Synthesis and magnetic properties of hexagonally packed ZnO nanorods

Large-scale uniform aligned ZnO nanorods with a hexagonal tip were successfully synthesized via a facile process at low temperature of (～140 °C) without using any additives and substrate. The process is based on a simple reaction of zinc powder and de-ionized water. The results reveal that the as-prepared ZnO products have an average length of 10 μm and a diameter in the range of 50–260 nm, possessing a single crystal wurtzite structure. The structure and morphology of the ZnO products are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectrometer (EDX). The possible formation mechanism of nanorods is proposed in brief. The optical properties of grown products were characterized by room-temperature. The magnetic property was tested with a vibrating sample magnetometer at room temperature and revealed a high hysteresis loop indicating a strong ferromagnetic nature of as synthesized ZnO nanorods. The yield producing nanorods with this method includes ease, flexibility, fast being low cost and ineffective on environment free.     

Preparation and characterization of nanocomposite ZnO–Ag thin film containing nano-sized Ag particles: influence of preheating,annealing temperature and silver content on characteristics

Nanocomposite ZnO–Ag thin film containing nano-sized Ag particles have been grown on glass substrate by spin-coating technique using zinc acetate dihydrate as starting precursor in 2-propanol as solvent and monoethanolamine as stabilizer. Silver nanoparticles were added in the ZnO sol using silver nitrate dissolved in ethanol-acetonitrile. Their structural, electrical, crystalline size and optical properties were investigated as a function of preheating, annealing temperature and silver content. The results indicated that the crystalline phase was increased with increase of annealing temperature up to 550 °C at optimum preheating temperature of 275 °C. Thermal gravimetric differential thermal analysis results indicated that the decomposition of pure ZnO and nanocomposite ZnO–Ag precursors occurred at 225 and 234 °C, respectively with formation of ZnO wurtzite crystals. The scanning electron microscopy and atomic force microscopy revealed that the surface structure (the porosity and grain size) of the ZnO–Ag thin film (the film thickness is about 379 nm) was changed compared to pure ZnO thin film. The result of transmission electron microscopy showed that Ag particles were about 5 nm and ZnO particles 58 nm with uniform silver nanoclusters. Optical absorption results indicated that optical absorption of ZnO–Ag thin films decreased with increase of annealing temperature. Nanocomposite ZnO–Ag thin films with [Ag] = 0.068 M and [Ag] = 0.110 M showed an intense absorption band, whose maximum signals appear at 430 nm which is not present in pure ZnO thin films. The result of X-ray photoelectron spectroscopy revealed that the binding energy of Ag 3d_5/2 for ZnO–Ag shifts remarkably to the lower binding energy compared to the pure metallic Ag due to the interaction between Ag and ZnO.     

Structural,optical and photoluminescence properties of Zn<Subscript>1−x</Subscript>Ce<Subscript>x</Subscript>O (x = 0, 0.05 and 0.1) nanoparticles by sol–gel method annealed under Ar atmosphere

Ce doped ZnO nanoparticles (Zn_1−xCe_xO, x = 0.0, 0.05 and 0.1) have been synthesized by sol–gel method at annealing temperature of 500 °C for 1 h under Ar atmosphere. The synthesized samples have been characterized by powder X-ray diffraction (XRD), energy dispersive X-ray studies, UV–Visible spectrophotometer and fourier transform infrared (FTIR) spectroscopy. The XRD measurements indicate that the prepared nanoparticles have a hexagonal wurtzite structure and CeO₂ crystallites. The calculated average crystalline varied from 21.97 to 15.62 nm with increase in Ce concentrations. The increase in lattice parameters reveals the substitution of Ce into ZnO lattice. The presence of functional groups and the chemical bonding is confirmed by FTIR spectra. PL spectra of the Zn_1−xCe_xO system show that the shift in near band edge emission from 386 to 363 nm and a shift in blue band emission from 517 to 485 nm which confirms the substitution of Ce into the ZnO lattice.     

