This paper describes the development of TiO 2 and ZnO particles by a chemical route, using two different wet synthesis methods: polymeric precursor (PP) and sol-gel (SG). This study aimed to shed a light on how the synthesis method affects the photocatalytic activity of these oxides. Rhodamine B (RhB) degradation was used as a probe reaction to test the as-synthesized TiO 2 and ZnO photoactivity. It was observed that surface availability, which is related to the presence of synthesis residue, is the key parameter to determine photoactivity. ZnO PP and ZnO SG presented degradation of 88% to RhB. Both samples presented synthesis residue on the surface. On the other hand, TiO 2 PP presented a better performance than TiO 2 SG, once 90% of RhB was degraded, while TiO 2 SG degraded 80% of the dye. In this case, TiO 2 PP was free of synthesis residue on the surface, while TiO 2 SG presented residues.
Poços de Caldas é um importante centro hidrotermomineral do Brasil, o qual apresenta depósitos de argilas não plásticas para as quais não há registros significativos a respeito da caracterização direcionada destes materiais, o que prejudica estudos de aplicação industrial. Estas argilas não plásticas, não aproveitadas, vêm sendo armazenadas em galpões ou a céu aberto, o que gera um elevado custo para a indústria, além de transformar-se em um passivo ambiental. No presente trabalho realizou-se o estudo químico-mineralógico de seis amostras de argilas de baixa plasticidade, além da caracterização preliminar destas amostras quanto à granulometria, plasticidade e propriedades cerâmicas básicas, visando ampliar os horizontes das investigações destes materiais. Este estudo preliminar mostrou que, de maneira geral, as amostras são compostas por minerais refratários como caulinita e gibbsita, apresentando teores menos significativos de outras fases, como quartzo, vermiculita e illita. Juntamente às análises químicas, estes dados permitiram o agrupamento das matérias-primas em dois grupos em função de sua refratariedade, norteando assim, a caracterização posterior. Dentre as amostras, há material com potencial uso na formulação de massas de porcelanato, além de uma amostra turfosa, cuja aplicação está relacionada à correção de solos.
This paper describes the development of ZnO semiconductors applied as photocatalysts for the degradation of water contaminants, with the shape of ceramic pellets thick enough to maintain their structures, prepared by slip casting and sintering. The samples presented porosities around 40% and densities around 3.4 g/cm 3 , which represented about 61% of the theoretical density of ZnO. After obtaining the ceramic samples, the degradation of Rhodamine B dye by photocatalysis was evaluated in six cycles of degradation. After the cycles, changes in the surface of the samples were verified, possibly due to leaching during photocatalysis since they presented mean grain sizes of 0.61 μm before and 0.36 μm after the photocatalysis. The ceramic ZnO samples were able to satisfactorily degrade Rhodamine B for several cycles, resulting in successful reuse of photocatalysts and increased facility of removing the photocatalysts from the medium after degradation compared to powders in suspensions.
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