سال:1398 | دوره: | شماره: |تعداد مقالات:10

The infection of Aspergillus flavus and its aflatoxin production pose a severe threat to humans, animals as well as plants life. Their inhibition using green techniques are considered as one of the important challenges. The present study outlines the antifungal activity of the ZnO nanoparticles (NPs) synthesized from lemongrass leaf extract and their effect on the mycelial growth of Aspergillus flavus and its aflatoxins production. The qualitative and quantitative analyses of aflatoxins were determined, respectively using thin-layer chromatography and spectrophotometric methods. The X-ray diffraction as well as scanning and transmission electron microscopy studies indicated the formations of hexagonal ZnO NPs having the sizes ranged between 7 and 14 nm. FTIR spectrum confirmed the formation of ZnO NPs. The ZnO NPs displayed 92. 25% inhibition of the growth of A. flavus and 100% inhibition of the aflatoxins production at the concentrations of 200 μ l/mL and 150 μ l/mL respectively. The present biosynthetic method is a simple, cost-effective, eco-friendly, high yield, green and handy protocol capable of synthesizing ZnO NPs, which might have accomplished due to the activities of plant metabolites and phytochemicals available in the lemongrass leaves parenchyma. This study revealed that ZnO NPs have the potential to forbid the growth of A. flavus and its aflatoxins production. Hence, ZnO NPs could be used in the plant protection and as a preservative for safe storage of food commodities to prevent A. flavus contamination and aflatoxins poisoning in coming future.

The role of enzyme engineering in biotechnology, biological and pharmaceutical process cannot be over emphasized. This study compared the adsorption of amylase and protease on to manganese ferrite (MnFe2O4). The metal ferrite was synthesized via a sol – gel technique and characterized with scanning electron microscopy (SEM), X-ray diffraction (XRD), Electron paramagnetic resonance (EPR) and Fourier transform infrared spectroscopy (FTIR). The adsorption was study in a batch process and the data were subjected to kinetics and isotherm models. The pseudo-first order best fitted the kinetic data with R2> 0. 99. The data were fitted well by the entire isotherm models considered with the maximum adsorption isotherm of 1. 602 and 7. 330 mg/g. The thermodynamic parameters give negative Gibb’ s free energy, Δ G, showing a spontaneous adsorption; positive Δ H indicated an endothermic favoured process, while Δ S values showed that the process progress with lower entropy change.

In this study, the potential of 8-Hydroxyquinoline grafted SBA-15 to extract of Cu2+ cations from aqueous solutions was investigated. SBA-15 nanoporous silica was chemically grafted with 8-Hydroxyquinoline groups according to the procedure in the literature. The presence of organic groups in the silica framework was demonstrated by FTIR spectrum. The grafted product showed the BET surface area 458 m2g-1 and pore diameter 54 º A, based on adsorption-desorption of N2 at 77 º K. . Flame atomic absorption spectrometry was used to determination of the ions concentration in the recovery and sample solution. The effects of several variables (amount of adsorbent, stirring time, pH and the presence of other metals in the medium) were studied. Cu2+ ions were completely extracted at pH= 4. 5-7 after stirring for 15 minutes. The maximum capacity of the adsorbent was found to be 31. 25 mg of Cu2+ per each gram of 8-Hydroxyquinoline grafted SBA-15. The minimum amount of acid for stripping of ions from grafted SBA-15 was tested and the preconcentration factor of the method was found 50. Finally, the proposed method was successfully applied as a new solid extractor to preconcentration and determination of trace amounts of Cu2+ ions in spiked distilled and tap water samples.

