Boosting the photocatalytic activity of g-C3N4/ZnO heterojunctions through optimal control of mass ratio

Carbon nitride (CN, g-C3N4) has appeared as a promising high-activity photocatalyst for photodegradation of organic pollutants, photogeneration of H2 and photoreduction of inorganic pollutants such as heavy ions, despite some disadvantages like fast electron-hole recombination. The formation of CN-based heterojunctions is a viable strategy to overcome unwanted recombination processes. However, the precise control of the experimental parameters during the heterojunction formation is still needed to boost the photocatalytic efficiency. Herein, the influence of the mass ratio on the photocatalytic performance of CN/ZnO heterojunctions was investigated. The samples were obtained at room temperature via impregnation method and ultrasonic treatment. Heterojunctions were characterized by XRD and FT-IR, and interactions between the components were evidenced by the shifts in the diffraction patterns and vibrational spectra. The morphologies were investigated via SEM/TEM, confirming the formation of heterojunction interfaces. A strong influence of the CN/ZnO ratio was found on bandgaps, crystallite sizes. Photocatalytic activity was evaluated using Rhodamine B dye in aqueous solution. High photocatalytic performances were obtained for CN/ZnO ≥1, and the best ratio was 2. The control of mass ratio changed the formation mechanism from type II heterojunction (CN/ZnO <1) to Z-scheme (CN/ZnO ≥1), enhancing the photocatalytic activity. Thus, the electronic properties and formation mechanism could be tuned through the optimal control of mass ratio of heterojunctions.