Selective superoxide radical generation and enhanced photocatalytic oxidation over g-C3N4/LDH/CoPcS ternary catalysts

Superoxide radicals (•O 2 − ) play a pivotal role in photocatalysis, yet studies on the selective enhancement of •O 2 − pathways to improve the degradation efficiency toward •O 2 − -sensitive pollutants remain scarce. Accordingly, we selected g-C 3 N 4 , which is recognized for generating •O 2 − as the primary reactive species in pollutant degradation, as the host photocatalyst for selectivity design. A g-C 3 N 4 /LDHs/CoPcS ternary photocatalyst with dual type-II heterojunction was synthesized via coprecipitation, calcination, and hydrothermal treatment. The material's properties were characterized by SEM, TEM, XRD, FTIR, XPS, and UV–vis DRS. Under visible light, the optimal g-C 3 N 4 /LDHs/Co-5 composite exhibited a 29.7 % increase in tetracycline degradation efficiency and a 2.25-fold increase in the reaction rate constant compared to pristine g-C 3 N 4 . Additionally, the photocatalytic mechanism was investigated through reactive species capture experiments and ESR analysis, with transient photocurrent responses, EIS measurements, Mott-Schottky analysis, and PL spectra providing complementary evidence. The results indicated that the positive surface charges of the composite accelerated electron transfer to O 2 , thereby speeding its reduction to •O 2 − , promoting selective •O 2 − generation and improving the photocatalytic degradation efficiency. This ternary composite advances g-C 3 N 4 from general photocatalytic use to •O 2 − -selective applications, providing an effective approach for degrading tetracycline and other •O 2 − -sensitive pollutants.