Banca de DEFESA: THERESA BEATRIZ OLIVEIRA NUNES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : THERESA BEATRIZ OLIVEIRA NUNES
DATE: 10/02/2022
TIME: 14:00
LOCAL: Sala virtual (videoconferência)
TITLE:

Influence of  synthesis method on the photocatalytic and photoluminescent properties of Ca1-xInxWO4

KEY WORDS:

CaWO₄, indium, photocatalytic activity, photoluminescence, sonochemical method, microwave-assisted hydrothermal method.

PAGES: 91
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

CaWO₄ is a semiconductor that is currently being investigated for having good optical properties. These properties are related to some processing factors such as different synthesis methods that generate distinct crystal structures and morphologies. Such morphological and structural characteristics will certainly affect the properties of the synthesized material. In this work, the photocatalytic and photoluminescent properties of CaWO₄ doped with indium (0, 1, 2, 4 and 8% mol) were investigated for 30 minutes by two different methods: the sonochemical method (MS) and the microwave-assisted hydrothermal method (MHAM). The crystal structures of the pure and doped samples and their morphologies were characterized by X-ray diffraction (XRD) and by field emission scanning electron microscopy (MEV-FEG), respectively. The photocatalytic activity was estimated from the degradation of methylene blue (MB) dye under UV light. CaWO₄ powders were tested in 3 cycles of reuse. Optical and photoluminescence properties were estimated from UV-Visible spectroscopy and the photoluminescence (FL) test. The diffractograms indicated no formation of secondary phases and the Rietveld refinement estimated the crystallite sizes where the samples synthesized by MS obtained a crystallite size of 31,85 nm for the pure sample which varied to 31,23 nm with a maximum doping (8% of In). For the samples synthesized by MHAM, the crystallite size varied between 35,98 nm for the pure sample and 36,73 nm for the 8% In sample. The average crystallite sizes of MS and MHAM samples were 33.51 and 34.69 nm, respectively. The SEM-FEG images indicated a clustered morphology with an irregular shape and in the form of rods and kibes. The photocatalytic activity increased in efficiency with increasing doping, and the samples doped with 4 and 8% of indium in each synthesis were the samples that showed the best photocatalytic efficiencies and the lowest bandgaps values. The sample synthesized by the hydrothermal method showed the smallest loss of efficiency during the 3 cycles of reuse, being the best alternative for applications in photocatalysis. The samples with 8% of In⁺³ ions showed lower FL intensities with maximum peak at 479 and 483 nm suggesting that there is a lower recombination pair e^-/h⁺, which led these samples to have a better photocatalytic performance.

BANKING MEMBERS:
Presidente - 1802888 - FABIANA VILLELA DA MOTTA
Interno - 1883170 - MAURICIO ROBERTO BOMIO DELMONTE
Externa à Instituição - ANA PAULA DE AZEVEDO MARQUES - UNIFESP