No / The emission of greenhouse gases on a global scale is predominantly caused by the utilization of fossil fuels. Various methods have been explored to address the recycling of CO2, which among, the CO2 conversion into high-value chemicals become so promising. The purpose of this book chapter evaluation is CO2 reduction and H2 evolution reactions for producing syngas. A comprehensive analysis shall highlight (i) the technical advantages and impediments of various reactor classifications, (ii) the effect of electrolytes on electrolyzers in the liquid phase, and (iv) the catalysts that are viable for the creation of important products such as CO.

Solar energy is the most abundant efficient and important source of renewable energy. The objective of this study is to develop highly efficient visible light responsive photocatalysts for overall water splitting. This is done by using silver or copper containing materials. Phosphate compounds have caught much attention due to their rigid structure, thermal stability and resistance to chemical attacks. Solid phosphates can be prepared by direct solid-state reaction between metal cations and phosphate anions at high temperatures. Double metal phosphates of the Nasion-type structure had shown further technological importance. It has been reported that well-crystallized double metal phosphate particles have excellent ordering and cationic conduction channels in the Nasicon framework. In this study, several Nasion-type structured materials have been synthesized by solid-state method (e.g. CuTi2(PO4)3 and AgTi2(PO4)3) heated up under different temperatures (400–1100C) in N2 or air atmosphere. These materials were characterized by XRD, SEM, DR-UV-Vis spectroscopy and tested for photocatalytic applications. A new method for direct synthesis of photoelectrode on Ti Plate had been demonstrated. Further investigations on controlling the size and morphology for better performance of single and double metal phosphates will be done.

CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Devido o contínuo desenvolvimento tecnológico e o crescimento populacional, o consumo de energia vem sendo cada vez maior ao longo dos anos. Neste aspecto, a fotocatálise atrai grande interesse devido seu potencial no aproveitamento da energia solar. No cenário nacional, os niobatos lamelares são materiais interessantes para atuarem como fotocatalisadores, uma vez que o Brasil detém 98% das reservas de nióbio no mundo. Dentro deste contexto, o presente trabalho apresenta as possibilidades do K4Nb6O17 como fotocatalisador tanto na forma em pó como imobilizado em filmes finos. O K4Nb6O17 foi preparado a partir da reação em estado sólido do Nb2O5 com K3CO2 e esfoliado em solução de hidróxido de tetrabutilamônio. O niobato esfoliado foi então modificado com platina, comparando-se dois diferentes precursores H2PtCl6 e [Pt(NH3)4]Cl2, e também combinado à nanopartículas de ouro. As amostras foram caracterizadas por diferentes técnicas e o desempenho fotocatalítico avaliado tanto para fotodegradação de azul de metileno e metanol como para a produção de H2. Na fotodegradação do corante, o niobato esfoliado sem qualquer co-catalisador apresentou a maior eficiência fotônica (ξ = 2,1%). Em contraste, para a fotodegradação de metanol e para a produção fotocatalítica de H2, as amostras modificadas apresentaram maior desempenho fotocatalítico em relação ao niobato esfoliado. Na produção de H2, foram obtidas eficiências fotônicas próximas a 0,2% para as amostras contendo tanto Pt como Au. Já na fotodegradação de metanol, as amostras de niobato e Pt resultaram em eficiências próximas a 4,0% e a modificada com ouro, 7,0%. A fabricação de filmes pode melhorar a aplicação dos fotocatalisadores por facilitar sua recuperação, prevenir perdas e diminuir a aglomeração de material. Os filmes de niobato e niobato com Pt foram montados utilizando a técnica Layer-by-Layer (LbL) devido sua facilidade e versatilidade. Os filmes foram caracterizados quanto às suas propriedades morfológicas, fotocatalíticas e fotoeletroquímicas. Na fotodegradação de azul de metileno, ambos os filmes resultaram em eficiências fotônicas semelhantes (ξ = 0,1%). Em contrapartida, para a produção fotocatalítica de H2, a presença da Pt nos filmes resultou em uma eficiência duas vezes maior (ξ = 1,2%) em relação ao filme de niobato (ξ = 0,6%). O aumento do número de bicamadas ocasionou o aumentou linear da velocidade de produção de H2, indicando que a imobilização do material não ocasionou a perda de sítios ativos. / As the technological development and population growth continuously increases, energy consumption is becoming higher over the years. In this aspect, photocatalysis attracts great interest due to its potential to harvest and convert solar energy. In a national scenario, layered niobates are interesting materials to act as photocatalysts, since Brazil accounts for 98% of the world’s niobium reserves. In this work application of K4Nb6O17 as a photocatalyst both, in powder form and immobilized as thin films, was investigated. K4Nb6O17 was prepared by the solid state reaction between Nb2O5 and K2CO3 and then it was exfoliated in tetrabutylammonium hydroxide solution. The exfoliated niobate was modified with platinum using two different precursors, H2PtCl6 and [Pt(NH3)4]Cl2, and it was also combined with gold nanoparticles. The samples were characterized by different techniques and the photocatalytic performance was evaluated for methylene blue and methanol oxidation and for H2 production. In the dye photodegradation, the unmodified exfoliated niobate exhibited the highest photonic efficieny (ξ = 2.1%). In contrast, for the methanol photodegradation and H2 evolution, the modified samples presented higher photocatalytic performance than the exfoliated niobate. For H2 evolution, photonic efficiencies close to 0.2% were obtained for samples modified by Pt and Au. For methanol photodegradation, the Pt-niobate composites exhibited photonic efficiencies close to 4.0% and the Au-niobate 7.0%. The assembly of thin films can favor the application as photocatalysts due to ease of recovering, smaller losses and reduced material agglomeration. The bare niobate and the Pt-niobate films were assembled by the Layer-by-Layer (LbL) technique because of its easiness and versatility. The films were characterized towards their morphology, photocatalytic and photoelectrochemical properties. For methylene blue photodegradation, both films resulted in similar photonic efficiencies (ξ = 0.1%). In contrast, for the H2 photocatalytic production, the presence of Pt in the films resulted in a photonic efficiency twice higher (ξ = 1.2%) than the bare niobate film (ξ = 0.6%). The increase in the bilayers number caused a linear increase of the H2 evolution rate, indicating that the material immobilization did not lead to the active sites losses. / Dissertação (Mestrado)