A Novel Nanocomposite Bioadsorbent Derived From Natural CaCO 3 for the Efficient Adsorption of Toxic Dyes: Synthesis, Characterization, and Application in Wastewater

ABSTRACT The textile dye industry releases dye‐laden effluents that contaminate water, especially those containing Eriochrome Black T (EBT), a commonly employed anionic dye that poses health risks to humans. To address this problem, increasing attention is being paid to the use of abundant, low‐cost, and nontoxic bioadsorbents as sustainable alternatives for wastewater treatment. This work assesses the potential of a new nanocomposite adsorbent (MnO:ES) obtained by combining natural calcium carbonate (CaCO 3 ) derived from eggshells with manganese oxide (MnO) as an active agent to improve its adsorption capacity. A straightforward physical approach was employed to fabricate the MnO:ES through planetary milling conducted at room temperature for 2 h at a rotational speed of 350 rpm. The synthesized MnO:ES was characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and scanning electron microscopy (SEM/EDX). The MnO:ES nanocomposite was used to efficiently remove EBT from colored water, achieving a removal efficiency of 98% corresponding to a maximum adsorption capacity of 6.6 mg/g. The optimal conditions were achieved at natural pH, a temperature of 20°C, a contact time of 30 min, and an initial EBT concentration of 100 mg/L. The adsorption experiments were performed using 0.75 g of MnO:ES adsorbent composed of 10 wt% MnO and 90 wt% ES. MnO:ES was found to be dispersible, insoluble in water, and highly paramagnetic. The adsorption of the EBT dye followed pseudo‐second‐order kinetics and the Langmuir isotherm model, and thermodynamic analysis indicated spontaneous adsorption. Furthermore, microbiological analysis indicated a total absence of pathogenic germs, and a total aerobic bacterial count (TABC) of 190 CEU/mL was observed, which is relatively low for this treated water. The findings indicate that the incorporation of natural CaCO 3 into a nanocomposite matrix significantly enhances its chemical stability and affinity adsorption efficiency toward target pollutants.