasing the dopant concentration. With an increase in Mn doping the band gap is observed to reduce from 3.14 eV to 3.01 eV which is due to band tailing effect. The luminescence of ZnO is quenched by increasing the dopant ions concentration which might be attributed to the quenching ability of Mn ions in the ZnO lattice. While 5% Mn doped ZnO (MZO) showed improved crystallinity, enhanced optical property and reduced particle size, we have chosen this concentration for thin film fabrication using Dip coating unit. At the same time, sodium iodide(NaI) doped Polypyrrole(PPy) powder synthesized by the chemical polymerization method exhibited a band gap of 2.57 eV. As the bandgap of NaI doped PPy falls in the higher range of visible region, it was taken further to make nanocomposite thin film by dip coating with 5% MZO nanoparticles. The photoluminescence intensity of the MZO-NaI PPy nanocomposite thin film got reduced drastically suggesting better electron-hole separation efficiency at the interface of MZO-NaI PPy nanocomposite thin film. Due to the improved electron-hole separation efficiency of the synthesized nanocomposite, it might find a possible application in the hybrid solar cell.

Syntheses of ZnO with Different Morphologies: Catalytic Activity toward Coumarin Synthesis via the Knoevenagel Condensation Reaction.

Heterogeneous catalysts are preferred in fine chemical industries due to their easy recovery and reusability. Here, we report an easily scalable method of ZnO catalysts for coumarin synthesis. Nanocrystalline ZnO particles with diverse morphologies and crystallite sizes were prepared using different solvents. The change in morphology results in changes in band gaps, defects, basicity, and textural properties (surface areas, pore volumes, and pore sizes). The catalytic performances of the synthesized ZnO materials were tested using coumarin synthesis via the Knoevenagel condensation. The catalyst synthesized using methanol shows the highest activity and selectivity (conversion of 74%, selectivity of 94%) with a turnover number of 14.69. The increased activity of the ZnO synthesized in methanol is attributed to the combined effects of moderate basicity and relatively high textural properties of the sample.

Chemical, morphological, structural, optical, and magnetic properties of Zn1−xNdxO nanoparticles

In the present investigation, we made an endeavor to fabricate the ZnO nanoparticles and achieved the tunable properties with Nd doping. The Nd-doped ZnO nanoparticles were characterized via X-ray diffraction (XRD), Raman, and X-ray photoelectron spectroscopy (XPS) studies that confirmed the successful doping of Nd ions in the ZnO crystal lattice without amending its hexagonal phase. The particle morphology revealed nearly spherical particles with uniform size distribution. The band gap of these samples was determined using diffuse-reflectance spectra (DRS) and was found to vary from 3.17 to 3.21 eV with increasing Nd concentration. A broad and intense emission band at 1083 nm for Nd doped ZnO nanoparticles is observed and is assigned to corresponding emission transition 4F3/2 → 4I11/2 of Nd3+ ions. Furthermore, the magnetic studies indicate that the Nd doping altered the magnetic behavior of nanocrystalline ZnO particles from diamagnetic to ferromagnetic at 300 K and that the magnetization of these samples decreased with increasing Nd concentration. The tunable optical band gap as well as room-temperature ferromagnetism of these samples may find applications in both optoelectronics and spintronics.

Investigating the effect of ultrasonic irradiation on preparation and properties of conductive nanocomposites

In the present study, the ultrasonic irradiation technique was employed as a new approach to prepare 0-3-dimensional polyaniline/ZnO shell-core composite particles. By taking advantage of the multiple effects of ultrasound, one can break down the aggregates of nanocrystalline ZnO particles. The polymerization of aniline proceeded while the nanoparticles were redispersed by ultrasound, and the synthesized polyaniline deposited on the ZnO particle, which formed polyaniline-coated nanocrystalline composite particles. The material was characterized by using transmission electron microscopy, XRD, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), and Thermogravimetric analysis (TGA). With increased ZnO content, the H-bonding interaction is strengthened and the characteristic peaks of benzoid and quinoid are shifted. X-ray photoelectron spectroscopy (XPS) shows that the ratio of the number of Zn and N atoms (Zn/N) on the surface is lower than that in the bulk. This is strong evidence for a PANI-encapsulated ZnO nanoparticles structure. The conductivity of the composites obtained through ultrasonic irradiation decreases with increasing ZnO content. Ultrasonic irradiation contributes to the increase in the conductivity compared with conventional stirring. Photocatalytic properties of PANI/ZnO nanocomposites were examined by degrading Reactive Black 5 (RB5) dye under visible light irradiation.

