Nano energy amplifier – the proposal and demonstration of triplet–triplet annihilation upconversion heterojunctions for photocatalysis using low-energy photons

Abstract

The photothermal effect does not qualify as real photocatalysis based on the optoelectronic characteristics of semiconductors and is generally considered an assisting approach rather than a substitute. Nearly all studies focus on thermal energy conversion from low-energy photons, highlighting that photothermal catalysis requires only sufficient temperature at local sites instead of heating the entire environment. The photothermal effect indeed contributes, but only when the corresponding photocatalytic reaction has been activated—a factor often neglected in published studies. A priori, one would expect underpowered low-energy photons to lead to extremely low catalytic efficiency, yet experimental observations often defy these expectations. Here, we propose a triplet–triplet annihilation upconversion (TTA-UC) heterojunction, constructed from MoS₂ and ZIF-FL, which enables near-infrared to blue-violet upconversion with excellent stability. The anti-Stokes shift is large (0.86 eV). Resonance energy transfer and interfacial migration bridges (Mo–N and Fe–S) facilitate efficient triplet–triplet energy transfer from ³MoS₂* to ³ZIF-FL*. When pollutants exist, energy is transferred in situ from TTA-generated high-energy singlets to reactants rather than being emitted as photons (tetracycline removal reaches up to 85.4% even at 5–10 °C), thereby avoiding reabsorption loss and achieving genuine NIR-driven photocatalysis. Finally, the energy-transfer mechanism among various excitons within the TTA-UC heterojunction is elucidated.