Biosynthesis of zinc oxide nanoparticles from Azadirachta indica for antibacterial and photocatalytic applications

Green synthesis of nanoparticles is gaining importance and has been suggested as possible alternatives to chemical and physical methods. The present work reports low-cost, green synthesis of zinc oxide (ZnO) nanoparticles using 25% (w/v) of Azadirachta indica (Neem) leaf extract. The biosynthesized nanoparticles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), UV–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR). The synthesized ZnO nanoparticles were pure, predominantly spherical in shape with size ranging from 9.6 to 25.5 nm. In the present work, the biosynthesized ZnO nanoparticles have been used for antibacterial and photocatalytic applications. The antibacterial activity of characterized samples was determined using different concentrations of biosynthesized ZnO nanoparticles (20 µg/mL, 40 µg/mL, 60 µg/mL, 80 µg/mL and 100 µg/mL) against Gram-positive and Gram-negative bacteria: Staphylococcus aureus, Streptococcus pyogenes and Escherichia coli using shake flask method. The obtained results revealed that the bacterial growth decreases with increase in concentration of biosynthesized ZnO nanoparticles. In Addition, Gram-positive bacteria seemed to be more sensitive to ZnO nanoparticles than Gram-negative bacteria. The biosynthesized ZnO nanoparticles showed photocatalytic activity under the UV light enhancing the degradation rate of methylene blue (MB), which is one of the main water-pollutant released by textile industries.     

Electrical properties of zinc oxide sputtered thin films

ZnO thin films were deposited on silicon substrate by rf magnetron sputtering from metallic zinc target. The electrical properties of ZnO are currently being studied. In this work, measurements of the ac conductivity properties of ZnO sandwich structures with silver and platinum electrodes are reported. The frequency dependence of both the ac conductivity and dielectric constant of thin films of ZnO have been investigated in the frequency range 5 kHz-13 MHz. It is shown that the total ac conductivity σ(ω), obeys the equation σ(ω)=Aω^S where s is an index which increases with frequency and decreases with temperature. It appears that for ZnO films, the conduction mechanism is thermally activated and both the overlap large polaron tunnelling and the correlated barrier-hopping of charge carrier over localized states fit the experimental data. The dielectric constant, ε_r, lies in the range 8-9 at room temperature and is independent of the frequency in the dielectric thin films.     

Synthesis of gallium oxide nanowires and their electrical properties

Gallium oxide (Ga₂O₃) nanowires have been synthesized using a novel method by high-frequency inductive heating in a room temperature environment. Nanowires with high-yield were grown on silicon substrates in less than 3 min, using Ga₂O₃/graphite as the source powder. Scanning electron microscopy showed nanowire diameters of 20-40 nm and lengths up to several tens of microns, and high-resolution transmission electron microscopy verified the single-crystalline lattice of the nanowires. Electrical properties were investigated by connecting a single Ga₂O₃ nanowire in the field-effect transistor configuration. This demonstration further illustrates the feasibility of an easy and large-scale synthesis of nanomaterials by using high-frequency inductive heating.     

Growth and characterization of ZnO nanowires on p-type GaN

ZnO nanowires were grown by catalyst-free metal-organic vapour-phase epitaxy on top of a p-type GaN buffer. The optical properties of the ZnO nanowires were investigated by temperature-dependent and time-resolved photoluminescence and compared to those of ZnO nanowires directly grown on sapphire. The luminescence intensity decrease with temperature of the nanowires grown on GaN reveals an original behavior since it is constant over 120 K, showing the existence of strong localization centers. In addition, the temperature-dependent decay time measurements indicate a lower density of non-radiative channels for the nanowires grown on GaN.     

