Facile synthesis of carbon quantum dots loaded with mesoporous g-C3N4 for synergistic absorption and visible light photodegradation of fluoroquinolone antibiotics

Abstract

The development of facile and efficient synthetic approaches of carbon quantum dots loaded with mesoporous g-C₃N₄ (mpg-C₃N₄/CQDs) is of critical urgency. Here, a facile strategy was developed to synthesize the mpg-C₃N₄/CQDs by using calcinations of the mixture of CQDs, cyanamide, and silica colloid. The obtained composite still retained a considerable total surface area, which could offer a larger population of adsorption sites; therefore enhance the capacity for the adsorption of fluoroquinolones antibiotics (FQs). Under visible light irradiation, mpg-C₃N₄/CQDs demonstrated a higher photocatalytic activity for FQs degradation than did bulk g-C₃N₄ or mpg-C₃N₄. This enhancement might have been ascribed to the high surface area of the mpg-C₃N₄, unique up-converted photoluminescence (PL) properties, and the efficient charge separation of the CQDs. The eradication of FQs followed the Langmuir–Hinshelwood (L–H) kinetic degradation model and absorption pseudo-second-order kinetic model, indicating that surface reactions and chemical sorption played significant roles during the photocatalysis process. The results of electron spin resonance (ESR) technology and reactive species (RSs) scavenging experiments revealed that the superoxide anion radical (O₂˙⁻) and photo-hole (h⁺) were the primarily active species that initiated the degradation of FQs. Based on the identification of intermediates and the prediction of reactive sites, the degradation pathways of ofloxacin (OFX) were proposed. A residual antibiotic activity experiment revealed that mpg-C₃N₄/CQDs provided very desirable performance for the reduction of antibiotic activity.