Estudo fotoeletroqu?mico do CuBi2O4 modificado com cobalto para produ??o de hidrog?nio via clivagem da ?gua.

Programa de P?s-Gradua??o em Qu?mica. Departamento de Qu?mica, Instituto de Ci?ncias Exatas e Biol?gicas, Universidade Federal de Ouro Preto.Denominado de kusachiite, o mineral de p-CuBi2O4 (CBO) possui um band-gap ?ptico entre 1,5-1,8eV e uma densidade de fotocorrente te?rica m?xima de 19,7- 29,0 mA.cm-2, al?m das energias das bandas de val?ncia e condu??o favor?veis ? oxida??o da ?gua e consequente produ??o de hidrog?nio. Todavia, a sua baixa densidade de fotocorrente e fotocorros?o (t?pica em ?xidos) o impossibilita de ser empregado como fotocatodo para produ??o de energia. Dentre as t?cnicas de deposi??o utilizadas, a de spray pyrolysis mostrou-se a melhor para a obten??o de filmes mecanicamente est?veis e uniformes (qualidades essas imprescind?veis para se alcan?ar reprodutibilidade). Sintetizado in situ sobre o substrato de vidro FTO utilizando spray pyrolysis, variando condi??es como: solvente, tempo de calcina??o, temperatura e espessura da camada depositada, fora alcan?ada uma densidade de fotocorrente superior ? literatura (?2.5 mA.cm-2 a 0.6 V vs RHE em H2O2) 1. No entanto, a problem?tica da fotocorros?o persistiu, sendo necess?rio um estudo mais detalhado a respeito do transporte de cargas minorit?rias ? interface semicondutor-eletr?lito. Este trabalho apresenta uma melhora na efici?ncia em correntes cat?dicas e instabilidade fotoqu?mica quando empregada a dopagem de Co2+. Nesses filmes preparados utilizando 3% de Co, n?o fora observada a fotorredu??o do material quando estudados em 0,5 M de Na2SO4 (pH~7), sob fonte de Xe (A.M 1,5G) a um potencial de -0,6V vs. Ag/AgCl, atingindo em m?dia, uma densidade de fotocorrente igual a -2,5 mA.cm-2. Valor esse superior ao encontrado em outros trabalhos. Pode-se inferir que a dopagem do material utilizando Co mostrou-se uma alternativa para evitar a fotorredu??o. Espera-se que este trabalho contribua para o melhoramento da estabilidade do p-CuBi2O4 para aplica??o em c?lulas fotoeletroqu?micas.Named as kusachiite, the mineral of p-CuBi2O4 (CBO) has an optical band gap between 1.5-1.8eV and a maximum theoretical photocurrent density of 19.7-29.0 mA.cm-2, in addition to the energies of the valence and conduction bands favorable to the oxidation of water and consequent evolution of hydrogen. However, its low density of photocurrent and corrosion (typical in oxides) makes it impossible material as a p-type semiconductor for Photoelectrochemical cells. Among the various deposition techniques used, spray pyrolysis proved to be the best for obtaining mechanically stable and uniform films (qualities that are essential to achieve reproducibility). Synthesized in situ on the FTO glass substrate using spray pyrolysis, varying conditions such as solvent, calcination time, temperature and layer thickness, a higher photocurrent density than the literature was achieved (?2.5 mA.cm-2 at 0.6 V vs RHE with H2O2) 1. However, the problem of photo corrosion persisted, requiring a more detailed study on the transport of minority charges to the semiconductor-electrolyte interface. This work presents an improvement in the efficiency in cathodic currents and photochemical instability when using Co2+ doping. In these films prepared using 3% Co, the reduction of the material when studied in 0.5 M Na2SO4 (pH ~ 7), under Xe source (1,5G AM) was not observed at a potential of -0.6V vs. Ag / AgCl, reaching, on average, a photocurrent density of -2.5 mA.cm-2. This value is higher than that found in other works. We can say that the doping of the study material using Co showed to be an alternative to avoid the undesired reduction. It is hope that this work will contribute to the improvement of the stability of p-CuBi2O4 for application in Photoelectrochemical cells (PEC?s)

