Simulation and Synthesis of Cobalt (Co) Nanoparticles by Gamma Radiation Technique

Cobalt nanoparticles were synthesized using the gamma radiolytic technique, and the particle size was found to be reduced from 12±1 to 7±1 nm by increasing the dose from 10 to 60 kGy. The UV-visible absorption spectra were measured and exhibited a steady absorption maxima at 517 nm in the UV region, which blue-shifted toward a lower wavelength with a decrease in particle size. By taking the conduction electrons of an isolated particle that are not entirely free but are instead bound to their respective quantum levels, the optical absorption of the cobalt nanoparticles can be calculated and simulated via intra-band quantum excitation for particle sizes comparable to the measured ones. We found that the simulated absorption maxima of electronic excitations corresponded to the measured absorption maxima. Moreover, the structural characterizations were performed utilizing dynamic light scattering (DLS), transmission electron microscopy (TEM), and X-ray diffraction (XRD).

Influence of Poly(vinylpyrrolidone) concentration on properties of silver nanoparticles manufactured by modified thermal treatment method

Very narrow and pure silver nanoparticles were synthesized by modified thermal treatment method via oxygen and nitrogen flow in succession. The structural and optical properties of the calcined silver nanoparticles at 600°C with diverse Poly(vinylpyrrolidone) concentrations varied from 2% to 4% were studied by means of different techniques. Fourier transform infrared spectroscopy was used to monitor the production of pure Ag nanoparticles at a given Poly(vinylpyrrolidone) concentration. The X-ray powder diffraction spectra are evidence for the transformation of the amorphous sample at 30°C to the cubic crystalline nanostructures at the calcination temperatures for all Poly(vinylpyrrolidone) concentrations. The transmission electron microscopy images showed the creation of spherical silver nanoparticles with the average particle size decreased by increasing Poly(vinylpyrrolidone) concentrations from 4.61 nm at 2% to 2.49 nm at 4% Poly(vinylpyrrolidone). The optical properties were investigated by means of UV-vis absorption spectrophotometer, which showed an increase in the conduction band of Ag nanoparticles with increasing Poly(vinylpyrrolidone) concentrations from 2.83 eV at 2% Poly(vinylpyrrolidone) to 2.94 eV at 4% Poly(vinylpyrrolidone) due to decreasing particle size. This was due to less attraction between conduction electrons and metal ions for smaller particle size corresponding to fewer atoms that made up the metal nanoparticles.

Size-Controlled and Optical Properties of Platinum Nanoparticles by Gamma Radiolytic Synthesis

Gamma radiolytic synthesis was used to produce size-controlled spherical platinum nanoparticles from an aqueous solution containing platinum tetraammine and polyvinyl pyrrolidone. The structural characterizations were performed using X-ray diffraction, and transmission electron microscopy. The transmission electron microscopy was used to determine the average particle diameter, which decreased from 4.4nm at 80kGy to 2.8nm at 120kGy. The UV-visible absorption spectrum was measured and found that platinum nanoparticles exhibit two steady absorption maxima in UV regions due to plasmonic excitation of conduction electrons, which blue shifted to lower wavelengths with a decrease in particle size. We consider the conduction electrons of platinum nanoparticles to follow Thomas-Fermi-Dirac-Weizsacker atomic model that they are not entirely free but weakly bounded to particles at lower-energy states {n = 5, l = 2 or 5d} and {n = 6, l = 0 or 6s}, which upon receiving UV photon energy the electrons make intra-band quantum excitations to higher-energy states allowed by the principles of quantum number that results the absorption maxima. We found an excellent agreement between the experimental and theoretical results, which suggest that the optical absorption of metal nanoparticles could be fundamentally described by a quantum mechanical interpretation, which could be more relevant to photo-catalysis and heterogeneous catalysis.

Structural and Optical Properties of Ag Nanoparticles Synthesized by Thermal Treatment Method

The modified thermal treatment method via alternate oxygen and nitrogen flow was successfully employed to synthesize very narrow and pure Ag nanoparticles. The structural and optical properties of the obtained metal nanoparticles at different calcination temperatures between 400 and 800 °C were studied using various techniques. The FTIR and EDX confirmed the formation of Ag nanoparticles without a trace of impurities. The XRD spectra revealed that the amorphous sample at 30 °C had transformed into the cubic crystalline nanostructures at the calcination temperature of 400 °C and higher. The TEM images showed the formation of spherical Ag nanoparticles in which the average particle size decreased with increasing calcination temperature from 7.88 nm at 400 °C to 3.29 nm at 800 °C. The optical properties were determined by UV-vis absorption spectrophotometer, which showed an increase in the conduction band of Ag nanoparticles with increasing calcination temperature from 2.75 eV at 400 °C to 3.04 eV at 800 °C. This was due to less attraction between conduction electrons and metal ions as the particle size decreases in corresponding to fewer numbers of atoms that made up the metal nanoparticles.