0D/2D Carbon Nitride Quantum Dots (CNQDs)/BiOBr S-Scheme Heterojunction for Robust Photocatalytic Degradation and H<sub>2</sub>O<sub>2</sub> Production

Abstract: The construction of heterojunctions is a method employed to inhibit the rapid recombination of photogenerated carriers. In this work, zero-dimensional (0D) g-C3N4 quantum dots (CNQDs) were composited with two-dimensional (2D) BiOBr for the first time using the typical hydrothermal method under the conditions of a high temperature and high pressure, and a 0D/2D CNQD/BiOBr S-scheme heterojunction with an intimate-contact interface was formed. The π-electrons in the heterocycle of the CNQDs were bound to BiOBr by interaction. The apparent reaction rate constants generated by CNQDs/BiOB-1.50% for tetracycline (TC) and ciprofloxacin (CIP) degradation and H2O2 production were 2.02, 2.91, and 1.54 times that of the original BiOBr, respectively. In the cycle test, CNQDs/BiOBr-1.50% displayed a relatively high photocatalytic activity and structural stability. X-ray photoelectron spectroscopy (XPS) analysis showed that the π electrons in the CNQDs interacted with BiOBr, and also confirmed the flow of photogenerated electrons in this heterojunction. This successfully constructed S-scheme exhibited extraordinary photocatalytic activity and stability. The more active species and stable catalytic activity were attributed to the distinctive transfer mechanism of the carriers. This work will provide reference for constructing 0D/2D S-scheme heterojunctions for the degradation of organic pollutants and in situ production of H2O2.