Bead materials of quail eggshells with or without zinc oxide modification for removing methylene blue dye

Using food waste as an adsorbent is a choice for wastewater treatment by the adsorption method to achieve sustainable resource and waste disposal and management. This study aimed to synthesize methylene blue dye (MB) adsorbents from quail eggshells with and without zinc oxide (ZnO), which were quail eggshell beads (QB) and quail eggshell modified with ZnO beads (QZB), and to characterize them using XRD, FESEM-FIB, EDS, FTIR, and pH pzc techniques. Batch experiments were used for investigating their MB removal performances, and their reusable abilities were examined by desorption experiments. Various isotherm and kinetic models were used for determining their adsorption patterns and mechanisms. Their temperature effects were explored by thermodynamic studies. QB and QZB were semi-crystalline structures and showed specific peaks of CaCO 3 . Moreover, QZB also detected specific peaks of ZnO. They had a sphere-shaped structure, and their surfaces were uneven and coarse with porous structures. Their main chemical compositions were C, O, Ca, Cl, and Na, while Zn was only found in QZB. The functional groups of O–H, C=O, C–O, and Ca–O were found in QB and QZB, while Zn–O was only detected in QZB. The pH pzc values of QB and QZB were 6.51 and 6.62. QZB demonstrated higher performance on MB adsorption in terms of MB removal efficiencies (%) and adsorption capacity ( q e ) at 86.82 %±3.04 and 51.97±2.97 mg/g than QB at 79.92±2.36% and 29.97±2.14 mg/g by approximately 7% and 22 mg/g, so ZnO could improve the material's ability, especially increasing q e by more than 1.7 times. The desorption experiments could confirm their reusable abilities for more than three cycles with high MB removal efficiencies of more than 71%. Freundlich and pseudo-second-order kinetic models were good at explaining their adsorption patterns and mechanisms related to multilayer adsorption on heterogeneous surfaces and a chemisorption process. Moreover, their MB adsorption was an exothermic process. Therefore, QZB might be a good choice for MB adsorption in further wastewater treatment.