Banca de QUALIFICAÇÃO: DÉBORA FERREIRA DOS SANTOS MORAIS

Uma banca de QUALIFICAÇÃO de DOUTORADO foi cadastrada pelo programa.
STUDENT : DÉBORA FERREIRA DOS SANTOS MORAIS
DATE: 12/11/2025
TIME: 14:00
LOCAL: Sala do Meeeting - virtual
TITLE:

Nb2O5-Based Materials Engineering: An Approach to Environmental Solutions and Energy Technologies

KEY WORDS:

Nb2O5; photocatalysis; heterojunctions; Na3V2(PO4)3; sodium-ion batteries; environmental sustainability.

PAGES: 172
BIG AREA: Engenharias
AREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
SPECIALTY: Cerâmicos
SUMMARY:

The growing demand for sustainable technologies has driven the development of new materials capable of meeting both environmental and energy challenges. In this context, niobium pentoxide (Nb2O5) has been gaining prominence due to its high chemical stability, abundance in Brazil, and versatility of applications. Therefore, this thesis aimed to investigate the multifunctional potential of Nb2O5 in two complementary areas: (i) as a photocatalyst in the degradation of organic pollutants and (ii) as a coating material in sodium-ion battery (SIB) cathodes.

In the first step, Nb2O5 was used in the synthesis of new binary and ternary heterojunctions, Ag@AgCl/Nb2O5 and g-C3N4/Ag@AgCl/Nb2O5, obtained through combined precipitation and calcination routes. Structural analyses (XRD, XPS, PL, and EIS) confirmed the formation of oxygen vacancies, metallic silver, and strong interfacial coupling between the phases, resulting in efficient charge separation and broadening of optical absorption into the visible spectrum. The ternary heterojunction NbA75CN exhibited superior photocatalytic performance, eliminating 99.9% of the Rhodamine B (RhB) dye in just 10 minutes of solar irradiation, with high structural and photocatalytic stability after multiple cycles. Furthermore, the material demonstrated significant antimicrobial activity against Staphylococcus aureus and Escherichia coli, highlighting its potential for environmental and health applications.

In the second phase, the use of Nb2O5 was evaluated as a coating on NASICON (Na3V2(PO4)3) cathodes synthesized via the citrus sol-gel route. The coating was applied at different concentrations (1%, 3%, and 5%), and morphological and spectroscopic analyses confirmed its homogeneous distribution on the particles. The coated samples exhibited improved electrochemical performance, particularly the NVP@Nb3 material, which exhibited a capacity of 96 mA h g⁻¹ at 3.2 V, corresponding to an energy density of 307.2 Wh kg⁻¹, in addition to 97% capacity retention after 300 cycles and excellent stability at -15°C. This improvement was attributed to reduced interfacial resistance, increased surface capacitive contribution, and greater ionic mobility in the electrode.

The results demonstrate the effectiveness of Nb2O5 as a multifunctional material, capable of both promoting efficient pollutant degradation and optimizing electrode performance in SIBs. Thus, this research reinforces the strategic role of Nb2O5 as a key material in the development of clean technologies, aligned with the principles of environmental sustainability and energy transition.

COMMITTEE MEMBERS:
Presidente - 1883170 - MAURICIO ROBERTO BOMIO DELMONTE
Interna - 1802888 - FABIANA VILLELA DA MOTTA
Interno - 3485163 - NIVALDO FREIRE DE ANDRADE NETO
Externo à Instituição - NEFTALÍ LENIN VILLARREAL CARREÑO - UFPel