Synthesis of radioactive and nonradioactive nanostructures through radiolytic and wet chemistry

In this work the synthesis of non radioactive and radioactive nanoparticles (NPs) through radiolytic and wet chemistry was studied. Non radioactive NPs of rhenium, iridium, and rhodium were synthesized from aqueous solutions containing the metal salt precursors by gamma irradiation. The solutions were irradiated to generate reducing species that led to the nucleation and growth of the nanoparticles. Amorphous rhenium oxide nanoparticles with average sizes ranging from 10 nm to 55 nm were obtained. Metallic iridium and rhodium nanoparticles were produced in polyvinyl-pyrrolidone (PVP) having narrow particle size distributions and average particle sizes from 2 nm to 6 nm. The stability of the NPs in PVP was explained based on the interaction of the metal with both of the functional groups, C-N and C=O, of the PVP. Iridium NPs supported on carbon nanotubes were also synthesized by gamma irradiation. The NPs were finely distributed on the surface of the nanotubes. The nanoparticle yield was found to increase with the radiation dose and the precursor concentration. The synthesis of radioactive NPs, specifically lanthanum phosphate containing ²²³Ra and ²²⁵Ra isotopes, was carried out in aqueous media using a precipitation method. The NPs crystallized in rhabdophane structure with a mean particle size of 3.4 nm and 6.3 nm for core and core-2 shells respectively. The ability of LaPO₄ NPs to retain the isotopes within their structure was investigated. It was found that core NPs retained up to 88% of the activity over a period of 35 days. It was also found that the addition of two LaPO₄ shells to the core NPs increases the retention ability up to 99.99%. This fact suggests that LaPO₄ NPs are potential carriers of radium isotopes for targeted alpha therapy. --Abstract, page iv

Production and characterization of supported palladium nanoparticles on multiwalled carbon nanotubes by gamma irradiation

Carbon nanotubes are being studied for a variety of applications due to their outstanding mechanical, chemical, electrical, and optical properties that make them interesting in different areas. Nowadays, different methods to modify the structure of the nanotubes are being developed in order to expand the application fields of such materials. In this work, palladium nanoparticles were directly produced and supported on multi-walled carbon nanotubes (MWCNT) by gamma irradiation. A solution with a 2:1 water-isopropanol ratio was prepared and mixed with palladium chloride as precursor of palladium ions. Radiolysis of water produces certain species that reduce the ions down to a zero-valent state. However, strong oxidizing agents are also produced during irradiation. Hence a scavenger, such as a secondary alcohol, has to be added to the solution in order to balance the reaction. Coalescence of the metal nanoparticles was controlled by the addition of the stabilizer sodium dodecylsulfate (SDS). The size and distribution of the nanoparticles on the nanotubes were studied at different surfactant concentration and radiation doses at a fixed concentration of palladium chloride. After irradiation, X-ray photoelectron spectroscopy revealed the palladium peaks Pd3d5/2 and Pd3d3/2 at binding energies of 335.9 and 341.1eV, respectively, which are characteristic of metallic palladium (Pd⁰), thus confirming the successful reduction of Pd⁺² to Pd⁰. Scanning transmission electron microscopy, and transmission electron microscopy were used for morphological characterization of the nanostructure Pd nanoparticles-CNTs. Nanoparticles obtained for doses between 10 and 40 kGy, ranged in size 5-30 nm. The smaller nanoparticles were obtained at the higher doses and vice versa. Histograms of particle size distributions at different doses are presented --Abstract, page iii