Preparation,characterization and photocatalytic properties of polythiophene-sensitized zinc oxide hybrid nanocomposites

The composites of polythiophene (PT)/zinc oxide (ZnO) nanoparticles with different PT wt%, (2%, 4%, 6%, 10% and 20%), were synthesized by an in situ chemical oxidative polymerization method. Zinc oxide nanoparticles, prepared by polymer pyrolysis method, with average particle size of 30 nm were used as inorganic phase of these composites. The particle size of ZnO powder was measured by transmission electron microscopy (TEM). FTIR measurements and X-ray diffraction analyses showed that PT/ZnO composites were successfully synthesized. Optical properties of the prepared composites were investigated by diffuse reflectance spectroscopy (DRS) that showed a broad peak in the visible region. The morphologies of the obtained composites were studied by scanning electron microscopy (SEM). Also Barrett–Emmett–Teller (BET) technique was used to measure the specific surface area of the samples. The photocatalytic activities of the composites were evaluated by degradation of methyl orange (MO) aqueous solution under visible light (9 W LED lamp) and sunlight irradiation.     

PLD法生长Al2O3基ZnO薄膜的特性

在不同衬底温度下,用脉冲激光沉积法(PLD),在Al2O3(0001)平面上生长了ZnO薄膜。研究了衬底温度对其结晶质量、电学性质以及发光性质的影响。结果显示:XRD在2θ为34°处出现了唯一的ZnO(0002)衍射峰;ZnO薄膜的电阻率随衬底温度的升高而增大;在衬底温度为500℃时,出现了位于410nm附近的特殊的光致发光(PL)峰。     

Properties of cobalt-doped zinc oxide thin films grown by pulsed laser deposition on glass substrates

Undoped and cobalt-doped zinc oxide (CZO) polycrystalline piezoelectric thin films (Co: 3, 5 at.%) using a series of high quality ceramic targets have been deposited at 450 °C onto glass substrates using a pulsed laser deposition method. The used source was a KrF excimer laser (248 nm, 25 ns, 2 J∕cm²). X-ray diffraction patterns showed that the Co-doped ZnO films crystallize in a hexagonal wurtzite type structure with a strong (0 orientation, and the grain sizes calculated from these patterns decrease from 37 to 31 nm by increasing Co doping. The optical waveguiding properties of the films were characterized by using a prism-coupling method. The distinct M-lines of the guided transverse magnetic (TM) and transverse electric (TE) modes of the ZnO films waveguide have been observed. With the aim of study the optical properties of the ZnO films, an accurate refractive index and thickness measurement apparatus was set up, which is called M-lines device. An evaluation of experimental uncertainty and calculation of the precision of the refractive index and thickness were developed on ZnO films. The optical transmittance spectra showed a good transparency in the visible region. Calculated optical band gap varying from 3.23 to 3.37 eV when the content of Co doping increases from 0 to 5 at.%.     

Electrical measurements of dielectric properties of molybdenum-doped zinc oxide thin films

Effects of molybdenum element content on electrical conductivity of ZnO sprayed thin films were investigated using the impedance spectroscopy method in the frequency ranging from 5 Hz to 13 MHz for temperature lying in 300–475 °C domain. It is observed that AC conductivity is a power law. The values of dielectric constants ε₁ and ε₂ were found to decrease with frequency and increase with temperature. The activation energy determined from the plot of both DC conductivity and the hopping frequency with 1000/T shows that the hopping conduction is the dominant mechanism. Also, experimental data of DC conductivity were analyzed using the small polaron hopping model. The impedance analysis of undoped ZnO and Mo-doped ZnO (1% and 2%) shows only one semicircle implying the response originated from a single capacitive element corresponding to the bulk grains. However, the same analysis for ZnO:Mo (3% ) shows two semicircles which proves the existence of grain boundaries. Finally, analyses of polaron hopping mechanism and Urbach tailing allow some explanations of these transport phenomena. This study shows an effective variation of electrical measurements of Mo-doped ZnO films in terms of temperature leading to possible use of such films as gas sensors.     

