Microwave assisted synthesis of gold nanoparticles and their antibacterial activity against <i>Escherichia coli</i> (<i>E. coli</i>)

Arshi, Nishat,Ahmed, Faheem,Kumar, Shalendra,Anwar, M.S.,Lu, Junqing,Koo, Bon Heun,Lee, Chan Gyu Elsevier 2011 Current Applied Physics Vol.11 No.1

<P><B>Abstract</B></P><P>We report a simple one step microwave irradiation method for the synthesis of gold nanoparticles using citric acid as reducing agent and cetyl trimethyl ammonium bromide (CTAB) as binding agent. The reaction was completed under two different microwave irradiation times (40 s and 70 s) for the production of two types of gold nanoparticles. The synthesized nanoparticles were characterized using UV–Vis absorption spectroscopy and transmission electron microscopy (TEM) measurements. UV–Vis study revealed the formation of gold nanoparticles with surface plasmon absorption maxima at 590 and 560 nm for 40 and 70 s irradiation time respectively. From TEM analysis, it is observed that the gold nanoparticles have spherical shape with particle size distribution in the range 1–10 nm and 1–2 nm for 40 s and 70 s irradiation time respectively. Antibacterial activity of gold nanoparticles as a function of particle concentration against gram-negative bacterium <I>Escherichia coli</I> (<I>E. coli</I>) was carried out in solid growth media. The two types of gold nanoparticles show high antibacterial activity with zone of inhibition of about 22 mm against <I>E. coli</I> (ATCC 25922 strain). Very small difference in the antibacterial activity for the two types of gold nanoparticles were observed. Though nanoparticles synthesized for 70 s irradiation time show slightly better antibacterial activity.</P> <P><B>Highlights</B></P><P>► Gold nanoparticles have been successfully synthesized using microwave irradiation technique. ► The mean diameter was ∼ 4.05 nm for 40 s and ∼1.05 nm for 70 s. ► Characteristic absorption peak was found to be 590 nm for 40 s and 560 nm for 70 s. ► The zone of inhibition for the two types of nanoparticles was almost similar (22 mm). ► Smaller size nanoparticles synthesized for 70s showed a slightly better antibacterial action.</P>

Observation of the magnetic entropy change in Zn doped MnFe2O4 common ceramic: Be cool being environmental friendly

Anwar M.S.,Koo Bon Heun 한국물리학회 2022 Current Applied Physics Vol.39 No.-

We report the detail investigation on the magnetic and magnetocaloric behaviour of polycrystalline Mn1-xZnxFe2O4 (0.0 ≤ x ≤ 0.7) ferrite. The magnetization analysis shows that the increase of Zn concentration in the samples results in decrease of saturation magnetization. The maximum magnetic entropy change, |ΔSmMax| is evaluated through M-H isotherms measurements and takes values of 1.25, 1.11, 1.07, and 0.64 Jkg-1K-1 for x = 0.0, 0.3, 0.5, and 0.7, respectively under a maximum applied magnetic field of 2.5 T. The corresponding relative cooling power (RCP) for these samples were found to be 102, 162, 96, and 89 Jkg-1 for x = 0.0, 0.3, 0.5, and 0.7, respectively. After the comparison of the obtained values of |ΔSmax M| and RCP with those reported earlier for the other compounds, recommend to explore such common soft ferrites based materials for magnetic refrigeration.

Study of Magnetocaloric Effect in (1—y)La_0.7Sr_0.3MnO₃/(y) Mn_0.5Zn_0.5Fe₂O₄ Composite

Anwar, M. S.,Cho, Hyeon Ji,Hussain, Imad,Koo, Bon Heun American Scientific Publishers 2016 Journal of Nanoscience and Nanotechnology Vol.16 No.11

<P>The structural, magnetic and magnetocaloric properties of (1-y)LSMO/(y)Mn0.5Zn0.5Fe2O4 (y = 0.00, 0.03, 0.05, 0.10) composite samples have been studied. All samples show mainly pervoskite phase with rhombohedral crystal lattice. The XRD peaks of Mn0.5Zn0.5Fe2O4 phase were not observed because of its very low concentration in the composite sample. The magnetization measurement reveals that the Curie temperature, T-C decreases significantly with increasing the Mn0.5Zn0.5Fe2O4 concentration in the composite samples. On the other hand, the temperature range of paramagnetic-ferromagnetic transition becomes broader in case of composite samples. The magnetic entropy evaluation shows that the Delta S-M(max) decreased in case of composite samples as compared to that of pure LSMO sample. In addition, an enhanced relative cooling power of 57 J/kg (at 1 T) was observed for the (0.97) LSMO/(0.03)Mn0.5Zn0.5Fe2O4 composite sample, which is due to the increased partial derivative T-FWHM over 62 K around room temperature.</P>