Capture of CO2 by vermiculite impregnated with CaO

Vermiculite samples were impregnated with different amounts of calcium oxide by the conventional thermal heating technique and subject to CO2 capture experiments in thermal analysis equipment. The amount of CO2 captured by calcium oxide increased from 13 g of CO2 per mol of CaO to 16.8 g of CO2 per mol of CaO when the experiments were carried out with pure calcium oxide and vermiculite impregnated with CaO (1:1), respectively. Integral isoconversional methods of Kissinger-Akahira-Sunose (KAS) and Osawa-Flynn-Wall (OFW) were used for the kinetic study of the process and good correlation coefficients were achieved. The apparent activation energy values showed that for low conversions (α  0.3) the apparent activation energy values suggest that the slow step is a chemical step (Ea> 40 kJ)

Ni?bio : um elemento qu?mico estrat?gico para o Brasil.

Niobium, in fact, is an essential element for Brazil. Their applications are so many and so special that they put it as one of the subjects treated by the wikiLeaks site as strategic and that it should be treated in the USA. It is one of the elements most exported by Brazil and is mainly used in the production of special alloys for use in gas pipelines, air turbines, among other applications. It is believed that niobium-based materials can be obtained for applications with higher added value and in equally strategic areas. Research to obtain active and selective drugs, materials to maximize the use of renewable energy, and new nanostructured materials to improve the performance of different components are ongoing and promise a revolution for the next few years

New synthesis method for a core-shell composite based on ?-Bi2O3@PPy and its electrochemical behavior as supercapacitor electrode.

New composite based on polypyrrole (PPy) and bismuth oxide (?-Bi2O3) was investigated as supercapacitor electrode. The ?-Bi2O3 was obtained by hydrothermal route at 500 ?C for 2 h. Cyclic voltammetry was used to electropolymerize PPy on graphite electrode (GE) or on GE/?-Bi2O3. The X-ray diffraction profile of Bi2O3 revealed the ?-Bi2O3 monoclinic structure with space group P21/c. The scanning and transmission electron microscopy images showed that PPy coated ?-Bi2O3. Raman spectra showed that PPy inhomogeneously coated ?-Bi2O3, but it was still possible to obtain a ?-Bi2O3@PPy core-shell hybrid composite with highly ordered ?-Bi2O3 with electronic interaction between the oxide and the polymer chain of the polymer. The GE/?-Bi2O3@PPy composite electrode (type I supercapacitor) displayed a predominantly capacitive profile with low impedance values and good electrochemical stability after 50 charge and discharge cycles. The specific capacitance of ?-Bi2O3@PPy composite was found in the range of 634 to 301 F g-1 to gravimetric current of 3 and 10 A g-1, respectively

Electrocatalytic performance of different cobalt molybdate structures for water oxidation in alkaline media.

Cobalt molybdates with different crystalline structures, i.e., ?, ?, and hydrated (H)-CoMoO4, were synthesized, and their electrocatalytic activities were thoroughly examined for catalyzing the oxygen evolution reaction (OER) in alkaline media. The material characteristics were associated with the electrocatalytic properties by evaluating the CoMoO4 crystal structures (XRD and Raman), morphologies (TEM), and electrochemical features (electrochemically active surface area, roughness factor, electrochemical impedance, Tafel analysis, and controlled-current electrolysis). These combined findings revealed that the electrocatalytic performance is greatly influenced by the crystalline structures of CoMoO4, following the order ?-CoMoO4 > H-CoMoO4 > ?-CoMoO4. The H-CoMoO4 catalysts crystallized in the triclinic space group, P[1 with combining macron] (#2), with Z = 4. On the other hand, the ?- and ?-CoMoO4 catalysts exhibited a monoclinic structure, C2/m (#12), with Z = 8. In the OER experiments, ?-CoMoO4 showed an overpotential of 0.43 ? 0.05 V compared to the 0.51 ? 0.05 V and 0.56 ? 0.04 V exhibited by the H-CoMoO4 and ?-CoMoO4 catalysts, respectively, to achieve 10 mA cm?2. All CoMoO4 structures displayed stability for at least 6 h at a controlled current density of 10 mA cm?2. Finally, computational simulations indicate that the coexistence of Co and Mo ions in edge-shared octahedral sites of ?-CoMoO4 may favor the interaction between the O atom of the water molecule and the metal adsorption sites due to its surface being electronically less dense than ?- and H-CoMoO4 surfaces, thus resulting in its higher performance for OER