Waste eggshell derived CaCO₃ modified MIL-101(Cr) for response surface methodology optimized photocatalytic malachite...

Organic dyes used in food products and the textile industry are a major source of environmental contamination, as they are nonbiodegradable, highly toxic to aquatic life, and carcinogenic to humans. A novel visible-light-sensitive CaCO₃@MIL-101(Cr) composite photocatalyst has been fabricated by unique calcium carbonate from eggshell waste modified with a chromium metal-organic framework for applying photocatalytic degradation of malachite green (MG) dye as a representative pollutant under the influence of visible light irradiation and providing a cost-effective and environmentally friendly approach. Synthesized samples MIL-101(Cr), CaCO₃, and CaCO₃@MIL-101(Cr) were characterized using a variety of techniques, including XRD, FT-IR, BET, SEM, XPS, and UV-Vis spectroscopy analysis. The improved photocatalytic activity of the CaCO₃@MIL-101(Cr) composite can be attributed to the synergistic interaction between CaCO₃ and MIL-101(Cr), which enhanced visible-light absorption, facilitated interfacial charge transfer, and suppressed electron/hole recombination. Using Response Surface Methodology (RSM) according to Central Composite Design (CCD), process parameters such as starting catalyst dosage, oxidizing agent, and dye concentration were optimized. The photocatalytic oxidative degradation of (MG) model dye (the optimized conditions were catalyst dose: 2.0 g L^-1, oxidizing agent: 2.25%, and dye concentration: 200 mg L^-1) resulted in a remarkable 98.86% efficiency via a waste eggshell-derived CaCO₃@MIL-101(Cr) composite. Furthermore, the optimized conditions were employed in treating real textile wastewater, and the waste eggshell-derived CaCO₃@MIL-101(Cr) composite achieved a removal efficiency of 96.20%. Additionally, with no decline in efficiency, the catalyst showed outstanding durability and reusability over six cycles. The potential of waste eggshell-derived CaCO₃@MIL-101(Cr) composite as a viable and recyclable photocatalyst for the effective removal of resistant organic contaminants from wastewater is demonstrated in this work.