In this work, the photocatalytic and photothermal effects of carbon-ring-doped graphitic carbon nitride materials against bacteria were systematically studied in a dispersed solution and on a membrane. C-doped graphitic carbon nitride materials C-CN 0.15, 1.5, and 7.5 were synthesized by mixing urea precursor with 0.15, 1.5, and 7.5 wt % glucose. With the increase in the doping level, the photothermal effect was clearly enhanced while the generation of reactive oxygen species (ROS) was slightly inhibited. With exposure to irradiation under a 100 mW cm-2 Xeon lamp with a cutoff filter (λ ≥ 420 nm), the ROS concentration of C-CN 1.5 increased 30% in the dispersed solution and its temperature increased about 10 °C in the dispersed solution and on the membrane compared to that of pristine carbon nitride. As a result, the bactericidal activity of C-CN 1.5 was improved by an order of magnitude in the dispersed solution and more than 2 orders of magnitude on the membrane immersed in a solution at 40 °C. To investigate the fundamental light absorption process on the membrane, an optical model using the finite-difference time-domain method was developed based on the topography of the membrane. The simulation results may explain that although C-CN produces more ROS in a solution; however, with a larger extinction coefficient, the power absorption is lower near the surface of the membrane. The ROS production is therefore inhibited and the bactericidal activity is dominated by the photothermal effect. Our experimental and simulation results provide a basis for designing high-performance photoactive disinfection materials and surfaces.
Keywords: C-doped graphitic carbon nitride; bacterial disinfection; bactericidal materials and surfaces; photocatalytic ROS production; photothermal effect.