Engineering novel ceramic metal borates containing carbon for efficient sequestration of Toluidine Blue O from wastewater

Toluidine Blue O is a cationic dye that can irritate human tissues and may accumulate in vital organs after repeated exposure, and its discharge into water bodies reduces light penetration and threatens aquatic life. In this work, B₂O₃/FeB₂O₄/AlBO₃/Fe₃BO₆/C and B₂O₃/Al₄B₂O₉/FeB₂O₄/Fe_2.964O₄/C nanohybrids named AFB500 and AFB700 were synthesized by a facile Pechini sol-gel route at 500 and 700 °C, respectively. The synthesized nanohybrids were applied for Toluidine Blue O removal from wastewater. XRD confirmed multiphase borate and iron oxide structures, and the average crystallite size increased from 66.69 nm for AFB500 to 81.74 nm for AFB700 due to stronger thermal treatment. EDX analysis revealed B, C, O, Al, and Fe in both nanohybrids, with higher carbon and lower Al and Fe in AFB500 and more inorganic enrichment in AFB700. FE-SEM showed plate-like and sheet-like aggregates for AFB500 and more compact granular particles for AFB700. HR-TEM images revealed mainly spherical nanoparticles for AFB500 and rod-like and plate-like crystallites for AFB700. Under optimized conditions (pH 10 and 298 K), AFB500 and AFB700 achieved Toluidine Blue O removal efficiencies of 91.62 and 64.16%, respectively. Langmuir analysis shows maximum capacities of 423.73 mg/g for AFB500 and 302.11 mg/g for AFB700. Kinetic and thermodynamic studies showed pseudo-first-order behavior and physical exothermic and spontaneous adsorption. The nanohybrids were effectively regenerated with hydrochloric acid and maintained high performance over several cycles, and they also removed Toluidine Blue O efficiently from real laboratory wastewater, which highlights their practical potential for dye-polluted effluents.