Near-infrared to visible photon transition by upconverting NaYF4: Yb3+, Gd3+, Tm3+@Bi2WO6 core@shell composite for bisphenol A degradation in solar light

Abstract

The effective use of sunlight by photocatalyst systems is challenging. Here, we report an active-core@inert-shell nanohybrid composite that converts incompatible near-infrared (NIR) radiation to functional ultraviolet-visible (UV-vis) photons. The active core is composed of NaYF4: Yb3+, Gd3+, and Tm3+ upconverting nanoparticles (UCNPs). An inert bismuth tungstate (Bi2WO6) shell with a narrow band gap (2.65 eV) was grown over the core via ethylenediaminetetraacetic acid-metal complex formation. Solar infrared photons were successfully converted to UV-vis photons, which activated the Bi2WO6 shell via Forster resonance energy transfer (FRET). The high UV-vis-NIR response of the UCNP@Bi2WO6 composite was demonstrated by 94% degradation of Bisphenol A in 180 min. Integrating UCNPs with Bi2WO6 resulted in a high quantum yield of 3.16 x 10(-5) molecules/photon, which is superior to the yield of the photocatalysts currently used. High photocurrent density (0.78 mA/cm(2)) confirmed the excellent photoelectrochemical potential for water splitting. Hydroxyl radicals generated at the valence band and superoxide radicals at defect sites in the Bi2WO6 explain the excellent catalytic activity of UCNP@Bi2WO6. A figure of merit (FOM) reflecting important operational parameters was calculated and compared with previous reports for catalytic performance evaluation. The high FOM value of the UCNP@Bi2WO6 hybrid composite indicates its excellent potential for practical applications.