Organic–inorganic nanocomposites of (2‐hydroxypropyl)cellulose as a precursor of nanocrystalline zinc oxide layers

The sol–gel method of synthesis of the hybrid nanocomposite films of ZnO/(2‐hydroxypropyl) cellulose (HPC) on silica glass is presented. The sol phases were prepared for different weight ratios of zinc acetate dihydrate to HPC in the presence of triethylamine (TEA). Raman spectrum of the mixture of ZnAc and HPC indicates coordinating interaction between zinc ion and HPC. The generation of ZnO nanoparticles in the HPC matrix proceeds in situ through the annealing of the gel phase at a temperature of 160°C. Identification of ZnO nanoparticles in the HPC matrix is done by using photoluminescence (PL), UV–Vis, and Raman spectroscopy. The films of ZnO/HPC nanocomposite are transparent in the visible light and show a higher energy value of absorption edge compared with ZnO in the bulk. Nanocrystalline films of ZnO were obtained by the calcination of ZnO/HPC nanocomposite at 500°C. ZnO films possess a good transparency for the visible light and high absorbance for UV light. Nanocrystallite sizes of ZnO particles were estimated from the X‐ ray lines broadening. The properties of ZnO layers were studied by the evaluation of PL, X‐ray investigation and atom force microscope (AFM) scanning, and the optical absorption edge. Copyright © 2008 John Wiley & Sons, Ltd.     

Optical and Raman studies of Zn1-xMgxO ceramic pellets

The undoped and Mg-doped ZnO ceramics have been successfully synthesized using the conventional solid state sintering method. The doping effect of MgO content on the structural properties of ZnO/MgO composites has been investigated by X-ray diffraction (XRD) and Raman spectroscopy. The XRD patterns reveal that all the samples are polycrystalline and have a prominent hexagonal crystalline structure with (002) and (101) as preferred growth directions. The formation of the hexagonal ZnMgO alloy phase and the segregation of MgO-cubic phase took place for an MgO composition x ≥ 20 wt%. This finding is in good agreement with the Raman spectroscopy measurements which prove the existence of multiple-order Raman peaks originating from ZnO-like and MgO phonons. The band gap energy and the carrier concentration of ZnO pellets were found to be dependent upon the Mg doping whose values vary from 3.287 to 3.827 eV and from 1.6 × 10¹⁷ to 5.2 × 10²⁰ cm⁻³, respectively.     

Photocatalytic degradation of acid blue 74 in water using Ag–Ag2O–Zno nanostuctures anchored on graphene oxide

Water pollution due to industrial effluents from industries which utilize dyes in the manufacturing of their products has serious implications on aquatic lives and the general environment. Thus, there is need for the removal of dyes from wastewater before being discharged into the environment. In this study, a nanocomposite consisting of silver, silver oxide (Ag₂O), zinc oxide (ZnO) and graphene oxide (GO) was synthesized, characterized and photocatalytically applied in the degradation (and possibly mineralization) of organic pollutants in water treatment process. The Ag–Ag₂O–ZnO nanostructure was synthesized by a co-precipitation method and calcined at 400 °C. It was functionalized using 3-aminopropyl triethoxysilane and further anchored on carboxylated graphene oxide via the formation of an amide bond to give the Ag–Ag₂O–ZnO/GO nanocomposite. The prepared nanocomposite was characterized by UV–Vis diffuse reflectance spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electronic microscopy (SEM), energy dispersive X-ray spectrometry (EDX), Fourier transformed infrared spectroscopy (FTIR), and Raman spectroscopy. The applicability of Ag–Ag₂O–ZnO/GO nanocomposite as a photocatalyst was investigated in the photocatalytic degradation of acid blue 74 dye under visible light irradiation in synthetic wastewater containing the dye. The results indicated that Ag–Ag₂O–ZnO/GO nanocomposite has a higher photocatalytic activity (90% removal) compared to Ag–Ag₂O–ZnO (85% removal) and ZnO (75% removal) respectively and thus lends itself to application in water treatment, where the removal of organics is very important.     

