In-depth insight into the mechanism on photocatalytic synergistic removal of antibiotics and Cr (Ⅵ): The decisive effect of antibiotic molecular structure

Antibiotics and heavy metal contaminants often coexist in wastewater but their simultaneous/synergistic removal remains a great challenge. Herein, a synergistic effect on the photocatalytic removal of antibiotics and hexavalent chromium (Cr (Ⅵ)) is realized using ultra-thin g-C3N4. The mechanism of synergistic effect is studied deeply at molecular level through experiments and theoretical calculation. Antibiotics molecules are first adsorbed on the surface of g-C3N4 by π-π interactions, and subsequently act as electron donors (hole sacrificial agents) to accelerate the separation of photo-generated electron-hole pairs and allow more electrons/holes to participate in the redox reaction. Another crucial finding is that there is a linear relationship between the electron-donating capacity and the synergistic efficiency. Detailly, the contaminant molecules with greater electron-donating capacity are more favorable to the improvement of synergistic efficiency. Our work systematically analyzes the mechanism of synergistic effect on contaminants removal and proposes reasonable methods to enhance the synergistic efficiency.