β-NaGdF4:Yb,Er@CdS/MWCNTs photocatalysts with efficient interfacial energy migration for full-spectrum light-driven antibiotic degradation: Construction and DFT insight

Currently, upconversion nanoparticles (UCNPs) based photocatalysts have been extensively developed to improve solar energy utilization. However, the mechanisms underlying interfacial energy migration of upconversion photocatalyst remain unclear. Herein, a promising composite photocatalyst with complementary properties is designed by integrating β-NaGdF4:Yb3+/Er3+ (NGFYE), CdS and multi-walled carbon nanotubes (MWCNTs). The morphology, structure and chemical properties of NGFYE@CdS/MWCNTs ternary photocatalyst are characterized. In addition, the existence of Förster resonance energy transfer process in NGFYE@CdS/MWCNTs photocatalysts, i.e., the migration of excitation energy from Er3+−4S3/2 excitation level and higher excitation level (e.g., Er3+−2H11/2) to CdS nanoparticles, was further confirmed by density functional theory (DFT) calculations. The optimized NGFYE@CdS/MWCNTs photocatalyst presents 71.65 % and 35.29 % degradation of tetracycline hydrochloride (TCH) and ciprofloxacin (CIP) under λ ≥ 800 nm irradiation for 3 h, respectively. This work not only illustrates the interfacial energy migration mechanism between NGFYE and CdS, but also provides insights for the rapid construction of heterojunction materials with efficient energy transfer interfaces.