Faheem Ahmed

Antibacterial and Cytotoxic Efficacy of Extracellular Silver Nanoparticles Biofabricated from Chromium Reducing Novel OS4 Strain of Stenotrophomonas maltophilia

Biofabricated metal nanoparticles are generally biocompatible, inexpensive, and ecofriendly, therefore, are used preferably in industries, medical and material science research. Considering the importance of biofabricated materials, we isolated, characterized and identified a novel bacterial strain OS4 of Stenotrophomonas maltophilia (GenBank: JN247637.1). At neutral pH, this Gram negative bacterial strain significantly reduced hexavalent chromium, an important heavy metal contaminant found in the tannery effluents and minings. Subsequently, even at room temperature the supernatant of log phase grown culture of strain OS4 also reduced silver nitrate (AgNO3) to generate nanoparticles (AgNPs). These AgNPs were further characterized by UV–visible, Nanophox particle size analyzer, XRD, SEM and FTIR. As evident from the FTIR data, plausibly the protein components of supernatant caused the reduction of AgNO3. The cuboid and homogenous AgNPs showed a characteristic UV-visible peak at 428 nm with average size of ∼93 nm. The XRD spectra exhibited the characteristic Bragg peaks of 111, 200, 220 and 311 facets of the face centred cubic symmetry of nanoparticles suggesting that these nanoparticles were crystalline in nature. From the nanoparticle release kinetics data, the rapid release of AgNPs was correlated with the particle size and increasing surface area of the nanoparticles. A highly significant antimicrobial activity against medically important bacteria by the biofabricated AgNPs was also revealed as decline in growth of Staphylococcus aureus (91%), Escherichia coli (69%) and Serratia marcescens (66%) substantially. Additionally, different cytotoxic assays showed no toxicity of AgNPs to liver function, RBCs, splenocytes and HeLa cells, hence these particles were safe to use. Therefore, this novel bacterial strain OS4 is likely to provide broad spectrum benefits for curing chromium polluted sites, for biofabrication of AgNPs and ultimately in the nanoparticle based drug formulation for the treatment of infectious diseases.

RAPID AND COST EFFECTIVE SYNTHESIS OF ZnO NANORODS USING MICROWAVE IRRADIATION TECHNIQUE

ZnO nanorods assembled in flower shaped morphology have been successfully synthesized using low power microwave irradiation in a very short duration. The diameter and length of the rods were within 150–190 nm (tip diameter ~15 nm) and 2 μm, respectively, with an aspect ratio of 20–22. The synthesized nanorods were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), Fourier transform infrared microscopy (FT-IR), photoluminescence (PL) and magnetization measurements. The XRD and FT-IR results indicate that ZnO nanorods have the pure wurtzite structure with lattice parameters a and c of 3.254 and 5.197 A, respectively. The selected area electron diffraction (SAED) pattern reveals that the ZnO nanorods are single crystal in nature and grow along [001] plane. Room-temperature PL spectrum of the as-grown ZnO nanorods shows a near-band-edge (NBE) emission peak and defect induced emissions. Magnetization measurements indicate that ZnO nanorods exhibit room temperature ferromagnetism with remanent magnetization (Mr) and coercivity (Hc) about 2.92 × 10-4 (emu/g) and 29.75 Oe, respectively, which may be due to the presence of defects in the ZnO nanorods.

Morphological evolution between nanorods to nanosheets and room temperature ferromagnetism of Fe-doped ZnO nanostructures

In this work, undoped and Fe-doped single-crystalline ZnO nanostructures were successfully synthesized by a facile microwave irradiation method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) results showed that Fe-doped ZnO was comprised of a single phase nature with a hexagonal wurtzite structure up to 5% Fe doping, however, secondary phase ZnFe2O4 appeared upon further increasing the Fe dopant concentration. Field emission scanning electron microscopy (FESEM) and TEM micrographs suggested that the length and diameter of the undoped ZnO rods are about ∼2 μm and ∼200 nm, respectively. Interestingly, the morphology of ZnO changed from nanorods (1% Fe) with length ∼500 nm and diameter ∼50 nm to nanosheets (5% Fe) having thickness and lateral dimension of ∼30 nm and ∼400 nm, respectively. NEXAFS and EELS studies revealed the absence of metal clusters up to 5% and Fe is found to be in a mixed (Fe2+/Fe3+) valence state with Fe2+ as the dominant state. Optical studies depicted that the absorption peak of Fe-doped ZnO was blue-shifted as the concentration of Fe increases from 1 to 5%. However, for dopant concentration >5%, the absorption peak was found to be red-shifted with an additional absorption peak of ZnFe2O4. Also, the band gap energy decreased monotonically with the increase of Fe concentration from 1 to 5%, while increasing on further doping, band gap increased. Raman scattering spectra of Fe-doped ZnO revealed the lower frequency shift of Ehigh2 mode with doping. Magnetic studies showed that Fe doped ZnO exhibit room temperature ferromagnetism (RTFM) and the value of magnetization increased up to 5% doping and then decreased for 7 and 10% Fe-doped samples.

