Banca de DEFESA: NIVALDO FREIRE DE ANDRADE NETO

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : NIVALDO FREIRE DE ANDRADE NETO
DATE: 04/02/2022
TIME: 14:00
LOCAL: Sala virtual (videoconferência)
TITLE:

Synthesis, characterization and study of the photocatalytic properties of the stable (a) and metastable (b and g) phases of silver tungstate

KEY WORDS:

Coprecipitation; a-Ag₂WO₄; b-Ag₂WO₄; g-Ag₂WO₄; photocatalytic properties.

PAGES: 92
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

In this work, all phases of silver tungstate (Ag₂WO₄) were obtained by the co-precipitation method. The stable phase (a-Ag₂WO₄) was studied by varying the precipitation temperature between 10 and 90 °C, while the metastable phases (b-Ag₂WO₄ and  g-Ag₂WO₄) were obtained by increasing the pH and using Polyvinylpyrrolidone (PVP) as surfactant. The diffractograms indicate that the temperature range used for the stable phase provides powders with high crystallinity and absent from secondary crystalline phases. Increasing the precipitation temperature from 10 to 90 °C alters the cross section of the square to hexagonal rods, and also changes the character of the particles, as shown by the tests against anionic and cationic dyes (methyl orange and methylene blue), the particles with square cross section have cationic character, while the hexagonal, anionic. The character of the particles directly influences the photocatalytic activity, where the powders obtained at higher temperatures have greater photocatalytic efficiency over methylene blue, while those obtained at lower temperatures, to orange. The metastable phases were obtained by raising the reaction pH to 10 and using PVP as a surfactant. The diffractograms indicated inhibition of a-Ag₂WO₄ when at least 0.1 g PVP was used. The g-Ag₂WO₄ phase, the main objective of this study, was stabilized using 0.3 g of PVP, without formation of any secondary phases, while in higher or lower amounts there is formation of the b-Ag₂WO₄ phase. SEM images indicate that the increase in reaction pH, in parallel to the non-use of PVP, forms agglomerated particles with brittle appearance. On the other hand, the addition of PVP results in the formation of phases b-Ag₂WO₄ and g-Ag₂WO₄ with well-defined rod and octahedron morphology, respectively. The photocatalytic activity indicates that the g-Ag₂WO₄ phase presents the best result compared to the others, resulting from the great effect of the H₂O₂ species generated during the process.

BANKING MEMBERS:
Presidente - 1802888 - FABIANA VILLELA DA MOTTA
Interno - 1883170 - MAURICIO ROBERTO BOMIO DELMONTE
Externo ao Programa - 2941160 - JOSE HERIBERTO OLIVEIRA DO NASCIMENTO
Externo à Instituição - ALBERTHMEIRY TEIXEIRA DE FIGUEIREDO
Externa à Instituição - ANA PAULA DE AZEVEDO MARQUES - UNIFESP