Decorating Upconversion Nanoparticles Mediated by Both Active and Inert Shells on NH2-MIL-101(Fe) for the Photocatalytic Degradation of Antibiotics and Organic Dyes

Photocatalysis is a promising pathway to degrade pollutants in water. Although numerous photocatalysts have been developed to remove organic dyes in water, the degradation of antibiotics is still a perplexing problem due to their excellent stability. The hybrid photocatalyst upconversion nanoparticle (UCNP)/metal–organic framework (MOF) has been developed with the aim to utilize the full solar light. However, the low upconversion efficiency results in an unsatisfactory photocatalytic activity. A novel core–shell–shell UCNP, NaYF4:Yb/Tm@NaYF4:Yb@NaYF4 (Tm@Yb@Y), is synthesized to increase the upconversion efficiency. Both the active and inert shells are introduced in the UCNPs, which not only are favorable to weaken the surface quenching but also are helpful to prompt the energy transfer back. As a result, the UC emission intensity is greatly improved as compared with Tm or Tm@Yb. Then, Tm@Yb@Y is combined with NH2-MIL101(Fe) (NMF) to fabricate the novel photocatalyst Tm@Yb@Y/NMF. It exhibits an excellent photocatalytic activity to degrade rhodamine B (RhB), levofloxacin (OFL), and tetracycline hydrochloride (TC). The contribution of near infrared (NIR) light and inert shell on the whole photocatalysis is considered. The possible photodegradation mechanism is proposed according to the photoelectrochemical measurements, free radical and hole trapping experiments, and pump power dependence of upconversion emission intensities. The outstanding performance of Tm@Yb@Y/NMF should be attributed to the synergistic effect including the wider light absorption range, increased UC emission intensity, and feasible electron–hole separation.