High-Capacity Be(II) Adsorption by a Multidentate TFP-HEDA Adsorbent: Mechanistic Insight and Statistical Validation

The selective removal of beryllium from aqueous matrices remains a critical environmental and industrial challenge due to beryllium’s extreme toxicity, strong hydration chemistry, and the difficulty of separating Be2+ from chemically similar cations such as Al3+. In this study, a novel multidentate Schiff-base porous organic adsorbent, TFP-HEDA, was synthesized by condensation of 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (TFP) with N-(2-hydroxyethyl)ethylenediamine (HEDA) followed by urethane post-functionalization and systematically characterized by FTIR, 1H/13C NMR, MALDI-TOF MS, elemental analysis, BET surface area analysis (617 m2 g−1), PXRD, and XPS. Batch adsorption experiments demonstrated rapid Be2+ uptake, achieving 90% removal within 20 min and equilibrium within 30 min. Among the isotherm models evaluated, the Langmuir model yielded the highest statistical consistency (R2 = 0.9835, RMSE = 5.15 mg g−1, χ2 = 1.137) with a predicted maximum adsorption capacity of 163.93 mg g−1 agreeing closely with the experimental value of 163.67 ± 6.42 mg g−1 (deviation < 0.2%); this mathematical adequacy is interpreted as compatibility with a finite, saturable set of inner-sphere coordination sites rather than confirmation of a flat, energetically uniform surface, with chemisorption independently and more rigorously established by Dubinin–Radushkevich analysis (E = 28.87 kJ mol−1) and post-adsorption FTIR and XPS evidence. Dubinin–Radushkevich analysis confirmed a chemisorption mechanism with mean adsorption energy E = 28.87 kJ mol−1, consistent with inner-sphere Be2+–O/N coordination. Process optimization using response surface methodology based on a central composite design achieved 99% Be2+ removal at pH 5, an adsorbent dose of 60 mg/20 mL, and a contact time of 30 min (R2 = 0.9892). Post-adsorption FTIR, XPS, BET, and TGA characterization confirmed framework integrity and the inner-sphere multidentate coordination mechanism. TFP-HEDA retained 82.4% of its initial capacity after nine adsorption–desorption cycles, demonstrating practical regenerability for Be2+ recovery applications.