A UV-visible-NIR active smart photocatalytic system based on NaYbF4:Tm3+ upconverting particles and Ag3PO4/H2O2 for photocatalytic processes under light on/light off conditions

Abstract

The development of broad-spectrum photocatalytic materials that allow the use of a larger portion (UV to NIR) of the solar spectrum for photocatalytic processes has attracted great attention. Among visible light-active photocatalysts, silver phosphate (Ag₃PO₄) stands out prominent for its high photocatalytic activity towards the degradation of different pollutants. However, the full potential of this photocatalyst is limited by its inherent low photostability arising from self-photoreduction and its inability to efficiently use light beyond the UV-Vis range of the solar spectrum. To address these fundamental limitations of Ag₃PO₄, we have developed a smart photocatalytic system by combining the interesting upconversion property of NaYbF₄:Tm³⁺ upconverting particles (UCPs) with the exceptionally high photocatalytic activity of Ag₃PO₄ and the oxidizing capacity of H₂O₂. In this UCPs/photocatalyst/oxidant (NaYbF₄:Tm³⁺/Ag₃PO₄/H₂O₂) system, the NIR-to-UV/visible UCPs can convert low energy NIR photons into high energy UV-visible photons that can be absorbed by Ag₃PO₄, thus photo-exciting (activating) it indirectly under NIR illumination. Similarly, the oxidant (H₂O₂) prevents self-reduction and/or assists in regeneration of Ag₃PO₄ through a Fenton-like process, thus ensuring the photostability and recyclability of Ag₃PO₄. Interestingly, the Ag₃PO₄/H₂O₂ system remains active generating reactive oxygen species even after the photoexcitation process is turned off (dark conditions). The proposed broad spectrum photocatalytic system (UCPs/Ag₃PO₄/H₂O₂) was found to exhibit a high photocatalytic response (98% degradation of crystal violet dye in 90 min) under NIR illumination from a 980 nm laser and still a higher response (100% removal in less than 8 min) under direct visible light from low-cost blue emitting LEDs.