An innovative strategy allowing the development of a new generation of easy-to-prepare and easy-to-use nano-sized catalysts with high tenability is presented. This strategy is based on the formation of hybrid polyion complexes (HPICs) from the complexation of copper with a block copolymer consisting of an ionizable complexing block and a neutral stabilizer block. These complexes have a well-defined structure and size with a hydrodynamic diameter around 29 nm. They are stable in aqueous solution over a pH range from 4 to 8 and are not sensitive to NaCl salt addition or dilution effects. As a proof-of-concept the degradation of naphthol blue black in water through the use of the Fenton or photo-Fenton reaction is studied. Their performances are comparable to a classical homogeneous reaction , whereas HPICs are easily recyclable by simple dialysis.