Enhancing Thiazine Dye Removal using Pyrolyzed Mytella falcata Shells: Characterization, Kinetics, Isotherm, and Regeneration through Photolysis and Peroxidation

Abstract

Abstract The potential of pyrolyzed Mytella falcata shells as an adsorbent for removing thiazine dye from aqueous solutions was investigated. The study found that the adsorbent produced at 600°C of pyrolysis temperature, with an adsorbent mass of 0.5 g, particle diameter 0.297 − 0.149 mm, and pH 12.0, demonstrated the highest dye removal efficiency of 82.41%. The material's porosity was observed through scanning electron microscopy (SEM), which is favorable for adsorption, while FTIR and XRD analyses confirmed the presence of calcium carbonate (CaCO3) in the crystalline phases. The pseudo-second order model was found to be the best fit for the data, suggesting that the adsorption mechanism involves two steps: external diffusion and diffusion via the solid pores. The Redlich-Peterson isotherm model better represented the equilibrium data, and the methylene blue adsorption was found to be spontaneous, favorable, and endothermic. The hydrogen peroxide with UV oxidation was found to be the most efficient method of regeneration, with a regeneration percentage of 63% achieved using 600 mmol.L− 1 of oxidizing agents. The results suggest that pyrolyzed Mytella falcata shells could serve as an economically viable alternative adsorbent, reducing the amount of waste produced in the local environment while removing pollutants from water. The material's adsorption capacity remained almost constant in the first adsorption-oxidation cycles, indicating its potential for repeated use.