Y. Ashok Kumar Reddy

Green synthesis and characterization of silver nanoparticles using Lantana camara leaf extract.

In this work, we have investigated on Lantana camara mediated silver nanoparticles (AgNPs) with different leaf extract (LE) quantity for the evaluation of efficient bactericidal activity. The AgNPs were prepared by simple, capable, eco-friendly and biosynthesis method using L. camara LE. This method allowed the synthesis of crystalline nanoparticles, which was confirmed by X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns. The X-ray photoelectron spectroscopy (XPS) analysis confirmed the formation of metallic silver and elucidates the surface state composition of AgNPs. UV-vis spectra of AgNPs and visual perception of brownish yellow color from colorless reaction mixture confirmed the AgNP formation. Involvement of functional groups of L. camara leaf extract in the reduction and capping process of nanoparticles was well displayed in Fourier transform infrared spectroscopy (FTIR). Decrement of particle size with an increment of leaf extract volume was evident in AFM, TEM images and also through a blue shift in the UV-vis spectra. The rate of formation and size of AgNPs were dependent on LE quantity. Meanwhile, these AgNPs exhibited effective antibacterial activity with the decrement of particle size against all tested bacterial cultures.

Biogenic nano-scale silver particles by Tephrosia purpurea leaf extract and their inborn antimicrobial activity.

In this paper we report the green synthesis of silver nanoparticles (Ag NPs) using Tephrosia purpurea leaf extract. The biomolecules present in the leaf extract are responsible for the formation of Ag NPs and they found to play dual role of both reducing as well as capping agents. The high crystallinity of Ag NPs is evident from bright circular spot array of SAED pattern and diffraction peaks in XRD profile. The synthesized Ag NPs are found to be nearly spherical ones with size approximately ∼20 nm. FTIR spectrum evidences the presence of different functional groups of biomolecules participated in encapsulating Ag NPs and the possible mechanism of Ag NPs formation was also suggested. Appearance of yellow color and surface plasmon resonance (SPR) peak at 425 nm confirms the Ag NPs formation. PL spectra showed decrement in luminescence intensity at higher excitation wavelengths. Antimicrobial activity of Ag NPs showed better inhibitory activity towards Pseudomonas spp. and Penicillium spp. compared to other test pathogens using standard Kirby-Bauer disc diffusion assay.

Biosynthesis of silver nanoparticles using Plectranthus amboinicus leaf extract and its antimicrobial activity

This study reports the simple green synthesis method for the preparation of silver nanoparticles (Ag NPs) using Plectranthus amboinicus leaf extract. The pathway of nanoparticles formation is by means of reduction of AgNO3 by leaf extract, which acts as both reducing and capping agents. Synthesized Ag NPs were subjected to different characterizations for studying the structural, chemical, morphological, optical and antimicrobial properties. The bright circular fringes in SAED pattern and diffraction peaks in XRD profile reveals high crystalline nature of biosynthesized Ag NPs. Morphological studies shows the formation of nearly spherical nanoparticles. FTIR spectrum confirms the existence of various functional groups of biomolecules capping the nanoparticles. UV-visible spectrum displays single SPR band at 428 nm indicating the absence of anisotropic particles. The synthesized Ag NPs exhibited better antimicrobial property towards gram negative Escherichia coli and towards tested Penicillium spp. than other tested microorganisms using disc diffusion method. Finally it has proven that the synthesized bio-inspired Ag NPs have potent antimicrobial effect.

Biosynthesis of silver nanoparticles using Momordica charantia leaf broth: Evaluation of their innate antimicrobial and catalytic activities.

Silver nanoparticles (AgNPs) were prepared through green route with the aid of Momordica charantia leaf extract as both reductant and stabilizer. X-ray diffraction pattern (XRD) and selected area electron diffraction (SAED) fringes revealed the structure of AgNPs as face centered cubic (fcc). Morphological studies elucidate the nearly spherical AgNPs formation with particle size in nanoscale. Biosynthesized AgNPs were found to be photoluminescent and UV-Vis absorption spectra showed one surface plasmon resonance peak (SPR) at 424nm attesting the spherical nanoparticles formation. XPS study provides the surface chemical nature and oxidation state of the synthesized nanoparticles. FTIR spectra ascertain the reduction and capping nature of phytoconstituents of leaf extract in AgNPs synthesis. Further, these AgNPs showed effective antimicrobial activity against tested pathogens and thus applicable as potent antimicrobial agent. In addition, the synthesized AgNPs were observed to have an excellent catalytic activity on the reduction of methylene blue by M. charantia which was confirmed by the decrement in maximum absorbance values of methylene blue with respect to time and is ascribed to electron relay effect.

Role of capping agents in controlling silver nanoparticles size, antibacterial activity and potential application as optical hydrogen peroxide sensor

The influence of capping agents on silver nanoparticles (AgNPs) was investigated through a rapid and single-pot chemical reduction method. Four capping agents were tested: polyethylene glycol (PEG), ethylenediaminetetraacetic acid (EDTA), polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA). FTIR studies demonstrated that the formed AgNPs were properly encapsulated by their respective capping agents. Structural and morphological studies confirmed the following relative average particle sizes: PEG-AgNPs > EDTA-AgNPs > PVP-AgNPs > PVA-AgNPs. Optical absorption and photoluminescence studies showed, respectively, a greater absorption blue shift and greater emission intensity for the smaller capped particles. Zeta potential analysis of the PVA-AgNPs showed a value of −46.6 mV, indicating their high stability. The PVA-AgNPs were thus not only observed to be the smallest, most blue-shifted and most stable of the tested AgNPs, but also they displayed the highest antibacterial activity. The PVA-AgNPs were therefore applied as a localized surface plasmon resonance (LSPR)-based H2O2 sensor, which is important because the detection of reactive oxygen species such as H2O2 is of significance in the medical and environmental fields. The sensor based on the PVA-AgNPs successfully detected H2O2 at concentrations as low as 10−7 M. New biosensors using these NPs should thus find promising opportunities in a variety of fields.

