M-MCM-41 molecular sieves (M = Ce or Cr) were prepared by a hydrothermal method and impregnated with TiO 2 . The materials were characterized by XRD, N 2 adsorption-desorption, DRS and XPS. Their potential application to photooxidize H 2 S in a wet gas stream was tested in a continuous flow reactor operating at a flow rate of 110 mL·min -1 at 50% relative humidity and using 30 ppm v of the pollutant. The photocatalytic efficiency using UV-A and visible-light was compared to the activity of TiO 2 /MCM-41 without heteroatoms incorporated into the MCM-41 structure. It was found that the incorporation of Ce did not improve the performance of TiO 2 /MCM-41, but Cr-containing samples presented higher initial efficiency and were able to photooxidize H 2 S without formation of SO 2 as a by-product, in contrast to the other prepared samples and to Degussa P-25 TiO 2 . Moreover, no other gaseous by-product was detected. The isomorphic incorporation of Cr into the structure of MCM-41 followed by TiO 2 incorporation produced photocatalysts that presented good adsorption capacity and were much more active under visible-light than under UV-light. This performance represents an important advantage for solar applications. Their photoactivity depended on the concentration of chromium; the highest efficiency was attained with samples with a Si/Cr ratio of 50. Finally, deactivation was observed as a consequence of sulfate accumulation on the surface of the catalyst and reduction of Cr 6+ .

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STRATEGIES AND MATERIALS USED IN HETEROGENEOUS PHOTOCATALYSIS APPLIED TO HYDROGEN GENERATION THROUGH WATER PHOTOLYSIS.Among the various technologies for the production of hydrogen fuel, heterogeneous photocatalysis is one of the most promising, especially with the use of semiconductors, notably TiO 2 . However, the use of TiO 2 is limited by hindrances for the photolysis of water, such as wide bandgap, a less negative conduction band reduction potential as compared to that of hydrogen evolution and the high electron/hole recombination rate. Deactivation of the semiconductor can be avoided by the addition of electron-rich compounds (sacrificial reagents) which react irreversibly with the hole, leading to a higher quantum efficiency. Another strategy is the Z scheme. In this system, two different photocatalysts (or photosystems) are combined using a suitable redox mediator. Furthermore, the bandgap can be adjusted by doping with transition metal oxides, with control of metal oxide valence band using p-orbitals of an anion, or s-orbitals of p-block metal ions, or by spectral sensitization. In view of these questions, the purpose of this review article is to describe and discuss recent studies that use a variety of materials for the photocatalytic generation of hydrogen.Keywords: hydrogen; photocatalysis; water splitting; Z scheme. INTRODUÇÃOA procura por fontes que assegurem o suprimento de energia, os altos preços do petróleo e as emissões crescentes de gases do efeito estufa constituem desafios ainda não resolvidos para a economia global e o clima do planeta. Há um consenso na comunidade internacional de que é preciso uma ação urgente para enfrentar os problemas de curto prazo sobre suprimento de energia e mitigar as mudanças futuras do clima, e que a tecnologia e a política são partes desta solução. Dentre as fontes alternativas de energia, o hidrogênio é uma opção atrativa, pois possui elevada energia por unidade de massa (1 kg de hidrogênio contém aproximadamente a energia de 2,7 kg de gasolina), o que facilita a portabilidade da energia. 4 Além disso, sua combustão não gera contaminante, mas apenas água. Embora a combustão do hidrogênio não produza gases de efeito estufa, cerca de 95% do hidrogênio consumido no mundo é gerado a partir de materiais fósseis, sendo obtido principalmente a partir da reforma a vapor de hidrocarbonetos como o metano e nafta (subprodutos do refino do petróleo).5 Este processo, além de demandar grande quantidade de energia para ocorrer (a decomposição do combustível em hidrogênio somente ocorre em temperaturas superiores a 700 o C), produz uma mistura de monóxido de carbono e hidrogênio. Para que a produção de hidrogênio seja considerada sustentável, é necessário o desenvolvimento de processos que atendam aos seguintes requisitos: que a fonte geradora seja renovável; que não haja grande demanda de energia; que não ocorra a produção de poluentes como subprodutos; e que seja um processo técnica e economicamente viável.Os avanços tecnológicos nas áreas de produção de hidrogênio de forma...

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Acid mine drainage (AMD) occurs when sulfide composite materials are exposed to oxygen gas, water, and microorganisms present in the environment. An alternative for the treatment of this residual water is the generation of hydrogen gas by electrolysis using a photovoltaic system. In this work, an electrolytic cell with 304 stainless steel electrodes was to form hydrogen gas. After 390 minutes of hydrogen generation, it was observed that the accumulated amount of H 2 was 254 mL when PV panels were used as the current source. When using AMD, hydrogen generation was 5.5 times higher compared to that using the sulfuric acid solution under the same experimental conditions. The electrolyte AMD conductivity diminished from 3850 μS cm −1 to 2960 μS cm −1. The decrease in conductivity may be related to removal of metal ions from the solution by the formation of insoluble compounds. After 390 minutes of testing, electrolysis using a PV panel resulted in a 9-fold increase in the total solid content. The reduction of iron and manganese ions in AMD samples was approximately 60% and 10%, respectively. No decrease in sulfate concentration and low pH variation were observed.

Este trabalho tem como objetivo identificar os modelos didáticos pessoais de um grupo de alunos regularmente matriculados em um curso de Pós-graduação lato sensu em Ensino de Ciências. Aplicamos um questionário a 28 alunos, sendo 14 estudantes de ensino de química e 14 estudantes de ensino de física. A partir das respostas obtidas com este instrumento calculamos o grau de hibridismo dos modelos didáticos bem como o grau de coerência em relação ao paradigma construtivista. Constatamos que os modelos didáticos dos alunos de ensino de física são mais híbridos que os modelos didáticos apresentados pelos alunos de ensino química. Estes últimos apresentam um grau de coerência mais alinhados aos modelos espontaneísta e alternativo. Somente dois alunos apresentaram um grau de coerência negativo, o que pode indicar uma desconstrução em potencial do modelo didático tradicional.