CONFINEMENT ENERGY OF QUANTUM DOTS AND THE BRUS EQUATION

A review of the ground state confinement energy term in the Brus equation for the bandgap energy of a spherically shaped semiconductor quantum dot was made within the framework of effective mass approximation. The Schrodinger wave equation for a spherical nanoparticle in an infinite spherical potential well was solved in spherical polar coordinate system. Physical reasons in contrast to mathematical expediency were considered and solution obtained. The result reveals that the shift in the confinement energy is less than that predicted by the Brus equation as was adopted in most literatures.

A Comparative Study of Theoretical Methods to Estimate Semiconductor Nanoparticles’ Size

In this paper, we compare four different methods to estimate nanoparticle diameters from optical absorption measurements, using transmission electron microscopy (TEM) images as a reference for the nanoparticle size. Three solutions of colloidal nanoparticles coated with thiophenol with different diameters were synthesized by thiolate decomposition. The nanoparticle sizes were controlled by the addition of a certain volume of a 1% sulphur solution in toluene. TEM measurements showed that the average diameter for each type of these nanoparticles was 2.8 nm, 3.2 nm, and 4.0 nm. The methods studied for the calculation of the nanoparticles diameter were: The Brus model, the hyperbolic band model (HBM), the Henglein model, and the Yu equation. We evaluated the importance of a good knowledge of the nanoparticle bandgap energy, and the nature of electronic transitions in the semiconductor. We studied the effects that small variations in the electron and hole effective mass values produced in the Brus equation and in the HBM model for CdS, PbS, and ZnS nanoparticles. Finally, a comparison was performed between the data provided by these models and the experimental results obtained with TEM images. In conclusion, we observed that the best approximation to the experimental results with TEM images was the Brus equation. However, when the bandgap energy was close to the bulk bandgap energy, the theoretical models did not adjust correctly to the size measured from the TEM images.

Hydrogen evolution from water using CdS as photosensitizer

Colloidal chemical approaches are increasingly utilised for the preparation and stabilization of semiconductor nanoparticles.We prepared a colloidal CdS in excess ofNa2Susing a method described in the literature and determined the particle size from its absorption spectrum by Brus equation. A diameter of about 50Å was calculated. For the stabilization of colloid we choosed from various tested polymers a 1% in weight copolymer (1/1), styrene/maleic anhydride. As redox catalyst we used colloidal Pt obtained “in situ” by irradiaton ofPtCl6K2. We established the role of each of the system partners as: CdS concentration,Na2Sexcess, Pt catalyst concentration, the irradiation time, and the system temperature. We studied the influence of each participant to the hydrogen evolution in order to optimize this system.The formation of nanosize composite particlesCd1−xZnxSshowed an increasing ofH2amount generated under irradiation, in comparison with CdS particles.The results obtained permitted us to calculate the turnover number (TO) of the system.