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Microwave-assisted syntheses of sustainable TiO2-based platforms for water remediation
Publication . Matias, Maria Leonor; Gomes, Daniela; Rodrigues, Joana; Machado, Ana Maria
The widespread contamination of aquatic ecosystems poses critical environmental
challenges, spurring intensive global research into advanced sustainable water remediation
technologies. Titanium dioxide (TiO2) nanostructures have emerged as prominent photocata-
lysts due to their physical/chemical stabilities, cost-effectiveness, and catalytic efficiency.
However, TiO2 has a wide band gap, restricting its utilization to the ultraviolet region. To en-
hance spectral responsiveness under visible light, various strategies were explored, including
the creation of a heterostructure (graphitic carbon nitride/TiO2), multi-dimensional defect en-
gineering, as well as doping with two abundant elements: Fe and Ca. To overcome the limita-
tions associated with the recovery and recyclability of nanopowders, TiO2-based nanostruc-
tures synthesized under microwave irradiation were either incorporated into or directly syn-
thesized onto green substrates, floating and non-floating. These substrates included cork, cel-
lulose-based materials, resin, and polyurethane foams. The TiO₂-based nanopowders and
platforms demonstrated excellent performance, achieving up to ~85 % combined adsorption
and degradation of methyl orange and rhodamine B, and ~80 % for tetracycline, within 180–
240 min, depending on the substrate type and synthesis conditions. These breakthroughs show
that TiO₂-based nanostructures can be synthesized at mild temperatures (90–230 °C) using
microwave-assisted methods and be easily integrated into eco-friendly substrates while ena-
bling sustainable water purification. Moreover, this PhD thesis aligns with the United Nations
Sustainable Development Goals by promoting circular economy principles through the devel-
opment of reusable and eco-friendly materials, fine-tuned to improve water quality.
2D Modelling of porous electrodes for electrochemical CO2 reduction in aqueous KHCO3 electrolyte
Publication . Fernandes, Inês S.; Antunes, Duarte; Reis-Machado, Ana S.; Mendes, Manuel J.; DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); LAQV@REQUIMTE; DQ - Departamento de Química
Sustainable Strategies for Solar Electrochemical Reduction of Carbon Dioxide to fuels
Publication . Messias, Sofia; Branco, Luís; Machado, Ana
The increasing concentration of greenhouse gases in the atmosphere led to global warming and climate changes. Among these gases, carbon dioxide has experienced the most significant increase, amplifying the urgency of addressing this issue. Thus, processes like electrochemical or photoelectrochemical conversion of CO2 have gained much attention, allowing the storage of intermittent and renewable sources of energy in the form of chemical building blocks and/or fuels. The aim of this work was focused on the development of a (photo)electrochemical process operating at high pressures for co-electrolyzing water and CO2 to produce syngas (H2 and CO) using aqueous ionic liquids (ILs) as electrolytes. A high electrochemical reactor with a configuration able to be used industrially for electrolysis in liquid phase was for the first time reported. The results obtained showed the possibility to achieve full conversions of CO2 into CO, as new reported for the high maturity process of gas phase CO2 electrolysis. Furthermore, operation at high pressure allows the direct coupling of the process under development with other high pressure processes, such as Fischer-Tropsch, which use syngas as a raw material. It is important to emphasise that the electrolyte plays a crucial role in (photo)electrochemical processes. Porous cathodes prepared using biopolymers, and non-critical materials, exhibited activity for syngas production. The development of a photoelectrochemical process using advanced photoanodes in collaboration with Cantabria and Oporto Universities have been performed. This thesis can open new avenues for sustainable energy solutions.
Electrochemical CO2 reduction in ionic liquids
Publication . Fernandes, Inês S.; Messias, Sofia; Martins, Rodrigo; Mendes, Manuel J.; Reis-Machado, Ana S.; DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DQ - Departamento de Química; LAQV@REQUIMTE; IOP Publishing
The escalating pressure to mitigate CO2 emissions calls for novel approaches to produce sustainable fuels and chemicals, as means to close the anthropogenic cycle. This study fulfills a critical need in this field, through the development of modeling tools capable of guiding groundbreaking technical advances in liquid-phase electrochemical CO2 reduction (ECR). An unprecedented 3D model for porous cathodes was designed for the co-electrolysis of CO2 and water to produce syngas, particularly considering aqueous and ionic liquid (IL) electrolytes to increase CO2 solubility in the electrolyte while lowering its density and kinematic viscosity to boost ECR process performance. The structural parameters of the cathode, i.e. porosity and pores geometry, were investigated, together with the effects of operational parameters such as type of electrolyte, flow rate, temperature and pressure. A key outcome was the demonstration of a flow electrolytic system, coupled with an improved porous zinc cathode, capable of producing CO partial current densities of 231 mA cm−2 at −1.1 V vs. RHE, with a composition suitable for up-stream methane production (H2:CO ratio of 3:1), at 10 bar, 45 °C, and 10 mL min−1, reaching the threshold for industrial-relevant yields. Such results show that the combination of tailored IL-based electrolytes and advanced cathode design enables to greatly overcome mass transport limitations and improve reaction dynamics. These results open a new path towards the use of computational smart-search methods to improve the industrial implementation of ECR in liquid-phase.
Multi-scale solar-to-hydrogen system design
Publication . Teixeira, Cristina; Alexandre, Miguel; Rodrigues, Leonardo; Vicente, António T.; Reis-Machado, Ana S.; Correia, Cristina B.; Ramos, Cristiano P.; Mendes, Adélio; Martins, Rodrigo; Mendes, Manuel J.; CENIMAT-i3N - Centro de Investigação de Materiais (Lab. Associado I3N); DCM - Departamento de Ciência dos Materiais; UNINOVA-Instituto de Desenvolvimento de Novas Tecnologias; LAQV@REQUIMTE; DQ - Departamento de Química; Elsevier Science B.V., Amsterdam.
Hydrogen produced from renewable energy holds significant potential in providing sustainable solutions to achieve Net-Positive goals. However, one technical challenge hindering its widespread adoption is the absence of open-source precise modeling tools for sizing and simulating integrated system components under real-world conditions. In this work, we developed an adaptable, user-friendly and open-source Python® model that simulates grid-connected battery-assisted photovoltaic-electrolyzer systems for green hydrogen production and conversion into high-value chemicals and fuels. The code is publicly available on GitHub, enabling users to predict solar hydrogen system performance across various sizes and locations. The model was applied to three locations with distinct climatic patterns – Sines (Portugal), Edmonton (Canada), and Crystal Brook (Australia) – using commercial photovoltaic and electrolyzer systems, and empirical data from different meteorological databases. Sines emerged as the most productive site, with an annual photovoltaic energy yield 39 % higher than Edmonton and 9 % higher than Crystal Brook. When considering an electrolyzer load with 0.5 WEC/WpPV capacity solely powered by the photovoltaic park, the solar-to-hydrogen system in Sines can reach an annual green hydrogen production of 27 g/WpPV and export 283 Wh/WpPV of surplus electricity to the grid. Continuous 24/7 electrolyzer operation increased the annual hydrogen output to 33 g/WpPV, with a reduced Levelized Cost of Hydrogen of €6.42/kgH2. Overall, this work aims to advance green hydrogen production scale-up, fostering a more sustainable global economy.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
Concurso de Projetos IC&DT em Todos os Domínios Científicos
Número da atribuição
PTDC/EQU-EPQ/2195/2021