Abstract: This review is an attempt to highlight some of the significant results of the work carried out on the photoluminescence from nanoparticles of the noble metals, particularly gold and silver, over the past two decades. Although quite an immense amount of reports can be found, those that have contributed in throwing some light on the underlying mechanism behind photoluminescence have been considered here. Interband radiative recombination of electrons in metals or photoluminescence (PL), though very weak, was first reported in Au, Cu and Au-Cu alloys. A simple model attributes the PL to the radiative recombination of conduction band electrons below the Fermi energy with d-band holes. Most of the mechanisms are based on this concept. Only small sized clusters are known to exhibit luminescence, with the appearance of additional features which changed with the surfactants suggesting ligand to metal charge transfer. Further, the observation that more polar ligands do indeed enhance the luminescence intensity supports ligand to metal charge transfer. A non-radiative decay of excited electrons from 6sp-band to interface electron energy levels or bands (IEEB), that could be created due to charge transfer from the ligand to the metal core, followed by radiative recombination of electrons from these levels with the hole in the d-band could be another possible mechanism, which is supported by the size independence of the PL emission peak position. However, it is possible that these mechanisms operate independently or even simultaneously depending on various factors like size, ligands, dispersion medium, particle surface topography and so on.
Abstract: Two different batches of Gallium (III) sulphide nanocrystals, (α-Ga2S3)1 and (α-Ga2S3)2 were synthesized at room temperature by the reaction of Gallium (III) chloride with sodium thiosulphate in water for 10 and 20 min respectively. The resultant nanoparticles were characterized by different spectroscopic techniques. TEM micrographs showed well-defined, close to hexagonal particles, and the lattice fringes in the HRTEM images confirmed their nanocrystalline nature. The sizes of (α-Ga2S3)1 and (α-Ga2S3)2 were 12 and 35 nm respectively with similar morphologies. Optical band gap energies (3.43 eV/3.41 eV) and photoluminescence peaks 635/641 nm (red shift) and 414/420 nm (blue shift) of the synthesized α-Ga2S3 nanocrystals suggest that they may be promising photocatalysts. Raman spectra for the α-Ga2S3, shows very sharp bands at 119, 135 and 148 cm-1 due to Ga-S2 scissoring.
Abstract: Gold nanoparticles were synthesized in chitosan suspension by one-pot chemical reduction method without any chemical reducing reagent. In aqueous acidic medium, chitosan exhibits polycationic nature due to protonation of amine groups of each glucosamine repeating units. The adsorption of AuCl4- ions occurs on chitosan through electrostatic attraction and further reduction of Au3+ to Au0 proceeds through a three electron transfer mechanism by oxidation of protonated amine groups of chitosan chain. The change of color from dirty yellow to intense red indicates the formation of gold nanoparticles in chitosan suspension which acts as both reducing and stabilizing agent. Characterization techniques such as UV-VIS, FTIR, Zeta potential measurement, FESEM and TEM were carried out in order to examine the reduction and stabilization phenomena rendered by chitosan.
Abstract: Pyrazinamine (PZA) is one of the most commonly prescribed anti-tuberculosis (anti-TB) drug due to its ability to significantly shorten the TB treatment period. However, excess PZA in the body causes hepatotoxicity and liver damage. This, therefore, calls for new methods for ensuring reliable dosing of the drug, which will differ from person to person due to interindividual differences in drug metabolism. A novel biosensor system for monitoring the metabolism of PZA was prepared with nanocomposite of multi-walled carbon nanotubes (MWCNTs), polyaniline (PANI) and cytochrome P450 3A4 (CYP3A4) electrochemically deposited on a glassy carbon electrode (GCE). The nanocomposite biosensor system exhibited enhanced electroactivity that is attributable to the catalytic effect of the incorporated MWCNTs. The biosensor had a sensitivity of 7.80 μA/μg mL-1 PZA and a dynamic linear range of 4.92 160 ng/mL PZA.
Abstract: Nanocrystalline ZnO powders have been synthesized by a novel and simple microwave-assisted combustion synthesis method using urea, glycine, carbohydrazine and citric acid as fuels and zinc nitrate as oxidant. The starting materials were directly mixed and a slurry precursor with high homogeneity was formed due to the hygroscopicity of the reactants. The precursor could be ignited at room temperature, resulting in dry, loose and voluminous ZnO powders. An interpretation based on an adiabatic flame temperature, amount of gases produced during reaction for various fuel-to-oxidizer molar ratios (ψ), has been proposed for the nature of combustion and its correlation with the characteristics of as-synthesized product. The variation of adiabatic flame temperature (Tad) with the ψ value was calculated theoretically according to the thermodynamic concept. The reaction process of the precursor was investigated by XRD techniques.