Effect of Silver-Modification of g-C3N4 on Photocatalytic Degradation of para-Nitrophenol and Antimicrobial Activity

Abstract

Graphitic carbon nitride (g-C₃N₄) exhibits promising photocatalytic and antibacterial properties. This study aimed to enhance these activities via silveration and to test its effects on the removal of para-nitrophenol (4-NP), a frequent aromatic water pollutant, and some dangerous bacteria under visible-light irradiation. The structural and optical properties of the silverized catalysts were characterized using XRD, SEM, FTIR, and UV-Vis-DRS techniques. Silveration led to a ca. 50-fold increase in the photocatalytic degradation of 4-NP through better light absorption and hindered charge recombination. Scavenging experiments proved that ^•O₂⁻ and ^•OH species play a decisive role in this process. The presence of H₂O₂ contributed dramatically to the efficiency of decomposition through a synergistic effect. The individual decomposition rates were two orders of magnitude lower than the result achieved with the combined application of Ag/g-C₃N₄ and H₂O₂, primarily due to the increased ^•OH formation. The degradation conditions were optimized in terms of component concentrations. Since the surface charge of the Ag/g-C₃N₄ catalyst is zero at pH 6.76 (pH_zpc), basic systems diminished the degradation efficiency due to repulsion between the negatively charged catalyst surface and deprotonated 4-NP. Although the antibacterial activity of Ag/g-C₃N₄ was not negligible against Escherichia coli and S. aureus in the dark, it became significantly enhanced under visible LED light or natural sunlight, photogenerating oxidative species that damage the cell wall. Therefore, the silver-doped g-C₃N₄ photocatalyst can be used efficiently for both the degradation of aromatic organic pollutants and the inactivation of dangerous bacteria in contaminated aqueous systems.