In_2O_3和ZnO混合薄膜的化学腐蚀特性研究

利用直流磁控溅射在未加热的BK-7玻璃基片上沉积In2O3与ZnO混合(IZO)薄膜,通过原子力显微镜(AFM)、分光光度计和四探针法研究IZO薄膜在HCl溶液中不同腐蚀时间前后的表面形貌以及光电性质的变化。结果表明:随着腐蚀时间的增加,薄膜的表面均方根粗糙度(RMS)和方块电阻(Rs)都呈现先增后减再增的现象;而薄膜的光学透射率则是先减后增再减。由于ZnO比In2O3更容易在HCl溶液中进行腐蚀,使得样品经腐蚀后出现孔洞结构,孔宽与孔深都随着腐蚀时间的增加而增大,这种具有纳米孔洞结构的透明导电薄膜在未来的光电子器件有潜在应用。     

Structural, optical and electrical properties of zinc oxide thin films deposited by a spray pyrolysis technique

Zinc oxide (ZnO) thin films were deposited on glass substrates by spray pyrolysis technique decomposition of zinc acetate dihydrate in an ethanol solution with 30 mL of deposition rate, the ZnO thin films were deposited at two different temperatures: 300 and 350 ℃. The substrates were heated using the solar cells method. The substrate was R217102 glass, whose size was 30 × 17.5 × 1 mm³. The films exhibit a hexagonal wurtzite structure with a strong (002) preferred orientation. The higher value of crystallite size is attained for sprayed films at 350 ℃, which is probably due to an improvement of the crystallinity of the films at this point. The average trans mittance of obtain films is about 90%-95%, as measured by a UV-vis analyzer. The band gap energy varies from 3.265 to 3.294 eV for the deposited ZnO thin film at 300 and 350 ℃, respectively. The electrical resistivity measured of our films are in the order 0.36 Ω·cm.     

ZnO纳米线的快速生长机理及其场发射性能研究

为了快速制备具有优良场发射性能的ZnO纳米线,对ZnO纳米线的生长机理及场发射性能进行研究。首先采用优化的两步法制备出高长径比的ZnO纳米线,其次采用SEM对ZnO的微观形貌进行表征,然后,在分析形貌特点的基础上,说明了强碱体系下ZnO纳米线薄膜的快速生长机理。最后,对典型样品的场发射性能进行了测试。测试果表明,优化后的两步法,只需3h即可获得直径为40~50nm,长度为2.2~2.7μm,长径比高达54的纳米线。薄膜的开启电场为3.6V/μm,阈值场强为9.1V/um,场增强因子β高达3 391。研究表明,高pH值溶液可以加快ZnO纳米线沿C轴方向的择优生长,获得高长径比的ZnO纳米线,进而获得优良的场发射性能。     

Influence of jute template on the surface,optical and photocatalytic properties of sol-gel derived mesoporous zinc oxide

Utility of bio-templates in the synthesis of crystalline solids is one of the preferred routes in green synthesis. The present study explores jute fiber as a biotemplate for the sol-gel synthesis of zinc oxide. AT-IR of the as synthesized sample clearly revealed the chelation between the metal and active groups of jute. The surface area enhancement and reduction in crystallite size in the templated samples were confirmed from BET and XRD analyses. ZnO prepared using 0.5 g/3 g of precursor possessed higher average crystallite size than the other samples. Surprisingly, the same sample also had a high surface area due to its distinct spherical morphology, highlighting the influence of morphology on the surface area of ZnO. Jute templated ZnO exhibited significant photocatalytic activity for degradation of crystal violet dye under visible light. Thus, jute has been proved to be an efficient template for the sol-gel synthesis of ZnO with controlled crystallite characteristics.     

Characterization and antibacterial capabilities of nanocrystalline CdS thin films prepared by chemical bath deposition

Antibacterial capabilities of nanocrystalline cadmium sulfide (CdS) thin films have been developed against Gram-positive and Gram-negative bacteria in dark and sunlight at 60 °C. For this purpose, a strain of Gram-positive Staphylococcus aureus, and two strains of Gram-negative bacteria (Pseudomonas aeruginosa, and Escherichia coli) were used. The nanocrystalline CdS thin films have been prepared using a chemical bath deposition (CBD) method at different thicknesses (50, 80 and 100 nm). The different deposition parameters including the speed of rotation of substrate, temperature of chemical bath, pH of solution and time of the deposition were optimized. The Polyvinylpyrrollidone (PVP) was successfully used as capping agent in order to stop the agglomeration in the CdS thin films. It was found that, CdS thin films have remarkable antibacterial activity in dark and sunlight and it could be applied as antimicrobial agent in medical field. In order to confirm the crystalline structure of CdS thin films, the polycrystalline nature of the deposited CdS thin films with hexagonal structure was obtained. Furthermore, the structural parameters including lattice parameters, cell volume, the space group, average grain size, dislocation density and the strain have been calculated. The topography and surface roughness of the CdS thin films have been studied before and after the bacteriostatic effect using Scanning Electron Microscopy (SEM). Furthermore, the compositions of nanocrystalline CdS thin films have been evaluated using Energy Dispersive X-ray emission (EDX) and a Transmission Electron Microscope (TEM). Based on the optical measurements in the range of 300–2500 nm, the band gap energy of the prepared CdS thin films was found to be 2.4 eV.     