Zinc Oxide nanoparticles (ZnO-NPs) and graphene carbon material, due to lower drug resistance, can replace antibiotics, and by decorating of graphene with Zn-NPs, their properties can be greatly improved. The purpose of this study was to evaluate the antioxidant and antibacterial effects of ZnO-NPs biosynthesized using Crocus Sativus petal extract, graphene and graphene decorated by ZnO-NPs biosynthesized using Crocus Sativus petal extract (G-ZnO). Their physicochemical characterizations were performed by UV-Vis spectroscopy, Transmission electron microscopy (TEM) and field emission scanning electron microscopy (FE-SEM), revealing that ZnO-NPs with a mean size of 25 nm and spherical-shape were distributed uniformly on the surface of the graphene without aggregation. The antioxidant activities of ZnO-NPs, graphene and G-ZnO were evaluated using DPPH and ABTS assays. Antibacterial activities of three compounds were tested against Gram negative bacteria Escherichia coli (E. coli) and Gram positive bacteria Staphylococcus aureus (S. aureus) using macrodilution method. The results of this study showed that these three compounds have antioxidant and antibacterial effects. And it was show that but also antioxidant and antibacterial activity of G-ZnO was higher than ZnO-NPs and graphene. G-ZnO could be useful as a natural antioxidant and antibacterial in the pharmacy industry.

The present work demonstrated a green approach of synthesis of gold nanoparticles using Eupatorium odoratum leaf extract as reducing and stabilizing agent assisted with microwave irradiation. Effects of various concentrations of leaf extract on the preparation of gold nanoparticles have been investigated and it was monitored by undertaking UV-vis spectroscopic studies. The experimental results showed that the surface Plasmon resonance (SPR) peak blue shifted with increase in the concentration of leaf extract indicating the decrease of nanoparticles size, which was further confirmed by the Dynamic light scattering (DLS) data. Synthesized particles were further characterized by Fourier Transform Infra-Red spectroscopy (FTIR) and Transmission Electron Microscopy (TEM). All the characterization results confirmed the formation of stable spherical mono-dispersed gold nanoparticles with size ranging from 10-20 nm. The catalytic activity of prepared gold nanoparticles was checked by reducing Nitrophenol to Aminophenol in presence of an excess amount of sodium borohydride. The progress of the reaction was examined by observing the absorbance peak of UV-vis spectroscopy. The study showed positive results and it was found that gold nanoparticles synthesized with 600 μ L leaf extract have greater catalytic activity. It was also found that gold nanoparticles remained stable for long duration of time.

In this paper, we proposed a 2-D analytical model for electrical characteristics such as surface potential, electric field and drain current of Silicon-on-Insulator Tunnel Field Effect Transistor (SOI TFETs) with a SiO2/ High-k stacked gate-oxide structure. By using superposition principle with suitable boundary conditions, the Poisson’ s equation has been solved to model the channel region potential. The modeled channel potential is to calculate both vertical and lateral electric field. 2-D Kane’ s model is used to calculate the drain current of TFET and the expression is taken out by analytically integrating the band-to-band tunneling generation rate over the thickness of channel region. The device is modeled in variation with different device parameters like channel length (LCH), dielectric thickness (tox), silicon thickness (tsi) and input voltage (Vds and Vgs). Also, the comparison of SiO2 and stacked high k dielectric TFET is obtained. It has been found from the presented results that the hetero-dielectric stacked TFET structure provides ON current 10-6A/um. However, SiO2 dielectric structure provides the ON current of 10-8A/um. The proposed model is validated by comparing it with Technology Computer-Aided Design (TCAD) simulation results obtained by using SILVACO ATLAS device simulation software.

In the present work, the exact diagonalization method had been implemented to calculate the ground state energy of shallow donor impurity located at finite distance along the growth axis in GaAs/AlGaAs heterostructure in the presence of a magnetic field taken to be along z direction. The impurity binding energy of the ground state had been calculated as a function of confining frequency and magnetic field strength. We found that the ground state donor binding energy (BE) calculated at c ω =2R * and * 0 ω = 5. 421R, decreases from BE=7. 59822 R * to BE=2. 85165 R *, as we change the impurity position from d=0. 0 a* to d=0. 5 a*, respectively. In addition, the combined effects of pressure and temperature on the binding energy, as a function of magnetic field strength and impurity position, had been shown using the effective-mass approximation. The numerical results show that the donor impurity binding energy enhances with increasing the pressure while it decreases as the temperature decreases.

