Probing the structural transformation of ZIF-L to ZnO for sustainable Congo Red Dye Removal

Abstract Severe water pollution due to industrial dye effluents has alarmed the scientific world to unravel a suitable technique and appropriate catalysts for dye removal and wastewater management. In the present work, the adsorbent capacity of ZnO was tuned by calcining ZIF-L, a class of Metal Organic Framework (MOF) at temperatures ranging from 300-600 oC. XRD, FTIR, FESEM-EDX and XPS analysis shows the decomposition of ZIF-L and the nucleation of ZnO at the higher calcining temperatures above 350 oC. The ZIF-L derived ZnO obtained at 420-500 oC exhibited higher CR removal capacity than ZIF-L and ZnO obtained through co-precipitation. The optimized calcining temperature was observed at 480 oC with a maximum Congo Red (CR) dye removal percentage of 94.8 %. The adsorption capacities increased from 24.88 mg g-1 to 117.07 mg g-1 as the initial adsorbent dosage decreased from 0.5 g L-1 to 0.1 g L-1. Further, the Langmuir and Freundlich isotherm studies predict the increase in adsorption capacity from 49.09 mg g-1 to 183.98 mg g-1as the initial dye concentration increases from 5 mg L-1 to 50 mg L-1 at the optimal Z480 adsorbent dose of 0.1 g L-1. The result shows that the dye adsorption kinetics and isotherm are well fitted with the Pseudo second order model and the Fruendlich model. The plausible mechanism of dye interaction with the surface of ZnO nanoparticles at different calcining temperatures is also discussed.