Development of multifunctional polydimethylsiloxane (PDMS)‐epoxy‐zinc oxide nanocomposite coatings for marine applications

Multifunctional epoxy‐polydimethylsiloxane nanocomposite coatings with antifouling and anticorrosion characteristics have been developed via in situ polymerization method at different loading (1, 3, and 6.5 wt.%) of ZnO nanoparticles to cater marine applications. A detailed comparative analysis has been carried out between epoxy‐polydimethylsiloxane control (EPC) and ZnO‐reinforced coatings to determine the influence of ZnO loading on various properties. The incorporation of ZnO in EPC led to increase in root mean square (RMS) roughness to 126.75 nm and improved hydrophobicity showing maximum contact angle of 123.5° with low surface energy of 19.75 mN/m of nanocomposite coating as compared with control coating. The differential scanning calorimetry (DSC) result indicated improved glass transition temperature of nanocomposite coatings with highest T_g obtained at 83.69°C in case of 1 wt.% loading of ZnO. The increase in hydrophobicity of the system was accompanied by upgraded anticorrosion performance exhibiting 98.8% corrosion inhibition efficiency (CIE) as compared with control coating and lower corrosion rate of 0.12 × 10^?3 mm/year. The Taber abrasion resistance and pull‐off adhesion strength results indicated an increment of 34.7% and 150.7%, respectively, in case of nanocomposite coating as compared with the control coating. The hardness of nanocomposite coatings was also improved, and maximum hardness was found to be 65.75 MPa for nanocomposite coating with 1 wt.% of ZnO. Our study showed that the nanocomposite coating was efficient in inhibiting accumulation of marine bacteria and preventing biofouling for more than 8 months. The developed environment‐friendly and efficient nanocomposite material has a promising future as a high‐performance anticorrosive and antifouling coating for marine applications.     

Electrochemical synthesis of orientation-ordered ZnO nanorod bundles

The high density and orientation-ordered ZnO nanorod bundles with wurtzite structures were prepared on Cu substrates by electrochemical deposition in solution of ZnCl₂ + tartaric acid at a temperature of 90 °C. This approach is a unique and size controlled synthetic method for the large-scale preparation of ZnO nanorod bundles. Cyclic voltammogram measured in solution of the mixture of ZnCl₂ and tartaric acid shows a restraining role of tartaric acid for the electro-reduction of Zn(II). The formation mechanism of ZnO on the surface of the cathode can be explained that the high temperature (⩾90 °C) promotes the corrosion of electrodeposited Zn via reacting with H₂O and O₂ to form the stable passive phase of ZnO. The compositions of the nanorod bundles can be entirely ZnO or Zn and ZnO composites determined by the temperature and deposition rate. The photoluminescence (PL) properties indicate that these ZnO deposits are highly crystallized and of excellent optical quality.     

ZnO/MgO nanocomposites generated from alcoholic solutions

A process was proposed for the synthesis of ZnO/MgO nanocomposites from alcoholic solutions by means or the consecutive precipitation of coprecipitation of alcoholic solutions of zinc acetate and magnesium with an alkali solution followed by annealing in the range 400–500°C. X-ray powder diffraction showed crystalline ZnO and MgO phases in the resulting composite. Zinc oxide particle sizes in the composite with magnesium oxide were determined by transmission electron microscopy and from X-ray diffraction peak broadening. The zinc oxide nanoparticle size was weakly affected by the molar ratio of zinc to magnesium and the concentration of the precipitated component. The ZnO exciton peak in cathodoluminescence spectra for nanocomposites synthesized at low temperatures (400 and 500°C) shifted toward the UV. At ≥600°C or higher, Mg_{1 ? x} Zn _x O solid solution was generated, as evidenced by X-ray diffraction and cathodoluminescence data.     

Preparation of nitrogen doped zinc oxide nanoparticles and thin films by colloidal route and low temperature nitridation process

Nitrogen doped zinc oxide (ZnO) nanoparticles have been synthesized using a colloidal route and low temperature nitridation process. Based on these results, 200 nm thick transparent ZnO thin films have been prepared by dip-coating on SiO₂ substrate from a ZnO colloidal solution. Zinc peroxide (ZnO₂) thin film was then obtained after the chemical conversion of a ZnO colloidal thin film by H₂O₂ solution. Finally, a nitrogen doped ZnO nanocrystalline thin film (ZnO:N) was obtained by ammonolysis at 250 °C. All the films have been characterized by scanning electron microscopy, X-ray diffraction, X-Ray photoelectron spectroscopy and UV–Visible transmittance spectroscopy.     

