Therefore, we hypothesize that the catalytically active residual Pd site has a favourable interaction for electron transfer with the BT unit. Perhaps, reduced PFBT with protonated BT units at acidic conditions even works as both electron proton channels to the active species. If the residual Pd is the only catalytic site in PFBT polymer, then the catalytically active Pd sites should be much less than the Pd amount detected by ICP, it is also evident from the comparable photocatalytic performance from the samples with 1000 ppm and less than 10 ppm Pd.