Fabregat, G.; Osorio, J.; Castedo, A.; Armelin, E.; Buendía, J.; Llorca, J.; Aleman, C. International Symposium Frontiers in Polymer Science Data de presentació: 2017-05-18 Presentació treball a congrés
We have fabricated potentially generalizable sensors based on polymeric-modified electrodes for the electrochemical detection of dopamine. Sensitive and selective sensors have been successfully obtained by applying a cold-plasma treatment during 1-2 minutes not only to conducting polymers (Figure 1) but also to electrochemically inert plastics, such as polyethylene, polypropylene, polyvinylpyrrolidone, poly(4-vinylphenol), polycaprolactone and polystyrene. The effects of the plasma in the electrode surface activation, which is an essential requirement for the dopamine detection when inert plastics are used, have been extensively investigated using X-ray photoelectron spectroscopy. Results clearly indicate that exposure of polymer-modified electrodes to cold-plasma produces the formation of a large variety of reactive species adsorbed on the electrode surface, which catalyse the dopamine oxidation promoting its detection. With this technology, which is based on the application of a very simple physical treatment rather than on the sophisticated chemical methods typically employed (e.g. functionalization, incorporation of catalytic nanoparticles and processing of the nanocomposites), we have defined a paradox-based paradigm for the fabrication of electrochemical sensors by using inert and cheap plastics.
Figure 1. SEM micrographs of (a) PEDOT and (b) PNCPy before (left) and after (right) plasma treatment using tcp= 2 min.
Figure 2. Control voltammogram of 10 ¿M DA in 0.1 M PBS at (a) polypropylene-, (b) polyvinylpyrrolidone-, (c) polycaprolactone- and (d) polystyrene-modified GCE.
Silicone microreactors containing microchannels of 500 µm width in a single or triple stack configuration have been manufactured, coated with an Au/TiO2 photocatalyst and tested for the photocatalytic production of hydrogen from water-ethanol gaseous mixtures under UV irradiation. Computational fluid dynamics (CFD) simulations have revealed that the design of the distributing headers allowed for a homogeneous distribution of the gaseous stream within the channels of the microreactors. A rate equation for the photocatalytic reaction has been developed from the experimental results obtained with the single stack operated under different ethanol partial pressures, light irradiation intensities and contact times. The hydrogen photoproduction rate has been expressed in terms of a Langmuir-Hinshelwood-type equation that accurately describes the process considering that hydrogen is produced through the dehydrogenation of ethanol to acetaldehyde. This equation incorporates an apparent rate constant (kapp) that has been found to be proportional to the intrinsic kinetic rate constant (k), and that depends on the light intensity (I) as follows: kapp = k·I0.65. A three-dimensional isothermal CFD model has been developed in which the previously obtained kinetic equation has been implemented. The model adequately describes the production of hydrogen of both the single and triple stacks. Moreover, the specific hydrogen productions (i.e. per gram of catalyst) are very close for both stacks thus suggesting that the scaling-up of the process could be accomplished by simply numbering-up. However, small deviations between the experimental and predicted hydrogen production suggest that a fraction of the radiation is absorbed by the microreactor components which should be taken into account for scaling-up purposes.
Fabregat, G.; Osorio-Madrigal, J.; Castedo, A.; Armelin, E.; Buendía-Morales, J.J.; Llorca, J.; Aleman, C. Applied surface science Vol. 399, p. 638-647 DOI: 10.1016/j.apsusc.2016.12.137 Data de publicació: 2017-03-31 Article en revista
We have fabricated potentially generalizable sensors based on polymeric-modified electrodes for the electrochemical detection of dopamine. Sensitive and selective sensors have been successfully obtained by applying a cold-plasma treatment during 1–2 min not only to conducting polymers but also to electrochemically inert polymers, such as polyethylene, polypropylene, polyvinylpyrrolidone, polycaprolactone and polystyrene. The effects of the plasma in the electrode surface activation, which is an essential requirement for the dopamine detection when inert polymers are used, have been investigated using X-ray photoelectron spectroscopy. Results indicate that exposure of polymer-modified electrodes to cold-plasma produces the formation of a large variety of reactive species adsorbed on the electrode surface, which catalyse the dopamine oxidation. With this technology, which is based on the application of a very simple physical functionalization, we have defined a paradox-based paradigm for the fabrication of electrochemical sensors by using inert and cheap plastics.
A silicone microreactor with 500 mu m-width microchannels coated with a Au/TiO2 photocatalyst was manufactured and tested for the photocatalytic generation of hydrogen from gaseous water-ethanol mixtures under dynamic conditions. The manufacture of the microreactor included the fabrication of a polylactic acid (PLA) mold with a 3D printer and casting with polydimethylsiloxane (PDMS) prepolymer. After curing, the silicone microreactor was peeled off and the microchannels were coated with a Au/TiO2 photocatalyst prepared by impregnation of preformed Au nanoparticles over TiO2, and sealed with a thin silicone cover. The microreactor was tested at room temperature and atmospheric pressure under different operational conditions (photon irradiance, residence time, photocatalyst loading, and water ethanol ratio). Hydrogen production rates of 5.4 NmL W-1 h(-1) were measured at a residence time of 0.35 s using a H2O:C2H5OH molar ratio of 9:1, a photocatalyst load of 1.2 mg cm(-2) and a UV irradiance (365 nm) of 1.5 mW cm(-2) achieving an apparent quantum efficiency of 9.2%. The photogeneration of hydrogen with commercial bioethanol was also tested. A long-term photocatalytic test of two days revealed a stable hydrogen photoproduction rate. The use of silicone microreactors represents an attractive and customizable solution for conducting photochemical reactions for producing hydrogen at low cost. (C) 2016 Elsevier B.V. All rights reserved.