TEDE Coleção:https://tedebc.ufma.br/jspui/handle/tede/51162026-04-11T20:00:50Z2026-04-11T20:00:50ZAvaliação eletrocatalítica de nanomateriais com diferentes composições: estudo teórico-experimentalRODRIGUES, Marta Venancia Françahttps://tedebc.ufma.br/jspui/handle/tede/68102026-03-02T16:34:55Z2025-10-17T00:00:00ZTítulo: Avaliação eletrocatalítica de nanomateriais com diferentes composições: estudo teórico-experimental
Autor: RODRIGUES, Marta Venancia França
Primeiro orientador: GARCIA, Marco Aurélio Suller
Abstract: This thesis is organized into four chapters, which address advanced strategies in the study of
metallic nanoparticles (NPs) applied to the oxygen reduction reaction (ORR) and the
electrooxidation of glycerol, with emphasis on the controlled synthesis of nanomaterials.
Chapter 1 presents a detailed literature review on the theoretical aspects of the ORR, synthesis
strategies for metallic NPs, and the use of these NPs in fuel cells. The reaction mechanisms, as
well as the influence of NP composition and morphology on electrocatalytic activity, are
discussed, along with the current challenges in developing more efficient and durable catalysts.
This review provides the conceptual foundation necessary for the subsequent experimental
studies. Chapter 2 describes the experimental methodology employed throughout this work,
divided into three parts: bimetallic platinum–molybdenum NPs applied to the ORR; trimetallic
NPs composed of platinum, rhodium, and tin applied to the same reaction; and the
physicochemical characterization of materials, along with electrochemical and theoretical
analyses. The synthesis procedures were optimized to achieve precise control over NP
composition, size, and dispersion, enabling the investigation of how these parameters influence
catalytic efficiency. Chapter 3 comprises complementary studies involving platinum and
rhodium NPs applied to electrooxidation and the controlled synthesis of platinum. The results
demonstrate how subtle variations in NP composition and morphology can significantly affect
electrocatalytic activity, providing valuable insights for the development of new catalysts.
Finally, Chapter 4 presents the general conclusions of the thesis, highlighting the benefits of
using metallic NPs in the ORR, including enhanced electron-transfer efficiency and improved
stability under operational conditions. The findings indicate that precise control over NP
composition and morphology is essential to optimize their electrocatalytic performance,
opening promising perspectives for the development of clean and sustainable energy-generation
technologies.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Tese2025-10-17T00:00:00ZPerfil químico e potencial biotecnológico antioxidante e anticancerígeno de nanoemulsões (o/a) dos óleos essenciais de Citrus limon (L.) Burn, Cymbopogon citratus (DC) Stapf e Citrus sinensis (L.) OsbeckEVERTON, Gustavo Oliveirahttps://tedebc.ufma.br/jspui/handle/tede/67052026-01-20T16:59:19Z2025-04-25T00:00:00ZTítulo: Perfil químico e potencial biotecnológico antioxidante e anticancerígeno de nanoemulsões (o/a) dos óleos essenciais de Citrus limon (L.) Burn, Cymbopogon citratus (DC) Stapf e Citrus sinensis (L.) Osbeck
Autor: EVERTON, Gustavo Oliveira
Primeiro orientador: MONTEIRO, Odair dos Santos
Abstract: This study characterizes the chemical profile, antioxidant activity, and in vitro anticancer
properties of essential oils (EOs) from Cymbopogon citratus, Citrus sinensis, and Citrus limon,
along with their nanoemulsions. Leaves of C. citratus and C. sinensis, along with C. limon
peels, were collected in Maranhão state, Brazil, with EOs extracted by hydrodistillation.
Nanoemulsions (NEOs) were prepared using phase inversion methodology. Chemical
composition of EOs and NEOs was determined by GC-MS-FID analysis. Antioxidant activity
was evaluated through radical scavenging assays (ABTS, DPPH, hydroxyl, superoxide, and
hydrogen peroxide). In vitro anticancer activity was assessed against human cancer cell lines
from colon, lung, liver, cervical, prostate, oral, and neuroblastoma tissues. Extraction yields
were 0.92% for C. citratus, 1.55% for C. sinensis, and 1.01% for C. limon EOs. GC-MS analysis
identified geranial and neral as major components in C. citratus, while limonene predominated
in C. sinensis (85.28%) and C. limon (75.12%). The NEOs exhibited droplet sizes of 57.00
71.66 nm, zeta potentials ranging from -21.15 to -20.11 mV, polydispersity indices of 0.21
0.28, and pH values between 4.12-4.77. Both EOs and NEOs demonstrated potent antioxidant
activity (IC50: 6.23-84.58 μg/mL). Significant cytotoxicity was observed against all tested cell
lines, with particularly strong effects against 502713 (colon; IC50=1.00 μg/mL), IMR-32
(neuroblastoma; 1.10 μg/mL), Hep-2 (liver; 1.20 μg/mL), and SiHa (cervical; 1.60 μg/mL).
