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RESUMO Um caso interessante da eletrooxidação de dopamina, acompanhada por sua eletropolimerização, em que tanto o monômero, como o polímero condutor resultante podem ser oxidados até à respectiva forma quinônica, foi investigado do ponto de vista teórico. A análise do modelo matemático, correspondente a este sistema, mostrou que o estado estacionário, neste sistema é fácil de manter estável, apesar de a zona topológica, correspondente a esta estabilidade, ser mais estreita. Já as instabilidades oscilatória e monotônica mostraram-se mais prováveis neste caso que em sistemas semelhantes.
SUMMARY An interesting case for dopamine electrooxidation, in which either a monomer, or a polymer may be oxidized to the correspondent quinonic form, has been investigated from the theoretical point of view. The analysis o the correspondent mathematical model has shown that in this system the steady-state is easy to maintain stable, despite of the more narrow extension of the topological zone, correspondent to this stability. Yet the oscillatory and monotonic instabilities may be more probable in this cast, than in the similar ones.
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In this work, the hybrid structures were created by electrochemical etching of silicon wafer and deposition of reduced graphene oxide (RGO) on the porous silicon (PS) layer. With the help of SEM and AFM, the formation of hybrid PS-RGO structure was confirmed. By means of current-voltage characteristic analysis and impedance spectroscopy, we studied electrical characteristics of PS-RGO structures. The formation of photosensitive electrical barriers in hybrid structures was revealed. Temporal parameters and spectral characteristics of photoresponse in the 400-1100-nm wavelength range were investigated. The widening of spectral range of photosensitivity of the hybrid structures in short-wavelength range in comparison with single-crystal silicon was revealed. The obtained results broaden the prospects of application of the PS-RGO structures in photoelectronics.
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Uma rota eletroquímica de eletrossíntese de anestesina (benzocaína), incluindo uma etapa anódica e uma catódica, foi avaliada, do ponto de vista mecanístico. Para tal, dois modelos matemáticos para cada passo foram desenvolvidos e analisados, mediante a teoria de estabilidade linear e a análise de bifurcações. Foram demonstradas as diferenças na pH-dependência da cinética de cada passo, bem como as diferenças nas condições de estabilidade do estado estacionário para ambas as etapas. A possibilidade do comportamento oscilatório e do monotônico também foi avaliada.
An electrochemical route for anesthesyne (benzocaine) electrosynthesis, including one anodic and one cathodic step was mechanistically evaluated. For that purpose, two mathematical models for each step were developed and analyzed, by means of linear stability theory and bifurcation analysis. The differences of pH-dependences of the kinetics of each step, like also in steady-state stability conditions, were investigated for both stages. The possibility for the oscillatory and monotonic behavior was also evaluated.
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We studied an effect of the graphene oxide (GO) layer on the optical and electrical properties of porous silicon (PS) in hybrid PS-GO structure created by electrochemical etching of silicon wafer and deposition of GO from water dispersion on PS. With the help of scanning electron microscopy (SEM), atomic-force microscopy (AFM), and Fourier transform infrared (FTIR) spectroscopy, it was established that GO formed a thin film on the PS surface and is partly embedded in the pores of PS. A comparative analysis of the FTIR spectra for the PS and PS-GO structures confirms the passivation of the PS surface by the GO film. This film has a sufficient transparency for excitation and emission of photoluminescence (PL). Moreover, GO modifies PL spectrum of PS, shifting the PL maximum by 25 nm towards lower energies. GO deposition on the surface of the porous silicon leads to the change in the electrical parameters of PS in AC and DC modes. By means of current-voltage characteristics (CVC) and impedance spectroscopy, it is shown that the impact of GO on electrical characteristics of PS manifests in reduced capacitance and lower internal resistance of hybrid structures.
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O desempenho de sensores fotoeletroquímicos, baseados no elétrodo Ti/TiO2 (sendo um exemplo de modelagem o sensor de hidrazina), foi descrito matematicamente e o respectivo modelo foi analisado por meio de teoria de estabilidade linear e análise de bifurcações. As condições do melhor desempenho destes sensores, bem como as de instabilidades oscilatória e monotônica, foram inferidas na base da análise do modelo.
The work of photoelectrochemical sensors, based on the Ti/TiO2 electrode (being an example for the modeling the hydrazine sensor), was described mathematically and the respective model was analyzed by means of linear stability theory and bifurcation analysis. The best response condition for this sensor, as also, the oscillatory and monotonic instabilities requirements, were inferred, basing on the model´s analysis.
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ABSTRACT: In this work, we have prepared film sensor elements based on a hybrid system poly(3,4-ethylenedioxythiophene)-porous silicon nanocrystals-carbon nanotubes on flexible polymer substrates. Our FTIR spectroscopy-based studies for the molecular structure of the materials obtained suggest some interaction of their components in the hybrid layer. The influence of adsorption of water molecules on the conductivity and capacitance of the hybrid composites has been investigated in the temperature range of 20°C to 40°C. We have detected essential changes in the electrical conductivity and capacitance which depend on the humidity of the surrounding atmosphere. For estimating the sensing properties of our composites, we have analyzed the sensing abilities of the hybrid systems and their dynamic characteristics. The hybrid composites as working materials for the sensors provide improved performance of the latter. In particular, the response time is reduced by 3 to 5 times. PACS: 73.63.-b, 73.61.Ph, 82.35.Np, 81.05.Rm.
