Surface Engineered Nanocrystals: EPR Radical Detection of Photoactivity

Environmental air and water remediation by nanocrystalline semiconductor photocatalysts has become increasingly important in recent years. TiO2 remains the most popular material for these applications due to its low cost, abundance, high activity, and stability under a variety of conditions, however its wide range utilisation is restricted due to limited efficiencies, absorbing only 3% of available solar energy (in the UV region). Commercial advancements require enhanced visible-light induced quantum yields of photogenerated charge carriers. Lattice doping of TiO2 with (non)metal ions is a highly promising approach for increasing photocatalytic efficiencies through modification of bandgap and band-edge potentials, which are intricately linked to resulting surface reactions. This utilises earth-abundant metals and is a step-change from modifying oxide materials with expensive noble metals.
The advent of synthetic strategies for controllable fabrication of TiO2 with specific morphologies and crystal facets has emerged as a promising way to improve charge-carrier quantum yield. This proposal aims at combining these tactics to develop a library of novel nanocrystalline materials, produced via readily scalable methodologies. This works seeks to build on our recent results. We have identified that co-doped titania catalysts (W,N-TiO2) are effective for improving the nitrate selectivity of the photocatalytic oxidation of NOx to nitrates. We have also identified specific oxygen-vacancy sites on the titania surface that act as preferential sites for catalysis. By combining these technologies, this could open new and exciting avenues in semiconductor photocatalysis for environmental remediation technologies in which the optimization of molecular oxygen reduction, together with the pollutant species to be oxidized, becomes a central element of the catalyst design without relying on the use of rare and expensive PGMs.
The novel materials will be characterised by a combination of advanced spectroscopic techniques. Primarily, Electron Paramagnetic Resonance (EPR) spectroscopy will directly probe the photo-induced paramagnetic charge carriers, determining the position of highly reactive lattice sites. Advanced hyperfine structure measurements will elucidate an atomic-level structural description and access the electronic properties of lattice dopants through unique spectral fingerprints. The nature of surface reactions will subsequently be explored through state-of-the-art Attenuated Total Reflectance spectroscopy, utilising pulsed lasers to obtain reaction dynamics on fs timescales. Target applications will be selective decomposition of volatile organic compounds and nitrogen oxides (NOx), both common airborne pollutants which are damaging to human health and implicated in climate change.
Our research program will have immediate impact on UK science, with academic beneficiaries within the chemical and materials sciences. The project will provide interdisciplinary training for the EPSRC PDRA and Cardiff University funded PhD student. The combination of multiple advanced spectroscopies will shed light on fundamental redox processes, which will have longer-term benefits in photovoltaics, organic synthesis and selective transformations of bulk chemicals. This New Investigator Grant will allow Dr Richards to develop an independent research programme investigating light-induced electron transfer processes, and provide a team of highly skilled researchers vital to advance her academic career.
Success in this programme will combine the results of synthesis, characterization and catalytic activity to guide the rational design of selective visible-light activated semiconductor photocatalysts.

Societal and Economic Impact
Air pollution, from road transport and industrial activity, harms our health and wellbeing, resulting in ~ 29,000 deaths and ~£16 billion associated costs in the UK per year. DEFRA 2016 statistics indicate 37 (of 43) UK monitoring zones exceeded the NO2 Air Quality Directive limit, and 42 exceeded the long-term objective for ozone. NOx air pollution is directly associated with mortality and damage to biodiversity, and can react with VOCs to produce secondary photochemical pollutants, implicated in climate change. The solar photocatalysis technology proposed in this project (~ $2.9B global market economy), can directly target both of these problems, making use of sunlight as an inexpensive, environmentally friendly, and universally applicable emerging technology, providing a sustainable route towards improvements in environmental statistics.

Detailed understanding of electron transfer processes in heterogeneous catalysts is required to improve efficiencies in the valuable area of oxidative chemistry. The work described will lead to structure-dynamic relationships that will provide real-world applications in industrial catalysis and environmental remediation. Our ability to study electron transfer processes will be transferrable to the fields of homogeneous photochemistry (utilizing solar energy to induce selective transformations in synthesis) and the optoelectronics industry. Our work will highlight the strength of Electron Paramagnetic Resonance spectroscopy as a versatile and powerful analytical method that can be exploited to provide advanced information on systems across the chemical, physical and life sciences.

Our research is at the interface of synthetic chemistry, state-of-the-art spectroscopy, and computational chemistry, with potential for short/medium/ long-term social and economic impact. In the short term this grant will directly benefit UK and international academics working in the fields of EPR spectroscopy and analytical chemistry, heterogeneous catalysis, and materials science. The combination of advanced spectroscopic techniques is anticipated to deliver new insights into fundamental redox processes and offers significant opportunities for advancements in rational catalyst design principles. Dissemination of research highlights to academic communities will be through peer-review journals in high impact general and specialist publications, and conference presentations or invited seminars at (inter)national meetings.
The project will provide an excellent training ground for the PDRA/ PhD student, allowing them to develop skills in performing and disseminating cutting-edge research in a vibrant and multi-disciplinary environment, and enhancing their future employability.
The themes of air pollution and renewable technologies forms excellent and timely topics for offering curriculum-enhancing outreach activities (school-based and general audience), designed to inspire the next generation of scientists and to advertise the benefits of our research to the wider public. The female PI will act as a positive role model of women in science, thereby directly addressing the gender gap within STEMM subjects.

Medium and longer term impact in the years following the grant will include full engagement with industrial beneficiaries, as the most active catalysts are identified and large scale synthetic methodologies are developed. The PI will consult with RIES of Cardiff University to identify potential industrial partners and identify current problems within commercial oxidative chemistry. Guidance from the Commercial Advisory Panel will pre-emptively identify any commercial opportunities and unique IP associated with the project. This will allow timely identification of routes to market and exemplification of potential patent positions.