Influence of imide functionalized organo‐modified Mg‐Al layered double hydroxide on the thermal and mechanical properties of new aliphatic‐aromatic poly (amide‐imide)

A new dicarboxylic acid modified Mg‐Al LDH (DLDH) containing imide groups was prepared and its effects on the thermal and mechanical properties of the new synthesized aliphatic‐aromatic poly (amide‐imide) (PAI) were investigated via preparation of PAI/nanocomposite films by solution casting method. The results of X‐ray diffraction (XRD), field emission‐scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM) showed a uniform dispersion for LDH layers into the PAI matrix. For comparison, the effects of polyacrylic acid‐co‐poly‐2‐acrylamido‐ 2‐methylpropanesulfonic acid (PAMPS‐co‐PAA) modified Mg‐Al LDH (ALDH) on the PAI properties were also studied. The thermogravimetric analysis (TGA) results exhibited that the temperature at 5 mass% loss (T₅) increased from 277 °C to 310 °C for nanocomposite containing 2 mass% of DLDH, while T₅ for nanocomposite containing 2 mass% of ALDH increased to 320 °C, along with the more enhancement of char residue compared to the neat PAI. According to the tensile test results, with 5 mass% DLDH loading in the PAI matrix, the tensile strength increased from 51.6 to 70.8 MPa along with an increase in Young's modulus. Also the Young's modulus of PAI nanocomposite containing 5 mass% ALDH reduced from 1.95 to 0.81 GPa.     

Oxidative Conversion of Hexane to Olefins-Influence of Plasma and Catalyst on Reaction Pathways

An integrated plasma-Li/MgO system is efficient for the oxidative conversion of hexane. In comparison to the Li/MgO catalytic system, it brings considerable improvements in the yields of light olefins (C₂⁼–C₅⁼) at relatively low temperatures indicating synergy from combination of plasma and catalyst. The study on the influence of temperature on the performance of the integrated plasma-Li/MgO system shows dominancy of plasma chemistry at the lower temperature (500°C), while contribution from the catalyst both in hexane activation and in enhancing olefin formation becomes significant at the higher temperature (600°C). At 500°C significant amount of acetylene formation is observed. This is minimized at 600°C at oxygen depleting conditions.     

Investigation and characterization by TG/DTG–DTA and DSC of the fusion of Riboflavin,and its interaction with the antibiotic norfloxacin in the screening of cocrystal

This work synthesized and characterized the NOR-RIB 1:1 (mol–mol) cocrystal. During a study of the reagents, Riboflavin (RIB) melted at 304 °C, which is different from the temperature previously reported in the literature (280–290 °C); therefore, this compound was characterized individually. Subsequently, the cocrystal was synthesized with the active pharmaceutical ingredient (API) norfloxacin (NOR) with the RIB coformer, and the mechanochemical synthesis route was adopted. NOR, RIB, and the cocrystal were characterized by thermogravimetry–differential thermal analysis (TG–DTA), differential scanning calorimetry (DSC), DSC coupled to a microscope (photo-DSC), mid-infrared spectroscopy (MIR), and powder X-ray diffraction. The results of thermal analysis showed that the RIB starts decomposition process (260 °C) and then melts (304 °C). The MIR found that beginning at 295 °C, the RIB passes into the form of a decomposition intermediate; therefore, the melting point observed in the DSC curve is related to this decomposition material. The cocrystal presented thermal stability (200 °C) lower than the API (235 °C) and the coformer (260 °C). The DSC curve did not contain a melting peak. The bands at 1726 cm^?1 (C=O of the carboxylic acid) for the NOR, and the band at 3326 cm^?1 (stretch O–H), among others, were not visible for the cocrystal in the MIR spectrum, indicating interactions in these regions. The X-ray diffractograms showed a new diffraction pattern, which proved the obtainment of a new phase and cocrystal formation.

