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Iridium oxide is the catalytic material with the highest stability in the oxygen evolution reaction (OER) performed under acidic conditions. However, its high cost and limited availability demand that IrO2 is utilized as efficiently as possible. We report the synthesis and OER performance of highly active mesoporous IrO2 catalysts with optimized surface area, intrinsic activity, and pore accessibility. Catalytic layers with controlled pore size were obtained by soft-templating with micelles formed from amphiphilic block copolymers poly(ethylene oxide)-b-poly(butadiene)-b-poly(ethylene oxide). A systematic study on the influence of the calcination temperature and film thickness on the morphology, phase composition, accessible surface area, and OER activity reveals that the catalytic performance is controlled by at least two independent factors, that is, accessible surface area and intrinsic activity per accessible site. Catalysts with lower crystallinity show higher intrinsic activity. The catalyst surface area increases linearly with film thickness. As a result of the templated mesopores, the pore surface remains fully active and accessible even for thick IrO2 films. Even the most active multilayer catalyst does not show signs of transport limitations at current densities as high as 75 mA cm-2.
O monitoramento das estruturas de concreto possibilita que o risco de corrosão seja estimado ao longo dos anos de sua utilização. Com o conhecimento desse risco, intervenções de prevenção da corrosão ou de controle da corrosão já estabelecida podem ser programadas e realizadas em períodos adequados. Na prática, o risco de corrosão é avaliado por meio da verificação periódica do estado da armadura e das alterações nas propriedades do concreto. Isso pode ser feito por meio do embutimento no concreto de cobrimento de sensores de aquisição contínua de dados. Há diferentes tipos de sensores de aquisição contínua de dados. Um dos mais conhecidos é o sensor galvânico que consta de um conjunto de barras de aço-carbono, eletricamente isoladas. Com o embutimento do sensor, essas barras ficam posicionadas em diferentes e conhecidas profundidades do concreto de cobrimento da armadura. O risco de corrosão da armadura é monitorado com a periódica medição da corrente galvânica em cada uma das barras do sensor. Essa medição, dentre outras informações do sensor galvânico foram abordadas em artigo anterior. Além do sensor galvânico, destacam-se o sensor de umidade e o de taxa de corrosão, que monitoram parâmetros importantes relacionados ao estabelecimento e evolução de processo corrosivo das armaduras. A seguir esses sensores são apresentados, bem como o sensor de fibra óptica, o qual apresenta algumas vantagens em relação aos demais mencionados, embora ainda seja de uso restrito.
A new metallosilicate based on yttrium was synthesized and characterized by XRD, FT-IR, 29Si MAS-NMR, and 89Y MAS-NMR. The mixed framework of the material was confirmed by the detection of distinct chemical shift groups using 29Si MAS-NMR (at -82 to -87 ppm, -91 to -94 ppm, -96 to -102 ppm, and -105 to -108 ppm), as well as four distinct chemical shifts in the 89Y MAS-NMR spectrum (at -89, -142, -160, and -220 ppm). Adsorption and kinetic analyses indicated the potential of the new material for the removal of lead and cadmium from aqueous media. The adsorption results for lead indicated that dynamic equilibrium was reached after five hours, with total lead removal of around 94 %, while for cadmium it was reached in the first hour, with total Cadmium removal of around 74 %. The adsorptions of lead and cadmium were modeled using pseudo-first order (PFO) and pseudo-second order (PSO) kinetic models. Although both models provided high R2 values (0.9903 and 0.9980, respectively), the PSO model presented a much lower χ2 red value (4.41×10−4), compared to the PFO model (2.12×10−3), which indicated that the rate-limiting step was probably due to the chemisorption of lead from the solution onto the yttrium-based metallosilicate.