05. Functionalized TiO2 nanostructures for application in photo-catalysis and sensors
Titania based nanostructures (nanotubes, nanorods, nanoparticles) present a unique combination of structural, physical and chemical properties. The large specific surface are combined with good intercalation and ion exchange properties make these structures very suitable for applications in photo-catalysis, solar energy conversion, but also as sensing materials. For these reason, they have attracted serious attention in the field of material science and technology. One of the main limitations for the extensive applications of TiO2 in photo-catalysis is a wide bandgap of 3.2 eV, so only UV part of the solar spectrum can be efficiently used in photo-catalytic degradation of waste water. However, titanium based nanostructures can be easily modified by linking various functional molecules and nanoparticles to their surface, but also by treatment in reducing and oxidizing atmospheres. This enables not only to alter the electronic structure and tune the band gap, but also to combine advantageous properties of two different nanostructured materials. These advantages will be used in our joined project in which we will investigate the enhancement of the optical properties of TiO2 nanotubes (NT) by functionalizing their surface with the aim of improving their efficiency.
SCIENTIFIC AIMS AND EXPECTED ACHIEVEMENTS:
The aim of the proposed project is to develop novel titanium-based nanostructured materials which will have potential as efficient photo-catalysts for waste water purification and as photo-electro-catalytic chemical sensors with high selectivity, and long lifetime. The hypothesis is that the functionalized titanium-based nanostructures (specifically, nanotubes) will show improved photo-catalytic and photo-electro-catalytic chemical sensing properties due to increase of the optical absorption in visible (vis) and near infrared (NIR) part of solar irradiation. Therefore, with the aim to increase its optical absorption, in the frame of the proposed project we will prepare, characterize and evaluate 1D titanate nanostructures functionalised by nano-layers or nano-particles of perovskite and noble metals (e. g. BaTiO2, SrTiO2 or Ar, Au, Pt etc.) and treated in reducing and oxidizing atmospheres.
The optical absorption in vis and NIR part could be achieved by the narrowing of the band-gap, that could be obtained by either structural or chemical modifications. Due to lattice disorder near the surface layer, oxygen vacancies or formation of Ti–OH and Ti–H groups are expected after treatment in reducing/oxidizing atmosphere, so the high density of localized donor/acceptor states would be created in forbidden gap of TiO2. Moreover, it is expected that the surface plasmon resonance caused by noble metal nanoparticles will further improve optical absorption in visible and NIR part of the solar irradiation.
With the aim to study functional properties and correlating them with structural properties, the prepared materials will be investigated by Raman spectroscopy, and by scanning and transmission electron microscopy of high resolution. Optical properties will be studied by UV-Vis-NIR spectroscopy.
Further evaluation of prepared tiO2-based nanostructures, will be divided in two main segments; investigation of the photo-catalytic properties for the purification of waste water and development of photo-electro-catalytic chemical sensors.
Photo-catalysis based purification of the waste water is a promising method due to simplicity, applicability, and cost efficiency. In this process, photons are used as the energy source to stimulate the catalytic decomposition of organic contaminant in waste water. TiO2 is energy efficient, cheap, non-toxic, reliable solution for the waste treatment, however it presents a real scientific and technical challenge due to the functionality only in the UV part of the spectrum. Using proposed modification, the photo-catalytic activity would be achieved also in the visible and NIR spectral range. The photo-catalysis will be studied on waste water that are closed to real pollutants as medicaments of hormones that could be released in nature by pharmaceutical industry.
In the part related to the development of chemical sensors, the focus will be on the development of photoelectric catalytic amperometric biosensors based on TiO2 nanotubes.Specifically, one of the basic problemswhich iscurrently preventingthe widespread development of photocatalytic biosensorswillbe addressed - the degradation of the biological receptor element in conditions where measurable photoelectric catalysis occurs in semiconductor materials based on TiO2, which imply the TiO2-electrode illumination by UV radiation.
By targeted modification of the TiO2-NT surface, electrodes that are photocatalytically active in the Vis part of the spectrum will be obtained, and are suitable for the immobilization of the enzyme as the receptor part of the biosensor. For the modification of the TiO2 nanotubes, semiconductor nanoparticles or thin films will be used, thereby enabling the production of hydrogen peroxide-sensitive photoenzymes, and bifunctional sensitizers, primarily from the phenothiazine dye group. They will enable covalent binding of the enzyme to the surface of the photocatalytic electrode while simultaneously acting as electron mediators in electrochemical oxidation or reduction of the enzyme cofactor (e.g., NAD (P) / NAD (P) H).
In the proposedway, photoelectric catalytic biosensors will be produced with selected enzymes from the oxidoreductase group, whose analytical performance will be tested in the analysis of biologically important analytes in real samples. Apart from conventionally used materials (Ti-foil, Ti thin films on solid substrates), the photo-electro-catalytic biosensors described will also be applied on flexible substrates such as polymer foil or textile materials to provide sensors for special applications , such as clothing integration.
The photo-catalytic and photo-electro-catalytic chemical sensing properties will be correlated with optical properties, morphology, crystal and electronic structure of the TiO2-based nano-materials before and after functional experiments.
The results collected in this project as fundamental research data will be published in international scientific journals. The gained knowledge could be used as the base for further application for the EU funding, while the developed materials will be further evaluated for possible technological development. Moreover, during the project three PhD students will be involved in the project, and educated in new synthesis and characterization techniques in both groups.