Effect of Fe doping on the structural, optical and magnetic properties of combustion synthesized nanocrystalline ZnO particles

In the present study, the effect of Fe substitution in nanocrystalline Zn1−xFexO (x=0, 0.01, 0.03, 0.05 and 0.07) particles synthesized through solution combustion are reported. The detailed structural and microstructural studies of as-synthesized samples were carried out through X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Further, the optical and magnetic properties were investigated respectively through Diffuse Reflectance Spectroscopy and Superconducting Quantum Interference Device (SQUID). The XRD results as well as the Rietveld refinement on XRD data reveals the single phase, polycrystalline nature of the prepared materials and no impurities such as ZnFe2O4, Fe2O3, Fe3O4 were seen, which confirms the substitution of Fe at Zn site. SEM and TEM studies reveal that, the samples are porous and agglomerated due to the evolution of large amount of gases during the combustion and also as-formed particles are found to be in nano-range with an particle size varies from 20–25nm. Optical studies show that, the absorption edge shifts to lower energy/higher wavelength. Room temperature magnetic (SQUID) studies shows that the undoped ZnO exhibit diamagnetic property where as Fe doped ZnO exhibit intrinsic room temperature ferromagnetism (RTFM) with increasing coercivity with Fe concentration and is attributed to the incorporation of Fe into ZnO host matrix.

Influence of Mn doping on the magnetic and optical properties of ZnO nanocrystalline particles

The structural, optical and magnetic properties of Mn doped ZnO nanocrystalline particles, Zn1-xMnxO, with different percentages of Mn content have been studied. XRD and XPS measurements showed that all samples with Mn doping up to x=0.1 possess typical wurtzite structure and have no other impurity phases. The incorporation of Mn ions into the ZnO lattice was also confirmed by FTIR and UV–Vis. spectroscopy results. Both XRD and SEM results indicated a slight decrease in the grain size with increasing the Mn doping level. The XPS results indicated an increase in the oxygen vacancies concentration with increasing the Mn doping level. The magnetization measurements revealed a weak ferromagnetic behavior at room temperature and a clear ferromagnetic behavior with relatively large coercive fields at low temperature. The ferromagnetic order is improved by increasing the Mn doping. In addition, we observed an increase in the concentration of oxygen vacancies, which is also induced by increasing the Mn doping level. A ferromagnetic coupling of the local moment of Mn dopants through the sp-d exchange interaction and oxygen vacancies, in addition to different magnetic contributions due to different forms of Mn ions that coexist in the Mn doped nanoparticles were presented in order to interpret the observed magnetic behavior. We observed a clear red shift in the direct band gap and an increase in the coercive field and saturation magnetization values with increasing the Mn doping level.

