Sonophotocatalytic degradation of sulfadiazine by integration of microfibrillated carboxymethyl cellulose with Zn-Cu-Mg mixed metal hydroxide/g-C₃N₄ composite

This research aimed to prepare a recoverable sonophotocatalyst, in which microfibrillated carboxymethyl cellulose (MFC) acted as the Zn-Cu-Mg-mixed metal hydroxide/graphitic carbon nitride (MMH/g-C₃N₄) carrier. The characteristics of bare and composite sonophotocatalysts were analyzed by the XRD, FT-IR, BET, DRS, PL and FE-SEM equipped with the EDX mapping. The performance of prepared composites (MMH/g-C₃N₄@MFC) with various weight ratios of the MMH/g-C₃N₄ was studied for the sonophotocatalytic degradation of sulfadiazine (SDZ) as the model emerging contaminant. 93% of SDZ was degraded using the most effective catalyst (MMH/g-C₃N₄@MFC₃) with 15% weight ratio of the MMH/g-C₃N₄ under the desired operating conditions including solution pH of 6.5, SDZ concentration of 0.15 mM and ultrasonic power of 300 W. The MMH addition to the g-C₃N₄ structure increased the separation of charge carriers generated via the visible light or ultrasound irradiations. Moreover, the MMH/g-C₃N₄ was dispersed uniformly on the MFC and consequently, more active sites were available to form reactive oxygen species (ROS), compared to powder form. Hydroxyl radicals (^•OH) were determined as the main ROS in the SDZ degradation by performing a series of scavenging experiments. Less than 10% decrease in the degradation efficiency of SDZ was observed during five subsequent experiments, which indicated the proper retention of the MMH/g-C₃N₄ particles in the MFC. The adequate mineralization of SDZ (83% decrease in chemical oxygen demand (COD)) was obtained after 200 min of treatment. Eventually, ten degradation intermediates were identified by the GC-MS analysis and a plausible degradation mechanism for the contaminant was proposed.