Projects / Programmes
Use of green energy sources: New functional nanomaterials on the base of polyoxometalates and TiO2 nanostrucutres for production of hydrogen by catalytic oxidation of water -NANOleaf
| Code |
Science |
Field |
Subfield |
| 2.04.01 |
Engineering sciences and technologies |
Materials science and technology |
Inorganic nonmetallic materials |
| Code |
Science |
Field |
| T153 |
Technological sciences |
Ceramic materials and powders |
| Code |
Science |
Field |
| 2.05 |
Engineering and Technology |
Materials engineering |
TiO2 nanostructures, polyoxometalates, photocatalysis, artificial photosynthesis, electron paramagnetic resonance
Researchers (9)
Organisations (2)
Abstract
Scientific and technological aim of the proposed project is development of a new hybrid nanomaterial on the base of titanate or TiO2 nanomaterials and molecules of polyoxometalates (POM). Titanate and TiO2 nanostructures will have, in the hybrid nanomaterial, double role:
· due to their high specific surface area they will enable anchoring of a large number of photochemically active molecules of polyoxometalates (POM)
· at the same time they will serve as a bridge for electron transfer that will be released at a photocatalytic oxidation of water at the oxygen evolving centre.
Polyoxometalates (POM) are inorganic molecules (M10[Ru4(H2O)4(µ-O)4(µ-OH)2(?-SiW10O36)2] (M = Cs, Li, Na)) that have two main advantages: (i) they are synthesized in gram quantities and (ii) they are stable in water in a wide pH range. Under light illumination in water, POM oxidize water by reaction 2H2O = O2 + 4H+ + 4e (oxygen evolving center, OEC). That released electrons would reach in the process of artificial photosynthesis a hydrogen evolving center there should be a linking unite so called bridge made from a material which energy levels would be similar to the one of POM (OEC) and also to HEC. Titanate and TiO2 materials satisfy this condition.
Starting phase will scope synthesis of 1D titanate nanostructures that will be synthesized under hydrothermal conditions from TiO2 and NaOH(aq) (or KOH(aq)). With the control of reaction conditions, (temperature and type of hydroxide), we will synthesize sodium/potassium titanates of different morphologies (nanotubes, nanoribbons and nanowires). In the next step alkali titanates will be by ion exchange transformed to protonated titanates. After heat treatment TiO2 of different morphologies and phases (anatase, TiO2-B) will be obtained. Electron properties of tianate nanomaterials will be altered by the addition of transition metal ions into the reaction mixture. Dopant ions when are present in the reaction mixture than to some extent exchange Ti4+ ions into the TiO6 octahedra.
In continuation in a research phase I by the surface functionalization of titanate and TiO2 nanostructures anchor sites for POM will be created. Functionalization will be directed into two directions:
· by chemically through functionalization of free -OH groups that are located on the surface of TiO2 and titanate nanostructures and
· by physical functionalization, that is by use of surfactants.
With chemical functionalization we will covalently bond organic chains of different lengths. On the other side of these chains there will be free functional groups like –NH2 that would be in a later steps transformed in to positively charged groups (nTi-L-NH3+, nTi-L-N+H2CH3, L is an organic group that is at one end covalently bonded to titanate and TiO2 nanostructure and it has a functional group that will serve a anchor for POM molecule). Positively charged groups will have a role of anchor sites for POM. Molecules of POM have negatively charged inorganic cage and for this reason they are attracted to positive charge.
After each functionalization step prepared materials will be characterized by means of ATR-FTIR, UV-Vis and 1H-NMR techniques. A level of functionalization of titanates (TiO2) nanostrctures will be determined by TGA analysis. On the other side HAADF-STEM will be used as a method for visual estimation of POM loading. This will be also estimated by TGA analysis.
In research phase II we will by EPR measurements of functional nanomaterials (POM-TiO2, POM-titanate) dispersed in water and illuminated with UV and Vis light determine active paramagnetic sites. EPR measurements will also give us information of successful electron transfer from POM to TiO2 or titanate nanostructures.
In the last phase from a hybrid nanomaterial that will load the highest number of POM and that will show the best result with EPR measurements will be in colaboration made a test cells for water oxydation.
