Three piperazine compounds as corrosion inhibitors for copper in 0.5 M sulfuric acid medium

•Electrochemical tests indicated the order of inhibition efficiencies: CP > LP > AP.•Surface characteristics (SEM, AFM, FT-IR and XPS) analysis provided valid evidences for the existence of inhibition films on Cu surfaces.•The adsorption of CP, LP, and AP on the Cu surfaces deferred to the Langmuir model.•Theoretical calculation results revealed that the three piperazine compounds were adsorbed onto Cu surfaces, owing to the N and O atoms in benzene rings and heterocycles.