Influence of Dose on Particle Size and Optical Properties of Colloidal Platinum Nanoparticles

Abstract

Attempts to produce colloidal platinum nanoparticles by using steady absorption spectra with various chemical-based reduction methods often resulted in the fast disappearance of the absorption maxima leaving reduced platinum nanoparticles with little information on their optical properties. We synthesized colloidal platinum nanoparticles in an aqueous solution of polyvinyl pyrrolidone by gamma radiolytic reduction method, which produced steady absorption spectra of fully reduced and highly pure platinum nanoparticles free from by-product impurities or reducing agent contamination. The average particle size was found to be in the range of 3.4–5.3 nm and decreased with increasing dose due to the domination of nucleation over ion association in the formation of metal nanoparticles by the gamma radiolytic reduction method. The platinum nanoparticles exhibit optical absorption spectra with two absorption peaks centered at about 216 and 264 nm and the peaks blue shifted to lower wavelengths with decreasing particle size. The absorption spectra of platinum nanoparticles were also calculated using quantum mechanical treatment and coincidently a good agreement was obtained between the calculated and measured absorption peaks at various particle sizes. This indicates that the 216 and 264-nm absorption peaks of platinum nanoparticles conceivably originated from the intra-band transitions of conduction electrons of (n = 5, l = 2) and (n = 6, l = 0) energy states respectively to higher energy states. The absorption energies, i.e., conduction band energies of platinum nanoparticles derived from the absorption peaks increased with increasing dose and decreased with increasing particle size.

Structural, Optical and Electrical Properties of PVA/PANI/Nickel Nanocomposites Synthesized by Gamma Radiolytic Method

“…The particle size decreased exponentially with increasing of dose from 10 to 50 kGy. This finding of decreasing particle size of metal nanoparticles with increasing dose is in agreement with the studies carried out previously [38,39]. At low doses, the nucleation concentration, Ni n ions, therefore, the Ninanoparticles were smaller in size at higher doses [34]: The morphology of composites PVA/PANI/Ni nanoparticles were studied by scanning electron microscope (SEM) shown in Figure 4.…”

“…Recently, optical absorption of metal nanoparticles based on quantum mechanics has been proposed [43,44] and confirmed experimentally [38,45]. In this theory of metal nanoparticles, the absorption of light can be described as a result of non-radiative intra-band excitations of conduction electrons from the lowest energy state assigned by the quantum numbers to higher energy states near the Fermi level of the conduction band.…”

Surface properties and catalytic performance of Pt–Ag supported on silica – The effect of preparation methods

“…290 nm is recorded for both above mentioned bimetallic materials. It can correspond to different cationic species made with both, platinum and silver [46][47][48][49][50].…”

Formation of a Colloidal CdSe and ZnSe Quantum Dots via a Gamma Radiolytic Technique

“…Hydroxyl and hydrogen radicals (OH * and H * ) are also strong oxidizing agents in aqueous colloidal solution. Therefore, to prevent their reactions, isopropanol (IPA) was added to the precursor solutions [27]. All organics in the reactant medium including PVP and IPA, can scavenge OH * and H * radicals and can simultaneously change into PVP and IPA radicals by the following reaction [33].…”

“…This technique was originally used for the synthesis of colloidal silver nanoparticles [25,26], colloidal platinum nanoparticles [27], and colloidal nickel-aluminum and copper-aluminum alloy nanoparticles [28,29], where the particle size of metal nanoparticles was found to decrease with increasing gamma radiation dose. This observation was explained by the competition between the nucleation and aggregation processes, where higher-dose nucleation dominates over aggregation, which allows for particle growth in which smaller particles are likely to be produce [30].…”