Z-scheme Bi2SiO5/Ni-doped Ag6Si2O7 heterojunction with remarkable photocatalytic performance for MO degradation with enhanced light absorption ability: Adjustment of electron transfer path and energy band structure

•Bi2SiO5/Ni-doped Ag6Si2O7 exhibited excellent photocatalytic activity under simulated sunlight irradiation.•On the basis of forming heterojunction, a Ni2+ impurity energy level was introduced into Ag6Si2O7 to further enhance optical and electrochemical property.•Theoretical calculation was carried out to prove the existence of the impurity energy level.•The direction of electron transfer in the photocatalytic process was clarified to prove the possible mechanism.•The roles of the impurity energy level in the Z-Scheme heterojunction were investigated.