The resulting structures allow for the synthesis of nanoparticles of cadmium sulfide at high temperatures
Studies of semiconductor nanoparticles, also called quantum dots, are rapidly growing in the last twenty years. Using such systems, due to their optical properties, is very attractive in the field of optoelectronics and bioanalytics.
The presently known methods of obtaining high quality crystals chalcogenids were investigated metals, including cadmium sulfide, based on the high organometallic synthesis (above 300 ° C), which requires, inter alia, the use of surfactants to stabilize the resulting nanoparticles. Typical temperatures for such polymers are thermal decomposition, which makes it impossible to obtain metallpolimernogo composite. But, it turned out, this problem has a solution.
Scientists of the Institute of organometallic compounds them. Nesmeyanov Academy of Sciences, together with colleagues from the University of Indiana (Indiana University, USA) was first used for cadmium sulfide nanocrystals synthesized by them polifenilenpiridilnye dendrimers (individual hyperbranched molecules with a high molecular weight), and investigated the effect of dendrimer architecture and the reaction conditions on the formation of cadmium sulfide nanoparticles.
Initially, the researchers were able to synthesize dendrimers, which are composed of phenyl and pyridine fragments. These structures have a high heat resistance and allow the synthesis of nanocomposites at high temperatures, and has been proven in the experiment.
To create nanocomposites scientists introduced into a solution of cadmium oxide dendrimer benzyl ether at high temperatures (265 ° C) and then injected in the same slurry solution of sulfur. Then the temperature was lowered to 30 ° C, accompanied by the formation and growth of oxide nanoparticles. To adjust the size of the nanoparticles, researchers had determined optimal conditions for the reaction, since it was found that not all the dendrimer molecules form a composite with cadmium sulphide — in the synthesis process may form aggregates of the polymer molecules with each other.
Use of dynamic light scattering and transmission electron microscopy identified size and particle size distribution of nanocomposites.
Based on the simple arithmetical reasons, the diameter of a particle nanocomposite CdS-FAP should include the sum of the diameter of the nanoparticles of cadmium sulfide (about 3.2 nm) plus 2 times the diameter of the dendrimer molecule. In general, the amount of such nanocomposite units must be of the order of 14 nanometers. According to the same dynamic light scattering, the size of the nanocomposite particles are much smaller. Therefore, the authors suggested that the dendrimer molecules enshroud nanoparticles of cadmium sulfide, forming an interpenetrating through the branches of the dendrimer shell, thereby reducing the estimated size of the composite unit. Scientists have proved that the CdS nanoparticles are not encapsulated within the cavity of a single dendrimer molecules, and are surrounded by several of its molecules.
Thus, the researchers found that dendrimer acts as a heat-stable matrix, allowing at the same time stabilize the nanoparticles of cadmium sulfide, and control their size. He also serves as a unique control agent nanoparticle formation of atypical structure.
Having studied the optical properties of the composite CdS-TFG and encouraged by the results received by the photoluminescence efficiency, the team concluded that the studies provide a basis for the development of areas in the chemistry of nanomaterials, based on dendrimers and metallic nanoparticles. In the practical application of the resulting composite can be used to create images in the displays of the new generation.
Source of information:
Nina V. Kuchkina, David Gene Morganb, Barry D. Steinc, Lada N. Puntusa, d, Alexander M. Sergeev, Alexander S. Peregudov, Lyudmila M. Bronsteinb, Zinaida B. Shifrinaa. Polyphenylenepyridyl Dendrimers as Stabilizing and Controlling Agents for CdS Nanoparticle Formation. Nanoscale.