A novel ZnMn2O4/g-C3N4 nanocomposites heterojunction photocatalyst: preparation, characterization, and investigation of photocatalytic behavior over toxic dyes

Spinel-type photocatalysts, e.g., ZnMn₂O₄, have been receiving intense interest owing to their high photochemical stability and visible light absorption. However, their photocatalytic activity is limited due to fast electron–hole recombination. In this work, we present the preparation of a new ZnMn₂O₄/g-C₃N₄ nanocomposite heterojunction photocatalyst by a simple ultrasonic technique to solve this disadvantage. With the tuning of ZnMn₂O₄ loading, the optimal loading for 10% ZnMn₂O₄/g-C₃N₄ nanocomposite presented excellent dye removal efficiency of 98.8% under visible light irradiation, which strong outperformed pristine g-C₃N₄ and ZnMn₂O₄ by 33.7% and 43.0%, respectively. Radical scavenging studies indicated that hydroxyl radical (·OH) was primarily involved in the degradation mechanism. The kinetic study also supported the high reaction rate constant (k = 0.0333 min^‒1). This work presents a promising route to develop efficient, recyclable, stable, and visible light-driven photocatalysts for wastewater treatment.