Strategic combination of nitrogen-doped carbon quantum dots and g-C3N4: Efficient photocatalytic peroxydisulfate for the degradation of tetracycline hydrochloride and mechanism insight

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• N-CQDs/g-C 3 N 4 /PDS photocatalytic system was firstly used for HTC degradation. • N-CQDs/g-C 3 N 4 efficiently activated PDS under visible-light irradiation. • Excellent charge separation efficiency can be obtained due to N-CQDs and PDS. • •SO 4 − , O 2 − and h + were found as the dominant contributors to the HTC degradation. • The mechanism of N-CQDs/g-C 3 N 4 /PDS photocatalytic system was proposed. Photo-assisted peroxydisulfate (PDS) activation has exhibited a great potential for pollution control. In this study, metal-free nitrogen-doped carbon quantum dots (N-CQDs) modified g-C 3 N 4 composite was fabricated and used to activate PDS under visible light to effectively remove tetracycline hydrochloride (HTC) in wastewater. Specifically, almost 90% of HTC (20 mg/L) was removed in 60 min under the conditions of an initial value of catalysis dose of 0.5 g/L and PDS dose of 0.6 g/L. Electron spin resonance analysis and trapping experiments confirmed that SO 4 − , O 2 − and h + were found as the dominant contributors to the HTC degradation. PDS and N-CQDs acted as an electron acceptor to transfer the photogenerated charges, resulting in the successful activation of PDS. The promoting visible light absorption can be ascribed to up-conversion effect of N-CQDs. The combination strategy provides an innovative approach to synthesize binary metal-free carbonaceous photocatalysts for implementing PDS-based oxidative degradation of pollutants.