These findings suggest that EOs and NEOs from C. citratus, C. sinensis, and C. limon show
promise as potential candidates for innovative therapeutic applications.
Keywords:
Instituição: Universidade Federal do Maranhão
Tipo do documento: Tese2025-04-25T00:00:00ZCompósito AG2MOO4/AG3PO4/Grafeno aplicado à degradação fotocatalítica de hidrocarbonetos aromáticosFRAZÃO, Ricardo Henrique Nascimentohttps://tedebc.ufma.br/jspui/handle/tede/63042025-06-27T17:10:17Z2025-05-30T00:00:00ZTítulo: Compósito AG2MOO4/AG3PO4/Grafeno aplicado à degradação fotocatalítica de hidrocarbonetos aromáticos
Autor: FRAZÃO, Ricardo Henrique Nascimento
Primeiro orientador: MACIEL, Adeilton Pereira
Abstract: Advanced oxidative processes stand out due to their direct contribution to the
degradation of pollutants, such as those derived from gasoline, including volatile
organic compounds (VOCs) like BTEX, which are highly harmful to human health.
Therefore, the development of new materials aimed at degrading organic pollutants—
those that may eventually reach aquatic environments inhabited by marine fauna or
even groundwater sources used for human consumption—is of great importance. In
this context, photocatalysts, which are semiconductor materials used in advanced
oxidative processes, can be employed to mineralize these pollutants. When supported
on or combined with other materials, they allow for more effective removal of the
photocatalyst after the degradation process. Thus, the overall objective of this work
was to synthesize a silver molybdate and silver phosphate composite on graphene
(Ag2MoO4/Ag3PO4/Graphene) for the photocatalytic degradation of BTEX. The
photocatalyst was synthesized via a simple precipitation method, adapted from
methodologies available in the literature. The graphene was obtained from the epicarp
of the babassu coconut (Attalea speciosa), collected at the Federal University of
Maranhão. The materials obtained were characterized using the following techniques:
Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Energy Dispersive
Spectroscopy (EDS), Fourier Transform Infrared Spectroscopy (FTIR), Raman
Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and Diffuse Reflectance
Spectroscopy (DRS). Photocatalysis tests, under visible light in a custom-built reactor,
showed that after 60 minutes of irradiation, the amount of BTEX present in the samples
complied with the parameters established by the Ministry of Health for drinking water.
These results indicate that the Ag2MoO4/Ag3PO4/Graphene composite has potential
for use as a photocatalyst.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Tese2025-05-30T00:00:00ZSíntese de um eletrocatalisador bifuncional baseado na dopagem de óxido de grafeno reduzido com nitrogênioOLIVEIRA, Eleilde de Sousahttps://tedebc.ufma.br/jspui/handle/tede/63032025-06-27T17:09:40Z2025-04-28T00:00:00ZTítulo: Síntese de um eletrocatalisador bifuncional baseado na dopagem de óxido de grafeno reduzido com nitrogênio
Autor: OLIVEIRA, Eleilde de Sousa
Primeiro orientador: TANAKA, Auro Atsushi
Abstract: The development of efficient and low-cost bifunctional catalysts for oxygen reduction (RRO)
and oxygen evolution (REO) reactions is essential for the advancement of fuel cell technologies.
In this sense, the present work presents a study carried out to develop a bifunctional catalyst
using phenanthroline as N-precursor for the doping of reduced graphene oxide (rGO). The
catalyst prepared under optimized conditions through a multivariate statistical study, using
parameters such as time (0.3 at 3.7 h), pyrolysis temperature (631.8 at 968.2 °C) and catalyst
mass (59.8 a 110.2 mg), exhibited considerable electrocatalytic activity against RRO, with the
involvement of 4 (four) electrons. Furthermore, the recorded Tafel slope (~150 mV dec-1
)
indicated the first electron transfer as the determining step of the reaction. Morphological and
physicochemical characterizations provided information about the structure of the material,
correlating the stability and catalytic performance observed with the temperature and pyrolysis
time. Notably, this study also showed that under optimized conditions, the same precursor can
produce diverse results. In this sense, the optimized catalyst showed electrocatalytic activities
ORR / OER (ΔE = 1,05 V) in alkaline media, with competitive performance compared to
commercial Pt/C catalysts and metal-free catalysts reported in the literature. The activity for
REO was evaluated by polarization curves, demonstrating the bifunctional performance of the
event.
Instituição: Universidade Federal do Maranhão
Tipo do documento: Tese2025-04-28T00:00:00Z