Investigation of Color Removal Mechanisms of Raw and Calcinated Eggshells, and Their Photocatalytic Properties for Selected Dyes

The present study thoroughly explores the efficacy of both raw and calcined eggshells in the removal of various dyes from wastewater. It was found that some studies have misinterpreted this phenomenon for certain dyes. The study specifically examines the ability of raw eggshell (RES) and calcinated eggshell (CES) to remove three dyes: fuchsine dye (FD), malachite green (MG), and methylene blue (MB). The research aims to determine whether the color removal is due to a photocatalytic process or a change in solution pH. Various methods were used to characterize the eggshell-derived photocatalysts, including diffuse reflectance UV–Vis spectroscopy (DR-UV–Vis), Fourier transform-infrared spectroscopy (FTIR), and electrochemical methods such as electrochemical impedance spectroscopy (EIS), photocurrent measurements, and Mott–Schottky analyses. In this study, it was found that the photocatalytic effect of RES and CES for FD and MG is not significant, while a noticeable photocatalytic effect was observed for MB. Therefore, it was concluded that some eggshell-based dye removal processes are not due to their photocatalytic properties; instead, the shift in solution color is linked to a change in pH.