A simple, facile in situ reduction approach is reported for the synthesis of Pd-nanoparticle-decorated phosphotungstic acid (PTA)-MIL-100(Fe) nanocomposites (Pd-H₃PW₁₂O₄₀-MIL-100(Fe), denoted Pd-PTA-MIL-100(Fe)). During the in situ synthesis, PTA is encapsulated into the matrix of MIL-100(Fe) and serves as a UV-switchable reducing agent, resulting in highly dispersed Pd NPs. Using the photocatalytic degradation of pharmaceuticals and personal care products as model reactions, the ternary Pd-PTA-MIL-100(Fe) hybrids exhibited enhanced photocatalytic activity compared with their foundation matrices, the binary PTA-MIL-100(Fe) nanocomposite. Based on photoelectrochemical analyses, the improved photocatalytic performance can be attributed to the well-known electronic conductivity of the Pd NPs, the fast electron transport of PTA, the intense visible-light absorption of MIL-100(Fe), and the matched energy levels of the three components: MIL-100(Fe), PTA, and Pd NPs. Importantly, almost no Fe and W ions were leached from the samples during the reaction, demonstrating the photostability of the Pd-PTA-MIL-100(Fe) composite. In addition, possible photocatalytic reactions mechanisms have also been investigated.

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles (Au, Pd, Pt) were immobilized on MIL-100(Fe) (denoted M@MIL-100(Fe)) using a facile room-temperature photodeposition technique. The resulting M@MIL-100(Fe) (M = Au, Pd, and Pt) nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange (MO) and reduction of heavy-metal Cr(Ⅵ) ions under visible-light irradiation (λ ≥ 420 nm) compared with blank-MIL-100(Fe). Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100(Fe) under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100(Fe) toward photocatalytic redox reactions. In particular, the Pt@MIL-100(Fe) with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100(Fe) (M = Au and Pd), which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.