دراسة الخواص البصرية و التركيبية لكبريتيد الكادميوم كونتم دوت المحضرة بوساطة الطرائق الكيميائية و الخضراء

Studying the Optical and Structural Properties for Semiconductor CdS Quntum Dot Using Chemical and Green Methods

Abstract
The CdS quantum dot were prepared successfully using chemical precipitation technique. CdCl2 and Na2S were utilized as precursors for Cd ions and sulfide ions in aqueous media, respectively. The effect of reaction temperature, reaction time and pH values on the growth process of CdS particles were investigated realizing that 30 oC , 6 hours and pH 11 are the best conditions for producing CdS nanoparticles. Structural features showed that CdS particles have a nearly spherical shape and the EDS measurement confirmed the presence of both cadmium and sulfur atoms in as-prepared particles. The band gap energy was calculated from the UV-Vis spectrum ~2.66 eV, which is high compared to that of bulk CdS (2.42 eV). XRD pattern showed that the zinc blend phase is dominated and the Crystal size was estimated to be around 3.2 nm using the Scherrer formula.
CdS nanometre-sized particles have also been prepared using an eco-friendly and low-cost method. This method relies on using parts of plants as reducing agents and protecting agents. Here, the synthesis of CdS nanoparticles using avocado peel extract, which converts Cd2+ to Cd atoms and then forms CdS nanoparticles, has been reported for the first time. The influence of pH, concentration of peel extract, and reaction time on the formation process of as-prepared CdS nanoparticles were studied. The structural properties of CdS nanoparticles were investigated using electron microscopic techniques Such as (FE-SEM and TEM), and a majority of CdS particles with elongated to spherical shapes were observed. The crystalline structure of CdS nanoparticles face-centered cubic (FCC) was confirmed using X-ray diffraction, and the Crystallites size was estimated from the Scherrer equation at nearly 2.5 nm.
Furthermore, in this work, the effect of the addition of poly Ethylene glycol polymer (PEG-4000) to CdS nanoparticles formed in the presence of Avocado was investigated through adding. This is to study the polymer’s effect on the prepared nanomaterial by studying the linear optical properties of the mentioned solutions, which include absorption spectra (A), emission spectra (T), reflectivity (R), linear absorption coefficient (α), attenuation coefficient (K) and refractive index (n) through:
Firstly: Dissolving different weights of cadmium sulfide nanoparticles (0.05, 0.1, 0.15, and 0.2) g in a fixed volum of the polymer solution (10 mL), where the effect of the nanomaterial on the spectrum of the polymer was shown through increasing the absorption spectrum with redshift of the absorption peak towards larger wavelengths. As a result, this nano-compound can be used to purify polluted water by increasing the polymer’s absorption of organic dyes in the water.
Secondly: Fixing the quantity of the cadmium sulfide nanoparticles solution (10 mL) with different weights of polymer (5×10-4, 5×10-3, 1×10-1, and 1.5×10-1)g. There was a significant effect of the polymer on the properties of the nanomaterial by investigation of the optical properties, where it is observed a decrease in absorption with a blueshift towards shorter wavelengths, an indication of the increase of the nanoscale properties through the nanoscale area of adsorption. Furthermore, increasing the energy gap of the compounds upon the increase of the polymer was another evidence of the nanosize according to the principle of quantum confinement, where the energy gap values were (3.96, 4.40, 4.44) eV at PEG values (5×10-4, 5×10-3 , and 1×10-1)g, respectively. However, when the polymer weight was increased up to 1.5 × 10-1 g, the energy gap decreased to 3.88 eV, that could be obtained better optical properties at this weight of the polymer.