A Selective and Efficient Germanium(IV) Adsorbent Based on Pyrogallol-Formaldehyde Cross-Linking

Selective recovery of Ge(IV) from low-concentration germanium-containing aqueous solutions remains challenging, mainly because of its low concentration and the interference from coexisting ions. In this work, a catechol-site-rich adsorbent (PGA-F) was prepared via the condensation of pyrogallol and formaldehyde for efficient Ge(IV) capture. Owing to the high density of adjacent hydroxyl groups in the material, PGA-F exhibited strong affinity toward hydrolyzed Ge(IV) species. Under the optimal conditions (pH 6, 298 K), the adsorption capacity reached 79.53 mg·g –1, and equilibrium was achieved within 120 min. The adsorption process was well described by the Langmuir isotherm model and Pseudo-second-order kinetic model, indicating a monolayer chemisorption-dominated process. Thermodynamic analysis further showed that the adsorption of Ge(IV) on PGA-F was spontaneous and endothermic. Meanwhile, PGA-F maintained good selectivity in the presence of competing cations, including As(III), Zn(II), Co(II), and Mn(II), as well as common anions such as SO 4 2–, Cl –, and PO 4 3– . After four adsorption–desorption cycles, more than 70% of the initial adsorption efficiency was retained, demonstrating satisfactory reusability. Combined spectroscopic characterization and density functional theory calculations revealed that Ge(IV) adsorption was mainly driven by the synergistic effect of adjacent hydroxyl chelation and anion exchange, accompanied by the formation of stable Ge–O coordination bonds. This work provides an effective strategy for the selective recovery of Ge(IV) from wastewater and hydrometallurgical leachates, and also offers molecular-level insight into the role of catechol sites in oxyanion recognition.