Magnetic and optical properties of Co-doped ZnO nanocrystalline particles

We carried out a systematic study on the effect of Co doping on the structural, magnetic and optical properties of ZnO nanocrystalline particles, using x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Quantum Design PPMS-9 magnetometry, and Ultra Violet-Visible spectroscopy. The Zn1-xCoxO nanoparticles with 0≤x≤0.1 were successfully prepared by the formal solid-state reaction method. The XPS results and the XRD analysis with full structural Rietveld refinement reveals that all Zn1-xCoxO nanocrystalline particles in this Co-doping range have hexagonal wurtzite structure. Co atoms have been successfully incorporated in tetrahedral sites and no secondary phases or Co rich clusters were detected. For all Co-doped ZnO nanoparticles under investigation, the field dependence of the magnetization curves exhibits ferromagnetic behavior with relatively small coercive fields at room temperature. The coercive fields increased with Co-doping and decreased with temperature, as expected. In addition, we found a signature for antiferromagnetic ordering between the Co ions. We also observed a strong correlation between the magnetic and optical behavior of the Co-doped ZnO nanoparticles. Optical diffuse reflectance and absorption spectra exhibit a red shift at room temperature in the absorption band edge with increasing Co-doping. The red shift is attributed to the sp-d exchange interaction between free charge carriers in ZnO band and the localized magnetic moments.

The effect of fuel and fuel-oxidizer combinations on ZnO nanoparticles synthesized by solution combustion technique

We report on the synthesis of nanocrystalline ZnO particles by solution combustion technique using new organic fuels such as l-Glutamine, Leucine and l-Valine. The thermal decomposition and combustion of nitrate-organic fuels (precursors) were investigated through TG-DTA and XRD techniques. The results show that, the nitrate-organic fuel (precursor) gels exhibit self-propagating behavior at 400°C after ignition in air. The effect of fuel and fuel to oxidizer ratio on structural properties of as-synthesized ZnO powder was investigated. It was observed that, the particle size of as-synthesized ZnO powder depends on F/O ratio, which influences the combustion process. The detailed analysis on the structure of as-synthesized ZnO powder was carried out by Rietveld refinement on XRD data and through TEM studies. Further, adiabatic temperature (Tad) was calculated through thermodynamic theoretical calculations for different fuel to oxidizer ratios. The results were discussed on the basis of the correlations established between the Tad, nature of the combustion and structural properties of the resulting powders.

Synthesis, characterization of Mo and Mn doped ZnO and their photocatalytic activity for the decolorization of two different chromophoric dyes

Using sol–gel method, nano crystalline ZnO particles doped with different concentrations of molybdenum (Mo) and manganese (Mn) (0.2–1.0%) were synthesized. The structural and optical properties were studied with standard analytical techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and UV–vis spectroscopy. The crystalline nature of undoped and doped ZnO is indicated by XRD analysis. The SEM images of undoped ZnO showed irregular shape while doped ZnO showed fused supramolecular structure with rough surfaces. The photocatalytic activity of the synthesized particles (ZnO doped with Mo and Mn) was tested by studying the decolorization of two different chromophoric dyes namely Direct Yellow 27 (azo dye) and Acid Blue 129 (anthraquinone dye) with a 500W halogen linear lamp in the presence of atmospheric oxygen as a function of irradiation time. The results indicate that ZnO with dopant concentration of 0.60% Mo and 0.80% Mn showed the highest photocatalytic activity as compared to the other dopant concentrations for the decolorization of both dyes. In the case of azo dye, 84% decolorization was found while in case of anthraquinone dye, 66% decolorization took place using 0.60% Mo in 390min.

Facile Preparation of Nanocrystalline ZnO Powder for Non-Volatile Memory Application

In this work, synthesis of ZnO nanoparticle by solution method and its application in non-volatile memory is reported. Nanocrystalline ZnO particles were prepared by a novel chemical route using the combination of zinc nitrate [Zn (NO3)2 6H2O] and sodium hydroxide [NaOH] at low temperature. The effects of temperature and bath concentration for the synthesis of ZnO powder have been studied. Synthesized powder was characterized by X-ray diffraction (XRD), UV-Vis spectrometer, transmission electron microscopy (TEM) and photoluminescence. Using the prepared ZnO nanoparticles with organic PMMA; non-volatile memory cells were prepared and studied its switching property.

