A facile pyrolysis synthesis of Ni doped Ce2O3@CeO2/CN composites for adsorption removal of Congo red: Activation of carbon nitride structure

•Ni doped Ce2O3@CeO2/CN composite is prepared in pyrolysis by tuning nickel doping.•CeO2 surface is reduced in air to form Ce2O3@CeO2 structure by carbon nitrides.•Carbon nitride structure is activated and positively charged by Ce2O3@CeO2 structure.•Ni doped Ce2O3@CeO2/CN composite has highest adsorption capability of Congo red.