     

Nanostructured spinel-type M(M = Mg,Co, Zn)Cr2O4 oxides: novel adsorbents for aqueous Congo red removal

Nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides with novel adsorbents for aqueous Congo red removal were synthesized by a polyacrylamide gel method and studied for their phase structure, microstructure, adsorption performance, and multiferroic behavior. The phase structure and purity analysis revealed that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides presented a spinel-type cubic structure, and the formation of a secondary phase such as Cr₂O₃, MgO, ZnO, or Co₃O₄ was not observed. The microstructure characterization confirmed that the spinel-type MCr₂O₄ oxides grew from fine spherical particles to large rhomboid particles. Adsorption experiments of spinel-type MCr₂O₄ oxides for adsorption of Congo red dye were fitted well with the pseudo-second-order kinetics. The adsorption capacity of the ZnCr₂O₄ oxide (44.038 mg/g, pH 7, temperature 28 °C, initial dye concentration 30 mg/L) was found to be higher than that of MgCr₂O₄ oxide (43.592 mg/g, pH 7, temperature 28 °C) and CoCr₂O₄ oxide (28.718 mg/g, pH 7, temperature 28 °C). The effects of initial adsorbent concentration, initial dye concentration, pH, and temperature between the ZnCr₂O₄ oxide and Congo red dye at which optimal removal occurs, were performed. The thermodynamic studies confirmed that a high temperature favors the adsorption of Congo red dye onto ZnCr₂O₄ oxide studied. The nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides that exhibited high adsorption performance for adsorption of Congo red dye can be ascribed to the synergistic effect of electrostatic interaction, pore filling, and ion exchange. The present work suggested that the nanostructured spinel-type M(M = Mg, Co, Zn)Cr₂O₄ oxides have excellent adsorption performance and multiferroic behavior, which shows potential applications for removal of the Congo red dye from wastewater, magnetic memory recording media, magnetic sensor, energy collection and conversion device, and read/write memory.     

Characteristics of Ga and Ag-doped ZnO-based nanowires for an ethanol gas sensor prepared by hot-walled pulsed laser deposition

Pure ZnO and Ga (3 % w/w) and Ag (3 % w/w)-doped ZnO nanowires (NWs) have been grown by use of the hot-walled pulse laser deposition technique. The doping characteristics of Ga and Ag in ZnO NWs were analyzed by use of photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) and the results were compared with those for pure ZnO NWs. We also fabricated gas sensors by use of pure ZnO and Ga and Ag-doped ZnO NWs. Among the NW sensors, the Ag-doped NW sensor was most sensitive. We synthesized the NWs on sapphire substrates under different conditions, for example temperature, time, gas flow, and distance between target and substrate. The diameter and length of NWs were <100 nm and several microns, respectively. To analyze the effect of Ag doping on ZnO NWs, we investigated the near band edge emission by use of low-temperature PL and XPS. Significant changes in resistance and sensitivity were observed. When the sensors were used at 300 °C for detection of 1 ppm ethanol vapor, the sensitivity of the pure ZnO and the Ga and Ag-doped ZnO NW gas sensors was 97, 48, and 203 %, respectively.     

Sodium-doped lithium zirconate nano squares: synthesis,characterization and applications for CO<Subscript>2</Subscript> sequestration

Nano squares of sodium-doped lithium zirconate have been synthesized by a simple citrate based sol–gel method at room temperature in the presence of cetyl trimethylammonium bromide (CTAB) as a surfactant. The structural and morphological properties were investigated by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM) respectively. XRD analysis of sample calcined at 900 °C for 4 h shows the formation of monoclinic lithium zirconate phase. The TEM shows the interesting morphology of formation of nano squares of sodium doped lithium zirconate sample. The carbon dioxide sorption capacity was carried out by TGA analysis at different high temperatures. It is observed that the sample shows ~20 wt% carbon dioxide sorption at higher temperature (650 °C) within 20 min which are better than the known reports.     

