Environmental application of semiconductor photocatalysts as a sustainable technology option has received significant attention over the past few decades with some notable commercial successes. But challenges still remain and are related to its relatively low efficiency of photosensitization by longer-wavelength, lower-energy light that is abundant in the solar spectrum. This project will develop a highly innovative approach of enhancing the visible light susceptibility of semiconductor-based photocatalytic process. This research aims at manipulating light to amplify its frequency via a unique photoluminescence process called upconversion (UC) based on a triplet-triplet annihilation (TTA) mechanism. Through the TTA-UC process, two photons of higher wavelength, which are otherwise wasted, are combined and converted to a single photon with lower wavelength; these upconverted photons are subsequently used to sensitize photocatalysts and to produce reactive oxygen species (ROS) that effectively degrade pollutants and inactivate microorganisms in water. Researchers will employ a pair of organic sensitizers and acceptors that enable a highly efficient visible to visible or blue to UVA upconversion. Researchers will select various chromophore pairs, encapsulate them into microcapsules, and couple them with selected semiconductor photocatalysts. Various photoluminescence and photocatalytic experiments and instrumental analyses will be performed to quantitatively evaluate the properties of this new system including quantum yield, excitation and emission spectra, kinetics of energy transfer process (time-resolved spectra), and ROS production. The material synthesis and system development will be specifically targeted and tested for contaminant degradation and microbial inactivation in water as well as separation and recovery after use.
Ensuring access to inexpensive and clean sources of water is one of the greatest global challenges of this century. Advanced materials technology, such as the one developed in this project, offers opportunities to leapfrog over traditional infrastructure-intensive technologies to develop more sustainable approaches in both industrialized and developing countries, as long as cost efficacy is assured and unnecessary collateral impacts are avoided. This project has a great potential to develop solar-based technology that efficiently harvests lower-energy portions of the solar spectrum which is otherwise wasted in any existing photocatalyst-based processes. Researchers expect that UC/photocatalysts with improved solar energy utilization efficiency and capability for easy separation can be readily implemented in various environmental engineering practices including solar photocatalytic disinfection (e.g., implemented using a solar concentrator), advanced oxidation, and photocatalysis. The project aims at achieving this goal through effective integration the photophysics of upconversion, material synthesis, semiconductor photocatalysis, environmental micropollutant control, and disinfection.