Morphological evolution of ZnO nanostructures and their aspect ratio-induced enhancement in photocatalytic properties

This work presented controllable growth of ZnO nanostructures with different aspect ratios by the microwave irradiation method and investigated the photocatalytic degradation of methyl red (MR). X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) measurements showed that all ZnO nanostructures were of a hexagonal phase structure. It was revealed by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) images that the morphology of ZnO can be effectively controlled as sheet-like, rod-like, brush-like, flower-like, prism-like, and pyramid-like only by changing the molar ratio (zinc acetate: KOH) and reaction time. With the increase of molar ratio and reaction time, modification in the E2(high) and E1(LO) Raman modes was observed. The energy band gap was found to be tuned by the aspect ratio of ZnO nanostructures. Photoluminescence spectroscopy revealed the low-intensity NBE emission and high and broad defect-related emission for high aspect ratio (14) nanorods. BET surface area porosity analysis confirmed the presence of a mesoporous network in all the nanostructures, showed high surface area and a uniform pore-size distribution for high aspect ratio nanorods. A terephthalic acid assay study confirmed the formation of hydroxyl radicals (OH) in MR dye solution treated with a ZnO nanostructures photocatalyst. The photodegradation of MR under UV light irradiation showed that ZnO nanorods with a high aspect ratio of ∼14 showed superior photodegradation (∼98% degradation of MR within 60 min) than that of the lower aspect ratio nanostructures. The apparent reaction rate constant for high aspect ratio (14) nanorods was higher than that of the lower aspect ratio nanostructures. The enhancement in photocatalytic performance could be due to the high surface area and enhanced charge separation and transfer efficiency of photoinduced charge carriers in the high aspect ratio nanorods.

Study of magnetic entropy change in La0.65Sr0.35Cu0.1Mn0.9O3 complex perovskite

The magnetocaloric properties of new complex magnetic material La0.65Sr0.35Cu0.1Mn0.9O3, suitable for the Ericsson cycle, have been investigated. For this material, the effect of Cu doping can be attributed to a combination of doping disorder, Cu-Mn super exchange interactions and a site-percolation mechanism, which suppress the metallic conduction and Curie temperature. The Curie temperature decreases to 355xa0K. The magnetocaloric study exposes a comparable value of the magnetic entropy change for La0.65Sr0.35Cu0.1Mn0.9O3 sample, the value of the maximum entropy change, increases from 1.132xa0J/kgK to 3.11xa0J/kgK as magnetic field increases from 1xa0T to 4xa0T. A large relative cooling power (RCP) has been observed for La0.65Sr0.35Cu0.1Mn0.9O3. As a result, the studied sample can be considered as potential material for magnetic refrigeration.

Study of A-Site Disorder Dependent Structural, Magnetic, and Magnetocaloric Properties in La0.7-xSmxCa0.3MnO3 Manganites

We report studies on the magnetocaloric effect of samarium doped lanthanum manganites with different Sm-concentrations. Polycrystalline La0.7-xSmxCa0.30MnO3 (0≤x≤0.3) samples were prepared using the conventional solid-state reaction method with phase purity and structure confirmed using X-ray diffraction. Temperature dependent magnetization measurements and Arrott analysis reveal first order ferromagnetic transition in parent sample and second order ferromagnetic transition in doped sample with Curie temperature decreasing progressively with increasing Sm concentration from ~182 K for x = 0.05 to 109 K for x = 0.30. A large magnetic entropy change (~1.75 J kg-1 K-1 at 0.5 T) has been observed in La0.7Ca0.3MnO3 sample, and is greatly suppressed as a function of disorder caused by Sm doping. This is ascribed to the gradual loss of first-order ferromagnetic transition. This investigation suggests that La0.7-xSmxCa0.30MnO3 compounds can be used as a potential magnetic refrigerating material with wide range of temperature.

