Rationally　constructing　functionalized　cocatalysts　for　removing　chemically　inert　polychlorinated　biphenyls　is　significant　and　challenging.　In　this　study,　we　have　synthesized　uniform　Pd　nanocrystals　(Pd　NCs)　with　cube　(CUB)　and　octahedron　(OCT)　geometries,　corresponding　to　the　exposed　(100)　and　(111)　facets,　and　they　were　incorporated　with　ultrathin　TiO2(B)　nanosheets　(TBs)　for　the　photocatalytic　dechlorination　of　polychlorinated　biphenyls　under　visible　light　illumination　(λ　≥　400　nm).　Photocatalytic　performance　experiments　revealed　that　CUB/TBs　is　more　efficient　with　a　200%　enhancement　higher　than　OCT/TBs.　Physicochemical　characterizations　reveal　that　the　CUB　possesses　higher　surface　charge　density　than　OCT,　which　promotes　the　activation　of　the　C–Cl　bond　of　polychlorinated　biphenyls,　leading　to　higher　dechlorination　performances　of　CUB/TBs　than　OCT/TBs.　This　study　not　only　fundamentally　elucidates　the　effect　of　facet-engineering　palladium　nanocrystals　on　the　photocatalytic　dechlorination　of　polychlorinated　biphenyls,　but　also　paves　the　way　for　rationally　fabricating　superior　photocatalysts　for　other　advanced　applications.　This　journal　is　©　The　Royal　Society　of　Chemistry