Solvothermal synthesis of nanocrystalline ZnO with excellent photocatalytic performance

We reported a facile way to synthesize nanocrystalline ZnO particles with excellent photocatalytic performance. Their microstructures and optical properties were characterized by X-ray diffraction, field emission scanning electron, transmission electron microscopy, photoluminescence spectra and ultraviolet–visible (UV–Vis) spectra. Photocatalytic tests showed the as-prepared ZnO particles had a good activity for photodegradation of organic dyes under UV–Vis light irradiation, which was comparable with that of P25 TiO2, a commercial standard photocatalyst. Furthermore, the sample could be easily sedimentary from the reaction system, which was favorable for the separation and reuse. Meanwhile, the photocatalytic performance of the samples exhibited no obvious reduction in the activity after five recycles of photodegradation, demonstrating its superior reusability. We attributed the superior performance to the efficient synergistic effect resulted from the small nano size, as well as the appropriate oxygen vacancies in the ZnO lattice. Our work might be promising for the application of ZnO-based photocatalysts due to its low cost, easy process, and good performance.

Spectroscopic investigation of an intrinsic room temperature ferromagnetism in Co doped ZnO nanoparticles

Pure and Co substituted ZnO nano crystalline particles were prepared by solution combustion technique using l-Valine as a fuel. As synthesized powder samples were characterized by X-ray diffractometer and SQUID magnetometer to confirm the formation of single phase wurtzite structure and to study the bulk magnetic response of the sample, respectively. Magnetic studies show that Co doped ZnO nanoparticles exhibit ferromagnetism (FM) at room temperature (RT). Furthermore, the electronic structure and element specific magnetic properties were investigated by near-edge X-ray absorption fine structure (NEXAFS) and X-ray magnetic circular dichroism (XMCD) measurements, respectively. The effect of Co substitution on the spectral features of Co–ZnO at O K-edge, Co L3,2 edge, Zn L3,2 edge have been investigated. The spectral features of NEXAFS at Co L3,2 edge is entirely different from the spectral features of metallic clusters and other impurity phases, which rules out the presence of impurity phases. The valence state of ‘Co’ ion is found to be in +2 state. The FM nature of the sample was confirmed through XMCD spectra, which is due to the incorporation of divalent ‘Co’ ions. Hence the presented results confirm the substitution of ‘Co’ ions at ‘Zn’ site in the host lattice, which is responsible for the RTFM.

Synthesis, Characterization, and Gas Sensing Properties of Pure and Mn-doped ZnO Nanocrystalline Particles

Nanocrystalline ZnO and Mn (1 wt.%)-doped ZnO particles have been synthesized via reverse micelle method. The structural, particulate, and optical properties of the synthesized nanoparticles have been studied by XRD, TEM, UV-Vis, and PL spectroscopy. The obtained data indicate the synthesis of the pure nanoparticles structure with wurtzite structure, average particle size of 18-21 nm, and high optical quality. Gas sensing properties of the nanocrystalline ZnO and Mn-doped ZnO particles toward gasoline and ethanol vapors have been investigated at different temperatures and concentrations. The results show that the optimum working temperature of the gas sensors based on ZnO and Mn-doped ZnO particles are about 633 and 620 K toward ethanol vapor and about 560 and 608 K toward gasoline vapor, respectively. Based on the results, although Mn impurities reduce the sensitivity of the ZnO gas sensor, they cause sensor to saturate at much higher gas concentration.

Preparation, structure and magnetic characterization of Ni doped ZnO nano-particles

Abstract The nature of magnetism in Ni-doped ZnO magnetic nano-particles ( x =0.0, 0.10, 0.15, 0.20, 0.30) are synthesized by the sol–gel technique using solutions of Ni and Zn based alkoxide which are dissolved into a solvent and a chelating agent. X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Vibrating Sample Magnetometer (VSM) were employed to understand how the Ni-doped influenced the structural and magnetic properties of the nano-crystalline ZnO particles. The grain sizes of the ZnNiO nano-particles were measured to be approximately 90 nm by means of a Scanning Electron Microscope. XRD measurements and SEM studies show that Ni-doped ZnO has wurtzite structures with NiO secondary phases. Room temperature ferromagnetism was observed for highly Ni-doped ZnO nano-particles.

