Efficient Selective Adsorption of Anionic Dyes by Modified Activated Alumina Spheres

ABSTRACT The persistent environmental threat from dye‐contaminated industrial wastewater necessitates advanced remediation solutions. Hydrochloric acid–modified activated alumina spheres (HAAs) are presented as efficient adsorbents for anionic dye removal. Comprehensive characterization (SEM, XRD, BET, FTIR, Zeta potential, NH 3 ‐TPD) confirmed the effects of acid treatment. The treatment enhanced crystallinity, amplified surface charge positivity, and enriched acid site density. These synergistic modifications endowed HAAs with exceptional orange II adsorption capacity (97.91% removal within 40 min at 50 ppm, pH 8). Its performance outperformed pristine activated alumina. Multimodal adsorption mechanisms were identified: 1) electrostatic attraction via sustained positive charge, 2) hydrogen bonding through hydroxyl groups, 3) Lewis acid–base coordination at enhanced acid sites, and 4) mesopore confinement. The process followed pseudo‐second‐order kinetics and Temkin isotherm confirming chemisorption‐dominated heterogeneous interactions. Notably, HAAs exhibited robust reusability and cost‐effectiveness, with facile solid–liquid separation advantages. Theoretical analysis suggests HAA demonstrates promising scalability and engineering adaptability for potential industrial dye wastewater treatment applications. This approach could potentially bridge laboratory‐scale innovations with practical environmental remediation scenarios, although actual implementation would require further validation.