S-scheme tubular g-C3N4/BiOI heterojunctions for boosting photodegradation of tetracycline and Cr(VI): Mechanism insight, degradation pathway and DFT calculation

•S-scheme tubular g-C3N4/BiOI heterojunctions were designed.•Photodegradation efficiencies for TC and Cr(VI) reach 90.1% and 96.8%.•Rate constants for photodegradation of TC and Cr(VI) are 0.1687 and 0.0718 min−1.•Three different degradation pathways for TC are proposed.•DFT calculations confirm the formation of S-scheme heterojunctions.