Synergistic sulfuric acid modification and calcination engineering of pseudo-boehmite for enhanced fluoride removal: mechanism, performance, and application in coking wastewater.

Fluoride contamination in water poses serious health risks. Herein, a novel η-Al2O3 adsorbent (SPB500) was fabricated through synergistic sulfuric acid modification and calcination of pseudo-boehmite. Compared with the unmodified pseudo-boehmite (specific surface area of 266.977 m2/g), SPB500 exhibited a significantly enhanced specific surface area of 359.149 m2/g and a well-developed mesoporous structure with an average pore size of 3.8684 nm. The saturated adsorption capacity reached 21.672 mg/g, and under identical conditions, the fluoride removal efficiency reached 93.92%, representing a 2.7-fold improvement over the unmodified material (34.5%). Mechanistically, treatment with sulfuric acid promoted the formation of mesopores and introduced surface sulfate species, while subsequent calcination induced the phase transformation to η-Al2O3 and preserved abundant surface hydroxyl groups. This synergistic modification not only increased the specific surface area and pore volume but also enhanced surface protonation capacity, collectively contributing to enhanced fluoride adsorption via electrostatic attraction and ligand exchange. Under optimized conditions, the fluoride removal efficiency of SPB500 reached 93.92%, with excellent performance in real coking wastewater and good regenerability (maintaining over 70% capacity after five cycles). This study provides a facile, low-cost strategy for developing high-performance aluminum-based fluoride adsorbents with well-defined structure-activity relationships.