Low temperature sintering study of nanosized Mn–Zn ferrites synthesized by sol–gel auto combustion process

The objective of present research was to sinter nanosized Mn–Zn ferrites (MZF) at low temperature (≤1,000 °C) by avoiding the formation of nonmagnetic phase (hematite). For this purpose, MZF powder was synthesized by sol–gel auto combustion process at 220 °C and further calcined at 450 °C. In calcined powder, single phase (spinel) was confirmed by X-ray diffraction analysis. Pellets were pressed, having 43% of the theoretical density and showing 47 emu gm⁻¹ saturation magnetization (M _s). Various combinations of heating rate, dwelling time and gaseous environment were employed to meet optimum sintering conditions at low temperature (≤1,000 °C). It was observed that sintering under air or N₂ alone had failed to prevent the formation of nonmagnetic (hematite) phase. However, hematite phase can be suppressed by retaining the green compacts at 1,000 °C for 180 min in air then further kept for 120 min in nitrogen. Under these conditions, spinel phase (comprising of nano crystallites), 90% of theoretical density and 102 emu gm⁻¹ of saturation magnetization has been achieved.     

Preparation of nanocrystalline CuAlO<Subscript>2</Subscript> through sol–gel route

Nanocrystalline powders of CuAlO₂ were synthesized through sol–gel method using nitrate-citrate route and also through solid state reaction method. We used a new set of precursor materials for the synthesis of CuAlO₂ through sol–gel route which were not reported in the past. A little lowering of the synthesis temperature (1,000 °C) was observed in case of sol–gel process compared to the solid state reaction method (1,100 °C) and also at shorter time duration. The particle size of the synthesized powders was determined through small angle X-ray scattering. It has been observed that the particle size prepared by nitrate-citrate technique is less than the particle size prepared by the solid-state reaction method. Chemical states of the atomic species were determined by X-ray photoelectron spectroscopy. The formation of phase pure CuAlO₂ were also confirmed by Fourier transformed infrared spectroscopy. A number of solvents were also used for finding the best possible combinations for obtaining phase pure CuAlO₂ at 1,000 °C and it was observed that only the combination of nitrate salts, citric acid and ethanol resulted phase pure CuAlO₂.     

Investigation of the growth parameters of hydrothermal ZnO nanowires for scale up applications

Zinc oxide nano-wires (ZnO NWs) are synthesized reproducibly with high yield via a low temperature hydrothermal technique. The influence of the growth duration time, growth temperature, zinc precursor and base concentration of Na₂CO₃ on the morphology of NWs is investigated. The growth products are characterised using scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). SEM analysis shows that the optimum growth temperature is 140 °C and finds that length and diameter of ZnO NWs have a relationship with growth duration time and base concentrations of Na₂CO₃. In addition, it is reported that a high (～90%) yield of ZnO NWs can be synthesised via using any of three different precursors: zinc chloride, zinc acetate and zinc nitrate. TEM and XRD results indicate the high purity and the single crystalline nature of the ZnO NWs. XPS confirms the absence of sodium contaminants on the surface and indicates a near flat band surface condition. PL shows a large visible band in the yellow part of the spectrum, and a small exciton emission peak, indicating a large defect concentration, which is reduced after annealing in air.     

Solution-based fabrication of a graphene–ZnO nanocomposite

Graphene-based composites represent a new class of materials with potential for many applications. Graphene can be attached to a metal, a semiconductor, or any polymer. In this work, our approach was to attach graphene to a well-known semiconductor, ZnO. We synthesized graphene–ZnO composites by a simple, low-cost, environmentally friendly solvothermal method, carrying out the reaction in different conditions in order to discover the optimum condition, and also to obtain a high-quality product. Our research demonstrated that the optimum temperature to obtain a high-quality product is 180 °C for 20 h. All obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy, electron dispersion spectrometry, X-ray photoelectron spectrometry, Raman spectroscopy, Fourier transform infrared spectrometry, UV–visible spectrophotometry, and thermogravimetric analysis. The XRD confirmed that the crystal structure of the ZnO in the nanocomposite was wurtzite type. The prepared composite was stable to 800 °C with its 80 % weight.