CeO2-g-C3N4 S-scheme heterojunctions for enhanced photocatalytic performance: Effects of surface C/N ratio on photocatalytic and adsorption properties

In this work, novel CeO2–C-g-C3N4 S-scheme heterojunctions with significantly enhanced photocatalytic performance were prepared for the first time by a facile one-step molten KCl–LiCl method. The formation mechanism of CeO2–C-g-C3N4 was discussed, where g-C3N4 turned to C by carbonizing and the surface C content was adjusted by controlling the synthesis conditions. The photocatalytic property of the ternary composites first increased and then decreased with synthesis temperature and time. The 580 °C 4h CeO2–C-g-C3N4 exhibited the best performance towards MB (Methylene blue) and TC (Tetracyclines) degradation with a removal degree of 99.9% and 92.5%, respectively. The surface C/N ratio was a key index that influenced the photocatalytic performance, and was calculated to be 0.918–1.352 for various CeO2–C-g-C3N4 catalysts. The 580 °C 4h CeO2–C-g-C3N4 had an appropriate C/N ratio of 0.930 and a narrow band gap. The formed S-scheme 2D heterojunctions and generated C clearly promoted the separation of photo-excited e-/h+. Besides, it was indicated that e- and ·O2− were the main active species for TC photodegradation. The 580 °C 4h CeO2–C-g-C3N4 exhibited a large BET surface area, high negative zeta potential, strong π-π electron donor-acceptor interaction, and an excellent MB adsorption ability. It was evident that chemisorption on catalyst surface played an important role for adsorbing MB. The formation mechanism of CeO2–C-g-C3N4 and the effects of the surface C/N ratio on photocatalytic performance, determined in this work, offer new insights for preparing and structuring highly effective photocatalysts, which is expected to promote further photocatalytic and adsorption applications.