Lantana camara leaf extract mediated silver nanoparticles: Antibacterial, green catalyst

Silver nanoparticles (AgNPs) have been synthesized by Lantana camara leaf extract through simple green route and evaluated their antibacterial and catalytic activities. The leaf extract (LE) itself acts as both reducing and stabilizing agent at once for desired nanoparticle synthesis. The colorless reaction mixture turns to yellowish brown attesting the AgNPs formation and displayed UV-Vis absorption spectra. Structural analysis confirms the crystalline nature and formation of fcc structured metallic silver with majority (111) facets. Morphological studies elicit the formation of almost spherical shaped nanoparticles and as AgNO3 concentration is increased, there is an increment in the particle size. The FTIR analysis evidences the presence of various functional groups of biomolecules of LE is responsible for stabilization of AgNPs. Zeta potential measurement attests the higher stability of synthesized AgNPs. The synthesized AgNPs exhibited good antibacterial activity when tested against Escherichia coli, Pseudomonas spp., Bacillus spp. and Staphylococcus spp. using standard Kirby-Bauer disc diffusion assay. Furthermore, they showed good catalytic activity on the reduction of methylene blue by L. camara extract which is monitored and confirmed by the UV-Vis spectrophotometer.

Bolometric properties of reactively sputtered TiO2−x films for thermal infrared image sensors

A heat-sensitive layer (TiO2−x ) was successfully deposited by RF reactive magnetron sputtering for infrared (IR) image sensors at different relative mass flow of oxygen gas (R O2) levels. The deposition rate was decreased with an increase in the percentage of R O2 from 3.4% to 3.7%. TiO2−x samples deposited at room temperature exhibited amorphous characteristics. Oxygen deficiency causes a change in the oxidation state and is assumed to decrease the Ti4+ component on the surfaces of TiO2−x films. The oxygen stoichiometry (x) in TiO2−x films decreased from 0.35 to 0.05 with increasing the R O2 level from 3.4% to 3.7%, respectively. In TiO2−x −test-patterned samples, the resistivity decreased with the temperature, confirming the typical semiconducting property. The bolometric properties of the resistivity, temperature coefficient of resistance (TCR), and the flicker (1/ f) noise parameter were determined at different x values in TiO2−x samples. The rate of TCR dependency with regard to the 1/ f noise parameter is a universal bolometric parameter (β), acting as the dynamic element in a bolometer. It is high when a sample has a relatively low resistivity (0.82 Ωcm) and a lower 1/ f noise parameter (3.16 × 10−12). The results of this study indicate that reactively sputtered TiO2−x is a viable bolometric material for uncooled IR image sensor devices.

Enhanced bolometric properties of TiO2−x thin films by thermal annealing

The effect of thermal annealing on the bolometric properties of TiO2−x films was investigated. The test-patterned TiO2−x samples were annealed at 300 °C temperature in order to enhance their structural and electrical properties for effective infrared image sensor device applications. The crystallinity was changed from amorphous to rutile/anatase in annealed TiO2−x films. Compared to the as-deposited samples, a decrement of the band gap and a decrease of the electrical resistivity were perceived in annealed samples. We found that the annealed samples show linear current-voltage (I−V) characteristic performance, which implies that ohmic contact was well formed at the interface between the TiO2−x and the Ti electrode. Moreover, the annealed TiO2−x sample had a significantly low 1/f noise parameter (1.21 × 10−13) with a high bolometric parameter (β) value compared to those of the as-deposited samples. As a result, the thermal annealing process can be used to prepare TiO2−x film for a high‐performance bolometr...

Effect of substrate temperature on structural, optical and electrical properties of sputtered NiO-Ag nanocrystalline thin films

NiO-Ag thin films were deposited on Corning 7059 glass substrates by DC reactive magnetron sputtering technique and investigated the substrate temperature (Ts) dependent properties of NiO-Ag thin films. X-ray diffraction results showed that crystalline films can be obtained at high Ts and all films have a preferred crystal growth texture with face centered cubic (fcc) structure and was also confirmed by Raman studies. The grain size, transmittance, band gap, mobility and carrier concentrations were increased with Ts. Room temperature deposited films have an average roughness around 6.9 nm where as increment of Ts resulted in increased roughness up to 14 nm with nanocrystalline morphology. The optimum substrate temperature to obtain NiO-Ag films was found to be 200°C. It was found that with increasing the Ts, resistivity of the films was significantly decreased.

Effect of sputtering pressure on microstructure and bolometric properties of Nb:TiO2−x films for infrared image sensor applications

This study aims to investigate the influence of the sputtering pressure (PS) on Nb:TiO2−x films to enhance the bolometric properties. A decrease in the growth rate with the sputtering pressure was perceived in amorphous Nb:TiO2−x films. The incorporation of oxygen with PS was confirmed in an X-ray photo electron spectroscopy analysis. The electrical resistivity was increased with an increase in PS due to a decrease in the number of oxygen vacancies. The linear I-V characteristics confirmed the ohmic contact behavior between the Nb:TiO2−x layer and the electrode material. The present investigation finds that the sample with lower resistivity has good bolometric properties with low noise and high universal bolometric parameters. Finally, the Nb:TiO2−x sample deposited at a sputtering pressure of 2 mTorr shows better bolometric properties than other materials for infrared image sensor applications.