Aim:We report synthesis of capped gold nanoparticles (C-AuNPs) of ≈20–30 nm by reducing HAuCl4 with flower and leaf extracts of Ocimum tenuiflorum, leaves of Azadirachta indica and Mentha spicata and peel of Citrus sinensis plants.Methods:Atomic force microscopy (AFM) and transmission electron microscopy (TEM) determined their size, shape and topographical structures. The C-AuNPs with UV-Vis spectrophotometer produced a maximum absorption within 530–535 nm wavelengths. Their Fourier transform IR stretching frequencies, from 450 to 4000 cm-1, have inferred HAuCl4 reduction to Au.Results:The 512 and 600 μgml-1 C-AuNP MICs were expressed on antimicrobial strains Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae, respectively.Conclusion:The chosen plant extracts have reduced the Au3+ to Au0 with simultaneous in situ capping with bacteria inhibiting activities. Green routes for C-AuNP synthesis could be an asset for several other biomedical and bioengineering applications.

Microwave irradiation was employed for spherical-shaped platinum nanoparticle (Pt NPs) preparation. Spherical Pt NPs indexed with (111) facets were prepared using Pt(II) precursor salt, glycerol as solvent and reducing agent, and polyvinylpyrrolidone (PVP) as a shape directer under microwave irradiation for 3–5 min at 300 °C. Electron spin resonance (ESR) peak at 336.000 mT (milli Tesla) confirmed the free radical formation from aqueous glycerol solution which acted as reducing species under microwave. The 2–8-nm diameter of particles was obtained by high-resolution transmission electron microscope. Dynamic light scattering was used to optimize the microwave dose followed by 33 and 48 nm size and 51 and 67 mV zeta potential of Pt NPs, respectively. The PVP was demonstrated as shape controlling agent investigated by Fourier transmission infrared spectroscopy (FTIR). The electrocatalytic performance of as-prepared Pt colloids was investigated using cyclic voltammetry which showed a higher catalytic activity for ethanol redox reaction.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1653-9) contains supplementary material, which is available to authorized users.

The Cu nanoparticles (Cu NPs) were grown in soda-lime glass matrix through Cu+ ↔ Na+ ion exchange methods under thermal annealing in an open environment and studied variation in their size on tunable plasmonic behaviour, optical absorption spectra and photoluminescence (PL). A blue shift from 570 to 560 nm was observed in localized surface plasmon resonance (SPR) of Cu NPs from 550 to 650 °C. A mutual relation between size and surface plasmon resonance with full width half maxima (FWHM) has been derived for plasmonic properties at variable temperatures. Structural investigations of embedded Cu NPs have been confirmed by using HRTEM and EDX. Grazing incidence X-ray diffraction (GIXRD) had identified a crystalline nature of Cu NPs under annealed conditions. XPS, Raman and secondary ion mass spectroscopies (SIMS) have identified an embedding behaviour of Cu NPs in glass matrix. Plasmonic and thermodynamic properties of embedded Cu NPs have explained their in situ thermal growth mechanism for efficient distribution where enthalpy (∆H), entropy (∆S) and Gibbs free energy (∆G) have interpreted their temperature driven Cu NPs growth. An interdependence of ∆H, ∆S and ∆G has been developed vis-a-vis activation energy on an extent of 12.54 J/mol.

Optical properties of noble metal nanostructures associated with localized surface plasmon resonance (SPR) are technically important for optical switches and plasmonic devices. In this work, silver nanoclusters are embedded inside the soda-lime glass matrix, followed by a thermal annealing process in an open air atmosphere for 1 h. The effects of thermal annealing on the plasmonic behavior of Ag nanoclusters embedded in the glass matrix are studied with UV–vis spectroscopy and photoluminescence. In the SPR spectra, a 14 nm blue shift is observed in the visible range under the influence of thermal annealing at a higher temperature. The thermal effects on Ag particle size and SPR have been illustrated for plasmonic properties. The structural and elemental investigation of as-grown Ag nanoclusters is confirmed by X-ray diffraction, high-resolution transmission electron microscope, and X-ray photoelectron spectroscopy. The structural, plasmonic, and thermodynamic properties associated with the growth mechanism of Ag nanoclusters have been explained under the thermal process. Enthalpy (Δ H ), entropy (Δ S ), and Gibbs energy (Δ G ) for Ag nanoclusters growth and nucleation are significantly calculated and interpreted at different temperatures. An empirical relation among the Δ H , Δ S , and Δ G is developed vis-a-vis activation energy (97.70 J/mol), which is calculated by the Arrhenius linear equation.

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