The inability of common environmental photocatalysts to utilize low-energy light limits the promise of semiconductor photocatalysis as a sustainable, low-infrastructure strategy for the remediation of polluted air and water. The reactive oxygen species (ROS) resulting from the electron-hole pairs generated by excited semiconductor photocatalysts are capable of degrading a variety of organic and inorganic pollutants. Unfortunately, the wide band gaps of suitable semiconductors prevent them from absorbing most of the photons present in sunlight and common indoor light sources, giving rise to a fundamental mismatch between the wavelengths of light prevalent in outdoor and indoor environments and the wavelengths of light that can be utilized by environmental photocatalysts. Amplifying the frequency of incident light through upconversion (UC) of two or more sub-bandgap photons to a single higher-energy photon can help to correct this mismatch, maintaining the photocatalysts’ high redox potentials while enabling them to absorb and utilize low-energy light that they would otherwise transmit.<br/>Triplet–triplet annihilation UC (TTA-UC), the only UC mechanism efficient under low-intensity noncoherent light, has traditionally been considered incompatible with applications in oxygen-rich conditions due to its need for a non-polar, deoxygenated host medium. However, the recent realization of practical solid-state TTA-UC films that provide robust oxygen protection and in which TTA-UC can operate with high quantum efficiencies has opened the door to integration of TTA-UC with technologies such as semiconductor photocatalysis. Our group has successfully employed these films to enhance photocatalytic ROS production in both aqueous and gas-phase environments. This research recently culminated in the production of sub-bandgap photocatalyst devices capable of degrading acetaldehyde, a prototypical volatile organic carbon (VOC). This is the first instance in which TTA-UC has been employed to drive the photocatalytic degradation of a pollutant of environmental relevance, providing the crucial first step toward use of TTA-UC to enhance the remediation of contaminated air and water. We will present an overview of this research, focusing on ongoing work in which we aim to improve device performance by incorporating multiple light-absorbing UC compounds in order to harness a broader range of incident photons.

Enhanced environmental remediation using triplet–triplet annihilation upconversion: Broadening the sub-band light absorption of semiconductor photocatalysts

254th National Meeting (2017)

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