A　simple,　facile　in　situ　reduction　approach　is　reported　for　the　synthesis　of　Pdnanoparticle-　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.　©　Tsinghua　University　Press　and　Springer-Verlag　GmbH　Germany　2017.