Construction of a novel double S-scheme heterojunction CeO2/g-C3N4/ Bi2O4 for significantly boosted degradation of tetracycline: Insight into the dual charge transfer mode

Constructing dual S-scheme heterojunction, as one kind of new strategy for the reinforcement of photocatalytic property, shows significant advantages in facilitating the migration of photoinduced charges and achieving high redox potentials. Herein, a novel double S-scheme heterojunction CeO2/g-C3N4/Bi2O4 was designed and synthesized successfully. The photodegradation of tetracycline (TC) over CeO2/g-C3N4/Bi2O4 was carried out under the irradiation of visible light. The double S-scheme interfacial charge transmission mode of CeO2/g-C3N4/Bi2O4 was investigated according to Fermi level, band structure, and the in-depth analysis of in situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and electron spin resonance (ESR) spectra. The CeO2/g-C3N4/Bi2O4 exhibits excellent catalytic activity with a high TC removal efficiency of 94 % and a remarkable mineralization efficiency of 51 %. The rate constant (0.05811 min-1) of TC degradation for CeO2/g-C3N4/Bi2O4 is 12.9, 7.8, 4.3, 2.2, and 3.1 times those for g-C3N4, CeO2, Bi2O4, g-C3N4/Bi2O4 and CeO2/g-C3N4, separately. The prominently boosted activity may be due to two factors. Firstly, the successful creation of the double S-scheme electron migration channel greatly boosts the transmission of photogenerated carriers, represses the recombination of electrons with holes, and ensures the strongest redox potential of CeO2/g-C3N4/Bi2O4. Secondly, the introduction of Bi2O4 with excellent visible-light absorption broadens the optical absorption region of CeO2/g-C3N4/Bi2O4. Additionally, the influence of the typical environmental factors (pH, inorganic anions, cations, and natural humus) on the photodegradation of TC was explored. The three probable pathways for TC degradation were inferred via analyzing intermediates. The current work offers a novel outlook for enhancing the activity of ternary heterojunction photocatalysts applied in environmental restoration.