Fe3O4 quantum dots/g-C3N4/coal-measure 3 N 4 /coal-measure kaolinite composite for efficient photo-Fenton degradation of tetracycline hydrochloride

In this study, a novel Fe3O4 quantum dots/g-C3N4/coal-measure kaolinite (FQ/GCK) composite was synthesized with high dispersion to activate H2O2 under visible light (vis) for the degradation of tetracycline hydrochloride (TCH). The 10 %FQ/GCK catalyst exhibited outstanding catalytic activity, achieving an 84.45 % degradation efficiency of TCH in the photo-Fenton system. This remarkable performance was attributed to the favorable specific surface area and pore volume of the g-C3N4/coal-measure kaolinite support, which enhanced the dispersion of Fe3O4 quantum dots (Fe3O4 QDs) and promoted effective TCH adsorption on the catalyst. The incorporation of Fe3O4 QDs improved the composite's vis absorption and accelerated TCH degradation through the Fe-II/Fe-III cyclic reaction. Additionally, coal-measure kaolinite was cost-effective, and its surface was rich in hydroxyl groups, which promoted the self-decomposition of H2O2. The reaction rate constant of the 10 %FQ/GCK/vis/H2O2 system was 6.38 times higher than that of the 10 %FQ/GCK/vis system and 3.92 times higher than that of the 10 %FQ/GCK/H2O2 system, indicating a synergistic effect between the photocatalytic and Fenton reactions. The 10 %FQ/GCK system also demonstrated excellent degradation efficiency at various pH levels and retained 78.68 % of its catalytic efficiency after three cycles. The intermediates formed during degradation of TCH were identified. Electron paramagnetic resonance tests and free radical scavenging experiments confirmed the involvement of OH, h(+), and O-2(-) in the degradation process. In addition to TCH, the 10 %FQ/GCK composite also demonstrated effective degradation and mineralization of chlortetracycline hydrochloride, oxytetracycline hydrochloride, levofloxacin, and rhodamine B. This study provides new insights into the design of efficient and stable kaolinite-based catalytic materials.