Significance for science
The first applied study studies of sodium titanate nanotube and nanoribbon properties have shown that these materials are promising in acidic/base catalysis for organic transformations, for energy storage, in the photochemical decomposition of some organic compounds and as fillers in the nanocomposites where they mechanically strengthen the polymer matrix. In some of these studies our project group has been taking part. We reached the following findings which are important for the further development in this area of research: In the field of transformation of protonated titanate nanotubes and nanoribbons to TiO2 under different conditions, where the emphasis was on morphology preservation we found: -to transform protonated titanate nanostructures to TiO2 nanostructures under hydrothermal conditions is necessary the presence of water and that regardless the reaction conditions (temperature and pressure) the conversion always yields anatase form of TiO2. -we found that transformation conditions significantly affect the photocatalytic ability derived materials; for example photochemical activity of antase nanoribbons were significantly lowered in comparison to those without N. Another area of research was to test sodium titanate nanotubes/nanoribbons and protonated titanate nanotubes/nanoribbons in acidic/base catalysis in organic chemistry. Two model reactions were selected: (i) aldol condensation (benzaldehyde + cyclohexanone) and (ii) Manich reaction (benzaldehyde + cyclohexanone +4-bromoaniline). Results suggest that these catalysts increase the reaction selectivity and in most cases also the yield is increased. We were one of the first on the world to use a combination of two techniques, NEXAFS and TXM, with improved spatial resolution that enabled to do NEXAFS measurements on the individual nanostructures: -taking the example of isolated bundles of hydrothermally prepared sodium titanate nanotubes, we are able to unravel the complex nanoscale structure from the NEXAFS–TXM data using multichannel multiplescattering calculations, to the extent of being able to associate specific spectral features in the O K-edge and Ti L-edge with oxygen atoms in distinct sites within the lattice. These can even be distinguished from the contribution of different hydroxyl groups to the electronic structure of the sodium titanate nanotubes -in the case of determining the oxidation state of manganese in sodium titanate and TiO2 nanostructures doped with Mn2+, measurements were done on the individual nanostructures and showed manganese oxidation state did not change during the synthesis of sodium titanate nanoribbons doped with manganese although Mn2+ is very unstable in alkaline conditions and tends to oxidize to Mn3+. The oxidation from 2+ to 3 and 4+ occurred on calcination of protonated titanate nanoribbons at 700 C in air. In the case of synthesis of sodium titanate nanotubes/nanoribbons and doped sodium titanante nanotubes/nanoribbons we have shown that the presence of dopants, Ag+ and Mn2+, effect on the change in morphology. In the presence of these dopants in the reaction mixture instead of titanate nanotubes partly rolled 2D nanostructures were formed built by 2-5 titanate layers. In the case of doping with silver, Ag+ was reduced to Ag0. In the case of sodium titanate nanoribbons doped with Mn2+, we have shown that the presence of manganese does not affect the morphology and that dopant did not chage its oxidation state.
Significance for the country
One-dimensional titanate and TiO2 nanomaterials have proved to have big potential for applications in the field of catalysis, namely the acidic/base catalysis in organic chemistry and photocatalysis for degradation of organic pollutants. They have also proved to be a good support material for the preparation of nanocomposites. The importance of the results obtained in the framework of the project for the development of Slovenia is in the education of udergraduate students and young researchers: (i) Ana Dergan graduated on the topic of the project g (photoactivity of TiO2 nanotubes, 2011, Faculty of Physics and Mathematics, University of Ljubljana, supervisor: prof. dr. Denis Arčon) (ii) Katja Vozelj will graduate on till end of august 2014 (EPR study of N doped TiO2 nanoribbons, Faculty of Physics and Mathematics, University of Ljubljana, supervisor: prof. dr. Denis Arčon) (iii) Melita Rutar, young researcher (catalytic properties of titanate and TiO2 1D nanostructures, deadline: May 2016, International Postgraduate School of Jožef Stefan, supervisor: dr. Polona Umek).
Most important scientific results
Annual report
2011,
2012,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2012,
final report,
complete report on dLib.si
