Banca de DEFESA: JOSE EWERTON DA SILVA

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : JOSE EWERTON DA SILVA
DATE: 12/12/2023
TIME: 14:00
LOCAL: Programa de Pós-Graduação em Ciência de Materiais
TITLE:

ELECTROSYNTHESIS OF AQUEOUS TERNARY CADMIUM CHALCOGENIDE ALLOYS

KEY WORDS:

Quantum dots; Nanoalloys; Semiconductors; Voltammetry.

PAGES: 132
BIG AREA: Outra
AREA: Multidisciplinar
SUMMARY:

In this study, quantum dots (QDs) of CdS, CdSe, CdTe, as well as ternary compounds of CdSxSe1-x, CdSxTe1-x and CdTexSe1-x (where x varies from 0.15 to 0.85) were synthesized by electrochemical method in a cavity cell in aqueous medium, using 3- mercaptopropionic acid (MPA) as stabilizer, pH 9 and thermal treatment of 2 hours. The electrochemical process involved a paired electrolysis, in which elemental sulfur, selenium and tellurium were reduced in a graphite powder macroelectrode, simultaneously generating S2- /Se2- ;S2- /Te2- and Te2- /Se2- ions, while a cadmium rod was oxidized, producing Cd2+ for the efficient formation of the QDs in the desired ratio. The CdSxSe1-x QDs were characterized by means of X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), UV-Vis absorption and emission spectroscopies, as well as cyclic and linear voltammetric analyses. The XRD analysis revealed lattice parameters that showed a linear reduction tendency as the molar ratio of sulfide increases in the crystalline structure. The HRTEM analysis allowed the determination of the nanoparticle sizes, which were 3.94 ± 0.70 nm (CdS), 4.23 ± 1.00 nm (CdS0.5Se0.5) and 4.12 ± 0.78 nm (CdSe). The band gap energy (Egopt) of the CdSxSe1-x QDs was determined by UV-Vis absorption spectroscopy and ranged from 2.42 eV to 2.84 eV, showing an increase with sulfide addition in the structure. The same behavior was observed for the Eg Elect, determined by cyclic and linear voltammetric analyses, indicating the nanoalloy nature of the ternary QDs electrosynthesized. For the CdSxTe1-x and CdTexSe1-x QDs, characterizations were performed by means of XRD and UV-Vis absorption and emission spectroscopies. The XRD analysis of CdSxTe1-x and CdTexSe1-x also revealed lattice parameters with a linear reduction tendency as the molar ratio of selenide and sulfide increased, respectively, in the crystalline structure. The Egopt of the CdSxTe1-x and CdTexSe1-x QDs presented values from 2.29 eV to 2.84 eV, and 2.30 eV to 2.83 eV, respectively. The results obtained demonstrate that the electrochemical method used allows the preparation of mixed cadmium chalcogenides with controllable properties.

COMMITTEE MEMBERS:
Externo à Instituição - ANDERSON CAIRES DE JESUS - UFMG
Externa à Instituição - CAROLINA ELSZTEIN - UFPE
Interno - 2457389 - EDUARDO PADRON HERNANDEZ
Presidente - 1301548 - MARCELO NAVARRO
Interno - 1354207 - SEVERINO ALVES JUNIOR