Enhanced relative cooling power of Ni_1-xZn_xFe₂O₄ (0.0≤x≤0.7) ferrites

Anwar, M.S.,Ahmed, F.,Koo, B.H. Elsevier Science 2014 Acta materialia Vol.71 No.-

We report on a detail study of the structural, magnetic and magnetocaloric properties of Zn-doped nickel-zinc ferrites with different Zn concentrations. Polycrystalline Ni<SUB>1-x</SUB>Zn<SUB>x</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> (0.0≤x≤0.7) ferrite samples were prepared using the conventional solid-state reaction method. The X-ray diffraction results indicate that the ferrite samples have a cubic spinel type structure without any impurity phase. Temperature-dependent magnetization measurements and Arrott analysis reveal second-order ferromagnetic transition in all samples, with the Curie temperature decreasing progressively with increasing Zn concentration, from ~845K for x=0.0 to 302K for x=0.7. An increase in magnetization at low temperature was observed for Zn doping up to x=0.5. A maximum in magnetic entropy change, |ΔS<SUB>M</SUB><SUP>max</SUP>| (~1.39Jkg<SUP>-1</SUP>K<SUP>-1</SUP> at 2.5T), was observed in the Ni<SUB>0.7</SUB>Zn<SUB>0.3</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> sample. The width of magnetic entropy curve was found to increase with the Zn concentration. Also, the |ΔS<SUB>M</SUB><SUP>max</SUP>| and relative cooling power were found to increase with increasing applied magnetic field, which indicates much greater cooling power is expected with a larger magnetic field. This investigation suggests that Ni<SUB>1-x</SUB>Zn<SUB>x</SUB>Fe<SUB>2</SUB>O<SUB>4</SUB> (0.0≤x≤0.7) ferrite samples are possible candidates for magnetic refrigeration across a wide range of working temperatures.

Effect of Zn on the Magnetic and Magnetocaloric Properties of (0.95)La0.7Ca0.3MnO3/(0.05)Mn1−x Zn x Fe2O4 Composites

Hussain, I.,Anwar, M. S.,Lee, S. R.,Koo, B. H. Springer Science + Business Media 2015 Journal of superconductivity and novel magnetism Vol.28 No.11

<P>We report the structural, magnetic, and magnetocaloric properties of (0.95)La0.7Ca0.3MnO3/(0.05)Mn1-x Zn (x) Fe2O4 (x = 0.0, 0.1, 0.3, 0.5) composites. Polycrystalline samples of the composite material were prepared using the solid-state reaction method. The phase purity and structure of the samples were confirmed using the X-ray powder diffraction (XRD) method. Scanning electron microscope (SEM) studies of the samples reveal that Mn1-x Zn (x) Fe2O4 is mainly distributed at the surface and grain boundaries of the perovskite matrix La0.7Ca0.3MnO3. The variation of magnetization (M) as a function of temperature and applied magnetic field was investigated. The M-T data plots indicate a paramagnetic to ferromagnetic transition upon cooling in all samples. The magnetic entropy change was also studied through the examination of measured magnetic isotherms, M (H, T) near Curie temperature T (C) . A magnetocaloric effect has been estimated in terms of isothermal magnetic entropy change. A maximum entropy change value of 1.72 J/kg K was recorded for a magnetic field change of 3 T with a relative cooling power (RCP) value of 177 J/kg for the (0.95)La0.7Ca0.3MnO3/(0.05)MnFe2O4 composite sample.</P>

Effect of Ni substitution on structural, morphological and magnetic properties of Zn_1-xNi_xO nanorods

Ahmed, F.,Arshi, N.,Anwar, M.S.,Lee, S.H.,Byon, E.S.,Lyu, N.J.,Koo, B.H. Elsevier 2012 Current Applied Physics Vol.12 No.suppl2

We report the preparation of Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods through a chemical route using microwave irradiation. The obtained Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Raman spectroscopy and magnetization measurements. XRD and TEM results showed that the Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods have single phase nature with wurtzite structure and Ni was successfully incorporated at Zn site into the ZnO. The shape of the nanorods changed from hexagon (length ~1.5 μm, diameter ~200 nm) to pencil like tip (length ~1 μm, diameter ~80 nm) by only changing the Ni content from 1% to 3% in ZnO. Concerning the Raman scattering spectra, the modification in the intensity of E<SUB>2</SUB><SUP>high</SUP> mode and sub-band edge emissions provides enough evidence for the existence of intrinsic defects associated with the O atoms. Magnetic measurement results revealed that Zn<SUB>1-x</SUB>Ni<SUB>x</SUB>O nanorods show the well-defined ferromagnetic features at room temperature and the value of M<SUB>s</SUB> increased with the increase of Ni concentration.

