Study On Properties Of Langmuir - Blodgett Membrane Of Violet - Carbon Nanotube Complex And Its Application In Load Hydrogenase

Carbon nanotubes (CNT) possess attractive thermal, mechanical and electrical properties that suggest a wide range of applications in the fields of nanoscience and nanotechnology including nanowires, field effect transistors, nanoelectronic devices and sensors, but their poor solubility or suspensions in solutions limited their fundamental research and practical applications. To overcome such a limitation, after their discovery, modification or functionalization of the CNT has been an interest and important research area.Based on the electrostatic interaction between the carboxyl carbon nanotubes and viologen, we prepared viologen-carbon nanotube composites, the composites can be dispersed in chloroform solution. We studied and characterized the nature of their monolayer films and Langmuir-Blodgett films properties, and explored the adsorption and promotion of hydrogenase redox reaction conditions. The main contents and results of the experiments are as follows:In the first part, amphiphilic viologens were electrostatically adsorbed on the surface of multiwalled carbon nanotubes (MWCNT) to form viologen-MWCNT composites. Thermal gravimetric analysis results showed that the content of viologens was about5-10%in weight. Although both viologens and MWCNT were hardly dispersed in the water-insoluble organic solvents, the as-prepared viologen-MWCNT composites were well dispersed in them with a strong long-term stability, the features of which provided a possibility to prepare their insoluble monolayers at the air-water interface. The surface pressure-area isotherms of these hybrids revealed that they could form stable monolayers, which were transferred on the substrate surfaces such as quartz, silicon and Indium tin oxide by the Langmuir-Blodgett (LB) method. Compared to the UV-visible spectroscopy of viologen-carbon nanotube composites dispersion, the LB films of viologen-carbon nanotube composites characteristic peaks position had a small red-shifts (0-4nm), which was usually caused by the molecules orderly arrangement in the LB films. We saw a linear relationship between the absorption peak intensity of the LB films and the number of layers, indicating that the LB films evenly distributed on the substrate. Morphologies of the LB films were characterized by using scanning electron microscopy and atomic force microscopy, the images of which revealed the formation of network two-or three-dimensional films of the functionalized MWCNT. As the layers increased, the density and height of carbon nanotubes in the LB films increased correspondingly. Each layer of LB films had an average thickness of about26±10nm, which was about the same thickness of a layer of carbon nanotubes (diameter10-20nm). Cyclic voltammograms of the LB films revealed one or two couples of one electron transfer process corresponding to the viologen-MWCNT composites with the cathodic and anodic potentials closely related to the alkyl chains of the viologens. With the increase in the number of LB film layer, the cathode potential shifted from-0.57V (vs. SCE) to about-0.7V, accompanied by a decrease of the peak current intensity. The calculated result showed that the square roots of the peak current density was directly proportional to the scan rates, which meaned the redox reaction of viologen in the LB film was diffusion-controlled process. Based on the ultra-high specific surface area of carbon nanotubes and the porous nature of LB films, we used the viologen-carbon nanotube composite LB films adsorbed cytochrome c, X-ray photoelectron spectroscopy verified the adsorption. Calculated by the quartz crystal microbalance, the adsorbed amount of cytochrome c in quartz wafer with LB films was42.6ng·cm-1. Carbon nanotubes has a high specific surface area and viologen can act as electron transfer media for many organic and inorganic compounds and protein, so the prepared viologen-carbon nanotube composite LB film can be used as functional carrier for the preparation of sensor or nanodevices.In the second part, based on carbon nanotubes high specific surface area and the electrochemical properties of viologen-carbon nanotube composites, we prepared viologen-carbon nanotube composites/hydrogenase modified electrodes by modifying viologen carbon nanotube composites and hydrogenase to the surface of the glassy carbon electrode in sequence. Infrared spectra data showed the viologen-carbon nanotube composites and hydrogenase peaks, indicating that both viologen-carbon nanotube composites and hydrogenase were well preserved in the modified electrodes. And there was no chemical reaction or change between carbon nanotube composites and hydrogenase molecules, which means viologen-carbon nanotube composites did not make hydrogenase degeneration. The scanning electron microscopy pictures showed viologen-carbon nanotube composites randomly dispersed on the surface of the substrate, hydrogenase coated viologen-carbon nanotube composites surface. Such a surface structure provided favorable condition for the oxidation-reduction reaction occurs on the electrode. We measured the electrochemical properties of the modified electrode in different electrolyte solutions by cyclic voltammetry. According to the increase of reduction peak current in the cyclic voltammetry curves, we speculated that this may be caused by the redox of [4Fe-4S]2+/1+cluster. Unfortunately, due to the redox potential of hydrogenase was very close to that of viologen and the current intensity of viologen-carbon nanotube composites modified electrode itself was too strong as compared with hydrogenase, the redox peaks of hydrogenase were masked to a certain extent. Therefore, no obvious characteristic redox peaks can be observed. In future studies, we will explore to promote the reactivity of hydrogenase and electrode surface electron transfer rate/efficiency and make viologen-carbon nanotube composites/hydrogenase modified electrode has a good response. We hope our research can provide a theoretical guidance and technical support for the research and development of hydrogen biosensors and so on.