Influence of nitrogen gas flow rate on the structural, morphological and electrical properties of sputtered TiN films

In this work, nanocrystalline titanium nitride (TiN) films have been deposited by reactive DC magnetron sputtering technique on the Si/SiO2 (100) substrates. The influence of nitrogen gas flow rate [0, 3, 5, 7 and 9xa0sccm (standard cubic centimeter per minute)] on the structural, morphological and electrical properties of the nanocrystalline TiN films has been studied. As-deposited TiN films have been characterized by using X-ray diffraction (XRD), XPS (X-ray photoelectron spectroscopy), FESEM (field emission scanning electron microscopy) and four point probe resistivity measurement, respectively. The XRD patterns revealed the HCP symmetry for pure Ti (N2xa0=xa00xa0sccm) with (002) preferred orientations, and the FCC symmetry for TiN (N2xa0=xa03, 5, 7 and 9xa0sccm) films having (111) preferred orientations. The lattice parameters were found to be axa0=xa02.950xa0Ǻ, cxa0=xa04.681Ǻ for the Ti (N2xa0=xa00xa0sccm) film and axa0=xa04.250Å for the TiN films. The presence of different phases such as TiN and TiO2 were confirmed by XPS analysis. The FESEM images showed a smooth morphology of the film with columnar grain structures. The grain size of the TiN films was found to decrease from 22 to 15xa0nm as the nitrogen flow rate is increased from 0 to 9xa0sccm. The electrical resistivity measurement showed that the resistivity of the film increased from 11xa0×xa010−6 to 17xa0×xa010−6xa0Ohmxa0cm on increasing nitrogen flow rate from 3 to 9xa0sccm, having the lowest resistivity of 11xa0×xa010−6xa0Ohmxa0cm for the film deposited at 3xa0sccm nitrogen flow.

Microwave-assisted synthesis of SnO 2 nanorods for oxygen gas sensing at room temperature

High-quality single-crystalline SnO2 nanorods were synthesized using a microwave-assisted solution method. The nanorods were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), ultraviolet-visible and Raman spectroscopy, Brunauer–Emmett–Teller (BET), and electrical resistance measurements. The XRD pattern indicated the formation of single-phase SnO2 nanorods with rutile structure. FE-SEM and TEM images revealed tetragonal nanorods of about 450–500 nm in length and 60–80 nm in diameter. The nanorods showed a higher BET surface area of 288 m2/g, much higher than that of previously reported work. The Raman scattering spectra indicated a typical rutile phase of the SnO2. The absorption spectrum showed an absorption peak centered at 340 nm, and the band-gap value was found to be 3.64 eV. The gas-sensing properties of the SnO2 nanorods for oxygen gas with different concentrations were measured at room temperature. It was found that the value of resistance increased with the increase in oxygen gas concentration in the test chamber. The SnO2 nanorods exhibited high sensitivity and rapid response-recovery characteristics to oxygen gas, and could detect oxygen concentration as low as 1, 3, 5, and 10 ppm.

Thickness effect on properties of titanium film deposited by d.c. magnetron sputtering and electron beam evaporation techniques

This paper reports effect of thickness on the properties of titanium (Ti) film deposited on Si/SiO2 (100) substrate using two different methods: d.c. magnetron sputtering and electron beam (e-beam) evaporation technique. The structural and morphological characterization of Ti film were performed using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM). XRD pattern revealed that the films deposited using d.c. magnetron sputtering have HCP symmetry with preferred orientation along (002) plane, while those deposited with e-beam evaporation possessed fcc symmetry with preferred orientation along (200) plane. The presence of metallic Ti was also confirmed by XPS analysis. FESEM images depicted that the finite sized grains were uniformly distributed on the surface and AFM micrographs revealed roughness of the film. The electrical resistivity measured using four-point probe showed that the film deposited using d.c. magnetron sputtering has lower resistivity of ∼13xa0μΩcm than the film deposited using e-beam evaporation technique, i.e. ∼60xa0μΩcm. The hardness of Ti films deposited using d.c. magnetron sputtering has lower value (∼7·9xa0GPa) than the film deposited using e-beam technique (∼9·4xa0GPa).

Facile synthesis of single-crystalline rutile TiO2 nano-rods by solution method

Abstract A convenient and scalable technique for the synthesis of rutile titanium dioxide (TiO2) nano-rods was presented by using bulk TiO2 powder, sodium hydroxide (NaOH) and distilled water as raw materials. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) studies indicate that the prepared sample is crystalline and free from any impurities, however, it has no distinct shape and possesses a huge degree of agglomeration, and the average crystal size is around 40 nm. After annealing the sample at 600 °C for 2 h, it is observed through FESEM that nano-rods are formed. And XRD analysis shows that the nano-rods are single crystalline with distinct and smooth surfaces in different sizes with average length of about 1 µm and diameter of about 80 nm. Further UV-visible spectroscopy and Raman studies were conducted for the prepared sample and the band gap of the final product is found to be 3.40 eV.