Near-infrared-activated Z-scheme NaYF4:Yb/Tm@Ag3PO4/Ag@g-C3N4 photocatalyst for enhanced H2 evolution under simulated solar light irradiation

Abstract

• NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag@g-C 3 N 4 photocatalyst active in UV–vis–NIR light is prepared. • Ag inhibits the rapid charge-carrier recombination in g-C 3 N 4 by swift injection of e - from Ag 3 PO 4. • NaYF 4 :Yb/Tm supply additional UV–visible photons to Ag 3 PO 4 /Ag@g-C 3 N 4 under solar light illumination. • NIR-inactive NaYF 4 @Ag 3 PO 4 /Ag@g-C 3 N 4 exhibited H 2 evolution rate of 16.32 mmol/g/h. • NIR-active NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag@g-C 3 N 4 showed H 2 evolution rate of 23.56 mmol/g/h. Upconversion (UC) active photocatalysts that absorb light beyond UV–visible region and catalyse reactions using the collected upconverted (NIR to UV–visible) photon energy have received incredible attention in renewable solar hydrogen production and environmental remediation. In this study, we report a facile synthesis strategy to produce the NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag@g-C 3 N 4 architectures responsive in full-spectrum solar light by sequentially depositing the Ag 3 PO 4 /Ag nanoparticles and g-C 3 N 4 nanosheets on UC NaYF 4 :Yb/Tm hexagonal disks. The overlapping of UV–visible emissions generated by the core NaYF 4 :Yb/Tm via UC process from the NIR photons in solar illumination and the absorption of Ag 3 PO 4 /Ag@g-C 3 N 4 shell allows additional photons to supplement the charge carrier separation in Ag 3 PO 4 /Ag@g-C 3 N 4 , which is confirmed by the photoelectrochemical measurements. The presence of metallic Ag inhibits the rapid recombination kinetics in g-C 3 N 4 through swift injection of electrons from Ag 3 PO 4 , thus redeeming more excited electrons in g-C 3 N 4 with high reducing power for H 2 production. The NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag@g-C 3 N 4 demonstrated 23.56 mmol/g/h photocatalytic H 2 evolution rate, which is 2.6 and 1.4 times higher compared to NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag (9.05 mmol/g/h) and NIR inactive NaYF 4 @Ag 3 PO 4 /Ag@g-C 3 N 4 (16.32 mmol/g/h) photocatalysts, respectively. Further, NaYF 4 :Yb/Tm@Ag 3 PO 4 /Ag@g-C 3 N 4 photocatalyst H 2 production activities under the illumination of separate NIR, visible, and UV lights are evaluated. The distinctive synthesis approach and underlined photocatalytic H 2 evolution mechanisms have the implications for rationally designing highly efficient UC-based broadband photocatalysts for harvesting full-spectrum solar energy.