In-situ sonosynthesis of cobblestone-like ZnO nanoparticles on cotton/polyester fabric improving photo,bio and sonocatalytic activities along with low toxicity and enhanced mechanical properties

For the first time in this study, in-situ sonosynthesis and deposition of ZnO nanoparticles under ultrasound irradiation was used to prepare multifunctional cotton/polyester fabric. The process was carried out at 80 ^°C in ultrasonic bath and was free from final heating of fabrics to convert zinc hydroxide to zinc oxide nanoparticles. This was due to the physical and chemical effects of ultrasound promoting the involved reactions and facilitating the nucleation and growth of ZnO nanoparticles. Central composite design was also used to statistically analyze the process, optimizing the applied condition including zinc precursor concentration, pH and the effect of dispersing agent namely cetyltrimethylammonium bromide surfactant (CTAB). The treated samples were further characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy-dispersive spectroscopy (EDX). Photocatalytic activities of the treated samples were assessed based on the ability of fabrics to degrade Methylene Blue dye stain under sunlight irradiation. The effect of synthesis parameters on photocatalytic activities (self-cleaning) was statistically optimized. Moreover, for evaluating the sonocatalytic efficiencies of the samples Reactive Blue 2 was applied and the activities were studied by visible spectroscopy. The cotton/polyester samples possessed multifunctional properties including self-cleaning, sonocatalytic, antibacterial, antifungal, low cytotoxicity and enhanced mechanical properties.     

Synthesis,physical properties and antibacterial activity of metal oxides nanostructures

Metal oxides (MOs) nanostructures represent a new class of materials which have been explored for the health related applications. Highly ionic MOs nanostrucrures are important for their unique physicochemical properties as well as antibacterial activity. In this work, MOs nanostructures (ZnO, CuO, SnO₂ and CeO₂) have been synthesized by chemical co-precipitation technique and characterized by XRD, SEM, EDS, FTIR and UV–visible spectroscopy analysis. XRD results reveal the single-phase formation of all metal oxides. Spherical nanoparticles are observed in case of ZnO, SnO₂ and CeO₂ samples, while hierarchal nanostructures are observed in case of CuO sample. Antibacterial activity of four different MOs nanostructures against E. coli bacterium has been assessed by agar disc method. The antibacterial activity results have shown that the ZnO nanostructures exhibit maximum sensitivity (10 mm ZOI) towards E. coli bacterium. The order of antibacterial activity for different MOs nanostructures is found to be the following: ZnO>SnO₂>CeO₂>CuO. Our findings suggest that the particle size, morphology and type of MOs nanostructures play vital role in their antibacterial activity. It is concluded from the present findings that ZnO nanostructures can be used as an efficient antibacterial agent.     

Ab initio study on physical properties of wurtzite,zincblende, and rocksalt structures of zinc oxide using revised functionals

To provide a more comprehensive understanding of zinc oxide (ZnO), the structural, optical, dielectric and thermodynamic properties of wurtzite (B4), zincblende (B3) and rocksalt (B1) phases are studied based on density functional theory with various revised functionals. It is found that the equilibrium volume, bulk modulus, phase transition point and covalent degree of B3-ZnO are close to those of B4-ZnO. Similar behaviors can be observed from optical properties, dielectric constants and Born effective charges. Moreover, thermodynamic parameters including isothermal bulk modulus, thermal expansion coefficients, Grüneisen parameter, and heat capacity with temperature of B3-ZnO are also in accordance with B4-ZnO. In contrast, B1-ZnO obviously undergoes dissimilar physical properties. Thus, it can be concluded that B3 phase may be the substitute of B4 phase in case of growing on the closely cubic lattice-matched substrates.     

