Simplistic synthesis of ZnO/g-C₃N₄ heterojunction photocatalyst for improved photodegradation performance

The objective of the present work is to develop a simple route for synthesis of visible light active ZnO/g-C₃N₄ type-II heterojunction photocatalysts with improved photodegradation performance. The g-C₃N₄ is synthesized by single step thermolysis method, whereas, ZnO and ZnO/g-C₃N₄ type-II heterojunction photocatalysts with different (10, 15, and 20 wt%) loading of ZnO are synthesized by a simple hydrothermal method. The structural, morphological and optical properties are analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, diffuse reflectance spectroscopy, and photoluminescence characterizations. The synthesized photocatalysts are used to degrade the rhodamine B (RhB) dye under 35 W Xe light lamp. The photocatalytic activity is investigated in detail via different experiments like effect of pH, trapping of reactive oxygen species (ROS), cyclic stability test, etc. The ZnO/g-C₃N₄ type-II heterojunction photocatalysts with 15 wt% loading of ZnO (15ZG) shows the best photodegradation performance with 0.52 min⁻¹ degradation rate constant and superoxide radicals (·O₂⁻) as major ROS. Further, it exhibits highest degradation rate in acidic medium (pH = 3) with its point of zero charge value 2.54 and possesses good cyclic stability with high activity (91% after 5 cycles). In addition, the photocurrent measurement study is conducted to explore the concept of capability of charge separation and transportation processes across the heterojunction. A photodegradation mechanism involved in the said activity is presented. The 15ZG heterojunction photocatalyst is very much capable for water purification applications.