Near-infrared-activated Z-scheme NaYF4:Yb/Tm@Ag3PO4/Ag@g-C3N4 Photocatalyst for Enhanced H2 Evolution under Simulated Solar Light Irradiation

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 NaYF4:Yb/Tm@Ag3PO4/Ag@g-C3N4 architectures responsive in full-spectrum solar light by sequentially depositing the Ag3PO4/Ag nanoparticles and g-C3N4 nanosheets on UC NaYF4:Yb/Tm hexagonal disks. The overlapping of UV-visible emissions generated by the core NaYF4:Yb/Tm via UC process from the NIR photons in solar illumination and the absorption of Ag3PO4/Ag@g-C3N4 shell allows additional photons to supplement the charge carrier separation in Ag3PO4/Ag@g-C3N4, which is confirmed by the photoelectrochemical measurements. The presence of metallic Ag inhibits the rapid recombination kinetics in g-C3N4 through swift injection of electrons from Ag3PO4, thus redeeming more excited electrons in g-C3N4 with high reducing power for H2 production. The NaYF4:Yb/Tm@Ag3PO4/Ag@g-C3N4 demonstrated 23.56 mmol/g/h photocatalytic H2 evolution rate, which is 2.6 and 1.4 times higher compared to NaYF4:Yb/Tm@Ag3PO4/Ag (9.05 mmol/g/h) and NIR inactive NaYF4@Ag3PO4/Ag@g-C3N4 (16.32 mmol/g/h) photocatalysts, respectively. Further, NaYF4:Yb/Tm@Ag3PO4/Ag@g-C3N4 photocatalyst H2 production activities under the illumination of separate NIR, visible, and UV lights are evaluated. The distinctive synthesis approach and underlined photocatalytic H2 evolution mechanisms have the implications for rationally designing highly efficient UC-based broadband photocatalysts for harvesting full-spectrum solar energy.