Cloning and expression of the insecticidal toxin gene “tccB” from Photorhabdus temperata M1021 in Escherichia coli expression system

Eun-Kyung Jang,정병권,Gun-Seok Park,Abdur Rahim Khan,Sung-Jun Hong,박영준,WON-CHAN KIM,JAE-HO SHIN,Khalid M S Al-Ghamdi,Bassam Oudh Al-Johny,Yasir Anwar,Muhammad Faisal Siddiqui,Ihsan Ullah 한국응용곤충학회 2020 Journal of Asia-Pacific Entomology Vol.23 No.1

Photorhabdus spp. has a high molecular weight Tc toxin with insecticidal activity. These toxins have been suggested as an alternative to BT toxin from Bacillus thuringiensis. Herein, we constructed a cosmid library with the genome of M1021 and screened the Escherichia coli clones showing insect toxicity by injecting each clone into Galleria mellonella larvae. In a total of 1020 clones, one clone with high insecticidal activity was selected and the nucleotide sequence of the cosmid of the clone was determined. In cosmid PtC28, a gene with 87% homology to the tccB gene of Photorhabdus temperata was found. Consequently, we have isolated the tccB gene cassette from the M1021 and expressed in E. coli expression vectors. The toxin was produced in the form of inclusion bodies but the denatured and refolded recombinant TccB showed strong mortality to the G. mellonella larvae.

Above room temperature magnetic transition and magnetocaloric effect in La_0.66_Sr_0.34_MnO₃

M. S. Anwar,샤런드라쿠마르,Faheem Ahmed,Nishat Arshi,김근우,구본흔 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.10

In this study, the magnetic and the magnetocaloric properties of the La0.66Sr0.34MnO3 (LSMO) compound were investigated. The X-ray diffraction result indicates that the LSMO sample has a single phase of rhombohedral symmetry without any impurity phase. The magnetic study reveals that the specimen La0.66Sr0.34MnO3 exhibits a ferromagnetic-paramagnetic transition at TC ∼ 376 K. Using Arrott plots, the phase transition from ferromagnetic to paramagnetic is found to be of second order. A maximum magnetic entropy change of 1.25 J/kgK has been observed for a low applied magnetic field of 1T. The relative cooling power values exhibit a nearly linear dependence on the applied magnetic field. Moreover, the analysis of the magnetocaloric effect (MCE) using the Landau theory o f phase transitions shows good agreement with the experimental results, confirming the importance of magnetoelastic coupling and electron interactions in the magnetocaloric properties of perovskite manganites. This investigation suggests that La0.66Sr0.34MnO3 can be used as a potential magnetic refrigeration material.

Dimensionality dependent magnetic and magnetocaloric response of La0.6Ca0.4MnO3 manganite.

Anwar, M S,Ahmed, Faheem,Koo, Bon Heun American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.11

<P>We report the sol-gel synthesis and impact of reduced dimensionality on the magnetocaloric properties of La0.6Ca0.4MnO3 manganite. The synthesized powders were characterized by using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and magnetization measurements. The XRD results indicated that the La0.6Ca0.4MnO3 nanoparticles have single phase nature with orthorhombic structure. FE-SEM results suggested that the nanoparticles are agglomerated and crystallite size increases with the annealing temperature. Magnetization measurements show that the La0.6Ca0.4MnO3 nanoparticles exhibit transition temperature (T(c)) below room temperature. The transition temperature was found to increase with the increasing the crystallite size. Maximum in magnetic entropy change, (δS(M))(max) shows interesting behaviour and was found to vary with the particle size. At magnetic field of 1 T, the value of (δS(M))(max) - 0.13 J/kg K was observed at 213 K for the sample annealed at 600 degrees C. Also, the increment in the value of (δS(M))(max) was observed at higher annealing temperature. This study shows that the magnetic entropy of pervoskite manganite can be tuned by tuning the crystallite size of the manganites.</P>

Microwave Assisted Hydrothermal Synthesis and Magnetocaloric Properties of La_0.67Sr_0.33MnO₃ Manganite

Anwar, M. S.,Kumar, Shalendra,Ahmed, Faheem,Kim, G. W.,Koo, Bon Heun American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.7

<P>We report microwave assisted hydrothermal synthesis and magnetocaloric properties of La0.67Sr0.33MnO3 manganite. The synthesized La0.67Sr0.33MnO3 nanoparticles was characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS) and magnetization measurements. The XRD results indicated that La0.67Sr0.33MnO3 nanoparticles have polycrystalline nature with monoclinic structure. FE-SEM results suggested that La0.67Sr0.33MnO3 nanoparticles are assembled into rod like morphology. Magnetization measurements show that La0.67Sr0.33MnO3 nanoparticles exhibit transition temperature (Tc) above room temperature. The maximum magnetic entropy change (deltaS(M))max was found to be 0.52 J/kg K near Tc approximately 325 K at applied magnetc field of 20 kOe. This compound may considered as potential material for magnetic refrigeration near room temperature.</P>