Synthesis of O-doped C3N4 decorated with C3N4 quantum dots: Construction of a homo junction photocatalyst for the enhanced photocatalytic degradation of tetracycline

• A homo junction photocatalyst was prepared by combining O-doped C 3 N 4 with C 3 N 4 qds. • The O doping and the quantum size effect of C 3 N 4 qds were two key factors. • An enhanced IEF formed in O-doped C 3 N 4 /C 3 N 4 qds facilitated charge transfer. • 1 O 2 was the major active species for the photocatalytic degradation of tetracycline. Constructing a homo junction was a promising approach to inhibit the recombination of photoexcited electrons&holes and improve the photocatalytic performance for pollutant removal. However, there were few reports on adjusting the internal electric field (IEF) intensity of a homo junction via energy band engineering. A homo junction photocatalyst (O-doped C 3 N 4 /C 3 N 4 quantum dots) was prepared by facile chemical oxidation and hydrothermal treatment. The results indicated that the quantum size effect of C 3 N 4 qds and O doping were the key factors for constructing the homo junction. This unique structure provided good inter-crystal compatibility and the feasibility to enhance the IEF intensity. Consequently, the separation of photoexcited charge carriers was promoted, and the photocatalytic performance was thus improved. As expected, the best degradation of tetracycline was obtained over O-doped C 3 N 4 /C 3 N 4 qds. The corresponding first-order kinetic constant was 2.43, 3.06 and 4.29 times that of C 3 N 4 /C 3 N 4 qds, C 3 N 4 /C 3 N 4 non-qds and the bulk phase C 3 N 4 , respectively. The reactive species capturing experiments verified that singlet oxygen was the major reactive species during the photocatalytic degradation of tetracycline. Additionally, the photocatalytic mechanism and the possible degradation pathways of tetracycline were proposed. This work offered a novel idea to prepare photocatalysts for wastewater treatment.