In-silico development of the potential of doped metal-oxide nanotubes as novel photo-catalysts for energy applications

As the situation regarding the costs of energy production becomes more challenging, due to both resource limitation and the impact of an oil-fuelled economy on the climate, the potential relevance of new materials and technologies capable of converting sunlight into industrially viable forms such as electrical power or chemical fuels is paramount. Crucial to this energy conversion is the presence of photo-catalysts (PCs).PCs are compounds which comply with the following: first, they absorb light, whose energy (related to the frequency of its photons) is used to excite one electron (e) of a PC to a higher-energy state (e*) leaving one hole (h) in the pristine electronic state. Once a photon has been absorbed, and one e*-h pair created, several competing processes may take place: 1) the e*-h pair may induce decomposition of the compound; 2) the e*-h pair can release some of its energy into the nuclear vibrations before e* decays, by emission of one photon, to his pristine state thus recombining with h, or 3) e* and h can separately react with other molecules or enter an electric circuit. Thus, viable PCs are characterized by photo-stability, and an e*-h recombination rate slower than the time it takes to the e*-h pair to separately react with other species. Typically, the farther e* is created from h, the slower the e*-h recombination. The chemical elegance of PCs emerge in that, due to the absorbed photon energy, the e*-h pair is highly reactive and may separately reduce-oxidize reactants, thus triggering a redox chemical reaction which can be used to convert light into chemical energy i.e. fuels. If, as it happens for natural photosynthesis, the photon energy comes from the Sun, then PCs can make Sun energy available on Earth as fuels, thus contributing to energy production. Notably, the energy stored in the e*-h pair can in principle be used also for other energetically expensive applications, such as, for instance, the production of ammonia and its derivative, or the decomposition of industrial polluting waste into substances less hazardous for the environment.The research focuses on open-ended metal-oxide nanotubes (MONTs), which are macromolecular tubes made of Al (Ge), Si, O and H. The project builds on recent findings about the possibility to create e*-h pair on different sides of MONTs walls which should provide rather long e*-h recombination times as required for PCs. Preliminary simulations of these systems suggest that it should also be possible to insert other atoms (dopants) into MONTs walls. It is anticipated that the chemical nature of the dopant will influence the photo-catalytic performances of doped MONTs (dMONTs). The proposed research aims at identifying key aspects of the relationship between the structure of dMONTs and their photo-activity. This insight will then be used to optimise dMONTs in terms of side-dependent photo-catalytic performances with special focus on the enhancement of e*-h chemistry over e*-h recombination. The theoretical research will rely on solving the quantum mechanical equations of motion for the electrons and the nuclei of dMONTs in order to characterize their geometrical and electronic properties. This will allow to identify systems with maximum e*-h separation and the largest affinity to e*-h transfer to other species. Theoretical and experimental insight about the light energy required to generate e*-h pairs for specific dMONTS will also be obtained. Finally, simulation of the time evolution of e*-h in dMONTs will provide insight into the factors governing the competition between e*-h recombination, and e*-h transfer which will make it possible to selectively frustrate the former while enhancing the latter, thence boosting the photo-catalytic performance of dMONTs. This knowledge will open the way to possible dMONTs-based applications in many different areas important for our economy such as fuel production, industrially targeted PCs, and decomposition of polluting waste.

The proposed research will explore innovative systems and concepts which could possibly lead to the definition of novel photocatalytic strategies for energy applications and environmental remediation. The multi-disciplinary and scientifically challenging nature of the project will create an ideal platform for training in cutting edge theories and methods, and for the development of independent multi-level thinking capabilities. The potential relevance of the research for energy production and environmental remediation - two themes tightly intertwined with the industrial and political sectors - readily defines an extremely wide range of external possible beneficiaries of the research. Identifiable short-term beneficiaries include the research students of the project and of the experimental counterpart who will receive training and education in a highly multi-disciplinary cutting-edge research project. The challenging nature of the project will foster the development of independent thinking capabilities, IT-skills, and also execution of an internationally recognisable PhD thesis. Additionally, employment at the Host Institution will also offer interaction with other international researchers, contributing to a more rounded and methodologically unbiased formation. Identified medium-long term beneficiaries include: * The Commercial Sector. The prospect of highlighting elements which could be optimised and fine-tuned to improve specific industrial processes could be of great import to the Commercial Sector. Besides being relevant to the already existing UK-based industries with interests in Photocatalysis and Energy Production (Johnson Matthey, Pilkington Glass, Croda, Tioxide, Millennium and Unilever, to name just a few) positive outcomes of the research could also generate medium-term impact such as patent registration and the creation of spin-off activities. * National and International Policy-makers. Generation of fuels from renewable sources using sunlight, or the prospect of effectively contributing to the general healthcare via carbon dioxide removal or water and air purification schemes would evidently be of remarkable interest to society as a whole, and consequently also to UK Policy-makers, especially for Institutions such as the Departments of Business, Energy and Climate Change, Environment, and Health. By extension, the same conclusion should also hold for the international politic scenario. * The Public Sector. The possible use of efficient photocatalysts for water and air purification would be of general interest not only to the industrial sector but, more generally, to any sector concerned with the quality of water and air in public areas such as for instance hospitals, public transportation, educational infrastructures, public entertainment, etc. Communication of the research outcomes to the identified Public Sector beneficiaries will be of upmost importance. Accordingly, the research results will be made available to the wider public via the creation of non-academic level informative WebPages, and via popular (scientific) press release. To this end, training in Public Communication skills will be also sought. Engagement with the UK Semiconductor Photochemistry Network will represent a privileged platform for broader dissemination of the acquired knowledge within Academic, Industrial and Public Information networks. In fact, participation in UK-SPC newsletters, conferences, technical workshops and industrial visits is anticipated to greatly favour both the dissemination of the results and a highly beneficial awareness of the actual industrial requirements. Last but not least, the Host Institution presence within the North-West Development Agency (NWDA) and the (N8) Northern Universities Consortium warrants for facile access to the existing close links to Industry and Policymakers which will further increase the chances of impact on the latter.