In this paper, the electrical characteristics and sensitivity analysis of staggered type p-channel heterojunction electron-hole bilayer tunnel field effect transistor (HJ-EHBTFET) are thoroughly investigated via simulation study. The minimum lattice mismatch between InAs/GaAs0. 1Sb0. 9 layers besides low carrier effective mass of materials provides high probability of tunneling current that eventually boosts the device performance. Unlike the conventional lateral tunnel field effect transistor (TFET), band to band tunneling (BTBT) in HJ-EHBTFET occurs in the electrically doped intrinsic channel and in the vertical direction which may considerably improve the on-state current. Due to the abrupt BTBT and steep transition from the off-state to on-state, subthreshold swing of 2mV/dec with on/off current ratio of 3. 85×1013 is obtained. The sensitivity of main electrical parameters is computed via calculating their related standard deviation and mean values with respect to the variation of device critical design parameters. The 2D variation matrix of threshold voltage is computed as a function of top and bottom gate workfunction for determining an optimum value aiming towards competent electrical characteristics. In addition, the sensitivity analysis reveals that the electrical parameters are rarely susceptible to the source doping density, which may considerably solve the limit of dopant solubility in III-V materials. Moreover, HJ-EHBTFET is dramatically unaffected by the variation of gate overlap length and drain voltage, which makes the device have efficient performance in nanoscale regime.

Mn3O4 nanoparticles has been synthesised from Manganese (II) acetate and Simarouba Glauca leaf extract using microwave heating. This novel method of synthesis of Mn3O4 is fast, low-cost, non-toxic and environment friendly. The synthesised product was characterised by powder X-ray diffraction(XRD), Fourier transform infrared spectroscopy( FT-IR), Ultraviolet-Visible spectroscopy( UV-Visible), X-ray photoelectron spectroscopy( XPS), Scanning electron microscopy(SEM) and Transmission electron microscopy(TEM). The prepared material was identified as of tetragonal hausmannite crystalline structure with spherical morphology and particle size 15 nm. Photo catalytic degradation ability of the synthesised product was examined by using it for the degradation of Malachite green dye in various experimental conditions under visible light. The synthesised Mn3O4 was found to be an efficient photo catalyst for the removal of Malachite green at the optimum conditions of pH 9, adsorbent dose 0. 1 g and dye concentration 20ppm. This study thus reveals the applicability of nanoparticles of Mn3O4 for the removal of pollutants from industrial waste water.

A Polyaniline/Manganese dioxide (PANI/MnO2) nanocomposite contains five weight percentages of MnO2. It has been successfully prepared by in situ polymerization. The structural, optical, and conductivity of nanocomposites remain relative to changes with respect to the weight percentage of MnO2. The structural, morphological, optical, and electrical conductivity investigation of pure MnO2, pure PANI, and nanocomposites were done with powder XRD, HRTEM, SEM, FT-IR, UV and Impedance spectra. XRD results of the PANI/ MnO2 nanocomposites say that the crystalline structure is converted into a very less crystalline structure due to the incorporation of MnO2 which is inside PANI chain. The HRTEM and SEM images are confirmed to the nanocomposite formation, morphology studies and also supported to the XRD results. From the optical spectra, MnO2 nanoparticles have been impressed in the surface of PANI. It works as the compensator in the formation of nanocomposites. UV spectral analysis reveals that the absorption of MnO2 modifies the absorption wavelength of under visible light in whole range. The absorption wavelength of nanocomposites is 288 nm and 337 nm. AC electrical conductivity of the prepared nanocomposites from impedance spectroscopy was carried out and compared with pure materials. The AC conductivity of as-prepared nanocomposites has been analyzed in the range of 298 K to 423 K. The AC conductivity of nanocomposites varies depending upon a change of logarithmic frequency.