Tunable emission property of biotin capped Gd:ZnS nanoparticles and their antibacterial activity

Gd doped ZnS nanoparticles have been successfully fabricated by a microwave irradiation method whose surface was passivated with biotin at different concentration. The structural property was investigated by characterizing the samples with the help of X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM). Energy dispersive spectroscopy (EDS) measurement showed the existence of Gd ion in the Gd-doped ZnS nanoparticles. Optical confirmation was done with the help of UV–visible and photoluminescence spectroscopy. Diffraction data confirmed the zinc blend structure for all the samples with grain size of 5.8 nm for uncapped and 3–4 nm for capped nanoparticles with varying concentration of biotin. Spherical shape with 7 nm (uncapped) and 4 nm (capped) were definite from TEM images. HRTEM images and SAED patterns with bright circular rings designated the cubical environment of these nanoparticles. Emission bands in the blue, green and red regions were observed for both the samples, which was blue shifted in case of capped nanoparticles with increased intensity. Enhanced luminescence property was observed in the case of capped Gd:ZnS nanoparticles when compared to uncapped and thus can be of biomedical uses. Notably these biotin capped Gd:ZnS nanoparticles proved to be a potential antibacterial agent against different pathogenic bacterial strains, which showed maximum zone of inhibition at concentration of 10 µg/ml. The bioactivity sums up that this surface passivated nanoparticle emerges as a new class of antibacterial agent.     

Tinospora cordifolia mediated facile green synthesis of cupric oxide nanoparticles and their photocatalytic,antioxidant and antibacterial properties

The study reports a facile method for the green synthesis of copper oxide nanoparticles (CuO Nps) by a solution combustion method using Tinospora cordifolia water extract. The Nps were characterized by XRD, SEM, TEM and UV–visible studies. XRD data indicates the formation of pure monoclinic crystallite structures of CuO Nps. SEM images show that the particles have sponge like structure with large surface area and the average crystallite sizes were found to be ~6–8 nm. These observations were confirmed by TEM analysis. Photocatalytic activity studies of CuO Nps reveal that they act as very good catalyst for the effective degradation of methylene blue (MB) in the presence of UV and Sun light. Also, the degradation of MB was found to be pH dependent. The Nps found to inhibit the activity of 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals effectively. CuO Nps exhibit significant bactericidal activity against Klebsiella aerogenes, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus. The study reveals a simple, ecofriendly and robust method for the synthesis of multifunctional CuO nanoparticle employing underutilized medicinal plants.     

Green synthesis of multifunctional zinc oxide (ZnO) nanoparticles using Cassia fistula plant extract and their photodegradative,antioxidant and antibacterial activities

The present study involves green synthesis of ZnO nanoparticles (Nps) using aqueous Cassia fistula plant extract as fuel by solution combustion synthesis. The ZnO Nps were characterized by Powder X- ray diffraction (PXRD), UV–visible studies and Transmission electron microscopy (TEM). The Nps were evaluated for photodegradative, antimicrobial and antioxidant activities. The extract was found to contain reducing components such as polyphenols (11%) and flavonoids (12.5%). The Nps were found to have a hexagonal wurtzite structure. UV–visible absorption of ZnO Nps showed absorption band at 370 nm which can be assigned to the intrinsic band-gap absorption of ZnO due to the electron transitions from the valence band to the conduction band. TEM image confirms the formation of nanoparticles and the average crystallite sizes were found to be ~5–15 nm. Methylene blue (MB) dye was effectively degraded under UV and Sun light illumination in the presence of ZnO Nps. Significant antioxidant activity was exhibited by Nps through scavenging of 1, 1-Diphenyl-2-picrylhydrazyl (DPPH) free radicals. Excellent bactericidal activity was shown by the Nps on Klebsiella aerogenes, Escherichia coli, Plasmodium desmolyticum and Staphylococcus aureus. Synthesis of multifunctional ZnO Nps using naturally occurring plant products has been advocated as a possible environment friendly alternative to chemical methods.