Preparation of Nano ZnO Particles by Microwave Assisted Hydrothermal Method and its Toxicity to Microalgae

In this paper, nanocrystalline ZnO particles were prepared feasibly by microwave assisted hydrothermal method with Zinc nitrate and NaOH as start materials. XRD results show the ZnO was crystallized well. The as-received powders are hexagonal platelets of about 20-100 nm in diameter. Toxicity experiments using wastewater microalgae (Chlorella sp.) revealed that the toxicity of ZnO is strongly related with the Zinc ions concentration in water.

Role of nanocrystalline ZnO coating on the stability of porous silicon formed on textured (1 0 0) Si

In this study, a colloid of nanocrystalline ZnO particles prepared by chemical route is sprayed on porous silicon layers. Porosity and thickness of PS layers were estimated by gravimetric analysis. Upon adsorption of ZnO colloids on PS films, oxidation of nanocrystalline Si causes shrinkage of the Si-core due to the breaking of SiSi bonds resulting in a blue-shift in PL spectra. The PL blue-shift can also be related to SiO species or due to defects and the silica networks on which OH groups are absorbed due to ZnO incorporation as also supported by our Fourier transform infrared (FTIR) and X-ray photoelectron (XPS) studies, respectively. From high resolution X-ray diffraction (HRXRD) studies, a better crystalline perfection and considerable reduction in stress/strain values were observed for PS/ZnO layers as compared to virgin PS layers. The changes in the chemical composition at the surface of PS upon adsorption of ZnO colloids as elucidated by FTIR and XPS studies could be responsible for different PL emission and lattice-mismatch characteristics. The improved stability properties of PS are attributed to the strong absorption/adsorption of ZnO into the highly porous vertical layers separating macroscopic domains of nanoporous silicon and the mechanism of light emission from PS/ZnO layers is discussed on the basis of proposed energy band gap diagram.

Application of impregnation combustion method for fabrication of nanostructure CuO/ZnO composite oxide: XRD, FESEM, DRS and FTIR study

Nanostructured CuO/ZnO composite oxide was prepared by a novel impregnation combustion method using copper nitrate and zinc oxide tetrapod. The X-ray diffraction patterns revealed that CuO/ZnO composite oxide was formed. The effects of different impregnation combustion parameters on the properties of composite were studied by field-emission scanning electron microscope (FESEM), powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and UV–vis diffuse reflectance spectrum (DRS). The synthesis of ZnO–CuO nanocomposites through impregnation of a zinc oxide tetrapod with copper nitrate aqueous sodium carbonate solutions is reported. During thermal treatment the samples evolve toward the formation of nanocrystalline ZnO particles (zincite phase) dispersed onto tenorite, CuO annealed at 450°C. XRD patterns of the precursors calcined at 450°C showed the formation of the zincite–tenorite phases. Field emission scanning electron microscopy (FESEM) exhibited loosely agglomerated hexagonal particles with uniform morphology having a size around 50nm.

Characterization and photo-chemical applications of nano-ZnO prepared by wet chemical and thermal decomposition methods

Nano-crystalline ZnO particles were synthesized using two different routes: soft-wet and dry methods. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to identify the particles structures and morphologies, while X-ray diffraction (XRD) was used for verifying the particles crystal structure. The thermal stabilities of the particles were examined through thermal gravimetric analysis technique and their surface areas were calculated using BET method. Moreover, the photocatalytic activities were evaluated using UV–vis spectroscopy and photoluminescence (PL) characterization. The results showed that all the prepared ZnO samples possess a hexagonal wurtzite structure with high purity. Different particle sizes and morphologies of spheres, rods and wires were obtained depending on the preparation method used. Particle sizes obtained by the dry method are smaller than that found by the wet chemical method. The effects of both particle size and morphology on each of surface as well as optical properties, photocatalytic activity, dye/ZnO solar cell efficiency and biological activity have been studied and discussed.