Sustainable dye removal using thermally treated ostrich eggshell as a high-performance adsorbent

• Calcined ostrich eggshell is an efficient low-cost adsorbent for textile dye removal • Achieved >99% Remazol Brilliant Blue R removal within 5 minutes at low concentrations • Maximum adsorption capacity of 43.5 mg/g confirmed by Langmuir and Kahn isotherms • Adsorption governed mainly by physical interactions with minor chemisorption effects • Valorizes protein-rich biowaste while mitigating hazardous synthetic dye pollution Synthetic textile dyes, such as Remazol Brilliant Blue R (RB), are recognized environmental pollutants with persistent, carcinogenic and phytotoxic properties. This study investigates the applicability of a novel, low-cost, biogenic adsorbent – calcined ostrich eggshell (COE). Eggshell waste poses environmental concerns due to its protein content, odor emissions, and susceptibility to microbial decay. Thermal treatment at 1000°C converted the OE into a porous, high-surface area, highly positively charged material (pH PZC = 12.61). Comprehensive characterization by FTIR, Raman spectroscopy, SEM–EDX, thermogravimetric, and UV–Vis analyses confirmed the favorable morphological, chemical, and surface characteristics of COE, thereby enabling efficient electrostatic interaction with anionic RB molecules. Adsorption experiments were conducted in batch mode by systematically varying pH (2–11), contact time, initial dye concentration (5–750 mg/L), adsorbent dosage (0.1–3 g/100 mL), and temperature (20 ± 1°C). The maximum adsorption capacity was 43.5 mg/g. Batch experiments demonstrated rapid and effective dye removal, achieving >99% removal within 5 min at low concentrations and >70% efficiency even at 750 mg/L. Adsorption kinetics followed a pseudo-second-order model, while equilibrium data fitted best to the linearized Langmuir (R 2 > 0.99) and non-linear Kahn (R 2 = 0.901, χ 2 = 10.21) isotherms. Overall, the results demonstrate that COE emerges as a rapid, highly effective, low-cost, and sustainable adsorbent with clear potential for practical application in the remediation of anionic textile dyes from wastewater.