Synthesis of novel eco-friendly CaO/C photocatalyst from coffee and eggshell wastes for dye degradation

For the first time, calcium oxide (CaO) and calcium oxide/carbon (CaO/C) are prepared by thermal decomposition from eggshell and coffee wastes as photocatalysts. The morphological, structural, chemical and optical properties of the prepared nanopowders were investigated using a variety of techniques. The crystallite size for plane (111) increases from 564.09 Å for CaO to 1654.67 Å for CaO/C, according to XRD. The CaO/C photocatalyst has a high increase in light absorption in the visible spectrum. The bandgaps of CaO and CaO/C are 1.73 and 1.52 eV, respectively. After 35 min of sunlight exposure, the photocatalytic removal of methylene blue (MB) dye employing CaO/C as a photocatalyst shown a significant improvement in removal (99.76 %) compared to CaO (88.04 %). The improvement is attributed to an increase in photocatalyst surface area and dye adsorption, which increases photocatalytic efficiency. The zero-, first-, and second-order kinetic parameters for CaO/C were investigated and discussed at various photocatalyst dosages. The current research can be used in the industry to remove toxic MB dye from wastewater and recycle coffee and eggshell wastes.